CN1811503A - Method for producing non-linear chirp optical fibre grating for 40 Gb/S optical communication system - Google Patents

Abstract

The present invention belongs to the field of optical fibre grating production technology. It is characterized by that said invention successively includes the following several steps: designing a nonlinear chirp optical fibre grating with tunable property, namely, its reflectivity and wavelength are formed into Gaussian curve change and its group delay and wavelength are formed into secondary curve change; utilizing reconstruction principle of grating to obtain reflectivity modulation function of grating, and utilizing said function to define sampling point position and exposure time, then utilizing designed result to make a nonlinear chirp optical fibre grating for 40 G b/s optical communication system.

Description

The nonlinearly chirped fiber grating method for making that the 40Gb/s optical communication system is used

Technical field

Present technique belongs to technical field of optical fiber communication, relates in particular to fiber grating and makes the field.

Background technology

The general indemnity fibre-optical dispersion can wait and realize as Dispersion Compensation Fiber Gratings, dispersion compensation etalon with dispersion compensating fiber or dispersion compensation device.The implementation method of this dispersion compensation is fixed, in case system design has been got well, the compensation rate of its chromatic dispersion just can not change.And the accumulation of chromatic dispersion is a time dependent process, system can be subjected to the influence of a lot of extraneous factors, as temperature variation, pressure etc., thus the chromatic dispersion of generation dynamic change, and this compensates with regard to the mode that needs the dynamic-tuning dispersion compensation device that tracking is monitored in the chromatic dispersion that is changing.Wherein, the implementation of adjustable chromatic dispersion is the core content of dynamic-tuning dispersion compensation device.There are some modes can realize adjustable chromatic dispersion, carry out linear superposition adjustment chromatic dispersion etc. as the chromatic dispersion that changes fiber grating of using thermal effect in fiber grating, to produce warbling of dynamic change, the variable time delay curve that utilizes a plurality of etalons to produce.Wherein the adjustable chromatic dispersion based on non-linear chirp is simple with it, effectively becomes one of noticeable method.

The time lag curve of nonlinearly chirped fiber grating is non-linear, by just can realize the change of fiber grating time delay to the heating of fiber grating, wherein when the time delay of fiber grating becomes quafric curve to change with wavelength, chromatic dispersion versus wavelength is linear, the relation curve of its time delay (group delay) and chromatic dispersion (dispersion) and optical wavelength (wavelength) as shown in Figure 1, 2, the tuning control of fiber grating this moment can be simpler.Therefore, the nonlinearly chirped fiber grating of the different structure of design just can be realized the better compensation to system dispersion.Owing to want fabricating quality higher non-linearity chirped fiber grating to need high-quality non-linear chirp template, and the non-linear chirp template need use electron beam lithography to make, obtain quite difficulty of high-quality non-linear chirp template, and price is also quite expensive.And different nonlinearly chirped fiber gratings needs different non-linear chirp phase masks, and this makes the design of above-mentioned tunable devices and application be subjected to certain restriction.

Owing to obtain the difficulty of high-quality non-linear chirp template, therefore occurred adopting even phase mask and sampling optical-fiber grating technology to obtain the method for non-linear chirp.People such as Jiang Dianjie, Chen Xiangfei had proposed to use warble the sample period (CSP) by sampled-grating to obtain the chirp grating cycle (CGP) of equivalence and adopt the precision optical machinery device to realize tuning method in " the design and fabrication method of adjustable chromatic dispersion compensator " Chinese invention patent (application number 200410000339.8) in 2004.

Though this method has realized using the phase mask of warbling to design and make the nonlinearly chirped fiber grating of equivalence, but when specific design, be merely able to the group delay curve of grating is controlled, can not control the grating reflection rate curve simultaneously, this has just reduced the performance of grating.In addition its to adopt precision optical machinery device to carry out tuning, but the precision optical machinery device costs an arm and a leg, volume is bigger, this has limited the application of this adjustable chromatic dispersion compensator to a certain extent.

