Hybrid AM/QAM video lightwave systems: performance of different laser transmitters in the presence of optical reflections

The effects of multiple optical reflections on the CNR and the bit error rate characteristics based on various optical transmitters in hybrid multichannel AM/16-QAM video lightwave transmission systems are compared. For reflections greater than -50 dB, the CNR and QAM bit error rate were significantly degraded in systems using the directly modulated DFB laser transmitter. For an externally modulated 1550 nm DFB laser transmitter-based system, the CNR and QAM bit error rate are impaired only at high level of reflections (>-35 dB). In contrast, for an externally modulated YAG laser transmitter-based system, the observed CNR and QAM bit error rate were essentially reflection-independent with the same AM modulation index and received optical power. The experimental results are in good agreement with a simple model