Thin-Film Dielectric Characterization by Fano Resonance in High Contrast Grating

Yi-Wen Lin^1*, Hsin-Yu Yao², Tsun-Hsu Chang¹

¹Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
²Department of Physics, National Chung Cheng University, Chiayi, Taiwan

* Presenter:Yi-Wen Lin, email:dk394xup643@gmail.com

Subwavelength high-contrast grating (HCG) is known for its ability to produce sharp and sensitive optical resonance with an ultra-high quality factor. Among this extraordinary phenomenon, we propose exciting a Fano resonance in a HCG system for thin film dielectric characterization in the sub-terahertz regime. By effectively controlling the interference of the waveguide-array modes excited in the grating, a strong field enhancement was observed on the grating surface. To assess the performance of the thin film covered on the HCG system, we demonstrate the correlation between the permittivity of the film and the reflection spectrum. In the context of a theoretical framework, we construct a contour map depicting the resonant condition det[I-ρ'φρφ] and the normalized resonant wavelength. In simulated experimental settings, we utilize a self-defined parameter to determine the permittivity of the thin film by analyzing the reflectivity spectrum. This design is an excellent candidate for non-destructive and efficient dielectric characterization of a thin film whose thickness is below one thousandth of the operating wavelength. Our work can facilitate the development of high frequency devices for the next generation high-speed communications.

Keywords: high-contrast grating, subwavelength grating, Fano resonance, thin-film dielectric characterization