Abstract: External phase modulation is usually applied to improve the SBS threshold in long distance EDFA cascaded 1 550 nm externally-modulated AM CATV. In this paper, composite second-order distortion (CSO) performance due to external phase modulation is studied theoretically. First, the external-PM and the self phase modulation (SPM) induced CSO is obtained analytically by solving the Schr-dinger equation with a perturbation method. Numerical results are then presented and discussed. According to the study, the CSO performance can be improved significantly by applying a suitable phase modulation index for any long distance AM-CATV.

Key words:
Raman amplifier,
self phase modulation (SPM), external phase modulation, perturbation, stimulated brillouin scattering (SBS), composite second-order distortion (CSO)