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Optical Modulation and Detection Techniques for High-Spectral Efficiency


The development of advanced multilevel modulation and detection technologies is important for enabling efficient lightwave transmission of high-bit rate services, such as 40G Synchronous Optical Network (SONET/SDH) and 100G Ethernet. In this dissertation, we proposed and experimentally demonstrated several modulation and detection techniques for different optical modulation formats.

Optimal duobinary was achieved by optimizing LPF, transmitter and receiver bandpass filter, which gains 4.4 dB better receiver sensitivity compared with conventional duobinary. The optimum RZ-duobinary was demonstrated and its performances of receiver sensitivity, fiber chromatic dispersion tolerance, and self-phase modulation nonlinearity tolerance were compared with NRZ-duobinary's. Surprisingly, and contrary to the case of on-off keying, we find the NRZ pulse shape to be superior, compared with RZ, for duobinary transmission in all the cases that were studied.

A new DPSK demodulation scheme employing a frequency discriminator filter followed by direct detection (FD-DD) was proposed, which achieved a 1.2 dB better sensitivity compared with NRZ-OOK. DQPSK operating at 20 Gb/s doubles the spectral efficiency. Our proposed FD-DD demodulation scheme offers 2 times better chromatic dispersion tolerance than conventional delay interferometer followed by balanced detection (DI-BD) scheme. FD-DD demodulation scheme for PolMux DQPSK operating at 40 Gb/s not only quadruples the spectral efficiency of NRZ-DPSK, but also maintains roughly the same chromatic dispersion tolerance of a 20 Gb/s DQPSK.

This research work improves system performances for more efficient next generation fiber communication.

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