CN1271431C - Fibre-optical raster of implementing arbitrary target response - Google Patents

Abstract

The present invention relates to an optical fiber raster implementing arbitrary target response, which belongs to the fields of optical fiber communication, optical sensing and other optical signal processing. The optical fiber grating with a sampling structure is realized by a scanning manufacturing method of a phase template. The period and the phase function such as, AS, fai S (z) and AS (z) of the initial end of the sampling optical fiber grating respectively are the period, the phase function and the apodization function of the initial end of any given optical fiber grating. The distance zk between a kth ultraviolet light exposing position and the initial end of the sampling optical fiber grating, and the refractivity modulation range Ak introduced in the zk position are obtained through the parameters. The present invention has the characteristic that each reflectance spectrum of the present invention has a multichannel type, wherein some a specific reflection peak justly has the characteristic of a required target reflection response, or target phase shift. The present invention does not have a specific requirement for phase templates required by manufacture and reduces control accuracy required by manufacture; thereby, the manufacture cost is reduced.

Description

A kind of fiber grating of realizing having the arbitrary target response

Technical field

The invention belongs to the field that optical fiber communication, light sensing and other relevant light signal are handled, relate in particular to the fiber grating filter structural design.

Background of invention

Optical filter much relates in the field that light signal handles in optical fiber communication, light sensing etc. important effect.In optical fiber communication, can be subjected to the influence of various factors when in optical fiber, propagating and broadening as the light pulse of information carrier, make correctly identifying information content of receiving end; Utilize specific optical filter just can remedy the distortion of light pulse, can offset the influence of chromatic dispersion in the Transmission Fibers such as dispersion compensator, the polarization mode compensator can be offset the effect of propagating polarization mode dispersion in the optical fiber, or the like.In optical sensor system, optical filter can be directly as sensing head, and its response spectral line changes along with the variation of extraneous factor, thereby reaches the purpose of sensing.Relate in the field of light signal processing at other, optical filter also plays a part crucial, for example the coding decoder in optical code division multiple access (OCDMA) communication.These optical filters above-mentioned all belong to the optical filter of single input, single output type.General, its characteristic can be described with the frequency response H (λ) of following form:

H(λ)＝R(λ)*exp[jθ(λ)] (1)

Wherein R (λ), θ (λ) represent the amplitude amplitude response and the phase response of wave filter respectively; Usually also use | R (λ) | ²Represent the power magnitude response of this wave filter; Group delay spectrum τ commonly used (λ) describes the phase response of wave filter in optical communication system, and the pass of it and θ (λ) is:

$\mathrm{\τ}\left(\mathrm{\ω}\right)=-\frac{{\mathrm{\λ}}^2}{2\mathrm{\πc}}\frac{\mathrm{d\θ}}{\mathrm{d\λ}}---\left(2\right)$

Fiber grating is the reflecting light wave filter of a kind of single input, single output.The method for making of phase mask-scanning that it is traditional is as shown in Figure 1: ultraviolet ray 13 is penetrated by ultraviolet laser 11, be fixed on earlier level crossing 14 on the translation stage 15 reflect, then again by 16 diffraction of phase mask, formation ± 1 order diffraction light; Because ± 1 order diffraction interference of light, form the light distribution of periodic undulations along template 16 directions (this cycle be phase mask cycle 1/2) at its overlapping region 18; One section light-sensitive optical fibre 17 is placed this zone, because the refractive index of light-sensitive optical fibre can obtain different subtle change under different ultraviolet light intensities, so its refractive index obtains a same periodic relief accordingly, promptly forms one section fiber grating in zone 18, claim this refractive index cycle to rise and fall and be the index modulation of fiber grating, the size of its fluctuating becomes the amplitude of index modulation, energy, light application time (for continuous wave laser) or the light pulse number (paired pulses laser instrument) of it and laser instrument 11 are relevant, and this relation can obtain by experiment repeatedly; 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.From above-mentioned manufacturing process and the result that obtains as seen, fiber grating is the fiber waveguide device of introducing the periodic refractive index modulation and form in optical fiber, and is general, and its structure is with the distribution of its index modulation on fiber length Expression:

