A coherent optical system for analogue multichannel video transmission

A heterodyne analogue system using optical phase modulation is well suited for analogue transmission of CATV signals with a large number of videochannels. The authors describe the realisation of a heterodyne transmission system using optical phase modulation and nonsynchronous demodulation. In the experimental setup 18 standard FDM multiplexed TV channels (PAL system) are modulated onto a single optical carrier; the system concept allows transmission of 30 channels. The power budget allows a further increase in capacity by using multiple (at least 10) optical carriers in optical FDM, each carrying 30 TV channels. In order to meet the stringent phase noise requirements, two novel concepts are presented for phase noise reduction: optical filtering and phase-noise compensation based on linear heterodyne detection. For reduction of the required receiver bandwidth, a new detection scheme has been developed, offering simultaneous phase diversity, intensity noise suppression and frequency demodulation with only two photodiodes