Leaky-wave metasurfaces for integrated photonics

TL;DR

This paper introduces leaky-wave metasurfaces based on symmetry-broken photonic crystal slabs that enable full control over amplitude, phase, and polarization of guided light, bridging free-space and integrated photonics functionalities.

Contribution

It presents a novel leaky-wave metasurface platform supporting quasi-bound states in the continuum, allowing comprehensive optical control in integrated photonic devices.

Findings

Demonstrated phase and amplitude control at 1.55 microns

Achieved full control over four optical degrees of freedom

Merged guided and free-space optics functionalities

Abstract

Metasurfaces have been rapidly advancing our command over the many degrees of freedom of light within compact, lightweight devices. However, so far, they have mostly been limited to manipulating light in free space. Grating couplers provide the opportunity of bridging far-field optical radiation and in-plane guided waves, and thus have become fundamental building blocks in photonic integrated circuits. However, their operation and degree of light control is much more limited than metasurfaces. Metasurfaces integrated on top of guided wave photonic systems have been explored to control the scattering of light off-chip with enhanced functionalities - namely, point-by-point manipulation of amplitude, phase or polarization. However, these efforts have so far been limited to controlling one or two optical degrees of freedom at best, and to device configurations much more complex compared to conventional grating couplers. Here, we introduce leaky-wave metasurfaces, which are based on symmetry-broken photonic crystal slabs that support quasi-bound states in the continuum. This platform has a compact form factor equivalent to the one of conventional grating couplers, but it provides full command over amplitude, phase and polarization (four optical degrees of freedom) across large apertures. We present experimental demonstrations of various functionalities for operation at wavelengths near 1.55 microns based on leaky-wave metasurfaces, including devices for phase and amplitude control at a fixed polarization state, and devices controlling all four optical degrees of freedom. Our results merge the fields of guided and free-space optics under the umbrella of metasurfaces, exploiting the hybrid nature of quasi-bound states in the continuum, for opportunities to advance in disruptive ways imaging, communications, augmented reality, quantum optics, LIDAR and integrated photonic systems.