Digital Modulation of Optical Carrier -- Coherent Optical Receivers and Ideal Performance -- Impairment to Optical Signal -- Nonlinear Phase Noise -- Compensation of Nonlinear Phase Noise -- Intrachannel Pulse-to-Pulse Interaction -- Wavelength-Division-Multiplexed DPSK Signals -- Multilevel Signaling -- Phase-Modulated Soliton Signals -- Capacity of Optical Channels.Fiber-optic communication s…