EP1987410A2 - Optical system with coherent feedback - Google Patents

Optical system with coherent feedback

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Publication number
EP1987410A2
EP1987410A2 EP06851253A EP06851253A EP1987410A2 EP 1987410 A2 EP1987410 A2 EP 1987410A2 EP 06851253 A EP06851253 A EP 06851253A EP 06851253 A EP06851253 A EP 06851253A EP 1987410 A2 EP1987410 A2 EP 1987410A2
Authority
EP
European Patent Office
Prior art keywords
light
feedback
optical
signal
detector
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP06851253A
Other languages
German (de)
French (fr)
Inventor
Aviram Sariel
Eyal Moses
Eyal Conforti
Shimon Levit
Javier Garcia
Yaron Hefetz
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Lenslet Ltd
Original Assignee
Lenslet Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Lenslet Ltd filed Critical Lenslet Ltd
Publication of EP1987410A2 publication Critical patent/EP1987410A2/en
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06E—OPTICAL COMPUTING DEVICES; COMPUTING DEVICES USING OTHER RADIATIONS WITH SIMILAR PROPERTIES
    • G06E3/00—Devices not provided for in group G06E1/00, e.g. for processing analogue or hybrid data
    • G06E3/001—Analogue devices in which mathematical operations are carried out with the aid of optical or electro-optical elements
    • G06E3/005—Analogue devices in which mathematical operations are carried out with the aid of optical or electro-optical elements using electro-optical or opto-electronic means

Definitions

  • the present invention is related generally io the fieM of ⁇ puoai processing, for yxasuple, io optical proo ⁇ o ⁇ * such as vect ⁇ r-veetor-muitiplkfs or v-eclor-matrix-muItipHsjs employing eoiierem feedback for reducing readout shot ncsi ⁇ e,
  • a fan in optics collects the attem p ted Hght indicative of atuit ⁇ ikaltoa of the corresponding clemeiits of the finjt 3_xi vectors and likcctjj it to a f Smto deiecto?.
  • Althoiigli Oic light source used may be a coherent SOU ⁇ UO such ass s kse?, ihe light collection process is incchexent r ⁇ _» ⁇ Uliag in total light i ⁇ vcssity cqvu ⁇ l ⁇ o the susn of mtonsitics of sil cdlected beams.
  • Shot aoisc W proportional to the square-root of the ⁇ ismbor of detected ph ⁇ toa ⁇ .
  • any increase in accuracy by one bk means; slowing *knva the calculation by
  • I factor v ⁇ f 4 hereasing the light power by a ikcior of 4, or a conibi ⁇ atfos of both jc ⁇ ultsag in four fold increase is the mimbct of photons used for representing a re-suiting value- This s ⁇ w a limii on the accuracy and ⁇ peed of optical computers.
  • Sisru&r shot noise pjoMems are eueoimtored when desngnmg accurate t ⁇ ucai me&sirotne ⁇ t system*. Specifically, it is cHfiteult to measure a small change in s iaige opdcal signal. Shot noise tha& hinders increase of dynamic iaage of optical computers sad
  • tMs is ii ⁇ ed tn t educe ⁇ Isomoise.
  • a value of the measured attenuation is extracted from state of the feedback loop when light on said critics! detector is at or near minimal intensity.
  • the optical attenuator to be measured represents a result of optica! coosputatjon such as: positive or bipolar multiplication of scaiars or vector-vector aniifipiieaiioa
  • One potential advantage of the above exemplary embodiment of the invention is its i ⁇ uuiity to variation in the intensity of the. coherent light Since balance of the attenuation is the two amis of the interferometer resuUs m n ⁇ ftim&l or no light ⁇ H ihe ai least one critical output, large variations of the light source krtens ⁇ y have negligible effect o.a the state of the feedback loop mainurirarrg balance. Thus, small vanauon of attenuation values may accurately nsessisred in spite of large variation of the light source.
  • This fact enables cost reduction as susple laser such as diode laser may be useci withmn ⁇ be need to passively or actively stabilising the laser output.
  • the coherence length and/or intensity stability length arc selected u> snatch the optical paths.
  • ihe optical pa&s are rnodified so that fey are seat equal in length.
  • a IighL detector having essentially rum-linear respcmse i ' o light miensiiy may be used, as long as ⁇ ia signal, an said mon-iinear detector dimmishes as Iigrii intensity diminishes.
  • an avalanche photodiodc having internal gain, which makes is a fast and sensitive photo detector . may be ⁇ sed.
  • the- ircmt-end amplifier for the photo detector may fee mm linear or with limited dynamic range or even binary in nature.
  • the system and method according io exemplary embodimcnis of the current invention uses "null detection” in which, at the point of calculation result, the deisetor is illussinated by a "dark fringe" of interferometer, lhas the light level delected by the detector is minimal, zx ⁇ the shot noise is eliminated or at least minimized to a value set by dark current at ⁇ l parasitic light ⁇ xa to Unite contrast of the interferometer.
  • coherent light from a singis laser is divided mtotxvo branches: a computation (or branch: m ⁇ feedback branch.
  • Ltghi m tho computation branch undergoes optics! processing similar to processing used an optscra! processor* known in the ait. However, in contrast to incoherent optical f r ⁇ ccssors, phase of the light Is maintained.
  • IB a Vector Vector Multiplier (YYMX coherent light enters the eotapuiatkm kaueh where it is: a> Divided ⁇ aso ⁇ g a pturalstj of channels typically corresponding to the number of vector elements h) T ⁇ r each channel %ht is modulated such tliat the light field amplitude rcpro ⁇ eal-s tho cone ⁇ fxmdi ⁇ g vaf ⁇ e of ilr ⁇ t vector element. c) For «aeh chsmie! amplitude of the hglit ⁇ further jJttenuatcd by factor represontmg tts ⁇ corxespondi ⁇ g value of second vector dement.
  • the light ar ⁇ plstade represents the
  • ⁇ Vector Matrix Mult ⁇ bcr may be represented as parallel VVM of ⁇ iirst vector wiut plurality oi ' secoud vector; sm ⁇ seatxangmg the planets Iwm the VVM operation as athir ⁇ ⁇ cetotv Tn a ⁇ "MM. enhej ⁇ ii light enters the coiaputation braticl ⁇ where it is: ai Divided amtntg the K niput channels, corresponding to the immhct of finst vectoi elemems.
  • each output channel light is i krth«r attenuated by a factor representing values of the Ourrcipondmg ⁇ k, m] matrix olcmcni ⁇
  • rcpi «sseuts the multiplication of values of fi? ⁇ t and a Taairi ⁇ element e)
  • Light tioin all ehan ⁇ eis corresponding to tfeu same row in a matnx is oohcrenily sddsd iogcthci to foun an output optical signal vviih Held amplitude representing a third ⁇ ect ⁇ u ekmcta of the ⁇ ectQr-jsatrix multiplication, which is the result of VMM mathematical operation.
  • Ati irKsofaereal VYM or VMK! processor wherein output UgM k detected and digitized, hi a? aieihod according to an cxemplasy embodiment of the present mve ⁇ iioa.
  • a feedback mechanism su the feedback branch acts on the feedback light to creates mm ⁇ xml li ⁇ i iv ⁇ mu ⁇ ty - ⁇ t nn output of ihe mter&xvsmcter, by providing feedback light with field smp ⁇ tude but opposiu; pb ⁇ stc of the compsMiem bnuich light signal.
  • a feedback loop attenuator is ⁇ pi ⁇ ona ⁇ iv used for providm ⁇ feedback light with th ⁇ dcsked absolute value amplitude.
  • Correct phase of the feedback loop light is optiwially maii ⁇ lam ⁇ d by the nature of the optical mtcrCsromsteric syste ⁇ i s ⁇ id'Oi usisg a plia&e shitliug etsme&t ⁇ optionally controllable).
  • OpticmaUy a f ha ⁇ c jjblft ⁇ r m the feedback loop h used to ensure I&e correct ph%;c of the feedback light.
  • the Hghi is not coherent when processed, but made cohcnsm after prooe ⁇ slrig. tor example, usiiig ⁇ coheresu light source whose amplitude is dcte ⁇ rii ⁇ ed bv i ⁇ ispinging of mcohetx. ⁇ t light in the form of a power and/or a control signal
  • the feedback loop aad reedbaek signal are aaaiog. and result is oht ⁇ iued by digitizing said feedback signsl.
  • the feedback loop is a digital loop, ⁇ s ⁇ ag digital steps to update the feedback CO ⁇ HM J signal and the computation results are obtaiscd t ⁇ oai diguu ⁇ status of the teedbacl. looo. fc some of these embodiment, ihe digital feedback loop uses a "successive approxiiaalioa algorithm " whescin the sue of stops used S ⁇ cbangmg ⁇ i ⁇ ? feedback control by factor of two ; ⁇ each successive step,
  • ihe number of bits depends on the t Anlagen ⁇ d accuracy of ⁇ he computation snJ ssuy ckmgs depending on the context of the compulation. For example, ormcai computations may he f erformed ai higher accuracy than Jion critical computations ui ways similar Jo ⁇ e aso of "double precision" used ia ebctroaic computer, however any auKiher ofbit ⁇ sx&y be selected,
  • coherent Lglit processing b advantageously « ⁇ ed by using both amplitude and phase of ihe light field as way of cepa'smU ⁇ g a vahe.
  • k coha ⁇ ent hght sisnmatioa ⁇ he light's electromagnetic fields sre added as 2-D vectors.
  • field smphv ⁇ da is tdciuified by a cM ⁇ pkx number in a Cartesia ⁇ -s cocuxlinatss.
  • ai «pH ⁇ udcs of cump ⁇ «alio ⁇ result field aad feedback field mus. be an exact negative of sach other. That is exactly the same intensity, bat v ⁇ ilh ⁇ hcir phases opposite to each other.
  • vaincss Usod in the computation* arc uacorrdsied ⁇ t p ⁇ eudo-raudom.
  • A.ddiiionaliy s in many f ⁇ plica ⁇ o ⁇ values may be rearranged (or otherwise modified, for cx ⁇ mpk by adding a random value) ⁇ o en ⁇ re tmc ⁇ rrekte ⁇ or pscudo- random aal&rc of the values.
  • n may improve fee accuracy by allowing only Jhc Seid from the beams' osatcr Iu mter&ic O ⁇ the detector.
  • the sire of the aperture is s «s t ⁇ > matcfe fac error iolcmuce iCt ⁇ aired ⁇ nd'or p ⁇ or knowladge otstatktical prttpertics of the input v&ucs.
  • fiber optics tn ⁇ y be usea to te-$lupc a bca ⁇ ti * for example a s-mgk ⁇ ⁇ sr ⁇ 1e fiber may be use-tl Ca a » shapc the fevam ⁇ vi s aesr dif ⁇ rsctsoa bmit ⁇ auis ⁇ an siiapc,
  • beam shape mampul ⁇ ticn may he dose o& oao oj ' tfee buutches or v-w both sep&ately.
  • a Mach-Zehader int ⁇ rferomet ⁇ may be used uS ⁇ jt dec ⁇ ro -optical smwmre in its arm to modulate the light tick!
  • a poic ⁇ d ⁇ i advantage of using sniuterfefomeier as s moJuiat>n" is that unlike && absorptive r ⁇ odoktor, it may abo ⁇ issd to r ⁇ veae the phase of tbe beam to ⁇ opr ⁇ «iC ⁇ $ n-egative values.
  • the exee ⁇ light oxi ⁇ s the iBterfemmcter &n ⁇ do ⁇ s ⁇ oi produce heat that has to be removed from the sys»lem>
  • a pliase shifting dc% tee may be used for ai ⁇ ectmg the phase of the heats to represent negative or complex vslaes.
  • Imerteronicteis may be mna ⁇ factated using freely pwpsgatkg beam ⁇ vismg mirrors, lenses, lensk't*, beam-splitters nnd'or other optical elemctus.
  • O «xHttj ⁇ 2asifmal optical systems may be constructed, losing single-mode optical fibers.
  • polarizaho ⁇ maiau ⁇ tiing Obers are used. Beam shape of light propagating m such iihcjs is maintained and dcpc ⁇ ds.
  • Combination oi i- ⁇ , 2- ⁇ and 5-D system maybe «sed to construe t th «j desired optical system.
  • ooa ⁇ potie ⁇ is used m the system according to the irrvctttioa w> mipedeci.
  • ct «mp osents itsed as! modulators may have imperfect response,
  • a Maeh- ⁇ &hsxkr iuterferometer used as modulator has a response.
  • pre-pnscsssbg of computation values is used for compensation.
  • pu£t-proeesMS3g of eonspoiation results may be used for eoinpOKsation
  • ei ⁇ jboiimwtsJ of lhs as ⁇ alucs of input vector ekmeMs are pre-processed before they are uss.
  • ' ⁇ is a modulator ⁇ O aflbci ihs light field.
  • input v&kias such as values of ⁇ r ⁇ t ⁇ x elcmeais are pre-processe before they are used in a modulator io ⁇ f&ei the light SeM.
  • Analog or digital or combination of aaalog and digital may be «sed lor the preprocessing, post- processing orisctb.
  • i&m ⁇ varying are ⁇ optionally &$t.
  • detectors, drivers md mmluiatois B.sed m the feedback loop optionally react ⁇
  • binary electronics is faster and consumes i «ss power than Linear eleetromcs with comparable speed
  • binary circuits are used for driving elements such as a feedback loop modulator of a coherent feedback optica! computing system according to some cmbodane ⁇ is of fee present invention.
  • the feedback SeM optionally changes in predetermined steps of diminishing size.
  • algorithms similar to the- "slgma delta" algorithm may be used.
  • APD Avalanche Photo-Diodes
  • the signal io be detected is less than 30%. less ihan 20°/ «, less than 10%, less than 5% (or intermedials values) in ampiiiude of the signal w be measured before intcrfercsace.
  • the range of the signal to be detected is less ⁇ nm 30%, less Shan 20%, less than 10%, less than 5%.
  • ⁇ ntpliiudc of the sigi ⁇ til io be measured before mterf ⁇ re-nc ⁇ .
  • ihe shoi «oisc* goes down by a factor of at le&jt ! .2, 2, 3, 4, 5, 10 or intemicdiak: values.
  • U jshosld ho ⁇ oted that a singh systens may include two or snore diiTwnt measurement ciremis. for esample ⁇ one using an mtcrfsarometric tcdjaiqiie $s described herein (c.g« for large valaes) and fee other usiag a standard or other type detector (e.g., for low values or if Um mterfcrom «tdc technique fails, fov example, due io over-coi ⁇ e!atiou of isiputs.
  • & mcasuf tfment $y$tom having coherent feedback is provided.
  • the sy& ⁇ m according to an effibodi ⁇ vont of the iavctuion uses ⁇ coherent feedback loop to increase speed ui ⁇ ht accamcy of the measurement in optical measareended systems used ia die art, a transducer Is used to generate or Bjodabttf a Light signal indicative of the measured value. This signal is then detected with a detector that converts the light to electric signal, which is usually digitized.
  • s beam splitter spUrtmg Ught from jjaki coh ⁇ e ⁇ t HgM :>o ⁇ rc ⁇ to a measurement branch and s feedback hru ⁇ cts; at least oac trafi-iduecr modulating li.uht in the raeaj»memeju branch to indicate ⁇ se ⁇ urcd value; at least OBO uiihi mcdulaior modulating light m the feedback branch: at least one tatcr ⁇ ror ⁇ ele* tor interfering light fe> ⁇ the measurement branch with light from the feedback branch, ⁇ t least one light dciceior dciec ⁇ ng light from dark fhngc of *a ⁇ i ititerioromotet . and a feedback loop, contruHmg h ⁇ t modulator at the feedback branch m rc-spon ⁇ o to signals from said ⁇ t icast one light d
  • the tratisdiicor modulates tiic intensity of light ia the me ⁇ 5suremom brauch atifl meastired value is fefesred from sntessity s ⁇ ts feaib ⁇ ok Ixgh? wh ⁇ n ileM fiinpljr ⁇ d ⁇ * in meaxajemc ⁇ t branch and moasaned aad feedback branch arc e ⁇ iiiai,
  • a feedback loop is used to track ⁇ ie changes m the external system to be measures mid a sample and hold is used to sample the state of the feedback signal.
  • high-frequeticy modulation is imposed osi die feedback S ⁇ gna! and irf used for the tracking.
  • Figure 1 depicts a .simple optical xmili ⁇ pHer as knovt'n sn the art
  • Figure 2 sofaumatioaily depicts a 2x2 optical V ⁇ cior-Vcctor MulupUtir (VMM) as known in the an
  • VMM V ⁇ cior-Vcctor MulupUtir
  • F i gure ⁇ Schematically depicts a coherent feedback optical tmihinlier according to an. embodiment of the current invention.
  • Fig ⁇ r « 4a Jcpic ⁇ >. as optical multiplier using a binary feedback loop according to an.