Wherein c.c represents last conjugation, and z is the distance to the fiber grating initial end, and Λ is the cycle of the initial end of fiber grating, this cycle be phase mask 16 initial end cycle 1/2; A (z) is the profile of index modulation amplitude, also claims to be defined as the variation of fiber grating index modulation amplitude with z by apodizing function; (z) is a phase function, the cycle of expression fiber grating is with the situation of change of z, its expression formula is by phase mask 16 decisions, the value of general provision phase function at fiber grating initial end place is zero, phase mask commonly used have the cycle with the constant even phase mask of z and cycle with two kinds of the linear chrip templates of z linear change, because evenly phase mask can be considered and has zero warbling, so general can be written as of phase function (z):

Wherein, chirp coefficient C is the rate of change of the cycle of fiber grating with z, it be phase mask 16 chirp coefficient 1/2.

Fiber grating is because volume is little, cost is low, insert advantages such as loss is little, technology is simple relatively, be subject to people's attention aspect the realization of optical filter, aspects such as for example above mentioned dispersion compensator, OCDMA coding decoder, fiber grating all has the application of comparison success.So given target reflection response H (λ) obtains corresponding optical fiber grating structure, is index modulation

And realize this index modulation, be the basis that fiber grating is used.The problems referred to above have in theory obtained solution: the restructing algorithm of fiber grating can respond H (λ) according to target reflection, calculate the structure of the fiber grating that can realize this response Comprising the profile (being apodizing function) of cycle, index modulation amplitude of initial end of this fiber grating and phase function (note: phase function value that equally will regulation fiber grating initial end is zero).Restructing algorithm commonly used has fourier transform method, DLP method etc.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.On the one hand, be because the fiber grating that obtains of restructing algorithm generally requires very complicated phase function (z), promptly needs to have the very complicated phase mask of warbling, and the phase mask that has only uniform and linear chrip of comparative maturity in the present phase mask manufacture craft, this just requires a kind of fiber grating of every making just to make a special template; The fiber grating method for making of other the phase function that can realize this complexity then requires manufacturing system to have the control accuracy of inferior nanometer scale.On the other hand, the profile that the fiber grating that is obtained by restructing algorithm generally all has continuous index modulation amplitude, be apodizing function A (z), and some apodizing functions require the index modulation amplitude that bigger variation is arranged in smaller length range, on the make will accurately realize it also being the comparison difficulty: this is because the hot spot of laser instrument output always has certain scale size, exposure each time always forms index modulation having on the optical fiber of certain-length, and the profile of the index modulation amplitude of this section that forms is by the light spot shape decision of laser instrument, if realize to need cut the toe profile, can only utilize the profile stack of these index modulation amplitudes to form, what need if the facula area of laser instrument is bigger cuts the toe profile variations relatively acutely, what need cuts the toe profile and just can not reach, thereby the reflex response of the fiber grating that obtains and desired value produce bigger deviation, if and dwindle the spot size of laser instrument, can cause the coherence who focuses on back laser instrument hot spot to descend on the one hand, influence the making of fiber grating, energy of lasers is utilized insufficient after perhaps dwindling hot spot, the scope in the zone 18 of the index modulation of exposure formation is each time dwindled on the other hand, and the Production Time of fiber grating will extend.These top problems all make the making of fiber grating complicated, cost improves, and also make the fiber grating that is obtained by restructing algorithm be difficult in practice realize.

