WO2005004245A2 - Photoluminescent infrared source - Google Patents
Photoluminescent infrared source Download PDFInfo
- Publication number
- WO2005004245A2 WO2005004245A2 PCT/GB2004/002709 GB2004002709W WO2005004245A2 WO 2005004245 A2 WO2005004245 A2 WO 2005004245A2 GB 2004002709 W GB2004002709 W GB 2004002709W WO 2005004245 A2 WO2005004245 A2 WO 2005004245A2
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- micro
- radiation source
- source according
- lenses
- radiation
- Prior art date
Links
- 230000005855 radiation Effects 0.000 claims abstract description 87
- 239000004065 semiconductor Substances 0.000 claims abstract description 20
- 238000001931 thermography Methods 0.000 claims abstract description 5
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 18
- 239000000758 substrate Substances 0.000 claims description 16
- 239000000463 material Substances 0.000 claims description 14
- 230000003595 spectral effect Effects 0.000 claims description 13
- 238000003491 array Methods 0.000 claims description 12
- 238000001020 plasma etching Methods 0.000 claims description 8
- 238000000576 coating method Methods 0.000 claims description 7
- 238000000034 method Methods 0.000 claims description 7
- 239000011248 coating agent Substances 0.000 claims description 6
- 239000000853 adhesive Substances 0.000 claims description 4
- 230000001070 adhesive effect Effects 0.000 claims description 4
- 238000004519 manufacturing process Methods 0.000 claims description 4
- 238000002161 passivation Methods 0.000 claims description 3
- 238000000151 deposition Methods 0.000 claims description 2
- 239000005350 fused silica glass Substances 0.000 claims description 2
- 238000004566 IR spectroscopy Methods 0.000 abstract 1
- 239000007789 gas Substances 0.000 description 12
- 239000000377 silicon dioxide Substances 0.000 description 7
- 229910000661 Mercury cadmium telluride Inorganic materials 0.000 description 6
- 238000010521 absorption reaction Methods 0.000 description 6
- MCMSPRNYOJJPIZ-UHFFFAOYSA-N cadmium;mercury;tellurium Chemical compound [Cd]=[Te]=[Hg] MCMSPRNYOJJPIZ-UHFFFAOYSA-N 0.000 description 6
- 238000007654 immersion Methods 0.000 description 5
- 230000003287 optical effect Effects 0.000 description 5
- 229910052710 silicon Inorganic materials 0.000 description 5
- 239000010703 silicon Substances 0.000 description 5
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 4
- WPYVAWXEWQSOGY-UHFFFAOYSA-N indium antimonide Chemical compound [Sb]#[In] WPYVAWXEWQSOGY-UHFFFAOYSA-N 0.000 description 4
- 238000005215 recombination Methods 0.000 description 4
- 230000006798 recombination Effects 0.000 description 4
- JBRZTFJDHDCESZ-UHFFFAOYSA-N AsGa Chemical compound [As]#[Ga] JBRZTFJDHDCESZ-UHFFFAOYSA-N 0.000 description 3
- 238000005229 chemical vapour deposition Methods 0.000 description 3
- 238000012986 modification Methods 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 229910001218 Gallium arsenide Inorganic materials 0.000 description 2
- 229910000673 Indium arsenide Inorganic materials 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 239000002360 explosive Substances 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- RPQDHPTXJYYUPQ-UHFFFAOYSA-N indium arsenide Chemical compound [In]#[As] RPQDHPTXJYYUPQ-UHFFFAOYSA-N 0.000 description 2
- 230000001678 irradiating effect Effects 0.000 description 2
- 238000004943 liquid phase epitaxy Methods 0.000 description 2
- 238000005086 pumping Methods 0.000 description 2
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- 229910004613 CdTe Inorganic materials 0.000 description 1
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 1
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 description 1
- 239000005977 Ethylene Substances 0.000 description 1
- 238000004026 adhesive bonding Methods 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- WATWJIUSRGPENY-UHFFFAOYSA-N antimony atom Chemical compound [Sb] WATWJIUSRGPENY-UHFFFAOYSA-N 0.000 description 1
- 239000011324 bead Substances 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 229910002091 carbon monoxide Inorganic materials 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 238000005137 deposition process Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000009189 diving Effects 0.000 description 1
- 235000013399 edible fruits Nutrition 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000005684 electric field Effects 0.000 description 1
- 239000003344 environmental pollutant Substances 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 239000010408 film Substances 0.000 description 1
- -1 for example Substances 0.000 description 1
- 238000007429 general method Methods 0.000 description 1
- 229910052732 germanium Inorganic materials 0.000 description 1
- GNPVGFCGXDBREM-UHFFFAOYSA-N germanium atom Chemical compound [Ge] GNPVGFCGXDBREM-UHFFFAOYSA-N 0.000 description 1
- 239000003292 glue Substances 0.000 description 1
- 238000003898 horticulture Methods 0.000 description 1
- 238000005286 illumination Methods 0.000 description 1
- 206010022000 influenza Diseases 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 238000000025 interference lithography Methods 0.000 description 1
- LQBJWKCYZGMFEV-UHFFFAOYSA-N lead tin Chemical compound [Sn].[Pb] LQBJWKCYZGMFEV-UHFFFAOYSA-N 0.000 description 1
- XJIHHCVBCQLUNJ-UHFFFAOYSA-N manganese mercury Chemical compound [Mn].[Hg] XJIHHCVBCQLUNJ-UHFFFAOYSA-N 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- YVUZUKYBUMROPQ-UHFFFAOYSA-N mercury zinc Chemical compound [Zn].[Hg] YVUZUKYBUMROPQ-UHFFFAOYSA-N 0.000 description 1
- 238000005065 mining Methods 0.000 description 1
- 238000001451 molecular beam epitaxy Methods 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 238000004806 packaging method and process Methods 0.000 description 1
- 230000000149 penetrating effect Effects 0.000 description 1
- 238000000206 photolithography Methods 0.000 description 1
- 231100000719 pollutant Toxicity 0.000 description 1
- 238000012805 post-processing Methods 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 150000003376 silicon Chemical class 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/40—Arrangement of two or more semiconductor lasers, not provided for in groups H01S5/02 - H01S5/30
- H01S5/42—Arrays of surface emitting lasers
- H01S5/423—Arrays of surface emitting lasers having a vertical cavity
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F2/00—Demodulating light; Transferring the modulation of modulated light; Frequency-changing of light
- G02F2/02—Frequency-changing of light, e.g. by quantum counters
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/04—Processes or apparatus for excitation, e.g. pumping, e.g. by electron beams
- H01S5/041—Optical pumping
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
- H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
- H01S5/18386—Details of the emission surface for influencing the near- or far-field, e.g. a grating on the surface
- H01S5/18388—Lenses
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/40—Arrangement of two or more semiconductor lasers, not provided for in groups H01S5/02 - H01S5/30
- H01S5/4025—Array arrangements, e.g. constituted by discrete laser diodes or laser bar
- H01S5/4087—Array arrangements, e.g. constituted by discrete laser diodes or laser bar emitting more than one wavelength
Definitions
- the present invention relates to the generation of radiation and, more specifically, though not exclusively, to an improved infrared source for generating infrared radiation up to about 12 microns wavelength.
