Reduction of optical beat interference and intensity noise in a subcarrier multiplexed optical fiber link by Miller linecoding

The performance analysis is presented for an optical transmission system with RF subcarrier multiplexing (SCM) for radio on fiber technology considering the effect of PM-IM conversion due to Mach-Zehnder modulator (MZM) and optical beat interference (OBI) generated during photodetection process. Delay modulation line code or Miller coding is applied to minimize the effect of OBI. The computed bit error rate (BER) performance results show that there is significant deterioration in system BER due to OBI and PM-IM conversion and the system suffers significant power penalty at a given BER. The penalty without linecoding is found to be approximately 5.8 dB, 11.0 dB, 13.5 dB, 15.0 dB, 17.0 dB for PM-IM conversion factor of -1, -2, -3, -4, - 5 and 18.0 dB, 18.5 dB, 20.5 dB, 21.5 dB, 22.0 dB for number of subcarriers of 2, 4, 8, 16, 32 respectively. It is also found that with Miller coding there is significant reduction in OBI induced power penalty for example, the above penalty values are 3.5 dB, 5.5 dB, 8.0 dB, 9.5 dB, 10.4 dB for Miller coded system.