Designing Of A Laser Beam Tracking System With High-precision

Laser beam auto-tracking technology is of great significance for laser system such as laser communications, laser ranging, laser-guiding. The system uses He-Ne laser as an emission light source. Laser transmission in atmosphere affected by atmospheric turbulence will produce a beam drift, beam jitter, beam intensity flashing. These factors easily cause random displacement of the spot. If the detection system can not real-time sensitively response on tiny displacement of spot and adjust receiver position, which will cause positioning not accurate or positioning without high precision, thus affecting the performance of the system.The paper designed a laser beam tracking system with high precision. The system consists mainly of four-quadrant detector, the signal processing circuit using MSP430(ultra low power microcontroller) as the core, stepper motor control system. Through designing the optical path rationally to reduce the impact of the background light, measuring the overall noise of the signal processing channels, detecting the consistency of the four signal processing circuits under changing temperature to improve positioning accuracy. Calculating the spot center coordinates and the coordinates after adjusted through correlate algorithm, proving that the method using voltage of the four channels to solve the coordinates of the spot center has good precision.The paper first described structure and working principle as well as application of various photodetectors for optoelectronic detector system. Through the analysis and considering experimental conditions and the requirements need to achieve, selecting the four-quadrant photodetector as the front-end detector, and taking the appropriate methods for the lack of four-quadrant detector to reduce the impact.In the signal processing circuit section, designing the preamplifier circuit, filter circuit, the true value conversion circuit, the secondary amplifier circuit. This section changes the output photocurrent signal of the detector into voltage signal which can be processed by single-chip.According to measurement requirements and peripheral devices, selecting the MSP430as controller, the single-chip is of ultra-low power consumption and processing power, rich on-chip peripherals, system stability, convenient development environment, can meet the requirements of automatic control system.The system requires photoelectric detectors to accurately track the spot position, this functionality is realized by two-dimensional direction stepper motor, step accuracy is1μm. Microcontroller real-time processes signal data through algorithms to accurately control the operation of the stepper motor.The experimental designed and debugged a system program, using closed-loop control method to achieve accurate real-time tracking of the detector to the spot center.The paper analyzed the characteristics of the laser spot, the relationship between the detector output voltage and the radiant flux radiates on the detector surface is derived and tested the relationship about the channel output voltage varies with temperature, a model used to correct the coordinate of the spot center was established to compensate the drift caused by temperature changes, measures was taking to control the working temperature to improve the spot positioning accuracy. The output characteristics of the four-quadrant detection system was detected to determine the linear range of the system, so as to ensure that the spot is on the best measurement area of four-quadrant detector.