- Infrared sources are required for many applications, for example in gas sensing applications, in spectrometers and in active thermal imaging.
- LEDs Light Emitting Diodes
- lamps or globars have been used in these applications.
- At room temperature and at infrared wavelengths up to about 12 ⁇ m LEDs generally perform poorly in terms of, for example, power output and efficiency.
- Thermal sources have relatively slow response times and may not be very safe in explosive environments .
- a photoluminescent radiation source comprising: a layer of semiconducting material which, when optically pumped, emits radiation in a desired wavelength range; and an output array of micro-lenses attached to an output surface of the semiconducting layer, wherein said output surface of the semiconducting layer is optically immersed by said output array of micro-lenses.
- the semiconducting material emits infrared radiation when optically pumped by a near-infrared laser source, for example a laser diode emitting radiation of a shorter wavelength than the required infrared emission wavelength.
- this may be a laser diode emitting in the range of 800 to lOOO ⁇ m, such as a Gallium Arsenide (GaAs) laser diode (which emits laser radiation of about 810nm) .
- GaAs Gallium Arsenide
- a strong emitter laser emitting outside this region for example emitting at 700nm or llOOnm, could equally be used.
- the invention enables a compact, bright source of infrared radiation to be provided, giving improved power output and efficiency as compared with prior art infrared sources.
- the array of micro-lenses is integrally formed with the semiconducting layer.
- the array of micro-lenses may conveniently comprise a substrate having an output surface on which a multiplicity of micro-lenses are fabricated and an input surface onto which the semiconducting layer is deposited or "grown".
- This enables wafer-scale integration of the luminescent layer and the micro-lens array, which makes the device suitable for mass fabrication.
- Multiple such photoluminescent radiation sources may thus be fabricated in the same wafer which may then be diced up prior to packaging as separate devices.
- the photoluminescent radiation source further includes an input micro-lens array which is attached to an input surface of the semiconducting layer, said input and output surfaces of the semiconducting layer being opposing surfaces.
- the input micro-lens array may conveniently be attached to the semiconducting layer by, for example, adhesive means.
- a respective micro-lens in the input micro-lens array there is a respective micro-lens in the input micro-lens array, the two arrays being formed and arranged such that the focal point of each micro-lens in the output array is substantially the same as the focal point of the respective micro-lens in the input array, whereby the input micro-lens array focuses incoming pump laser radiation onto a plurality of regions in the semiconducting layer and the output micro-lens array receives and collimates radiation emitted from the same said regions.
- the micro-lenses in each micro-lens array may be diftractive or refractive lenses.
- the micro- lenses in the input array are hexagonally close packed. This optimises the field of view for both the input and output arrays.
- the materials of which the semiconducting layer and the output micro-lens array are made preferably have the same, or substantially the same, refractive index.
- the material of which the input micro-lens array is made also has substantially the same said refractive index.
- the micro-lenses in the output array are Fresnel lenses which may conveniently be formed using Reactive Ion Etching (RIE) on a layer of infrared transmitting material such as, for example, silicon, Germanium or Gallium Arsenide.
- RIE Reactive Ion Etching
- the input array of micro-lenses may conveniently be formed using RIE to etch a layer of fused silica (Si0 2 ) .
- one or both of the micro-lens arrays may be formed using other processing techniques such as photolithography, holographic lithography, direct e-beam writing, or any other suitable micro-fabrication technique.
- the repeat distance between the Fresnel lenses in the output micro-lens array may be in the range of 20 to
- the thickness of the semiconducting layer is preferably less than, but may in some cases be approximately equal to, the absorption length of the semiconducting material for the emitted radiation.
- the thickness of the semiconducting layer is desirably greater than, or approximately equal to, the absorption length for the exciting (i.e. pump) radiation.
- the semiconducting layer may, for example, be InSb where the desired wavelength range of radiation emitted by the photoluminescent source is 4 to 7 ⁇ m, or Cadmium Mercury Telluride (CMT) for emitted radiation of up to 12 ⁇ m wavelength.
- a reflective coating may be provided on the input surface of the semiconducting layer, the coating being designed to reflect radiation in at least a portion of the spectral range emitted by the semiconducting layer. (It will be appreciated that this reflective coating must allow the pump laser radiation to be transmitted therethrough.)
- multi-layer dielectric stacks may be provided on both the input and output surfaces of the semiconducting layer to form a resonant cavity therebetween.
- photonic band gap structures for example a layer of material having a wider photonic band gap than the semiconducting material
- a passivation layer may be provided at the interface between the semiconducting layer and the first micro-lens array.
- the semiconducting layer may comprise a plurality of regions of different semiconductor material, each said material emitting radiation in a different spectral region, when optically pumped.
- the semiconducting layer may thus comprise a plurality of interlaced grids of different materials. These grids may be irradiated simultaneously or separately, by differently angled pump laser beams.
- a spectrally narrow output may be obtained by irradiating one grid, or a spectrally broad output may be obtained by irradiating a number of grids simultaneously.
- the differently angled pump laser beams may be produced in various ways, for example by several differently angled lasers, or by a single pump laser incident on a Diffractive Optical Element (DOE) .
- DOE Diffractive Optical Element
- the input micro-lens array can be designed such that when illuminated by a single pump laser beam one or more of the different grids are irradiated simultaneously, whereby a plurality of different wavelengths are emitted from the output micro-lens array.
- Fig.l is a side schematic view of a prior art device comprising an LED with a hemispherical immersion lens attached thereto;
- Fig.2 is a side schematic part-view of a photoluminescent infrared source, according to one embodiment of the invention
- Fig.3 is a plan schematic part-view of a semiconducting layer for use in an infrared source according to another embodiment of the invention
- Fig.4 is a side schematic view of an infrared source incorporating the semiconducting layer of Fig.3;
- Fig.5 is a block diagram of a gas sensing system incorporating a photoluminescent radiation source.
