Investigation On Generation And Phase Regeneration For Advanced Optical Modulation Formats

With the ongoing increasing of traffic demands, novel modulation formats have been playing an important role recently in high-speed large-capacity systems due to their contribution to transmission performance in wavelength division multiplexing (WDM) systems. Supported by the Foundation of Huawei Technologies Co. Ltd.—All-optical Relaying Technology in High Speed DWDM System, some researches on spectrum properties and spectrum processing approaches of existing modulation formats, modulation methods of novel modulation formats and regeneration technologies and new advances in phase modulation methods are presented in this thesis. Research contents and main research results are listed as follows:(1) Based on literatures home and abroad, the significance of the research on novel modulation formats, the classification of existing modulation formats and their corresponding characteristics have been clarified. An overview of the researches on phase-modulated optical signal regeneration technologies was given and their characteristics are induced.(2) Analysis of the formation principle of optical signal spectrum has been made. The base-band spectrum properties of a periodic digital signal sequence in the frequency domain were studied. Signal spectra were separated into analog and digital parts. Spectrum expressions and spectral shapes were derived for random signals with different modulation formats and power spectrum utilization for amplitude modulation and phase modulation formats were compared. Spectrum expressions and spectral shapes of OOK and MPSK format pseudo-random sequence signals were also derived. An analysis of the line spectra intensity formed in digital part of the power spectrum has been made for finite length signals.(3) Aimed at the format conversion schemes based on filters our research group has put forward before, a theoretical model for filters to directly process the optical signals in the spetrum domain was built. Base band spectrum transformation of a digital signal sequence by a filter was analyzed. Signal filtering transformations were classified into analog pulse transformation and digital sequence transformation and spectrum transformation processes for different format conversions were analysed and disscussed. Influences on the spectrum brought about by familiar attenuation, dispersion, and SPM effect in fiber were simulated and analyzed by VPI software.(4) Novel schemes for generating M-QAM by two parallel PM or the cascade structure of MZM and PM were proposed and the proposals are verified. Theoretical results are simulated using VPI software.(5) The properties of phase-sensitive amplification (PSA) produced by degenerate four wave mixing (FWM) were studied using Matlab simulations. By utilizing HNLF (high nonlinear fiber) produced PSA, the regeneration property of DPSK signal was investigated numerically.