Perfect absorption of violet light enabled by rotated Mie resonators

Abstract

The absorption of a free-standing ultra-thin film supporting a single resonant mode is, in principle, limited to 50%. Based on the degenerate critical coupling (DCC) of dipole modes, silicon Mie resonators can overcome the absorption limit and achieve perfect absorption in the green light range. DCC requires that the radiative loss of each dipole mode matches material loss. Due to the material properties of silicon, the material loss varies with wavelength. Therefore, flexible tuning of radiative loss to match the wavelength-dependent material loss is crucial for realizing DCC-based perfect absorbers. In this study, we propose that a 45-degree rotation of cubic Mie resonators enhances the radiative loss of electric dipole mode. Hence, the DCC-based perfect absorption can be extended to the violet light range. In addition to applications in photodetectors and imaging sensor pixels, the proposed perfect absorber has great potential to become nonlinear elements based on the photothermal effect for photonic neuromorphic computing due to its temperature-dependent scattering.