- Fig.2 shows a layer 10 of semiconductor material sandwiched between two arrays of micro-lenses 8,9.
- the first or "output" array 8 of micro-lenses is in the form of a silicon substrate 12 approximately 0.5mm thick and having a multiplicity of Fresnel diffractive micro-lenses 13 (only two shown in Fig.2) fabricated, by Reactive Ion etching, on an output face 14 of the substrate 12.
- the semiconducting layer 10 is integrally formed on an input face 15 of this substrate 12, by deposition.
- the second or "input" micro-lens array 9 is in the form of a layer of silica 16 having an array of convex refractive lenses 17 (only two shown in Fig.2) formed, also by Reactive Ion etching, in an input face 18 of the silica layer, an output face 19 of the silica layer being attached to an input surface 11 of the semiconducting layer 10 by a thin film of glue (not shown) .
- the repeat distance D between the micro-lenses 13 in the output array is of the order of 200 ⁇ m.
- the semiconducting layer 10 is optically pumped by near-infrared radiation R (typically about 810nm wavelength) emitted from a GaAs laser diode (not shown) and directed so as to be incident upon the silica micro-lenses 17 of the input micro-lens array.
- R typically about 810nm wavelength
- the input and output micro- lens arrays are configured and arranged such that the silica lenses 17 of the input array focus the incident laser radiation R x onto respective regions 20 (typically of approximately 25 ⁇ m in diameter) of the semiconducting layer 10, from which regions 20 photoluminescent infrared radiation emitted therefrom is collected by respective ones of the Fresnel micro-lenses 13 of the output micro-lens array and output therefrom as collimated infrared output radiation R Q .
- Three paths P ⁇ ,P 2 ,P 3 of typical light rays are traced through the device in Fig.2, to illustrate this.
- the output face 15 of the semiconducting layer is optically immersed by the silicon substrate 12 having the Fresnel diffractive micro-lenses fabricated therein. This optimises the power extracted from the luminescent layer. Also, if the micro-lenses are designed to be hyperspherical the directionality of the beam of output radiation emitted from the device can be improved. Optical immersion techniques are well understood in the art, for example as described in "Immersed radiation detectors", Jones R C, Appl. Opt. Vol.
- Fig.2 the materials of the semiconducting layer 10 and the substrate 12 are chosen to have substantially the same refractive indices. The greater any mismatch between these refractive indices the lower will be the extraction efficiency of the device, so the closer these refractive indices are the better.
- This invention presents for the first time a combination of a diffractive micro-lens array and optical immersion, in order to provide an improved photoluminescent radiation source.
- the thickness of the semiconducting layer is less than the absorption length of the semiconductor material for the radiation R 0 emitted therefrom. Also, the thickness of the semiconducting layer is greater than or about equal to the absorption length for the near-infrared pump radiation R x . This means that as many as possible of the exciting photons are absorbed while as few as possible of the emitted photons will be re-absorbed.
- the semiconducting layer is made of InSb which emits radiation of wavelength 4 to 7 ⁇ m, and a typical device thickness may be about 1 micron.
- the thickness of the semiconducting layer approximately equal to the absorption length for the emitted radiation R 0 . It will be appreciated that the above embodiment is well suited for mass fabrication at wafer level.
- a plurality of the output micro-lens arrays can be readily fabricated in one silicon wafer 12 and a semiconducting layer deposited (e.g. by Chemical Vapour Deposition, or otherwise) on the input face 15 thereof.
- the silica layer 16 containing the required respective input arrays of micro-lenses would then be assembled to the exposed input surface 11 of the semiconducting layer 11, by a layer (or beads) of adhesive.
- the assembled structure would then be diced up to form individual photoluminescent source chips, each chip having a desired size of output microlens array. (For simplicity all chips from one wafer would preferably be of the same array size.)
- the chips may be diced from the wafer before the silica input micro-lens arrays are attached thereto, but this is less preferred as it would require individual post-processing assembly of each chip.
- the input face 19 of the semiconducting layer may be coated with a reflective coating designed to transmit the near-infrared pumping radiation but reflect longer wavelength radiation emitted by the semiconducting material. This would provide a near factor of two improvement in efficiency since this modification reflects forward the infrared radiation which would otherwise be lost through the back of the device.
- multi-layer dielectric stacks may be provided on both the input and output surfaces of the semiconducting layer, designed to form a resonant cavity, thereby increasing the output power at a specific (desired) wavelength.
- a further possible embodiment may alternatively or additionally incorporate a photonic band gap structure in the semiconducting layer 10, designed to improve power output at a specific (desired) wavelength.
- Such band gap structures would be formed, for example, photolithographically in or on the semiconducting layer.
- surface recombination effects which would reduce the power output from the device, are reduced by arranging a low recombination interface at the output surface 15 of the semiconducting layer 10.
- a surface passivation layer which produces an accumulated surface at which the energy bands are bent, resulting in an electric field which opposes minority carriers from reaching the surface. Examples are an anodic film on n- type CMT or InSb or a ZnS layer on p-type CMT.
- the other general method is to use a wider gap alloy at the surface, for example CdTe evaporated onto CMT and annealed to interdiffuse it.
- the materials used to create the reflective coating or resonant cavity coatings in the afore-mentioned possible embodiments may be used to provide a low recombination interface.
- the semiconducting layer need not always be made of InSb.
- Alternative semiconducting materials could be used depending on the desired spectral output of the device. For example, CMT could be used to give emitted radiation of up to 12 ⁇ m wavelength.
- the semiconducting layer 10 is made up of a plurality of regions of different semiconducting materials. Each material emits infrared radiation in a different spectral region, when optically pumped.
- Fig.3 is a schematic part-view of such a layer which has a honeycomb-like construction made up of a series of interlaced grids, each grid comprising a multiplicity of regions of one semiconducting material, so that the different regions A,B,C,D,E... are hexagonally close packed. Typically, the hexagonal regions may be 25 ⁇ m in diameter.
- a plurality of differently angled pump laser beams P1,P2 may be used to simultaneously, or separately, illuminate the device, as illustrated in Fig.4.
- this embodiment offers a choice of output spectrum, for example a broad-band spectral output for spectrometers and a narrow-band output for sensing a particular gas.
- This embodiment may open up the possibility of new small portable infrared spectrometers.