  • Figure 4b depicts an optical multiplier using a digital feedback loop according to aa erakxlimem of the eu ⁇ ent invention
  • F ⁇ gtue 4c deraetsi su ⁇ tteal inuitiplier adapted for handling, bipolar ⁇ aiues according to au exemplary embodiment of the invention
  • Figtuv 5a epicts an optical computalioa sy&iem witij & coherent signed feedback loop aecordtng to naoiher aspect of the current invention
  • Figure 5b depicts -iu optical coiapulation..system with a coherent ⁇ nsdbitiary feedback loop according ir- an embodiment of ibc current invention
  • Fipfc 5c depicts m optical computattoa system with a coherent signed feedback k ⁇ Kce ⁇ rding TO yet another sspect of the current ia ⁇ cation;
  • Figure 0 depicts a sehcmatio block diagram ola eoiaputational branch of ait optical
  • Fsguvc ? sohematiesllv depicts a block diagram of a computaftoas! branch of ao optical VVM using beam !>
  • Figure £ depicts a sekoma ⁇ c bioek diagram of computational braiioli of as optical VVM using len$es for sp lilting m ⁇ eombinkg beams scc ⁇ rdmg to sn embodiment of the current kivont ⁇ O ⁇ ;
  • Figure ⁇ schematically depicts aa optical VMM hoving a coherent feedback loop according to ,J ⁇ exetr ⁇ imy eajbodinjem of the current invention:
  • Figure 10 depict? a schematic block diagram of a measurement system a ⁇ -tsg c ⁇ hercat feedback accotding Io an exemplary embodiment of the current invention. asx!
  • £igu*e 11 depicts a schematic block diagram of a measurement syUerr* us ⁇ sg coherent feedback csp&hle of measuring both attenuation and phase shift according io m exemplary f ⁇ shHlatir ⁇ t olthe current invention.
  • Jt i? io be lisjderstocd Lku ihc invention is not limited iaits application io tbs details of oonstKfet ⁇ on and tfe aiTunger ⁇ nt x>t the ootspontsnls set forth in the follow mg deseriptimi or ⁇ lustmed in the d ⁇ nvmgi ⁇ .
  • the invctstio ⁇ is? capsbb of other embodiments or of being practiced or earned oat in various ways ⁇ Lo. it u to be understood that the phraseology axi ⁇ tera ⁇ m»iogy employed hereui is &n ilic purpose of description and should not be regarded as limiting.
  • Hie ⁇ -a ⁇ i ⁇ gs axe gene-tally aot Iu scale. for clsriiy. Bon-eksentiai elements were omiti ⁇ d from souio o ⁇ ths drawmgs. Ai « us «d heteia, &n e!ome» ⁇ or ⁇ tep recited its the siogubf a»d proceeded with the wot J s V or vv 3 ⁇ r should bo understood as aot excluding pluial elements or steps, UGicss ⁇ uch exclusion is
  • Figute I depicts a simple optical oiuinplkr UK> as known us fee art.
  • Input light 102 emitted froai light source 104 caters the optical multiplier which comprises of tv* ⁇ light ifficusrty attenuators 10(ja and 10(A situated along the op ⁇ eai path of ixrput light 102, in the sapletaematioss used in the art, light, source 104 may emit either coherent or meohcrs ⁇ ? r&diaiion.
  • intensity attemialo ⁇ s 106a and 106b are efc ⁇ roakaJIy controlled by electronic derives ⁇ i)U& m ⁇ 108b respectively sack fuse that the.
  • ⁇ & ⁇ &n ⁇ Tr ⁇ asxmssk>n are the i ⁇ msmiita ⁇ ce ofaUenuaiors 106a and 106b respectively;
  • Arbitrary is an arbitrary coefficient, which depends on system consu ⁇ ction;
  • Exit light 110 impinges ors a light detector 112 and is converted to an electrical signal pmporiional io the i «tensity of the exit light.
  • an Analog Io Digital Convener ihDC) 114 OGx$v «ris the dectdcal signal frotn Hghl detector 112 to digital form.
  • FIG. 2 scheasaticaUy depicts an optical 2x2 Vector-Vector Multiplier (VVM) 200 ; ⁇ s an.
  • VVM Vector-Vector Multiplier
  • Inp ⁇ i lighi 202 emitted from a light source 204 is split to two branches of equal intensity 202-1 avid 202-2 by beam splitter 205,
  • Light of sack branch passes through an optical l ⁇ ultiplier which comprises two Sight intensity Multiplier I comprises attenuators 206a 1 and 206b 1 , wfeiie multiplier 2 comprises atle ⁇ uators 206&2 and 2G ⁇ b2.
  • Sight intensity Multiplier I comprises attenuators 206a 1 and 206b 1
  • wfeiie multiplier 2 comprises atle ⁇ uators 206&2 and 2G ⁇ b2.
  • two tttul ⁇ plkrs are shows, however fte number of xmd ⁇ iir ⁇ may be larger.
  • light source 204 may ejri ⁇ t either coherent or incoherent radiation.
  • intensity aitcimaiors 206 am aketromcally controlled by decitonsc delivers 208 such that ihsi the transparency of each attemiator is proportional to Xhz co ⁇ resptmdi ⁇ g numerical values 209a! , a2, bl
  • the system may bo extended to larger dimension vectors by creating as many channels as the dimensionality otihc vectors. Extension of ihiss type of system to a Vector-Matrix Multiplier (VMM) b known in the art " .
  • VMM Vector-Matrix Multiplier
  • VMM vecmr raauix multiplication
  • analog eJccU'Ome vector matrix multiphea ⁇ oamul is described, for example, in "Programmable ⁇ aaJog Vcctor-Mairix Multipliers", by F. Kub, K. Moon, L Mack, F. i..o ⁇ g, in 5 BEE Journal of Solid-State Circuits, vol. 25 C ⁇ ) pp. 207-214. 1990, which is incorporated herein by roiVrence.
  • the optics! systems aad methods according to some embodiments of the current mvetuion operate wkik the optical iatessity on the critical detector (or criCical detectors) is rornsmai or > ⁇ ttu!Iy trull ⁇ p ⁇ testkl advantage of ⁇ x ⁇ » is* that the above himutUtm may be overcome.
  • ⁇ system sccotdujg to as exemplary embodiment of the mvcnuos uses a coherent & ⁇ &Ua ⁇ »U%$ * ' interference between light beams: the first be ⁇ na vcpresenCmg the value to be measured, for example the computation result: and the second beasj ⁇ s generated ana comtolled by s Feedback loop.
  • the first and the second beara ihe hght intensity at the outpm is ⁇ st n rm ⁇ ima and Uw noise associated WHk its detection is small
  • the nKmurod value is safened ixom the ieecback loop CHci ⁇ tjy.
  • Cohcrsmi mrui ligbj.302 oriHied fro ⁇ i a oohsirent light source 304 is spht ;o m r o pa ⁇ ?; a eompumtioa chanaci input beam 3UX and a feedback chaimei mptH beam 302V by be?«n ssphttcr 305
  • AsipMade sttenuaiois 305 ate cbcironically coMrolkd by elscirOBio dcs.t ⁇ c ⁇ 3 ⁇ 'H s?uch ti ⁇ at that the ampiiuiJc tjansparctjcy of each attenuator K pioponi ⁇ ai w a uunseiicai vsi ⁇ cf. " «" m ⁇ b' 1 to be muiuplwd i ⁇ t ⁇ * ⁇ m ⁇ ,1 30% respcctivsly),
  • a coherent detection umi 325 controls feedback smpli ⁇ ide attemsator 306f so that ⁇ l ⁇ output 315 is obtained when amplitude of computational channel exit HgM 3 IOC is equal to amplitude of feedback channel exn HgIn 310F.
  • amplitude transmission * T * ⁇ f smpli ⁇ ude attenuation ol attenuator 306f is equal io the combined amplitude transmission of attenuators 306a and 3 ⁇ b, thus f TM a*b
  • colr ⁇ r ⁇ n detection unit 325 compares at teasl oae beam &pUticr, When two baams enters, a beam splitter, an iuter&aenee ooctns between the tvtc* beams $uch feat at o ⁇ o exit of tho beam epluter ihc Iigbi OeId amplitude is the sum of the amplitudes of ihc two inccmmg b ⁇ as ⁇ s, whiles ir? the other exit light field amplitude is the difference of the amplitudes of tbi two mcomi ⁇ g beams.
  • coherent detection unit 325 comprises a beam splitter 311 receiving computaticmaiL channel exit light 310C and feedback channel exit iigin 310F.
  • a bright fhngc is marked by fall heavy arrow, while dark frmgo is xnar ⁇ «£ by a dashed heavy gm>w St ⁇ tmg fb- i example with iaput light 302 v, ith intensity of 2,0 (arbitrary ui ⁇ u) or field of 2i) ⁇ usmg a 50:50 h ⁇ &m sphuss Si)S tlicre is m cq ⁇ al field amplitude of LO ⁇ arbitrary ⁇ mts) at Uw input of each of channels 3OX' ⁇ ad 3O2F. After passing through the attenuators in each cluoBOl.
  • Feedback io ⁇ ic 32O r «ceis'es*igmU irot ⁇ detector 312 and controls alternator " ⁇ ) ⁇ f ihtovish driver 308 in order to achieve ihe baiasc ⁇ coaditioa whiSi output 315 is chiasms!
  • uie emb ⁇ dli ⁇ usm feedback logic 320 sweeps or ⁇ mips (hrougb possible s alues of C & ⁇ ⁇ cGgtn/u ⁇ s tl ⁇ o Blest hk ⁇ ly ⁇ aius of f thai creates null signal ai detector 312
  • ADC 314 fusy be a ⁇ gger at the uixie during the sweep %l ⁇ &n Mgaal of detector 312 is below s sm&H preset tlueshoid Is another es ⁇ bodjr ⁇ ent feed bad logic 320 searches through possible values of f for a value that tn ⁇ mm/es the sigm ⁇ of detector 312 For example.
  • tnmsmiyaUon raeU ⁇ cts described in "'Hixmrnm ⁇ Rec-jpcV (William H, Pi ess eiai, Cambridge University pi ess, Ctepte ⁇ i ⁇ page ⁇ 274-27?) may be used, ⁇ i sbouM be noted that sigm ⁇ l on the detector is a concave hmcU ⁇ a of ihe ina* value for f, zix ⁇ ⁇ sisgk ⁇ nhnum cxi5>U> and w eassily found ⁇ n fact, in sume ci&ev this f ⁇ euoa it» appjoximatelv pa ⁇ olic. allowing methods opamizcd lor such a shape to be used
  • numm ⁇ ii dark lrsngs may be ⁇ ch ⁇ e ⁇ «d uh*s ⁇ f C* a*h ⁇ herc C is some numerical c ⁇ n ⁇ t
  • Figure 4a depicts an emhodii-o ⁇ ni oi a binaty feedback loop variation of the optic ⁇ truitipher of figure 3 in whwh s ⁇ alog coherent detection unit 325 « replaced v- ith a bi ⁇ arv- eoherest dciection ua ⁇ t 425
  • ⁇ pulse geaeiat ⁇ r 430 produces pultses at high rate.
  • hi operations aa analog aci-'uinulator 420 aceimiui ⁇ tos tho charge m the pulses ii ⁇ m pulse ⁇ eaef &tot ⁇ 3 ⁇ , civais ⁇ g a ratup analog voltsge whien is received by analog dm er 30Sf
  • a digsia! ⁇ ccam «ktur 418 accumulates (counts) she pulses gcnei ⁇ t Rg d jgjial sufsbci ⁇ j.>i$s5 ⁇ tal: ⁇ *; of f.
  • Tiiis vsah ⁇ dhmeut is l ⁇ scd ibt 4e«i ⁇ iistratiag S ⁇ impl ⁇ ffientat ⁇ >a of bki&ry feedback loops? aocofdasg to some embodiments of the current fcivea «o» ft should be noted ikn the ⁇ urabsr of cycles may needed to r ⁇ seh the final v&luc may be large. Additionally, there is a danger that BOXSC on che dctecior or comparator may cause the loop not to close as fee threshold may not " be crossed if the ftoise is aecideutaliy above the preset threshold. Additionally, She ncemacy ts limited by the comparator pje ⁇ ci thieshold valine.
  • Fsgisre 4b depicts an embodiment of a digital feedback loop variation of the optical multiplier of % «re 4a in which the binary coherent detection unit 425 is replaced with a digital coherent deieoUoa imit 455,
  • a digital ramp generator 460 produces digital ramp value which is received by a digual d ⁇ «r 40Sf. near s ⁇ etx ⁇ threshold value.
  • Figuiv 4c depicts an optical multiplier 400 adapted for kuidli% bipolar values gceordmg to as. exeisplary embodiment of ⁇ ic invcation, Ui ih& embodiment, a t>base shifter 306' JS added m line whh each aiteauat ⁇ r 30o. fin a commutation b ⁇ tnch 4S()C ⁇ phase ihiftets. 306'a and 3(HVb were added in Hue with mtessttRtois 30 ⁇ a u «d 306b respeeuveiy. ⁇ t should he no ⁇ d that the order of attenuators and phase SfKiHe...
  • Phase shifters 3(V receive from 308 signals Isdicativc of the sig? ⁇ ofthe (positive i»r ⁇ ?gMivc) end afibci a phast; shift of IHO degrees accordingly.
  • AitomativaK. only o ⁇ c phase shifter per jm ⁇ tiplleatson channel m&y be installed ir>. (h ⁇ computation branch, asd h$ status determined by ihe combined signs of the two values to be mu ⁇ &plkd.
  • the siga of smgle multiplier result may be determioed electronically by the cotabmad signs of the two values to be multiplied and presented together ⁇ * Uh the of the result Howev ⁇ i, as ⁇ hatl be ⁇ !e. ⁇ ioastra.ied Mtw, wJisai the c-osipuiation brcmch cot ⁇ spiises r ⁇ UJplc cha ⁇ sels ⁇ bi perforrnmg more complex operations ⁇ uch as ⁇ X ⁇ , the us? of at least one phas£ shilki per ckmncl to reprssscnt bipolar valoes curs ha udvantag ⁇ us.
  • Figure 5a depbu. ss optics! oamputauos system with coherent i ⁇ ig ⁇ ed feedback loop 5 € ⁇ ) secordisig to another aspect of the currant invention.
  • ⁇ dia ⁇ back of minima searching algorithm is that error signal pcod ⁇ cMby the detection swtem and usicd by the feedback loop do not eoatain iafbittiaiiou an ihs dtreciioa in which to change the trial va ⁇ us. DirecUouai information ts gathered by successive "trial and error' " stc
  • Systera 500 comprises thteo sub units: s computation branch 40BC: an * >f t ⁇ cal i ⁇ >tct fem:Betcr 502; aad * ⁇ ssgaed feedback loop 501,
  • Optical bnedemmeter 502 receives, input light from cohersM light ⁇ aurce 304 and produces at kasit v&o opdcal oulp «ij ⁇ 523PD mi ⁇ 532ND to be used by signed feedhaek loop 501 to puxluc ⁇ a signed sigr.a! for closing the loop.
  • Optical ⁇ iierfc ⁇ moier 502 b constructed such ⁇ ni st least both optical outputs are at or nc&r ?cro optical stgnal when ike ir ⁇ erlerotietcr ts balanced.
  • optical interferometer 502 comprise? a pickoif beam splitter 520 spUtlmg a small amount of light m the form of a weak bias beam 5026 from input beam 302. The majority of the light exits pickoi ⁇ b ⁇ am splitter 520 as main. ⁇ tipxit beam 5 ⁇ 2.
  • Baom ijpliu «r 505 splits rnaia input beam 502 to computation input beam S02C and feedback in ⁇ i beans S02P,
  • Computation channel exit light 510C is SfI it w two equal beam* 5 JOT * b ⁇ a beam sphtter 522- ⁇ i ihtt feedback chsuaeL feedback liranch 4S0F aCfccis tlw beam producing fce ⁇ back channel CX ⁇ light 5 Wi ⁇ &r ⁇ t$ beam 5O2d i ⁇ ititorfercd wUh feedback channel CM* light 3 ⁇ OF si Desm sjplitrer52] pixxkicmg nvo slightly unequal beams: Pssithe Feedback beam 51 OFF and Negative Feedback SIt ) FN depending on the sign of the field jnterfereace atbcsn? spliitcr 521.
  • Bear ⁇ 5 IOC is equally split to two identical b ⁇ sms 510C each having a ⁇ ppmask ⁇ f
  • beam 523PD has the amplitude of
  • beam splitter 523R beam 523PN has the amplitude of:
  • S 14 may be triggered vain® the feedback loop has iseftk ⁇ , for example by observing a stnali signal at Uic output of ⁇ tTerenisal amplifier 520, or it t&sy be U ⁇ ggefoJ St preset USBC or presei number ⁇ f cycks? depending on ths? desired accuracy after aew values of a and b were mput at the eompxitatso ⁇ branch 4OJ5C
  • 5b depicts an optical compa ⁇ atiun ssvsicm 570 w ⁇ h. » eol ⁇ erent signed binary feedhaek i,r ⁇ according to aaoihcr embodiment of flic cutTent inv ⁇ ittoit.
  • Binary comparator 530 compares ifec signals of dct ⁇ -ctojs 5!2P and 5I2K producing a single ⁇ ni equal to either > 1 or -1 depesxlmg on which signal is larger.
  • feedback loop is reset to a preset value after ihe cempletjojn of s computation pnx'ess
  • the pi ⁇ set initial value k at mid-range.
  • the ssz « uf ibe step depends o « the tuagmtudo of the dit ⁇ rcaee &g3Ul ⁇ % ⁇ £ two d ⁇ t ⁇ clors. as ⁇ kte ⁇ ti$ned by the difference of the S ⁇ g ⁇ sls of the ⁇ * O comparator ⁇
  • Opueal mterfoi ⁇ metei 602 compnses of splitter 505 splitting the light of input beam 302 tp die eoa ⁇ putatioeal br«ftcli408C a «d feedback branch 40SF.
