Underwater acoustics beamforming based on acousto-optic deflection.

Abstract

In underwater acoustics, beamforming techniques commonly employ a finite number of transducers to construct discrete array structures. However, these structures' spatial sampling characteristics can easily lead to spatial aliasing phenomena. To tackle this issue, this paper introduces an underwater acoustic beamforming method that utilizes the acousto-optic deflection effect. This method exploits the deflection mechanism of acousto-optic interaction, using laser beams that traverse the acoustic field to continuously integrate acoustic signals. Each segment of the laser beam can be considered as an individual acoustic sensor, deflecting in accordance with the modulation of the propagating sound wave, thereby forming a laser array with continuous, infinite aperture characteristics. This design fundamentally circumvents the discrete summation mechanism of conventional finite-number hydrophone arrays, effectively eliminating the spatial aliasing problem. In addition, the laser converts complex underwater acoustic signals into deflection angle information as it passes through the acoustic field, achieving high sensitivity through the light path extension technique. Experiments demonstrate that the proposed method successfully extends the beamforming system's effective anti-spatial aliasing bandwidth to the frequency range from 20 to 80 kHz. Specifically, a laser propagation path of only 17 cm achieves angular resolution equivalent to that of an 18-element hydrophone array.