Summary of the invention

The objective of the invention is in order to break through existing technology, and overcome the weak point of prior art, the special sampling optical-fiber grating that a kind of new method designed and made the non-linear chirp effect with equivalence has been proposed, and it is tuning to adopt new mode that grating is carried out, thereby realizes the adjustable chromatic dispersion compensation.This fiber grating adopts even stencil design, by reconstruct, equivalence to grating, and control when realizing to group delay curve and reflectance curve.Then even metal coating is carried out on the fiber grating surface that completes, the thermal effect that produces when utilizing electric current to pass through the coat of metal realizes moving of grating centre wavelength, thus the compensation rate of control chromatic dispersion.

We adopt sampled-grating reflection peak-1 a grade inferior group delay spectrum to be used for dispersion compensation.

Designed grating reflection characteristic is as follows:

Reflectance curve:

$R\left(\mathrm{\&lambda;}\right)=\frac{\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="A20061001141100162.png"\; state="\{\{state\}\}">e</figure-callout>}}{\sqrt{2}}\exp [-{\left(\frac{\mathrm{\&lambda;}-{\mathrm{\&lambda;}}_0}{B/2}\right)}^{2m}]---\left(1\right)$

Group delay curve: τ (λ)=a (λ-λ ₀) ²+ b (λ-λ ₀)+c (2)

R in the formula (λ) is the grating reflection rate; λ is an optical wavelength; λ ₀Be centre wavelength, be taken as 1553.5mm; B is the three dB bandwidth of optical grating reflection spectrum, is taken as 2nm; τ (λ) is the group delay of grating; A, b, c are the design tuner parameters of compensator, get a=-100ps/nm ², b=-300ps/nm, c=900ps; M be superelevation this cut the toe coefficient, get m=4.The group delay of grating becomes quafric curve to change with wavelength, and its chromatic dispersion versus wavelength is linear, so its tuning control can be simple more, stable.In addition, in the design process of grating, considered its group delay characteristic and reflectivity Characteristics simultaneously, realized common control, obtained the more smooth zone of reflections, therefore can obtain the grating of superior performance the two.

Utilize the interchange index modulation function and the relation of the Fourier transform between the reflection characteristic of grating, obtain the interchange index modulation function of grating:

$\mathrm{Ac}\left(z\right)=j\frac{2n{\mathrm{\&Lambda;}}_0}{\mathrm{\&pi;}}{\&Integral;}_0^{l}R\left(\mathrm{\&lambda;}\right)\exp [-\mathrm{j\&theta;}]\&CenterDot;\exp \left[\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="A20061001141100162.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&sigma;z}\right]\mathrm{d\&sigma;}---\left(3\right)$

Wherein, $\mathrm{\&theta;}={\&Integral;}_0^{\mathrm{\&lambda;}}\frac{2\mathrm{\&pi;}}{{{\mathrm{\&lambda;}}_0}^2}\mathrm{\&tau;}\left({\mathrm{\&lambda;}}^{\&prime;}\right)d{\mathrm{\&lambda;}}^{\&prime;},$ $\mathrm{\&sigma;}=\frac{2\mathrm{n\&pi;}}{\mathrm{\&lambda;}}-\frac{\mathrm{\&pi;}}{{\mathrm{\&Lambda;}}_0},$ Λ ₀=λ ₀/ 2n, n are the mean refractive index of grating.

Ac (z) is written as the form of complex-exponential function:

Ac(z)＝A(z)exp[j(z)] (4)

Utilize sampled-grating to realize above-mentioned index modulation, the position z of its each sampling spot _kCalculate by equation (5):

P is a sampling parameter in the formula, gets P=0.12mm usually; K represents k sampling spot of sampled-grating, k=1, and 2,3 ....

