Dual-layer orthogonal acousto-optic sensor for alias-suppressed high-precision DOA sensing

High-frequency underwater direction-of-arrival (DOA) sensing is crucial for improving target detection, localization, and imaging resolution. However, compact sensing configurations remain constrained by spatial aliasing and limited precision under restricted-aperture conditions. To address this, we propose a dual-layer orthogonal acousto-optic sensor, i.e., DLOA, that enables alias-suppressed and high-precision DOA estimation. The sensor employs six parallel laser beams to establish a non-contact orthogonal dual-baseline geometry, which maps the one-dimensional DOA parameter into a two-dimensional joint spatial-frequency domain. This configuration induces a physically admissible solution set that inherently rejects geometrically inconsistent grating lobes. Numerical simulations and water-tank experiments demonstrate broadband anti-aliasing performance across 20-80 kHz and high-precision DOA sensing at 75 kHz, achieving a relative tracking root-mean-square error of 0.015°. Additional evaluations under reduced signal-to-noise ratio and nearshore shallow-water measurements further confirm stable high-frequency undersampled DOA sensing in practical conditions.