Electromagnetically induced transparency due to quasi-BIC in tilted guided-mode resonance gratings for transmissive sensing

We propose a single-layer tilted guided-mode resonance (GMR) grating that supports an electromagnetically induced transparency (EIT)-like quasi-bound state in the continuum (qBIC) mode. The qBIC-EIT occurs when two interfering resonances, specifically the GMR mode with a broadband stop spectrum and the qBIC mode, overlap spectrally, resulting in a sharp peak observed in transmission mode. We calculate the transmission spectra and confirm their tunability by modifying structural parameters, such as grating thickness and fill factor. Importantly, the electric field distribution of the qBIC-EIT mode is concentrated within the grating grooves, thereby enhancing the interaction between light and matter. The wavelength shifts in response to changes in the refractive index of the analyte, enabling sensing in transmission mode. Numerical results yield bulk and surface sensitivities of 736 and 81 nm/RIU, respectively. The easily fabricated structure enables transmissive monitoring of analyte concentration and composition in compact sensing systems.