The traditional acoustic wave sensing method mainly relies on the piezoelectric effect. Although this technology is relatively mature, there have been several inherent problems. First, the acoustic phase resolution of the piezoelectric transducer has a high phase resolution threshold mainly due to the unclear start and end points of the acoustic signal of the mechanical vibration. In underwater target detection applications, this problem leads to the loss of some details of target motion information hidden in the phase. Second, the piezoelectric effect sensing of acoustic waves requires a piezoelectric transducer to "contact and collide" with the acoustic wave. Consequently, some acoustic information is destroyed while sensing the acoustic wave, resulting in a loss of some phase information. Third, the "collision" between the piezoelectric transducer and the acoustic wave is accompanied by the reflection, diffraction, scattering, and other physical phenomena of the acoustic wave. Combining these physical phenomena and the target acoustic wave leads to phase loss, which is also a manifestation of the baffle effect. Fourth, the traditional piezoelectric transducer composed of an array is more difficult to use in engineering due to its volume and mechanical structure. This affects the quality of acoustic sensing since large array systems are inconvenient to install and use. Furthermore, the regular maintenance cost of the equipment is high, and the detection and calibration are difficult. Therefore, in this paper, we proposed an acousto-optic effect laser array method for high-quality sensing of acoustic signals.

We proposed a Raman-Nath detection acoustic signal using laser sensing for the hydro-acoustic signal detection method. Here we focused on the colinear problem of levels zero and one diffracted light, respectively. A performance analysis of relevant influencing elements was conducted. Furthermore, we derived the underwater target tracking method using the principle of mutual correlation to solve the acoustic field localization. Subsequently, we analyzed the quality and characterization of the acousto-optical signal. An experimental setup was built for principle verification (Fig. 4). We compared the time- and frequency-domain characteristics of the acousto-optical effect with those of the piezoelectric effect (Fig. 5), focusing on the phase information of the acousto-optical signal. Finally, we built an underwater target tracking system, designed and fabricated a laser sensing device (Fig. 11), and constructed and completed the experimental system in an anechoic pool laboratory.

By comparing both the time- and frequency-domain signal characteristics of the laser sensing method and the ultrasonic transducer method (Figs. 6 and 7), we prove that the signal received using the laser sensing method is of good quality with clear starting and finishing points. The phase characteristics show that the laser sensing method achieves an accurate perception of the ultrasonic phase (Figs. 9 and 10). For the tracking experiments of underwater targets, we set the number of moving steps of the ultrasonic transducer target to 20, and the minimum moving steps are 25 mm and 5 mm respectively, in which the shape of the ultrasonic transducer moving trajectory is the Chinese character "Zhong" , and the results are shown in Figure 14. The moving path of the ultrasonic transducer is set as a curve with 31 moving steps with a random moving step length. The detection tracking of the laser sensing device is consistent with the actual motion track. The actual positioning tracking results are shown in Fig. 15, and the positioning results of the three moving methods are shown in Table 1. The results show that the standard deviation of the x- and y-direction measurements are better than 10.42 mm and 1.88 mm, respectively. Moreover, the positioning standard deviation is better than 10.58 mm, and the angular resolution is better than 0.047°. Our laser sensing method outperforms the ultra-short baseline (USBL) device in terms of positioning accuracy and angular resolution index. The performance of our equipment is close to that of fiber optic hydrophones, as shown in Table 2.

In this paper, we propose a novel underwater high-resolution tracking method using laser sensing. Here, we deduce the principle of acousto-optical effect using Raman-Nath diffraction and the target tracking model. Based on these principles, we validate the phase-sensing capability of the acousto-optical effect for underwater acoustic waves and design a new small-aperture laser sensing device. Furthermore, we establish an experimental system for underwater tracking and experimentally verified the target tracking. The experimental results show that the measurement capability of hydro-acoustic phase sensing under the laser sensing mechanism is effectively improved. Laser sensing methods enable truly interference-free detection. Additionally, the angular resolution of underwater target tracking using our method is better than 0.05°. The laser sensing device provides a research reserve for developing new underwater target tracking and positioning technology with high resolution.