CN102523048B - Optical fiber nonlinear effect restraining device - Google Patents

Abstract

An optical fiber nonlinear effect suppressing device belongs to optical fiber communication devices and solves the problem of limited transmission rate or high complexity caused by existing suppressing devices. The present invention consists of an arbitrary waveform generator, a driving amplifier and an electro-optic phase modulator in series in sequence. The clock signal is input to the trigger terminal of the arbitrary waveform generator, and the arbitrary waveform generator outputs a periodic parabolic waveform signal, which is amplified into an electric driving signal by the driving amplifier. The output data signal of the optical transmitter of the optical fiber link is sent to the input end of the electro-optical phase modulator, and the output end of the electro-optic phase modulator is connected to the optical fiber link. The invention has a simple structure, reduces dependence on electronic processing chips and device power consumption, and ensures transmission rate while suppressing optical fiber nonlinear effects, and is applicable to various modulation formats and transmission rates; in long-distance large-capacity ultra-high-speed optical fiber communication systems , especially in the dense wavelength division multiplexing system has great application potential.

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 speed fiber optic communication systems, to suppress the nonlinear impairments in optical fiber telecommunications system, improve systematic function.

Background technology

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

On the other hand, along with the luminous power in optical fiber increases, the number of channel increases, fiber nonlinear effect becomes the principal element that affects systematic function.Nonlinear effect in optical fiber is divided into two classes: inelastic process and elastic process.The inelastic process being caused by stimulated scattering, electromagnetic field and polarization medium have energy exchange, mainly contain stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS).The elastic process being caused by nonlinear refractive index (Kerr effect), electromagnetic field and polarization medium do not have energy exchange, mainly contain from phase-modulation (SPM), Cross-phase Modulation (XPM) and four wave mixing (FWM).These nonlinear effects are crosstalked and Power penalty the generation of multichannel WDM interchannel, and introduce nonlinear phase noise, thus transmission capacity and the maximum transmission distance of limit fibre communication.

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

Summary of the invention

The invention provides a kind of fiber nonlinear effect restraining device, solving existing electric restraining device causes transmission rate to be subject to Digital Signal Processing speed restriction and the higher problem of light restraining device complexity, in suppressing fiber nonlinear effect, ensure 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 (Arbitrary Waveform Generator), driving amplifier and electro-optic phase modulator, it is characterized in that:

Take from the optical sender clock signal of optical fiber link and input described AWG (Arbitrary Waveform Generator) trigger end, AWG (Arbitrary Waveform Generator) 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 the Relation Parameters of time, v _ppfor the peak-to-peak value of AWG (Arbitrary Waveform Generator) output cycle parabolic type waveform signal voltage, 025v < V _pp≤ 1v; T is the time; T is the cycle of f (t), identical with clock signal period, and n is periodicity;

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

The gain G of described driving amplifier meets wherein V _πbe the half-wave voltage of electro-optic phase modulator, the required driving voltage size adding is spent in expression phase modulation position 180.

Described fiber nonlinear effect restraining device, is characterized in that:

The cycle of described AWG (Arbitrary Waveform Generator) output cycle parabolic type waveform signal equals the cycle of clock signal;

Described AWG (Arbitrary Waveform Generator) comprises address counter, waveform data memory, D/A converter, low pass filter and the amplifying circuit of series connection successively; Clock signal triggers port by AWG (Arbitrary Waveform Generator) and inputs described address counter, and described amplifying circuit produces cycle parabolic type waveform signal f (t), by the output output of AWG (Arbitrary Waveform Generator).

According to non-linear Schrodinger equation:

$\frac{{\&PartialD;A}_j}{\&PartialD;z}+\frac{\mathrm{\&alpha;}}{2}{A}_j+{\mathrm{\&beta;}}_{1j}\frac{{\&PartialD;A}_j}{\&PartialD;t}+\frac{i}{2}{\mathrm{\&beta;}}_{2j}\frac{{\&PartialD;}^2{A}_j}{{\&PartialD;t}^2}=\mathrm{i\&gamma;}({\left|A_j\right|}^2+2\underset{k\&NotEqual;j}{\mathrm{\&Sigma;}}{\left|A_k\right|}^2);$

Wherein A _jfor the normalization amplitude of input data signal, α is fibre loss coefficient, β _1jfor 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, and j, k represent different channel labels, and i is 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)；

Wherein L _efffor the effective length of optical fiber.The frequency chirp Δ f that fiber nonlinear effect causes so _nL(t):

${\mathrm{\&Delta;f}}_{\mathrm{NL}}\left(t\right)=\frac{{\mathrm{d\&phi;}}_{\mathrm{NLj}}(z,t)}{\mathrm{dt}};$

For Gaussian pulse, near pulse center, can be similar to and think that the frequency chirp of its generation is linear, and square phase-modulation that the present invention produces is exactly to produce linear frequency chirp, as long as suitably select symbol and the size of modulation Induced Chirp, the frequency chirp that phase noise that just can the generation of compensated fiber nonlinear effect causes.

