CN1238741C - Producing method for optical fibre raster with object reflective response realized by amplitude template - Google Patents
Producing method for optical fibre raster with object reflective response realized by amplitude template Download PDFInfo
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Abstract
The present invention relates to a producing method for optical fiber rasters with object reflective response realized by an amplitude template, which belongs to the technical field of an optical filter. The present invention is characterized in that an amplitude template is led in a producing method for phase templates used by the optical fiber rasters for realizing an optical fiber raster designed by a reconstruction-equivalent-chirp method; thereby, the optical fiber raster is suitable for large-scale production. The present invention comprises a vibration amplitude template, a phase template and a fiber, wherein the vibration amplitude template, the phase template and the fiber are orderly parallel and tightly placed; thereby, ultraviolet laser beam vertically emits to the core diameter of a photosensitive optical fiber orderly through the vibration amplitude template and the phase template. The present invention provides a computational formula for the central position, the period and the length of a transparent slit of the vibration amplitude template; no apodization is realized through a mode of changing the slit length, the no apodization compensation is realized through a mode of changing the period of the transparent slit, and a corresponding formula is provided. The result tallies with the design value through the certification of examples.
Description
Technical field
The present invention relates to the field that optical fiber communication, light sensing and other relevant light signal are handled, relate in particular to optical filter wherein.
Background of invention
Fiber grating much relates in the field of light signal processing in optical fiber communication, light sensing etc., is widely used as single input, single optical filter of exporting.So-called fiber grating is to form the fiber waveguide device that the periodic refractive index modulation forms in optical fiber upper edge optical fiber direction.The method for making of phase mask-scanning that it is traditional is as shown in Figure 1: ultraviolet ray 13 is by ultraviolet laser 11 outputs, be fixed on earlier level crossing 14 on the translation stage 15 reflect, then again by 16 diffraction of phase mask, form ± 1 order diffraction light, form along the light distribution of the periodic undulations of template 16 directions at its overlapping region 18, make the refractive index of light-sensitive optical fibre 17 obtain a same periodic relief accordingly, promptly form one section fiber grating.Deserving to be called and stating the refractive index cycle fluctuating is the index modulation of fiber grating, the energy of its amplitude and laser instrument 11, light application time (for continuous wave laser) or light pulse number (paired pulses laser instrument) are relevant, and this relation can obtain by experiment repeatedly; The cycle of index modulation is half of template cycle.Thereby mobile translation stage 15 moving areas 18 are controlled energy, light application time or the number of pulses of laser instrument 11 simultaneously, just can be, obtain different index modulation amplitudes in the diverse location exposure of optical fiber 17, thus obtain the more complicated fiber grating of structure.
Utilizing fiber grating to realize the reflex response of target, is the basis that fiber grating is used, and is subjected to people's attention always.In theory, people have proposed the restructing algorithm of fiber grating: utilize the target reflection response to ask the structure of fiber grating, the i.e. distribution of index modulation
Wherein, z is the distance to the fiber grating initial end, A
S(z) more than or equal to zero, the index modulation amplitude function of expression fiber grating; Λ
SIt is the cycle of index modulation;
S(z) be phase function, characterize warbling and phase shift of fiber grating; C.c represents last conjugation.But, the fiber grating that is obtained by restructing algorithm adopts the method for making of traditional phase mask-scanning to be difficult to realize: the fiber grating that obtains of reconstruct often requires the complicated toe of cutting on the one hand, and cuts toe and the toe of cutting that thereupon brings compensates and makes manufacturing process loaded down with trivial details or be difficult to control; The phase mask of comparative maturity comprises all phase masks of even linear chrip now on the other hand, makes the fiber grating that obtains by this phase mask and traditional phase mask-scan method and has fixing phase function
Wherein, Λ is the average period of making the fiber grating that obtains, C is the rate of change of the cycle of this fiber grating to z, and the fiber grating that reconstruct obtains often has complicated warbling and phase shift, realize it or utilize special phase mask, perhaps require the control accuracy of nanometer scale, make the cost of manufacture raising or be unfavorable for large-scale production.