The time shutter T of each sampling spot _kDetermine by formula (6):

$T_k=T_{\max }\&CenterDot;\frac{A\left(z_k\right)}{\max \left\{A\left(z_k\right)\right\}}---\left(6\right)$

T wherein _MaxFor the maximum exposure time of sampling spot, get T usually _Max=100s; Max{A (z _k) represent all sampling spot z _kIndex modulation A (z _k) in maximal value.

The method for designing of adjustable chromatic dispersion compensator described in the invention is characterized in that it contains following step successively:

(1) to have tunable characteristic be that reflectivity becomes this curvilinear motion of superelevation, group delay to become the non-linear chirp grating of quafric curve variation with wavelength with wavelength in one of design, and the grating reflection characteristic is:

$R\left(\mathrm{\&lambda;}\right)=\frac{\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="A20061001141100162.png"\; state="\{\{state\}\}">e</figure-callout>}}{\sqrt{2}}\exp [-{\left(\frac{\mathrm{\&lambda;}-{\mathrm{\&lambda;}}_0}{B/2}\right)}^{2m}]$

τ(λ)＝a(λ-λ ₀) ²+b(λ-λ ₀)+c

Wherein, R (λ) is the grating reflection rate; λ is an optical wavelength; λ ₀Be centre wavelength, setting value; B is the three dB bandwidth of optical grating reflection spectrum, and unit is nm; τ (λ) is the group delay of grating, and unit is ps; A, b, c are design parameter, setting value, the unit of a is ps/nm ², the unit of b is ps/nm, the unit of c is ps.

(2) according to the grating reflection characteristic, utilize the reconfiguration principle of grating to obtain the grating index modulation function, the grating index modulation function is calculated by following formula:

$\mathrm{\&Delta;n}\left(z\right)=\mathrm{Ac}\left(z\right)\exp (-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="A20061001141100162.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;z}}{{\mathrm{\&Lambda;}}_0})$

Wherein, z is the optical fiber axial length; Δ n (z) is the grating index modulation function; Λ ₀Be the grating index modulation cycle, by the centre wavelength decision of grating: Λ ₀=λ ₀/ 2n, n are the mean refractive index of grating,

Ac (z) is called the interchange index modulation function of grating, can be calculated by following formula:

$\mathrm{Ac}\left(z\right)=j\frac{2n{\mathrm{\&Lambda;}}_0}{\mathrm{\&pi;}}{\&Integral;}_0^{l}R\left(\mathrm{\&lambda;}\right)\exp [-\mathrm{j\&theta;}]\&CenterDot;\exp \left[\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="A20061001141100162.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&sigma;z}\right]\mathrm{d\&sigma;}$

Wherein, $\mathrm{\&theta;}={\&Integral;}_0^{\mathrm{\&lambda;}}\frac{2\mathrm{\&pi;}}{{{\mathrm{\&lambda;}}_0}^2}\mathrm{\&tau;}\left({\mathrm{\&lambda;}}^{\&prime;}\right)d{\mathrm{\&lambda;}}^{\&prime;},$ $\mathrm{\&sigma;}=\frac{2\mathrm{n\&pi;}}{\mathrm{\&lambda;}}-\frac{\mathrm{\&pi;}}{{\mathrm{\&Lambda;}}_0}$

Ac (z) is written as complex exponential form, for: Ac (z)=A (z) exp[j (z)]

Wherein, Ac (z) and A (z), (z) all can utilize the computer numerical Calculation Method to obtain according to the design reflectivity characteristic of grating in the step (1).

(3) the sampling spot position z of sampled-grating _kDetermine by following equation:

P is a sampling parameter in the formula, gets P=0.15mm usually; K represents k sampling spot of sampled-grating, k=1, and 2,3 ...., the time shutter T of each sampling spot _kDetermine by following formula:

$T_k=T_{\max }\&CenterDot;\frac{A\left(z_k\right)}{\max \left\{A\left(z_k\right)\right\}}$

T wherein _MaxFor the maximum exposure time of sampling spot, get T usually _Max=100 seconds; Max{A (z _k) represent all sampling spots

z _kIndex modulation A (z _k) in maximal value.

