CN100480755C - Broadband fiber optic tap - Google Patents

Abstract

A broadband optical fiber tap for transferring optical energy out of an optical fiber having an optical fiber with a primary and secondary microbends for the purpose of coupling optical energy into the higher-order modes of the fiber, and a reflecting surface formed in the cladding of the fiber and positioned at an angle so as to reflect, by total internal reflection, higher-order mode energy away from the optical fiber. In the preferred embodiment, the two microbends are spaced apart by a distance approximately equal to one-half of the intermodal beat length for LP01 and LP11 modes of a single-mode fiber.

Description

Broadband fiber optic tap

[0001] technical field

[0002] the present invention relates to be used for the assembly of luminous energy from optical fiber coupling output, the particularly fiber optic tap that in the wavelength coverage of relative broad, luminous energy is coupled effectively and exports.

[0003] background technology

[0004] DESCRIPTION OF THE PRIOR ART

[0005] complicacy of growing fiber optic network has produced the need for equipment to the luminous energy that can measure the optical fiber of flowing through.This device is used for network monitoring and control, and it is the similar gauge glass that is used for monitoring flow through the current of pipeline aspect a lot.

[0006] for the flowing of luminous energy in the measuring optical fiber, the fraction in the luminous energy must change the direction of exporting and enter detecting device from optical fiber.Detecting device is the electric signal as the luminous energy that flows in the expression optical fiber with transform light energy.The device that is commonly called " optical tap " is carried out the function that shifts a part of luminous energy from optical fiber.

It is [0007] multiple that to be used for the technology that light comes out from the optical fiber tap be known in this area.U.S. Patent application 10/390,398 (" 398 application ") is illustrated a this technology, uses CO in this application ₂Laser beam produces the two-part structure in the optical fiber of being made up of annealed microbends and reflecting surface, and these two parts form in the covering of optical fiber, is used for by microbend the side derivation from optical fiber of the light of scattering.

[0008] though this technology provides many gratifying features, little as size, insertion loss is low and easy manufacturing, because the guide properties of optical fiber, it is subjected to the influence of intrinsic wavelength dependence.

[0009] a kind of measurement of this wavelength dependence is that tap efficiency is with wavelength change.Tap efficiency is defined as the ratio that luminous energy that branch picks out accounts for total luminous energy of loss because coupler is introduced optical channel.Go out fibre core when light scattering but can not be, but when the point downstream generation loss of coupler, tap efficiency reduces from the coupler output fiber.

[0010] unfortunately, according to ' 398 applications ' theory, in the optical tap of making in general communication optical fiber, in the wavelength range of 1310nm to 1550nm, tap efficiency has the variation of as many as 400%.If, also seldom relates to the arrowband and use, and broadband application needs tap efficiency to keep constant relatively in the wavelength region may of 1310nm to 1550nm though wavelength dependence has.

[0011] summary of the invention

[0012] advantageously, the invention provides a kind of insensitive relatively to wavelength, thereby the optical tap that can in the wavelength coverage of relative broad, work.

[0013] according to theory of the present invention, the present invention is by having two employings such as CO ₂Laser emission and be formed on the single-mode fiber of the annealed microbends in the optical fiber, and the reflective surface that forms in the covering in the downstream of these two microbends is realized.Reflecting surface is to adopt and the identical CO that forms microbend in the covering of optical fiber with laser ablation generation otch ₂Laser forms.Described otch is formed in the covering of optical fiber, thereby produces the reflecting surface that approximately becomes 44 degree angles with the fiber axis vertical line, thereby causes whole internal reflections of the incident light on this plane.Two microbends with the distance of long half of the intermode beat that approximates LP01 mould and LP11 mould greatly at interval separately, thereby cause the antiresonance coupling.When the population in making the more effective more higher mode of coupling output increased, the antiresonance coupling reduced the relative quantity of light among the mould LP11.Thereby greatly reduced the wavelength dependence of coupler, therefore greatly expanded the wavelength coverage of coupler.

