Overcoming Intrinsic Dispersion Locking for Achieving Spatio-Spectral Selectivity with Misaligned Bi-metagratings

TL;DR

This paper introduces a novel photonic structure that overcomes intrinsic dispersion locking, enabling precise spatio-spectral selectivity through angle-dependent radiation control and Fano interference, demonstrated experimentally with high resolution.

Contribution

It presents a new method using radiation asymmetry and Fano interference in misaligned bi-metagratings to achieve single-mode selectivity at specific angles and wavelengths, overcoming dispersion locking.

Findings

Achieved double narrow Fano-like reflection in angular and wavelength bandwidths

Demonstrated high-contrast spatio-spectral selective imaging

Provided a phase diagram for designing angle-controlled radiation-directionality

Abstract

Spatio-spectral selectivity, the capability to select a single mode with a specific wavevector (angle) and wavelength, is imperative for light emission and imaging. Continuous band dispersion of a conventional periodic structure, however, sets up an intrinsic locking between wavevectors and wavelengths of photonic modes, making it difficult to single out just one mode. Here, we show that the radiation asymmetry of a photonic mode can be explored to tailor the transmission/reflection properties of a photonic structure, based on Fano interferences between the mode and the background. In particular, we find that a photonic system supporting a band dispersion with certain angle-dependent radiation-directionality can exhibit Fano-like perfect reflection at a single frequency and a single incident angle, thus overcoming the dispersion locking and enabling the desired spatio-spectral selectivity. We present a phase diagram to guide designing angle-controlled radiation-directionality and experimentally demonstrate double narrow Fano-like reflection in angular (5{\deg}) and wavelength (14 nm) bandwidths, along with high-contrast spatio-spectral selective imaging, using a misaligned bilayer metagrating with tens-of-nanometer-scale thin spacer. Our scheme promises new opportunities in applications in directional thermal emission, nonlocal beam shaping, augmented reality, precision bilayer nanofabrication, and biological spectroscopy.