- each pump laser (illuminating a respective one of the interlaced grids of different semiconductors) could be individually modulated at a distinct frequency. This feature would be useful in, for example, gas sensing applications where it would enable separate measurements to be made simultaneously in several distinct spectral regions e.g. to sense different gases. It will be appreciated that the above-described invention has many different possible applications.
- Fig.5 shows schematically an example gas sensing arrangement incorporating a photoluminescent infrared source like that of Fig. 2.
- the arrangement comprises a gas cell 30 having inlet/outlet ports 31,32 and sealed at each end by a respective window 33,34.
- the infrared source 40 according to Fig.2 is disposed between one such end window 33 and a lens 35 arranged to focus the beam from a pump laser diode 36 provided for pumping the infrared source 40.
- optical filters 37,38 At the other end of the gas cell 30, optical filters 37,38 and disposed between the cell end window 34 and detectors 39 for detecting predetermined wavelengths.
- Another possible application of the above-described embodiments is in active thermal imaging.
- the inventive device will provide fast powerful sources for active thermal imaging e.g. range-gated systems for penetrating scattering media such as fog, and improved robotic vision for smoky and/or mist- filled environments.
Landscapes
- Physics & Mathematics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Optics & Photonics (AREA)
- Investigating Or Analyzing Materials Using Thermal Means (AREA)
- Investigating Or Analysing Materials By Optical Means (AREA)
Abstract
A photoluminescent radiation source, particularly for generating infrared radiation. The source is made from a layer of semiconducting material which, when optically pumped, emits radiation in a desired wavelength range, and an output array of micro-lenses attached to an output surface of the semiconducting layer. The output surface of the semiconducting layer is optically immersed by the output array of microlenses. In the preferred embodiment a further, input microlens array is attached to an input surface of the semiconducting layer to focus pump laser irradiation on to the semiconducting layer. The source has many applications, for example in gas sensing, active thermal imaging and infrared spectrometry.
Description
PHOTOLUMINESCENT INFRARED SOURCE The present invention relates to the generation of radiation and, more specifically, though not exclusively, to an improved infrared source for generating infrared radiation up to about 12 microns wavelength. Infrared sources are required for many applications, for example in gas sensing applications, in spectrometers and in active thermal imaging. Traditionally, Light Emitting Diodes (LEDs) , lamps or globars have been used in these applications. At room temperature and at infrared wavelengths up to about 12μm LEDs generally perform poorly in terms of, for example, power output and efficiency. Thermal sources have relatively slow response times and may not be very safe in explosive environments . In order to increase the power and/or directionality of radiation emitted from an LED it is known to attach mechanically (by gluing) a hemispherical immersion lens 2 to the emitting face of the LED 1, as illustrated in Fig.l. However, this requires a skilled and time-consuming mounting operation to be performed individually for every LED to which it is desired to attach an immersion lens. It is an aim of the present invention to provide an infrared source which avoids or minimises one or more of the foregoing disadvantages. According to a first aspect of the invention there is provided a photoluminescent radiation source comprising: a layer of semiconducting material which, when optically pumped, emits radiation in a desired wavelength range; and an output array of micro-lenses attached to an output surface of the semiconducting layer, wherein said output surface of the semiconducting layer is optically immersed by said output array of micro-lenses. Preferably, the semiconducting material emits infrared radiation when optically pumped by a near-infrared laser
source, for example a laser diode emitting radiation of a shorter wavelength than the required infrared emission wavelength. Typically, this may be a laser diode emitting in the range of 800 to lOOOμm, such as a Gallium Arsenide (GaAs) laser diode (which emits laser radiation of about 810nm) . However, it will be appreciated that a strong emitter laser emitting outside this region, for example emitting at 700nm or llOOnm, could equally be used. The invention enables a compact, bright source of infrared radiation to be provided, giving improved power output and efficiency as compared with prior art infrared sources. Preferably, the array of micro-lenses is integrally formed with the semiconducting layer. For example, the array of micro-lenses may conveniently comprise a substrate having an output surface on which a multiplicity of micro-lenses are fabricated and an input surface onto which the semiconducting layer is deposited or "grown". This enables wafer-scale integration of the luminescent layer and the micro-lens array, which makes the device suitable for mass fabrication. Multiple such photoluminescent radiation sources may thus be fabricated in the same wafer which may then be diced up prior to packaging as separate devices. In a preferred embodiment, the photoluminescent radiation source further includes an input micro-lens array which is attached to an input surface of the semiconducting layer, said input and output surfaces of the semiconducting layer being opposing surfaces. The input micro-lens array may conveniently be attached to the semiconducting layer by, for example, adhesive means. Advantageously, for every micro-lens in the output micro- lens array there is a respective micro-lens in the input micro-lens array, the two arrays being formed and arranged such that the focal point of each micro-lens in the output array is substantially the same as the focal point of the
respective micro-lens in the input array, whereby the input micro-lens array focuses incoming pump laser radiation onto a plurality of regions in the semiconducting layer and the output micro-lens array receives and collimates radiation emitted from the same said regions. The micro-lenses in each micro-lens array may be diftractive or refractive lenses. Advantageously, the micro- lenses in the input array are hexagonally close packed. This optimises the field of view for both the input and output arrays. The materials of which the semiconducting layer and the output micro-lens array are made preferably have the same, or substantially the same, refractive index. Advantageously, the material of which the input micro-lens array is made also has substantially the same said refractive index. Preferably, the micro-lenses in the output array are Fresnel lenses which may conveniently be formed using Reactive Ion Etching (RIE) on a layer of infrared transmitting material such as, for example, silicon, Germanium or Gallium Arsenide. The input array of micro-lenses may conveniently be formed using RIE to etch a layer of fused silica (Si02) . Alternatively one or both of the micro-lens arrays may be formed using other processing techniques such as photolithography, holographic lithography, direct e-beam writing, or any other suitable micro-fabrication technique. The repeat distance between the Fresnel lenses in the output micro-lens array may be in the range of 20 to
2000μm, preferably approximately 200μm. The thickness of the semiconducting layer is preferably less than, but may in some cases be approximately equal to, the absorption length of the semiconducting material for the emitted radiation. The thickness of the semiconducting layer is desirably greater than, or approximately equal to, the absorption length for the exciting (i.e. pump) radiation. The semiconducting layer may, for example, be InSb where the desired wavelength range of
