  The achievable information rates of optical communication networks have been
widely increased over the past four decades with the introduction and
development of optical amplifiers, coherent detection, advanced modulation
formats, and digital signal processing techniques. These developments promoted
the revolution of optical communication systems and the growth of Internet,
towards the direction of high-capacity and long-distance transmissions. The
performance of long-haul high-capacity optical fiber communication systems is
significantly degraded by transmission impairments, such as chromatic
dispersion, polarization mode dispersion, laser phase noise and Kerr fiber
nonlinearities. With the entire capture of the amplitude and phase of the
signals using coherent optical detection, the powerful compensation and
effective mitigation of the transmission impairments can be implemented using
the digital signal processing in electrical domain. This becomes one of the
most promising techniques for next-generation optical communication networks to
achieve a performance close to the Shannon capacity limit. This chapter will
focus on the introduction and investigation of digital signal processing
employed for channel impairments compensation based on the coherent detection
of optical signals, to provide a roadmap for the design and implementation of
realtime optical fiber communication systems.
