CN102075257A - Method and system for inhibiting four-wave mixing effect in O-OFDM system - Google Patents

Abstract

The invention discloses a method for inhibiting a four-wave mixing effect in an optical-orthogonal frequency division multiplexing (O-OFDM) system. The four-wave mixing effect is inhibited by regulating configuration parameters in an optical fiber link; and the configuration parameters comprise optical signal power of a transmitting end of an O-OFDM system and the optical signal power of a receiving end of the O-OFDM system. The invention also provides the O-OFDM system for inhibiting the four-wave mixing effect. By the method and the system, the transmission quality of an optical fiber communication system can be improved, and the bandwidth resource of the O-OFDM system can be utilized to the greatest extent; and the method and the system are easily realized on hardware.

Description

The method and system that suppress four-wave mixing effect in the O-OFDM system

Technical field

The present invention relates to belong to optical communication field, particularly a kind of inhibition light positive is handed over the method and system of four-wave mixing effect in frequency division multiplexing (O-OFDM) system.

Background technology

OFDM (Orthogonal Frequency Division Multiplexing, OFDM) be a kind of special multi-carrier modulation form, its operation principle is data flow is at a high speed cut apart and to be carried on the experimental process carrier wave, the frequency spectrum of each subcarrier overlaps and quadrature mutually, so just obtain very high spectrum efficiency, utilize frequency spectrum quadrature characteristics to rely on multiple sharp leaf transformation that each subcarrier demodulation is come out at receiving terminal.OFDM can resist the frequency selective fading in the mobile communication environment, and the scholar that these characteristics have been moved the communications field has carried out extensive studies and carried out sufficient application.At present, OFDM has been applied to LAN protocol, in video and the audio broadcasting standard.It is the more recent application of OFDM modulation format in optical communication system that light positive is handed over frequency division multiplexing (O-OFDM), and Fig. 1 is the spectrum diagram of O-OFDM.

Because spectrum efficiency is very high, in the O-OFDM system between each subcarrier frequency differ very little, this makes that the walk-off effect between the subcarrier is very weak, be easy to satisfy the condition that four-wave mixing effect produces, the phase noise that brings out therefrom is superimposed upon on each subcarrier systematic function produced and has a strong impact on, and the subcarrier of One's name is legion often makes the signal after synthesizing produce very big peak-to-average power ratio (Peak to Average Power Ratio, PAPR), thus aggravation O-OFDM (Optical-OFDM) channel non-linearity effect to the influence of systematic function.In general O-OFDM transmission system, the position of each image intensifer and the power gain of the section of striding/decay whenever wait the optical fiber link configuration parameter all to immobilize, and the four-wave mixing effect odds also is changeless in such system.

Inhibition method about four-wave mixing effect in the O-OFDM system mainly comprises following a few class at present:

(1) data preprocessing method

The part carrier wave is filled by adopting, the selectivity mapping method reduces the four-wave mixing effect odds.The part carrier wave is filled and is meant to have only parton carriers carry valid data in the O-OFDM system, other subcarrier is padding data not, the interference frequency component that produces when four-wave mixing effect takes place and the subcarrier spectrum overlaid of padding data not, will suppress the influence of four-wave mixing effect like this to systematic function, thus the nonlinear tolerance of elevator system.The selectivity mapping method adopts PAPR as standard, select one group of phase sequence vector to be loaded on each subcarrier at transmitting terminal, by conversion rotatable phase constantly, finally select one group of sample of PAPR minimum to transmit, thereby suppress the influence of nonlinear effect.

Although this method can reduce the nonlinear effect of system effectively, can reduce the availability of frequency spectrum.The part carrier wave is filled and is made data can only load on the parton carrier wave, and the frequency spectrum resource of the subcarrier correspondence of padding data is not sacrificed; If adopt the selectivity mapping method, receiving terminal must know which signal transmitting terminal selects transmit, and the information of could correctly carrying out is recovered, so will transmit the additional information of expression branch road message sequence number.So also can sacrifice the part bandwidth of system.

(2) phase compensating method

Australia scholar A.J.Lowery proposes to adopt phase compensation method to suppress nonlinear noise.The starting point of nonlinear phase precompensation is the non-linear Schrodinger equation of simplifying.By in non-linear Schrodinger equation, ignoring the influence of chromatic dispersion, can see that optical fiber is the nonlinear phase modulation that superposeed to the influence of signal on time-domain signal, and this phase place superposition value can be tried to achieve resolvedly.According to this basic principle, can consider to add Signal Pretreatment at the transmitting terminal of O-OFDM system, in this preliminary treatment, signal simulated by a negative non linear coefficient optical fiber, allows light signal have a reverse additive phase in advance.When signal is admitted to when carrying out actual transmissions in the optical fiber, real nonlinear phase will be offset by additive phase, and then has realized the inhibition of nonlinear impairments.

