Ultra-Fast High-Contrast Optical Modulation in Si Metasurfaces

Ultra-fast modulation of dielectric metasurfaces has shown a great promise for novel optical switching [1] and wavelength conversion [2]. A number of mechanisms have been recently explored, however the overall transmission modulation in such all-optical processes has remained low, typically a few percents. To increase the modulation contrast, high-quality factor metasurfaces manufactured on stable materials are required. Here, we demonstrate a high-contrast transmission modulation metasurface with ultra-fast response. In our metasurface design, the interference of the non-radiative asymmetric bound-state in the continuum (BIC) channel and a radiative electric dipole form a kink-type transmission response. Based on this engineered response, we demonstrate absolute transmission modulation of over 25% with a few tens of picoseconds time-response, driven by carrier injection in the crystalline silicon metasurface.