Optical frequency comb generation via pulsed gain-switching in externally-injected semiconductor lasers using step-recovery diodes

We report on the experimental generation of high-quality Optical Frequency Combs (OFCs) at low repetition rates in an externally-injected gain-switched semiconductor laser using a Step-Recovery Diode (SRD) as the pulsing source. The use of an SRD as the electrical pulse generator allows us to produce high-quality OFCs with over 900 comb tones spaced by 100 MHz. Through experimental measurements, supported by simulations, the timing jitter of the electrical source has been demonstrated to impact the quality of the generated OFCs giving rise to a non-uniform Carrier-to-Noise Ratio which is higher around the injection and reduces with decreasing frequency. Nevertheless, comparing the OFC quality obtained using an SRD with those obtained with a costly pulse pattern generator, we conclude, that despite the slightly degraded OFC quality, the use of SRDs could reduce the cost, size and footprint of the equipment required for low repetition rate OFC generation.