A low jitter passively mode locked laser diode at 40 GHz using regenerative feedback via an optical fiber loop

Mode-locked laser diodes (MLLDs) are excellent candidates for generating ultrashort high frequency pulses for a number of applications. Although more prone to noise than active MLLDs, passive MLLDs do not require any external electrical oscillator. But many applications for such lasers require highly stable optical pulses with sub-picosecond timing jitter and in this paper, a technique for reducing the RF phase noise in a passive MLLD is reported. Regenerative mode locking is a technique used to significantly reduce the timing jitter by providing a self-referencing mechanism to continuously correct the phase timing of the pulses. However, many of the current techniques used are based on electrical extraction and high-Q RF filtering of the pulses, which adds several components and considerable system complexity. A simplified all-optical regenerative mode locking technique which can provide significant reductions in phase noise and timing jitter is presented. The proposed method requires an optical fiber loop which relays the output pulse stream from the laser back into its resonator to induce self-beating intensity modulation of the pulses.