This paper reported our discovery on the cross-phase-modulation（XPM） imposed degradation of the signal-to-noiso ration（SNR） in on-off keying （OOK） coherence multiplexed systems

Analytical expression was obtained for one channel case and numerical results were given for multiple simultaneous channels case. According to our research. channel power and encoder delays should be as small as possible to minimize the phase-perturbation degradation.