The way basic principle of phase compensation is only to have nonlinear effect in the supposing the system, calculates the nonlinear phase of time domain in the O-OFDM system, carries out precompensation or post-compensation then.Specifying informations such as the concrete length of the strict dependence of this method optical fiber link and power configuration, flexibility ratio is not enough, needs to pay extra measurement work in engineering design, and is also relatively more responsive to the power jitter in the optical-fiber network simultaneously.And present development of optical network trend, the appearance of dynamic reconfigurable network, transmission range will cause this algorithm greatly limited in practice flexibly.

(3) based on the method for electric territory Digital Signal Processing

This method is left intact to data at transmitting terminal, does not also do any compensation in the optical fiber link, according to the characteristics of optical channel, combine with coherent detection technology at receiving terminal, design Nonlinear Processing algorithm embeds it in post-processing module of electric territory, thereby reaches the purpose of eliminating nonlinear effect.

This method utilizes digital signal processing algorithm in electric territory nonlinear impairments to be compensated, and is higher usually in order to reach the perfect compensation effect algorithm complex, requires hardware to have very high processing speed, therefore uses difficulty in real system.

Summary of the invention

(1) technical problem that will solve

The technical problem to be solved in the present invention is: how to design and a kind ofly can improve the transmission quality of optical fiber telecommunications system, farthest utilize the bandwidth resources of O-OFDM system, and the scheme of four-wave mixing effect in the inhibition O-OFDM system that on hardware, easily realizes.

(2) technical scheme

For solving the problems of the technologies described above, the invention provides the method for four-wave mixing effect in a kind of O-OFDM of the inhibition system, by the configuration parameter adjustment in the optical fiber link is suppressed described four-wave mixing effect, make the minimum that square reaches with the non-linear effective length mould of multi-span value.

Wherein, described configuration parameter also comprises the optical signal power of each fiber span on the transmission light path of described O-OFDM system, and the position of the image intensifer in the described O-OFDM system.

Wherein, also by the transmitting terminal of described O-OFDM system and the optical signal power adjustment of receiving terminal are suppressed described four-wave mixing effect.

Wherein, also by the length adjustment of each fiber span on the transmission light path of described O-OFDM system is suppressed described four-wave mixing effect.

Wherein, adjust described optical signal power by variable gain optical amplifiers and attenuator.

The present invention also provides a kind of O-OFDM system that suppresses four-wave mixing effect, comprises transmitting terminal, receiving terminal and a plurality of fiber span, and described system also comprises:

Power adjustment unit is used for the optical signal power of described transmitting terminal, receiving terminal and each fiber span is adjusted.

Wherein, described power adjustment unit comprises variable gain optical amplifiers and attenuator.

(3) beneficial effect

At first, the present invention so that with the non-linear effective length mould of multi-span value square to reach minimum be standard, by the configuration parameter adjustment in the optical fiber link is suppressed described four-wave mixing effect, thereby improved the transmission quality of optical fiber telecommunications system, promoted the nonlinear tolerance of system and made systematic function obtain optimization.Second, because by function to the isoparametric dynamic adjustment realization inhibition four-wave mixing effect of power configuration in the optical fiber link, all subcarriers all are used for carrying data, also do not need to send supplementarys such as training sequence, have therefore farthest utilized the bandwidth resources of O-OFDM system.The 3rd, no matter be applied to line model or off-line mode, this method all only need dynamically be adjusted parameters such as power configuration in the optical fiber link, can use existing electronic building brick to realize, simple, need be by the digital signal processing module of any high speed, lower to the requirement of hardware.

Description of drawings

Fig. 1 is existing O-OFDM system spectrum figure;

Fig. 2 is the transmission link schematic diagram of O-OFDM of the present invention system;

Fig. 3 is the off-line applicating flow chart of method of the present invention;

Fig. 4 is the online applicating flow chart of method of the present invention.

Embodiment

Below in conjunction with drawings and Examples, the specific embodiment of the present invention is described in further detail.Following examples are used to illustrate the present invention, but are not used for limiting the scope of the invention.

The method that the present invention proposes so that with the non-linear effective length mould of multi-span value square to reach minimum be standard, by the configuration parameter adjustment in the optical fiber link is suppressed four-wave mixing effect, physical quantity and the physical device that can regulate comprise:

(1) optical signal power in each fiber span on the light path, it can carry out dynamic adjustments (but being the gain/attenuation dynamic adjustments) at passage or wavestrip;

(2) position of each image intensifer, it can be adjusted according to prioritization scheme in the network planning stage.

