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

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.