Metasurface-controlled high-speed tunable external cavity lasers.

Tunable lasers are essential for optical communication, spectroscopy, and precision sensing, where fast and stable wavelength control is required. Conventional tuning approaches rely on either current or temperature tuning, mechanical actuation, or bulky external modulators, limiting speed, stability, or integration. Here, we introduce an external cavity semiconductor laser incorporating a resonant electro-optic metasurface as the external mirror, enabling ultrafast frequency and amplitude control within a compact, motion-free platform. The metasurface provides narrowband feedback that ensures single-mode operation and voltage-controlled tuning across a wide current range. We demonstrate mode-hop-free linear frequency tuning with rates up to 180 terahertz per second and frequency excursions reaching 110 megahertz under a 10-volt peak radio-frequency drive. By biasing the laser near threshold, we further achieve intensity modulation efficiencies exceeding 100% at 4 volts. These results establish electro-optic metasurfaces as a powerful route toward compact, high-speed, mode-hop-free tunable lasers for free-space communication, ranging, and high-resolution spectroscopy.