  • feedback hzmxch 480F (computing an atten ⁇ ato? and opttonaliy a phase sMtor) affects the beam producing feedback channel etit light 510?.
  • tlio dUTereacs 1 bel ⁇ oea the ⁇ sgnsis produced by ⁇ eieousrs, we v&rt witli po% er al ooh «sont sourct; ⁇ f2.0 m &ontc arbttrarj' mtcus ⁇ t>" ⁇ niH.
  • Besan 61 OFF has ing amphtode oBr*P ⁇ B-#, and Bea ⁇ n (>1 OFF h& ⁇ i ⁇ g ; ⁇ « ⁇ U ⁇ «do of Yi *"f*(1 -d ⁇ -
  • beam 623?D has ⁇ ic amplitude of: v> ! l *a*!>S s *f*(l fd>; while iU ike dark fringe output of brain splitter n23K 5 beam 623 PN has the ⁇ mplittsde of; J //'*a*b-lj *f*(l-d).
  • the power on U ⁇ tector 512P is gtven by v,'- ⁇ *h-// ⁇ f ⁇ ! 1 Cl)F •- ⁇ ilanviy ⁇ d'f « i » ⁇ D-PM 2 s whew D - ⁇ a*b-i denotes the difTer «uo « beuvefen Xhc computsttoa value a*b and the feedback value C
  • the power o « detector 512?, given by VHPd)" is small when f - a v b.
  • the power on defector S12N is given by: >V»a v b- 1 ': N f*(1 - ⁇ f « * ⁇ ta*£K ⁇ U*df - 'VH_Hf*df Thcpov ⁇ on defector 5CN, given b> 5 Z ⁇ (PtIr is small when f ⁇ a*b.
  • a pickup beam splitter (liot ⁇ hown) picking sosic of the light from computation ehanxieS cx ⁇ Ught i ⁇ IOC ⁇ v&i directs t ⁇ to a dueet iseaswome «t photo detector (noi *ho ⁇ vn) ituiy Iv «$e ⁇ Op ⁇ nssliy, if ssjgntsl ⁇ n direct m ⁇ a ⁇ iiresient photo detector is beiuw a pteset value, ⁇ U> signal is « ⁇ >ed for ⁇ etemHU ⁇ ng IMc result while if us signal j « * above A preset valtis.
  • sigaai from the feedback loop ⁇ «J «SC»3.
  • IB digital feedback loop 601 epioteu JK the embodiment of %ure 5c.
  • a ⁇ soNt d ⁇ gm?cr 624 digitizes the analog ⁇ lgn ⁇ l ⁇ un differential amph ⁇ er 520.
  • Figure 5 ie-pkisS a schematic block diagram of a compatatiosal branch 4SO of mi optte&i VVM u ⁇ i ⁇ g coherent feedback according to an embodiment of the current t ⁇ vent ⁇ otiu box simpivzity, input xectois aye shows as hax ⁇ ng two dements.
  • IK the example of Sgur ⁇ 6.
  • ihe tipper channel is affected by hvo attenuators; 60 ⁇ al aad 606b 1; while the lower channel is af&cied by uvo attenuators; 6Q6:t2 m ⁇ 606b2,
  • Coherer * ! beam coaabmor 611 coherently combine the two ohaa ⁇ els to produce « computational output beam MdC with amplitude proportroual to al*bl-&2 ⁇ b2.
  • Ths optical system is ⁇ xtcsided to higher dimension vector by adding more ehan&ds ⁇ o the csalci ⁇ latioa branch. Exemplar)' embodiments tor such cxteas ⁇ oa are depicted in ⁇ he felloe ⁇ ng figure.
  • Figure 7 sdiemaiic-aliy ⁇ L*piet_> a block diagraro of a cor ⁇ puvatio ⁇ ai bniach 480 of an op ⁇ cal VVM using beam j»pUuers aceordi ⁇ ig to an embodiment of the cunvsnt
  • Oo ⁇ putauoa canael input beam 302C is successiv ⁇ ly split to two equal beams by a plurality ni " spliters 71 1 , ibmusg N * cha ⁇ nds wlicre IN (S ⁇ 2 ia tbis exa ⁇ sipie) is the & «mber of k*vcls ⁇ ofspiUtis%.
  • Each beam is aikcujd by tw ⁇ ⁇ n ⁇ d ⁇ latQis.
  • Ia the ⁇ gure " ?, light in first cbiai ⁇ d is atYected by modulators &l and b! , second ehaxujel by modulators a2 and b2, ate.
  • Coherent eombiuiisc of ibe beams from ail channels is ⁇ Q» « with successive addiiioas nf ihe biiimi amp liiudcs using beasi splitters 7 LI .
  • a bright fringe is selected trcr ⁇ ibe miederei-ce on beam j»phttsrs 713 to produce a computatioaaS outpui beam 310C wl& a ⁇ iiUKic proportional ⁇ > al*bl • »a2 t l ⁇ +a3*b3' ⁇ -a4*b4- i. srg%;r number of channels the number of levels of spiiaing. it should he noted thai uaswidsbiy some of ihc light intensity IM lost through the dark fringe oiuput of the combining beam splitters 713,
  • ⁇ compact system maybe consuucled by tJsmg a mmiaturo free space ptop&gstmg beam. ⁇ he» ⁇ « ⁇ th'ely ⁇ fiber optica taay be tisod for coustructiag the optical comporsaus. ⁇ itc ⁇ v ⁇ tively, optical curaponentii may be Hthographleally produced cnt tliia transparent turn,
  • Confutation esu&oi input beam 3O2C is split to N equal channels by fas out optics Sl 1 -
  • i&n out optics Sl 1 comprise? tv-o lenses, t* beam diverging km! &1S and a eoFhmatmg fens 81&.
  • a ien&let array is used to assist the coHi ⁇ naiios of the light M ⁇ ⁇ hc computational channels.
  • light is each v-ompytaUoa channel is atfected by modulators 812.
  • s pmhols aperture 825 is inserted at tlw tl ⁇ a! ⁇ ou*t of converging k ⁇ ?s S25.
  • Th ⁇ s ma> be useful for rejecting scattered light end/Or hici casing the spatial oohejvnco of oc ⁇ apuuit ⁇ nial output bean? 31 OC.
  • the fan in/ fan out system d»jpwted in figure 8 leads itself to the use of «> ⁇ u> atsd two dimensional light modul ⁇ tkm mmys as attenuators 812.
  • Tra sJjuJti ⁇ ag or rcUcctmg att ⁇ j ⁇ maU ⁇ rs may be a>icd xvithin the general scope of ⁇ e current invention.
  • Ii should be- aoted that jntorfcromslers a ⁇ d feedback loops of any of (he types awclosed in the preceding Ogursi. may be used for the optical VVM.
  • Ftgur ⁇ ⁇ J sehcmatscaliy depicts m npticai VMM haviag a coherent feedback loop ⁇ ?0U according to m exempkry emlwdiii-ient of the current invention.
  • Optical VMM 4 X)O compr ⁇ ucx a vjohenjnt light source 304 Light from coherent hgk 5OtJJVCS 304 is piojactcd by a hort ⁇ onlal fan out optics (not shown for clarity) onto a ⁇ ector KttoHuatioii array c ) 10 havmg k individually controllable attenuators 9lO( 1 ⁇ to 910(k) , snd to ft feedback vyrdeal fan out Of ties % X 4.
  • F ⁇ ⁇ b aitemjaior 910 ⁇ o) mo ⁇ luiat «s the light passing through it to rcpre ⁇ mt a xaku v(c) of s vector ⁇ kmeat “c” of vector "v” having dimensioualtty k, to be multiplied wttb a matnx m.
  • r,c) in the 2-L> army 920 modulate the light pawing through it ⁇ Q represent a value m(r.c) of a matrix element to multiplied with the vector. Consequently, tho amplitude oHight at ⁇ in output of attenuator 920(r,o ⁇ is proportional to ⁇ (c)*-m(>v).
  • Each attenuator 9_.0foe is associated with hnriyonial fan in optics (not shows for clarity ⁇ which Jiroct hght from all afees-oators i» row V to the coherent detection dement ⁇ ) ⁇ l ⁇ ) m arr&x C >1 ! otn eieme «ts.
  • the aa ⁇ iitude of light at the input to coherest dtfteciion t ⁇ kaicnt ⁇ 1 l(r) is equal to Sie vector element V ⁇ r) wherein V is a ⁇ ccajr ox ' dm ⁇ onsionahiy ⁇ . ⁇ ?ieate4 b> t ⁇ ui ⁇ ply ⁇ g x ector x- "with matrix m,
  • Light ltom feedback vertical fan out optics 91)4 is pn>jeetcd ot&a & veitkal feedback sfecnuatjos army ⁇ O having B individually controllable feedback attenuatoa 950(1) to °50(u).
  • light f ⁇ >m feedback artcnusCor **50(ri is directed to cofeensxt detection eleme t 91 i ⁇ r) where it isterfcres with light arfivmg &on plurality of atteauator Q 20(r,c) in rov. V.
  • fcaiL'h cohcf est dofectiOR elemcat 911 (r) is associated -VvItIi ⁇ edbaok loop 930 ⁇ t ⁇ f only two f Q 30(l> and Q 30 ⁇ 2) arc shows f ⁇ x clarity), whioh controls the e ⁇ i ⁇ es ⁇ o? ⁇ kng ibodhsok aU ⁇ auator 95« %x) em ⁇ produces the de ⁇ red digital ouljmt ⁇ jsult * ⁇ >! 5 ⁇ r>.
  • Ix should be noted IbM inkjferoiRcter topologies and feedback nj ⁇ thods depicted xn the pjec ⁇ dmg figures may be «&cd for coherent detection element 91 i and fesdbsdc loop O 30.
  • each feedback atictiuator 95 ⁇ f r) may be associated with a weak sii-aiteuuausd beam to enable eobereni det ⁇ tinn topology of fiprtj 5a.
  • ts>mmetrie beam spii ⁇ er ⁇ vithin each dotecuos olemmt V'l l(r) enables fee use of coherent detection topology ol figure 5c.
  • ⁇ coherent source 750 provide* -coheroat light ⁇ o an intf rferometor 7o Q .
  • fcsomctcr ?o9 ⁇ hght froai coherent SOII ⁇ CC 750 is divided between aft upper sieasoreme ⁇ t eh ⁇ and raid a IOWU ⁇ ilvtftack ehaxtnei by a beam splitter 757.
  • transducer 752 may be Cached to the external syster ⁇ or may musg ⁇ d pail of the* externa! system * oj optica! properties of external system tasy be used.
  • transducer 752 may be Cached to the external syster ⁇ or may musg ⁇ d pail of the* externa! system * oj optica! properties of external system tasy be used.
  • Fox example temperature dependence the absorption of an optical ⁇ bei may be used ks modulate the light by changing the iraB&parcney of said fiber.
  • changes m iisikdion, abssorpUo ⁇ pola ⁇ uatioti etc. maybe used.
  • both phase and arsipiimde ⁇ f the light m the mea&ujfemeni chan&d. may be. ai ⁇ eet ⁇ d by the state of the externa! sysiem, however, m ftguies IO nnfy amplitude changes sue con ⁇ ktered, while m figure 11. both phase and amplitade are ticked sn ⁇ opiion ⁇ h' measured Dy the feedback bop.
  • any method of coherent lee ⁇ baek loop (sig ⁇ eJ or imsigaedj ⁇ m ⁇ specifically those depicted in tho ⁇ teccdmg ilguscs may be used.
  • ⁇ sidg, bita ⁇ iy audftr digital feedback ⁇ oops may be used.
  • a signal yen somehown- 761 generates signal st n frequency considerably htgher tha ⁇ the desired sampling ''Me nf system 7 60
  • Signal frosn a NSgBuI geraaator 7 ⁇ j 1 is added to the feedback ioop at a s ⁇ mrmng jimcuoa "71 oM the resulting ⁇ igaal is fed io an ktUnmator 753 through a driver 754.
  • ConscqueaiK. light mtesmtv in the feedback loop performs high, frequency dither around its mean value.
  • a tmad amplifier such si a lock «s amplifier ?5& optionally syschrom/cd to signal generator " ⁇ 1, receives detected Sigcals i ⁇ or ⁇ a detector 755 and extents a sigaed error signal proporaoa&i to tlic HBbalatice ot un ⁇ sfenm ⁇ etoy 769.
  • Op ⁇ otsally a filer, for exaiiipk a low-pass-filte? or a notch filter or both are ⁇ ed for c.t ⁇ 3i ⁇ atioxi ol fee high frequency nxxiuiauoB , before feedback sipui sampling cr a* digital post pri>ces5>ing after it.
  • Figure ⁇ ⁇ dupiet* a sehcm&uc block diagram ofn mcassure ⁇ ieii system $60 u ⁇ ng C ⁇ N hercnt feedback ⁇ ad. capable of measurisig botb ⁇ tt «a «ation and phase shift aeeordmg to an exemplary ombcdtr ⁇ ei ⁇ t of the cmxent invention.
  • UnitUentiotsal relative phase changes T «ay also be eased by changes in the meaiuremcat or the feedback cham ⁇ ei for example due io iueehatucai stress or thssui ⁇ l e ⁇ aasion.
  • phase mc ⁇ iulstor 953 is ⁇ jscrtcc1 mi ⁇ the feedback e-Kur ⁇ ei, In ⁇ x ⁇ exemplary «mb ⁇ di ⁇ i ⁇ t of llg ⁇ re 1 Iu h & ⁇ .
  • IB eostraki to o&er coh « ⁇ jut detection methods used iw the an such aj» the amplitude hcs ⁇ sitsve heterodyne detcetio ' n, commonly used to measure small sigxmK the method according to sotno eaibodsments of the c « ⁇ r?m iBveatios JS sensitive to both pktse and amplitude.
  • Dixeci mcasurcxjjciu of tins light may Iv use « pn ⁇ set ⁇ slue. Co be used as ⁇ al result, Opiio ⁇ aily. with one branch closed and Uis other braach open to a linowti vsiuo, the output light ⁇ n the interfcromctsjr output is proportional to the output of the coherent %lu source.

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Abstract

An optical measurement system sensitive to light field amplitude is disclosed. The system uses an interferometer while a feedback loop maintains, at a low level, the light intensity exiting from at least on optical output of the interferometer. Shot noise of a detector placed at the output of the interferometer is thus reduced, enabling high speed and high accuracy measurement without requiring is stronger light source. The measurement system may be used in optical computing.

Description

Optica! System with Cp.here&t Feedback
EmATEDMPliCΛTIONS
This sppiicauos claims fee benefit aader 119(e) of US provisional application number U£60'7<l&4::2. f|k?a oa December 8Λ 2005 and entitled "Optical Multiplier with Cobereru Feedback", fee diselo-sujo of which i>> incorporated herem by reference.
The present invention is related generally io the fieM of αpuoai processing, for yxasuple, io optical proo^oπ* such as vectϋr-veetor-muitiplkfs or v-eclor-matrix-muItipHsjs employing eoiierem feedback for reducing readout shot ncsiάe,
Optϊcαl in jisaeral, are knowa is the art.
h\ optical VV^-I desigtte knmvn in ihώ art, values of eleroentø oi' a fir&ϊ x'ώctor are rcpro^entcd a<; light signals xvhsjrem light Intensity rcpressnb the values tt* be muldpilad. Each %h> s&gv&l is passscd thϊoagh a Iigkt sUcmiaior with light tπ*a?ϊϊjiιtancc representative of ihe coiTOSpondiag dement is the seoond vector. A fan in optics collects the attempted Hght indicative of atuitφikaltoa of the corresponding clemeiits of the finjt 3_xi vectors and likcctjj it to a f Smto deiecto?. Althoiigli Oic light source used may be a coherent SOUΓUO such ass s kse?, ihe light collection process is incchexent rε_»ιUliag in total light iπvcssity cqvuαl εo the susn of mtonsitics of sil cdlected beams.
Υbc mdύ, sotircc of&^e iathos« systems is shot noUo o& the dctceton? com cniαg the saalc»g light signal repteseadug the computational results into wx dectric sigaai u'hich is ih∞ convened w Jigάal form i&iag Aaalug to Digital Converter (ΛOC)>
Shot aoisc; W proportional to the square-root of the Ωismbor of detected ph^toa^. At the accuracy luϊist, any increase in accuracy by one bk means; slowing *knva the calculation by
I factor vϊf 4, hereasing the light power by a ikcior of 4, or a conibiαatfos of both jc^ultsag in four fold increase is the mimbct of photons used for representing a re-suiting value- This sεw a limii on the accuracy and ^peed of optical computers.
