Abstract

Papers on the research and development of heterodyne/coherent optical-fiber communications began to appear in 1979-1980,^1,2 Since then re- search/development activities have been accelerated mainly because of the expectation for the possibility of receiver-sensitivity improvement up to 20-30 dB.^2,3 However, to realize the heterodyne/coherent systems many technical difficulties must be overcome; these are laser-frequency stabilization, laser-spectrum purification, polarization-state stabilization (or correction) in the fiber waveguide, heterodyne or homodyne detection technique, and coherent modulation/demodulation techniques.

© 1984 Optical Society of America