Investigations on Spectral Efficiency of Optical Communication System Using Wavelength Division and Sub Carrier Multiplexing

The growth of optical fiber communication had been tremendous over the past few decades. Multichannel optical systems using Time Division Multiplexing (TDM), Wavelength Division Multiplexing (WDM), Sub Carrier Multiplexing (SCM) and their combinations were developed in order to utilize the huge bandwidth provided by the optical fiber. In WDM, several optical carriers of different wavelengths modulated by low bandwidth baseband data streams are transmitted. In SCM, several Gigahertz wide sub carriers each carrying analog or digital data are multiplexed in radio frequency domain and this composite signal is subsequently modulated on to a Terahertz optical carrier. SCM makes better use of available bandwidth when compared to WDM. The most significant advantage of SCM in optical communication is its ability to place different optical carriers closely together. The bandwidth utilization is further improved by a hybrid WDM/SCM system in which each WDM wavelength carries an SCM composite signal. The simulation and performance comparison of a four channel WDM, a four channel SCM and a hybrid WDM/SCM system was done using Optisystem 12.0.