Research On Key Technologies Of Fiber Optic Phased Array Coherent Lidar System

With the rapid development of modern radar stealth and infrared stealth technology,whether it is space-to-earth observation or air-to-ground target reconnaissance,all kinds of radars face severe challenges to infrared stealth targets.It is hoped that the development of a technology can solves the problem of long-range stealth target detection.In addition,in order to obtain long-range laser interference capabilities,it is urgent to develop a new high-power laser detection technology system that can cover a wide field of view and long distances.Fiber Optic Phased Array Coherent Lidar(OPA Lidar)has the advantages of high power,high detection accuracy and large field of view coverage.A new hot spot in the development of military technology.At present,there are still many difficulties and key technologies to be overcome in optical phased array lidar,among which the core problem is "the fusion of optical phased array technology and coherent lidar technology".Therefore,the research on fiber optical phase control technology and coherent lidar technology is carried out,and the shortcomings of their schemes are solved and performance optimization schemes are proposed to achieve high-performance far-field detection capabilities,and provide the development of mature new system lidar prototypes.Technical Support.This paper first analyzes optical phased array technology and coherent lidar technology from theoretical modeling,explores the principle of lidar detection,designs related hardware systems,optimizes each system scheme,improves the performance of the entire system,and conducts field experiments to verify and analyze.The main research contents of this thesis are summarized as follows:A microchannel heat dissipation structure model based on the bionic topology method is constructed.In view of the high heat flux density of high-power optical phased array antenna,the heat dissipation performance is poor,and the heat concentration damages the components,a micro-channel topology heat dissipation structure is proposed.Various types of microchannel topologies are designed,and the heat dissipation performance and the internal flow characteristics of the microchannel are simulated and analyzed.Among them,the leaf vein-type microchannel topology has the best heat dissipation performance.The phased array antenna has a heat flow of 2 kW/m2.The temperature is lowered to 25.7°.Based on the basic theory of convective heat transfer and fluid mechanics,the heat transfer principle of the new microchannel structure is studied,and the influence of its specific parameters on the heat dissipation performance is analyzed.By optimizing the design of the microchannel structure parameters,the optimal performance of the microchannel heat dissipation topology is obtained,which provides technical support for the design of the optical phased array heat dissipation structure in the future.A structure optimization method for optical phased array performance is proposed.Considering that the grating lobe problem of the main beam of the optical phased array has a great influence on the detection accuracy of the far-field target,a design method based on the genetic algorithm to optimize the array element spacing is proposed for the grating lobe suppression of the optical phased array.For the classical genetic algorithm(GA),it often falls into the local optimal solution.The crossover method is improved,and the spacing of optical phased array elements is optimized.The optimized unequal spacing array has the effect of suppressing grating lobes.obvious.Using this optimization algorithm,the grating lobe suppression effect of the multi-beam array based on sub-aperture(SA)is mainly discussed,and the grating lobes under different beam steering angles are compared,which is an important factor for the optical phased array coherent lidar system.Parameter design and performance optimization provide the basis.The verification method of optical phased array technology results is discussed,and the fiber optical phased array beam control technology is verified.Aiming at the far-field beam shift caused by the phase jitter of each beam in the optical phased array caused by thermal noise and mechanical vibration in the optical fiber,the beam phase locking control technology of SPGD algorithm is used to improve the energy concentration of the target surface and improve the contrast of the center fringe.A set of one-dimensional and two-dimensional beam scanning systems with wide field of view is 58°×32°and narrow beam steering angle of 0.98°.On the basis of the above theory,the optical phased array control mode is analyzed,and the flexible combination of the phase-locking period and the scanning period provides an important technical basis for the detection and tracking of the optical phased array coherent lidar system.The main technical problem in the OPA-based coherent lidar detection system is to estimate the far-field target information from the backscattered signal of the modulated laser emitted by the optical phased array antenna.It involves the mixing of the local oscillator light signal and the echo signal light on the surface of the detector,the alignment and field matching of the two plane waves are analyzed,and the influence of the plane wave misalignment on the coherent detection technology is analyzed.Beam coherence structures can reduce spatial alignment requirements.Aiming at the extraction of noise and clutter interference target information parameters in the backscattered echo signal of the target,matched filtering is used to denoise the echo signal,and then Fourier transform is performed to obtain the target information.Using the beam control technology of the optical phased array to detect targets within 2km the detection field of view,the target can be tracked.