Two difficulties above the reconstruct-equivalent chirp method that proposes has got around recently, this method has detailed description in the middle of list of references " Dai Yitang, Chen Xiangfei, the lunar calendar, Jiang Dianjie and the clock of passing away; ' a kind of fiber grating of realizing having the arbitrary target response '; Chinese invention patent, application number: 200410007530.5 ".This theory shows, utilizes the sampling optical fiber grating and the common phase template of special construction, though the sampling optical fiber grating that obtains only has the phase function suc as formula 2 expressions, also can obtain the target reflection response.Its ultimate principle is: the sampling function of sampling optical fiber grating is carried out suitable warble and cutting toe, promptly control exposure position and exposure in the sampling optical fiber grating manufacturing process, thereby reach the cutting toe and warble of its a certain non-zero order reflection peak (normally-1 grade), make this reflection peak have the target reflection response.
Amplitude template with sub-micrometer precision has been unusual proven technique in semiconductor technology, and Fig. 2 is the synoptic diagram of an amplitude template, and wherein 21 and 22 is respectively printing opacity slit and lightproof part.Claim that below total number in printing opacity slit is N, the midpoint in k bar printing opacity slit is z to the distance of amplitude template initial end
k, the length in this printing opacity slit is L
k, and the cycle that defines this printing opacity slit be
As seen, utilize the amplitude template method can realize control accurately to exposure position.
The method of variable duty cycle is used to realize the toe of cutting of sampling optical fiber grating, and the size of the exposure spot of this method by controlling each exposure position place is come the control of the realization of equivalence to exposure intensity, thereby realizes the toe of cutting to sampling optical fiber grating.And the size of control everywhere exposure spot can be by the amplitude template control of being represented by Fig. 2.The variable duty cycle method has been avoided the toe of cutting of sampling optical fiber grating, because the exposure of each exposure station is identical, so the manufacturing process of fiber grating is reduced to Fig. 3: ultraviolet light is expanded bundle from ultraviolet laser 31 outputs by beam expander 32, covers whole optical fiber grating region; Amplitude template 33 is near phase mask 34, and the ultraviolet light that sees through the amplitude template forms fiber grating on the ad-hoc location 36 of light-sensitive optical fibre 35.As seen,, simplified the method for making of fiber grating, be fit to large-scale fiber grating and make in conjunction with the amplitude template.
Cut toe compensation and be always the important step during fiber grating is made.Cut toe and can cause fiber grating direct current index modulation difference everywhere, thereby introduce additional warbling; Cutting the toe compensation is exactly that this additional warbling is compensated.The relation of direct current index modulation D and fiber grating index modulation A is generally
D＝αA (4)
α be one more than or equal to 1 number, can estimate by experiment repeatedly.The re-expose method be use always cut the toe compensation technique, this method is removed phase mask after fiber grating is made, fiber grating is exposed once again, makes double exposure fiber grating total exposure amount unanimity everywhere afterwards.Yet this method has two shortcomings: the one, remove phase mask after light path change, the 2nd, for the second time exposure position be subjected to making the influence of platform precision may be not exclusively and primary overlapping, these two shortcomings all can cause the re-expose can not full remuneration direct current index modulation inconsistency.
Summary of the invention
Purpose of the present invention is to introduce the amplitude template in the phase mask method that fiber grating is made, and realizes the fiber grating by the design of reconstruction-equivalent chirp method, and makes it be fit to large-scale the making.For this reason, the present invention proposes a kind of method for making of fiber grating, this method is by amplitude template, phase mask and optical fiber that place successively, parallel and that press close to, and vertical incidence and see through amplitude template, phase mask successively and the UV laser beam that incides on the optical fiber is formed.
