A novel self-seeding technique for timing jitter reduction in gain switched DFB laser

Gain-switched DFB lasers are widely used to generate short optical pulses for soliton transmission, optical time division multiplexed communication and optical signal processing. However, they are more susceptible to timing jitter than gain-switched F-P DFB lasers. The pulse to pulse time jitter will transfer to the relative intensity noise (RIN) and seriously degrade the bit error rate performance of optical switching controlled by control and signal pulses, such as nonlinear optical loop mirror and semiconductor laser amplifier in an optical loop mirror. Techniques for addressing this problem include external continuous wave (CW) light injection and self-seeding. CW light injection needs an additional CW light source and its wavelength should be selected to match the wavelength of the injected pulse source. We present a novel method to reduce timing jitter in a gain-switched DFB laser with a fiber loop mirror (FLM) containing a polarization controller (PC) and a fiber stretcher. Self-seeding injection is to use a portion of output pulse power, so that seeding injection power and appropriate delay time will play important roles for stabilizing the spontaneous emission fluctuations to obtain short optical pulses with low time jitter. We examine these effects experimentally and show dramatic timing jitter reduction from 5.7 ps to 1.2 ps.