[0014] description of drawings

[0015] by hereinafter in conjunction with the accompanying drawings detailed description, can more easily understand theory of the present invention, in the accompanying drawings:

[0016] Fig. 1 has described the side view of the embodiment of the fiber optic tap of inventing 100;

[0017] Fig. 2 has described the structural drawing of the device 200 that is used to make fiber optic tap shown in Figure 1;

[0018] Fig. 3 has described NE BY ENERGY TRANSFER between the fiber mode of coupler in the presentation graphs 1 as the energy level diagram of the function of its position;

[0019] Fig. 4 has described in conventional single curved fiber coupler tap efficiency as the chart of the function of spacing between its microbend and the reflecting surface;

[0020] Fig. 5 has described in conventional single curved fiber coupler the tap output signal as the chart of the function of wavelength;

[0021] Fig. 6 has described in the conventional single-mode fiber intermode beat length between the LP01 mould and LP11 mould as the chart of the function of wavelength;

[0022] Fig. 7 has described tap efficiency when the fiber optic tap wavelength is 1310nm among Fig. 1 as the chart of its microbend function at interval;

[0023] Fig. 8 has described insertion loss when the fiber optic tap wavelength is 1310nm among Fig. 1 as the chart of its microbend function at interval;

[0024] Fig. 9 has described tap efficiency when the fiber optic tap wavelength is 1550nm among Fig. 1 as the chart of its microbend function at interval;

[0025] Figure 10 has described insertion loss when the fiber optic tap wavelength is 1550nm among Fig. 1 as the chart of its microbend function at interval;

[0026] Figure 11 has described the chart of the tap output signal of fiber optic tap among Fig. 1 as the function of wavelength;

[0027] Figure 12 has described the chart of the tap output signal of the conventional single curved fiber coupler that constitutes as the function of wavelength in high numerical aperture fiber; And

[0028] Figure 13 has described according to theory of the present invention, and the tap output signal of the coupler that constitutes in high numerical aperture fiber is as the chart of the function of wavelength.

[0029] in order to help the reader understanding, identical Reference numeral is used for representing the same or analogous assembly of different accompanying drawings.Accompanying drawing must not drawn in proportion.

[0030] embodiment

[0031] referring to accompanying drawing, the fiber optic tap 100 that Fig. 1 describes comprises optical fiber 102, first microbend 104, second microbend 122 and reflecting surface 106.Reflecting surface 106 and microbend 104,122 are by adopting single CO described below ₂The radiation of laser forms.At this, microbend refers to have the sweep with the optical fiber of the similar radius-of-curvature of fibre diameter.On the contrary, macrobending refers to compare with fibre diameter the sweep with relatively large radius-of-curvature.In a preferred embodiment, microbend 104 and 122 is annealed microbends, means that they form by more than softening temperature optical fiber being carried out spot heating.Therefore the structure of microbend 104 and 122 in optical fiber is permanent, unstressed (stress).

[0032] as hereinafter describing in detail, microbend 104 and 122 plays the effect that luminous energy is scattered to fibre cladding from the fibre core of optical fiber 102.Scattared energy reflects a side of optical fiber 102 by reflecting surface 106.Preferably, reflecting surface 106 is with angle θ shown in Figure 1 _sForm, herein θ _sAngle more than or equal to whole internal reflections.As known in the art, the angle θ of whole internal reflections _tRefractive index n by fibre cladding 110 _CladRefractive index n with the medium of wound fiber 102 _sDetermine, and by formula θ _t=arcsin (n _s/ n _Clad) expression.For example, for have by air around the optical fiber of non-doped silicon covering, whole angle θ of internal reflections _tBe approximately 44 degree.Therefore, suppose scatteringangle _cLess, angle θ _sShould be more than or equal to about 44 degree.

