An Integrated Passively Q-switched Nanophotonic Laser in the NIR Based on Two-Dimensional Materials

Two-dimensional (2D) materials demonstrate appealing characteristics for CW and pulsed light-emitting sources due to their strong emission and absorption properties, novel nonlinear effects, and compatibility with the silicon-on-insulator (SOI) platform [1], [2]. Contemporary 2D materials have been exploited either as gain media for CW nanophotonic optical sources [1], or as ultrafast and low-power saturable absorbers enabling pulsed lasing operation [2]. In this work, we propose and numerically evaluate an integrated nanophotonic passively Q-switched lasing element in the near-infrared (NIR), which is based on a disk resonator configuration and utilizes 2D materials for providing both the gain and saturable absorption (SA) mechanisms. The MoS 2 /WSe 2 transition metal dichalco-genide (TMD) hetero-bilayer is chosen as the gain medium, which is optically pumped at 740 nm (1.675 eV) and emits light at 1128 nm (1.1 eV) via an inter-layer exciton. Optical pumping is conducted by exciting a resonant cavity mode near the pump wavelength using guided light. Both the pumping and lasing processes are rigorously treated by induced electric polarization fields describing homogeneously broadened Lorentzian transitions. Over-all, the TMD hetero-bilayer is a three-level gain medium described by semiclassical carrier rate equations. The Q-switched operation is achieved by additionally harnessing the ultrafast and broandband SA response of a graphene monolayer. To numerically study and design the structure, we rigorously develop a temporal coupled-mode theory framework fed by linear finite-element method simulations. Our approach enables the accurate evaluation of the lasing characteristics in a computationally efficient manner.