Multiple optical reflections in hybrid AM/16-QAM multichannel video lightwave transmission systems

The effects of multiple optical reflections on bit-error-rate characteristics using a directly-modulated DFB laser transmitter and an externally-modulated YAG laser transmitter are compared in hybrid multichannel AM/16-QAM video lightwave transmission systems. The measured 16-QAM bit-error-rate is increased from 10/sup -10/ at reflections of -60 dB to 10/sup -1/ at reflections of -20 dB for a 16-QAM modulation index of 0.22% using the DFB laser transmitter (AM modulation index of 3.3%) with an analog CNR of 52 dB. In contrast, the observed 16-QAM bit-error-rate is essentially unaffected by reflections using an externally-modulated YAG laser transmitter with the same AM modulation index and received optical power.<
>