Ultimate principle of the present invention: reconstruct-equivalent chirp method shows, can realize the target reflection response by the sampling optical fiber grating with the distribution of suitable index modulation amplitude profile and sampling period in its-1 grade of reflection peak; The present invention utilizes that amplitude mode is firm and hard have been showed above-mentioned sampling period and distribute.Sampling optical fiber grating is made up of the fiber grating of a lot of sections weak points, the toe of cutting to sampling optical fiber grating is that each short fiber grating section of requirement has different reflectivity in essence, and the reflectivity of fiber grating is not only relevant with its index modulation amplitude, but also it is relevant with its length, so the length by each section of appropriate design fiber grating keeps its index modulation amplitude constant, also can reach the toe of cutting to sampling optical fiber grating; The present invention is by the firm and hard control that has showed the length of each section fiber grating of amplitude mode.Coupled-mode theory by fiber grating, the direct current index modulation of sampling optical fiber grating, be equivalent to do a phase shift in each short fiber grating section back, the equivalent phase shift theoretical proof can compensate this phase shift by the sampling period of adjusting sampling optical fiber grating; The present invention utilizes the firm and hard adjustment that shows this sampling period of amplitude mode.
Thus, the present invention proposes a kind ofly, it is characterized in that it contains following steps successively with the firm and hard method for making that now has the fiber grating of target reflection response of amplitude mode:
1) parallel successively from top to bottom and placement amplitude template, phase mask and the light-sensitive optical fibre pressed close to are regulated light path, make UV laser beam vertical incidence and being mapped on the core diameter of light-sensitive optical fibre by amplitude template, phase mask successively;
Described phase mask is common phase mask, comprises uniformly and the phase mask of linear chrip that the sampling optical fiber grating that is obtained by this phase mask and traditional phase mask-scan method has fixing phase function:
Wherein z is the distance to the fiber grating initial end, and Λ is the average period of sampling optical fiber grating, and C is the rate of change of the cycle of this sampling optical fiber grating to z;
The printing opacity slit and the lightproof part of described amplitude template are determined by following formula:
It is a tolerance in sampling period greater than zero number that SP is one, and it is a tolerance of sampling dutycycle greater than zero less than 1 number that γ is one, Δ (z)=
S(z)-and (z),
S(z) obtain by arbitrary target response reconstruct or the phase function of given fiber grating arbitrarily, (z) is the phase function of sampling optical fiber grating, the fraction part of x is asked in " { x} " expression, be that x deducts the maximum integer less than x, can obtain the distance z of the center in k printing opacity slit of amplitude template to amplitude template initiating terminal by this formula
k, cycle P
kAnd length L
k, total number in printing opacity slit is N;
Described given fiber grating that obtained by the reconstruct of any template reflex response or any has following index modulation and distributes:
A wherein
S(z) 〉=the 0th, the index modulation amplitude distribution function of this fiber grating, c.c are represented last conjugation;
The index modulation amplitude A that on sampling optical fiber grating, forms in the place's exposure of k printing opacity slit of amplitude template
kExpression;
2) width of adjusting UV laser beam makes its maximal value greater than the printing opacity gap length of amplitude template;
3) laser beam is moved to z
kThe place, k=1 is to N, exposes and forms required index modulation amplitude A
k
Described γ=0.5 o'clock, the index modulation amplitude A that on sampling optical fiber grating, forms in the place's exposure of k printing opacity slit
kBe A
S(z) mean value in this printing opacity slit is divided by 0.32.
In the above-mentioned method for making with the firm and hard fiber grating that now has a target reflection response of amplitude mode, the length in k printing opacity slit of described amplitude template is done according to following formula and is exempted to cut the toe correction:
Wherein, L
k, L '
kBe respectively former amplitude template and the length of revising k printing opacity slit of amplitude template, P
kIt is the cycle in k printing opacity slit of former amplitude template; A
kBe the index modulation amplitude of k exposure station correspondence of former sampling optical fiber grating, A
MaxBe all A
kIn maximal value.The index modulation amplitude that forms on sampling optical fiber grating in the place's exposure of k printing opacity slit of amplitude template is A
Max
Above-mentioned cuts in the toe correction with firm and hard method for making and above-mentioned the exempting from that now has the fiber grating of target reflection response of amplitude mode, and described amplitude template is done according to following formula and exempted to cut toe compensation correction:
Wherein, P
k, P '
kBe respectively the cycle in k printing opacity slit of former amplitude template and correction amplitude template, L
kBe the length in k printing opacity slit of former amplitude template, A
kBe the index modulation amplitude of k exposure station correspondence of former sampling optical fiber grating, α is the ratio of direct current modulation amplitude and ac modulation amplitude, and n is the mean refractive index of sampling optical fiber grating, and Λ is the average period of sampling optical fiber grating.
