| Fiber nonlinearity has always been the key issue degrading the transmissionperformance in fiber optic communication systems, especially in dense wavelength divisionmultiplexing (WDM) systems, which has been widely concerned over these years. With thematurity of optical devices and electronic signal processing technology, some progresseshave also been made on the research of fiber nonlinearity suppression.In this thesis, two novel nonlinearity suppression methods based on the preprocessingtechnique are proposed and studied, namely prechirp method and FRFT (fractional Fouriertransform)-based pre-distortion method. The influence of fiber nonlinear Kerr effects, mainlyreferred to self phase modulation (SPM) and cross phase modulation (XPM), isapproximately regarded as some kind of linear chirp, making it apparent to clarify theprinciple of prechirp compensating for nonlinearity impairments. The prechirp module isimplemented by using a phase modulator and then applied in system simulations with VPI(VPItransmissionMakerTM) software and the related experiment platform. The nonlinearitymitigation ability of prechirp is simulated, analyzed and experimentally verified in anintensity-modulated WDM system. On the other hand, the principle of FRFT-basedpre-distortion scheme is originated from the hybrid effect of dispersion and Kerr nonlinearity,combined with the FRFT definition of time-frequency rotation. Then phase modulators and adispersive medium are employed to realize the time-domain FRFT module, followed by anintensity-modulated WDM system simulation. The improvements of pre-distortion methodcompared to traditional ways are obtained and illustrated.Simulation and experimental results have validated the effectiveness for both schemeson fiber nonlinearity suppression with received bit-error-rate (BER) reduced by at least3orders of magnitude at the advantage of simplicity, flexibility and lower power consumption,thus to be quite promising nonlinearity preprocessing technologies. |
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