CN102420661A - Device for compensating non-linear damage of optical fiber - Google Patents

Abstract

The invention discloses a device for compensating a non-linear damage of optical fiber, belongs to an optical fiber communication device, solves the problem of limitation on transmission speed rate or higher complexity of the conventional restraint device, and guarantees the transmission speed rate of an optical fiber system during compensation of the non-linear damage of the optical fiber. The device comprises an arbitrary waveform generator, a driving amplifier, a first electro-optical phase modulator, a dispersion medium and a second electro-optical phase modulator, wherein a clock signal is input to a trigger end of the arbitrary waveform generator; the arbitrary waveform generator outputs a periodic parabola type waveform signal, and the periodic parabola type waveform signal is amplified by using the driving amplifier into an electric driving signal and sent to driving ends of the first electro-optical phase modulator and the second electro-optical phase modulator at the same time; an optical transmitter outputs a data signal to an input end of the first electro-optical phase modulator; and an output end of the second electro-optical phase modulator is connected with an optical fiber link. The invention has the advantages that: an adopted optical device is simple; the bit error rate of signal receiving reaches 10<-7> to 10<-9>; optical power cost is reduced by about 3 dB; and the device is applicable to a long-distance high-capacity and ultra-high-speed optical fiber communication system of all kinds of modulation formats and transmission speed rate.

Description

A kind of nonlinear fiber damage compensation arrangement

Technical field

The invention belongs to fiber optic telecommunications equipment, be specifically related to a kind of nonlinear fiber damage compensation arrangement, be applied in the speed fiber optic communication systems,, improve systematic function with the nonlinear impairments in the compensated fiber communication system.

Background technology

Optical fiber communication has become the element of modern communication networks, along with the rapid emergence of amount of information explosive growth, especially internets such as voice, image and data, constantly enlarges the optical fiber communication capacity trend that has been inevitable.Wavelength division multiplexing (WDM) and erbium-doped fiber amplifier (EDFA) are fully to excavate the fiber bandwidth ability, realize the best means of big capacity, high-speed communication.In high speed long-distance optical fiber communication system, 100G and above be current development trend, chromatic dispersion and nonlinear effect are two big principal elements of limiting telecommunication power system capacity.Chromatic dispersion causes pulse stretching and wave distortion, and nonlinear effect causes the crosstalking etc. of variation and interchannel of pulse frequency spectrum, and they all can make signal produce distortion, and cause the increase of error rate of system.Therefore control and compensation that need be in addition suitable in communication system to chromatic dispersion and nonlinear effect, present dispersion compensation is technological, and like comparative maturity such as dispersion compensating fiber (DCF), electrical dispersion compensation module, the commercialization degree is very high.

On the other hand, along with the luminous power in the optical fiber increases, the number of channel increases, fiber nonlinear effect becomes the principal element that influences systematic function.Nonlinear effect in the optical fiber is divided into two types: inelastic process and elastic process.By the inelastic process that stimulated scattering causes, electromagnetic field has energy exchange with the polarization medium, mainly contains stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS).By the elastic process that nonlinear refractive index (Kerr effect) causes, electromagnetic field does not have energy exchange with the polarization medium, mainly contains from phase modulated (SPM), cross-phase modulation (XPM) and four wave mixing (FWM).These nonlinear effects make multichannel WDM interchannel produce and crosstalk and Power penalty, and the introducing nonlinear phase noise, thus the transmission capacity and the maximum transmission distance of limit fibre communication.

Present non-linear restraining device is divided into two types: electrical way and optical mode.The electricity restraining device mainly depends on the digital signal processor (DSP) of system receiving terminal; Adopt software that the nonlinear effect and the effect of dispersion of optical fiber are compensated simultaneously by digital signal processor, the transmission rate of fibre system receives the restriction of DSP chip processing speed.And light restraining device implementation complexity is high; Like optical phase conjugation (OPC) equipment; The structure more complicated is had relatively high expectations to the frequency unicity of the used laser of middle mixing, and the intermediate phase conjugator needs to be arranged on more exactly the half the place of total dispersion value; Also to control the polarization fluctuation, in order to avoid influence the time reversal characteristic of phase conjugate wave.

Summary of the invention

The present invention provides a kind of nonlinear fiber damage compensation arrangement; Solving existing electric restraining device causes transmission rate to receive the Digital Signal Processing speed limit and light restraining device complexity problem of higher; In the compensated fiber nonlinear impairments, guarantee the transmission rate of fibre system.

