Coherent Perfect Diffraction in Metagratings

Abstract

Metasurfaces are 2D engineered structures with subwavelength granularity, offering a wide range of opportunities to tailor the impinging wavefront. However, fundamental limitations on their efficiency in wave transformation, associated with their deeply subwavelength thickness, challenge their implementation in practical application scenarios. Here, it is shown how the coherent control of metagratings through multiple wave excitations can provide new opportunities to achieve highly reconfigurable broadband metasurfaces with large diffraction efficiency, beyond the limitations of conventional approaches. Remarkably, energy distribution between the 0th and higher diffraction orders can be continuously tuned by changing the relative phase difference between two excitation waves, enabling coherent control, with added benefits of enhanced efficiency and bandwidth. This concept is demonstrated for a thin electric metagrating operating at terahertz frequencies, showing that coherent control can overcome several of the limitations of single‐layer ultrathin metastructures, and extend their feasibility in various practical scenarios.

Extreme Diffraction Control in Metagratings Leveraging Bound States in the Continuum and Exceptional Points

“…[26][27][28] Currently, both BICs and EPs in metasurfaces have been mostly focused on the manipulation of the spectral/temporal properties of the impinging optical signals, namely, to control the zeroth diffraction-order transmission/reflection features for incident plane waves. [10][11][12][13][23][24][25] In parallel, few-diffraction-order (FDO) metagratings, capable of suppressing undesired diffraction orders and redirecting the incident power to preferred directions with unitary efficiency, have been developed for efficient and extreme wavefront engineering with less spatial resolution demand [29][30][31][32][33][34][35][36][37][38][39][40] when compared with conventional phase-gradient metasurfaces. [41,42] In this paper, we introduce a platform to control the emergence of BICs and EPs near the Brillouin edge of an FDO metagrating, tailoring the diffraction spectra in extreme ways.…”

Discrete Huygens' Metasurface: Realizing Anomalous Reflection and Diffraction Mode Circulation with a Robust, Broadband and Simple Design

“…However, more complicated designs are required to manage the diffraction of more propagating modes. Some researchers introduce more degrees of freedom with extra inclusions in each period [4], [30], [32], [43], which complicates the theory and structure, as the mutual couplings among the inclusions are difficult to rigorously analyze. Some researchers use iterative optimization methods to design metagratings based on multimode geometrical structures [18], [33], which needs a lot of simulation iterations, and the optimized performance may differ depending on the specific application and the optimization algorithm.…”

Stepwise Dual‐Fabry–Pérot Nanocavity for Grayscale Imaging Encryption/Concealment with Holographic Multiplexing

“…Coherent interference, as a fundamental phenomenon of electromagnetic waves, is utilized to construct the light intensity modulation and numerous optical devices rely on the interference operation, such as interferometers, optical antennae, spectrometers, coherent perfect absorption, etc. [1][2][3][4][5][6][7] During the last decade, ultrathin films stacks by metal−insulator−metal (MIM) has been proposed and extensively studied based on In addition to grayscale imaging encryption/concealment, such DFP nanocavity design also allows for near-field grayscale nanoprinting with far-field holographic multiplexing. By spatially designing the stepwise DFP cavity, it creates the simultaneous manipulation reflection intensity and phase shift, which essentially achieves the dual-channel for imaging information storage and multiplexing: a near-field grayscale image and a far-field holographic image.…”