In the making of fiber grating, phase-shifting technique is the basis that makes the fiber grating with complex reflex response.So-called phase shift causes the transition of its phase function (z) exactly in the somewhere of fiber grating.For example, suc as formula the fiber grating of 3 expressions, if at z=x place introducing target phase shift ₀, then its phase function (z) has following variation:

Physically, phase shift is exactly in 1 acute variation of locating the cycle of fiber grating of z=x, normally produces with the micrometric displacement between fiber grating and the template in actual fabrication.Because the cycle of fiber grating is very little, realize accurately that this micrometric displacement requirement manufacturing system has the control accuracy of nm magnitude, perhaps require expensive phase shift phase mask.This has caused very big obstacle to the application of phase shift in fiber grating.

To studies show that of sampling optical fiber grating, the method for utilization sampling can solve the problem in the above-mentioned making.Sampling optical fiber grating (it is made as shown in Figure 1) designed on light-sensitive optical fibre 17, discrete position z _kLast exposure reasonable time or pulse number are to form the index modulation amplitude A that needs _k, and guarantee that each exposure station does not overlap and obtain.From above-mentioned manufacturing process and the result that obtains as seen, so-called sampling optical fiber grating, the fiber grating that utilizes ultraviolet photoetching to obtain respectively on the discrete position of optical fiber exactly has the represented index modulation of following formula:

Wherein, s (z) is the profile of the index modulation amplitude of this sampling optical fiber grating, the i.e. apodizing function of this sampling optical fiber grating, the apodizing function of it and other fiber grating different, just be that it is to utilize ultraviolet photoetching to obtain owing in the manufacturing process respectively on the discrete position of optical fiber, so it has the represented form of following formula:

$s\left(z\right)=\underset{k}{\mathrm{\Σ}}{A}_{k}q(z-z_k)---\left(7\right)$

Wherein, z _kThe position that is k sampling, promptly exposes, A _kBe the index modulation amplitude of k sampling, and the single sampling that q (z) is normalization, be the caused index modulation amplitude of single exposure profile, be the apodizing function of single sampling, so-called normalization is meant that the maximal value of q (z) is 1.The definition sampling optical fiber grating cycle, be the distance between adjacent two exposure stations, be P _k=z _K+1-z _k, because adjacent sampling can not be overlapping, thus the non-vanishing length of q (z) should be less than minimum period of whole sampling optical fiber grating, be P _k ^Min

The maximum characteristics of sampling optical fiber grating are that its reflex response presents a plurality of channels, is the characteristics of a plurality of reflection peaks.Regulation and Λ correspondence, be that centre wavelength is that the reflection peak of 2n Λ (n is the mean refractive index of fiber grating) is the zero order reflection peak, by the zero level peak be designated as successively to the reflection peak of shortwave direction+1 ,+2 ..., by the zero level peak be designated as-1 ,-2 successively to the reflection peak of long wave direction ...

The advantage of sampling optical fiber grating on making at first can be found out from the making of its index modulation amplitude profile, the difficulty that it has avoided above-mentioned continuous apodizing function to exist.Sampling optical fiber grating (it is made as shown in Figure 1) is as long as position z that designed on light-sensitive optical fibre 17, discrete _kLast exposure reasonable time is to form the index modulation amplitude A that needs _k, and guarantee that each exposure station does not overlap and get final product that this can simply be controlled or utilize method of focusing to realize by diaphragm 12.Because each hot spot does not overlap, the exposure of every bit and point on every side have nothing to do and are easy to control, so easy realize many of continuous apodizing function that the apodizing function Billy of sampling optical fiber grating obtains with restructing algorithm.

