Analysis of laser overmodulation techniques in subcarrier multiplexed optical fibre systems

A method of determining the significant intermodulation distortion products that occur in an overmodulated subcarrier multiplexed system is described. The analysis is based on obtaining a third-order polynomial that represents the laser light-current characteristics when the laser is operated beyond its linear region. It is shown that the level of distortion is determined by the overall RMS (root mean square) modulation depth, rather than individual subcarrier modulation depths or the number of subcarriers. The model developed can be used to predict the performance of overmodulated subcarrier multiplexed systems where individual subcarriers may be of equal or different magnitudes