Experimental Demonstration of Underwater Optical Ranging with Enhanced Accuracy in Scattering Medium using Multiple Bessel Modes

Scattering underwater environments can degrade the performance of a time-of-flight-based ranging system due to temporal pulse spreading. Alternatively, underwater ranging using the transverse spatial information of a light beam may be more resilient to scattering. Such an approach utilizes the z-dependent angular rotation of a spatially structured beam consisting of two Bessel modes for underwater ranging. In this present work, we further enhance the performance of this scheme by combining multiple (>2) Bessel modes to achieve (1) higher peak power, and (2) narrower angular extension of the structured beam. We experimentally demonstrate a 0.4-m underwater optical ranging system under scattering conditions. Results show that the average ranging error decreases from ∼16 mm to ∼3 mm when the number of modes increases from 2 to 8 under an attenuation coefficient of 5 m-1. We also conduct a 10-m simulation under an attenuation coefficient of 0.4 m-1 to support the effectiveness of the proposed scheme for longer distances. The simulated ranging errors within the 10-m range are 25.1 cm, 10.3 cm, and 7.7 cm for 2-, 4-, and 8-mode beams, respectively.