Transition metal dichalcogenides (TMD) heterostructure is widely applied for second harmonic generation (SHG) and holds great promises for laser source, nonlinear switch, and optical logic gate. However, for atomically thin TMD heterostructures, low SHG conversion efficiency would occur due to reduction of light–matter interaction length and lack of phase matching. Herein, we demonstrated a facile directional SHG amplifier formed by MoS₂/WS₂ monolayer heterostructures suspended on a holey SiO₂/Si substrate. The SHG enhancement factor reaches more than two orders of magnitude in a wide spectral range from 355 to 470 nm, and the radiation angle is reduced from 38° to 19° indicating higher coherence and better emission directionality. The giant SHG enhancement and directional emission are attributed to the great excitation and emission field concentration induced by a self-formed vertical Fabry–Pérot microcavity. Our discovery gives helpful insights for the development of two-dimensional (2D) nonlinear optical devices.

Two-dimensional (2D) transition metal dichalcogenide (TMDC) semiconductors not only hold great promises for the development of ultra-thin optoelectronic devices with low-energy consumption, but also provide ideal platforms to explore and tailor light-matter interaction, e.g., the exciton-photon interaction, at the atomic level, due to their atomic thickness, large exciton binding energy, and unique valley properties. In recent years, the exciton-photon interactions in TMDC semiconductor microcavities, including the strong exciton-photon coupling and lasing, have drawn increasing attention, which may open up new application prospects for transparent, on-chip coherent, and quantum light sources. Herein, we review the research progresses of strong exciton-photon interaction and lasing of TMDC semiconductors. First, we introduce the electronic structure, exciton, and emission properties of semiconducting TMDCs in the weak exciton-photon coupling regime. Next, the progresses on strong exciton-photon interaction and exciton-polaritons of these TMDCs are discussed from the aspects of photophysics, materials and fabrications, spectroscopies, and controls. Further, the progresses on TMDC lasers are introduced in the aspects of cavity types and materials, and finally, the challenges and prospects for these fields are discussed.