Inventive embodiments shows, in certain physically realizable scope, this method can match the reflex response of sampling optical fiber grating and design load aspect two of power reflection spectrum and group delay spectral lines: in the three dB bandwidth power reflection of example sampling optical fiber grating compose and design load between error on average at 0.1dB, and the error of group delay is on average at 2.6ps.
The present invention introduces the amplitude template in the phase mask method that fiber grating is made, realize the fiber grating by reconstruct-equivalent chirp method design, makes reconstruct-equivalent chirp method be fit to large-scale fiber grating and makes.
Description of drawings
The phase mask that Fig. 1 is traditional-scanning synoptic diagram.
Fig. 2 amplitude template synoptic diagram.
Fig. 3 utilizes amplitude template-phase mask realization variable duty cycle to cut the sampling optical fiber grating synoptic diagram of toe.
The amplitude template that Fig. 4 is general-phase mask method realizes the making platform synoptic diagram of sampling optical fiber grating.
The structure of amplitude template among Fig. 5 inventive embodiments I:
The center in 54 printing opacity slits is with the change curve of sampling number,
The length in 55 printing opacity slits is with the change curve of sampling number.
The distribution of index modulation amplitude among Fig. 6 inventive embodiments I:
Place, 63 printing opacity slits index modulation amplitude is with the change curve of sampling number.
The reflex response of sampling optical fiber grating among Fig. 7 inventive embodiments I:
The power reflection spectrum spectral line of 74 these sampling optical fiber gratings,
The power reflection spectrum spectral line of 75 designs,
The group delay spectral line of 76 these sampling optical fiber gratings,
The group delay spectral line of 77 designs.
The length distribution in amplitude template light penetrating slit crack among Fig. 8 inventive embodiments II:
The length in 83 printing opacity slits is with the change curve of sampling number.
The reflex response of sampling optical fiber grating among Fig. 9 inventive embodiments II:
The power reflection spectrum spectral line of 94 these sampling optical fiber gratings,
The power reflection spectrum spectral line of 95 designs,
The group delay spectral line of 96 these sampling optical fiber gratings,
The group delay spectral line of 97 designs.
The distribution of center, amplitude template light penetrating slit crack among Figure 10 inventive embodiments III:
The center in 103 printing opacity slits is with the change curve of sampling number.
The reflex response of sampling optical fiber grating among Figure 11 inventive embodiments III:
The power reflection spectrum spectral line of 114 these sampling optical fiber gratings,
The power reflection spectrum spectral line of 115 designs,
The group delay spectral line of 116 these sampling optical fiber gratings,
The group delay spectral line of 117 designs.
The distribution of center, amplitude template light penetrating slit crack among Figure 12 inventive embodiments IV:
The center in 123 printing opacity slits is with the change curve of sampling number.
The reflex response of sampling optical fiber grating among Figure 13 inventive embodiments IV:
The power reflection spectrum spectral line of 134 these sampling optical fiber gratings,
The power reflection spectrum spectral line of 135 designs,
The group delay spectral line of 136 these sampling optical fiber gratings,
The group delay spectral line of 137 designs.
Embodiment
Implement device of the present invention as shown in Figure 4, concrete technological process is as follows:
I. adjust light path, make: UV laser beam impinges perpendicularly on the amplitude template 42; Phase mask 43 is near amplitude template 42; Light-sensitive optical fibre 44 stretching and be fixed on phase mask 43 after, as far as possible near but do not stick, its placement should make the ultraviolet luminous energy that sees through amplitude template 42 and phase mask 43 be radiated on its core diameter.
