Comparative Performance of Twin-Channel and Single-Channel Optical-Frequency Receivers

This paper describes a theoretical comparison of the noise immunity of direct-detection binary single-channel with direct-detection binary twin-channel optical digital communication systems. The conclusion is that a simple ON-OFF single-channel system is usually superior to twin-channel systems (such as polarization modulation and differentially coherent phase-shift systems) in noise immunity as well as simplicity. This result is quite different from the radio frequency case where twin-channel systems exhibit up to 6-dB advantage relative to single-channel systems.