[0033] in addition, in a preferred embodiment, reflecting surface 106 is positioned at the d place, downstream of distance first microbend 104, on the direction that light is propagated by optical fiber 102, its be enough to make energy 120 expand to covering 110 outer wall beyond, but can't make the side of energy 120 output fiber 102 before running into reflecting surface 106.For little bending angle θ ₁And θ ₂, preferred distance falls into following scope

(n _cladD)/NA<d<(2n _cladD)/NA (1)

N herein _CladBe the refractive index of cladding glass, D is a fibre diameter, and N Λ is the numerical aperture of optical fiber.For numerical aperture is 0.14 general communication optical fiber, cladding index 1.45,125 microns of diameters, reflecting surface 106 should and first microbend 104 at a distance of between the 1.3mm to 2.6mm.

[0034] compares with the middle coupler of describing that comprises single microbend of U.S. Patent application 10/390,398 (" 398 application "), by controlling the angle of bend θ of two microbends ₁And θ ₂, the spacing △ between the microbend and the degree of depth h and the position d of reflecting surface 106, can make that coupler 100 of the present invention shows improved wavelength performance and efficient among Fig. 1.As will be detailed later, microbend 104 and 122 spacing approximately and preferably equal half of intermode beat of LP01 mould and LP11 mould.

[0035] Fig. 2 illustrates the device that is used to make optical tap 100, its with ' 398 the application ' in the explanation device similar.From CO ₂The radiant light of laser 202 is passed lens 204,206 and 208 by guide, and these lens are jointly adjusted and focused on the optical fiber 102 radiant light of laser instrument.Optical fiber 102 is clamped in the focused beam 232 by anchor clamps 210 and 212, and each anchor clamps is respectively by fibre clip being held between the grip block 214 and 216,218 and 220 and grip optical fiber.Adjustment is applied to holding force on the optical fiber 102 by anchor clamps 210 and 212, thereby when keeping sufficient power that optical fiber is clamped to suitable position simultaneously, can avoid the induced loss in the optical fiber.

[0036] before being installed to anchor clamps, the part of the protective sleeve of optical fiber 102 is removed, and makes it expose one section exposed covering.The clad section that will expose is placed on the zone between anchor clamps 210 and 212 then.

[0037] the luminous energy coupling from second lasing light emitter 224 is input to optical fiber 102, and power meter 226 is measured from the luminous energy of optical fiber 102 outputs simultaneously.

[0038] after optical fiber 102 is installed to anchor clamps 210 and 212, and applying from CO ₂Before the radiation of laser 202, by anchor clamps 212 are moved to anchor clamps 210, optical fiber 102 is crooked and form macrobend.Fiber guide (guide) 228 and 230 makes optical fiber crooked on the radiation direction of laser.Preferably, the radius of the macrobend that generates in the optical fiber 102 should be enough little, thereby stress is provided in optical fiber, and this stress by accidental distortion or the bending unrelieved stress that cause of optical fiber in anchor clamps, and makes the excess loss in the optical fiber minimize greater than any simultaneously.For example, about 0.5 inch bending radius satisfies this condition of Corning SMF-28 single-mode fiber usually.

[0039] from CQ ₂The focused radiation of laser 202 is applied to the sweep of optical fiber 102, and 226 pairs of luminous energy of power meter are measured simultaneously.By absorbing from CO ₂The luminous energy of laser 202, glass optical fiber 102 is heated on its softening temperature, forms permanent microbend 104 (see figure 1)s in optical fiber.By adjusting the parameter of the laser beam that laser 202 produces, for example focal spot size, power level and time shutter, the microbend that forms can scatter to the predetermined portions of the luminous energy fibre core from optical fiber 102 in the covering, and this is by measuring with the variation of power meter 226 measurement through-put powers.Preferably, focal spot size should be adjusted to similar to the diameter of optical fiber, thus the scope of involved area in the optical fiber is minimized and the microbend radius that keeps inducting enough little.So just avoided the hyperchannel influence, otherwise will cause producing in the coupler polarization correlated.For example, to use laser spot to be of a size of 400 microns, power level be 3.5 watts, be operated in wavelength is 10.6 microns CO ₂Laser is to generating 0.5 decibel loss in 1 second with the exposure of the Corning SMF-28 single-mode fiber of 0.5 inch radius bend clamping.By monitor the loss that microbend 104 generates on one's own initiative in its forming process, can control crooked size and do not need angle θ in the direct survey sheet 1 ₁

