Mid-IR Light Modulators Enabled by Dynamically Tunable Ultra High-Q Silicon Membrane Metasurfaces

Abstract: Metasurfaces have emerged as a powerful platform to control free-space light at the subwavelength scale, enabling applications in sensing, lasing, nonlinear optics, and quantum photonics. However, their practical deployment is hindered by two key limitations: a tradeoff between low-Q resonances and weak amplitude contrast, and their predominantly static nature allowing only passive functionalities. These challenges are further aggravated in the application-relevant mid-infrared (mid-IR) range, where the lack of suitable low-loss materials and the strong absorption of common substrates such as silicon oxide or sapphire severely constrain performance and scalability. Here, we address these issues with actively tunable single-crystalline silicon membrane metasurfaces that combine high-Q resonances, strong amplitude contrast, and wafer-scale fabrication compatible dimensions for high throughput manufacturing. Our platform achieves record-high measured Q-factors up to 3000 in the mid-IR spectrum, supporting efficient dynamic modulation through two distinct schemes: (i) on-chip electro-thermal tuning via Joule heating, sustaining 50% modulation depth at CMOS-compatible voltages and speeds up to 14.5 kHz, and (ii) ultrafast all-optical modulation via carrier generation in silicon, reaching nanosecond response times and estimated sub-GHz modulation rates. By uniting sharp resonances, strong contrast, large-scale manufacturability, and dynamic tunability, our active silicon membrane metasurfaces advance the frontier of mid-IR nanophotonics and open new opportunities in sensing, free-space communication, thermal radiation management, and quantum technologies.