E€ect of Optical ®ltering on Pulses Generated with a Gain-switched Dfb Laser

Gain-switched laser diodes are widely used to generate short optical pulses, which ®nd several applications in optical ®ber measurements and high-speed optical communication systems. Temporal and spectral properties of the gain-switched pulses can be tailored by ®ltering their optical spectrum. Optical ®ltering leads to suppression of frequency chirp and generation of transform-limited pulses. We show that tuning of the center frequency of an optical bandpass ®lter can result in not only pulse compression, but also in the generation of a series of secondary oscillations after the primary pulse. The origin of these secondary oscillations is investigated both experimentally and analytically.