A kind of nonlinear fiber damage compensation arrangement of the present invention comprises AWG, driving amplifier, first electro-optic phase modulator, dispersive medium and second electro-optic phase modulator, it is characterized in that:

Said AWG and driving amplifier are connected successively, and the said first electro-optic phase modulator output connects the second electro-optic phase modulator input through dispersive medium;

Take from the optical sender clock signal of optical fiber link and import said AWG trigger end, AWG output cycle parabolic type waveform signal f (t):

$f\left(t\right)=\underset{n=0}{\overset{\&infin;}{\mathrm{\&Sigma;}}}a{(t-\mathrm{nT})}^2,(-\frac{T}{2}\&le;t\&le;\frac{T}{2});$

A is cycle parabolic type waveform signal and time relation parameter, V _PpBe the peak-to-peak value of AWG output cycle parabolic type waveform signal voltage, 025v＜V _Pp≤1v; T is the time; T is the cycle of f (t), and is identical with clock signal period, and n is a periodicity;

Said cycle parabolic type waveform signal f (t) is enlarged into electric drive signal through driving amplifier and sends into first, second electro-optic phase modulator drive end simultaneously; The optical sender outputting data signals of optical fiber link is sent into the first electro-optic phase modulator input, and the second electro-optic phase modulator output connects optical fiber link;

Said dispersive medium is optical fiber Bragg raster (FBG) or monomode fiber;

The gain G of said driving amplifier satisfies

V wherein _πBe the half-wave voltage of electro-optic phase modulator, the required driving voltage size that adds of expression phase modulation position 180 degree.

Described nonlinear fiber damage compensation arrangement is characterized in that:

The cycle of said AWG output cycle parabolic type waveform signal equals the cycle of clock signal;

Said AWG comprises address counter, waveform data memory, D/A converter, low pass filter and the amplifying circuit of series connection successively; Clock signal triggers port through AWG and imports said address counter, and said amplifying circuit produces cycle parabolic type waveform signal f (t), through the output output of AWG.

Described nonlinear fiber damage compensation arrangement is characterized in that:

Said dispersive medium adopts positive dispersion, transfer function

β wherein ₂Be the 2nd order chromatic dispersion constant, z is a dispersive medium length, and ω is an optical carrier frequency, total dispersion value β ₂The span of z is 0＜β ₂Z＜50ps/nm.

The effect of dispersive medium is that its transfer function and input data signal frequency spectrum multiply each other on frequency domain.

Mathematical Modeling of the present invention can be represented with following formula:

$X_P\left(u\right)=\sqrt{\frac{1-i\cot \mathrm{\&alpha;}}{2\mathrm{\&pi;}}}\exp (-i\frac{1}{2}{u}^2\tan \frac{\mathrm{\&alpha;}}{2})\&CenterDot;\left\{\right[x\left(t\right)\exp \left({-\mathrm{it}}^2\frac{1}{2}\tan \frac{\mathrm{\&alpha;}}{2}\right)]\&CircleTimes;\exp \left(i\frac{1}{2}{\csc \mathrm{\&alpha;t}}^2\right)\}$

Wherein, x (t) and X _P(u) be respectively input and output signal; Deflection angle

P ≠ 2n, n are integer, and conversion order p characterizes modulation depth;

Can be divided into three the step realize; Input data signal is sent into first electro-optic phase modulator earlier and is carried out a square phase modulated and obtain g (t); Get into one section dispersive medium again and carry out the time domain convolution and obtain g ' (t), send into second electro-optic phase modulator at last and carry out obtaining exporting signal X after square phase modulated _p(t):

$g\left(t\right)=x\left(t\right)\exp \left({-\mathrm{it}}^2\frac{1}{2}\tan \frac{\mathrm{\&alpha;}}{2}\right)$

$g^{\&prime;}\left(t\right)=g\left(t\right)*\exp \left(i\frac{1}{2}{\csc \mathrm{\&alpha;t}}^2\right)$

$X_p\left(t\right)=g^{\&prime;}\left(t\right)\sqrt{\frac{1-i\cot \mathrm{\&alpha;}}{2\mathrm{\&pi;}}}\exp (-i\frac{1}{2}{t}^2\tan \frac{\mathrm{\&alpha;}}{2})$

The present invention is a kind of full optical processing scheme, is applicable to the compensation of various modulation formats and transmission rate nonlinear fiber damage.

When light signal transmits, can receive the influence of optical nonlinearity Kerr effect in optical fiber, produce nonlinear impairments, influence in the coherent detection system of transmission performance, especially phase modulated of system.