radiation emitted by the photoluminescent source is 4 to 7 μm, or Cadmium Mercury Telluride (CMT) for emitted radiation of up to 12μm wavelength. Advantageously, a reflective coating may be provided on the input surface of the semiconducting layer, the coating being designed to reflect radiation in at least a portion of the spectral range emitted by the semiconducting layer. (It will be appreciated that this reflective coating must allow the pump laser radiation to be transmitted therethrough.) Alternatively, multi-layer dielectric stacks may be provided on both the input and output surfaces of the semiconducting layer to form a resonant cavity therebetween. Additionally, or alternatively, photonic band gap structures (for example a layer of material having a wider photonic band gap than the semiconducting material) may be provided on one or both said surfaces of the semiconducting layer and/or throughout the thickness of the semiconducting layer. These measures may increase the photoluminescent emission from the device. Optionally a passivation layer may be provided at the interface between the semiconducting layer and the first micro-lens array. Optionally, to obtain broader spectral emission from the device, the semiconducting layer may comprise a plurality of regions of different semiconductor material, each said material emitting radiation in a different spectral region, when optically pumped. The semiconducting layer may thus comprise a plurality of interlaced grids of different materials. These grids may be irradiated simultaneously or separately, by differently angled pump laser beams. For example, a spectrally narrow output may be obtained by irradiating one grid, or a spectrally broad output may be obtained by irradiating a number of grids simultaneously. The differently angled pump laser beams may be produced in various
ways, for example by several differently angled lasers, or by a single pump laser incident on a Diffractive Optical Element (DOE) . Alternatively, the input micro-lens array can be designed such that when illuminated by a single pump laser beam one or more of the different grids are irradiated simultaneously, whereby a plurality of different wavelengths are emitted from the output micro-lens array. In another possibility, if no input micro-lens array is provided, illuminating the semiconducting layer with a single pump laser beam would cause all the grids to be irradiated, whereby again a plurality of different wavelengths would be emitted from the output micro-lens array. Preferred embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings in which:
Fig.l is a side schematic view of a prior art device comprising an LED with a hemispherical immersion lens attached thereto;
Fig.2 is a side schematic part-view of a photoluminescent infrared source, according to one embodiment of the invention; Fig.3 is a plan schematic part-view of a semiconducting layer for use in an infrared source according to another embodiment of the invention; Fig.4 is a side schematic view of an infrared source incorporating the semiconducting layer of Fig.3; and
Fig.5 is a block diagram of a gas sensing system incorporating a photoluminescent radiation source. Fig.2 shows a layer 10 of semiconductor material sandwiched between two arrays of micro-lenses 8,9. The first or "output" array 8 of micro-lenses is in the form of a silicon substrate 12 approximately 0.5mm thick and having a multiplicity of Fresnel diffractive micro-lenses 13 (only two shown in Fig.2) fabricated, by Reactive Ion etching, on an output face 14 of the substrate 12. The semiconducting layer
10 is integrally formed on an input face 15 of this substrate 12, by deposition. Any suitable deposition process may be used, such as Molecular Beam epitaxy (MBE) , Chemical Vapour Deposition (CVD) , or Liquid Phase Epitaxy (LPE) . The second or "input" micro-lens array 9 is in the form of a layer of silica 16 having an array of convex refractive lenses 17 (only two shown in Fig.2) formed, also by Reactive Ion etching, in an input face 18 of the silica layer, an output face 19 of the silica layer being attached to an input surface 11 of the semiconducting layer 10 by a thin film of glue (not shown) . In this embodiment the repeat distance D between the micro-lenses 13 in the output array is of the order of 200μm. In use of the device, the semiconducting layer 10 is optically pumped by near-infrared radiation R (typically about 810nm wavelength) emitted from a GaAs laser diode (not shown) and directed so as to be incident upon the silica micro-lenses 17 of the input micro-lens array. (It will be readily appreciated that the afore-mentioned adhesive must be capable of transmitting the near infra-red pump radiation.) The input and output micro- lens arrays are configured and arranged such that the silica lenses 17 of the input array focus the incident laser radiation Rx onto respective regions 20 (typically of approximately 25μm in diameter) of the semiconducting layer 10, from which regions 20 photoluminescent infrared radiation emitted therefrom is collected by respective ones of the Fresnel micro-lenses 13 of the output micro-lens array and output therefrom as collimated infrared output radiation RQ. Three paths Pι,P2,P3 of typical light rays are traced through the device in Fig.2, to illustrate this. It will be appreciated that, by being in optical contact with the silicon substrate 12, the output face 15 of the semiconducting layer is optically immersed by the silicon substrate 12 having the Fresnel diffractive micro-lenses
fabricated therein. This optimises the power extracted from the luminescent layer. Also, if the micro-lenses are designed to be hyperspherical the directionality of the beam of output radiation emitted from the device can be improved. Optical immersion techniques are well understood in the art, for example as described in "Immersed radiation detectors", Jones R C, Appl. Opt. Vol. 1, pp607-13 (1962), and "Mid-infrared gas detection using optically immersed, room-temperature, semiconductor devices2, Crowder J G, Hardaway H R and Elliot C T, Meas. Sci. Technol. Vol 13, pp882-884 (2002). In the embodiment of Fig.2 the materials of the semiconducting layer 10 and the substrate 12 are chosen to have substantially the same refractive indices. The greater any mismatch between these refractive indices the lower will be the extraction efficiency of the device, so the closer these refractive indices are the better. This invention presents for the first time a combination of a diffractive micro-lens array and optical immersion, in order to provide an improved photoluminescent radiation source. The thickness of the semiconducting layer is less than the absorption length of the semiconductor material for the radiation R0 emitted therefrom. Also, the thickness of the semiconducting layer is greater than or about equal to the absorption length for the near-infrared pump radiation Rx . This means that as many as possible of the exciting photons are absorbed while as few as possible of the emitted photons will be re-absorbed. In the embodiment of Fig.2 the semiconducting layer is made of InSb which emits radiation of wavelength 4 to 7μm, and a typical device thickness may be about 1 micron. However, in some cases where surface recombination is expected to be very high it would be desirable to make the semiconducting region as thick as possible without causing a lot of re-absorption of photons and
