The Application Research Of Lightwave Time-space Duality In The High Speed Optical Transmission Systems

With the explosive development of ultra-capability, ultra-distance DWDM technologies, recently the transmission speed has been 40 Gbit/s per channel, even 100 Gbit/s, over a long distance, and the capability per fiber has been 3.2 Tbit/s, which will lead to serious impairments to the system performance. These impairments are:ASE noises caused by the EDFAs; chromatic dispersion (Group Velocity Dispersion (GVD) and polarization mode dispersion (PMD)); nonlinear effects, which contain self phase modulation (SPM), cross phase modulation (XPM), four-wave mixing (FWM), stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS). All these impairments should be overcome in high-speed optical communications.In this thesis, we present new methods and theories of dispersion compensation and noise suppression based on all-optical inverse Fourier transform/Fourier transform (OIFT/OFT) and fractional Fourier transform (FRFT).We begin with nonlinear Schrodinger equation (NLSE) and time-space duality, the OIFT/OFT device based on time lens is implemented. Here time lens is simply a quadratic phase modulation. As we know, the spectrum envelop of signal will keep unchanged during linear transmission. Thus a novel transmission method-optical frequency domain transmission based on time lens is proposed which could be used in high-speed optical transmission, over 100 Gbit/s per channel. At the transmitter, the OIFT device, which consists of the first time lens and two high dispersive elements, is used to transform the initial optical pulses. The OFT, consisting of the second time lens and another two high dispersive elements, rebuilds the initial optical pulses at the receiver. The system containing OIFT/OFT can propagate over a long haul distance without PMD compensation and with a very low cost. Another advantage is that the OIFT/OFT device could be used in the existed 10 Gbit/s system directly. Our OIFT/OFT-based system successfully transmits through 200-km G.655 fibers at the speed of 20 Gbit/s without any dispersion compensation, with the BER being 10-12.Furthermore, an in-band noise filter is designed based on the principle of FRFT and time lens. The signals and noises are transformed into another domain using FRFT method. Then we could separate the signals and noises at the receiver. We also analyze the system performance through the simulations and the results show that there is 6-dB improvement of signal-to-noise ratio (SNR) using this in-band noise filter.