Analysis of simultaneous digital and analogue signal transmission in a coherent optical subcarrier multiplexed system

The performance of the coherent subcarrier multiplexed system with mixed digital and analogue signals is analysed. The result shows that the performance of the digital channels in this system may be better than the pure digital system if the modulation index of the analogue channel is less than half of the modulation index of the digital channel. It is predicted that the system will have a 14 dB improvement over the corresponding intensity modulation/direct detection system.