The difference of design of the present invention, the method for making fiber grating and " the design and fabrication method of adjustable chromatic dispersion compensator " patent is:

The present invention realizes the common control to grating group delay curve and reflectance curve by equivalence, reconstruct to grating, thus the fiber grating that obtains having the ideally-reflecting characteristic.In addition in realizing the process of fiber grating tuning, we are not that to adopt the precision optical machinery device to carry out tuning, but adopt the method for the even plated film of grating surface, utilize thermal effect that the chromatic dispersion of grating is regulated.Such design and method for making not only can be simplified the manufacturing process of grating, and have greatly reduced the cost of adjustable chromatic dispersion compensator, have reduced its volume.

The making of adjustable chromatic dispersion compensator is characterized in that it contains following steps successively:

(1) ordinary optic fibre is carried hydrogen and handle and peel off one section coat;

(2) above-mentioned optical fiber is fixed on even template after, make it;

(3) adjust the luminous power that laser instrument is output as 50mW;

(4) adjust light path, the hot spot through the scanning reflection mirror reflection is radiated on the fiber core;

(5) open the scanning mobile platform and the laser instrument control program of microcomputer, following parameter is set in input:

Exposure station position (providing) by formula (5):

Time shutter (providing) by formula (6): $T_k=T_{\max }\&CenterDot;\frac{A\left(z_k\right)}{\max \left\{A\left(z_k\right)\right\}}$

(6) start scanning platform, make it, make the optical fiber after the exposure become fiber grating with non-linear chirp characteristic according to setup parameter operation in (5).

(7) fiber grating that completes is placed in the oil removing alkali lye, 75 ℃ of following water-baths heating 30 minutes, oil removing alkali lye was by following four kinds of solution 1: 1: 1 by volume: 1 is formulated:

NaOH: 40g/L, sodium silicate: 40g/L, sodium carbonate: 30g/L, sodium phosphate: 30g/L

(8) fiber grating after will cleaning is placed in the sensitizing solution and soaked 10 seconds, changes over to then in the activating solution and soaks 10 seconds, changes sensitizing solution again over to.4～5 times so repeatedly, become dark brown up to the fiber grating surface.Being formulated as follows of sensitizing solution and activating solution:

Sensitizing solution: stannous chloride, 30g/L, 20ml

Activating solution: palladium bichloride, 0.1g/L, 20ml

(9) fiber grating is placed in the nickel plating solution, 50 ℃ of following water-baths were heated 2 hours, made the even metallic nickel plated layer of fiber grating surface coverage one deck.Being formulated as follows of nickel plating solution:

Nickelous sulfate: 30g/L, 35ml

Sodium pyrophosphate: 90g/L, 30ml

Inferior sodium phosphate: 30g/L, 25ml

Ammoniacal liquor: 40ml/L, 5ml

(10) fiber grating that will be coated with the even coat of metal is welded on the electrode and is encapsulated in the metal sleeve.

(11) the RS-232 port with computing machine links to each other with the communication pin of single chip computer AT 89C52, and by the digital signal output of computer control single-chip microcomputer, the scope of single-chip microcomputer output binary digital signal is 000000000000～111111111111.

(12) the digital signal output pin with single-chip microcomputer links to each other with the digital input pin of DA converter MAX508, utilizes the DA converter that the digital signal of single-chip microcomputer is converted to simulating signal, and the scope of DA converter output voltage simulating signal is 0～10V.

(13) the voltage analog signal output pin with the DA converter links to each other with pliotron (Darlington transistor) input pin, utilizes pliotron that voltage signal is carried out power amplification.

(14) output port of pliotron is linked to each other with electrode in the above-mentioned steps (10), thereby realize changing the voltage at electrode two ends, and then realize changing the chromatic dispersion that compensator provides by computing machine by computing machine.

