CN101504473B - Multi-channel high-density optical fiber grating filter - Google Patents

Abstract

The invention discloses a multi-channel high-density optical fiber grating filter, which is manufactured on a basis of the Talbot effect generated by a novel Gauss sampling Bragg optical fiber grating, has the characteristics of wide frequency domain, concentrated channels, excellent channel isolation, and the like, and is applicable to optical wave division multiplexer elements requiring multi-channel (more than 40 channels) and high density (more than two channels per nanometer). Compared with uniform conventional vibration amplitude sampling Bragg optical fiber grating of the channels of the same requirement, the novel Gauss sampling Bragg optical fiber grating, under the Talbot effect, can realize the characteristics such as high energy efficiency, excellent channel isolation and convenient manufacturing, and has obvious advantages in manufacturing difficulty reduction, channel quality improvement and other aspects.

Description

A kind of multi-channel high-density optical fiber grating filter

Technical field

The present invention relates to a kind of fiber grating filter, particularly a kind of wide frequency domain, multi-channel filter belong to the optical information technical field.

Background technology

Hyperchannel Bragg fiber grating has caused that people more and more pay close attention in making the multi-channel filter system.Because the characteristic of aspects such as the filtering of sampling Bragg fiber grating in hyperchannel, dispersion compensation is very suitable for International Telecommunications Union's standard, so it can be used for the making of hyperchannel device and equipment.Sampling Bragg fiber grating can obtain by with the amplitude sampling function in cycle or phase sample function the refractive index of optical fiber being modulated.In this structure, the unique cycle P that regulates sampling optical fiber grating that depends on of the Free Spectral Range of comb filter (FSR).Studies show that in recent years, the grating cycle variation of warbling in fiber grating, its chirp coefficient and grating sampling period meet some requirements down, just the Talbot effect that the amplitude type fiber grating occurred, at this moment, Free Spectral Range just not only depends on the cycle of grating, but also is decided by the variation of warbling of grating.Since the Talbot effect in the amplitude sampling grating the design of optical fiber with compare uniform amplitude sampling grating aspect the optical fiber energy efficiency is utilized very big advantage arranged, promote people further to be familiar with and to understand the inner structure of fiber grating.

But because the congenital deficiency that has capacity usage ratio and index modulation aspect of amplitude sampling optical fiber grating, at present, the phase sample fiber grating is with the unique advantage of its high capacity usage ratio, the smooth reflection channel person's that causes the optical research very big interest.Yet, in the phase sample fiber grating, to reach desired hyperchannel by modulation to optical fibre refractivity, the wave filter of high-energy utilization factor, just need accurately locate (precision is a nanometer scale) to the point of the phase sample in each cycle, this is a very difficult thing to optical designers and experiment making, and all the time, people constantly explore optimal design method and simplify the experiment manufacturing technology.At " Phase-only sampled 45 channel fiber Bragg gratingwritten with a diffraction-compensated phase mask " (Optics Letters, Vol.31 Issue 9, pp.1199-1201 (2006)) in, a kind of even phase place sampling optical fiber grating experiment manufacturing technology of 45 passages is disclosed, adopted described " no stitching error " lithographic technique to make position phase template, manufacture difficulty is difficulty quite; At " Broadband high-channel-count phase-onlysampled fiber Bragg gratings based on spectral Talbot effect; " (OpticsExpress, Vol.16 Issue 20, pp.15584-15594 (2008)) in, theoretical modeling with phase sample point seldom, under the Talbot condition, realize multichannel theoretical prediction, to later realization hyperchannel, a new thinking has been opened up in the manufacturing of high reflectance DWDM and design, but its still need to phase place accurately locate in the hope of good reflection channel, this has just brought certain requirement to making, and difficulty is also bigger.So, seek a kind of easy to manufacturely, and it is wide to produce frequency domain, the good multi-channel filter technology of isolation is the target that the deviser pursues always.

Summary of the invention

In order to overcome the deficiency that prior art exists, the invention provides a kind of channels uniformity, energy efficiency height, the fiber grating filter of high-isolation with wide frequency domain, excellence.