Secondly, people have carried out deep research to sampling optical fiber grating, have proposed the method for equivalent chirp, thereby for utilizing the complicated group delay spectral line of sampling optical fiber grating realization to lay a good foundation.General people are to the application of sampling optical fiber grating, each sampling period, are that distance between the adjacent exposure station equates; The equivalent chirp method is then introduced in the sampling period of sampling optical fiber grating and is warbled, promptly allows sampling period P _kChange with z, thereby make the particular channel of reflectance spectrum have the group delay spectrum that needs.The equivalent chirp method on fiber grating is made, have very big advantage: it can realize nonlinear group delay spectral line, but the phase mask in the manufacturing process is not had specific (special) requirements; Because the sampling period is much larger than the fiber grating cycle, so manufacturing system only needs the control accuracy of sub-micron to get final product.But existing equivalent chirp method itself does not point out should have the equivalent chirp of which kind of form, i.e. equivalent phase function at the response of target reflection arbitrarily fiber grating, therefore only be confined in the realization of some group delay spectral line, and do not realize any given target phase response; And this method only considered fiber grating time delay, be on the phase propetry of reflex response, ignored fiber grating another key property, be the amplitude characteristic of reflex response, so also do not realize any given target magnitude response.These top problems make the equivalent chirp method be limited in fiber grating is realized, and do not bring into play its advantage in fiber grating is made.

Summary of the invention

Purpose of the present invention is to be difficult to realize and traditional equivalent chirp method can't realize arbitrary target phase response and ignore the problem of fiber grating amplitude response with traditional phase mask-scan method in order to solve the above-mentioned structure of utilizing the fiber grating that restructing algorithm obtains and phase-shifting technique.For this reason, the present invention proposes a kind of fiber grating of realizing having the arbitrary target response, can make of traditional phase mask-method for scanning, can in the non-zero order reflection peak of sampling optical fiber grating, realize having the fiber waveguide device of arbitrary target response, also can have the phase shift feature, and do not have specific (special) requirements to making needed phase mask, can reduce and make required control accuracy, thereby reduce cost of manufacture.

In order to be used to have the optical filter of arbitrary target reflex response, the present invention proposes a kind of fiber grating of realizing having the arbitrary target response, this fiber grating is the fiber grating that utilizes the sampling structure of phase mask-scanning method for making realization, the fiber waveguide device that its structure obtains for the periodic refractive index modulation that utilizes varying strength and the ultraviolet photoetching amount of time (pulse) to introduce different amplitudes at the diverse location place of one section optical fiber; It is characterized in that: the position of k ultraviolet photoetching is apart from the distance z of this sampling optical fiber grating initial end _kWith at z _kThe amplitude A of the index modulation that the place introduces _kDetermine by following formula:

Wherein,

M is and Δ Λ

The nonzero integer of opposite in sign, F _mBe one greater than 0 less than 1 positive number, Λ and (z) are respectively the cycle and the phase functions of the initial end of this sampling optical fiber grating, Λ _S, _S(z) and A _S(z) be cycle, phase function and the apodizing function of the initial end of arbitrarily given fiber grating respectively.

The present invention is on the basis of above-mentioned sampling structure, also proposed a kind of in order to realize having the fiber grating of target phase shift feature, be that exposure position and index modulation range value that above-mentioned formula (8) is determined are revised, make the m level reflection peak of revised sampling optical fiber grating in original reflex response, produce and have the feature of target phase shift; It is characterized in that, in the position of k ultraviolet photoetching of above-mentioned sampling optical fiber grating to the distance z of this sampling optical fiber grating initial end _kWith at z _kThe amplitude A of the index modulation that the place introduces _kBy the following formula correction:

A _k′＝A _k

Wherein, z _k' and A _k' be that the position of k ultraviolet photoetching of revised sampling optical fiber grating is to the amplitude of the index modulation of the distance of this given sampling optical fiber grating initial end and the introducing of this place, ₀Be the target phase shift that the x place of the m level sub-gratings of the sampling optical fiber grating before correction introduces, P _x ⁰It is the distance between adjacent two the ultraviolet photoetching positions, sampling optical fiber grating x place before revising.

Above-mentioned Λ _S, _S(z) and A _S(z) can be according to the arbitrary target reflex response, utilize the restructing algorithm of fiber grating to obtain; Also given arbitrarily.

Advantage of the present invention: utilize traditional phase mask-scan method and common evenly or the linear chrip template just can make the fiber grating that fiber grating filter with arbitrary target reflex response or realization have the phase shift feature, and do not need high-precision control or expensive, have complicated warbling or the phase shift phase mask, do not need to realize the profile of continuous index modulation amplitude yet, thereby reduced cost of manufacture; Compare with the equivalent chirp method, then enlarged the scope of the reflex response that can realize, expanded the range of application of fiber grating.