The optics that the present invention adopts is very simple, adopt the mode of full optics, input signal is added to certain linear chrip amount, the less frequency chirp producing in order to the effect of compensated fiber small nonlinearity, suppress the more weak nonlinear effect that light signal transmits in optical fiber, such as the number of channel is less, laser transmitting power is lower, the nonlinear effect producing in the situations such as channel frequency separation is larger, obviously reduces the error rate that receives signal; Can not adopt dsp chip processing at receiving terminal, reduce the dependence to electron process chip, reduce the power consumption of device simultaneously, be applicable to various modulation formats and transmission rate; In growing apart from high-capacity and ultra high-speed optical fiber telecommunications system, particularly dense wavelength division multiplexing system, there is very large application potential.

Brief description of the drawings

Fig. 1 is embodiment of the present invention schematic diagram;

Fig. 2 is the structural representation of AWG (Arbitrary Waveform Generator);

Fig. 3 is the schematic diagram of the present invention for dense wave division multipurpose optical fiber telecommunications system.

Embodiment

As shown in Figure 1, embodiments of the invention, by AWG (Arbitrary Waveform Generator), driving amplifier and electro-optic phase modulator are followed in series to form, take from the optical sender clock signal of optical fiber link and input described AWG (Arbitrary Waveform Generator) trigger end, AWG (Arbitrary Waveform Generator) 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 electro-optic phase modulator drive end, the optical sender outputting data signals of optical fiber link is sent into electro-optic phase modulator input, electro-optic phase modulator output connects optical fiber link.

As shown in Figure 2, described AWG (Arbitrary Waveform Generator) comprises address counter, waveform data memory, D/A converter, low pass filter and the amplifying circuit of series connection successively, clock signal triggers port by AWG (Arbitrary Waveform Generator) and inputs described address counter, by making address counter add 1 OPADD that changes the address production electric circuit being formed by address counter, each address in the inswept waveform data memory of address counter order is until the end of Wave data, Wave data in each address is sent in D/A converter, so that digital signal is converted to analog signal, low pass filter carries out smoothing processing to the transition edge of D/A converter outputting analog signal, produce required any period parabolic type waveform signal f (t) through amplifying circuit again, by the output output of AWG (Arbitrary Waveform Generator).

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

Driving amplifier is amplified to the output signal amplitude of AWG (Arbitrary Waveform Generator) can meet the required maximum phase modulation value of electro-optic phase modulator.The bandwidth of driving amplifier should match with the transmission rate of optical fiber telecommunications system.The 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 heterojunction bipolar transistor (HBT), be a low cost, high power and high efficiency amplifier integrated circuit, applicable frequency is 2.4GHz～2.5GHz.

The present embodiment electro-optic phase modulator, the LiNbO of the employing model PMS1527-EX of Beijing Shi Weitong company ₃multi-functional phase place modulator, this phase-modulator is based on lithium columbate crystal phase-modulator, adopt titanium diffusion or proton exchange technique 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, insertion loss <=4.0dB.

Lithium columbate crystal is uniaxial crystal, optical homogeneity is good, after applying electric field on crystal, to cause the redistribution of bound charge, and may 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.In the time that extra electric field is parallel to crystal Z axis, the refractive index of this direction becomes:

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

Wherein n _e, γ ₃₃, E ₃be respectively e optical axis refractive index, electro-optic coefficient and z direction electric field, the phase place that light produces by this modulator is changed to

Wherein V (t) is additional 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:

Be N road signal optical fibre nonlinear effect restraining device by expanded application of the present invention, N optical sender adopts DWDM wavelength and the wavelength interval of standard, N circuit-switched data signal and clock signal synchronization; Electric drive signal after overdriven amplifier amplifies is sent into respectively the electro-optic phase modulator that each transmitter is corresponding; The output signal of N electro-optic phase modulator accesses wave multiplexer input simultaneously, and wave multiplexer output connects optical fiber link.

Claims (2)

1. a fiber nonlinear effect restraining device, is followed in series to form by AWG (Arbitrary Waveform Generator), driving amplifier and electro-optic phase modulator, and clock signal and data-signal are all taken from the optical sender of optical fiber link, and the gain G of described driving amplifier meets wherein V _πbe the half-wave voltage of electro-optic phase modulator, the required driving voltage size adding is spent in expression phase modulation position 180; It is characterized in that:

Described clock signal is inputted described AWG (Arbitrary Waveform Generator) trigger end, AWG (Arbitrary Waveform Generator) 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 the Relation Parameters of time, v _ppfor the peak-to-peak value of AWG (Arbitrary Waveform Generator) output cycle parabolic type waveform signal voltage, 0.25v<V _pp≤ 1v; T is the time; T is the cycle of f (t), identical with clock signal period, and n is periodicity;

Described cycle parabolic type waveform signal f (t) is enlarged into electric drive signal through driving amplifier and sends into electro-optic phase modulator drive end, described data-signal is sent into electro-optic phase modulator input, and electro-optic phase modulator output connects optical fiber link.

2. fiber nonlinear effect restraining device as claimed in claim 1, is characterized in that:

The cycle of described AWG (Arbitrary Waveform Generator) output cycle parabolic type waveform signal equals the cycle of clock signal;

Described AWG (Arbitrary Waveform Generator) comprises address counter, waveform data memory, D/A converter, low pass filter and the amplifying circuit of series connection successively; Clock signal triggers port by AWG (Arbitrary Waveform Generator) and inputs described address counter, and described amplifying circuit produces cycle parabolic type waveform signal f (t), by the output output of AWG (Arbitrary Waveform Generator).