The technical solution adopted in the present invention is: a kind of fiber grating filter is provided, and it comprises sampling function, fiber grating, it is characterized in that: what cycle of described fiber grating, linear or other arbitrary form took place warbles chirp coefficient c _gSatisfy the Talbot condition; Described sampling function s _p(z) be Gaussian function:

$s_p\left(z\right)=\exp [-g{\left(\frac{z^{\′}}{P/2}\right)}^2]$

Wherein, P is the sampling period of sampling function, and z ' is the length in a sampling period ,-P/2＜z '＜P/2, and g is the gaussian coefficient of decision Gauss sampling function form.

Linear chrip, chirp coefficient c take place in the cycle of described fiber grating _gFor:

$c_g=\frac{s}{m}\left(\frac{{\mathrm{\Λ}}_0}{P^2}\right)$

Wherein, s is an integer, and m is a positive integer, and s/m is an irreducible ratio, Λ ₀Be the index modulation cycle of centre wavelength, P is the sampling period of sampling function.

Studies show that, for the sampling Bragg fiber grating of warbling, as sampling period and chirp coefficient c _gWhen meeting some requirements, can produce spectrum from the imaging phenomenon, i.e. Talbot effect, this is that interference effect has caused periodically discrete reflectance spectrum, the present invention just is being based on above mechanism, and the variation of warbling of selective light grid cycle is offset reflectance spectrum, thereby causes the spectrum interference.When the condition of warbling satisfied the Talbot condition, the reflection peak number increased, and the wave spectrum broadening has so just been realized utilizing the Gauss's sampling function that is simple and easy to realize in sampling Bragg fiber grating, thereby realized multichannel possibility.Referring to accompanying drawing 1, it is in the chirped fiber grating, and index modulation Δ n (z) is with the distribution schematic diagram of grating length.

Referring to accompanying drawing 2, it is the comparison diagram of Gauss's sampling function structure of being adopted of conventional vibration amplitude sampling function and present embodiment.Among the figure, image a represents the distribution situation of sampling function in the conventional vibration amplitude sampling optical fiber grating, and wherein, P is the sampling period, P ₁Be the grating cycle.In the conventional vibration amplitude sampling optical fiber grating, be difficult to solve wave spectrum width and wavestrip energy this to contradiction because will expect wide wavestrip, grating cycle P ₁Must be very little, but the little reduction that just causes the reflection peak energy of grating cycle.Image b represents the distribution situation of sampling function in Gauss's sampling optical fiber grating that the present invention adopts, and Gauss's optical fiber of sampling has solved the contradiction that the conventional vibration amplitude fiber grating is faced.In Gauss's sampling optical fiber grating, sampling grating spreads all over the overall optical grid cycle, can realize high-octane reflection channel, if under Talbot effect condition, increase along with the grating total length, the wave spectrum scope is expanded, so just obtained to realize the reflection frequency of wide wave spectrum, also can realize the absolute filter of high-octane reflection channel, and because novel Gauss's sampling optical fiber grating adopts Gaussian function as its sampling function, reduced the program that traditional amplitude sampling grating needs apodizing function that grating is cut toe, made making easier, quick.

Referring to accompanying drawing 3, it is that the conventional vibration amplitude sampling optical fiber grating is along with grating cycle P ₁Increase the higher order reflection spectrum comparison diagram that produces.Wherein, grating length is 2cm, the refractive index change delta n in grating cycle ₀=6.0 * 10 ^-4, the sampling period is P=1.0mm, the sampling period is counted N=20, chirped grating coefficient s=1, m=2.Among Fig. 3, image a is grating cycle P ₁During=0.1mm, reflection peak situation when the Talbot effect takes place the conventional vibration amplitude fiber grating; Image b is grating cycle P ₁During=0.3mm, reflection peak situation when the Talbot effect takes place the conventional vibration amplitude fiber grating; Image c is grating cycle P ₁During=0.5mm, reflection peak situation when the Talbot effect takes place the conventional vibration amplitude fiber grating.As seen from Figure 3, in the conventional vibration amplitude sampling optical fiber grating, increase along with the grating cycle, the degradation of reflection channel, channel isolation degenerates, and the reflection channel usability that obtains reduces, so under conventional vibration amplitude sampling optical fiber grating Talbot condition, expect that the good reflection channel grating cycle should be much smaller than the sampling period, so just limited and increase the possibility that the grating cycle improves reflectance spectrum.Therefore, for general conventional vibration amplitude sampling optical fiber grating, want to obtain more channel and mean that just grating length and sampling period it (duty cycle) in a sampling period are very little, because the energy efficiency and the port number of grating are inversely proportional to, have only the grating length of increase and refractive index modulation degree so expect high-octane reflection peak, the practicality that this has just increased the difficulty of experiment and has reduced device.And for the phase sample fiber grating, though can obtain high-energy, multichannel reflection peak, but need carry out pinpoint to each phase sample cycle, precision will reach nanoscale, and this has just increased the experiment difficulty, experiment there is very high requirement, is difficult to produce in batches.

