| We investigated high speed optical fiber communication systems using optical pi-DPSK, pi/2-DPSK, DQPSK and Offset-DQPSK modulation techniques, focusing on the system modeling and comparison of performance. The electronic precoder of optical pi/2-DPSK was yet unknown, and its logic and basic circuit are presented in this thesis. We also compared the system performance with the impact of inter symbol interference (ISI) caused by fiber nonlinear effect, narrowband inline optical filtering and residual chromatic dispersion. It is shown that DQPSK has the narrowest signal bandwidth among four phase modulation schemes; Offset-DQPSK has two main lobes in its optical spectrum; Offset-DQPSK has the best tolerance to ISI induced by fiber nonlinear effect; pi-DPSK has the best tolerance to optical filtering; and DQPSK has the best tolerance to residual chromatic dispersion. pi-DPSK has better tolerance to residual chromatic dispersion than pi/2-DPSK. All of these works were verified on Optism, a commercial optical simulation software platform. |