Sisru&r shot noise pjoMems are eueoimtored when desngnmg accurate tφucai me&sirotneαt system*. Specifically, it is cHfiteult to measure a small change in s iaige opdcal signal. Shot noise tha& hinders increase of dynamic iaage of optical computers sad
SUMMARY OF ϊlJEJ!£SΕNΥi0N
It is as object oi sunse ετnbodirøents of the pn?sseot m%'emioπ to use coherent Ixghi and a &k\l back loop for extracting measured values. Optionally, tMs is ii^ed tn t educe ^Isomoise. Some of ibe atiboxltmcnlss alknv higher speed and more acctuate optical computation and moainircmeai v^^hout excessive incresse of User power. Some of the embodiments enable optica! eomr<«tatksn aad ms-a^axβmeut v^hiϊe reducing the adverse effect of one or few svstem imp^itccuoa Deli as: Light &oαrca instability, optical «y.stεm insishility, Jεk*«or tjotsc, detector uon-liae^rity aad limited d^aπjk range of sydtemV wmponents. 0&e aspect of tbe invention is? io enable accurate measurement of the αtteauaiion of αa optica! atteτiuau>r without uϋing excessively strong light source or losg integration time. OptioriδH), ύύά i$ cchkvα! by reducing the Ugbϊ detected by a detector. Optionally* ihϊ light is reduced by pr*Λ ϊdmg an interfciXMnctsr, one input of which i^ known amVor controllable and whoss output reflects a dastrucUvc iaterfereiice on the detector. For ihsΛ aim, -an. interferometer is constructed having the attenuator ts? b^ measured m a
Vtτ$i ar<i5 and α feedback atienua tor in the second arm. Coherent light from a lighi søUice is sp Sn befwecn the uvo arms of the interferometer After passing through dio measurαl attcau*U*r m & first ams and s feedback attenuator in the second arm. light fk>m the two arms laterfαv* w»h eacb Either, vjxήing through Rt kast one critical output. The isirerfcrooeϊer 5? co»st-;uot*d $*> that lighi intcBsky exiting the critical output is minimal or some- other desired value, when the sϊbim&tbn at the tΛ\o srxn is cqunL Λ tK\!back loop controls the feedback aliess&tor such ύuxt Iigbi inieπ^ky i^ tsminisl In R&iά at least njxc critical output of the interfetomc-es. Shot noise St the weakly ύhmhisuxi ileiector pkwcd at the critical output of the uuatferoneter, prøpi^rtϊonal i>) sqijaje toot of the witettauy on said detector is thereby rcdαced. A value of the measured attenuation is extracted from state of the feedback loop when light on said critics! detector is at or near minimal intensity.
IH one embodiment, the optical attenuator to be measured represents a result of optica! coosputatjon such as: positive or bipolar multiplication of scaiars or vector-vector aniifipiieaiioa
One potential advantage of the above exemplary embodiment of the invention is its iεαπuuiity to variation in the intensity of the. coherent light Since balance of the attenuation is the two amis of the interferometer resuUs m nύftim&l or no light <H ihe ai least one critical output, large variations of the light source krtensήy have negligible effect o.a the state of the feedback loop mainurirarrg balance. Thus, small vanauon of attenuation values may accurately nsessisred in spite of large variation of the light source. This fact enables cost reduction as susple laser such as diode laser may be useci withmn έbe need to passively or actively stabilising the laser output. Optionally, the coherence length and/or intensity stability length arc selected u> snatch the optical paths. Alternatively or additionally, ihe optical pa&s are rnodified so that fey are seat equal in length.
AtsOthet ^oreatiai advantage of some embodbuetits of the mvciϊtiαri rest ost die £aet thai the <lynasύc rasge of the sysicrø is limited by the feedback loop instead of ihe dynamic πmge of the. detectors. The eleetroirk^ of ihe and fee attenuator IK the feedback loop may be designed with the needed dynamic range of the measureaie»t values. 1« contrast, light intensity on fee detector stays wilhia 8 limited raiige during the critical time when the me&sivremerit is taken. ϋptkxrssliy, a IighL detector having essentially rum-linear respcmse i'o light miensiiy may be used, as long as ύia signal, an said mon-iinear detector dimmishes as Iigrii intensity diminishes. For example, an avalanche photodiodc having internal gain, which makes is a fast and sensitive photo detector .may be αsed. Similarly v the- ircmt-end amplifier for the photo detector may fee mm linear or with limited dynamic range or even binary in nature.
Specifically, the system and method according io exemplary embodimcnis of the current invention uses "null detection" in which, at the point of calculation result, the deisetor is illussinated by a "dark fringe" of interferometer, lhas the light level delected by the detector is minimal, zxύ the shot noise is eliminated or at least minimized to a value set by dark current atκl parasitic light ώxa to Unite contrast of the interferometer. In a method according to some embodiments of the invention, coherent light from a singis laser is divided mtotxvo branches: a computation (or branch: mύ feedback branch.
Ltghi m tho computation branch undergoes optics! processing similar to processing used an optscra! processor* known in the ait. However, in contrast to incoherent optical f røccssors, phase of the light Is maintained.
1. IB a Vector Vector Multiplier (YYMX coherent light enters the eotapuiatkm kaueh where it is: a> Divided αasoπg a pturalstj of channels typically corresponding to the number of vector elements h) T<υr each channel %ht is modulated such tliat the light field amplitude rcproβeal-s tho coneϋfxmdiπg vaføe of ilr^t vector element. c) For «aeh chsmie! amplitude of the hglit Ϊ^ further jJttenuatcd by factor represontmg ttsε corxespondiυg value of second vector dement. Thus the light arøplstade represents the
ΩTuihplϊcatsoϊi o^eoπespomUag values of first and sceoad vector elements, d) 1 tght trosϊϊ all channels is coherently added together to fomi ΆΆ output opucaj signal having s field amplitude leprajcnting the sum of the elorαent nπdαpiication, which is the .xss»h csf V\ M mttthe^atxcal opetatioα.
2, Λ Vector Matrix Multφbcr (VMM) may be represented as parallel VVM of α iirst vector wiut plurality oi'secoud vector; smύ seatxangmg the revolts Iwm the VVM operation as athirα \ cetotv Tn a \"MM. enhej<κii light enters the coiaputation braticlϊ where it is: ai Divided amtntg the K niput channels, corresponding to the immhct of finst vectoi elemems. h> For each iϊψat channel, light is modulated such that ∑ts field amphmde the- value of the corresponding first vector eiesaeπt. c1) lighi from each føput ehaanεl is turther divided among tho K output channels ccnrc&poadiTig to Ae number of second vector elements <!o£mingK"K*M chstvαeU) - ά) Ψ nr each output channel light is i krth«r attenuated by a factor representing values of the Ourrcipondmg \k, m] matrix olcmcni^ The field amplitude ©flight in the elκuιts.e! rcpi«sseuts the multiplication of values of fi? δt and a Taairiλ element e) Light tioin all ehanαeis corresponding to tfeu same row in a matnx is oohcrenily sddsd iogcthci to foun an output optical signal vviih Held amplitude representing a third \ect<u ekmcta of the γectQr-jsatrix multiplication, which is the result of VMM mathematical operation.
1$ should be acted that value used in the calculation may be divided to pans and eompatatios tkπio m parts. Vector (or matτrs.c-i. or both) v* Uh dimensionality larger \haκ the available chamusus rcsay be multiplied is pans (e.g., series and/or parallel) -and the faults combined. Additionally or ahcπnttivaly, elements of α vector (or s matrix or bom) ma> be divided to part*, for example individual hits or group of bits, the calculation doae on these parts, and the rostUts combined wiak taking into account the relative position CM the bus or group of bus.
In contrast so ati irKsofaereal VYM or VMK! processor, wherein output UgM k detected and digitized, hi a? aieihod according to an cxemplasy embodiment of the present mveπiioa. output light is hiteϊ&aoiϊϊeteneaUy combined with light from « feedback branck A feedback mechanism su the feedback branch acts on the feedback light to creates mmπxml liφi ivάmuήty -Λt nn output of ihe mter&xvsmcter, by providing feedback light with field smpϋtude but opposiu; pbαstc of the compsMiem bnuich light signal. A feedback loop attenuator is υpiϊonaϊiv used for providm^ feedback light with thώ dcsked absolute value amplitude. Correct phase of the feedback loop light is optiwially maiiϊlamεd by the nature of the optical mtcrCsromsteric systeøi sϊid'Oi usisg a plia&e shitliug etsme&t {optionally controllable). OpticmaUy a f haϋc jjblftδr m the feedback loop h used to ensure I&e correct ph%;c of the feedback light. the condition υf tninimal light Is achieved oa ϊhe detector, fee SeId amphtαde dvse U> Lhe reaction of ihe feedback loop, of the feedback KgIn represeBts the desired computational result
Iu some embtxlimtfais, the Hghi is not coherent when processed, but made cohcnsm after prooeδslrig. tor example, usiiig ^ coheresu light source whose amplitude is dcteπriiαed bv iϊispinging of mcohetx.πt light in the form of a power and/or a control signal
In yioxns «f Asso embodiment the feedback loop aad reedbaek signal are aaaiog. and result is oht^iued by digitizing said feedback signsl.
Is other embodiments, the feedback loop is a digital loop, υsϊag digital steps to update the feedback COΪHM J signal and the computation results are obtaiscd tϊoai diguuϊ status of the teedbacl. looo. fc some of these embodiment, ihe digital feedback loop uses a "successive approxiiaalioa algorithm" whescin the sue of stops used SΏ cbangmg ϋi<? feedback control by factor of two ;ύ each successive step,
Ia RiJBe of the embodiments asiag approximaticm algontUm, the smmber of s»tops eotrespoiu.!.; to the number of bits m the eoinputatson results.
ITS some embodiments, ihe number of bits depends on the tfektϊd accuracy of έhe computation snJ ssuy ckmgs depending on the context of the compulation. For example, ormcai computations may he f erformed ai higher accuracy than Jion critical computations ui ways similar Jo ώe aso of "double precision" used ia ebctroaic computer, however any auKiher ofbit^ sx&y be selected,
It should be noted iksx in some methods 4o e<empiary embodiniεaϊts of the mvenuoϊi. compma«oo tirøo ss g.pproxmu5tdy Imaxi with U?e accuracy. in soffit' embodimeβϊs v»f successive appjoxiraaϋon, the nuiisber of bits {eorreϋpoαdmg to the accuracy oi'coinpuUdiosi sesolution) is equal to the mimbor of steps? aad thus propos^onal to the ccβipώistion tiπse. This in contrast to the methods of the jut t& w, hicfh sϊgsai iutcgrauon time is propordonal to the square of the accuracy.
According to an aspect of some embodiments of the iavcnύon. coherent Lglit processing b advantageously «^ed by using both amplitude and phase of ihe light field as way of cepa'smUήg a vahe. k cohaϊent hght sisnmatioa, ϊhe light's electromagnetic fields sre added as 2-D vectors. Thus, field smphvύda is tdciuified by a cM^pkx number in a Cartesia^-s cocuxlinatss. To null the light on a dctecior, ai«pHιudcs of cumpι«alioα result field aad feedback field mus. be an exact negative of sach other. That is exactly the same intensity, bat v^ilh ϊhcir phases opposite to each other.
Since gtf»eτally, ih« detector has a finite area, electric current generated bv the light on ιh« d«toc«A>r is the Integrated .^«ΏJ of the total light power impinging on the detector surface. The power h given at eaea point by the absolute value of square of the tϊeld on the detector giv«» ss s vector bsm of the eomputalion and feedback tϊehS>s at that point, the teqairemestsj of eijyaϊ amplitude and opposite phase su> optionally raainiained or at ieasSt approximately rαaύuahied ovei &e entire detector's active area. b mauy applications, it can he tisi>ii?ned that the vaincss Usod in the computation* arc uacorrdsied ύt p^eudo-raudom. A.ddiiionaliys in many fψplicaπoΩ values may be rearranged (or otherwise modified, for cxεmpk by adding a random value) ϊo en^αre tmc^rrekteά or pscudo- random aal&rc of the values. It was estimated, using simulations, iMt random nature of ths V3iue& of inp^t vectors and matrix elements products a bean with, a sliape whuh statistically remains -similar amter. most hiptti situations.
Cot^ecpjesitiaUy. a ieedback beam which approximatelymslcl.es the computation, result beam shape may bo produced and used, causing minor or negligible cm>r,
Alternatively or additionally limiting the detector'* active area, for etampie by placing n» aperture ift from of the detector, may improve fee accuracy by allowing only Jhc Seid from the beams' osatcr Iu mter&ic OΏ the detector. Since the noise is less dependent on fee asKnmt ofiight 03 the defector, ths adverse effect of Sight loss due 10 ihe spettiae is sαialK For exαπψb, asi aperture allowing 90fe/ό of the loial bcai\i power may be selected, alterriaiix cly αu speϊtutv aiiowttsg only 2ύ% to 30% tho total beam power mixγ be selected.
In some embodimeM? of the mventioru the sire of the aperture is s«s tχ> matcfe fac error iolcmuce iCt^aired αnd'or pπor knowladge otstatktical prttpertics of the input v&ucs.
Ah«matiYe1y, a "sofl" or apodisrtng aperture, for example serrated edge aperture or grs>- level apcnurc naay he used. Optionally or alternatively, fiber optics tnύy be usea to te-$lupc a bcaϊti* for example a s-mgkι~srκχ1e fiber may be use-tl Ca a»shapc the fevam έvi s aesr dif ϊrsctsoa bmit ^auis^an siiapc, Opuosally or alternatively, beam shape mampulαticn may he dose o& oao oj'tfee buutches or v-w both sep&ately.
In soϊβtf sjjtibodiaieali* of ih« invention, at least some of the light modulators used iϊi ihε ss'siem soconlhigto the current invention are inteifee^ce ϊnodαlatcuά.
For example, a Mach-Zehader intεrferometα may be used uS δjt decεro -optical smwmre in its arm to modulate the light tick!, A poicβdαi advantage of using sniuterfefomeier as s moJuiat>n" is that unlike && absorptive røodoktor, it may abo ^issd to r^veae the phase of tbe beam to ϊoprβ«iCΩ$ n-egative values. Moreover, unlike aa absorptive iaαdiilaior. the exee^ light oxiδs the iBterfemmcter &nύ do^s αoi produce heat that has to be removed from the sys»lem>
Λdditioϊullj or alternatively, a pliase shifting dc% tee may be used for aiϊectmg the phase of the heats to represent negative or complex vslaes.
Imerteronicteis may be mnaαfactated using freely pwpsgatkg beam^ vismg mirrors, lenses, lensk't*, beam-splitters nnd'or other optical elemctus.
As m altemntϊvs to a 3-D construction of optical s^terns^ a plaaar opitesi system IΏ whkh the iiglu is confined m one cHmeasion. to a thin layer of dtoicctπcj maienal may be used. Optica! c^smpon^is for thsse 2-T5.systems are, for example mu.ά& by lithography on a thin layer of gkss or uther optically transparent substrate with thickness of &sme order of raagdtadss as the v. svds?«g4h of the propagating light
Problems related m light scaturr tuxύ beam spread &t«- optionally minimised m ihcsc 2-O ^ystenis as hgli! aiay seaiter Oi spread effectively øaiy withui the layer. Moreover, beam shδps.' is optionally mairϋamed in the dimensions supporting one ΌT a small number of transverse modes,
O»«xHttj<ι2asifmal optical systems may be constructed, losing single-mode optical fibers. Optionally, polarizahoα maiauύtiing Obers are used. Beam shape of light propagating m such iihcjs is maintained and dcpcβds. HI some CJΪSCS, only on the fiber (i should be that 1 ~D optica! sysiem may be lithographically made hy etching thin tighi coπduiis on. a thin Ltyor of trsaspsα-ont Mibsirale.
Combination oi i-ϋ, 2-ϋ and 5-D system maybe «sed to construe t th«j desired optical system.
to some embodsffissns, ooaϊpotieπis used m the system according to the irrvctttioa w> mipedeci. For es^unple. ct«mp osents itsed as! modulators may have imperfect response, For example, a Maeh-∑&hsxkr iuterferometer used as modulator has a response. Optionally, pre-pnscsssbg of computation values is used for compensation. ΛvϊditioRaJily or alternatively, pu£t-proeesMS3g of eonspoiation results may used for eoinpOKsation In some eiϊjboiimwtsJ of lhs as ^ alucs of input vector ekmeMs are pre-processed before they are uss.'ά is a modulator ΪO aflbci ihs light field. ϊrs some emboάimeRt of the invenuos, input v&kias such as values of πrαtπx elcmeais are pre-processe before they are used in a modulator io αf&ei the light SeM.
In 5*αme embodiment of the rav'entinru output vaJαes values of detected light signals, or feedback Loop signals &rv post-processed before they are a&κi For cxasTiple. output signals representing calculation results tasy bo post processed to correct for system's uonHncarjtiss or ksowii systematic %sτors.
Analog or digital or combination of aaalog and digital may be «sed lor the preprocessing, post- processing orisctb.
To achieve fast computation eyclc. dπvcrs. lbr <il) i&mβ varying are ■optionally &$t. For example, detectors, drivers md mmluiatois B.sed m the feedback loop optionally react <|«kMy to minimize ihe signal on the dotecior in Unse equal or shorter than the computation cycle ihne. Generally, binary electronics is faster and consumes i«ss power than Linear eleetromcs with comparable speed,
In some cmbødixnems of the invention, binary circuits are used for driving elements such as a feedback loop modulator of a coherent feedback optica! computing system according to some cmbodaneαis of fee present invention.
For example, in a successive approximation feedback loop-, the feedback SeM optionally changes in predetermined steps of diminishing size. Alternatively, algorithms similar to the- "slgma delta" algorithm may be used.
Is seme embαdimeais of fee un-ention fet Avalanche Photo-Diodes (APD) are used as deiecΛors. These detectors are fast mxύ sensitive. Optionally, an APD is ijsed otusMe iis linear range tor added sensitivity and sψeed in a noα-iinear or btxmzy feedback loop without compromising the total accuracy. As the system approaches balance between ihcs brandies, the signal on the detector diminishes} and the AFD typically enters iis Uaear operaticm range. Similarly, t&bs technique maybe used to adjust the signal that is to be detected io be wϊtiii« 8 window of beet accuracy of a detector.
