Research On Design Method Of High-frequency Scanner Based On Laser Diode

For the past few years, the laser radar has been widely used in the fields of surveying and mapping for emergency response,3D digital scenic spots, power line selection, inspection of transmission lines, the surveying and mapping of forest, topographic survey, reconnaissance of water conservancy facilities and many fields of military. But, as the main part of laser radar, the laser scanner is mostly dependence on import. Because there is no domestic laser scanner competing to the imported laser scanners, the imported laser scanners are very expensive. At present, there are a lot of units in China studying on high power laser scanners. Because of the high cost of the high power lasers, there is a design method of a low cost laser radar of high repetition frequency based on lower cost laser diodes to meet the small cost of applications.In this design, the laser diode is used as light-emitting source. A high current driving circuit is designed to drive the laser diode to emit pulse laser with high repetition frequency, narrow pulse width and high-peak power. To ensure the quality of the laser beam, the output of the laser has to be collimated. There are two circuits to achieve the START signal. One of them uses the PIN detector to process the start signal, and the other one uses the monitor signal of the drive circuit to be the START signal. APD is used to process the echo signal. In order to obtain a steep rise in tallied and satisfy the requirement of large dynamic range of echo signal, a large bandwidth, large dynamic range automatic gain amplifying circuit is designed to deal with the echo signal. After AD conversion circuit, the time-of-flight counting circuit can tell the distance from the scanner to the target.45°rotating mirror is selected as the scan mirror owe to its stability and low cost. The gap of the scanning spot can be regulated by means of adjusting the rotate speed and laser transmitting frequency depending on the detection range. Angle information from the encoder and the distance information are handled with FPGA. The rotating speed and the synchronization of system components are also controlled by FPGA. In addition, for multiple echo processing requirements, there is a new circuit design method proposed for dealing with multiple echo.In this paper, the laser scanner is integrated with these designed components and debugged. Preliminary realized the system of laser scanner with high repetition based on laser diode whose peak power is 30W, repetition frequency is from 1 Hz to 200kHz, pulse width is 12ns, and detect range is 200 miters.