Remarkable advantage of the present invention is: owing to utilized Gauss's sampling function that sampling optical fiber grating is sampled, make sampling grating spread all over the overall optical grid cycle, improved capacity usage ratio greatly, channel isolation also is significantly improved simultaneously, therefore, when the Talbot effect takes place, obtained fat pipe, energy-efficient, the effect of high-isolation.This greatly reduces difficulty to making multichannel wave filter, compares making conventional vibration amplitude sampling optical fiber grating and also wants simple, convenient; Compare with the technology of the uniform phase sample fiber grating of existing making, the present invention adopts the Gaussian function sampling optical fiber grating of Talbot effect, only need be positioned at a millimeter magnitude, and accuracy requirement is not high, realizes easily.Therefore, the hyperchannel of Gauss's sampling optical fiber grating of the present invention, homogeneity and high-energy have brought great making convenience and wide application prospect to the multi-channel filter system.

Description of drawings

Fig. 1 is in the chirped fiber grating, and index modulation Δ n (z) is with the distribution schematic diagram of grating length;

Fig. 2 is that (the structure comparison diagram of Gauss's sampling function that figure a) is adopted with technical solution of the present invention (figure b), wherein, P is the sampling period to the conventional vibration amplitude sampling function, P ₁Be the grating cycle;

Fig. 3 is that the conventional vibration amplitude sampling optical fiber grating is along with grating cycle P ₁Increase the higher order reflection spectrum comparison diagram that produces;

Fig. 4 is the Gauss's sampling optical fiber grating of the embodiment of the invention 1 technical scheme preparation and the higher order reflection spectrum comparison diagram of conventional vibration amplitude sampling optical fiber grating;

Fig. 5 is Gauss's sampling optical fiber grating of the embodiment of the invention 1 technical scheme preparation and the conventional vibration amplitude sampling optical fiber grating changes generation along with grating cycle chirp coefficient group delay (the dotted line scope is interior among the figure) comparison diagram;

Fig. 6 is the higher order reflection spectrum comparison diagram by Gauss's sampling optical fiber grating of the embodiment of the invention 2 technical schemes preparation and conventional vibration amplitude sampling optical fiber grating;

Fig. 7 is the higher order reflection spectrum comparison diagram by Gauss's sampling optical fiber grating of the embodiment of the invention 3 technical schemes preparation and conventional vibration amplitude sampling optical fiber grating.

Fig. 2 is conventional vibration amplitude sampling function (the structure comparison diagram of Gauss's sampling function that figure a) is adopted with technical solution of the present invention (figure b); Wherein, P is the sampling period, P ₁Be the grating cycle; As seen from Figure 2, the sampling function that the present invention adopts has spread all over the whole sampling period, therefore can utilize grating well, obtain very high energy efficiency, and in the traditional sampling function, in order to obtain channel isolation preferably, the grating length in each sampling period must be limited in the sampling period 1/3 or below.

Embodiment

Below in conjunction with embodiment and accompanying drawing the present invention is further described.

Embodiment 1:

Referring to accompanying drawing 1, it is in the chirped fiber grating, and index modulation Δ n (z) is with the distribution schematic diagram of grating length.In the present embodiment, Bragg fiber grating grid cycle is linear chrip (also can be warbling of arbitrary form), i.e. Λ (z)=Λ ₀(1+c _gZ), chirp coefficient c _gSatisfy the Talbot condition of spectrum:

$c_g=\frac{s}{m}\left(\frac{{\mathrm{\Λ}}_0}{P^2}\right)$

Wherein, s is an integer, and m is a positive integer, and s/m is an irreducible ratio.Be Λ the modulation period of grating centre wavelength ₀, chirp coefficient is c _g, the sampling period is P.

