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Concentrating light at the deep subwavelength scale by utilizing plasmonic effects has been reported in various optoelectronic devices with intriguing phenomena and functionality. Plasmonic waveguides with a planar structure exhibit a two-dimensional degree of freedom for the surface plasmon; the degree of freedom can be further reduced by utilizing metallic nanostructures or nanoparticles for surface plasmon resonance. Reduction leads to different lightwave confinement capabilities, which can be utilized to construct plasmonic nanolaser cavities. However, most theoretical and experimental research efforts have focused on planar surface plasmon polariton (SPP) nanolasers. In this study, we combined nanometallic structures intersecting with ZnO nanowires and realized the first laser emission based on pseudowedge SPP waveguides. Relative to current plasmonic nanolasers, the pseudowedge plasmonic lasers reported in our study exhibit extremely small mode volumes, high group indices, high spontaneous emission factors, and high Purell factors beneficial for the strong interaction between light and matter. Furthermore, we demonstrated that compact plasmonic laser arrays can be constructed, which could benefit integrated plasmonic circuits.

We report GaN-based vertical-cavity surface-emitting lasers (VCSELs) capable of high-temperature operation. The GaN-based VCSELs include double dielectric distributed Bragg reflectors and epitaxially grown p–i–n InGaN multiple-quantum-well active layers initially deposited on c-plane sapphire substrates that are bonded to a silicon substrate with a p-side-down and patterned mirror configuration, allowing effective heat dissipation. GaN-based VCSELs with an emission aperture 10 µm in diameter were fabricated, and their temperature-dependent lasing characteristics revealed that the VCSELs can endure 350 K, as measured under quasicontinuous-wave operation conditions. The temperature-dependent lasing wavelength shift occurs at a rate of dλFP/dT ≈ 0.012 nm/K. The high-temperature operation of GaN-based VCSELs was attributed to the well-matched gain-mode offset, the p-side-down configuration, and the reduced lateral size of the bottom distributed Bragg reflector with recessed metal.

Optical absorption is one of fundamental light-matter interactions. In most materials, optical absorption is a weak perturbation to the light. In this regime, absorption and emission are irreversible, incoherent processes due to strong damping. Excitons in monolayer transition metal dichalcogenides, however, interact strongly with light, leading to optical absorption in the non-perturbative regime where coherent re-emission of the light has to be considered. Between the incoherent and coherent limits, we show that a robust critical coupling condition exists, leading to perfect optical absorption. Up to 99.6% absorption is measured in a sub-nanometer thick MoSe2 monolayer placed in front of a mirror. The perfect absorption is controlled by tuning the exciton-phonon, exciton-exciton, and exciton-photon interactions by temperature, pulsed laser excitation, and a movable mirror, respectively. Our work suggests unprecedented opportunities for engineering exciton-light interactions using two-dimensional atomically thin crystals, enabling novel photonic applications including ultrafast light modulators and sensitive optical sensing.