Beyond 20 nm frequency comb generation through a two-section quantum well passively mode-locked semiconductor laser

We demonstrate an optical comb with a -3 dB bandwidth of 20.93 nm and a -10 dB bandwidth of 37.26 nm, generated by a two-section InGaAlAs/InP QW passively mode-locked semiconductor laser. This exceptional bandwidth is attributed to the broad and flat-topped gain profile enabled by an optimized strain-compensated MQW structure. These are the widest optical bandwidths reported to date, to the best of our knowledge, for any directly electrically pumped passively mode-locked semiconductor laser. In the same mode-locked state, the pulse duration was measured to be 874.5 fs, with an RF beat-note -3 dB linewidth of 15.2 MHz and an SNR reaching 32 dB.