A STUDY OF OPTICAL BEAT INTERFERENCE BETWEEN FABRY-PEROT LASERS

Optical beat interference can be the dominant source of noise in subca rrier-multiplexed (SCM) passive-optical networks (PON's), We have stud ied how the relative-optical-beat-interference noise (ROBIN) between F abry-Perot (FP) lasers varies using lasers with both equal, and unequa l mode spacing. In our experiments, ROBIN ranged from -96 dB/Hz to -11 5 dB/Hz, Because the noise level depends on the distribution of optica l power in the lasers' modes, using lasers with different mode spacing led to a 4-dB improvement over using lasers with equal mode spacing. The noise is also correlated with the linewidth of the interfering mod es. Broadening these modes by driving the lasers below threshold lower ed the noise by an additional 10 dB.