Optical regeneration technique using an electro-absorption modulator (EAM) is reviewed. Simple 3R optical regeneration using an EAM was proposed and verified at 20 Gbit/s. The optical nonlinearities including cross-absorption modulation (XAM) and cross-phase modulation (XPM) induced in an EAM were quantitatively characterized by experiment. High bit-rate 2R type all-optical regeneration (wavelength conversion) at 100 Gbit/s was demonstrated by an EAM in conjunction with a delayed interferometer (DI) with required optical pulse energy of 1.5 pJ. It was verified that the operable bandwidth of the EAM-DI wavelength converter at 40 Gbit/s covered almost full range of C-band without tuning operation conditions.

All optical regenerations or wavelength conversions using SOA-based polarization discriminated switch injected by an assist light were investigated. First of all, cross gain modulation (XGM) and cross phase modulation (XPM) in a SOA injected by an external assist light were quantitatively analyzed. A simple measurement technique of XGM and XPM was shown to confirm that the injection of assist light could reduce a gain recovery time with some sacrifice for XGM and XPM efficiency. All-optical 3R regeneration using two-stage SOA-based polarization discriminated switch at 40 Gbit/s and its tolerances for some degradation against intensity deviation and optical signal-to-noise ratio (OSNR) were also shown. Finally, regeneration capability was evaluated through a dispersion shifted fiber (DSF)-based re-circulating loop transmission experiment. Those results indicate that the SOA-based polarization discriminated switch is a promising candidate for all-optical regenerator from the practical point of view.