II. adjust the width of UV laser beam 41, make its maximal value greater than the printing opacity slit of amplitude template 42.
III. make k from 1 to N, laser beam is moved to z
kPlace's exposure is to form the index modulation amplitude that needs.
The present invention proposes a kind ofly, it is characterized in that it contains following steps successively with the firm and hard method for making that now has the fiber grating of target reflection response of amplitude mode:
1) parallel successively from top to bottom and placement amplitude template, phase mask and the light-sensitive optical fibre pressed close to are regulated light path, make UV laser beam vertical incidence and being mapped on the core diameter of light-sensitive optical fibre by amplitude template, phase mask successively;
Described phase mask is common phase mask, comprises uniformly and the phase mask of linear chrip that the sampling optical fiber grating that is obtained by this phase mask and traditional phase mask-scan method has fixing phase function:
Wherein z is the distance to the fiber grating initial end, and Λ is the average period of sampling optical fiber grating, and C is the rate of change of the cycle of this sampling optical fiber grating to z;
The printing opacity slit and the lightproof part of described amplitude template are determined by following formula:
It is a tolerance in sampling period greater than zero number that SP is one, and it is a tolerance of sampling dutycycle greater than zero less than 1 number that γ is one, Δ (z)=
S(z)-and (z),
S(z) obtain by arbitrary target response reconstruct or the phase function of given fiber grating arbitrarily, (z) is the phase function of sampling optical fiber grating, the fraction part of x is asked in " { x} " expression, be that x deducts the maximum integer less than x, can obtain the distance z of the center in k printing opacity slit of amplitude template to amplitude template initiating terminal by this formula
k, cycle P
kAnd length L
k, total number in printing opacity slit is N;
Described given fiber grating that obtained by the reconstruct of any template reflex response or any has following index modulation and distributes:
A wherein
S(z) 〉=the 0th, the index modulation amplitude distribution function of this fiber grating, c.c are represented last conjugation;
The index modulation amplitude A that on sampling optical fiber grating, forms in the place's exposure of k printing opacity slit of amplitude template
kExpression;
2) width of adjusting UV laser beam makes its maximal value greater than the printing opacity gap length of amplitude template;
3) laser beam is moved to z
kThe place, k=1 is to N, exposes and forms required index modulation amplitude A
k
Described γ=0.5 o'clock, the index modulation amplitude A that on sampling optical fiber grating, forms in the place's exposure of k printing opacity slit
kBe A
S(z) mean value in this printing opacity slit is divided by 0.32.
In the above-mentioned method for making with the firm and hard fiber grating that now has a target reflection response of amplitude mode, the length in k printing opacity slit of described amplitude template is done according to following formula and is exempted to cut the toe correction:
Wherein, L
k, L '
kBe respectively former amplitude template and the length of revising k printing opacity slit of amplitude template, P
kIt is the cycle in k printing opacity slit of former amplitude template; A
kBe the index modulation amplitude of k exposure station correspondence of former sampling optical fiber grating, A
MaxBe all A
kIn maximal value.The index modulation amplitude that forms on sampling optical fiber grating in the place's exposure of k printing opacity slit of amplitude template is A
Max
Above-mentioned cuts in the toe correction with firm and hard method for making and above-mentioned the exempting from that now has the fiber grating of target reflection response of amplitude mode, and described amplitude template is done according to following formula and exempted to cut toe compensation correction:
Wherein, P
k, P '
kBe respectively the cycle in k printing opacity slit of former amplitude template and correction amplitude template, L
kBe the length in k printing opacity slit of former amplitude template, A
kBe the index modulation amplitude of k exposure station correspondence of former sampling optical fiber grating, α is the ratio of direct current modulation amplitude and ac modulation amplitude, and n is the mean refractive index of sampling optical fiber grating, and Λ is the average period of sampling optical fiber grating.
