Active nonlocal metasurfaces

Abstract

Actively tunable and reconfigurable wavefront shaping by optical metasurfaces poses a significant technical challenge often requiring unconventional materials engineering and nanofabrication. Most wavefront-shaping metasurfaces can be considered “local” in that their operation depends on the responses of individual meta-units. In contrast, “nonlocal” metasurfaces function based on the modes supported by many adjacent meta-units, resulting in sharp spectral features but typically no spatial control of the outgoing wavefront. Recently, nonlocal metasurfaces based on quasi-bound states in the continuum have been shown to produce designer wavefronts only across the narrow bandwidth of the supported Fano resonance. Here, we leverage the enhanced light-matter interactions associated with sharp Fano resonances to explore the active modulation of optical spectra and wavefronts by refractive-index tuning and mechanical stretching. We experimentally demonstrate proof-of-principle thermo-optically tuned nonlocal metasurfaces made of silicon and numerically demonstrate nonlocal metasurfaces that thermo-optically switch between distinct wavefront shapes. This meta-optics platform for thermally reconfigurable wavefront shaping requires neither unusual materials and fabrication nor active control of individual meta-units.

Wavefront-selective Fano resonant metasurfaces

“…34 We propose a possible fabrication procedure in Sec. S2 in the Supplemental Materials based on extending recent efforts demonstrating single-layer q-BIC metasurfaces, 19,27,28 and we study the influence of misalignment of the two layers in Sec. S3 in the Supplemental Materials, concluding that standard tolerances more than suffice to demonstrate these concepts in the near-infrared.…”

“…Recently, Fano resonant metasurfaces capable of shaping the wavefront of light at resonance have been demonstrated based on the symmetry features of q-BICs. 14,21,[26][27][28] In Ref. 21, it was demonstrated that the orientable linear dichroism afforded by the p2 space group can carry a geometric phase when excited by circular polarization.…”

“…The local response to a linear polarization of choice may, therefore, be spatially varied, locally imparting a controlled geometric phase due to scattering from the nonlocal q-BIC mode. As a result, aperiodic functionalities, such as frequency-selective focusing of incident light, can be demonstrated using this technique, 27,28 but with efficiencies fundamentally limited by the achirality of the underlying structure. Incident circular polarization is not the selected polarization state at any point across the surface; therefore, the functionality of these systems is afforded by an incomplete projection of the incoming polarization to the locally selected states.…”

Integrated Quantum Nanophotonics with Solution‐Processed Materials

“…Recently, this platform was extended to a 2D guided mode resonator, also called a non‐local metasurface. [ 185 ] Dang et al. demonstrated strong coupling between the metasurface and the exciton resonance with a Rabi splitting in the 200 meV range.…”

Photoelastic plasmonic metasurfaces with ultra-large near infrared spectral tuning

“…Thanks to the extensive research on stimuli-responsive materials, such as phase-change materials, electro- and magneto-optical materials, and liquid crystals, various active metasurfaces have been reported. 10,19,20 Modulated metasurfaces for tunable absorption, 21 beam steering, 22,23 varifocal metalenses, 24 and ultrafast optical nonlinearity 25 have been demonstrated, holding great potential for applications in tunable photonics. For conventional phase-changing materials based on modification of the refractive index of the substrate or the medium around the plasmonic units, 26–30 it is challenging to obtain large spectral tuning range due to limited refractive-index changes and optical losses.…”