Analysis Of Some Technology In SCM/WDM Optical Fiber Communication Systems

High-speed data transmission utilizing optical subcarrier multiplexing (SCM/WDM)techniques was recently studied by experiments and simulations in several works. SCM/WDM may have better spectral efficiency than WDM and SCM/WDM system could be less subjected to fiber dispersion than TDM system because the data rate at each subcarrier is low.There are two major limiting factors for the system performance, namely nonlinear distortion and accumulated ASE noise. For SCM/WDM system, the nonlinear interference between subcarrier channels is severe because the channel spacing is very narrow and the interference components fall into the signal frequencies. In order to limit nonlinear interference, the signal optical power can't be too high. On the other hand, in order to keep an acceptable signal-to-noise ratio (SNR) in the presence of accumulated ASE noise, the optical power can't be too small. Therefore parameter optimization is essential in the system design.In our study, duobinary modulation was used due to its high spectral efficiency and simple demodulation. Duobinary modulation can significantly decreases the dispersion penalty and limit nonlinear interference. Optical-single-side-band modulation (OSSB) was used since it further increases the spectrum efficiency and significantly decreases the dispersion penalty.A major benefit of DUOBINARY SCM/WDM systems is their immunity to fiber dispersion and nonlinear interference. So this type of systems is suitable to be used in those situations that require high spectrum efficiency and do not have dispersion compensation.