Research On Four-quadrant Detection Technology Based On Coherent Detection

With a series of excellent performance and characteristics such as high working frequency,narrow beam,high resolution,and non-contact measurement,laser radar has obvious technical advantages in high-precision wind field measurement.The laser radar is divided into two systems,coherent and non-coherent.For different applications and measurement requirements,these two systems have their own advantages and disadvantages,and they can complement each other.The detection sensitivity of coherent lidar is close to the quantum noise limit and has a higher signal-to-noise ratio.Compared with direct detection,lower laser emission power is required.However,it does not match the increasingly sophisticated speed and distance measurement capabilities of the coherent detection radar,which has not yet developed an ability to accurately loc ate targets.Therefore,this article tries to use a method commonly used in spot positioning —fourquadrant detection method to locate the signal light echo spot of coherent lidar.The main work content is as follows:First,it introduces the research backg round and significance of the subject,the current status and analysis of lidar research at home and abroad,the main research content and structural arrangement.Secondly,the principle of the four-quadrant detector and the principle of coherent detection are analyzed.The basic demodulation algorithm of four-quadrant detection-addition and subtraction algorithm,and the influence of spot size,detector noise and dead zone of four-quadrant detector on the accuracy of four-quadrant detection are introduced.And analyze the basic principle of coherent detection and its signal-to-noise ratio,and make a simple comparison with the direct detection method.Then,the optical receiving part and the spot position data detection and processing part of the four-quadrant detection system based on coherent detection are designed.The idea of converting the photodetector into a coupling lens is proposed,modeling and simulation are carried out,the field of view of the system is analyzed,and the spot position is compare d with the traditional method of directly using a four-quadrant detector to demodulate the spot position.It is concluded that the system can effectively detect the spot position.In addition,the received echo signal strength was estimated by the radar equation,and the subsequent I/V conversion,voltage amplification and voltage signal processing procedures were discussed using the estimated data,and a simple design of the basic amplifying circuit was made.Finally,the optical path of the confirmatory e xperiment was built.The field of view of the system was calculated by measuring the divergence angle of the light beam and drawing the oscilloscope voltage-light position and distance curve of the lens array,and the result was close to the simulation.After introducing the local oscillator light to generate the beat signal,the spectrum analysis was carried out,and the addition and subtraction algorithm was used to demodulate the spot position,which verified that the system can basically realize the cal ibration of the spot position.