[0040] form after the microbend 104, by mobile anchor clamps 210 and 212 simultaneously, optical fiber 102 has moved apart from △ along the direction shown in the arrow 236, normally to the left.Form second microbend 122 according to program and the time shutter identical then with first microbend 104.

[0041] form after second microbend 122, anchor clamps 212 move back to its reference position, to discharge the stress in the optical fiber 102.Utilize anchor clamps 210 and 212, optical fiber 102 moved to a certain position, on this position, from the laser beam of laser 202 gather optical fiber 102 a bit, this on away from the direction of light source 224 and with the distance of first microbend 104 be d. Mobile lens 206 and 208 is readjusted the size of focus then.By laser being applied the pulse with preset frequency, moving fiber 102 passes the focal area simultaneously, laser emission is applied on the optical fiber 102, thereby forms otch 108.In order in the covering of optical fiber 102, to form V-notch, adjust laser power level, focal spot size and duration of pulse, so that the temperature increase of the glass-clad of optical fiber 102 is on the required temperature of vaporization glass material in the zonule.After forming otch, utilize photoelectric detector 234 to measure the luminous energy that goes out from a lateral reflection of optical fiber.

[0042] for the excess molten that makes the circle cut port area minimizes, thereby avoids being out of shape the excessive loss who causes, should adopt big peak power density level and short pulse duration by fibre core.For example, be published in the 15th volume of the OPTICS LETTERS that publishes September 1 nineteen ninety by K.Imen, the 17th phase, " Laser-fabricated pulses should bcused " on the 950-952 page or leaf illustrates that the duration of pulse greater than 10 milliseconds (msec) can generate remarkable fusing in the zone around laser mechanism otch in multimode optical fiber.In single-mode fiber, even a small amount of fusing of fibre core herein all can generate and can survey loss, preferably will remain in the duration of pulse below 1 millisecond (msec).

[0043] for result in this announcement, to utilize to have 100 watts of peak powers, in the duration of pulse of 50 microseconds, focal spot size is about 50 microns, and the power density of optical fiber surface is about the CO of 5 megawatts spy/square centimeter ₂Laser forms the otch 108 among Fig. 1.In order to obtain the desired angle of reflecting surface 106 among Fig. 1, laser is applied pulse with 1 pulsating wave of about per second, simultaneously optical fiber 102 is passed laser beam with the speed of 12 microns of about per seconds.Under the situation of this sweep speed and pulsed frequency, each scanning has about 10 pulsating waves to impact optical fiber.It should be noted that the process that forms optics coupler 100 can easily be suitable for full automatic processing, coupler 100 is along forming on the multiple spot of single fiber lengths in this production run.By on single optical fiber total length, making a plurality of couplers,, can guarantee greatly to reduce production costs owing to avoid the optical fiber connector of each coupler is stopped the needs of (terminate).

[0044] gets back to coupler 100 among Fig. 1, suppose that optical fiber 102 comprises that refractive index is n _Corc Central fibre core 112, this fibre core is had than low-refraction n _CladCovering 110 around.In certain embodiments, one of fibre core or covering or the two can have the index distribution of complicacy and change of shape.In addition, the luminous energy 114 of supposing the optical fiber 102 of flowing through is the wave guide mode of optical fiber before entering fiber optic tap 100.Well known in the artly be, when light when the length direction of optical fiber is propagated, when the radial distribution of luminous energy was maintained fixed, light was considered to wave guide mode.The major part of the luminous energy of this wave guide mode also typically is positioned at the high index of refraction core region of optical fiber.Contrast ground, when light when the length direction of optical fiber is propagated, when the radial distribution of luminous energy changed, light was considered at non-wave guide mode.In addition, typically, most of luminous energy of non-directional light is in the low-refraction covering around fibre core.In a preferred embodiment, optical fiber 102 is step-refraction index, single-mode fiber.This optical fiber is only to the waveguide of LP01 mould.More higher mode is non-waveguide as LP11, LP02 etc., although they may propagate several millimeters or longer distance in optical fiber before by attenuation generation energy loss.

