Characteristics Of Optical Orthogonal Frequency Division Multiplexing System Based On Wavelet Transform

Coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems have the advantages of high spectrum efficiency, high communication capacity, strong resistance to chromatic dispersion and polarization mode dispersion, and high receiving sensitivity. Since CO-OFDM technology was proposed, various types of CO-OFDM systems have been proposed and verified theoretically and experimentally. Meanwhile, the existing optical transmission network can be simply upgraded, because CO-OFDM is highly compatible with wavelength division multiplex(WDM) system. Therefore, the OFDM technology provides a promising technical solution for the next generation of100Gbit/s optical transmission network.CO-OFDM technology is extremely sensitive to phase noise, with the defect of high peak to average power ratio(PAPR). The wavelet transform can provide orthogonality between OFDM subcarriers. Meanwhile, wavelet transform can reduce the PAPR of the OFDM system, and can be operated more efficiently. Wavelet transform based OFDM system doesn’t require a cyclic prefix, which further enhances the spectral efficiency. Therefore, investigation on the wavelet transform based optical orthogonal frequency division multiplexing(WT-OOFDM) has attracted a great deal of attention in optical communication field.This research is mainly about characters of wavelet based optical OFDM transmission system. Firstly, a simple analysis on both the basic principles of OFDM technology and the method of wavelet transform construction is given. Secondly, the structure of wavelet transform based optical orthogonal frequency division multiplexing system is discussed. Then, the function of system modules is analysed, meanwhile, the transmitting and receiving of the signals are completed using numerical simulation. Numerical simulation on wavelet transform based CO-OFDM single-mode fiber transmission system and multi-mode fiber system is carried out. Compared to that using Fourier transform, PAPR, bit rate error, and dispersion tolerance of the WT-OOFDM system are analysed. In addition, the modal dispersion suppression for multi-mode fiber transmission system based on WT-OOFDM is analyzed. Finally, phase noise effect in the long haul WT-OOFDM system is discussed. Starting from the nonlinear Schrodinger equation, four wave mixing and amplified spontaneous emission in amplifiers induced nonlinear phase noise is derived. Then, nonlinear phase noise generation mechanism is discussed under different chromatic dispersion. Also, impact of the wavelet transform on phase noise effect is analyzed. Finnally, the relationship between total phase noise and the bit rate, subcarrier number, the launch power is studied.Simulation results are listed as follows.(1) Compared to the system using Fourier transform, wavelet transform based system can effectively reduce the PAPR. Transmission distance of WT-OOFDM single mode fiber transmission system is increased by50km, and the dispersion tolerance is increased by800ps/nm.(2) WT-OOFDM technology enables lOGbit/s very short reach multimode fiber transmission system, and a transmission distance up to450m is achieved with more flexible system design.(3) For100Gbit/s long haul WT-OOFDM system, when the transmission distance reaches1500km, the total system phase noise is reduced by15%, and the nonlinear phase noise is reduced by20%.