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

Here, we propose an etchless bismuth iron garnet layer assisted by a one-dimensional resonant grating waveguide to enhance transverse magneto-optical Kerr effect (TMOKE) via the excitation of a 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 the TMOKE is strongly related to the linewidth of the quasi-bound states in the continuum resonance and local field enhancement, which are pivotal factors in the design and optimization of photonic devices. 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.