Strong light−matter coupling, characterized by a coherent exchange of energy between an emitter and cavity, plays an important role in, for example, quantum information science and thresholdless lasing. To achieve strong coupling, precise spatial and spectral overlap between the emitter and cavity is required, presenting a significant challenge to move from individually strongly coupled cavities to a large number of cavity-coupled systems, as required for future practical applications. Here we demonstrate a versatile platform for realizing strong coupling that scales uniformly from individual nanocavities up to millimeter-scale metasurfaces, while the coupling strength can be tuned dynamically. Fluorescent dye molecules are sandwiched between silver nanocubes and a metallic film creating a plasmonic cavity with a mode volume of only ∼0.002 (λ/n) 3 . A prominent anticrossing behavior is observed which corresponds to a large Rabi splitting energy of 152 meV. The plasmon resonance can be tuned up to 45 nm (∼210 meV) enabling real-time control of the Rabi splitting as well as tuning from the weak to the strong coupling regime. This scalable, easily fabricated structure opens the door for use in integrated onchip nanophotonic devices.

Dielectric metasurfaces made of high refractive index and low optical loss materials have emerged as promising platforms to achieve high-quality factor modes enabling strong light–matter interaction. Bound states in the continuum have shown potential to demonstrate narrow spectral resonances but often require asymmetric geometry and typically feature strong polarization dependence, complicating fabrication and limiting practical applications. We introduce a novel approach for designing high-quality bound states in the continuum using magnetic dipole resonances coupled to a mirror. The resulting metasurface has simple geometric parameters requiring no broken symmetry. To demonstrate the unique features of our photonic platform we show a record-breaking third harmonic generation efficiency from the metasurface benefiting from the strongly enhanced electric field at high-quality resonances. Our approach mitigates the shortcomings of previous platforms with simple geometry enabling facile and large-area fabrication of metasurfaces paving the way for applications in optical sensing, detection, quantum photonics, and nonlinear devices.

Plasmonics can dramatically improve the radiative properties of fluorescent materials by precisely tailoring the local density of states, but has largely been dismissed for practical optoelectronic applications due to losses and lack of scalability to macroscopic areas. Here, we demonstrate a low-loss plasmonic metasurface that can collect fast-modulated light with a 3 dB bandwidth exceeding 14 GHz and a 120º acceptance angle and convert it to a directional source with, to the best of our knowledge, a record-high overall efficiency of ∼ 30 % . This large-area metasurface composed of fluorescent dye coupled to nanopatch antennas, exhibits a 910-fold increase in the overall fluorescence and a 133-fold emission rate enhancement—values previously only observable for isolated, highly optimized single nanostructures. Critical for future applications ranging from optoelectronics to biosensing, this metasurface was created over macroscopic areas with scalable techniques and the performance was validated over centimeter-scale regions. In particular, we believe this approach shows promise for the burgeoning field of visible/near-infrared wireless communications, where radical new designs and materials are needed for ultrafast, efficient, omnidirectional detectors and incoherent sources.

Plasmonic structures are promising to enhance and control nonlinear optical processes as the subwavelength-scale elements not only increase the local electric field intensities, but also result in relaxed phase matching conditions. This opens the possibility to observe and further manipulate multiple nonlinear optical processes simultaneously, which would be forbidden in bulk crystals due to incompatible phase matching requirements.Here we enhance and control the relative strength between third harmonic generation (THG), sum frequency generation (SFG), and four wave mixing (FWM) arising from 1 to 7 nm Al 2 O 3 layers sandwiched between a gold film and silver nanorectangles. We demonstrate that the relative strength of the three, simultaneous nonlinear optical processes can be precisely controlled by either the ratio between the powers of the two excitations or the thickness of the Al 2 O 3 layer. Furthermore, enhancements up to 10 6 -fold for THG and FWM are observed along with 10 4 -fold enhancements for SFG response when the resonance of the transverse and longitudinal mode of the cavity are matched to the two pump excitations. The ability to obtain and control multiple, nonlinear optical processes simultaneously open new capabilities for advanced on-chip manipulation and processing of optical signals on the deep nanoscale.