so in such cases it may be preferable to make the thickness of the semiconducting layer approximately equal to the absorption length for the emitted radiation R0. It will be appreciated that the above embodiment is well suited for mass fabrication at wafer level. A plurality of the output micro-lens arrays can be readily fabricated in one silicon wafer 12 and a semiconducting layer deposited (e.g. by Chemical Vapour Deposition, or otherwise) on the input face 15 thereof. The silica layer 16 containing the required respective input arrays of micro-lenses would then be assembled to the exposed input surface 11 of the semiconducting layer 11, by a layer (or beads) of adhesive. The assembled structure would then be diced up to form individual photoluminescent source chips, each chip having a desired size of output microlens array. (For simplicity all chips from one wafer would preferably be of the same array size.) In an alternative possibility, the chips may be diced from the wafer before the silica input micro-lens arrays are attached thereto, but this is less preferred as it would require individual post-processing assembly of each chip. Various modifications and improvements to the above- described embodiment are possible without departing from the scope of the invention. For example, the input face 19 of the semiconducting layer may be coated with a reflective coating designed to transmit the near-infrared pumping radiation but reflect longer wavelength radiation emitted by the semiconducting material. This would provide a near factor of two improvement in efficiency since this modification reflects forward the infrared radiation which would otherwise be lost through the back of the device. In an alternative embodiment, multi-layer dielectric stacks may be provided on both the input and output surfaces of the semiconducting layer, designed to form a resonant
cavity, thereby increasing the output power at a specific (desired) wavelength. A further possible embodiment may alternatively or additionally incorporate a photonic band gap structure in the semiconducting layer 10, designed to improve power output at a specific (desired) wavelength. Such band gap structures would be formed, for example, photolithographically in or on the semiconducting layer. In another possible embodiment, surface recombination effects, which would reduce the power output from the device, are reduced by arranging a low recombination interface at the output surface 15 of the semiconducting layer 10. There are two types of methods in common use to form such an interface. One is the use of a surface passivation layer which produces an accumulated surface at which the energy bands are bent, resulting in an electric field which opposes minority carriers from reaching the surface. Examples are an anodic film on n- type CMT or InSb or a ZnS layer on p-type CMT. The other general method is to use a wider gap alloy at the surface, for example CdTe evaporated onto CMT and annealed to interdiffuse it. Alternatively, or additionally, the materials used to create the reflective coating or resonant cavity coatings in the afore-mentioned possible embodiments may be used to provide a low recombination interface. It will be appreciated that the semiconducting layer need not always be made of InSb. Alternative semiconducting materials could be used depending on the desired spectral output of the device. For example, CMT could be used to give emitted radiation of up to 12μm wavelength. Depending on the radiative efficiency required for any particular application, other possible candidates are indium arsenide (emitting up to 3.4 microns), Indium arsenide antimonide (emitting out to about 9 microns) , Lead tin telluride, mercury zinc telluride
and mercury manganese telluride (emitting out to beyond 12 microns . ) In another embodiment, the semiconducting layer 10 is made up of a plurality of regions of different semiconducting materials. Each material emits infrared radiation in a different spectral region, when optically pumped. Fig.3 is a schematic part-view of such a layer which has a honeycomb-like construction made up of a series of interlaced grids, each grid comprising a multiplicity of regions of one semiconducting material, so that the different regions A,B,C,D,E... are hexagonally close packed. Typically, the hexagonal regions may be 25μm in diameter. By changing the angle of illumination of the incident pump laser beam one can change which honeycomb regions A,B,C,D,E... are illuminated, and thus change the spectral range of the infrared radiation output from the semiconducting layer. In one possible embodiment a plurality of differently angled pump laser beams P1,P2 may be used to simultaneously, or separately, illuminate the device, as illustrated in Fig.4. It will be appreciated that this embodiment offers a choice of output spectrum, for example a broad-band spectral output for spectrometers and a narrow-band output for sensing a particular gas. This embodiment may open up the possibility of new small portable infrared spectrometers. In a further modification, where a number of pump lasers are being used, each pump laser (illuminating a respective one of the interlaced grids of different semiconductors) could be individually modulated at a distinct frequency. This feature would be useful in, for example, gas sensing applications where it would enable separate measurements to be made simultaneously in several distinct spectral regions e.g. to sense different gases. It will be appreciated that the above-described invention has many different possible applications. It is particularly well suited for gas sensing applications since most gases
absorb radiation strongly in the wavelength range from 4 to 12 microns. E.g. Carbon dioxide (used in the medical, brewing, diving and horticulture industries), NOx and SOx (pollutants from vehicle exhausts and power station flues), hydrogen sulphide (oil exploration) , carbon monoxide (mining and waste disposal sites) , and ethylene (perishable fruit transport) . The above-described invention will improve the performance and cost-effectiveness of gas sensing instrumentation in these areas, compared with prior art sensing instrumentation previously used (such as chemical sensors). Moreover, as the inventive source operates at room temperature it is particularly suitable for use in explosive environments, where safety is paramount. Fig.5 shows schematically an example gas sensing arrangement incorporating a photoluminescent infrared source like that of Fig. 2. The arrangement comprises a gas cell 30 having inlet/outlet ports 31,32 and sealed at each end by a respective window 33,34. The infrared source 40 according to Fig.2 is disposed between one such end window 33 and a lens 35 arranged to focus the beam from a pump laser diode 36 provided for pumping the infrared source 40. At the other end of the gas cell 30, optical filters 37,38 and disposed between the cell end window 34 and detectors 39 for detecting predetermined wavelengths. Another possible application of the above-described embodiments is in active thermal imaging. The inventive device will provide fast powerful sources for active thermal imaging e.g. range-gated systems for penetrating scattering media such as fog, and improved robotic vision for smoky and/or mist- filled environments.
Claims
1. A photoluminescent radiation source comprising: a layer of semiconducting material which, when optically pumped, emits radiation in a desired spectral range; and an output array of micro-lenses attached to an output surface of the semiconducting layer, wherein said output surface of the semiconducting layer is optically immersed by said output array of micro-lenses.
2. A radiation source according to claim 1, wherein the semiconducting material emits infrared radiation when optically pumped by a near-infrared laser source.
3. A radiation source according to claim 1 or claim 2, wherein the array of micro-lenses is integrally formed with the semiconducting layer.
4. A radiation source according to claim 3, wherein the array of micro-lenses comprises a substrate having an output surface on which a multiplicity of micro-lenses are fabricated and an input surface onto which the semiconducting layer is deposited.
5. A radiation source according to any preceding claim, further including an input micro-lens array.
6. A radiation source according to claim 5, wherein said input micro-lens array is attached to an input surface of the semiconducting layer, said input and output surfaces of the semiconducting layer being opposing surfaces.
7. A radiation source according to claim 5 or claim 6, wherein the input micro-lens array is attached to the semiconducting layer by adhesive means.