Utilize this adjustable chromatic dispersion compensator in the 40Gb/s optical communication system, to test, record light signal through the Power penalty behind the dispersion compensation less than 0.7dB, be lower than the Power penalty upper limit of the 1dB that stipulates in the communication standard, illustrate that this adjustable chromatic dispersion compensator has goodish actual performance.

In sum, the present invention can go out high performance fiber grating according to system and user's needs flexible design, and the manufacturing process of grating is also fairly simple, reliable, and tuner is simple in structure, stable performance, the more important thing is that this adjustable chromatic dispersion compensator is with low cost, very big use potentiality are arranged.

Description of drawings:

Fig. 1: the group delay (Group Delay) and optical wavelength (Wavelength) relation curve of design grating;

Fig. 2: the chromatic dispersion (Dispersion) and optical wavelength (Wavelength) relation curve of design grating;

Fig. 3: make the grating reflection rate curve;

Fig. 4: the group delay curve of making grating;

Fig. 5: fiber grating producing device synoptic diagram;

Fig. 6: the tuner synoptic diagram of adjustable chromatic dispersion compensator;

Fig. 7: the control device synoptic diagram of adjustable chromatic dispersion compensator;

Fig. 8: the adjustable chromatic dispersion compensator electrode voltage with the dispersion measure relation curve is provided;

Fig. 9: the 40Gb/s adjustable chromatic dispersion compensator is made process flow diagram.

Concrete embodiment:

Adjustable chromatic dispersion compensator method for making of the present invention is divided into the two large divisions: the one, have the design of the sampled-grating of twice time lag curve and this reflectance curve of superelevation, and the 2nd, the making of adjustable chromatic dispersion compensator.Concrete embodiment is described with reference to the accompanying drawings as follows.

One, the design of the fiber grating of adjustable chromatic dispersion compensator use

For formula (1), get B=2nm, λ ₀=1553.5nm, m=4; For formula (2), get a=-100ps/nm ², b=-300ps/nm, c=900.

Utilize Fourier transform, draw A (z) and (z) in the interchange index modulation function of grating by formula (3).

Utilize formula (5) to obtain k sampling spot position of sampled-grating z _k, and utilize formula (6), obtain the time shutter T at k sampling spot place _k

Grating reflection rate curve that completes and time lag curve are respectively shown in Fig. 3,4: in bandwidth was the scope of 2nm, its chromatic dispersion changed to-60ps/nm from-260ps/nm.

Two, the making of adjustable chromatic dispersion compensator

The device of this embodiment preparing grating as shown in Figure 5.Wherein, light source adopts continuous 244nm frequency multiplication Argon ion laser 51 (production of U.S. coherent company).Scanning reflection mirror 52 is fixed on the ESP6000 scanning mobile platform (production of Newport company) 53, and scanning mobile platform kinematic accuracy is 0.1mm.Catoptron 52 has the function of scanner uni folded light beam, and the ultraviolet light of laser instrument 51 outputs is reflexed on the even phase mask 54, and this phase mask length is 60mm, and ultraviolet light is radiated at it down on the standard single-mode fiber 55 that year hydrogen is handled through phase mask.ESP6000 scanning mobile platform links to each other with the PIO mouth (not marking among the figure) of microcomputer.By the drive software that operation on microcomputer designs in advance, change the motion state (move distance, run duration etc.) of mobile platform, it is moved according to a certain characteristics of motion, just can obtain the fiber grating that needs.

2, the making of adjustable chromatic dispersion compensator is characterized in that it contains following steps successively:

(1) ordinary optic fibre is carried hydrogen and handle and peel off one section coat;

(2) above-mentioned optical fiber is fixed on even template after, make it;

(3) adjust the luminous power that laser instrument is output as 50mW;

(4) adjust light path, the hot spot through the scanning reflection mirror reflection is radiated on the fiber core;

(5) open the scanning mobile platform and the laser instrument control program of microcomputer, following parameter is set in input: exposure station position and time shutter.

