Plasmonic nanostructures hold promise for the realization of ultra-thin sub-wavelength devices, reducing power operating thresholds and enabling nonlinear optical functionality in metasurfaces. However, this promise is substantially undercut by absorption introduced by resistive losses, causing the metasurface community to turn away from plasmonics in favour of alternative material platforms (e.g., dielectrics) that provide weaker field enhancement, but more tolerable losses. Here, we report a plasmonic metasurface with a quality-factor (Q-factor) of 2340 in the telecommunication C band by exploiting surface lattice resonances (SLRs), exceeding the record by an order of magnitude. Additionally, we show that SLRs retain many of the same benefits as localized plasmonic resonances, such as field enhancement and strong confinement of light along the metal surface. Our results demonstrate that SLRs provide an exciting and unexplored method to tailor incident light fields, and could pave the way to flexible wavelength-scale devices for any optical resonating application.

The interplay between localized surface plasmon (LSP) resonances and their collective responses, known as surface lattice resonances (SLRs), in metal nanoparticle arrays can lead to resonances with high Q-factors (∼100). These responses have in the past usually been studied for LSP resonances in the plane of the array of the nanoparticles (assumed to be nonmagnetic), thus restricting efficient coupling to particles separated along a specific direction. In the present study, we demonstrate that LSPs oscillating perpendicular to the plane of the surface can lead to stronger inter-particle coupling, which enhances the SLRs. This stronger coupling occurs because the out-of-plane oscillations can couple in all directions within the plane of the array. We study the resulting SLRs for square and hexagonal lattices using the discrete-dipole approximation, and we predict much larger Q-factors in the wavelength range near 650 nm. This prediction suggests that SLRs could be very useful in enhancing various optical processes, and in many applications such as sensing and nonlinear optical wave mixing.

We report on the efficient nonlinear optical interactions in AlGaAs strip-loaded waveguides with a wafer composition specifically designed to increase the nonlinear coefficient. We demonstrate a broad-band self-phase modulation with a nonlinear phase shift up to 6π, and four-wave mixing with a 20-nm tuning range and signal-to-idler conversion efficiency up to 10 dB. Our samples are several times shorter than similar devices used for wavelength conversion by XPM and FWM in previous reports, but the efficiency of the observed effects is similar. Our experimental studies demonstrate the high potential of AlGaAs for all-optical networks.

It is well known that the optical response of a medium depends on the local field acting on an individual emitter rather than on the macroscopic average field in the medium. The local field depends very sensitively on the microcopic environment in an optical medium. It is thus possible to achieve a significant control over the local field by intermixing homogeneous materials on a nanoscale to produce composite optical materials. A combination of local-field effects and nanostructuring provides new degrees of freedom for manipulating the optical properties of photonic materials. Especially interesting opportunities open up in the nonlinear optical regime where the material response depends on the local-field correction as a power law. The goal of this review is to present a conceptual overview of the influence of local-field effects on the optical properties of photonic materials, both homogeneous and composite. We also give a summary of recent achievements in controlling the optical properties by local-field effects and nanostructuring.

Resonant metasurfaces are devices composed of nanostructured subwavelength scatterers that generate narrow optical resonances, enabling applications in filtering, nonlinear optics, and molecular fingerprinting. It is highly desirable for these applications to incorporate such devices with multiple high-quality-factor resonances; however, it can be challenging to obtain more than a pair of narrow resonances in a single plasmonic surface. Here, we demonstrate a multiresonant metasurface that operates by extending the functionality of surface lattice resonances, which are the collective responses of arrays of metallic nanoparticles. This device features a series of resonances with high-quality factors (Q ∼ 40), an order of magnitude larger than what is typically achievable with plasmonic nanoparticles, as well as a narrow free spectral range. This design methodology can be used to better tailor the transmission spectrum of resonant metasurfaces and represents an important step toward the miniaturization of optical devices.