| Laser Ranging technique, particularly, phase-laser ranging technique, is widely used in distance measurement with high precision, available in day and night, and reliable, and is widely used in the engineering measurement. Normally, phase-modulated laser ranging uses a continuous light wave signal for the launch system, by frequency mixing, and automatic phase measuring technique, measuring "modulated waves". Based on the phase difference between the reflected signal and the local emitting signal, the unknown distance can be obtained. However, the light wave with continuous waveform modulation is easily changed in the transmission, and with the increase in modulation frequency, modulation depth will be reduced, especially at high frequencies; Compared with the pulsed laser ranging, continuous light modulation has large power consumption, and can not be used in the long distance situation. In order to overcome the drawbacks of continuous light wave Modulation, we propose a pulse-modulation scheme.In this method, the constant periodic pulse modulation of laser light waves is used, instead of continuous modulation laser light wave. The pulse position represents the zero position of continuous modulated signal, and the amplitude and width of the laser light pulse remain unchanged. Therefore, when the laser power is unstable, the intensity variation of the laser pulse will not affect the phase information of the modulation signal. In this paper, based on DDS frequency synthesis technology and the design theory of the high-frequency circuit, a pulse-modulated laser ranging system has been designed, the relationship between a continuous high-frequency sinusoidal signal and the same frequency of pulses(square wave) signal is analyzed. By use of CPLD-based digital phase detection technique the signal processing system is made.It is expected that this method could be used in the space laser communication, high-precision, long-range laser ranging on non-cooperative targets. |
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