Multiple colliding pulse mode-locking in a semiconductor laser: experiment and theory

Abstract

We present a modified monolithic passive colliding pulse mode-locked (CPM) laser configuration, which can generate 2, 3, or 4 pulses in the cavity, giving the second, third, or fourth harmonic of the repetition rate. The laser has a contiguously electrically connected gain section and 3 separated sections placed at every quarter of the cavity length. Its operation can be switched between 2, 3, or 4 pulses depending on the bias (forward or reverse) applied to each of its 3 independent sections, changing the position and number of saturable absorbers in the cavity. The laser is a stripe loaded waveguide fabricated on a 4 quantum well GaAs/ AlGaAs material. Its structure and the fabrication procedure are similar to the CPM laser described in Ref. 1. The total length of the laser is 600 µm and each one of its 3 independent sections is 30 pm long. It generates 120, 180, or 240-GHz repetition rate. Figure 1 shows the cross-correlation interferogram2 for 4 pulse operation, where we measure 1.2-ps pulse width at 240-GHz repetition rate. Figure 2 shows the optical spectra for the same configuration. The time bandwidth product is 0.35. This is the first observation of multiple CPM laser operation.