Research On Key Techniques Of Optical System Distortion Measurement Based On Laser Beam Splitter

With the continuous development of aerospace mapping technology and the growing demand for aerospace mapping,the measurement accuracy requirements for mapping camera systems are becoming higher and higher.Distortion is a key factor affecting the positioning accuracy of mapping cameras,and thus research on its high-precision measurement methods has also received increasing attention.On one hand,through the early optimization design to ensure that the distortion of the optical system is as small as possible,on the other hand,errors will inevitably be caused during the installation and adjustment of the optical system,which causes the system distortion to be different from that in the design.Therefore,the high-precision measurement and correction of distortion directly affects the measurement accuracy of the mapping camera system.This paper mainly studies how to measure the distortion of the optical system with high accuracy,there are mainly two traditional methods of distortion measurement for mapping camera systems.One is to use collimator to simulate object points at infinity.After passing through the optical system,the object points are imaged on the image surface.The precision turntable then drives the camera lens to rotate,and thus the distortion of the system can be calculated according to the positions of the corresponding image points at different FOV.This method is called the star point method;The other one is called precision angle measurement,which measures distortion by measuring the field of view of the system corresponding to the actual image height at the image plane of the camera system.The actual image height is aided by a high-precision grid plate.The angle is measured by using a high-precision turntable.Both of the two methods require a large-size and high-precision turntable,thus the measuring cost is relatively high.What’s more,because the distortion of all FOVs cannot be measured at the same time,the measurement will take a long time to complete,and the measurement efficiency is low.Furthermore,the two method is based on the time domain,the results are more susceptible to interference.The laser beam splitter(LBS)is a special diffractive optical element(DOE)that can output multiple beams with the same mode as that of incident light.Due to this characteristic,LBS has a very wide range of applications in the fields of laser sensing,laser optical communication,spaceborne lidar mapping,and parallel manufacturing,especially in face recognition,which has emerged in recent years.The application value of the LBS is more prominent.Under the above background,this paper proposes the measurement of optical system distortion based on LBS.The LBS is used to generate multiple beams with different angles at the same time,and it is not necessary to use the turntable to perform distortion measurement like the traditional method,thereby greatly reducing the measurement cost,improving the measurement efficiency,and avoiding the effect on the measurement result in time domain.The proposed method has simple and efficient advantages.Aiming at the requirement of high-precision distortion measurement for high-accuracy FOV,an innovative method for high-precision calibration of the beam splitter angles of the LBS by using a self-collimator was proposed.The measuring optical path of a coaxial optical system based on the LBS was set up,and a two-dimensional measurement model of distortion was established to realize high-precision measurement of distortion.In addition,for the measurement of the distortion of the large-aperture optical system,the feasibility of using a small-sized LBS for measuring large-aperture optical system is analyzed,which provides a theory and technical support.In this paper,the following aspects are studied for the technology of optical system distortion measurement using LBS:1.The development of distortion measurement technology for optical systems is reviewed,and the traditional principles and methods for distortion measurement of mapping camera systems are introduced.The shortcomings of existing measurement technologies are analyzed,and the current application status of LBSs is introduced.Based on this,a method for measuring the distortion of optical systems based on LBS is proposed,and the advantages of this method are discussed.The design principle and manufacturing method of the LBS are studied,and the feasibility of the method is initially verified by simulating the transmission characteristics of the LBS.2.Aiming at the requirement of high accuracy of the FOV in the distortion measurement,a method of high-precision calibration of the beam splitter angle of the LBS by using a self-collimator is proposed.Based on the measuring principle of the self-collimator,an external source is innovatively adopted to achieve the calibration of the beam splitting angle of the LBS.The error sources affecting the measurement results are theoretically analyzed.On the premise of avoiding the measurement error,the two-dimensional angular distribution of the LBS with 9×9 and 5×5 beam splitters was achieved,and the uncertainty analysis was used to verify that the method can achieve high-precision angular calibration for LBS.3.The principle verification experiment of the optical system distortion measurement based on the laser beam splitter was designed and completed.Based on the completion of the 9×9 LBS angle calibration,an optical path for measuring the distortion of a coaxial optical system using a 9×9 LBS was constructed,and the influence of errors on the measurement results was analyzed.On the premise that the errors are suppressed to be negligible,data processing is performed on the collected spot array,and the spot centroid extraction algorithm is used to quickly extract the centroid position of each spot,and a two-dimensional measurement model of distortion was established,and then the distortion coefficient in the corresponding FOV was calculated.In addition,the measurement uncertainty of distortion was analyzed and calculated to prove that this method can achieve high-precision distortion measurement.4.From the theoretical and simulation point of view,the feasibility analysis is performed on measuring the distortion of large-aperture optical system based on LBS,i.e.,measuring big with small method.Considering the errors introduced by measuring big with small method.The influence of primary aberrations on the distortion measurement of an optical system is analyzed,the wave aberrations of an off-axis three-reverse system after adjustment are measured,and the influence of wave aberration on system distortion measurement was simulated and analyzed.In addition,the relationship between image plane adjustment error and system distortion detection accuracy is deduced theoretically.The simulation results show that by properly selecting the size of the LBS,it is possible to meet the requirements of distortion measurement accuracy.This provides theoretical and technical guidance for the application and realization of LBS in the measurement of large-aperture optical systems.In this paper,the research of the optical system distortion measurement technology based on LBS,from the proposed measuring theory,the feasibility verification of the preliminary simulation,to the design and manufacturing of LBS,error analysis,angle calibration of LBS,principle verification of optical system distortion measurement with LBS step-by-step,and the feasibility analysis of future LBS for distortion measurement in large-aperture systems,which lays the foundation for the LBS to be better applied to the measurement of mapping optical systems.