Optomechanical Modulation Spectroscopy of Bound States in the Continuum in a Dielectric Metasurface

Elusive features in photonic and electronic devices can be detected by means of advanced, time-domain spectroscopic techniques. In this paper we introduce a modulation spectroscopy based on the optomechanical interaction of photonic and mechanical modes. Applying the technique to a Si metasurface and its drumlike mechanical modes, we detect narrow-band quasi-bound-state-in-the-continuum (quasi-BIC) modes close to normal incidence, where their measurement can be hindered by a high-symmetry protection and undesired background modes. Showing a visibility enhancement of more than one order of magnitude, the optomechanical modulation spectroscopy can be an innovative tool for precise spectroscopy of a wide set of photonic devices, including the goal of measuring purely symmetry protected BIC resonances.