Semiconductor laser sources for coherent optical-fibre systems

Reliable detection of a phase-modulated optical carrier has been demonstrated over 500 m of graded-index optical fibre using a semiconductor-laser source and mode-mode interference. The system performance is limited by the noise and spectral properties of the optical source. Spectral measurements indicate that transmission over several kilometres should be possible. This has direct significance for amplitude-modulated systems with semiconductor-laser sources as it implies that modal noise can occur at fibre connections up to several kilometres from the optical source.