Linear Frequency Modulated Continuous Wave Laser Radar Based On Beat-Frequency Method

The laser ranging technique develops rapidly and its application areas have been continuously expanding.At present,it has been widely used in military and civil areas.In the military it can be used to measure the trajectory of various flying target,such as the tracking to the initial segment of rockets and missiles,the precise satellite orbit determination and so on.Meanwhile the laser ranging radar combines with the infrared system,television and other photoelectronic devices and can form the fire control system of ground,shipborne and airborne.The system can complete the search,recognition,tracking and measurement of the object.This paper studies the linear frequency modulated continuous wave laser radar and demonstrates a frequency modulation continuous wave laser radar system based on beat frequency method.At first the paper analyzes the principle of linear frequency modulation laser ranging technique.By analyzing all of the factors that affecting the precision of ranging,the paper puts forward the optimized plan of linear frequency modulation continuous wave laser ranging system.The diode laser is modulated by its current directly to reduce cost.The beat method is used to reduce the demands for the photoelectric detector and increase the accuracy.Then the ranging system is built experimentally.The beat signal of the response signal and the reference signal are received by the APD photoelectric detector designed independently.In the range of 22.5 GHz,the linear continuous frequency modulation of DFB 852 nm semiconductor laser has been got by using a homemade frequency discrimination optoelectronic feedback loop.The coefficient of frequency modulation is 1.50 THz/s by analyzing the hyperfine spectrum of Cs ground states,by means of the beat signal between the echo from 2 meter far object and the reference,the beat spectrum with 30 Hz bandwidth is obtained at 19.3 KHz experimentally,and the measured spatial resolution is about 3 mm which is better 3 times than the result without frequency discrimination optoelectronic feedback loop.The experiment also realizes the measurement of two objects simultaneously by the beat technique.This article studies on the linear frequency modulation laser ranging technique in the displacement sensor of laser radar and realizes the high precision measurements on static medium distance.The results can be used as a reference on the research of linear modulated laser radar.