[0045] in order to understand the course of work of the optical tap 100 among Fig. 1 better, and its advantage compared with prior art, by figure expression coupler 100 is useful, and this chart Mingguang City can be at the function of the distribution between the mould of optical fiber 102 as the position on its optical fiber.Such figure is commonly called energy level diagram.

[0046] energy level diagram of the coupler 100 in Fig. 3 presentation graphs 1.Horizontal line is represented the mould (i.e. " energy level ") of optical fiber, these moulds or sky (dotted line) or full (solid line).Arrow shows moving of luminous energy.Position on optical fiber is represented by the horizontal level among the figure.

[0047] as shown in Figure 3, input luminous energy 114 enters the low order LP01 mould in the coupler 100.Because this is a wave guide mode, luminous energy 114 remains in this mould up to running into first microbend 104.Be coupled in the LP11 mould by microbend 104 less energy.The stiffness of coupling of microbend 104 refers to be delivered to the relative quantity of the energy of LP11 mould, and along with the angle among Fig. 10 ₁Increase.For explanation herein, be coupled to the energy that number of times is higher than the mould of LP11 by first microbend 104 and be assumed to be it is negligible.As known in the art, the microbend trend is more effective to the coupling of other mould to the coupling ratio of LP11 mould to the LP01 mould.

[0048] because the LP11 mould is not a wave guide mode, the mould energy 116 of LP11 is along with it is down propagated and radiation enters more higher mode and enters covering along optical fiber.More higher mode enters energy emission the covering of optical fiber 102 again.

[0049] the mould energy 116 as LP11 runs into second microbend 122, and energy is divided into three parts.A part is coupled into more higher mode.The second portion feedback coupling enters waveguide LP01 mould, and third part is retained in the LP11 mould.Behind second microbend 122,, and determine at the relative phase of microbend 122 LP01 of place moulds and LP11 mould at the luminous energy of each part of these parts stiffness of coupling by microbend 104 and 122.As known in the art, because the LP01 mould has different phase velocities with the LP11 mould, the spacing between the microbend 104 and 122 is determined the relative phase at microbend 122 place's moulds.

[0050] in the downstream of microbend 104 and 122, enter the energy 120 of covering and higher mode energy 320 more by energy 116 radiation of non-waveguide LP11 mould, collision (impinge) reflecting surface 106 also penetrates couplers 100 as tap output energy 120.The efficient of coupler 100 depends on the efficient that light ray radiation enters the covering of optical fiber 102 and the face 106 that therefore is reflected is caught.Be retained in the luminous energy that non-wave guide mode is interior or the face 106 that is not reflected is caught in covering, be radiated optical fiber 102, the farther place in coupler 100 downstreams.This " loss " energy reduces the efficient of coupler 100, is unfavorable therefore.

[0051] according to theory of the present invention, if making approximately, the stiffness of coupling of microbend 104 and 122 equates, and adjust the microbend spacing so that LP01 mould and LP11 mould produce 180 degree phase differential at microbend 122 places, the energy in the LP11 mould is approximately zero after microbend 122 so.This coupling is called as the antiresonance coupling.In order to obtain antiresonance completely coupling, the spacing between the microbend 104 and 122 need equal long half of the intermode beat of LP01 mould and LP11 mould, claps long L _BBe defined as

L _B＝λ/△n (2)

