Electrical Threshold Gain Engineering for High-Speed Direct Modulation in Two-Dimensional Semiconductor Laser

Abstract

Lasers are essential optical modulation sources because of their narrow line width and high coherence. Two-dimensional transition-metal dichalcogenides (TMDCs) exhibit strong exciton binding energy and high material gain and are promising candidates for use in compact, low-threshold semiconductor lasers. Although their intrinsically short exciton lifetimes imply faster modulation compared with bulk semiconductors, no direct TMDC laser modulator has yet been realized. This paper presents a high-speed, room-temperature direct modulator based on a threshold-gain-tunable monolayer tungsten disulfide (WS2) microdisk laser. In this modulator, gate voltage can be tuned to modulate the intensity of the lasing output through both carrier density variation and threshold gain control, achieving 50% greater modulation depth compared with normal spontaneous emission. Electrical tuning simultaneously affects the carrier density, dielectric environment, and optical confinement between the WS2 monolayer and the cavity. Radiofrequency measurements revealed a 3 dB intensity modulation bandwidth exceeding 120 MHz. Overall, these results demonstrate the feasibility of high-speed direct optical modulation with TMDC lasers, creating opportunities for the development of compact, energy-efficient optoelectronic systems.