Performance Limitations of A Subcarrier Multiplexed Optical Transmission System Due to Optical Beat Interference

A theoretical performance analysis is presented for a subcarrier multiplexed (SCM) optical transmission system in presence of optical beat interference (OBI) which occurs during the photodetection process for non-return to zero (NRZ) and delay modulation (DM) linecoding. A suitable bandwidth of 890-950 MHz is selected and channel bandwidth of 200 KHz and carrier separation of 250 KHz is considered. Results are evaluated in terms of signal to OBI ratio for the two linecoding schemes. It is found that there is a significant increase in the SIR and hence the number of subcarriers can be achieved by employing Miller code compared to NRZ for the same data rate. For example, for a number of subcarriers of 10, the achievable SIR is about 36 for Miller coded system compared to 10 dB for NRZ coded system.