Description of drawings

Fig. 1 is " phase mask-scanning " making platform of traditional fiber grating, the experiment porch that inventive embodiments is used.

Fig. 2 is the sampling period distribution plan of the sampling grating among the embodiment of the invention I and the index modulation intensity distribution of normalized each sampling.

Fig. 3 is the experimental result curve of embodiment of the invention I.

Fig. 4 is the experimental result of embodiment of the invention II.

Embodiment

A kind of fiber grating of realizing having the arbitrary target response that the present invention proposes, structure embodiment and accompanying drawing are described in detail as follows:

Implement device of the present invention as shown in Figure 1, concrete technological process is as follows:

I. open laser instrument 11, adjust light path, make: the moving direction of translation stage 15 is parallel to the incident direction of ultraviolet light 13; Ultraviolet light 13 impinges perpendicularly on the phase mask 16 after being fixed on level crossing 14 reflection on the translation stage 15; The plane that ± 1 order diffraction light is constituted is parallel with translation stage 15 moving directions.

II. light-sensitive optical fibre 17 is peelled off the coat of suitable length (greater than the design length of fiber grating), with it stretching and be fixed on phase mask 16 after, make it as far as possible near but do not stick.

III. adjust optical fiber 17 positions, make in the process that moves at translation stage 15, can be radiated on the core diameter of optical fiber 17 after ultraviolet light 13 sees through phase mask 16.

IV. initialization should be made platform and its control program: input exposure position sequence z _kWith index modulation amplitude sequence A _kAdjust diaphragm 12, make to be radiated at the spot diameter of the ultraviolet light on the optical fiber 17 less than sampling interval P _kMinimum value, P wherein _k=z _K+1-z _k Close laser instrument 11.

V. each position z that mobile successively translation stage 15 provides to the exposure position sequence _k, open laser instrument 11, the exposure reasonable time makes and produces A in the light-sensitive optical fibre 17 _kThe index modulation amplitude.

The invention is characterized in the exposure position sequence z in the middle of the process flow steps IV _kWith index modulation amplitude sequence A _kDetermine by following formula:

Wherein,

Λ be phase mask 16 initial end cycle 1/2, (z) is the phase function of this sampling optical fiber grating, its form is:

C be phase mask 16 chirp coefficient 1/2, m is non-vanishing integer, but require and

Opposite in sign, the level of the reflection peak that it has represented actual utilization in whole sampling optical fiber grating reflection peak time; F _mBe one greater than 0 less than 1 positive number, it has represented in the sampling optical fiber grating that effective index modulation amplitude, the index modulation amplitude of promptly using in order to form needed reflex response in the m level reflection peak account for total index modulation amplitude, are the ratio of the index modulation amplitude of sampling optical fiber grating in the reality, its numerical value need elicite in experiment or emulation pilot scale, initial value generally fix on 0.7 or more than, concrete numerical value is by experiment or emulation, decide according to the anastomose property of result and target reflection response.Λ _S, _S(z) and A _S(z) be cycle, phase function and the apodizing function of the initial end of arbitrarily given fiber grating, these three parameters can be directly given, and they can respond H (λ) according to target reflection, utilize the restructing algorithm of fiber grating to obtain.

The technological process that obtains having the reflex response of target phase shift feature in the m level channel of above-mentioned sampling optical fiber grating with above-mentioned technological process is: the exposure position sequence z in the middle of the above-mentioned process flow steps IV _k' and index modulation amplitude sequence A _k' determine by following formula:

A _k′＝A _k

Wherein, z _kAnd A _kThe distance of this given sampling optical fiber grating initial end and the amplitude of the index modulation that this place introduces, are arrived in the position that is k ultraviolet photoetching of the sampling optical fiber grating before revising ₀Be the target phase shift that the x place of the m level sub-gratings of the sampling optical fiber grating before correction introduces, P _x ⁰It is the distance between adjacent two the ultraviolet photoetching positions, sampling optical fiber grating x place before revising.