The parameter that present embodiment uses is as follows: grating effective refractive index Δ n ₀=6.0 * 10 ^-4, the grid cycle Λ at grating center ₀=521.8855nm, relevant Bragg wavelength X _B=1550nm, the sampling period is P=1.0mm, s=1, m=2.Grating length is 4cm.In the traditional sampling, P ₁=0.1mm.

Sampling function is:

$s_p\left(z\right)=\exp [-g{\left(\frac{z^{\′}}{P/2}\right)}^2]$

Wherein, P is the sampling period of sampling function; Z ' is the length in a sampling period;-P/2＜z '＜P/2; G is a gaussian coefficient, the form of decision Gaussian function, in the present embodiment, gaussian coefficient g=8, P=1.0mm.

Fig. 4 is Gauss's sampling optical fiber grating of present embodiment technical scheme preparation and the higher order reflection spectrum comparison diagram that the conventional vibration amplitude sampling optical fiber grating produces along with grating cycle chirp coefficient changes, wherein, chirped grating coefficient s=1, m=2, the refractive index change delta n in grating cycle ₀=6.0 * 10 ^-4, the sampling period is P=1.0mm, and the sampling period is counted N=40, and grating length is 4cm.Among Fig. 4, reflection peak situation when figure a for the amplitude fiber grating Talbot effect takes place, reflection peak situation when figure b is present embodiment Gauss sampling function generation Talbot effect.Referring to accompanying drawing 4, when the Talbot condition was satisfied in the chirp coefficient variation, the channel spacing of reflectance spectrum (being Free Spectral Range) was 0.4nm.As seen from Figure 4, than the conventional vibration amplitude sampling optical fiber grating, take place in Gauss's sampling optical fiber grating of Talbot effect, the bandwidth distribution of its each passage is very even, isolation between the passage obviously strengthens, and channel distribution obtains very large-scale expansion.

Fig. 5 is Gauss's sampling optical fiber grating of present embodiment technical scheme preparation and the conventional vibration amplitude sampling optical fiber grating changes generation along with grating cycle chirp coefficient group delay (the dotted line scope is interior among the figure) comparison diagram.Wherein, grating length is 4cm, chirped grating coefficient s=1, m=2, the refractive index change delta n in grating cycle ₀=6.0 * 10 ^-4, the sampling period is P=1.0mm, the sampling period is counted N=40.Among Fig. 5, reflection peak group delay situation when image a for the conventional vibration amplitude fiber grating Talbot effect takes place, reflection peak group delay situation when image b is present embodiment Gauss sampling function generation Talbot effect.Referring to accompanying drawing 5, when the Talbot condition is satisfied in the chirp coefficient variation, the group delay figure of conventional vibration amplitude fiber grating reflectance spectrum and the group delay figure of Gauss's sampling function very similar (presenting bell), this explanation conventional vibration amplitude fiber grating is suitable equally under novel Gauss's sampling optical fiber grating in the character that is satisfied under the Talbot condition.

Embodiment 2

In the present embodiment, Bragg fiber grating grid cycle is linear chrip, i.e. Λ (z)=Λ ₀(1+c _gZ), chirp coefficient c _gSatisfy the Talbot condition of spectrum:

$c_g=\frac{s}{m}\left(\frac{{\mathrm{\Λ}}_0}{P^2}\right)$

The parameter that present embodiment uses is as follows: grating effective refractive index Δ n ₀=1.0 * 10 ^-3, chirp coefficient c _g=3.4724 * 10 ^-4(s=2, m=3), the sampling period is P=1.0mm to/mm.Grating length is 4cm.In the traditional sampling, P ₁=0.1mm.

Sampling function is:

$s_p\left(z\right)=\exp [-g{\left(\frac{z^{\′}}{P/2}\right)}^2]$

Wherein, P is the sampling period of sampling function; Z ' is the length in a sampling period;-P/2＜z '＜P/2; G is a gaussian coefficient, the form of decision Gaussian function, in the present embodiment, gaussian coefficient g=15, P=1.0mm.

