Research Of DWDM System Of Modulation Formats And Dispersion Compensation Schemes

Optical fiber communication system is developing to the high-speed,wide bandwidth,large capacity direction.The DWDM system adapts to this development requirement,the40Gbps optical fiber communication system has gradually begun to commercial.The increase of the transferring bit rate,the dispersion toleration of the system decrease absolutely.The use of the optical amplifier and low-loss transfer fiber makes the loss what happens in the transmission fiber into the second reason.The dispersion and non-linear effects makes an firstly important reason,and signal modulation formats has an very important influence to the nonlinear effects.It is the key of the design of the system to select the appropriate modulation format and reasonable dispersion compensation schemes.The main work is as following:1. In this paper,based on the nonlinear Schrodinger equation,there is an analysis in linear and unlinear of the transmission optical pulses from a mathematical point when the optical pulses transmit in the fiber,providing information about the mathematical analysis of the corresponding dispersion compensation schemes and commeonly used approximations.The mathematical formulas about influence of DWDM system coming from the fiber dispersion and nonlinear effects are educed;2. There are detailed classification of the dispersion and several common dispersion compensation schemes specifically,there are analysis about their advantages and disadvantages in theoretical; there are summary about generation of common code type modulation and simulation about their performance in DWDM system.3. One of the precoding scheme about modified optical duobinary modulation format(It is used in the40Gbps system) was proposed;the analysis of theoretical showed that this scheme can reduce the inter-code interference leaded from dispersion and correct the wrong code;4. Simulative analysis modulation formats and dispersion compensation schemes of16x40Gbit/s DWDM system with long haul (500～2000km) has been carried out. The DWDM system has been analyzed for different dispersion compensation schemes (pre、post and symmetrical compensation schemes) and different modulation formats (Carrier-Suppressed Return-to-Zero (CSRZ)%Optical Duobinary (ODB) and Modified Duobinary Return-to-Zero (MDRZ)). It is found that the performance of DWDM system is improved by using MDRZ format to suppress all the discrete frequency tones,the decline in the Q value and the expansion of optical spectra will happen using CSRZ or ODB modulation formats when the transmission distance is beyond1500km;It is found that as the signal input power increase from-3dB to OdB,the Q value increases,the Q value begin to descend when the input power surpass1dB,because of the nonlinear effects,including FWM (Four Wave Mixing) and XPM (XPM Cross Phase Modulation).It has also been observed that symmetrical compensation is superior to pre and post dispersion compensation schemes.It is established that the highest Q value and the best performance of system appear when the optical communication system assemble the symmetrical compensation and MDRZ modulation formats.