Research On Precision Positioning Of Laser Spot Based On QD

Laser positioning technology is widely used in the fields of laser guidance,industrial precision detection and free optical communication.In this paper,a precise laser positioning system based on four quadrant detector QD is designed with laser guidance as application background.Advantages and disadvantages of three common photodetectors are compared and analyzed.Finally,a four-quadrant detector is selected as the core device of the laser positioning system.QD output four-channel spot position information current needs to be amplified and collected to facilitate location calculation.The amplification and filtering circuit and the acquisition and conversion circuit based on high-speed AD9226 are designed.Data acquisition,conversion,buffer storage and transmission are realized by driving AD and controlling SDRAM and USB3.0 FX3 with main control core FPGA.Data caching part uses double SDRAM to form table tennis operation to realize data real-time caching,reading and writing,and FIFO to solve the problem of asynchronous data transmission.The design of the system is based on laser guidance,which will be interfered in practical application.The hardware part adds pseudo-random code and gate locking to reduce interference and ensure accuracy.The collected data are processed by NIOS II soft core.The position information is transmitted to the host computer through USB3.0 for display and storage,which is convenient for data processing by MATLAB.An improved spot location fitting algorithm is proposed by combining geometric approximation method and polynomial fitting method to simulate and verify it.The experimental system compares the errors between geometric approximation method and fitting algorithm through experiments,which proves the superiority of fitting algorithm,reduces the amount of calculation and parameters,and improves the accuracy at the same time.The four-way amplifier circuit is tested by experiment,and the amplification factor meets the requirement.Compared with the geometric approximation method and the fitting algorithm under different spot radius,the error and root mean square error of the fitting algorithm are smaller.The location resolution of the spot location fitting algorithm in the detection range of [-0.8mm~0.8mm] is better than 3.5um.The whole system can be applied in real-time detection and precise positioning.