λ is a light wavelength herein, and △ n is the poor of effective refractive index between LP01 mould and the LP11 mould.In the step index optical fiber more than the cutoff wavelength that is operated in the LP11 mould, refringence △ n can roughly be provided by following

△n＝b ₀₁*(n _core-n _clad) (3)

N herein _CoreAnd n _CladBe the refractive index of fibre core and covering, b ₀₁Be known LP01 mould the normalization propagation constant (for example, see people such as D.Marcuse " Guiding Propertics ofFibers ", (S.E.Miller and A.G.Chynoweth edit the 3rd chapter, Academic Press, Inc., Boston, the fiber crops state, the 37-45 page or leaf of the Optical Fiber Telecommunications that published in 1979)) (the " Marcuse text ").

[0052] eliminate by antiresonance coupling most of, if not the result of the mould energy of whole LP11, because more higher mode enters covering than the easier emittance of LP11 mould usually, so the efficient of coupler 100 can be higher.This result is especially correct to the wavelength near the cutoff wavelength of LP11 mould.At these wavelength, though the LP11 mould is non-waveguide, it still can be propagated long distance and not give covering with its NE BY ENERGY TRANSFER in optical fiber.

[0053] as using ' 398 applications ' described in single crooked coupler, only rely on the LP11 mould that energy emission is entered fibre cladding.As a result, this coupler shows the efficient of reduction near cutoff wavelength, thereby compares with the coupler 100 among Fig. 1, and wavelength dependence increases.

[0054] Fig. 4 has represented according to ' 398 applications ' a series of single bend tap of making of theory in tap efficiency as microbend and reflecting surface between at interval the chart of function.The normalized tap efficiency of drawing among the figure luminous energy that to be the photocurrent that produces of the detecting device 234 among Fig. 2 measure divided by power meter 226 is again divided by the ratio of whole part losses of coupler.Data when 1310nm and 1550nm all have demonstration.Loss is that 0.20 decibel microbend forms coupler when having 1550nm by inducting in Corning SMF28 single-mode fiber.The corresponding loss of measuring during 1310nm is 0.17 decibel.The cutoff wavelength of optical fiber approximately is 1260nm, and the step-refraction index of fibre core covering is 0.0025.Penetraction depth approximately is that 34 microns otch is to form reflecting surface 106 in each coupler in covering.

[0055] Fig. 4 shows, along with the interval between microbend and the reflecting surface diminishes, tap efficiency is near zero, and this is not enter covering owing to the luminous energy that is coupled out from fibre core by microbend is radiated, and the face that therefore is not reflected is collected.In the data of two wavelength Ping Qu, at interval greater than 1.5mm the time, the efficient of 1310nm data significantly reduces.Because near the cutoff wavelength of LP11 mould, the mould power of LP11 is not easy radiation at 1310nm to 1310nm wavelength ratio 1550nm wavelength more, and cause the efficient of this wavelength to reduce by five times.

[0056] Fig. 5 has represented according to ' 398 applications ' the wavelength dependence of similar single bend tap of making of theory.Reflecting surface is positioned at 1.6mm place, microbend downstream.From the whole wavelength interval of 1275nm to 1575nm, relevant response shows the significant correlation to wavelength, and it shows efficient and greatly reduces near cutoff wavelength the time.

[0057] use the benefit that second microbend obtains in the coupler of inventing among Fig. 1 in order to be illustrated in, the intermode beat of measuring between LP01 mould and the LP11 mould in Corning SMF28 single-mode fiber sample is long.By in the optical fiber of pushing between the corrugated plate of different cycles, the Wavelength Dependent Loss in the measuring optical fiber is determined to clap long, and people such as this and R.C.Youngquist were in 1984 OPTICS LETTERSThe 9th the volume, the 5th phase, method is similar described in " the Two-modefiber modal coupler " of 177-179 page or leaf.

