تکنیکهای مدلاسیون پیشرفته در سیستمهای نوری همدوس
The recently developed digital coherent receiver enables us to employ a variety of spectrally efficient modulation formats such as M-ary phase-shift keying and quadrature-amplitude modulation. Moreover, in the digital domain, we can equalize all linear transmission impairments such as group-velocity dispersion and polarization-mode dispersion of transmission fibers, because coherent detection preserves the phase information of the optical signal. In this talk, we will review the history of research and development related to coherent optical communications and describes the principle of coherent detection. In addition, we discuss about the advanced modulation techniques for the coherent optical system such as probabilistic and geometric shaping, faster than Nyquist and coded modulation. Also, we will talk about practical challenges and some possible solutions for coherent optical communication systems.