Monolithic 9 GHz passively mode locked quantum dot lasers directly grown on on-axis (001) Si

Abstract

Optical frequency comb direct generation on silicon by mode locked lasers (MLLs) is promising as it offers high wavelength channel counts and ultrashort pulses that will benefit future large-scale high capacity silicon photonic integrated circuits. Here, we demonstrate two-section quantum dot (QD) MLLs that are directly grown on a complementary metal–oxide–semiconductor compatible on-axis (001) silicon substrate by employing molecular beam epitaxy. The lasers, incorporating five layers of InAs QDs, operate in the O-band wavelength range with a pulse repetition rate around 9 GHz. A pulsewidth reduction of 48% of the narrowest achievable pulse from each QD MLL is obtained when the saturable absorber (SA) section length ratio is increased from 8% to 23%. The device with the longest SA section exhibits a more than 50 dB fundamental RF peak signal to noise floor ratio with 1.3 ps pulses.