A compensation method for dispersion-induced third-order intermodulation distortion using an etalon

A method to compensate dispersion-induced third-order intermodulation distortion (IM3/sub CD/) in subcarrier multiplexing (SCM) optical transmission systems is proposed. It is confirmed theoretically and experimentally that IM3/sub CD/ can be compensated by interference-induced third-order intermodulation distortion (IM3/sub IN/). Simple analytic expressions of IM3/sub CD/ and IM3/sub IN/ are derived from the same expression of optical electric field which includes exact phase term taking into account the phase of laser chirp. From the theoretical analyses, we clarified the conditions of IM3/sub CD/-compensation. IM3/sub IN/ can be easily generated by an etalon which is a kind of interferometer and a optical glass plate. More than 30 dB of IM3/sub CD/-compensation was achieved, and IM3/sub CD/-compensation was achieved regardless of the transmission distance by adjusting tilt angle of the etalon. Using this method, high quality signal transmission can be realized even though the wavelength of laser diode (LD) is not coincident with the fiber zero dispersion wavelength.