Fig. 6 is the higher order reflection spectrum comparison diagram by Gauss's sampling optical fiber grating of present embodiment technical scheme preparation and conventional vibration amplitude sampling optical fiber grating.Its sampling period P=1mm, index modulation Δ n ₀=1.0 * 10 ^-3, periodicity N=40, chirp coefficient c _g=3.4724 * 10 ^-4/ mm (s=2, m=3), gaussian coefficient g=15.Referring to accompanying drawing 6, when the Talbot condition was satisfied in the chirp coefficient variation, the channel spacing of reflectance spectrum (being Free Spectral Range) was reduced to 0.27nm.Among Fig. 6, image a is a conventional vibration amplitude sampling optical fiber grating under the Talbot effect: as can be seen, when reflectivity is got 20dB, reflection peak top unevenness, it is very poor to reflect peak-to-peak isolation, and the secondary peak on each side, main channel is a lot, influences channel transfer.Image b is a present embodiment Gauss sampling optical fiber grating under equal conditions: as can be seen, isolation is very clear between the reflection peak, and peak-peak is very smooth, and secondary peak seldom is well suited for multichannel filtering.

Embodiment 3

In the present embodiment, Bragg fiber grating grid cycle is linear chrip, i.e. Λ (z)=Λ ₀(1+c _gZ), chirp coefficient c _gSatisfy the Talbot condition of spectrum:

$c_g=\frac{s}{m}\left(\frac{{\mathrm{\Λ}}_0}{P^2}\right)$

The parameter that present embodiment uses is as follows: grating effective refractive index modulation Δ n ₀=8.0 * 10 ^-4, chirp coefficient c _g=2.6094 * 10 ^-4(s=1, m=2), the sampling period is P=1.0mm to/mm.Grating length is 4cm.In the traditional sampling, P ₁=0.1mm.

Sampling function is:

$s_p\left(z\right)=\exp [-g{\left(\frac{z^{\′}}{P/2}\right)}^2]$

Wherein, P is the sampling period of sampling function; Z ' is the length in a sampling period;-P/2＜z '＜P/2; G is a gaussian coefficient, the form of decision Gaussian function, in the present embodiment, gaussian coefficient g=10, P=1.0mm.

Fig. 7 is under Talbot effect condition, and when requiring port number to be 70, the conventional vibration amplitude sampling optical fiber grating is composed comparison diagram with the higher order reflection of Gauss's sampling optical fiber grating of pressing the preparation of present embodiment technical scheme.Its sampling period P=1mm, index modulation Δ n ₀=8.0 * 10 ^-4, periodicity N=80, chirp coefficient c _g=2.6094 * 10 ^-4/ mm (s=1, m=2), gaussian coefficient g=10.

Among Fig. 7, image a is a conventional vibration amplitude sampling optical fiber grating under the Talbot effect; Image b is a present embodiment Gauss sampling optical fiber grating under equal conditions.As can be seen, when reflectivity is got 35dB, need wide frequency domain, during multichannel reflection peak, no matter Gauss's sampling optical fiber grating is at the isolation of passage, or the smooth degree of reflection peak, all is much better than the amplitude type sampling optical fiber grating on the utilization ratio of energy.

Claims (2)

1. multi-channel high-density optical fiber grating filter, it comprises sampling function, fiber grating, it is characterized in that: described fiber grating is the amplitude type fiber grating; What cycle of described fiber grating, linear or other arbitrary form took place warbles chirp coefficient c _gSatisfy the Talbot condition; Described sampling function s _p(z) be Gaussian function:

$s_p\left(z\right)=\exp [-g{\left(\frac{z^{\′}}{P/2}\right)}^2]$

Wherein, P is the sampling period of sampling function, and z ' is the length in a sampling period ,-P/2＜z '＜P/2, and g is the gaussian coefficient of decision Gauss sampling function form.

2. a kind of fiber grating filter according to claim 1 is characterized in that: linear chrip, chirp coefficient c take place in the cycle of described fiber grating _gFor:

$c_g=\frac{s}{m}\left(\frac{{\mathrm{\Λ}}_0}{P^2}\right)$

Wherein, s is an integer, and m is a positive integer, and s/m is an irreducible ratio, Λ ₀Be the index modulation cycle of centre wavelength, P is the sampling period of sampling function.

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