[0058] Fig. 6 represents the bat length the measured functional arrangement as wavelength.Theoretical curve among the figure is produced by expression formula (2) and (3) above, and known fibre core-cladding index difference is 0.0025, normalization propagation constant b ₀₁Value be 0.48.The value in back data from the 43rd page of chapter 3 figure of Marcuse text obtain, and supposition V number is 212.

[0059] by in Corning SMF28 single-mode fiber, making a series of couplers, tap efficiency and insertion loss are measured as the function of the spacing △ between the microbend 104 and 122 of Fig. 1.For all couplers, otch-degree of depth is between 34 microns and first microbend and the reflecting surface 106 to be 1.8mm apart from d.

[0060] Fig. 7 and Fig. 8 represent the tap efficiency obtained when operation wavelength is 1310nm and the data of insertion loss respectively.First and second microbends are formed has the stiffness of coupling that approximately equates, and to produce in optical fiber respectively approximately be 0.5 decibel loss.

When [0061] data among Fig. 7 show the microbend spacing and are 0.26mm, the tangible peak value of tap efficiency.According to the bat long data of Fig. 6, this claps long half during corresponding to 1310nm.At this at interval, second microbend 122 among Fig. 1 makes the antiresonance Coupled Feedback of LP11 mould enter the LP01 mould.Because luminous energy enters covering by higher mode radiation more, therefore improved the efficient of coupler.

[0062] energy back of LP11 mould is coupled in the data that the LP01 mould is reflected in the insertion loss among Fig. 8 too, and wherein to appear at the microbend spacing equally be the 0.26mm place to the tangible minimum value of insertion loss.

[0063] Fig. 9 and Figure 10 represent respectively identical coupler when wavelength 1550nm tap efficiency and the data of insertion loss.Data during with 1310nm are different, and the peak value of tap efficiency does not appear in the data among Fig. 9 during 1550nm.This differs enough big this fact by 1550nm and cutoff wavelength and causes, in described cutoff wavelength, the LP11 mould and more higher mode radiation efficiency much at one.Therefore the redistribution of the energy that is caused by the antiresonance coupling is inoperative.Compare mutually, the tangible decline of the similar insertion loss of data when the insertion loss tables of data during 1550nm shown in Figure 10 reveals to 1310nm, this shows that LP11 mould energy has entered the LP01 mould by the second microbend feedback coupling.

[0064] Figure 11 is illustrated in the functional arrangement of the relevant response of the optical tap made from two microbends of interval 0.30mm in the Corning SMF28 optical fiber as wavelength.Select at interval 0.30mm with the smoothness of optimization spectral shape, good tap efficiency when keeping 1310nm simultaneously.Whole losses of the coupler during 1310nm are 0.10 decibel, and the whole losses during 1550nm are 0.12 decibel.Figure 11 has represented to compare the significantly improvement of spectrum smoothness with the single bend tap among Fig. 5.

It should be noted that [0065] theory of the present invention can be applicable to multiple optical fiber.For example, the single-mode fiber that fibre core-cladding index difference is big is called high numerical aperture fiber, because the tendency that non-waveguide LP11 mould does not enter covering with its energy emission when propagating, it is difficulty especially that high numerical aperture fiber forms single bend tap.

[0066] Figure 12 and Figure 13 represent to use the single curved design of prior art and the spectral response of the coupler that tangent bend of the present invention design is made respectively in high numerical aperture fiber.The cutoff wavelength of used high numerical aperture fiber is 1500nm, and fibre core-cladding index difference is 0.0125.Calculate with above expression formula (2) and (3), this optical fiber is when 1550nm, and the intermode beat length between LP01 mould and the LP11 mould is 0.25mm.Clap length at this, the interval of the antiresonance coupling in this optical fiber approximately is 0.125mm.This is used for making the coupler of Figure 13 at interval.The loss that above-mentioned two kinds of couplers are measured at 1550nm all is 0.1 decibel.

[0067] Figure 12 and 13 comparison shows that are compared with single bend tap of the prior art, and in the high numerical aperture fiber of the coupler of inventing in using Fig. 1, tap efficiency has improved greater than 10 times.Simultaneously, with respect to prior art, greatly improved the spectrum smoothness.

