Robust and Active Visible-Light Integrated Photonics on Thin-Film Lithium Tantalate for Underwater Optical Wireless Communications

Visible-light integrated photonics enables compact platforms for sensing, precision metrology, and free-space data links at visible wavelengths. However, many applications remain limited by the lack of high-speed and robust modulators in the blue-green band. Here we report, both operating at 532 nm, thin-film lithium tantalate waveguides of propagation losses of dB/cm scale and modulators with a flat frequency response to ~50 GHz. The modulator remains stable when delivering 5 dBm modulated optical power, which cannot be achieved by thin-film lithium niobate based counterparts under similar conditions and structures. We validate system-level underwater wireless optical communications (UWOCs) by transmitting 112 Gb/s signals over a 3-m underwater link. This represents the first integrated external modulator-based UWOC system, overcoming the bandwidth-power-chirp trade-offs of traditional directly modulated laser based systems. We further demonstrate dual-drive modulators for optical single-sideband and electro-optic frequency-comb generations in the green-wavelength band. These results provide a foundation for complex, robust, and active visible-light photonic integrated circuits for underwater optical applications.