Abstract: When subcarrier multiplexing (SCM) technology is applied for optical transmission, intermodulation products originate from two different nonlinear effects. There are intrinsic nonlinearities cause by the mixing ofphotons and electrons in the laser cavity. The other is the nonliearity of thelaser P-I curve. As the frequency of subcarrier become more and more high ,theeffect of harmonic and intermodulation distortion on distortion originated fromthe intrinsic nonlinearities of semiconductor laser become more and more important. Using rate equation of laser, Analysis and calculates the harmonic and intermodulation distortion,and analysis the approach of decreasing the distortion.

Key words: subcarrier multiplexing, harmonic distortion, intermodulation distortion, CNR