[0068] as United States Patent (USP) 6,535, illustrates among the 671B1, optically-coupled is entered the LP11 mould of optical fiber, can realize the additional embodiment of the fiber optic tap 100 invented by the utilization alternative method.In these embodiments, for example be offset welding (offset fusion splices), make optical fiber and grating be tapered (taper).

[0069] although above description comprises many detailed descriptions, this can not be interpreted as the restriction to invention scope, and only can be as to explanation of the present invention.For example, the inclination angle of reflecting surface can be used for producing the high optical tap of polarization sensitivity less than the angle of all internal reflections.This coupler can be used for the polarization sensor in the fibre system.Alternately, can use film coating on the reflecting surface 106 in Fig. 1, with the extensive variation of wavelength dependence that optical tap sensitivity is provided.In addition, can use the microbend more than two in particular fiber, wherein the spacing of at least two microbends is or near long half of intermode beat.

Claims (6)

1. broadband fiber optic tap that is used in wide wavelength coverage, luminous energy being migrated out effectively optical fiber, this coupler comprises:

The optical fiber that comprises fibre core and covering;

First structure that in optical fiber, forms, it transfers to the first non-wave guide mode with luminous energy from the wave guide mode of described optical fiber;

Second structure that in optical fiber, forms, it is positioned at from the position of the preset distance △ of described first structure on the downward direction of propagation of light, it shifts luminous energy and gets back to the described wave guide mode and transfer in the second non-wave guide mode of described optical fiber from the described first non-wave guide mode, the described second non-wave guide mode is the more higher mode of comparing with the described first non-wave guide mode, wherein saidly approximates long half of the intermode beat of described wave guide mode and the described first non-wave guide mode apart from △; And

The reflecting surface that forms in the covering of described optical fiber, it is positioned at from the predetermined distance d of described first structure on the downward direction of propagation of light, is used for the luminous energy that will propagate at described covering and goes out from a lateral reflection of described optical fiber.

2, fiber optic tap as claimed in claim 1, wherein said reflecting surface forms by with laser emission clad material being ablated.

3, fiber optic tap as claimed in claim 1, each of wherein said first and second structures comprises annealed microbends.

4, fiber optic tap as claimed in claim 1, wherein said reflecting surface are positioned at the relative position that becomes more than or equal to 44 degree angles of vertical line with the optical fiber longitudinal axis.

5, fiber optic tap as claimed in claim 1, wherein said definite by following formula apart from d:

$\frac{n_{\mathrm{clad}}D}{\mathrm{NA}}<d<\frac{{2n}_{\mathrm{clad}}D}{\mathrm{NA}}$

Herein: n _CladBe the refractive index of clad material,

D is the diameter of optical fiber, and

NA is the numerical aperture of optical fiber.

6, a kind of fiber optic tap that is used for luminous energy is migrated out optical fiber, this coupler comprises:

The optical fiber that comprises fibre core and covering;

First structure that in optical fiber, forms, it is coupled the luminous energy between at least two moulds of described optical fiber;

Second structure that in optical fiber, forms, its and with described first structure of the luminous energy between described two moulds of described optical fiber coupling position at a distance of predetermined space △; And

The reflecting surface that in the covering of described optical fiber, forms, it is positioned at from the predetermined distance d of described first structure on the downward direction of propagation of light, is used for the lateral reflection of luminous energy from described optical fiber gone out;

Wherein, described predetermined space △ approximates long half of the intermode beat of described wave guide mode and the described first non-wave guide mode, is describedly determined by following formula apart from d:

$\frac{n_{\mathrm{clad}}D}{\mathrm{NA}}<d<\frac{{2n}_{\mathrm{clad}}D}{\mathrm{NA}}$

Herein: n _CladBe the refractive index of clad material,

D is the diameter of optical fiber, and

NA is the numerical aperture of optical fiber.

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