Extinction ratio improvement by strong external light injection and SPM in an SOA for OTDM pulse source using a DBR laser diode

We demonstrate above 6-dB extinction ratio (ER) improvement by strong external light injection for 20-GHz optical pulses generated from a gain-switched high-speed distributed Bragg reflector (DBR) laser diode. The pulses also exhibit a reduced chirp accompanied with a reduced total root-mean square noise. Above 12-dB pulse ER improvement was further obtained with self-phase modulation (SPM) effect in a semiconductor optical amplifier (SOA) followed by an optical bandpass filter. Stable 40-GHz pulses were demonstrated through passively multiplexing the pulses with 6-ps pulsewidth.