Abstract
Over the past years, photonic metasurfaces have demonstrated their remarkable and diverse capabilities in advanced control over light propagation. Here, we demonstrate that these artificial films of deeply subwavelength thickness also offer new unparalleled capabilities in decreasing the overall dimensions of integrated optical systems. We propose an original approach of embedding a metasurface inside an optical cavity—one of the most fundamental optical elements—to drastically scale-down its thickness. By modifying the Fabry–Pérot interferometric principle, this methodology is shown to reduce the metasurface-based nanocavity thickness below the conventional λ/(2n) minimum. In addition, the nanocavities with embedded metasurfaces can support independently tunable resonances at multiple bands. As a proof-of-concept, using nanostructured metasurfaces within 100-nm nanocavities, we experimentally demonstrate high spatial resolution colour filtering and spectral imaging. The proposed approach can be extrapolated to compact integrated optical systems on-a-chip such as VCSEL’s, high-resolution spatial light modulators, imaging spectroscopy systems, and bio-sensors.
Highlights
Over the past years, photonic metasurfaces have demonstrated their remarkable and diverse capabilities in advanced control over light propagation
Photonic metasurfaces[1,2,3,4,5,6] have enabled a new paradigm of controlling light by passing it through planar arrays of nanostructured antennas to induce a swift change in phase and/or polarization
Even though a given metasurface could be ultrathin, an integrated optical system that requires cascading of the metasurface with another optical component may not fully utilize its capability to reduce the overall dimensions of the system
Summary
Photonic metasurfaces have demonstrated their remarkable and diverse capabilities in advanced control over light propagation. Photons propagating through metasurfaces could be ‘processed’ to undergo a change to their momentum, angular momentum, and/or spin state This has led to a relaxation of Snell’s law[2], a pivotal relation in optics, and has enabled an entirely new family of flat optical elements. We show that embedding a metasurface inside a most fundamental optical element—an optical cavity—can substantially reduce the cavity thickness (up to two times) Such significant reduction in the transverse dimension is achieved without changing the optical mode for the sake of cascading and integration with other optical devices. This is especially useful for building multiple cavities of the same thickness on a planar chip resonating at different wavelengths These additional degrees of freedom allow us to obtain dualband resonances or even produce coloured images by using a single planar nanocavity of the same thickness by choosing the appropriate design for the internal metasurface
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