(6) start scanning platform, make it, make the optical fiber after the exposure become fiber grating with non-linear chirp characteristic according to setup parameter operation in (5).

(7) fiber grating that completes is placed in the oil removing alkali lye, 75 ℃ of following water-baths heating 30 minutes, oil removing alkali lye was by following four kinds of solution 1: 1: 1 by volume: 1 is formulated:

NaOH: 40g/L, sodium silicate: 40g/L, sodium carbonate: 30g/L, sodium phosphate: 30g/L

(8) fiber grating after will cleaning is placed in the sensitizing solution and soaked 10 seconds, changes over to then in the activating solution and soaks 10 seconds, changes sensitizing solution again over to.4～5 times so repeatedly, become dark brown up to the fiber grating surface.Being formulated as follows of sensitizing solution and activating solution:

Sensitizing solution: stannous chloride, 30g/L, 20ml

Activating solution: palladium bichloride, 0.1g/L, 20ml

(9) fiber grating is placed in the nickel plating solution, 50 ℃ of following water-baths were heated 2 hours, made the even metallic nickel plated layer of fiber grating surface coverage one deck.Being formulated as follows of nickel plating solution:

Nickelous sulfate: 30g/L, 35ml

Sodium pyrophosphate: 90g/L, 30ml

Inferior sodium phosphate: 30g/L, 25ml

Ammoniacal liquor: 40ml/L, 5ml

(10) fiber grating that will be coated with the even coat of metal is welded on the electrode and is encapsulated in the metal sleeve.

(11) the RS-232 port with computing machine links to each other with the communication pin of single chip computer AT 89C52, and by the digital signal output of computer control single-chip microcomputer, the scope of single-chip microcomputer output binary digital signal is 000000000000～111111111111.

(12) the digital signal output pin with single-chip microcomputer links to each other with the digital input pin of DA converter MAX508, utilizes the DA converter that the digital signal of single-chip microcomputer is converted to simulating signal, and the scope of DA converter output voltage simulating signal is 0～10V.

(13) the voltage analog signal output pin with the DA converter links to each other with pliotron (Darlington transistor) input pin, utilizes pliotron that voltage signal is carried out power amplification.

(14) output port of pliotron is linked to each other with electrode in the above-mentioned steps (10), thereby realize changing the voltage at electrode two ends, and then realize changing the chromatic dispersion that compensator provides by computing machine by computing machine.Wherein the relation curve between the chromatic dispersion that provides of electrode voltage (Voltage) and compensator as shown in Figure 8.

The synoptic diagram of the tuner that the making adjustable chromatic dispersion compensator uses as shown in Figure 6.Metal sleeve 61 is made by steel, and other critical piece is all directly or indirectly fixed on it.Two electrodes are fixed on the metal sleeve two ends by insulating gel.Grating 62 two ends that are coated with metal nickel dam 63 are welded on the electrode 64, and two section leads 65 are drawn by two electrodes 64.The voltage that two electrodes are 64 is provided by numerical control voltage source circuit 66, and numerical control voltage source circuit 66 links to each other with the RS232 PORT COM of computing machine by Serial Port Line 67.68 is fibre-optical splice, links to each other with optical communication system 68 during use.

Adjustable chromatic dispersion compensator control device synoptic diagram as shown in Figure 7.The RS232 port 71 of computing machine links to each other with the digital signal input pin of single-chip microcomputer 72 (AT89C52) by Serial Port Line 67; Single-chip microcomputer 72 is converted to the Parallel Digital voltage data with the serial digital voltage data that computing machine sends, and is sent into the digital signal input pin of DA converter 73 (MAX508) by its digital signal output pin.DA converter 73 is converted to analog voltage signal with digital signal, sends into pliotron 74 by its aanalogvoltage output port and carries out power amplification.The output pin of pliotron 74 links to each other with electrode 64 by lead 65.