In. s& exemplary embodimexϊt of the invention the signal io be detected is less than 30%. less ihan 20°/«, less than 10%, less than 5% (or intermedials values) in ampiiiude of the signal w be measured before intcrfercsace. Alternatively or additwnally, the range of the signal to be detected is less ύnm 30%, less Shan 20%, less than 10%, less than 5%. k$s ϊhan 2% lor jaiermsdiate values) in. αntpliiudc of the sigiϊtil io be measured before mterfεre-ncβ. Optionally, ihe shoi «oisc* goes down by a factor of at le&jt ! .2, 2, 3, 4, 5, 10 or intemicdiak: values.
U jshosld ho Ωoted that a singh systens may include two or snore diiTwnt measurement ciremis. for esample^ one using an mtcrfsarometric tcdjaiqiie $s described herein (c.g« for large valaes) and fee other usiag a standard or other type detector (e.g., for low values or if Um mterfcrom«tdc technique fails, fov example, due io over-coiτe!atiou of isiputs.
in another broad aspect of some embodiments of the invention, & mcasuf tfment $y$tom having coherent feedback is provided.
The sy&ϊm according to an effibodiπvont of the iavctuion uses δ coherent feedback loop to increase speed uiάht accamcy of the measurement in optical measareaient systems used ia die art, a transducer Is used to generate or Bjodabttf a Light signal indicative of the measured value. This signal is then detected with a detector that converts the light to electric signal, which is usually digitized. The- resolution of the system csmnot be better th<m the shot noise on the- detector, liescc fee necosδny for strong »ignals %«" 1^8§ satcgiatiofi tisse liscrfssromeiej ic measurement methods are IOKWB 'm the art bur are usually limited 10 transducers thai modulate the phase of lsght sig&ai. Au εxaiHpta of such a system is a M ickshon interferometer eoαsmαπly used for accurate distance measurements. Of optica! gyrosscopa? measuring rate- of rotaύos.
It u> die object of SΠTΏC cmbodimosts of the current m-vcntion to provkk 5 modSurεmuRt vϊyjstoiϊi using c^liererst feedback loop in which the amplitude of light signal is indjcaαvo of the miStsur«d valiiv". it is! ajiotli^s object s>f soma cmNniimeπts of the current invcsUαα to provkle a moa^urcm^at »> *Um using coherent feedback loop k\ which both, umpbtuds; mid plia^o of light Mgnal iϊTw isϋicadve of the measured % altnsi.
te osc embod.roc»t of ihc iπveiitioa, the optical measurement ss>stora using coborenl fe?dbs^k coϊsi|ϊi3scϋ. a eohcteπt hght source providing coherent Uglit. s beam splitter, spUrtmg Ught from jjaki cohώeπt HgM :>o^rcϋ to a measurement branch and s feedback hruπcts; at least oac trafi-iduecr modulating li.uht in the raeaj»memeju branch to indicate αse^ϋurcd value; at least OBO uiihi mcdulaior modulating light m the feedback branch: at least one tatcrάrorøele* tor interfering light fe>π^ the measurement branch with light from the feedback branch, βt least one light dciceior dciecϋng light from dark fhngc of *aκi ititerioromotet . and a feedback loop, contruHmg hφt modulator at the feedback branch m rc-spon^o to signals from said ^t icast one light dcttwiof.
In some embodiments, the tratisdiicor modulates tiic intensity of light ia the me<5suremom brauch atifl meastired value is fefesred from sntessity sϊύts feaibάok Ixgh? whύn ileM fiinpljrαdε* in meaxajemcπt branch and moasaned aad feedback branch arc e^iiiai,
In anotbci «jχeiapU>ry embodimeut the transducer modulates* "both, the ijstsn^ty and pba&e of light m fee measurement branch and a feedback modulator modulates hΛhtho mtonsity ajxl nha^e Oi light in the feedback branch.
In sc∑sse eabodlmont^ ?atd feedback loop is a aoa-iine&r feedback loop. in isome cmbiMiimtsitjJ. said »on-liaear feedback bop is binary feedback bop,
income smbυώmemj> of dxe ϊnvenlion, direct measurement oi the ooirptuaiJon or ϊΩomjred value isj taken fronj a ilrst light detector while the light mtCB&ny on said first detector H siϊkύh while jncssuremαit of the commutation or roeasaied vslue Is takw tmxn a feedback lθ loop, I'pUonaliy using a second ϋgbi detector when light intensity on said first detector is larger than a preset vakte.
ϊn some ώsbodimεnls of ihc invenαoa, a feedback loop is used to track ύie changes m the external system to be measures mid a sample and hold is used to sample the state of the feedback signal. IB smrse- embodiments, high-frequeticy modulation is imposed osi die feedback Sϊgna! and irf used for the tracking.
Unie^ otherwise defined, all technical and scientific terms used lieruin have ύiύ same meaning «s connaoBJy uadcτxι»od by ojse of oaføaiy iskili is the art tα %vbidi this invention belongs. Although methods and materials similar or cquivakM (o ihcse described herein csn be used iι\ the pjacdce or iesimg of the present invention, suitable methods and maioήals arc described below. In case of conflict, lite pafeαt specification, including definitions, vΛW control In addiUtiπ, Jhe materials, methods, and examples are iilmtraiive only and not intended to bo Hrøking,
The invention is herein described, by way of example- only. With reference to the accompanying drawings. With specific rcferenee now to the drawings in detail it is sirassed ϊhat ilic pmicuiars shows are by of example and for purposas of iliustrative di$cussύm of ώe prcfoircd embodiments of the present invention only, and are presented in ibo cause of providing what is believed to bo the most useful and readily understood description of the pήxicψks and conceptual 'aspects of the invention, in this regard, so attempt is made w show sstroousia! details of the invention in more detail than is necessary for s fαndsmeat-al understanding of the mv«i«uon» the description taken nviih lhe drawings making apparent to ihose iskilied m xhύ art how the severs! ibπas of the inventioa tuny be embodied ia praciie*,
In ihe drawings:
Figure 1 depicts a .simple optical xmiliϊpHer as knovt'n sn the art; Figure 2 sofaumatioaily depicts a 2x2 optical Vβcior-Vcctor MulupUtir (VMM) as known in the an;
Figure Λ -schematically depicts a coherent feedback optical tmihinlier according to an. embodiment of the current invention.;
Figαr« 4a Jcpicι>. as optical multiplier using a binary feedback loop according to an. embodiment c^ώe eartvat mvamcrn;
Figure 4b depicts an optical multiplier using a digital feedback loop according to aa erakxlimem of the euαent invention;
Fϊgtue 4c deraetsi su <ψtteal inuitiplier adapted for handling, bipolar \ aiues according to au exemplary embodiment of the invention;
Figtuv 5a epicts an optical computalioa sy&iem witij & coherent signed feedback loop aecordtng to naoiher aspect of the current invention;
Figure 5b depicts -iu optical coiapulation..system with a coherent ^nsdbitiary feedback loop according ir- an embodiment of ibc current invention;
Fipfc 5c depicts m optical computattoa system with a coherent signed feedback k\ψ Kceαrding TO yet another sspect of the current ia\ cation;
Figure 0 depicts a sehcmatio block diagram ola eoiaputational branch of ait optical
V VM aeeorc&βg to tm embodiment of the coπ'eαt invention;
Fsguvc ? sohematiesllv depicts a block diagram of a computaftoas! branch of ao optical VVM using beam !>|>liπers according to j^ emboUim«it of the otsrre-xn inveπtk'n;
Figure £ depicts a sekomaυc bioek diagram of computational braiioli of as optical VVM using len$es for sp lilting mά eombinkg beams sccαrdmg to sn embodiment of the current kivontϊOΩ; Figure ^ schematically depicts aa optical VMM hoving a coherent feedback loop according to ,JΏ exetrφimy eajbodinjem of the current invention:
Figure 10 depict? a schematic block diagram of a measurement system a^-tsg cøhercat feedback accotding Io an exemplary embodiment of the current invention; asx!
£igu*e 11 depicts a schematic block diagram of a measurement syUerr* usϊsg coherent feedback csp&hle of measuring both attenuation and phase shift according io m exemplary fϊshHlatirøt olthe current invention.
DESCRIPTION OF THF FREFBRRBP EMBODIMENTS
The followssg detailed description is of the best presently eotnϋmplaicd niodes of carryϊΩg out the present mvs$iUo«. This ok-senptiαa is not to be taken Lu a liαύtfeg scase, but is made merely for ϋic ψmposc the general principles fe accotdaαcc Willi the ps appended claims.
Bofortf sλplauύng at lea^t one tsxnbodjmeot of the invention, m detail. Jt i? io be lisjderstocd Lku ihc invention is not limited iaits application io tbs details of oonstKfetϊon and tfe aiTungerø^nt x>t the ootspontsnls set forth in the follow mg deseriptimi or ϋlustmed in the dπnvmgiέ. The invctstioα is? capsbb of other embodiments or of being practiced or earned oat in various ways ΛLo. it u to be understood that the phraseology axiά teraϊm»iogy employed hereui is &n ilic purpose of description and should not be regarded as limiting.
Ia 4tbCU?siθB of tho uvrious figures dcscnbcd herein below, like numbers rvfβr to ltke
Hie ώ-a^iπgs axe gene-tally aot Iu scale. for clsriiy. Bon-eksentiai elements were omitiέd from souio oϊths drawmgs. Ai« us«d heteia, &n e!ome»ι or βtep recited its the siogubf a»d proceeded with the wot J s V or vv3∑r should bo understood as aot excluding pluial elements or steps, UGicss^uch exclusion is
Wϊtli reference to the tfeavirigs. Figute I depicts a simple optical oiuinplkr UK> as known us fee art.
Input light 102 emitted froai light source 104 caters the optical multiplier which comprises of tv*σ light ifficusrty attenuators 10(ja and 10(A situated along the opύeai path of ixrput light 102, in the sapletaematioss used in the art, light, source 104 may emit either coherent or meohcrsα? r&diaiion. intensity attemialoϊs 106a and 106b are efcαroakaJIy controlled by electronic derives \i)U& m\ά 108b respectively sack feu that the. transparency of each atte&uator is proportional to a numerical values 109a sad 109b to bs multiplied. Ia a typical optkal multiplier, atsmsήcai values lCKhs snd 109b to be- multiplied are in the form of digital values which are converted Io ajsa'iog ekctncd signals by drivers 108.
■Jαiessityof exit light UO is give&by:
Exii '« Input * Transmission (*i) * Tr&nsmisskva (b) ~ Arbitrary * Valise (a) * Value (b) Wherein Exit is the- exit light mlerujity; laput is the Input light intensity;
{&} &nύ Tr<ιasxmssk>n (b) are the iπmsmiitaκce ofaUenuaiors 106a and 106b respectively; Arbitrary is an arbitrary coefficient, which depends on system consu^ction; ssά Value (a) and Value (Ki 4ire the two numericsl values Io be muiiiplied.
Exit light 110 impinges ors a light detector 112 and is converted to an electrical signal pmporiional io the i«tensity of the exit light. t?ma%, an Analog Io Digital Convener ihDC) 114 OGx$v«ris the dectdcal signal frotn Hghl detector 112 to digital form.
For clariiy. digital signals are depicted by thin arrows, analog electric signals by medium arrøwa and light path by Iioavy arrows.
Figure 2 scheasaticaUy depicts an optical 2x2 Vector-Vector Multiplier (VVM) 200 ;^s an.
Inpαi lighi 202 emitted from a light source 204 is split to two branches of equal intensity 202-1 avid 202-2 by beam splitter 205,
Light of sack branch passes through an optical lΩultiplier which comprises two Sight intensity Multiplier I comprises attenuators 206a 1 and 206b 1 , wfeiie multiplier 2 comprises atleπuators 206&2 and 2Gόb2. For simplicity two tttulϋplkrs are shows, however fte number of xmdφiirø may be larger. light source 204 may ejriϊt either coherent or incoherent radiation. intensity aitcimaiors 206 am aketromcally controlled by decitonsc delivers 208 such that ihsi the transparency of each attemiator is proportional to Xhz coπresptmdiαg numerical values 209a! , a2, bl md b2 to be muiiipϊied.
ΪΩiensiCy of exit light 2.10-1 is thus proportional to Value (a!.) * Value (bi). Similarly. Intensity of exit light 210-2 is ttes proportional to Val«e (a2) * VahiC (fal). Exit ligM signals 210-1 and 210-2 are incoherently combined in combiner 2! 1 and She resulting light impinges on a light detector 212 whero the resulting HgM is converted to electrical signal Finally, an ADC 214 converts the electrical signal from light detector 212 to digital form. Using this optical multiplier, digital output 215 represent the mathematical operation of a!*bϊ-i-a2*h2. This operation, is equivalent to vector multiplication α£ vector A :::- (a1,a2> by a vector B ~ {bljbl >.
The system may bo extended to larger dimension vectors by creating as many channels as the dimensionality otihc vectors. Extension of ihiss type of system to a Vector-Matrix Multiplier (VMM) b known in the art".
A processor architecture referred to as "Stanibrd optica! VMM", described for example in Oror Q. Fietelsou, "Optical Computing". Chapter 43, MIT press 1988, the disclosure of which is incorporated hereiaby reference, suggests perform ing vecmr raauix multiplication (VMM) suing an optical model based on a transparency matrix. As analog eJccU'Ome vector matrix multipheaύoa unii is described, for example, in "Programmable ΛaaJog Vcctor-Mairix Multipliers", by F. Kub, K. Moon, L Mack, F. i..oπg, in 5 BEE Journal of Solid-State Circuits, vol. 25 Cϊ) pp. 207-214. 1990, which is incorporated herein by roiVrence.
US patents 4,937,776» 5,448,749 and 5,321.63% the disclosures of wfakh «c mcorpoπited herein by rcl'erc^ce, apparently describe axduteetures includmg opticsl components, which are suggested foriise for πiatrix/vector manipυlauøft.
One liϊBitation on ϊhc accuracy of optical computers is theimsvoidabls "shot noise" on the? Uctector. Bveβ in as ideaf light detector, the noise is at least equal to the square-root of the siumber of detected pbotoas* Thus, to measure a signal with high aco^iracy, large aumber of pboions is required. Large number of photons may be achieved by ushig a stroag light source or long mtegistian time.
As conscqaeϊice, csch additsoaal bit of output accuracy requires eiihcr: slowing down the calcuknkss by factor of 4, morcasiitg the light power by a factor of 4, or a sombmatkm of bo-ih. sknviβg άinvn the c«l«ulation and iβcreaϋiag the light power. Thus generally set*? a limit on the accaraoy aaά &peed of optical computers.
The optics! systems aad methods according to some embodiments of the current mvetuion operate wkik the optical iatessity on the critical detector (or criCical detectors) is rornsmai or >Ηttu!Iy trull Λ pι<testkl advantage of ύxι» is* that the above himutUtm may be overcome. Λ system sccotdujg to as exemplary embodiment of the mvcnuos uses a coherent &ι&Ua<»U%$*' interference between light beams: the first beαna vcpresenCmg the value to be measured, for example the computation result: and the second beasj \s generated ana comtolled by s Feedback loop. When balance is achieved between the first and the second beara ihe hght intensity at the outpm is <st n rmΛima and Uw noise associated WHk its detection is small The nKmurod value is safened ixom the ieecback loop CHciπtjy.
hiμmc 3 tkp&ts & ^dis&izitc iepi mentation oi δ coherent feedbέicL opi&ai mulϋplkr 3(Kf ϊiccouϋjϊg n^ an ensbodtnsentof the cunent m\ontion.
Cohcrsmi mrui ligbj.302 oriHied froΩi a oohsirent light source 304 is spht ;o mro paώ?; a eompumtioa chanaci input beam 3UX and a feedback chaimei mptH beam 302V by be?«n ssphttcr 305 Cobei cat ϊxght soyice 304 παy be a ia^et, pjcfembiy a scM state bsεr such as a dlυde Ja^er OJ. d V<a ileal Cu\ sty Sυϊfece Emittusg La^er (VCSHLh "Light ol'the cumpuuiUou mput channel 3G2C pas&cs tkough as optncol multiplier, coisspπses two %fct amphiαdc attesaato^. The mulUpϊkn coftipits^s atleαuatoss ^ 06a ana ?06ix
AsipMade sttenuaiois 305 ate cbcironically coMrolkd by elscirOBio dcs.t\c^ 3^'H s?uch tiϊat that the ampiiuiJc tjansparctjcy of each attenuator K pioponiυπai w a uunseiicai vsiαcf. "«" mύ b'1 to be muiuplwd iβtø* <m<,1 30% respcctivsly),
IntsΩ^itv oflif&t U ρn<ραmonal to the absolute value of the equated amr^htαde oi the light r;dd Tliud a dijvei 30$ ofsmplitude attenuaiαi 306 *s cunllgurcd so that the αmpiκ-ud« ϋf tlio attoπusteU bsarn is piopotuoaai to the dcsjred value. For example to sepreserJ toe vslue Li), ^ unosmy tmaspsrescy of i 0 (completely transparent) may be us*3. to iφfeseαt the vsku; 0.0, -άii sx&cύύty uanspar^ncy ofO 0 (completely opaque^ BKJ>> be uucά: aαid to yepre&cm thώ -value ø,5v an intets^tj- teansparcucj of 025 { 05'') røay be «j»od, ϊn contrast to incoherent optical processor wherein αcgatrvc numbers sre not directly rep?csca>ιed b> the always positive hghi uKrøsMy ; negative amptuude i^ oplkmαLy- achieves! by 1 Bl) degrees phase shift io the light fidd This could optiotωSiy be sohtevcd b\ a α>ntft>llablo phaj>e Khmer (not sshmva). It s*houI4 be uotcd that u\ some cmbodm-urni.. u ss imponam ihat titωπaator^ 33o would not indues umateαtional und/or unknots phaϋo shift,
.Λπφhtude ι*f compulauύftdiannei exit light 31QC s^ tbus proporiionsi to ά*b. If sliσule be noted tsat br4> a ami b may Mve positive and-'or ucgauvv' value?. light of feedback cbatmcl i&ptn k'aro 303F passes ihrosgh a feedback amplitude attenuator 306f drives by feedback attenuator driver 30Sf. Iu this example, itψst to feedback attonaaior άrh sr 3ϋ8f is In analog form.
