Attenuation-resilient underwater optical ranging using a spatially petal-like structured beam with tailorable longitudinal intensity

Scattering in turbid water attenuates optical ranging signals, limiting detectable distance. In this study, we experimentally demonstrate attenuation-resilient underwater optical ranging using a petal-like structured beam such that the detectable ranging distance is increased. The structured beam is generated by combining Bessel-Gaussian (BG) modes with two different orbital angular momentum (OAM) orders, each order contains multiple longitudinal wavenumbers (kz). This creates a transverse spatial intensity profile with a two-petal-like feature in a central region that (i) angularly rotates during propagation and (ii) has a tailorable longitudinal intensity profile. Despite scattering-induced loss, the power in the central petal region is preserved by strategically redistributing energy from the sidelobes to the beam center. The proposed ranging beam enables (i) an extended detectable distance and (ii) adaptability to tailor the longitudinal intensity distribution under different turbid underwater environments. Experimental results show (i) a ~ 13 dB enhancement in petal power at a propagation distance of 0.4 m as compared to a conventional optical ranging approach using a two-kz structured beam; (ii) an average ranging error < 5 mm across the full 0.4 m in turbid water, while the conventional beam fails beyond 0.25 m and shows an over-80 mm average error. Underwater optical ranging systems face distance limitations due to power loss caused by scattering in turbid water. The authors demonstrate an attenuation-resilient approach using a petal-like structured beam with a tailorable longitudinal intensity profile, which provides a distance-dependent center power gain to ensure accurate ranging in challenging underwater environments.