Inventive embodiments I
The present invention realized a three dB bandwidth 1.5nm, have the wave filter of the chromatic dispersion that changes with frequency linearity from-500ps/nm to-100ps/nm.
Implement device such as Fig. 4 of this example represent that the wavelength of Ultra-Violet Laser is 244nm, and it is the even phase mask of 1066nm that phase mask adopts average period, and the mean refractive index of light-sensitive optical fibre is 1.4512.
Utilize Fourier transform to do fiber grating restructing algorithm and formula (5), obtain the center z of amplitude template
kLength L with the printing opacity slit
kDistribution, and the refractive index amplitude distribution function A of sampling optical fiber grating
k, represent by Fig. 5, Fig. 6 respectively.Horizontal ordinate 51 is sampling number k among Fig. 5, and left side ordinate 52 is center z of amplitude template
kUnit is mm, and right side ordinate 53 is the length L in each printing opacity slit of amplitude template
k, unit is mm, curve 54 and 55 has been represented z respectively
kAnd L
kThe variation with k.Horizontal ordinate 61 is sampling number k among Fig. 6, and ordinate 62 is index modulation amplitude A
k, curve 63 is A
kCurve with sampling number k variation.
When utilizing the above-mentioned design of transfer matrix method emulation ,-1 grade of reflex response of the sampling optical fiber grating that obtains and design curve are as shown in Figure 7.Wherein horizontal ordinate 71 is wavelength, unit is nm, the power reflectance of left side ordinate 72 expression fiber gratings, unit is dB, the group delay of right side ordinate 73 expression fiber gratings, unit is ps, and curve 74 and 75 has been represented the power reflection spectrum and the group delay spectral line (in the three dB bandwidth) of this sampling optical fiber grating that emulation obtains respectively, and curve 76 and 77 has been represented the power reflection spectrum and the group delay spectral line (in the three dB bandwidth) of design respectively.As seen, utilize the reflex response of the sampling optical fiber grating that the present invention obtains and design load very identical all aspect two of power reflection spectrum and group delay responses: in the three dB bandwidth, the power reflection spectrum of the sampling optical fiber grating of example and the difference maximal value of design load are 0.65dB, and average error is 0.069dB; The group delay spectral line of example sampling optical fiber grating and the difference maximal value of design load are 2.35ps, and average error is 0.53ps.
Inventive embodiments II
The present invention realized a three dB bandwidth 1.5nm, have the wave filter of the chromatic dispersion that changes with frequency linearity from-500ps/nm to-100ps/nm.
The implement device of this example is with inventive embodiments I.
This example on the basis of example I, to the amplitude template carry out as formula (6) thus correction avoided the toe of cutting in the manufacturing process.The center z in each printing opacity slit of revised amplitude template
kWith the curve among Fig. 5 54, and the length L in printing opacity slit
kDistribute as shown in Figure 8.Wherein horizontal ordinate 81 is represented hits, the length L in ordinate 82 expression printing opacity slits
kDistribution, unit is mm, the 83rd, L
kDistribution curve with sampling number.The index modulation amplitude A that the exposure in each printing opacity slit causes in this example
kBe 3.13*10
-4
When utilizing the above-mentioned design of transfer matrix method emulation ,-1 grade of reflex response of the sampling optical fiber grating that obtains and design curve are as shown in Figure 9.Wherein horizontal ordinate 91 is wavelength, unit is nm, the power reflectance of left side ordinate 92 expression fiber gratings, unit is dB, the group delay of right side ordinate 93 expression fiber gratings, unit is ps, and curve 94 and 95 has been represented the power reflection spectrum and the group delay spectral line (in the three dB bandwidth) of this sampling optical fiber grating that emulation obtains respectively, and curve 96 and 97 has been represented the power reflection spectrum and the group delay spectral line (in the three dB bandwidth) of design respectively.As seen, utilize the reflex response of the sampling optical fiber grating that the present invention obtains and design load very identical all aspect two of power reflection spectrum and group delay responses: in the three dB bandwidth, the power reflection spectrum of the sampling optical fiber grating of example and the difference maximal value of design load are 0.66dB, and average error is 0.072dB; The group delay spectral line of example sampling optical fiber grating and the difference maximal value of design load are 3.76ps, and average error is 1.13ps.