The present invention carried out the distortion of optical phase with signal before light signal gets into optical fiber, make that the light signal after the distortion has certain frequency chirp amount and phase factor, got in the optical fiber link then and transmitted.When the chromatic dispersion full remuneration in the transmission system, through optimizing the various parameters of this conversion, the time-frequency composite characteristic of sort signal can effectively suppress the influence that nonlinear fiber produces signal to a great extent, improves the transmission performance of system.Can see the effect expression formula of input data signal from the present invention, signal introduced the two-stage phase distortion, can carry out comprehensive compensation the linear nonlinear impairments of data-signal through square phase modulated.See that from another kind of angle the present invention is a kind of incomplete Fourier transform.Signal can transform from the time domain to another transform domain, and this transform domain is certain intermediate field between waveform and frequency spectrum, shows as the rotation of time frequency space reference axis, can have a series of continuous transform domains between can thinking from the time domain to the frequency domain hypothetically.Accordingly, dispersion interaction is a linear action, and is only influential to time domain waveform; And nonlinear interaction is only influential to the frequency domain envelope, therefore can think that the influence to waveform envelope also is a kind of continuous change procedure from the time domain to the frequency domain.Just chromatic dispersion is " 0 " for " 1 " at frequency domain in the time domain influence, and nonlinear interaction in contrast.On the other hand, research is illustrated in that nonlinear impairments can be suppressed under the situation that chromatic dispersion exists.For commercial dispersion managed fiber communication system, the signal of process predistortion of the present invention has new transmission performance, and its time-frequency composite characteristic can be thought under the situation of introducing a small amount of chromatic dispersion, to realize compensation of nonlinearity.

The optics that the present invention adopts is simple, adopts the mode of full optics, and input signal is added certain distortion, in order to the nonlinear impairments of compensated fiber, makes the error rate that receives signal obviously reduce; Can not adopt dsp chip to handle at receiving terminal, reduce dependence, reduce the power consumption of device simultaneously, be applicable to various modulation formats and transmission rate electron process chip; The error rate that receives signal reaches 10 ^-7To 10 ^-9', reduce the about 3dB of luminous power cost.In growing, has very big application potential apart from high-capacity and ultra high-speed optical fiber telecommunications system, particularly dense wavelength division multiplexing system.

Description of drawings

Fig. 1 is an embodiment of the invention sketch map;

Fig. 2 is the structural representation of AWG;

Fig. 3 is used for the sketch map of dense wave division multipurpose optical fiber telecommunications system for the present invention.

Embodiment

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

As shown in Figure 1, embodiments of the invention comprise AWG, driving amplifier, first electro-optic phase modulator, dispersive medium and second electro-optic phase modulator;

Said AWG and driving amplifier are connected successively, and the said first electro-optic phase modulator output connects the second electro-optic phase modulator input through dispersive medium;

Take from the optical sender clock signal of optical fiber link and import said AWG trigger end; AWG output cycle parabolic type waveform signal f (t); Cycle parabolic type waveform signal f (t) is enlarged into electric drive signal through driving amplifier and sends into first, second electro-optic phase modulator drive end simultaneously; The optical sender outputting data signals of optical fiber link is sent into the first electro-optic phase modulator input, and the second electro-optic phase modulator output connects optical fiber link;

Said dispersive medium is a monomode fiber.

As shown in Figure 2, said AWG comprises address counter, waveform data memory, D/A converter, low pass filter and the amplifying circuit of series connection successively; Clock signal triggers port through AWG and imports said address counter; Through make address counter add 1 change the address production electric circuit that constitutes by address counter OPADD; Each address in the inswept waveform data memory of address counter order is up to the end of Wave data; Wave data in each address all is sent in the D/A converter, and to convert digital signal into analog signal, low pass filter carries out smoothing processing to the transition edge of D/A converter output analog signal; Produce required any period parabolic type waveform signal f (t) through amplifying circuit again, through the output output of AWG.

Present embodiment adopts the AWG of the model AWG7122C of U.S. Imtech, and maximum sample rate 24GS/s, waveform length 32M or 64M, maximum analog output amplitude are 1Vpp (2.5GHz), produces cycle parabolic pulses signal.

Driving amplifier is amplified to the output signal amplitude of AWG can satisfy the required maximum phase modulation value of electro-optic phase modulator.The bandwidth of driving amplifier should be complementary with the transmission rate of optical fiber telecommunications system.Present embodiment adopts the radio frequency amplifier chip RF Amplifier TM1001 of Taiwan TaiwanMicro company; This chip is made with the technological design of GaAs HBT (HBT); Be a low cost, high power and high efficiency amplifier integrated circuit, suitable frequency is 2.4GHz～2.5GHz.

The present embodiment electro-optic phase modulator, the LiNbO of employing Beijing model PMS1527-EX of generation Wei Tong company ₃Multi-functional phase-modulator; This phase-modulator is based on the lithium columbate crystal phase-modulator; Adopt titanium diffusion or proton exchange technology to make waveguide, device insertion loss is little, driving voltage is low, and optical fiber and waveguide adopt accurate tiltedly coupling can obtain low back-reflection.The half-wave voltage V of operation wavelength 1550nm place _π＜=5.0V, electric bandwidth＞=2.5GHz inserts loss＜=4.0dB.