8. A radiation source according to any of claims 5 to 7, wherein for every micro-lens in the output micro-lens array there is a respective micro-lens in the input micro-lens array, and the two arrays are formed and arranged such that the focal point of each micro-lens in the output array is substantially the same as the focal point of the respective micro-lens in the input array, whereby, in use, the input micro-lens array focuses incoming pump laser radiation onto a plurality of regions in the semiconducting layer and the output micro-lens array receives and collimates radiation emitted from the same said regions.
9. A radiation source according to any preceding claim, wherein the micro-lenses in at least one of the input and output micro-lens arrays are diffractive lenses.
10. A radiation source according to any preceding claim, wherein the micro-lenses in at least one of the input and output micro-lens arrays are refractive lenses.
11. A radiation source according to any preceding claim, wherein the micro-lenses in the input array are hexagonally close packed.
12. A radiation source according to any preceding claim, wherein the materials of which the semiconducting layer and the output micro-lens array are made have substantially the same refractive index.
13. A radiation source according to any preceding claim, wherein the micro-lenses in the output array are Fresnel lenses etched on a substrate of infrared transmitting material .
14. A radiation source according to claim 13, wherein the repeat distance between the Fresnel lenses in the output micro-lens array is in the range of 20 to 2000μm.
15. A radiation source according to any preceding claim, wherein the input array of micro-lenses is formed using RIE on a layer of fused silica (Si02) .
16. A radiation source according to any preceding claim, wherein the semiconducting layer emits infrared radiation in the range of 4 to 7μm when optically pumped with radiation in the range of 800 to lOOOnm.
17. A radiation source according to any of claims 1 to 15, wherein the semiconducting layer emits infrared radiation of up to 12um wavelength when optically pumped with radiation in the range of 800 to lOOOnm.
18. A radiation source according to any preceding claim, further including a reflective coating provided on the input surface of the semiconducting layer and formed and arranged to reflect radiation in at least a part of said desired spectral range.
19. A radiation source according to any of claims 1 to 17, further including multi-layer dielectric stacks provided on both the input and output surfaces of the semiconducting layer to form a resonant cavity therebetween.
20. A radiation source according to any preceding claim, further including photonic band gap structures for increasing photoluminescent emission from the device.
21. A radiation source according to any preceding claim, further including a passivation layer film provided at the interface between the semiconducting layer and at least one of the input and output micro-lens arrays.
22. A radiation source according to any preceding claim, wherein the semiconducting layer comprises a plurality of regions of different semiconductors, each said semiconductor emitting radiation in a different spectral region, when optically pumped.
23. A radiation source according to claim 22, wherein the semiconducting layer comprises a plurality of interlaced grids of different semiconductors.
24. A radiation source according to any preceding claim, further including pump laser means.
25. A radiation source according to claim 24, wherein the pump laser means comprises a laser diode.
26. A radiation source according to claim 22 or claim 23, further including a plurality of laser diodes arranged so that their respective output beams of pump laser radiation are incident on the semiconducting layer at different angles.
27. A radiation source according to claim 26, wherein each said laser diode is modulated at a distinct frequency.
28. A gas sensor including a photoluminescent radiation source according to any of claims 1 to 27.
29. A portable gas sensing system including a gas sensor according to claim 28.
30. A thermal imaging system including a photoluminescent radiation source according to any of claims 1 to 27.
31. A portable spectrometer including a photoluminescent radiation source according to any of claims 1 to 27.
32. A method of fabricating photoluminescent radiation sources comprising the steps of: providing a wafer substrate capable of transmitting radiation in a desired spectral range; fabricating on one side of said wafer substrate a multiplicity of arrayed micro-lenses; depositing on an opposite side of the wafer substrate a layer of semiconducting material which, when optically pumped, emits radiation in said desired spectral range, the semiconducting layer being optically immersed on one side by said multiplicity of micro-lenses fabricated on the wafer substrate; and dicing the wafer so as to release a plurality of separate chips therefrom, each chip comprising a respective array of said micro-lenses having a semiconducting layer attached thereto.
33. A method according to claim 32, wherein, prior to said dicing step, a substrate comprising a further multiplicity of arrayed micro-lenses is attached to an exposed surface of the semiconducting layer.
34. A method according to claim 32, wherein a respective input array of micro-lenses is then attached to an exposed surface of the semiconducting layer of each chip.
35. A method according to any of claims 32 to 34, wherein the micro-lenses fabricated in the wafer substrate are Fresnel lenses formed by Reactive Ion Etching (RIE) of the substrate.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GBGB0315177.6A GB0315177D0 (en) | 2003-06-28 | 2003-06-28 | Photoluminescent infrared source |
GB0315177.6 | 2003-06-28 |
Publications (2)
Publication Number | Publication Date |
---|---|
WO2005004245A2 true WO2005004245A2 (en) | 2005-01-13 |
WO2005004245A3 WO2005004245A3 (en) | 2005-06-02 |
Family
ID=27676285
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/GB2004/002709 WO2005004245A2 (en) | 2003-06-28 | 2004-06-24 | Photoluminescent infrared source |
Country Status (2)
Country | Link |
---|---|
GB (1) | GB0315177D0 (en) |
WO (1) | WO2005004245A2 (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE102007050167A1 (en) * | 2007-10-19 | 2009-04-23 | Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. | Microlens array with integrated illumination |
