Theoretical Analysis of Integrated Nanophotonic Q-Switched Laser Based on Gain and Saturable Absorption by Two-Dimensional Materials

Abstract

A nanophotonic passively Q-switched lasing element in the near infrared is proposed and theoretically investigated. It consists of a silicon-rich nitride disk resonator enhanced with the contemporary ${\text{MoS}}_2/{\text{WSe}}_2$ hetero-bilayer and a graphene monolayer to provide gain and saturable absorption, respectively. The two-dimensional materials are placed on top of the disk resonator and are separated by a spacer of hexagonal boron nitride. ${\text{MoS}}_2/{\text{WSe}}_2$ emits at 1128 nm due to the radiative recombination of interlayer excitons after being optically pumped at 740 nm. Optical pumping is conducted in a guided-wave manner aiming at achieving a high overall efficiency by critically coupling to a cavity mode near the pump transition. The response of the proposed pulsed laser is assessed by utilizing a coupled-mode theory framework fed with linear finite-element method simulations, rigorously derived from the Maxwell–Bloch equations. Following a meticulous design process and exploiting the guided pumping scheme, an ultralow lasing threshold of just $24.2$μW is obtained. Overall, the Q-switched laser delivers pulsed light inside an integrated bus waveguide with mW peak power, ps duration, and GHz repetition rates requiring sub-mW continuous wave pumping. These properties are highly promising for communication applications and highlight the potential of two-dimensional materials for nanophotonic light sources.