Effects of laser direct intensity modulation index on optical beat interference in subcarrier multiplexed wavelength division multiple access networks

Degradation in carrier-to-interference ratio (CIR) due to optical beat interference (OBI) in subcarrier multiplexed wavelength division multiple Access (SCM/WDMA) networks using direct photodetection is evaluated. The subcarriers are assumed to directly intensity modulate separate lasers. A large signal model for the modulated laser light is used. The discrepancy in CIR between this model and the small signal model commonly used in the literature is important at high modulation indices (4.5 dB at about unity modulation index). This justifies the introduction of the large signal model for analyzing OBI. It is found from analytical results that OBI is lower for higher intensity modulation indices.<>