Utilize this adjustable chromatic dispersion compensator in the 40Gb/s optical communication system, to test, record light signal through the Power penalty behind the dispersion compensation less than 0.7dB, be lower than the Power penalty upper limit of the 1dB that stipulates in the communication standard, illustrate that this adjustable chromatic dispersion compensator has goodish actual performance.

In sum, the present invention can go out high performance fiber grating according to system and user's needs flexible design, and the manufacturing process of grating is also fairly simple, reliable, and tuner is simple in structure, stable performance, the more important thing is that this adjustable chromatic dispersion compensator is with low cost, very big use potentiality are arranged.

Claims (1)

1, the nonlinearly chirped fiber grating method for making used of 40Gb/s optical communication system is characterized in that described method contains following steps successively:

Step 1: design a sampled-grating with following reflection characteristic and group delay characteristic according to following setup parameter:

Reflectance curve: $R\left(\mathrm{\&lambda;}\right)=\frac{e}{\sqrt{2}}\exp [-{\left(\frac{\mathrm{\&lambda;}-{\mathrm{\&lambda;}}_0}{B/2}\right)}^{2m}],$

Group delay curve: τ (λ)=a (λ-λ ₀) ²+ b (λ-λ ₀)+c,

Wherein: R (λ) is the grating reflection rate,

λ is an optical wavelength,

λ ₀Be centre wavelength, establish λ ₀=1553.5nm,

B establishes B=2nm for the three dB bandwidth of this optical grating reflection spectrum,

τ (λ) is the group delay of this grating,

A, b, c establishes a=-100ps/nm for the design tuner parameters ², b=-300ps/nm, c=900ps,

m＝4；

Step 2: according to the design parameter of step 1, by following setup parameter, with the index modulation function Δ n (z) of this sampling optical-fiber grating of COMPUTER CALCULATION:

$\mathrm{\&Delta;n}\left(z\right)=\mathrm{Ac}\left(z\right)\exp (-j\frac{2\mathrm{\&pi;z}}{{\mathrm{\&Lambda;}}_0}),$

Wherein, z is this sampled-grating coordinate vertically,

Λ ₀Be the index modulation cycle of this sampled-grating: Λ ₀=λ ₀/ 2n,

N is the mean refractive index of this sampling optical-fiber grating,

Function Ac (z) is the interchange index modulation function of this sampled-grating, is calculated as follows by computing machine:

$\mathrm{Ac}\left(z\right)=j\frac{2n{\mathrm{\&Lambda;}}_0}{\mathrm{\&pi;}}{\&Integral;}_0^{l}R\left(\mathrm{\&lambda;}\right)\exp [-\mathrm{j\&theta;}]\&CenterDot;\exp \left[j2\mathrm{\&sigma;z}\right]\mathrm{d\&sigma;},$

Wherein, $\mathrm{\&theta;}={\&Integral;}_0^{\mathrm{\&lambda;}}\frac{2\mathrm{\&pi;}}{{{\mathrm{\&lambda;}}_0}^2}\mathrm{\&tau;}\left({\mathrm{\&lambda;}}^{\&prime;}\right)d{\mathrm{\&lambda;}}^{\&prime;},0\&le;{\mathrm{\&lambda;}}^{\&prime;}\&le;\mathrm{\&lambda;},$

$\mathrm{\&sigma;}=\frac{2\mathrm{n\&pi;}}{\mathrm{\&lambda;}}-\frac{\mathrm{\&pi;}}{{\mathrm{\&Lambda;}}_0},$

L is the length of this sampled-grating,

The complex exponential form of function Ac (z) is:

Ac(z)＝A(z)exp[j(z)]；

Step 3: the index modulation function that utilizes step 2 to obtain, determine the position z of each sampling spot by following formula _k:

Wherein, P is a sampling parameter, gets P=0.12mm;

K represents k sampling spot of this sampled-grating, k=1, and 2,3 ...;

Be calculated as follows out the time shutter T of each sampling spot again _k:

$T_k=T_{\max }\&CenterDot;\frac{A\left(z_k\right)}{\max \left\{A\left(z_k\right)\right\}}$

Wherein, T _MaxFor the maximum exposure time of sampling spot, get T _Max=100 seconds;

Max{A (z _k) represent all sampling spot z _kIndex modulation amplitude A (z _k) in maximal value;

Step 4: according to the following steps, make the nonlinearly chirped fiber grating that described 40Gb/s optical communication system is used:

Step 4.1: ordinary optic fibre is carried hydrogen handle and peel off one section coat;

Step 4.2: after the optical fiber that obtains in the step 4.1 is fixed on even template, make it;

Step 4.3: adjust the luminous power that laser instrument is output as 50mW;

Step 4.4: adjust light path, the hot spot through the scanning reflection mirror reflection is radiated on the fiber core;

Step 4.5: open the scanning mobile platform and the laser instrument control program of microcomputer,, set the following parameter of input according to the result of calculation of step 3:

The exposure station position:

Time shutter: $T_k=T_{\max }\&CenterDot;\frac{A\left(z_k\right)}{\max \left\{A\left(z_k\right)\right\}};$

Step 4.6: start scanning platform, make this platform, make the optical fiber after the exposure become fiber grating with non-linear chirp characteristic according to setup parameter operation in the step 4.5;

Step 4.7: the fiber grating that completes is placed in the oil removing alkali lye, 75 ℃ of following water-baths heating 30 minutes, oil removing alkali lye was by following four kinds of solution 1: 1: 1 by volume: 1 is formulated:

NaOH: 40g/L, sodium silicate: 40g/L, sodium carbonate: 30g/L, sodium phosphate: 30g/L;

Step 4.8: the fiber grating after will cleaning is placed in the sensitizing solution and soaked 10 seconds, changes over to then in the activating solution and soaks 10 seconds, changes sensitizing solution again over to, 4～5 times so repeatedly, becomes dark brown up to the fiber grating surface; Being formulated as follows of sensitizing solution and activating solution:

Sensitizing solution: stannous chloride, 30g/L, 20ml;

Activating solution: palladium bichloride, 0.1g/L, 20ml;

Step 4.9: fiber grating is placed in the nickel plating solution, and 50 ℃ of following water-baths were heated 2 hours, made the even metallic nickel plated layer of fiber grating surface coverage one deck; Being formulated as follows of nickel plating solution:

Nickelous sulfate: 30g/L, 35ml;

Sodium pyrophosphate: 90g/L, 30ml;

Inferior sodium phosphate: 30g/L, 25ml;

Ammoniacal liquor: 40ml/L, 5ml;

Step 4.10: the fiber grating that will be coated with the even coat of metal is welded on the electrode and is encapsulated in the metal sleeve;

Step 4.11: the RS-232 port of computing machine is linked to each other with the communication pin of single chip computer AT 89C52, and by the digital signal output of computer control single-chip microcomputer, the scope of single-chip microcomputer output binary digital signal is 000000000000～111111111111;

Step 4.12: the digital signal output pin of single-chip microcomputer is linked to each other with the digital input pin of DA converter MAX508, utilize the DA converter that the digital signal of single-chip microcomputer is converted to simulating signal, the scope of DA converter output voltage simulating signal is 0～10V;

Step 4.13: voltage analog signal output pin and pliotron (Darlington transistor) input pin of DA converter is linked to each other, utilize pliotron that voltage signal is carried out power amplification;

Step 4.14: the output port of pliotron is linked to each other with electrode in the above-mentioned steps 4.10, realize changing the chromatic dispersion of this sampled-grating by computing machine.

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