Sixty-channel coherent FM-SCM system for video distribution

Abstract

Subcarrier multiplexing (SCM) techniques offer an attractive approach for broadband distribution of FM video signals in the subscriber loop. To allow for distribution to many subscribers via passive optical splitting, improvements in the receiver sensitivity over direct detection systems are necessary. Possible approaches include using an APD detector1 or optical amplifiers as a repeater/ preamplifier.2,3 An alternative is to employ coherent detection techniques. We report the transmission of sixty FM video channels using coherent SCM. To obtain a CNR of 17 dB and a corresponding SNR of 56 dB, the detected optical power was —32 dBm with a phase modulation index of β = 0.07. This represents a 15.2- dB improvement over a similar sixty-channel direct detection FM- SCM system4 and a 5.6-dB improvement compared with the system when an optical preamplifier was used.3