A coherent detection umi 325 controls feedback smpliαide attemsator 306f so that ύlφϋά output 315 is obtained when amplitude of computational channel exit HgM 3 IOC is equal to amplitude of feedback channel exn HgIn 310F. Ai this condition, ass amplitude transmission *T* ϋf smpliεude attenuation ol attenuator 306f is equal io the combined amplitude transmission of attenuators 306a and 3ϋδb, thus f ™ a*b
(lonelily, colrørøn detection unit 325 compares at teasl oae beam &pUticr, When two baams enters, a beam splitter, an iuter&aenee ooctns between the tvtc* beams $uch feat at oαo exit of tho beam epluter ihc Iigbi OeId amplitude is the sum of the amplitudes of ihc two inccmmg b^asαs, whiles ir? the other exit light field amplitude is the difference of the amplitudes of tbi two mcomiπg beams. In 5h« example o I' figure 3, coherent detection unit 325 comprises a beam splitter 311 receiving computaticmaiL channel exit light 310C and feedback channel exit iigin 310F. Two beams exit beam *sp!itter 3! ! : & bright fringe 310B and a tla∑k fniϊge 31 OD,
For darity, a bright fhngc is marked by fall heavy arrow, while dark frmgo is xnarκ«£ by a dashed heavy gm>w Støtmg fb- i example with iaput light 302 v, ith intensity of 2,0 (arbitrary uiύu) or field of 2i) \ usmg a 50:50 hύ&m sphuss Si)S tlicre is m cqαal field amplitude of LO {arbitrary υmts) at Uw input of each of channels 3OX' αad 3O2F. After passing through the attenuators in each cluoBOl. tho ϊhϋ amplitude at UΪ© ehaund $xit light 310F iat f. Λi the outputs of the 50:50 beam splitter 311 ike bright fringe 310B field ;iroplu«de is eqΩsi to:
B - 1'2 Ha*b*fi, aad theialeusity u.: lBf « il-2'' (a*b^!2 * lli*(a*h)- * vi*^ J a*b*f; while st thy ώϊrk fringe 310D field amplitude is equal to: D - 1C" *<aHvl). and the mtensiiy is: JOf *~ |1^'': *(ft*b-OI: ^ :-» *<»*b)2 * V^t2 - a*b*f , Thus. UglH is mimiual at the dark fringe, that is on iktoctor H2 when f =• a*b.
Feedback io^ic 32O r«ceis'es*igmU irotυ detector 312 and controls alternator "Α)ήf ihtovish driver 308 in order to achieve ihe baiascδ coaditioa whiSi output 315 is chiasms! In uie embødliϊusm feedback logic 320 sweeps or αmips (hrougb possible s alues of C &ιιύ ∞cGgtn/uϊs tlϊo Blest hk^ly \ aius of f thai creates null signal ai detector 312 For example ADC 314 fusy be a ϊgger at the uixie during the sweep %l\&n Mgaal of detector 312 is below s sm&H preset tlueshoid Is another esϊbodjrαent feed bad logic 320 searches through possible values of f for a value that tn^mm/es the sigmύ of detector 312 For example. tnmsmiyaUon raeUωcts described in "'Hixmrnmύ Rec-jpcV (William H, Pi ess eiai, Cambridge University pi ess, Ctepte ϊi\ page^ 274-27?) may be used, ϊi sbouM be noted that sigm^l on the detector is a concave hmcUσa of ihe ina* value for f, zixά α sisgk πήnhnum cxi5>U> and w eassily found ϊn fact, in sume ci&ev this fαβeuoa it» appjoximatelv paπώolic. allowing methods opamizcd lor such a shape to be used
it s*hM*Λ! be noted thai beam spIH&is with raUosi OUWJ ύue& 5U:50 in&\ be u?αi
W 3th 5de?l or sea* ideal attenuators, capable of aclueviαg Cu?! tranβpai«ϊicyt the u?e of two 50 50 spliueΛ >ιelds ι!ie optimal i e of light. Oiffeieut sphtimg ^tios ma\ he u?ed to coi^penjsate fox unbalance btftweeu the two channels. Wheuiϊjjing splitting TSXIM other ϋsan
50 5C- a numm<ii dark lrsngs may be άchιe\«d uh*sα f C* a*h <λherc C is some numerical c^n^βt
Figure 4a depicts an emhodii-o^ni oi a binaty feedback loop variation of the optic ύ truitipher of figure 3 in whwh sαalog coherent detection unit 325 « replaced v- ith a biπarv- eoherest dciection uaϊt 425
Λ pulse geaeiatαr 430 produces pultses at high rate. hi operations aa analog aci-'uinulator 420 aceimiuiβtos tho charge m the pulses iiøm pulse ^eaef &tot ^3{^, civais^g a ratup analog voltsge whien is received by analog dm er 30Sf At the same Urns, a digsia! αccam«ktur 418 accumulates (counts) she pulses gcneiαt Rg d jgjial sufsbci ιβj.>i$s5ώπtal:\*; of f.
A c*>mparau*r 416 eo;a|x«-eό ύm sumal horn hght detectot 312 to α preset, near zero ϊΩresjhold value When the umssliαld! value is ciosseJ, mdicatittg that the bgM c>» Ueϊeetos 312 is nest 21^? o, oompaϊΛtor 41o halts the couwung ami causes digϊitii aocumtslai^r ^l^ ic pscsetu its s &ιnc &ia digital tV3s«it 315
Tiiis vsahϋdhmeut is lϊscd ibt 4e«iθiistratiag SΏ implθffientatκ>a of bki&ry feedback loops? aocofdasg to some embodiments of the current fcivea«o» ft should be noted ikn the τιurabsr of cycles may needed to røseh the final v&luc may be large. Additionally, there is a danger that BOXSC on che dctecior or comparator may cause the loop not to close as fee threshold may not "be crossed if the ftoise is aecideutaliy above the preset threshold. Additionally, She ncemacy ts limited by the comparator pje≤ci thieshold valine.
Fsgisre 4b depicts an embodiment of a digital feedback loop variation of the optical multiplier of %«re 4a in which the binary coherent detection unit 425 is replaced with a digital coherent deieoUoa imit 455, A digital ramp generator 460 produces digital ramp value which is received by a digual dπ\«r 40Sf. near s^etx^ threshold value. When the tlirt-shold value JS crossed, mdjαttsng ifeat the light on defector 312 s& near ?ero, eonaparaior 4tt> halts the rsiiipmg and causes digital raiϊip geaerstor 4oO to present iti vnly e as digital result 315»
It should be txncd that although the embodrmcju of figtue 4b appears simpler thaα that of %ut e -*ά. cosiStiuetion of high speed analog aecmmslator and digital couatet uisy ^>e simpler u> thtm th« coastnsetion of a high speed digstai driver. While ike digital driven 3OJk and 30Sb vary their \ aiue at «ach consptnstson cyeie, feedback drivers such as 30$f and -Oδf change thc.r % αke on eaeh feedback c>o!e, txnύ me opharvzlly mad* tmixi faster eom^o&etus tli8« dmerβ <30ϊ^.b) of the attenuators of the computation cbanπd,
Figuiv 4c depicts an optical multiplier 400 adapted for kuidli% bipolar values gceordmg to as. exeisplary embodiment of ύic invcation, Ui ih& embodiment, a t>base shifter 306' JS added m line whh each aiteauatυr 30o. fin a commutation bπtnch 4S()Cλ phase ihiftets. 306'a and 3(HVb were added in Hue with mtessttRtois 30βa u«d 306b respeeuveiy. ϊt should he noωd that the order of attenuators and phase SfKiHe... maybe aifoitrδ)y since matberøatkaJi> their etϊscts itstay he r^presemed a^ jπulupUcatioϊϊ ofthe light Held with & complex constant, and m«I%lkaUon operetiocs eomπitttale.
Phase shifters 3(V receive from 308 signals Isdicativc of the sig?ι ofthe (positive i»r Λ<?gMivc) end afibci a phast; shift of IHO degrees accordingly. AitomativaK. only oκc phase shifter per jmϋtiplleatson channel m&y be installed ir>. (h^ computation branch, asd h$ status determined by ihe combined signs of the two values to be muϊ&plkd.
1« α &cdhack branch 4S0F. a phase shifter 30ό'iVas added in line with dUesuator 3ø{>£ receivmg signal from driver 8081 aκl affecting a phase shut of 180 degrees to the light in the ϊccdhack path when needed.
Alternative.}, the siga of smgle multiplier result may be determioed electronically by the cotabmad signs of the two values to be multiplied and presented together \* Uh the of the result Howevαi, as ^hatl be {!e.ϊioastra.ied Mtw, wJisai the c-osipuiation brcmch cotϊspiises røαUJplc chaπsels ϊbi perforrnmg more complex operations ^uch as \X\Ϊ, the us? of at least one phas£ shilki per ckmncl to reprssscnt bipolar valoes curs ha udvantagα^us.
Figure 5a depbu. ss optics! oamputauos system with coherent i^igπed feedback loop 5€<) secordisig to another aspect of the currant invention.
Λ dia^back of minima searching algorithm is that error signal pcodαcMby the detection swtem and usicd by the feedback loop do not eoatain iafbittiaiiou an ihs dtreciioa in which to change the trial vaϊus. DirecUouai information ts gathered by successive "trial and error'" stc|\s which may reduce the speed of ihe system.
According Ui m aspeci of the mvo«aoα. at least to detectors are ascd m the ieedback loop, each receiving Hght &Ό3Ώ α different output port of the interfcroTSKstct and sigtied error signal is deduced from eonjparing the signal front t5aid at least two detector*;.
Systera 500 comprises thteo sub units: s computation branch 40BC: an *>f tϊcal iϊ>tct fem:Betcr 502; aad *ι ssgaed feedback loop 501,
Λs ,ike<5dy d^cnboJ, computation bnaach 408C aUect the UgIu pas&røg. teΛtgliit by sLUcauatson sad possibly by causing phase reversal .
Optical bnedemmeter 502 receives, input light from cohersM light ^aurce 304 and produces at kasit v&o opdcal oulp«ijι 523PD miά 532ND to be used by signed feedhaek loop 501 to puxlucδ a signed sigr.a! for closing the loop. Optical ύiierfc^moier 502 b constructed such ύni st least both optical outputs are at or nc&r ?cro optical stgnal when ike irαerlerotietcr ts balanced.
2*1 ITΪ she exemplary timbυdimcnl of Egure 5a, optical interferometer 502 comprise? a pickoif beam splitter 520 spUtlmg a small amount of light m the form of a weak bias beam 5026 from input beam 302. The majority of the light exits pickoiϊb^am splitter 520 as main. ϊtipxit beam 5υ2. Baom ijpliu«r 505 splits rnaia input beam 502 to computation input beam S02C and feedback inψΛi beans S02P,
At sh« computation chaaael, computation blanch 480C affects the beam producing computation cb&aβe! exit light 510C. Computation channel exit light 510C is SfI it w two equal beam* 5 JOT* b\ a beam sphtter 522- Λi ihtt feedback chsuaeL feedback liranch 4S0F aCfccis tlw beam producing fceαback channel CXΪΪ light 5 Wi\ &r<t$ beam 5O2d i^ ititorfercd wUh feedback channel CM* light 3 ^ OF si Desm sjplitrer52] pixxkicmg nvo slightly unequal beams: Pssithe Feedback beam 51 OFF and Negative Feedback SIt)FN depending on the sign of the field jnterfereace atbcsn? spliitcr 521.
Bach of. positi ve leedback beam 51 OFP and πegαih e feedback 51 OFK as e imeribred with tmc of beams 5 iOC, and the resulimg dark fnnges^ S23PD axύ 523ND jcsspCv-uvdy vsxiϊ the υ-pjie&f isstotferottieter 502 and are detected by photo dcleciors 512F and 512K respectively.
te Uiδ Hmit whore baft^ beam 502d bas negligible intensity, and ihe mtcjfctometev b balaacei? ^thai is f ■ a%). both άsxk lhngos 533PD a»d 523ND present zero opiicυi pow ei to *?etcc*o?s 5 ! 1P HII»1 $12N.
However, weak bw h«irø 502d breaks the symmotiy Lvtwoeii daife fringes 52?PD and 573 MD csat>lkg the determination of fee ύp\<$d feedback sigaa! by comparing the signals on detecfcrøs 512P and 5? 2K-
To sr.aly/ώ the dilTetence behvtf<ϊ» the isigsaak produced by detector, we stan v^hh power at coherent source 304 of 2iHd"k soine aibtoty intensity ι\nύs. With kickofTheam spHtujr S2ϋ picking olYd" pt*wer of beam 302. beam 502 has amplitude sif 2÷i; % bile heam 502d has iimplϊi^c of d. After splitting b<jsm 502 by beam splitter 505, both beam.; Si)ZC tmά 502F have ssΩψiiiude of LO; ilϊtss, beams 5 IOC asd 51OF has saipBtude of «*b and f iv$ρecuveiy.
Bearø 5 IOC is equally split to two identical bεsms 510C each having aεppmask ^f
Buaτ« 510F intcrfe^e^ with beam.502d to produce the foliowmg two beasss: Scam 510FF haviag amplitude of /_•' "*•_>*'_**& aad Bsxuu SlOFK havmg amplitude of M-^P/^d.
Λs. (he άxά. fήxψa output of beam splitter 523P, beam 523PD has the amplitude of,
at she dark fringe output of beam splitter 523R beam 523PN has the amplitude of:
ConsequeaUy, the fmvεr on detector 512? Is given by: 5 j %*b-C '""-f1 λ r*d)f - l/^*KanH>df -~ 1 P £MJr wae 0 " a¥b-f ϋenotos &c difϊerciice beϊwerø. the compuUttkm value »*•!> and ihc feedback value f, The power on detector 512P. gnviϊ by ^D-d2 -"id" « small whc« f - a*b,
Shrvlbriy, the power oa dstcctos: 512M ϊs given b>".
P';>'*aΛb-(>= **^' '*<*) ^ ~ ^*!(.a*b-fH d ' H* D . d': The pιm« ca detector 512M given by >-\H is email whea f~ a*b.
To pf«x!hkv a sjgnct! feedback Signal, difibrsnUal araphfier 520 analogicallv subtracts ιh« sϊ«sκϊl oϊ dctvctoi 512? ϊxoin signal ι?f detector 51.1K to gh c: s^*)D*d[' ~ JK D-1 d-"1" ά*D "■ d*ia*b~l) . which is a signed vaϊαo proportional io ihc err^r in ihe fyedbaek loop a*b-f.
In ths «κeiu])!ary embodiment of figure 5a* an analog integratoi 525 wstegjat^s the ^ixor sigππl txosn ώfferentia! umpϋfe-j 52<> and feeds jtto the feedback bratich 4&0K ihus-ck^mu the foedbtϊck loop. 4DO 514 di^itij'csj the feedback ύg«sl to pioduce the desired digital result 315. ADC
S 14 may be triggered vain® the feedback loop has iseftkά, for example by observing a stnali signal at Uic output of άtTerenisal amplifier 520, or it t&sy be UΕggefoJ St preset USBC or presei number ^f cycks? depending on ths? desired accuracy after aew values of a and b were mput at the eompxitatsoΩ branch 4OJ5C
^'sgu«\? 5b depicts an optical compaϊatiun ssvsicm 570 wύh. » eolϊerent signed binary feedhaek i,rø according to aaoihcr embodiment of flic cutTent invαittoit.
^i«rπ 570 ^ a vananoa of the eaiboUimwU of the kvaiuαα depicted in %x?r« 5a. therein ϊmis&ύ. of signed fewdback loop 501, ϊήυaiy signed feedback loop 371 i^ used. Binary comparator 530 compares ifec signals of dctϊ-ctojs 5!2P and 5I2K producing a single \ni equal to either > 1 or -1 depesxlmg on which signal is larger.
Λαstøg UϊUϊgπϊtα* 535 intεgi atcs the output rf comparator 530 and proJuces the feedback stgsui. Concurrently, digital mteguttor 534 integrates the output of comparator 530 ami pϊodwcos the sk&rcd digua! result 315.
