1 GHz InP on-chip monolithic extended cavity colliding-pulse mode-locked laser.

A record low-repetition rate from an on-chip monolithic InP extended cavity colliding-pulse mode-locked laser is experimentally reported. The device, fabricated in generic InP-based active-passive integration technology, makes use of integrated mirrors to enable its use as a building block within a photonic integrated circuit. This structure allows us to generate an electrical frequency comb with mode spacing of 1 GHz, determined by the 40.5 mm long resonator. Passive and hybrid mode-locking regime conditions are experimentally demonstrated. In the passive regime, an electrical beat tone at the fundamental repetition rate with an electrical linewidth (LW) of 398 kHz and a signal-to-noise ratio (SNR) >30  dB is measured. In the hybrid regime, the optical comb is locked to a continuous wave signal source, improving the LW of the generated signal and the SNR>40  dB.