Generally speaking, the invention that obtains having the reflex response of target phase shift feature in the m level channel of sampling optical fiber grating is that a kind of of invention to the fiber grating filter of realizing having the arbitrary target reflex response replenishes.But the former also can use separately, be z _kAnd A _kAlso can be arbitrarily.

Ultimate principle of the present invention is: because the reflex response of sampling optical fiber grating has a plurality of reflection peaks, then can think each reflection peak all corresponding a strip fiber grating, this reflection peak is corresponding sub-optical fibre grating reflection response.The sub-optical fibre grating that claims m level reflection peak correspondence is a m level sub-optical fibre grating, the parameters such as the cycle with initial end, apodizing function and phase function that this sub-optical fibre grating is same, these parameters are determined by the sampling function s (z) of former sampling optical fiber grating: the z in sampling function s (z) _kAnd A _kWhen satisfying formula (8), cycle, apodizing function and the phase function of the initial end of m level sub-optical fibre grating are respectively Λ _S, _S(z) and A _S(z).These parameters can be given arbitrarily; If Λ _S, _S(z) and A _S(z) obtained by restructing algorithm according to target reflection response H (λ), the m level reflection peak of sampling optical fiber grating will have reflex response H (λ) so.If after obtaining the target reflection response, introduce the feature of phase shift again therein, promptly introduce at the z=x place of m level sub-optical fibre grating ₀The target phase shift, then as long as according to formula (5) to _S(z) revise, utilize the formula (8) just can be once more, be i.e. formula (9) in the hope of correction to former sampling optical fiber grating exposure position and index modulation amplitude.

Thereby realization thinking of the present invention is exactly: given target reflection response H (λ), utilize the restructing algorithm of fiber grating to obtain the sub-optical fibre grating index modulation, be parameter Λ _S, _S(z) and A _S(z), perhaps directly provide these parameters, utilize formula (8) to try to achieve the sampling function exposure position of sampling optical fiber grating and the index modulation amplitude of requirement; If in the m level reflection peak of any sampling optical fiber grating, obtain the reflex response that phase shift has same effect with target, then utilize formula (9) that the exposure position and the index modulation amplitude of former sampling optical fiber grating are done correction.At last, utilize traditional phase mask-scan method to make this sampling optical fiber grating, the reflex response that the m level reflection peak of the sampling optical fiber grating that obtains accordingly will have target perhaps has the reflex response of target phase shift.

The present invention is described in further detail by specific embodiment

Example I

Present embodiment can be realized a fiber grating that can be used for the third-order dispersion compensation.

The device that present embodiment adopted as shown in Figure 1, wherein

A. ultraviolet laser 11 adopts continuous 244nm argon ion frequency double laser, is produced by U.S. coherent company.

B. translation stage 15 is that German PI company produces, and model is MS85E, and kinematic accuracy is 0.1 μ m.

C. the cycle of the initial end of the phase mask 16 of Cai Yonging is 2 Λ=1061nm, and chirp coefficient is 2C=-0.048nm/cm.

D. the light-sensitive optical fibre 17 of Cai Yonging is the PS-RMS-50 type light-sensitive optical fibre that Canadian INO company produces.

The Λ of this example _S, _S(z) and A _S(z) obtain by the target reflection response; The character of the target reflection response of adopting is as follows:

A. amplitude reflectivity with the expression formula of wavelength variations is $R\left(\mathrm{\Δ\λ}\right)=\exp [-0.5\ln 2*{(2\mathrm{\Δ\λ}/B)}^8],$ Wherein Unit be

Nm, the distance of expression wavelength departure centre wavelength; B is the power reflection response of the fiber grating represented with nm

Three dB bandwidth is got B=1.2.