In some embodiments, feedback loop is reset to a preset value after ihe cempletjojn of s computation pnx'ess Optionally the piεset initial value k at mid-range. Optionally. Ihώ initial vaku* ci 'T ;Ώ the loop remains same as the rssuU of previous Optiøaally the iniiuά value of "f ' is dctecu?d to be fee must probable value
In .some einbodmiems rue size*; of the stepjj takeu by analog iutegra(«r 5^3 dimtnisϊies UΪ each cosssecmix e step, In these onifoodimesis, digital integrator 534 K replaced hy an ΛOC coΩϊjccted. to the output t*f anaiug Integrator 535. In some embodiments the %u& cf the sts?ps 1>> a incior of two m each co«s>3cαUvc step. m koine embodiment the ssz« uf ibe step depends o« the tuagmtudo of the dit^rcaee &g3Ul ύ%<£ two dεtεclors. as <kteπti$ned by the difference of the Sϊgβsls of the ΓΛ* O comparator^
It ahodd be noted that the order of beam splitters 505 :n\ά 520 mciy be revcissd witiiout changttig ;he chelation of the s^tem.
figure 5c<Jopιets as optical computation system 600 with a coherent slg&xi teedback 3<H>O aecotxilng L>~> another aspset of the cunent mvciuκm. ftgαro 5o, the mibaLmee beUv«c?i the iwo detectors :s eaxised by Λ small inibaUwε of a bcx?m spUrter t>21 used to split the light fioxn feedback branch iato two beams oiOFP miύ ύ 3 Oi- N respectively,
Opueal mterfoiυmetei 602 compnses of splitter 505 splitting the light of input beam 302 tp die eoaαputatioeal br«ftcli408C a«d feedback branch 40SF.
Λi Ute comp^utauon channel, computation biaach 480C atϊect>> the h&sm prodocing computation channel eάt light 5 ! OC. Computation channel odt light 5 iOC U &ρlit to two equal bwau. 51 OC" by beam splitiej 522.
At the feedback cliamid, feedback hzmxch 480F (computing an attenαato? and opttonaliy a phase sMtor) affects the beam producing feedback channel etit light 510?.
2J Asymmetric beam splitter. 62! unequally splits exit light 510F to s shghUy stiosgor positive feedback beans 610FP and slightly weaker uegaibe feedback beam 610FK.
Hdch oi posmvo feedback beam 6!0FP aad negative feedback δiOFN h» *myrter«d with one of beams 5iOC\ and the remltbg dark fringe 623PD and 623ND rasp«jcrive?> exit the optical mterfcrosjctcr 50« and are detected by photo dαectors 5 \ 2V mid 512N respectively.
At the Uϊϊjji vilieie fee imbalance of asymmetric beam Sf Utter 621 is negligible, ami the mUartemuieier Is balanced (thai Is f - s*b), both tiat friages 623PB and £23NB ptoses! zero jptk'ol pov^cr ϊi> detectors 51.IP and 512N. However, ihc small ssymmytry breaks the s«yinmc5xy bctw eε& dark mngcs 623FD and
623N O cttabhng t5tc deiemtiπatioo of the signed feedback signal h\ comparing the signals on detector* 512P and 512K
To analy/.t; tlio dUTereacs1 bel^ oea the ^sgnsis produced by ^eieousrs, we v&rt witli po% er al ooh«sont sourct; øf2.0 m &ontc arbttrarj' mtcusϊt>" αniH.
-\ftcr !?piittiτιgbedJB by beam spHitcr 505, both beams 50X and 502F havsj amplitude of LO; ϊb«!«, btfams SU)C and 5 U)F has aαiplitudc of a*b aadf r<jsp«sti\ciy.
Sesm 510C* *$ equally split to two identical beam*.51 OC each liavtsg amplitude of Ms ^aH-! Bε&ύx S uJF Eji unoqaaHy j^pHt by asymmetric beam jφhϊtεr 621 to prodiK^ the follo ing two bearaά;
Besan 61 OFF has ing amphtode oBr*P{B-#, and Bea∑n (>1 OFF h&\ iøg ;α«ρUϊ«do of Yi *"f*(1 -d}-
At the dark fxmge oαtpuϊ of beam splitter 623P. beam 623?D has ϋic amplitude of: v>! l*a*!>S s*f*(l fd>; while iU ike dark fringe output of brain splitter n23K5 beam 623 PN has the αmplittsde of; J//'*a*b-lj *f*(l-d).
Coaseqaeaily, the power on Uύtector 512P is gtven by v,'-^*h-//^f{! 1Cl)F •- ^^ilanviy^d'f « i«^D-PM2 s whew D -■ a*b-i denotes the difTer«uo« beuvefen Xhc computsttoa value a*b and the feedback value C The power o« detector 512?, given by VHPd)" is small when f - avb.
Similarly, the power on defector S12N is given by: >V»avb-1': Nf*(1 -ύf «* ^ta*£K}U*df - 'VH_Hf*df Thcpov^on defector 5CN, given b> 5Z^(PtIr is small when f ~ a*b.
To produce a signed feedback signal, differential amplifier 520 analogically subtracts the signs? of detector 512P from signal nf detector 512 to give: k^jOH^dj*' -!':* i>fx! '" fSi^D *= i%d*(aΗ>D which is a signed value proportional to th« raror iύ. ϋaε feedback loop,
Signed feedback error signal produced by optical interferometer o02 dimύu&hes as ώ« Redback x alias approaches zero-
As noted ditTiCttlHes m accurate msasraeraent of corapussiion values is? «c«c at high valuer due to shot aoi$t% while aϊ lo^' values the shot nαi&e small. Thus., a. combmoil system co^ibiuing άnύύi tncas.ui'ftnjent of computation resisit at W computation x alue^ and using an mtcrferomeier to acαjtΛteK me&»ure computation results at high values? comά he cossifuoted, For example a pickup beam splitter (liot ^hown) picking sosic of the light from computation ehanxieS cxή Ught i^ IOC <v&i directs tϊ to a dueet iseaswome«t photo detector (noi *ho\vn) ituiy Iv «$eα Op^nssliy, if ssjgntsl ^n direct mόa^iiresient photo detector is beiuw a pteset value, ΪU> signal is «}>ed for άetemHUΪng IMc result while if us signal j«* above A preset valtis. sigaai from the feedback loop Ϊ«J «SC»3. Optionally- signals ϊmm direct ad mdhve-t arc combined, IB digital feedback loop 601 epioteu JK the embodiment of %ure 5c. a αsoNt dϊgm?cr 624 digitizes the analog βlgnώ lκun differential amphϊϊer 520. |>$ educing for example a digital ϋivuiai h»\mg value of » 1, 0 or 4. Digital iatcgmtor 625 mtegvates the results of digitizer 624 and presents H to feedback loop kti»di 4$(W*
Wlien the value "0" is measured by dsgήker 624, the feedback loop is balanced and tile digital result J i 5 is presented.
C*ptjor>al!y« digitizer 624 h&\ t* diiϊetvnt set of values, for example f ♦•! and -1 ); {"-"2; -H ; 0; -J; »2K ctc.
Options!] v other methods ^ic uϋcd to determine the balance C>f tlie- imetictϋmctor. for example a $βl ααnsber of step?, a sepstiiive change of &ign of the output of digift/cr 624. etc. U should be tjoujd that sigired feedback loop 60 L 75 L and 501 may be iΩέm:fomged.
Figure 5 ie-pkisS a schematic block diagram of a compatatiosal branch 4SO of mi optte&i VVM u^iΩg coherent feedback according to an embodiment of the current tπventϋotiu box simpivzity, input xectois aye shows as haxϊng two dements. Computation camiel input beαro 3O2C i& split to tvu> equal beams by a splitter 6§i),
Each beam I? aϊ&ctcd by a plurality of modulator 6Oo driven by a plurality of driver 6OB according to vector element values 609. IK the example of Sgurθ 6. ihe tipper channel is affected by hvo attenuators; 60δal aad 606b 1; while the lower channel is af&cied by uvo attenuators; 6Q6:t2 mύ 606b2,
Coherer*! beam coaabmor 611 coherently combine the two ohaaαels to produce « computational output beam MdC with amplitude proportroual to al*bl-&2Ϋb2.
Ths optical system is αxtcsided to higher dimension vector by adding more ehan&ds \o the csalciϊlatioa branch. Exemplar)' embodiments tor such cxteasϊoa are depicted in ^he felloe ϊng figure.
Figure 7 sdiemaiic-aliy <L*piet_> a block diagraro of a corøpuvatioαai bniach 480 of an opύcal VVM using beam j»pUuers aceordiϊig to an embodiment of the cunvsnt
For simplicity, the case of inp«t vectors having four elesoests is demonstrated OoϊΩputauoa canael input beam 302C is successivύly split to two equal beams by a plurality ni" spliters 71 1 , ibmusg N* chaαnds wlicre IN (S~2 ia tbis exaϊsipie) is the &«mber of k*vclsϊ ofspiUtis%.
Each beam is aikcujd by twυ ϊnυdαlatQis. Ia the ϋgure "?, light in first cbiaiαd is atYected by modulators &l and b! , second ehaxujel by modulators a2 and b2, ate. Coherent eombiuiisc of ibe beams from ail channels is <ΪQ»« with successive addiiioas nf ihe biiimi amp liiudcs using beasi splitters 7 LI . A bright fringe is selected trcrø ibe miederei-ce on beam j»phttsrs 713 to produce a computatioaaS outpui beam 310C wl& aπφiiUKic proportional κ> al*bl •»a2tlώ+a3*b3'<-a4*b4- i. srg%;r number of channels the number of levels of spiiaing. it should he noted thai uaswidsbiy some of ihc light intensity IM lost through the dark fringe oiuput of the combining beam splitters 713,
Λ compact system maybe consuucled by tJsmg a mmiaturo free space ptop&gstmg beam. Λhe»ϊ«ιth'elyγ fiber optica taay be tisod for coustructiag the optical comporsaus. Λitcπvαtively, optical curaponentii may be Hthographleally produced cnt tliia transparent turn,
4^UC of an Nx2 opϋcαi VVM tJsmg fan out optics SIl tor spiitiisg. the input beam 3O2C into separate chssnels. and fan m opucs KIl for enmbmmg t&o charøeii? into a» output beam 31OC. according to an embodiment M' the current invention.
Confutation esu&oi input beam 3O2C is split to N equal channels by fas out optics Sl 1 -
]« the exemplary ei&bodbftem of figure B, i&n out optics Sl 1 comprise? tv-o lenses, t* beam diverging km! &1S and a eoFhmatmg fens 81&. Optionally, a ien&let array is used to assist the coHiϊnaiios of the light M^ ϊhc computational channels. light is each v-ompytaUoa channel is atfected by modulators 812.
Fas in optics 82 ϊ focuses light from ilie piuraiity of chaϊinols crcatiϊsg the coherent compiuadoiiiy outpαtboaiu Viϋ€ having amplitude proportional to the sum of amplitudes ol' all
OptioaaUy, s pmhols aperture 825 is inserted at tlw tlκa! ρou*t of converging kτ?s S25.
Thϊs ma> be useful for rejecting scattered light end/Or hici casing the spatial oohejvnco of ocϊapuuitύnial output bean? 31 OC. The fan in/ fan out system d»jpwted in figure 8 leads itself to the use of «>τu> atsd two dimensional light modulδtkm mmys as attenuators 812. Tra»sJjuJtiϊag or rcUcctmg att<jτmaUϊrs may be a>icd xvithin the general scope ofώe current invention.
It shouU! Hc noted feat light musnsuy may b* lost at pmhoic
SI-^. A? noϊed, lost oflighi in a Jeedback ba$cd system do iwt incres^e the macouracy in the Λ system maybe conslradtfd by υstng mkiattire tree space- propagating beam. ΛHema^vdy, wo dύuen>.teπa! optical oomponeats may be lithographically profeceil
Ii should be- aoted that jntorfcromslers aød feedback loops of any of (he types awclosed in the preceding Ogursi. may be used for the optical VVM.
Ftgur^ ^J sehcmatscaliy depicts m npticai VMM haviag a coherent feedback loop <?0U according to m exempkry emlwdiii-ient of the current invention.
Optical VMM 4X)O comprϊucx a vjohenjnt light source 304. Light from coherent hgk 5OtJJVCS 304 is piojactcd by a hortΛonlal fan out optics (not shown for clarity) onto a \ ector KttoHuatioii array c) 10 havmg k individually controllable attenuators 9lO( 1} to 910(k), snd to ft feedback vyrdeal fan out Of ties %X4.
F<χb aitemjaior 910{o) moιluiat«s the light passing through it to rcpreβmt a xaku v(c) of s vector ^kmeat "c" of vector "v" having dimensioualtty k, to be multiplied wttb a matnx m.
2? Buch attenuator *H0(c> w associated with a vertical fan. out optics {not shov>& for clarity* which spread* the light OΏ a vertical column wo" of πuαm auomiauαa array ®20 havi∑ig uMk $siώ\ iduaUy ύomrollabk aUeaaators °20{ Ll ) to 920{n,kX
Kach .tttesiuatoi *>20|r,c) in the 2-L> army 920 modulate the light pawing through it ΪQ represent a value m(r.c) of a matrix element to multiplied with the vector. Consequently, tho amplitude oHight at ύin output of attenuator 920(r,o} is proportional to γ(c)*-m(>v).
Each attenuator 9_.0foe) is associated with hnriyonial fan in optics (not shows for clarity} which Jiroct hght from all afees-oators i» row V to the coherent detection dement ^)ϊ l\ι) m arr&x C>1 ! otn eieme«ts. Coβ^εqucntly, the aaψiitude of light at the input to coherest dtfteciion tϊkaicnt ^ 1 l(r) is equal to Sie vector element V{r) wherein V is a \ ccajr ox' dmϊonsionahiy π. \?ieate4 b> tϊϊuiύplyύϊg x ector x- "with matrix m,
Light ltom feedback vertical fan out optics 91)4 is pn>jeetcd ot&a & veitkal feedback sfecnuatjos army ^O having B individually controllable feedback attenuatoa 950(1) to °50(u). light fΛ>m feedback artcnusCor **50(ri is directed to cofeensxt detection eleme t 91 i^r) where it isterfcres with light arfivmg &on plurality of atteauator Q20(r,c) in rov. V. fcaiL'h cohcf est dofectiOR elemcat 911 (r) is associated -VvItIi ώedbaok loop 930{t } f only twof Q30(l> and Q30{2) arc shows fύx clarity), whioh controls the eυiτesρo?κkng ibodhsok aUϋauator 95« %x) emά produces the de^red digital ouljmt πjsult *■>! 5{r>.
Ix should be noted IbM inkjferoiRcter topologies and feedback nj^thods depicted xn the pjec^dmg figures may be «&cd for coherent detection element 91 i and fesdbsdc loop O30. FΛΓ example, each feedback atictiuator 95ϋf r) may be associated with a weak sii-aiteuuausd beam to enable eobereni det^tinn topology of fiprtj 5a. Similarly, ts>mmetrie beam spiiαer ^vithin each dotecuos olemmt V'l l(r) enables fee use of coherent detection topology ol figure 5c. Opiionaily^ dstTercmt oic«ic«t$ intxy use ^jffcreat mefeodis, for exsmpk\ so the s^tem may rc&ύ oαt ssome compiϊtatioa vskses &ster ai lower accuracy than otheie.
In aiioihcr broad a&pect of some embodiments of the invmtioa a nieasusemeftt s^teai ut,mg coherent iVoUback is provide,
Flgiuo 10 Jepicts a schematic Mock diagram oi's niessxwem*nt system ?ov^ xieisg cohorøu foeαbsck accordmg to an exemplary embodiment oi" the cmrent im entjo«.
Λ coherent source 750 provide* -coheroat light εo an intf rferometor 7oQ. In imes fcsomctcr ?o9Λ hght froai coherent SOIIΪCC 750 is divided between aft upper sieasoremeαt ehαand raid a IOWUΓ ilvtftack ehaxtnei by a beam splitter 757.
2S Λ transducer^ modulates the light m the measures-merit teach m response to a state or rate eϊehaago of external system 751 For example, transducer 752 may be Cached to the external systerø or may musgπd pail of the* externa! system* oj optica! properties of external system tasy be used. Fox example temperature dependence the absorption of an optical δbei may be used ks modulate the light by changing the iraB&parcney of said fiber. Ssmilarly, changes m iisikdion, abssorpUoαpolaεuatioti etc. maybe used.
OeπeralK. both phase and arsipiimde ύf the light m the mea&ujfemeni chan&d. may be. aiϊeetύd by the state of the externa! sysiem, however, m ftguies IO nnfy amplitude changes sue con^ktered, while m figure 11. both phase and amplitade are ticked snά opiionήh' measured Dy the feedback bop.
TUe aim *,*£ th« feedback loop is to rniaimj^e or rcdaet? the tight hrtsusily OΏ ihe 4e.seto- k> below a th.esho]d IcveL
It should be noted iha« any t>p« oisiatcrfciomefcf aaU any method of coherent leeύbaek loop (sigαeJ or imsigaedj άmϊ specifically those depicted in tho ^teccdmg ilguscs may be used. Λϊϊsidg, bitaΛiy audftr digital feedback \oops may be used.
Optionally, external system and measurement ss^iem ma> «sc p!umlit> of tvanswiαeerss, for exaraplt; located at &e^ciai locsttoπs m the exteπsal sy^e∑n, Traftsducetfr au\ be singed along the ss-ϋaϋurcmcnt channel, oi the light iroai coherent source ϋ> lu^tiiivided among the fraΩN'duceri* tmd than combined to tous a weighted average of the signal ys^πg metiiocts shoun IW the eompa&tiona? branch, a? seen h\ pfcccdiag figures.