Lithium columbate crystal is a uniaxial crystal, and optical homogeneity is good, after applying electric field on the crystal; To cause the redistribution of bound charge, and possibly cause the miniature deformation of ionic lattice, its result will cause the variation of dielectric constant; Finally cause the variation of crystal refractive index; Making is that isotropic medium produces birefringence originally, is that the birefringence characteristic of optically anisotropic crystal changes originally, i.e. electro optic effect.When extra electric field was parallel to crystal Z axle, the refractive index of this direction became:

$n_z=n_e-\frac{1}{2}{n}_e^3{\mathrm{\&gamma;}}_{33}{E}_3$

N wherein _e, γ ₃₃, E ₃Be respectively e refracted rate, electro-optic coefficient and z direction electric field, light through the phase change that this modulator produces does

Wherein V (t) is for adding the driving voltage function, and d, l are the sizes of crystal.

Dispersive medium adopts monomode fiber, and the monomode fiber cost is low, but the flexible dispersion values.The SiO of monomode fiber itself ₂Material just has the dispersion characteristics that depend on wavelength, and the different wavelengths group velocity is different in transmission; It is 200m that present embodiment adopts the length of company of Wuhan Changfei, and abbe number is the general single mode fiber of 16ps/nm/km.

Dispersive medium also can adopt FBG, FBG since in the grating CGCM of different wave length can produce reflection in different positions according to the difference in grating cycle, make different wavelengths produce delay inequality, be chromatic dispersion, the chromatic dispersion span is bigger, structure is compact more; FBG like the model DCM-CI-1550.12-N200-FC/APC of Wuhan GuangXun Co., Ltd.

The present invention is applied in dense wave division multipurpose (DWDM) system, and is as shown in Figure 3, and the present invention is expanded to N road signal optical fibre nonlinear impairments compensation arrangement.N optical sender adopts the DWDM wavelength and the wavelength interval of standard, and N circuit-switched data signal and clock signal are synchronous; Electric drive signal behind overdriven amplifier is sent into the corresponding N of each transmitter first, N second electro-optic phase modulator respectively; The output signal of N second electro-optic phase modulator inserts the wave multiplexer input simultaneously, and the wave multiplexer output connects optical fiber link.

Claims (3)

1. a nonlinear fiber damage compensation arrangement comprises AWG, driving amplifier, first electro-optic phase modulator, dispersive medium and second electro-optic phase modulator, it is characterized in that:

Said AWG and driving amplifier are connected successively, and the said first electro-optic phase modulator output connects the second electro-optic phase modulator input through dispersive medium;

Take from the optical sender clock signal of optical fiber link and import said AWG trigger end, AWG output cycle parabolic type waveform signal f (t):

$f\left(t\right)=\underset{n=0}{\overset{\&infin;}{\mathrm{\&Sigma;}}}a{(t-\mathrm{nT})}^2,(-\frac{T}{2}\&le;t\&le;\frac{T}{2});$

A is cycle parabolic type waveform signal and time relation parameter,

V _PpBe the peak-to-peak value of AWG output cycle parabolic type waveform signal voltage, 025v＜V _Pp≤1v; T is the time; T is the cycle of f (t), and is identical with clock signal period, and n is a periodicity;

Said cycle parabolic type waveform signal f (t) is enlarged into electric drive signal through driving amplifier and sends into first, second electro-optic phase modulator drive end simultaneously; The optical sender outputting data signals of optical fiber link is sent into the first electro-optic phase modulator input, and the second electro-optic phase modulator output connects optical fiber link;

Said dispersive medium is optical fiber Bragg raster (FBG) or monomode fiber;

The gain G of said driving amplifier satisfies

V wherein _πBe the half-wave voltage of electro-optic phase modulator, the required driving voltage size that adds of expression phase modulation position 180 degree.

2. nonlinear fiber damage compensation arrangement as claimed in claim 1 is characterized in that:

The cycle of said AWG output cycle parabolic type waveform signal equals the cycle of clock signal;

Said AWG comprises address counter, waveform data memory, D/A converter, low pass filter and the amplifying circuit of series connection successively; Clock signal triggers port through AWG and imports said address counter, and said amplifying circuit produces cycle parabolic type waveform signal f (t), through the output output of AWG.

3. according to claim 1 or claim 2 nonlinear fiber damage compensation arrangement, it is characterized in that: said dispersive medium adopts positive dispersion, transfer function

β wherein ₂Be the 2nd order chromatic dispersion constant, z is a dispersive medium length, and ω is an optical carrier frequency, total dispersion value β ₂The span of z is 0＜β ₂Z＜50ps/nm.

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