Giant enhancement of the transverse magneto-optical Kerr effect in etchless bismuth-substituted yttrium iron garnet empowered by quasi-bound states in the continuum

TL;DR

This paper demonstrates a significant enhancement of the transverse magneto-optical Kerr effect in a bismuth-substituted yttrium iron garnet layer using a resonant grating waveguide, enabling advanced magneto-optical device applications.

Contribution

It introduces an etchless fabrication method combined with quasi-bound states in the continuum to greatly enhance TMOKE, with detailed theoretical and numerical analysis.

Findings

TMOKE amplitude reaches 1.978, close to maximum of 2

Enhanced TMOKE is linked to quasi-BIC resonance linewidth and local field

Designed a highly sensitive refractive index sensor with FOM of 299.3 RIU$^{-1}$

Abstract

Here, we propose an etchless bismuth-substituted yttrium iron garnet layer assisted by a one-dimensional resonant grating waveguide to enhance transverse magneto-optical Kerr effect (TMOKE) via the excitation of quasi-bound state in the continuum. The TMOKE amplitude can be tailored by manipulating the perturbation parameter, and it can reach as high as 1.978, approaching the theoretical maximum value of 2. Additionally, a single-mode temporal coupled-mode theory is employed to further reveal the underlying physical mechanism. It is found that TMOKE is strongly related to the line width of the quasi-BIC resonance and local field enhancement, which are pivotal factors in the design and optimization of photonic devices. As a potential application, we design and numerically demonstrate a refractive index sensor based on the resonantly enhanced TMOKE, with the optimal sensitivity of 110.66 nm/RIU and the corresponding maximum figure of merit of 299.3 RIU$^{-1}$. Our work provides a simple and efficient approach for enhancing TMOKE based on an easy-to-fabricate platform, laying the groundwork for exploring and developing magneto-optical devices such as sensors, magnetic storage devices, and nonreciprocal photonic devices.