In the O-OFDM system four-wave mixing effect to the influence of systematic function and the non-linear effective length mould of multi-span value square | D _FWM| ²Be directly proportional, by changing the power gain/decay of image intensifer position and each fiber span, can regulate by the two and unite decision | D _FWM| ²Size, thereby reach the purpose of improving the system transmissions quality.The non-linear effective length mould of multi-span value square embodied a concentrated reflection of the image intensifer position, whenever optical fiber link configuration parameter such as the section of striding gain/attenuation is to the material impact of four-wave mixing effect, its expression formula is:

${\left|D_{\mathrm{FWM}}\right|}^2={\left|{\mathrm{\Σ}}_{s=0}^{N_{\mathrm{span}}-1}{e}^{-\mathrm{j\Δ\β}{z}_s}{L}_{\mathrm{FWM}}\left[s\right]\right|}^2$

$L_{\mathrm{FWM}}\left[s\right]=\underset{z_s}{\overset{z_{s+1}}{\∫}}{e}^{-{\mathrm{\α}}_{s}z}{e}^{-\mathrm{j\Δ\βz}}\mathrm{dz}$

L wherein _FWM[s] is the non-linear effective length of single span section, α _sComprise optical power gain and dampening information in each fiber span, z _sExpression fiber span length, Δ β is the poor of subcarrier propagation constant, s represents s fiber span, N _SpanTotal number of expression fiber span.With the non-linear effective length mould of multi-span value square | D _FWM| ²As optimizing index, whenever different parameter combinations is selected as regulating parameter in the optical signal power gain/attenuation of the section of striding and image intensifer position in the span of given power gain/decay and image intensifer position, makes | D _FWM| ²Get minimum value, thus the nonlinear tolerance of elevator system and make the systematic function optimization.

In addition, can also be to the optical signal power of transmitting terminal and receiving terminal, and the length adjustment of each fiber span suppresses described four-wave mixing effect, wherein, can carry out dynamic adjustments to the optical signal power of transmitting terminal and receiving terminal at passage or wavestrip.

The present invention also provides a kind of O-OFDM system that suppresses four-wave mixing effect, as shown in Figure 2, comprises transmitting terminal (O-OFDM Tx), receiving terminal (O-OFDM Rx) and N fiber span, and described system also comprises:

Power adjustment unit is used for the optical signal power of described transmitting terminal, receiving terminal and each fiber span is adjusted.Described power adjustment unit comprises variable gain optical amplifiers and attenuator.

Among Fig. 2, EDFA is an erbium-doped fiber amplifier, and ellipsis is represented other N-2 fiber span, and SMF represents standard single-mode fiber, and DCF represents dispersion compensating fiber.

According to the difference of application scenarios, this method has following two kinds of application models:

(1) off-line mode

At first, said method can be applied in the network planning stage, is used for the optimization to the optical fiber link configuration parameter, and restrictive condition is the adjustable extent of gain/attenuation and image intensifer position in each fiber span.In the span of given every fiber span gain/attenuation and image intensifer position, choose different parameter combinations, make | D _FWM| ²Get minimum value, thereby every link configuration Parameter Optimization value such as the section of being striden power gain/decay and image intensifer position makes finally system's nonlinear tolerance get a promotion, concrete steps as shown in Figure 3.

(2) line model

Line model is meant in the optical-fiber network running, this optimization method combines with the optical property monitoring modular, the index whether light signal meets the requirements and dynamically adjust as to the optical fiber link configuration parameter in the Q of the receiving terminal factor, by the value of gain/attenuation in each fiber span of dynamic adjustment, make | D _FWM| ²Minimize, suppress four-wave mixing effect, guarantee that the performances such as the Q factor of system receiving terminal reach requirement, restrictive condition is the adjustable extent of the power gain/decay of every fiber span.This optimization method can be used as a module and is embedded in the network management plane, finishes transmission quality dynamic optimization function end to end, and concrete steps as shown in Figure 4.

Above execution mode only is used to illustrate the present invention; and be not limitation of the present invention; the those of ordinary skill in relevant technologies field; under the situation that does not break away from the spirit and scope of the present invention; can also make various variations and modification; therefore all technical schemes that are equal to also belong to category of the present invention, and scope of patent protection of the present invention should be defined by the claims.

Claims (7)

1. a method that suppresses four-wave mixing effect in the O-OFDM system is characterized in that, by the configuration parameter adjustment in the optical fiber link is suppressed described four-wave mixing effect, makes the minimum that square reaches with the non-linear effective length mould of multi-span value.

2. the method for claim 1 is characterized in that, described configuration parameter also comprises the optical signal power of each fiber span on the transmission light path of described O-OFDM system, and the position of the image intensifer in the described O-OFDM system.

3. the method for claim 1 is characterized in that, also by the transmitting terminal of described O-OFDM system and the optical signal power adjustment of receiving terminal are suppressed described four-wave mixing effect.

4. the method for claim 1 is characterized in that, also by the length adjustment of each fiber span on the transmission light path of described O-OFDM system is suppressed described four-wave mixing effect.

5. as claim 2 or 3 described methods, it is characterized in that, adjust described optical signal power by variable gain optical amplifiers and attenuator.

6. an O-OFDM system that suppresses four-wave mixing effect comprises transmitting terminal, receiving terminal and a plurality of fiber span, it is characterized in that described system also comprises:

Power adjustment unit is used for the optical signal power of described transmitting terminal, receiving terminal and each fiber span is adjusted.

7. system as claimed in claim 6 is characterized in that described power adjustment unit comprises variable gain optical amplifiers and attenuator.

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