17 GHz lossless InP-membrane active metasurface

High-speed active metasurfaces enable spatiotemporal light control within an ultra-thin device layer, offering new possibilities for optical communication, sensing, and computing. However, a tradeoff between electrical conductivity and optical loss has hindered the realization of a high-speed, low-loss device. Here, we experimentally demonstrate an active metasurface operating at 1.5-μm wavelength range that achieves a record-high 17.5 GHz modulation bandwidth while maintaining a high quality (Q) factor of 102 and ultra-low optical loss of 0.56 dB. This is enabled by the indium phosphide (InP) membrane platform, where n-InP offers high electron mobility and low free-carrier absorption simultaneously. A high-Q Friedrich-Wintgen quasi-bound-state-in-the-continuum mode within the InP-membrane high-contrast grating (InP HCG) traps light in the organic electro-optic material for efficient modulation. The InP HCG also functions as an ultralow-resistance interdigitated electrode, enabling 50-fold faster modulation than silicon-based counterparts. Our work paves the way towards active metasurfaces for high-speed spatiotemporal light control beyond the