B. group delay with the expression formula of wavelength variations is $\mathrm{\τ}\left(\mathrm{\Δ\λ}\right)=150{\mathrm{\Δ\λ}}^2-400\mathrm{\Δ\λ},$ Wherein the unit of τ is ps.

Other parameter or the method that adopt are as follows:

A. restructing algorithm adopts fourier transform method.

B.m＝-1。

C. $\mathrm{\Δ\Λ}=0.69\mathrm{nm}.$

D.A _kMaximal value be ${A_k}^{\mathrm{Max}}=2*{10}^{-4}.$

Utilize formula (8), the A that obtains _kAnd P _kDistribution as shown in Figure 2.Wherein, horizontal ordinate 21 is the coordinates along the fiber grating direction, and unit is mm; The left side ordinate 22 be between adjacent two samplings distance, be P _k, unit is mm; The A that right side ordinate 23 is normalization _k, be A _k/ A _k ^Max

Utilize above-mentioned technological process, make fiber grating, and utilize the Q7760 type chromatic dispersion test instrument of ADVANTEST company to obtain the reflectivity spectral line of fiber grating-1 grade and group delay spectral line as shown in Figure 3.Wherein, horizontal ordinate 31 is incident light wavelengths, and unit is nm; Left side ordinate 32 is power reflectances of incident light, and unit is dB; Right side ordinate 33 is group delays of incident light, and unit is ps; The represented group delay curve of solid line is the result that the group delay (discrete point is represented) of utilizing quadratic function that actual measurement is obtained fits among the figure.-1 grade of peak measurement result of the actual fiber grating that obtains is:

A.3dB power reflectance is 1.2nm.

B. the group delay value of fitting is $\mathrm{\τ}\left(\mathrm{\Δ\λ}\right)={147.92\mathrm{\Δ\λ}}^2-396.44\mathrm{\Δ\λ}+{\mathrm{\τ}}_0.$

With the character contrast of target reflection response, very the realization of Wen Heing the target reflection response.

Inventive embodiments II

Present embodiment can obtain having π phase shift feature in-7 grades of channels of sampling optical fiber grating reflex response.

Present embodiment combines the invention that realization has the optical filter of arbitrary target reflex response, i.e. the exposure position z of the former sampling optical fiber grating in the present embodiment _k ⁰With the index modulation amplitude A of introducing _k ⁰Obtain by formula (8), and the Λ that requires in the formula (8) _S, _S(z) and A _S(z) be given.

The device that present embodiment adopted as shown in Figure 1, wherein

A. ultraviolet laser 11 adopts continuous 244nm argon ion frequency double laser, is produced by U.S. coherent company.

B. translation stage 15 is that German PI company produces, and model is MS85E, and kinematic accuracy is 0.1 μ m.

C. the cycle of the initial end of the phase mask 16 of Cai Yonging is 2 Λ=1061nm, and chirp coefficient is 2C=-0.048nm/cm.

D. the optical fiber 17 of Cai Yonging is the PS-RMS-50 type light-sensitive optical fibre that Canadian INO company produces.

The needed Λ of this example _S, _S(z) and A _S(z) directly provide the target phase shift of these parameters and introducing ₀Character as follows:

A. $A_S/{A_S}^{\mathrm{Max}}\≡1,$ _S≡0，0≤z≤0.05。

B.x＝0.025， ₀＝π。

Other parameter that adopts in the experiment is as follows:

A.m＝-1。

B. $\mathrm{\Δ\Λ}=0.69\mathrm{nm}.$

C.A _kMaximal value be ${A_k}^{\mathrm{Max}}=2*{10}^{-4}.$

Utilize formula (8) and formula (9), obtain the exposure position of sampling optical fiber grating and the index modulation amplitude of response and be:

A. $z_k=\left\{\begin{array}{cc}{\hat{z}}_k& {\hat{z}}_k\≤0.025\\ {\hat{z}}_k-2.06\×{10}^{-4}& {\hat{z}}_k>0.025\end{array},\right.$ Wherein ${\hat{z}}_k=\frac{k*8.235\×{10}^{-4}}{1+\sqrt{1+k*2.86\×{10}^{-3}}},$ 0≤k＜120。

B. $A_k/{A_k}^{\mathrm{Max}}\≡1.$

Utilize above-mentioned technological process, make fiber grating, and utilize reflectivity spectral line that the Q7760 type chromatic dispersion test instrument of ADVANTEST company obtains fiber grating-1 grade as shown in Figure 4.Wherein, horizontal ordinate 41 is incident light wavelengths, and unit is nm; Ordinate 42 is power reflectances, and unit is dB.-1 grade of peak center place of the actual fiber grating that obtains has-the power reflectance depression of 15dB, show the phase shift that has realized π at the middle part of-1 grade of pairing sub-optical fibre grating of reflection peak preferably.

According to above-mentioned inventive embodiments, the present invention proposes a kind of fiber grating that can realize, have the novel sampling structure with the method for making of traditional phase mask-scanning, can realize having the fiber waveguide device of arbitrary target response, the fiber grating that realization has target phase shift feature.

Advantage of the present invention is: utilize traditional phase mask-scan method and common evenly or the linear chrip template just can make the fiber grating that optical filter with arbitrary target reflex response or realization have the phase shift feature, and do not need high-precision control or expensive, have complicated warbling or the phase shift phase mask, do not need to realize continuous index modulation profile yet, thereby reduced cost of manufacture; Compare with the equivalent chirp method, then enlarged the scope of the reflex response that can realize, expanded the range of application of fiber grating.

Claims (4)

1. a realization has the fiber grating that arbitrary target responds, this fiber grating is the fiber grating that utilizes the sampling structure of phase mask-scanning method for making realization, the fiber waveguide device that its structure obtains for the periodic refractive index modulation that utilizes the ultraviolet photoetching amount of varying strength and pulse to introduce different amplitudes at the diverse location place of one section optical fiber; It is characterized in that: the position of k ultraviolet photoetching is to the distance z of this sampling optical fiber grating initial end _kWith at z _kThe amplitude A of the index modulation that the place introduces _kDetermine by following formula:

$A_k=\frac{A_S\left(z_k\right)}{F_m}$

Wherein, Δ Λ=Λ _S-Λ, Δ (z)= _S(z)-and (z), m is the nonzero integer with the opposite in sign of Δ Λ, F _mBe one greater than 0 less than 1 positive number, Λ and (z) are respectively the cycle and the phase functions of the initial end of this sampling optical fiber grating, Λ _S, _S(z) and A _S(z) be cycle, phase function and the apodizing function of the initial end of arbitrarily given fiber grating respectively.

2. as the said sampling optical fiber grating of claim 1, it is characterized in that: the position of said k ultraviolet photoetching is to the distance z of this sampling optical fiber grating initial end _kWith at z _kThe amplitude A of the index modulation that the place introduces _kBy the following formula correction, make it have the fiber grating of phase shift feature:

${A_k}^{\′}=A_k$

Wherein, z _k' and A _k' be that the position of k ultraviolet photoetching of revised sampling optical fiber grating is to the amplitude of the index modulation of the distance of this given sampling optical fiber grating initial end and the introducing of this place, ₀Be the target phase shift that the x place of the m level sub-gratings of the sampling optical fiber grating before correction introduces, P _x ⁰It is the distance between adjacent two the ultraviolet photoetching positions, sampling optical fiber grating x place before revising.

3. as claim 1 or 2 said sampling optical fiber gratings, it is characterized in that: said Λ _S, _S(z) and A _S(z) be according to the arbitrary target reflex response, utilize the restructing algorithm of fiber grating to obtain.

4. as claim 1 or 2 said sampling optical fiber gratings, it is characterized in that: said Λ _S, _S(z) and A _S(z) be given arbitrarily.

Images