US8709592B2 (en) | 2007-05-15 | 2014-04-29 | Rolls-Royce Plc | Sensor coating |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5073041A (en) * | 1990-11-13 | 1991-12-17 | Bell Communications Research, Inc. | Integrated assembly comprising vertical cavity surface-emitting laser array with Fresnel microlenses |
US5513204A (en) * | 1995-04-12 | 1996-04-30 | Optical Concepts, Inc. | Long wavelength, vertical cavity surface emitting laser with vertically integrated optical pump |
US6353502B1 (en) * | 2000-06-13 | 2002-03-05 | Eastman Kodak Company | VCSEL field correction |
Family Cites Families (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH1183734A (en) * | 1997-09-05 | 1999-03-26 | Mitsubishi Heavy Ind Ltd | Gas detector and gas detecting method |
-
2003
- 2003-06-28 GB GBGB0315177.6A patent/GB0315177D0/en not_active Ceased
-
2004
- 2004-06-24 WO PCT/GB2004/002709 patent/WO2005004245A2/en active Application Filing
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5073041A (en) * | 1990-11-13 | 1991-12-17 | Bell Communications Research, Inc. | Integrated assembly comprising vertical cavity surface-emitting laser array with Fresnel microlenses |
US5513204A (en) * | 1995-04-12 | 1996-04-30 | Optical Concepts, Inc. | Long wavelength, vertical cavity surface emitting laser with vertically integrated optical pump |
US6353502B1 (en) * | 2000-06-13 | 2002-03-05 | Eastman Kodak Company | VCSEL field correction |
Non-Patent Citations (6)
Title |
---|
ASIF KHAN M ET AL: "VERTICAL-CAVITY, ROOM-TEMPERATURE STIMULATED EMISSION FROM PHOTOPUMPED GAN FILMS DEPOSITED OVER SAPPHIRE SUBSTRATES USING LOW-PRESSURE METALORGANIC CHEMICAL VAPOR DEPOSITION" APPLIED PHYSICS LETTERS, AMERICAN INSTITUTE OF PHYSICS. NEW YORK, US, vol. 58, no. 14, 8 April 1991 (1991-04-08), pages 1515-1517, XP000209750 ISSN: 0003-6951 * |
BLUM O ET AL: "Vertical-cavity surface-emitting lasers with integrated refractive microlenses" ELECTRONICS LETTERS, IEE STEVENAGE, GB, vol. 31, no. 1, 5 January 1995 (1995-01-05), pages 44-45, XP006002297 ISSN: 0013-5194 * |
GOURLEY P L ET AL: "SURFACE-EMITTING SEMICONDUCTOR LASER STRUCTURES FABRICATED BY MICROLITHOGRAPHY" JOURNAL OF NONLINEAR OPTICAL PHYSICS & MATERIALS, WORLD SCIENTIFIC PUBLISHING, CO, SI, vol. 4, no. 1, January 1995 (1995-01), pages 27-81, XP000494886 ISSN: 0218-8635 * |
MURAKAMI A ET AL: "PROPOSAL OF OPTICALLY PUMPED TUNABLE SURFACE EMITTING LASER" JAPANESE JOURNAL OF APPLIED PHYSICS, PUBLICATION OFFICE JAPANESE JOURNAL OF APPLIED PHYSICS. TOKYO, JP, vol. 40, no. 9A/B, PART 2, 15 September 2001 (2001-09-15), pages L935-L936, XP001110859 ISSN: 0021-4922 * |
PATENT ABSTRACTS OF JAPAN vol. 1999, no. 08, 30 June 1999 (1999-06-30) & JP 11 083734 A (MITSUBISHI HEAVY IND LTD), 26 March 1999 (1999-03-26) * |
POPOVIC Z D ET AL: "TECHNIQUE FOR MONOLITHIC FABRICATION OF MICROLENS ARRAYS" APPLIED OPTICS, OPTICAL SOCIETY OF AMERICA,WASHINGTON, US, vol. 27, no. 7, 1 April 1988 (1988-04-01), pages 1281-1284, XP000118684 ISSN: 0003-6935 * |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US8709592B2 (en) | 2007-05-15 | 2014-04-29 | Rolls-Royce Plc | Sensor coating |
DE102007050167A1 (en) * | 2007-10-19 | 2009-04-23 | Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. | Microlens array with integrated illumination |
US8792174B2 (en) | 2007-10-19 | 2014-07-29 | Fraunhofer-Gesellschaft Zur Foerderung Der Angewandten Forschung | Array of microlenses with integrated illumination |
Also Published As
Publication number | Publication date |
---|---|
GB0315177D0 (en) | 2003-08-06 |
WO2005004245A3 (en) | 2005-06-02 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
US8039800B2 (en) | Light detector, light detecting apparatus, infrared detector and infrared detecting apparatus | |
US6881979B2 (en) | One-chip micro-integrated optoelectronic sensor | |
EP2109146B1 (en) | Infrared detector, infrared detecting apparatus, and method of manufacturing infrared detector | |
US9515238B2 (en) | Micro-LED array with filters | |
KR101633146B1 (en) | Stimulated emission luminescent light-guide solar concentrators | |
US8198530B2 (en) | Method and means for a high power solar cell | |
WO2008024201A2 (en) | Optically enhanced multi-spectral detector structure | |
US9263605B1 (en) | Pulsed stimulated emission luminescent photovoltaic solar concentrator | |
US20150098481A1 (en) | Optical signal amplification | |
US20060130892A1 (en) | Highly efficient photovoltaic converter for high luminous intensities manufactured using optoelectronic technology | |
US5567955A (en) | Method for infrared thermal imaging using integrated gasa quantum well mid-infrared detector and near-infrared light emitter and SI charge coupled device | |
CN106716748B (en) | Compact, power efficient stacked broadband optical transmitter | |
US6521967B1 (en) | Three color quantum well infrared photodetector focal plane array | |
CN107532995A (en) | Optical assay device | |
US9046673B2 (en) | Optoelectronic apparatus | |
RU2570603C2 (en) | Medium-wave infrared semiconductor diode | |
WO2005004245A2 (en) | Photoluminescent infrared source | |
JP6721431B2 (en) | Quantum cascade detector | |
US7701025B2 (en) | Method and device for concentrating light in optoelectronic devices using resonant cavity modes | |
CN114400265A (en) | Photoelectric conversion device for solar photovoltaic power generation | |
JP3427125B2 (en) | Semiconductor device with optical lens function | |
JP2013191697A (en) | Solar cell | |
RU2647977C2 (en) | Multi-channel infrared photoreceiving module | |
Meriggi | Antimonide-based mid-infrared light-emitting diodes for low-power optical gas sensors | |
WO2002007230A1 (en) | Light emitting diodes |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
AK | Designated states |
Kind code of ref document: A2 Designated state(s): AE AG AL AM AT AU AZ BA BB BG BR BW BY BZ CA CH CN CO CR CU CZ DE DK DM DZ EC EE EG ES FI GB GD GE GH GM HR HU ID IL IN IS JP KE KG KP KR KZ LC LK LR LS LT LU LV MA MD MG MK MN MW MX MZ NA NI NO NZ OM PG PH PL PT RO RU SC SD SE SG SK SL SY TJ TM TN TR TT TZ UA UG US UZ VC VN YU ZA ZM ZW |
|
AL | Designated countries for regional patents |
Kind code of ref document: A2 Designated state(s): GM KE LS MW MZ NA SD SL SZ TZ UG ZM ZW AM AZ BY KG KZ MD RU TJ TM AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IT LU MC NL PL PT RO SE SI SK TR BF BJ CF CG CI CM GA GN GQ GW ML MR NE SN TD TG |
|
121 | Ep: the epo has been informed by wipo that ep was designated in this application | ||
122 | Ep: pct application non-entry in european phase |