Impact of local oscillator intensity noise on performance of coherent subcarrier multiplexing system using common local oscillator (CLO)

The impact of local oscillator intensity noise on the performance of a coherent subcarrier multiplexing (CSCM) system using a common local oscillator (CLO) is analysed. For a given LO power, RIN noise, and thermal noise, the CNR can be expressed in terms of x, the ratio of sigma _sh²+ sigma _th² over sigma _RIN² and, for x<<1, the CNR decreases as LO power increases; for x>>1, the CNR increases as the LO power increases; as x approaches 1, there exist an optimum value of local oscillator power and a corresponding maximum CNR. For a system with RIN=-150 dB/Hz, P_S=-20 dBm, beta =0.02, N=40, NF=3 dB and B=10 MHz, the (P_LO)_opt is found to be -4 dBm and (CNR)_max 22.5 dB.