CN102523048A - Optical fiber nonlinear effect restraining device - Google Patents

Abstract

The invention discloses an optical fiber nonlinear effect restraining device, which belongs to an optical fiber communication component and solves the problem that the existing restraining device causes restriction of the transmission rate or high complexity. The optical fiber nonlinear effect restraining device is composed of an arbitrary waveform generator, a driving amplifier and an electro-optic phase modulator connected in series in sequence, wherein a timer signal is input to a triggering end of the arbitrary waveform generator; the arbitrary waveform generator outputs a periodic parabolic waveform signal which is amplified as an electric drive signal by the driving amplifier and then sent to a drive end of the electro-optic phase modulator; an optical sender in an optical fiber link outputs a data signal and sends the data signal to an input end of the electro-optic phase modulator; and an output end of the electro-optic phase modulator is connected with the optical fiber link. The optical fiber nonlinear effect restraining device of the invention has simple structure, reduces the dependence on electronic processing chips and power consumption of components, ensures the transmission rate as well as restricts nonlinear effect of the optical fiber, is suitable for various modulation formats and transmission rate, and has great application potency in a long-distance large-capacity super-speed optical fiber communication system, in particular in a dense wavelength division multiplexing system.

Description

A kind of fiber nonlinear effect restraining device

Technical field

The invention belongs to fiber optic telecommunications equipment, be specifically related to a kind of fiber nonlinear effect restraining device, be applied in the speed fiber optic communication systems,, improve systematic function to suppress the nonlinear impairments in the optical fiber telecommunications 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 fiber nonlinear effect restraining device; Solving existing electric restraining device causes transmission rate to receive the Digital Signal Processing speed limit and light restraining device complexity problem of higher; When suppressing fiber nonlinear effect, guarantee the transmission rate of fibre system.

A kind of fiber nonlinear effect restraining device of the present invention is followed in series to form by AWG, driving amplifier and electro-optic phase modulator, it is characterized in that:

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):

$f\left(t\right)=\underset{n=0}{\overset{\∞}{\mathrm{\Σ}}}a{(t-\mathrm{nT})}^2,(-\frac{T}{2}\≤t\≤\frac{T}{2});$

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 the electro-optic phase modulator drive end; The optical sender outputting data signals of optical fiber link is sent into the electro-optic phase modulator input, and the electro-optic phase modulator output connects optical fiber link;

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 fiber nonlinear effect restraining device 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.

According to non-linear Schrodinger equation:

$\frac{{\∂A}_j}{\∂z}+\frac{\mathrm{\α}}{2}{A}_j+{\mathrm{\β}}_{1j}\frac{{\∂A}_j}{\∂t}+\frac{i}{2}{\mathrm{\β}}_{2j}\frac{{\∂}^2{A}_j}{{\∂t}^2}=\mathrm{i\γ}({\left|A_j\right|}^2+2\underset{k\≠j}{\mathrm{\Σ}}{\left|A_k\right|}^2);$

A wherein _jBe the normalization amplitude of input data signal, α is the fibre loss coefficient, β _1jBe signal longitudinal propagation constant in optical fiber, β _2jBe signal 2nd order chromatic dispersion coefficient in optical fiber, γ is the non linear coefficient of optical fiber, j, the different channel label of k representative, and i is an imaginary unit; The phase noise φ that the nonlinear effect of optical fiber causes _NLj:

φ _NLj＝γL _eff(|A _j| ²+2|A _k| ²)；

L wherein _EffEffective length for optical fiber.The frequency chirp Δ f that causes of fiber nonlinear effect so _NL(t):

${\mathrm{\Δf}}_{\mathrm{NL}}\left(t\right)=\frac{{\mathrm{d\φ}}_{\mathrm{NLj}}(z,t)}{\mathrm{dt}};$

For Gaussian pulse; Near pulse center, can be similar to and think that the frequency chirp of its generation is linear; And square phase modulated that the present invention produces is exactly to produce linear frequency chirp; As long as suitably select the symbol and the size of warbling due to the modulation, the frequency chirp that phase noise caused that just can the generation of compensated fiber nonlinear effect.

The optics that the present invention adopts is very simple, adopts the mode of full optics, and input signal is added certain linear chrip amount; Less frequency chirp in order to compensated fiber small nonlinearity effect generation; Suppress the more weak nonlinear effect that light signal transmits in optical fiber, less such as the number of channel, the laser transmitting power is lower; The nonlinear effect that produces under the situation such as channel frequency separation is bigger 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; 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

As shown in Figure 1; Embodiments of the invention; Be followed in series to form by AWG, driving amplifier and electro-optic phase modulator; 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 the electro-optic phase modulator drive end; The optical sender outputting data signals of optical fiber link is sent into the electro-optic phase modulator input, and the electro-optic phase modulator output connects optical fiber link.

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:

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

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.

Apply the present invention in dense wave division multipurpose (DWDM) system, as shown in Figure 3:

With expanded application of the present invention is N road signal optical fibre nonlinear effect restraining device, and 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 after overdriven amplifier amplifies is sent into the corresponding electro-optic phase modulator of each transmitter respectively; The output signal of N electro-optic phase modulator inserts the wave multiplexer input simultaneously, and the wave multiplexer output connects optical fiber link.

Claims (2)

1. a fiber nonlinear effect restraining device is followed in series to form by AWG, driving amplifier and electro-optic phase modulator, it is characterized in that:

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):

$f\left(t\right)=\underset{n=0}{\overset{\∞}{\mathrm{\Σ}}}a{(t-\mathrm{nT})}^2,(-\frac{T}{2}\≤t\≤\frac{T}{2});$

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 the electro-optic phase modulator drive end; The optical sender outputting data signals of optical fiber link is sent into the electro-optic phase modulator input, and the electro-optic phase modulator output connects optical fiber link;

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. fiber nonlinear effect restraining device 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.

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