Research On Advanced Modulation Formats In High-speed Fiber Communication Transmission

Transmission system of optical fiber communication has a tendency of developing high speed, large-capacity and long-haul fiber transmission system.With the advantanges in spectral efficiency, integration and OAM cost, 40Gb/s high rate optical transmission system will gradually replace 10Gb/s system. However, with the improvement of transmission rate and channel capacity, transmission system meet transmission impairments caused by group-velocity dispersion(GVD), polarization mode dispersion(PMD), fiber nonlinear effects and so on. As one of the key technologies of optical transmission system, advanced modulation format code could decrease transmission impairments without great changes in the existing transmission system.This thesis focus on the study of two main modulation formats i.e. amplitude and phase modulation formats in theory for the 40Gb/s transmission system. Main achievements are listed as follow.1. Based on the theories of modulation and demodulation processes of different modulation formats, the demodulation process of DPSK is analyzed in detail.The eye diagrams and modulated spectrum are obtained by simulating system model of amplitude and phase modulation formats. Modulated spectrum is also obtained through simulating of different modulation formats.2. The influences of fiber nonlinear effects on a proposed sytem model of different modulation formats are studied. DPSK modulation formats have more tolerance with fiber nonlinear effects than any other modulation format.In particular, 33%RZ-DPSK has the highest tolerance with non-linearity.3. The influences of dispersion on a proposed system model of different modulation formats are analyzed and the dispersion resistant performance of different modulation formats is calculated. DQPSK modulation formats have higher tolerance with chromatic dispersion than others. NRZ-DPSK in which we have investigated has the best dispersion resistant performance.4. The influences of polarization-mode dispersion on a proposed system model of different modulation formats are investigated. The simulation results show that DQPSK modulation formats have more PMD tolerance than any other modulation formats by comparing their eye open factors. 5. Using the modulated DPSK and DQPSK formats as the signals in the different dispersion compensation systems,the code-based modulation and dispersion compensation technology is successfully achieved. Then Q versus fiber input powers and eye diagram of best value point where Q factor has max value after compensation are received. When Q factor has a certain value, the symmetry compensation is more effective than others because the allowed input power is bigger than any other.