Inventive embodiments III
The present invention realized a three dB bandwidth 1.5nm, have the wave filter of the chromatic dispersion that changes with frequency linearity from-500ps/nm to-100ps/nm.
The implement device of this example is with inventive embodiments I.
This example on the basis of example I, to the amplitude template carry out as formula (7) thus correction avoided cutting the toe compensation in the manufacturing process.The length L in each printing opacity slit of revised amplitude template
kDistribute as the curve among Fig. 5 55, and center z
kDistribute as shown in figure 10.Wherein horizontal ordinate 101 is represented hits, the center z in ordinate 102 expression printing opacity slits
kDistribution, unit is mm, the 103rd, z
kDistribution curve with sampling number.The index modulation amplitude A that the exposure in each printing opacity slit causes in this example
kDistribution such as Fig. 6.α＝1。
When utilizing the above-mentioned design of transfer matrix method emulation ,-1 grade of reflex response of the sampling optical fiber grating that obtains and design curve are as shown in figure 11.Wherein horizontal ordinate 111 is wavelength, unit is nm, the power reflectance of left side ordinate 112 expression fiber gratings, unit is dB, the group delay of right side ordinate 113 expression fiber gratings, unit is ps, and curve 114 and 115 has been represented the power reflection spectrum and the group delay spectral line (in the three dB bandwidth) of this sampling optical fiber grating that emulation obtains respectively, and curve 116 and 117 has been represented the power reflection spectrum and the group delay spectral line (in the three dB bandwidth) of design respectively.As seen, utilize the reflex response of the sampling optical fiber grating that the present invention obtains and design load very identical all aspect two of power reflection spectrum and group delay responses: in the three dB bandwidth, the power reflection spectrum of the sampling optical fiber grating of example and the difference maximal value of design load are 0.57dB, and average error is 0.078dB; The group delay spectral line of example sampling optical fiber grating and the difference maximal value of design load are 13.73ps, and average error is 5.12ps.
Inventive embodiments IV
The present invention realized a three dB bandwidth 1.5nm, have the wave filter of the chromatic dispersion that changes with frequency linearity from-500ps/nm to-100ps/nm.
The implement device of this example is with inventive embodiments I.
This example on the basis of example II, to the amplitude template carry out as formula (7) thus correction avoided cutting the toe compensation in the manufacturing process.The length L in each printing opacity slit of revised amplitude template
kDistribute as the curve among Fig. 8, and center z
kDistribute as shown in figure 12.Wherein horizontal ordinate 121 is represented hits, the center z in ordinate 122 expression printing opacity slits
kDistribution, unit is mm, the 123rd, z
kDistribution curve with sampling number.The index modulation amplitude A that the exposure in each printing opacity slit causes in this example
kBe 3.13*10
-4α＝1。
When utilizing the above-mentioned design of transfer matrix method emulation ,-1 grade of reflex response of the sampling optical fiber grating that obtains and design curve are as shown in figure 13.Wherein horizontal ordinate 131 is wavelength, unit is nm, the power reflectance of left side ordinate 132 expression fiber gratings, unit is dB, the group delay of right side ordinate 133 expression fiber gratings, unit is ps, and curve 134 and 135 has been represented the power reflection spectrum and the group delay spectral line (in the three dB bandwidth) of this sampling optical fiber grating that emulation obtains respectively, and curve 136 and 137 has been represented the power reflection spectrum and the group delay spectral line (in the three dB bandwidth) of design respectively.As seen, utilize the reflex response of the sampling optical fiber grating that the present invention obtains and design load very identical all aspect two of power reflection spectrum and group delay responses: in the three dB bandwidth, the power reflection spectrum of the sampling optical fiber grating of example and the difference maximal value of design load are 0.46dB, and average error is 0.15dB; The group delay spectral line of example sampling optical fiber grating and the difference maximal value of design load are 10.60ps, and average error is 3.77ps.
