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

TL;DR

This paper introduces high-speed, stable visible-light modulators on thin-film lithium tantalate for underwater optical wireless communication, enabling high data rates over several meters with improved robustness.

Contribution

It reports the first integrated external modulator based UWOC system operating at 532 nm with high bandwidth and stability, surpassing previous lithium niobate devices.

Findings

Achieved 112-Gb/s transmission over 3 meters underwater

Demonstrated 64-Gb/s transmission over 9 meters underwater

Developed modulators with flat frequency response up to ~50 GHz

Abstract

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 for an hour, which cannot be achieved by thin-film lithium niobate based counterparts under similar conditions and structures. System-level underwater optical wireless communication (UWOC) is validated with 112-Gb/s transmission over 3-m and 64-Gb/s transmission over 9-m underwater links. 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.