Research on optical guidance technology using four-quadrant photodetectors

With the continuous advancement of underwater vehicle guidance and recovery technologies, acoustic and visual systems have proven effective for both long-distance and short-distance navigation. However, significant limitations persist in mid-range guidance. To address these blind spots in underwater mid-range guidance, this paper proposes a visible light guidance device based on a quadrant photodetector.

By leveraging the advantages of underwater optical technology, such as high precision, strong real-time performance, and low power consumption, the device provides an efficient and reliable technical solution for the mid-range recovery of unmanned underwater vehicles. A system prototype was implemented for horizontal guidance, with the same principles applicable for vertical guidance. Future work aims to integrate spatial theoretical models to address the challenge of accurately determining the position and orientation of underwater vehicles after extended missions as they approach a docking station. This paper begins by introducing the fundamental principle of using visible light and quadrant photodetectors to measure position and attitude data. In a simple setup with a single light source and detector, small changes in position or angle become difficult to detect over longer distances. To overcome this limitation, a “two-light, two-detection” model is proposed, utilizing two sets of LEDs (light emitting diodes) as light sources, with double-point analysis achieved through time-division illumination. The receiving end consists of two sets of quadrant photodetectors, enabling synchronized data collection from each light source. This model forms a network on the horizontal plane, facilitating effective measurement of relative position and attitude data. Extensive experimental data was collected using the prototype system, and a neural network model was developed by applying deep learning techniques. Finally, the two quadrant photodetectors on the horizontal plane simultaneously captured weak light signals instantaneously. These signals were processed using conversion, amplification, and noise reduction techniques to extract valid data. After further modularization and normalization, the processed data were fed into a pretrained model to calculate the relative distance, offset, and deflection angle on the horizontal plane, thereby providing real-time information on the position and orientation of the light source relative to the detector. In the experimental setup, parameters such as light source power, detector sensitivity, and circuit amplification factor were adjusted according to the measurement distance and environmental medium to ensure accurate data under varying conditions.

The experimental results demonstrate that the measurement error for the horizontal distance between the light source and the detector remains within 2%, with lateral offset errors limited to 2 centimeters and heading angle measurement errors controlled within 2°. Furthermore, incorporating additional light sources and detectors in the vertical direction, as well as increasing the number of measurement points and data volume, offers the potential to further optimize the experimental results. This study successfully met its objectives by employing multiple quadrant photodetectors and LED visible light sources, enabling accurate determination of the light source’s position and orientation at mid-range distances. This research provides valuable technical support for advancing underwater light guidance technology.