Claims (5)
1, with the firm and hard method for making that now has the sampling optical fiber grating of target reflection response of amplitude mode, it is characterized in that it contains following steps successively:
1) parallel successively from top to bottom and placement amplitude template, phase mask and the light-sensitive optical fibre pressed close to are regulated light path, make UV laser beam vertical incidence and being mapped on the core diameter of light-sensitive optical fibre by amplitude template, phase mask successively;
Described phase mask is common phase mask, comprises uniformly and the phase mask of linear chrip, has fixing phase function by this phase mask and sampling optical fiber grating even or that linear chrip phase mask-scan method obtains:
Wherein z is the distance to the fiber grating initial end, and Λ is the average period of sampling optical fiber grating, and C is the rate of change of the cycle of this sampling optical fiber grating to z;
The printing opacity slit and the lightproof part of described amplitude template are determined by following formula:
SP be one greater than zero number, be a tolerance in sampling period, γ be one greater than zero less than 1 number, be a tolerance of sampling dutycycle, Δ (z)= S (z)- (z), S (z) is obtained by arbitrary target response reconstruct or the phase function of given fiber grating arbitrarily, and (z) is the phase function of sampling optical fiber grating
Expression is asked
Fraction part, promptly
Deduct less than
Maximum integer, can obtain the distance z of the center in k printing opacity slit of amplitude template by this formula to amplitude template initiating terminal
k, cycle P
kAnd length L
k, total number in printing opacity slit is N;
Described given fiber grating that obtained by the reconstruct of arbitrary target reflex response or any has following index modulation and distributes:
A wherein
S(z) 〉=the 0th, the index modulation amplitude distribution function of this fiber grating, c.c are represented last conjugation;
The index modulation amplitude A that on sampling optical fiber grating, forms in the place's exposure of k printing opacity slit of amplitude template
kExpression;
2) width of adjusting UV laser beam makes its maximal value greater than the printing opacity gap length of amplitude template;
3) laser beam is moved to z
kThe place, k=1 is to N, exposes and forms required index modulation amplitude A
k
2, described according to claims 1 with the firm and hard method for making that now has the sampling optical fiber grating of target reflection response of amplitude mode, it is characterized in that, described γ=0.5 o'clock, the index modulation amplitude A that on sampling optical fiber grating, forms in the place's exposure of k printing opacity slit of amplitude template
kBe A
S(z) mean value in this printing opacity slit is divided by 0.32.
3, described according to claims 1 with the firm and hard method for making that now has the sampling optical fiber grating of target reflection response of amplitude mode, it is characterized in that the length in k printing opacity slit of described amplitude template is done according to following formula and exempted to cut the toe correction:
Wherein, L
k, L '
kBe respectively former amplitude template and the length of revising k printing opacity slit of amplitude template, P
kIt is the cycle in k printing opacity slit of former amplitude template; A
kBe the index modulation amplitude of k exposure station correspondence of former sampling optical fiber grating, A
MaxBe all A
kIn maximal value.
4, described according to claims 3 with the firm and hard method for making that now has the sampling optical fiber grating of target reflection response of amplitude mode, it is characterized in that the described index modulation amplitude that forms in the place's exposure of k printing opacity slit of amplitude template is A on sampling optical fiber grating
Max
5, it is characterized in that with the firm and hard method for making that now has the sampling optical fiber grating of target reflection response of amplitude mode that according to any one claim in claims 1 or 3 is described described amplitude template is done according to following formula and exempted to cut toe compensation correction:
Wherein, P
k, P '
kBe respectively the cycle in k printing opacity slit of former amplitude template and correction amplitude template, L
kBe the length in k printing opacity slit of former amplitude template, A
kBe the index modulation amplitude of k exposure station correspondence of former sampling optical fiber grating, α is the ratio of direct current modulation amplitude and ac modulation amplitude, and n is the mean refractive index of sampling optical fiber grating, and Λ is the average period of sampling optical fiber grating.
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