High-speed electro-absorption semiconductor light modulator for soliton pulse generators

A simple and stable technique of optical short pulse generation for soliton transmission based on an electro-absorption (E-A) modulator is presented. By using the nonlinearity of the absorption characteristics of the modulator, ultrashort optical pulse trains having a shape close to a sech² shape can be generated just with sinusoidal modulation. Quasi-transform-limited optical pulses with a time-bandwidth product of 0.32 were successfully generated by the sinusoidally driven InGaAsP E-A modulator up to a 20 GHz repetition rate. The high quality of the modulator-generated pulses has been proven by long-distance soliton transmissions. As for the applications of this scheme, a λ/4-shifted DFB laser/E-A modulator integrated light source and a tandem-integrated E-A modulator (TEAM) to form a single-chip soliton transmitter are also described.