Compact underwater single-photon imaging lidar

Underwater target imaging is important for marine resource exploration, underwater navigation, and related fields. Lidar, with its high angular resolution, excellent depth resolution, and long-distance 3D imaging capabilities, has become an essential tool for target imaging. However, the strong absorption and scattering properties of water, along with the constraints of lidar power consumption and system size, present significant challenges for high-performance lidar systems that are deployable in underwater and even deep-sea environments. To address these challenges, this work proposes and demonstrates a compact, all-fiber underwater imaging lidar. This lidar incorporates highly sensitive single-photon detection technology and features a cylindrical design with a diameter of 0.18 m and a length of 0.68 m. To achieve miniaturization, time-division multiplexing based on fiber arrays is employed, enabling the imaging of small underwater targets using two single-pixel detectors and a two-channel acquisition card. Additionally, an algorithm is introduced to effectively extract and subtract scattering signals from suspended particles in the water column. Tank experiments confirm that the system achieves imaging distances exceeding 10 times the optical attenuation length, and its distance and lateral resolutions are validated using step and stripe targets. With its outstanding performance and broad application potential, this compact lidar system is poised to complement imaging sonar and play a key role in underwater target monitoring and search operations.