Metasurface–TMDCs for Strong Coupling and Emerging Nanoscale Light Sources

Metasurface–transition metal dichalcogenide (TMDC) monolayer hybrids are a promising platform for strong coupling and compact quantum nanophotonic devices. In this review, we discuss the main theories, design approaches, recent experiments, and applications of these systems, focusing on single-photon emission and lasing. We explain how the mode volume and quality factor work together in these systems. Dielectric and plasmonic metasurfaces provide different balances of optical loss and field confinement. Because the reported systems differ in TMDC material, temperature, exciton linewidth, and field overlap, their Rabi splittings alone cannot establish an intrinsic ranking of the two platforms. In the strong coupling regime, polariton nonlinearities could enable photon blockade and high-purity single-photon emission, but achieving this at room temperature is still mostly theoretical. Photon lasing has been shown in metasurface–TMDC systems, but clear evidence of polariton lasing from a TMDC monolayer combined with dielectric or plasmonic metasurfaces is still missing. The main challenges include exciton–exciton annihilation and weak mode overlap in dielectric structures, as well as very short photon lifetimes in metallic resonators. Finally, we discuss experimental benchmarks and the scalable cleanroom fabrication of high-Q plasmonic metasurfaces, including dielectric metasurfaces. These are applicable to room-temperature, directional, ultrafast, and energy-efficient nanoscale light sources. Furthermore, low-loss dielectric metasurfaces are summarised for manipulating the generated emitted light, which is crucial for directing and manipulating the light on-chip and for directly collimating and aligning it with an optical fibre.