In contrast to computational .sysicm vvhsrom lϊipiU olkn changes HI abrupt and random m jaslawu most me-a^uremeni s>stem change thctr state ccmtitmousiy. TIΪUS, to mea^renieat ■sj stems, iosdback loop is opbo»al!y allowed to track the state of the measured external ^iem and sis ssgnal is sampled when needed, I he tui<i of change generally dictate the πmtmai ϊ»aπiphn^ raie of ihe iπ«asi3jχmeτtt!*, Oftsft, tlie optical stgϊiαl:* arc small tor example -ft lies {he exfemai sysU'tπ 5i> in A txmote location or when powr coftsusnpuou is lursked, SlKH-&ei&e- Ihrø^ed d^tOkjaosj j^stctisj hmk the -accuniey at high sampling rate.
In tlxe otejaplmy embodiment of Rgure 10, ligln in the feedback channel pas»s«s Umwgh attennalor 753 aud iftterfercs wiife light fiom the nieasuremcat chssmel on beaiϊi splitter "56, Dark fikgs? ώom beam splitter 756 βαtε»s the feedback loop 7t*4 where it impinges sin detector 755. In the txempl&iy embodiment depicted in flgxue LO, a signal yeneraun- 761 generates signal st n frequency considerably htgher thaα the desired sampling ''Me nf system 760 Signal frosn a NSgBuI geraaator 7{j 1 is added to the feedback ioop at a sαmrmng jimcuoa "71 oM the resulting δigaal is fed io an ktUnmator 753 through a driver 754. ConscqueaiK. light mtesmtv in the feedback loop performs high, frequency dither around its mean value. A tmad amplifier such si a lock"«s amplifier ?5& optionally syschrom/cd to signal generator "^1, receives detected Sigcals iτorø a detector 755 and extents a sigaed error signal proporaoa&i to tlic HBbalatice ot unϋsfenm^etoy 769.
\a iniejOTlor 11H inkgratos fee cnca signal and feeds it to the feedback attenuator 753 ihsottgh suπjjrang jun^tios 7"! and driver 754,
Λn ΛD<^ '7S^ digjUΛCS ?he feedback signal mdlcauve of the Ntate of ώxten^l system 751 and presents it a^ a dtgital resαli T63,
Opπotsally a filer, for exaiiipk a low-pass-filte? or a notch filter or both are α^ed for c.tπ3iπatioxi ol fee high frequency nxxiuiauoB , before feedback sipui sampling cr a* digital post pri>ces5>ing after it.
Figure \ ϊ dupiet* a sehcm&uc block diagram ofn mcassureπieiii system $60 u^ng CχNhercnt feedback αad. capable of measurisig botb αtt«a«ation and phase shift aeeordmg to an exemplary ombcdtrøeiϊt of the cmxent invention. In ϋotac cases,, a tiM&kee? ^52 eauscs chaages m both amplitude and. phwe of the light k the αeasimsmsntehamiel. UnitUentiotsal relative phase changes T«ay also be eased by changes in the meaiuremcat or the feedback cham^ei for example due io iueehatucai stress or thssuiαl e<φaasion.
In oϊder to measure and/or eorupensate for these phase chaBgcs, a phase mcπiulstor 953 is ύ\jscrtcc1 miύ the feedback e-Kurøei, In ύx<ύ exemplary «mbαdiαiεαt of llgαre 1 Iu h &ιφ.
■ficqucacy ph<t$u shifter θ^ jnJncss small phase variations arouαdthe me<rø pliss^ m response to high frequency signal from signal generator 96 L Frequency of signal produced by signal generator Qb \ L* chosen u> be different than that of signal generator 761. Thus, lock-m aitjpUfier S)58s uhkh h $φx<xhsxΑiι/Λ>ά to signa! gαnerator 961, and receives detected ^igna* ftom detcetor 755 ^an extract βigssed error signal ptoporύosal to the phase imbalance of mter forometer. Au integrate ^7S iiitαgraJes tho phase røir aignai and feed it to a fecdteck phase sliϊftcr V5^ tlsougiϊ a dπve? 954. Aa alternative njcihod to avotd confusion. bcKvecπ the offeotώ of amplitude change and p1ta.se άhilt Is to activate the two feedback bop ia eoiisecstivo imher taea ssirniUisueoaj» manaet..
31> Λa ADC 959 digitfecs the feedback signal Inchoative of die state; αf external system 75 -L
I? should br nested that the embodiments pretested 3« lϊgeres 10 and 13 tor both interferometer ~oi> and feedback loop ?64 were give?* for deroønstratioa of the broad aspect of the Un ea&oϊϊ. Au> uuederome-ier topologies and feedback methods depicted is the preceding tigurts. maybe αs>cd tor coheres* measuxvmeat system aecυαUsg to the ctimsn isvmvωπ,
In eorarasl κo other coherent detection methods used In the art such as the ptee seusirhe Michdson mtertcmmetcr, coxnmouϊy used to me-asuje small distance changes, the SJctlw48ccori3S|> to &όι&c embodiments of the current esdon is sensitive m bodi phase and amplitude.
IB eostraki to o&er coh«κjut detection methods used iw the an such aj» the amplitude hcsϊsitsve heterodyne detcetio'n, commonly used to measure small sigxmK the method according to sotno eaibodsments of the c«πr?m iBveatios JS sensitive to both pktse and amplitude.
Additionally m comv^st to hotcrodyue detection, the UCUΌIOΓ and its electronics operate wύto s&sli & hiϊuted dynamic range.
It Sfhouid be aotcd that light emitted tτom bπghi (or dark) frϊtsge of any of ώe røa> be a&ed tbi tsahbϊaUoti. for detcnamaUou of initial value for feedback valuώ 1T' or ibr niMTiiioπs'sg purposes*. For esanipb with feodback loop branch completely blocked, tor example at ώc ?Lari of a compuMjon or measurement cycle, output light in the interferon urtεr output i? pn>p©t.u>_ia1 to the light iX3 computation fcvαmii. Dixeci mcasurcxjjciu of tins light, may Iv use « pn^set \ slue. Co be used as ήαal result, Opiioπaily. with one branch closed and Uis other braach open to a linowti vsiuo, the output light ϊn the interfcromctsjr output is proportional to the output of the coherent %lu source.
The ΫoWcw, iαg applications by applicants Lcnskt Lab?, ct aL, the disclosiues of whieli arc mcojporatcd hcreis by reference, describe methods and apparatus which nia> Ua useful k\ coϊϊjuncdoD with tJbe above embodiments, for ^λarnpl«, for coBSMictitig VJ.1M s> stems:
K M^ OO PCr'ILOO'trø? OpUΛsl Processor Λxchtscctose WO υϋ 72 UW
While the iπvmtioΩ has been described with reference to certain exemplary ejϊibtxiϊmctsϊ&. variotis moiHfieaUoss v. ill be icadily apparent to a»d raav be readily sccoϊQpUshcd b> pcrsoas sblkd m the art without departing from UK spirit and scopώ of the above teachings.
It should bo understood that featocs and/or stsps described with respect Lo ons enibodiϊ&eai m&y be used %iιh olhei tanbodime^us and that not all embodiments of the UΪ\ ύtiiiύϊϊ h&\ t all of Uu? features snd or ^ieps show a iu a particular figuns or de&αibed with tsφuct to ont ot the efabodimani"*. Vsriadons of embodiments described will v>«cur to pώrsor& of tl^e art.
It is not'vd Uial sαrø>j of the sbovc described ci»bc4imcats sπaj' describe the best moάt oontctt^latcd by ihe snvontors sad therefbrc iticliidc structure, acts or dβtasls of structeres and acts that may n^t be essential to the mveofcoα and whicfc ate described as exanifi&su Strocturc snJ ac?N Jesicrώcjd herein arc replaceable by cqιu\ alcms which porfoπn the aante Luπcuon. eves if the smicture or sets are different, ss known m fee art. Therefore, the scope «f She invention is limited Oiuyby thy elements and limitations ss used Iu the dnims. The terms "comprise". "iϊichsd^"" asJ then ctmjugatcs. aά u^εd herein .mean mclude but are «ot uee^ss^rih' ϋmiied tox'

Claims

1. An optical measurement system issmg coherent feedback comprising: a cohsseat MgIn .source; a beasi splitter, positioned at the optical path of light from &&iύ colxcresit fight source; at Is-tsi one light modulating transducer situated aioag a first optical path of hght iτom &\tά ht-am splitter; ax least oae feedback light modulator situated along a second optical path cflight Sx?m sam beam ^pliU^n st least cae mteribromcter reoesvl&g hghi fiom said first and second optics! path*; at lea$t ono light vl«ujctor recei\Ing light frotn yaid mferfeiθtα«tdr,
«sd a fovidbaok ϊo<ψ receiving signals from said dcusetor and tr^tt^rniidag sigmύs te said fΛ*db;^k hφA modαlato?;
Λxhcreb said hght modulaimg transducer and said one feedback hght taodulatoA aitect (lie uH<?ii$5ty of Hght m said Srst aad second opucai paths of bgln tespectiveiy, sn-i ^lisacm said feedback loop maintains minimal light mtesisny on at least one light d^&ctor .
2 A cober^Λt tl^dback Imear optical msasureme&t system using non4mcar detector coiapfiJsing; a coherent light ^tsurc^ a \~>Qt\m splϊticr, pnsttsonsd &ι the optical patixυf light fioxa said cshorent light soun;*!: o$ least a$u light modulating transducer situated aimg a β?st optical path of light from βaκ1 bcnm βplHtcπ at least OtH' fse^bπck IigHϊ modulator siuusted along a second optical path of isght from said beam spisttcr; at iexv^ one intcrϊerometer rwcdvm^ light from said first a&d ^ocond v»ptical paths?; ΛΪ lcasst \ia\c hthi άβi&cUyt receiving hght from said mterferoπictcr;
a. lVodhack teo-p reccivisg signal from said detector and transmitimg signals to said feedback Hght modulator: wherein said at UMSI one light deSeαw has jβo-a4røear rcsspotisw, and wheidti vaid feedback loop maintains miuimal light intensity on. at least one light detector, and wherein msasuiyd dgital is extracted from said feedback loop.
3. ΛΏ optical cjαmputation system havitig large dynamic range comprising: a coherent Sight sosrcie: abeam splitter, positioned at the optical path o night flora saiα coherent light source; plurainy of computation light modulator* situated along a fsrst optical path of light from said beam splmcr; at least orse feedback light modulator situated along a second optical path of hght from said beam sputter; at least one imerfevosϊieter receiving light from said first and second optical paths; at least c»ne light detector receiving: light ftx>m said mterfcromcteπ sad a feedback hnψ receiving signals from said detector aad traasraiUmg sigαab ic ^aM feedback fϊgb.t modulator, wheichi said feedback loop msύnaim ttύmma! light iiUesissi^ on at ieast cse hght detector, and wherein compuuitϊos result is extracted from said tecdtiaok \o$\\ s&ά w'hsmn djuamic range c-f the computation is limited by the dynamic nage oi'said ibcdbsck loop,
4, AA accurate optical meapurtaneot ^yatem using coherent iVeαbsck comprising: a Cι>ted5it άμht source;
& b&sm spHiι«r. positioned al tfee optical path oflighi trom said light source; at least one light modulating transducer situated along a tlrsi optical path of lighi Itorn said beam spliter; βf teas* one feedback light modulator situated alosg a second optical path oflight iτ»»m duidbeani splitter; at ksasϊ one tnterferomeier receiving light from said first and second optical paths: sx least ons light detector receiving light from said inter&rørøeter;
a feedback loop receiving sigmds trots said detector and tratωmittmg sigaais tcv susά feedback light modulator; whϋreis* πrnd light modulating transducer and said one feedback light modulator arteet the ιjneβ»sily oflighi in said tlrst and second optical patb^ oflight r^pectivc!y> atκl wherein said feedback loop msintaϊm minimal light intensity øκ ai least one light detector, and wherein tnsαsured signal is extracted from said feedback loop, and wherein relative intensity variations in output of said at eofaeyem source are larger thaa relative accuracy of sseasured signal
5. Aa optica! csmpatøticm system comprising; a coherent light source; a beam spSiUer, positioned at the optical path of light from said coherent light source; plurality of corαpuiaiioa light modulators situated along s first optica! path of HgUt from said b&am splitter; at k∑ssi o.ne fcedbaek light modulator situated along & second optical path of light from ssid beam xpiitusr: st least OBe iaterfeix>xneter receiving tight from said fiτsi and second optical paths; at least o«s light detector receiving light from said interferometer;
a feedback loop receiving signals from said detector and transKsittiag signals to said feedback light mtxiαlator.
6, The optical comp^taiioa system of claim 5 whercm said optical computadoϊj comprises n VVM.
7, The opticas coΩipwtatioϊj system of claim 5 wherehi said optical computation comprises a YMM.
8. TUs optical computation system erf claims 5 wherein said feedback loop is a noa- ifeear ibedbaok loop.
9, The optical computation -system of claim 5 wherein said sion-liiiear feedback loop is a binary feedback loop.
10. The optical computation system of any of claims 5 wherein $ήύ feedback loop is coafigϋyβd to mkύmixs light intensity oa said at least one detector. i U AB optical mesj.ureme.pl system using cohere foedlwek comprising, a cohereai Mφi soitrce; a bears spbiter, positioned at the øpόeai path øfUght from sai<! coherent light source: as. kast OIK* light modulating transducer situated ahτ% a first optica! path of UgM from said beam splmβπ
&i \&&,t one feedback light modulator eituated along s secoad optical path oflight lk>m said hsam splitter; st kasl one mterierometer raceivmg light ftorn. seάά fiϊst and sβcoad opucal t>aths: aϊ least cvtc Ugliϊ deiectot receiving light Som &aid iuterfejoxϊieier.
α feedback loop ret'cήm^ sjϊgaals δoai said detector and trai^mituiig signals to said feedback light mi^ial&tor.
VZ. The opHcai mcasureακ*nt system of claim 11 whcnjϊn ϊπiid transducer modulate:» the intensity of light m the measurement braadt.
13. T:m upticdl measurement syϋiem of dajtti 11 wheiem said u∞Mαoer moddales the iutei^itv and phase of UgUt us the measurement braαclu
14 The opuci! measurement system of claims 1 ! w herein $&ιά feedback loop is a noa- iusear feedback loop.
11 ► The viptϊcai iacasarement system of daura 14 whcrau s>aid »os-H»ear tvNjdback \π<ψ is a blna£> tcedback \tssp
12. The opUeal moasusvmeiϊl system of any of claims 11 whtaein said feedback loop is configured io rsimim^c hφi intensity on said at bast onw detector.
13. Λ mcthv'd of sne^urmg atj<muation of iigfai i« iir&i be^m comprising iho ^fcps of jsphttiiϊg, cohca-m bgUt to feϋj atj^ ssscond beasw: aUenuatiδg iighJ in first beam; ontroliably attαmuitbg hght it? second beam; intδiierkig attempted light ixom δrsi and second light; detecting Hgnal indicative of light rø&ulwd from said latcriercncc of attenuated I^ht from firs* aad second light; aaά w.:ng said detected *Ig«a! lύ control satd attenuation of light of second beam.
14, A method of optical detection* eoϊspming:
\.&ϊ generating a hgh sigaal to be measured: il«) gtsneϊamig M amplitude i»odulausd Light signal;
(C) iftier&snng the tsxo light signals to achieve a desired iϊueϊmty level cm u detector; and
(<0 cstiiaafing the signal io be measured base am a modulation applied during said gcδcratϊca.
15, A method aceorώπg to ύhmk 14. wherein φ) comprojϊitpes sphtUag light UϊsCd to. (a) .usd modufouog ssαid Isght.
16. Λ method ac^ording to cfaέϊΩ \4, whererø saM interfering comprises rsduoiag an unessiiy level by at least. 50% reiauvc to said light signal
i 7. Apparαuts IVr opucαl demotion, comprising*
(») na >-!f heal signal gcnesator which generates at ka^t one signal yutpm knirig an αmphfeuk:,
(h) a feedback signal g^aerator which generates αu amplitude modulated light, and (C) a detector configured to receive an optical signal rcpiesenting an intcifea^cs between said ύyεnύ output and said modulated light; «?jd
(d) e trcmtrv adapted Io extract a valtie of said sjgtjaf output froBi a contrcliing of said feedback signal generator.
IS. A method of measuriflg light sigmil compiising:
iπtcrfensg a light signal with a controllable light, wherein «aid mterfereπce prodxicos niterferenee light having intensity smaller than said UgM signal; nnά
de-ttxtbg a 5?i§aai in.dwa«>r e of said interfesvace light*
3?
19. The metliod of measuring light signal of claim IS, further comprising tssmg said detected signal to control the intensity of said controllable light.
20. The method of. jaatf&sudng light signal of claim 19, wherein using said detected signal to control the mteashy of said controllable iigbl eomprises ttsmg said detected signal iu a feedback loop.
21. The r&etiiod of measuring light signal of claim 19* whcreiti $ of measured light signal is saierred from a status of said feedbaddoop.
22. The meihod of measuring light sigtial of claim 21, wherein a value of measured light .signal is mferred from SΪ stains of said feedback loop whan intensity of interference is below a sresujt value.
EP06851253A 2005-12-08 2006-12-08 Optical system with coherent feedback Withdrawn EP1987410A2 (en)

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US8953950B2 (en) 2009-07-24 2015-02-10 Technion Research And Development Foundation Ltd. Ultra-high-speed photonic-enabled ADC based on multi-phase interferometry
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