Advanced Technologies For Next Generation Coherent Optical Communications

"Next generation coherent optical transports for core networks are anticipated to further approach the Shannon limit for a higher fiber capacity by delivering 400 Gb/s or 1 Tb/s data rates per channel, and providing flexibility and agility to maximize the network resource utilization. This thesis looks into novel system architectures and digital signal processing (DSP) algorithms to fulfill those design targets. The single carrier and orthogonal frequency-division multiplexing (OFDM) modulation schemes are both potential candidates for the underlying transceiver architecture. We provide the analysis and investigation of the optical channel impairments for both systems in the context of >100 Gb/s transmissions with higher symbol rates and higher order quadrature amplitude modulation (QAM). With an increased accumulated chromatic dispersion (CD) for a single channel, the impacts of laser phase noise and fiber nonlinearities manifest new characteristics which are not evident in current 100G systems. We propose novel and energy-efficient DSP algorithms and system designs to increase laser linewidth tolerance and reduce nonlinear noise. The performances of the proposed designs are experimentally evaluated using a leading-edge optical long-haul transmission testbed, which was custom built for this thesis. The single carrier and OFDM systems are separately explored and compared, and it is shown that OFDM has certain multi-carrier advantages when a large accumulated CD exists. This result implies that the OFDM scheme may be a better option for next generation transceivers than the currently employed 100G single carrier transceiver scheme. In the last part, we concentrate on the design of flexible optical transceivers for future software-defined optical networks. The following novel techniques are proposed to achieve a full flexibility without increasing the cost: format-transparent DSP platform, agile bandwidth allocation, and continuous modulation format." --