Coherent detection in lightwave transmission systems can improve receiver sensitivities by 10-20dB over direct detection sensitivities. In phase-shift-keyed (PSK) systems the information is impressed on the phase of the optical field while the amplitude is held nominally constant. A phase-modulated (PM) optical wave with no amplitude modulation propagating in an optical fiber will be adversely affected by group velocity dispersion in the fiber. In particular, the various frequency components of the PM wave will arrive at the end of the fiber at slightly different times. This causes amplitude modulation of the received signal which in turn leads to a penalty in coherent transmission systems.[1,2]

© 1986 Optical Society of America

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