Mid-IR light modulators enabled by dynamically tunable ultra-high-Q silicon membrane metasurfaces.

Metasurfaces enable subwavelength control of free-space light for applications in sensing, 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 particularly severe in the mid-infrared (mid-IR), where the scarcity of low-loss materials constrains performance and scalability. Here, we demonstrate actively tunable single-crystalline silicon membrane metasurfaces combining high-Q resonances, strong amplitude contrast, and wafer-scale manufacturability. Our platform achieves record-high measured Q-factors up to 3000 in the mid-IR and supports two dynamic modulation schemes: electro-thermal tuning via Joule heating with  >50% modulation depth at CMOS-compatible voltages and speeds up to 14.5 kHz, and ultrafast all-optical modulation via carrier generation in silicon with nanosecond response times and estimated sub-GHz rates. These results establish silicon membrane metasurfaces as a scalable platform for active mid-IR photonics.