Research On Spot Accurate Alignment Experiment In Wireless Laser Communication System

Wireless laser communication is a technology that uses laser beam as information carrier to transmit information in space in two directions, which was also known as "free space laser communication". In the Wireless laser communication system, because the laser beam is narrow and the directionality is strong, it is required that the field power of the transmitter really reach the photodetector of the receiver, which brings difficulties to the establishment and maintenance of communication link. Therefore, it is particularly important. Acquisition, pointing and tracking system technology is the key to establishing and ensuring reliable connectivity of communication links, which is critical to wireless laser communication systems. The main work of this paper is as follows:First, this research compared the performance of three photodetectors comImonly using in spot detection units in acquisition, pointing and tracking systems. The method of calculating the offset of four-quadrant detector under different spot energy distribution models was researched.The calculation formula of offset in Gaussian elliptic model and the annular spot model were deduced.Second, the alignment technique of beam in the optical axis was analyzed, and model of broken spot was constructed as a Gaussian elliptical spot, in addition, the position error of broken spot and the Gaussian complete spot was analyzed. When errors exist in case of both azimuth offset and pitch, an optical axis alignment method for acquisition, pointing and tracking systems was proposed.Third, a spot detection precision alignment system, with a four-quadrant detector as photoelectric conversion device, was achieved using STM32. The system scheme was determined, including optical devices, drive circuits, power modules, data transmission interface and design of terminal software. In addition, system experimental platform is set up,including hardware architecture platform and software environment platform.The experiment of spot detection and adaptive threshold alignment is completed. It was verified that the method could effectively detect the state value of incident beam and improve the accuracy of detection. In the same way, it was proved that the method has the advantages of simple implementation, high accuracy and low complexity of data processing.