Quad-narrowband perfect absorption in near infrared for optical switching and sensing based on quasi-bound states in the continuum

Abstract

The absorption of light based on quasi-BICs is a significant factor influencing the performance of solar cells and photodetectors. Nevertheless, the development of multiple narrowband perfect absorbers remains a significant challenge. In this study, three distinct types of BIC were first discovered to coexist within a metasurface structure. This paper proposes a dual grating metasurface (DGM) structure based on three classes of BICs supported by near-infrared spectroscopy. It achieves perfect absorption in four narrow bands dominated by quasi-BICs, with each of the peaks exceeding 99.5%. The physical mechanism of each resonance has been analysed using temporal coupled mode theory, which has revealed the existence of the Symmetry-Protected BIC, Friedrich–Wintgen BIC and Fabry–Pérot BIC. Moreover, the underlying mechanisms of the distinct resonance modes are revealed through the multipolar decomposition of these resonances. The metasurface has significant potential for utilisation as an optical switch, which is capable of achieving an optimal modulation depth, switching contrast, extinction ratio, and insertion loss of 99.9%, 127 932%, −31.1 dB, and 0.0007 dB, respectively. The DGM structure offers a superior quad-frequency synchronised optical switch in comparison to conventional optical switches. And it also exhibited a maximum sensitivity of 328.6 nm RIU⁻¹ and a maximum FOM of 93.9 RIU⁻¹ when used as a sensor. The work presented herein will facilitate the exploration of a novel avenue for the study of ultra-high performance multifunctional devices based on a multitude of types of BICs.