Optical Design Of Airborne Large Field Of View Wide Band Polarization Spectral Imaging System Based On PSIM

Polarization is another one-dimensional optical information of a target beyond geometry,intensity,spectrum,and radiation.Polarization Spectral Intensity Modulation(PSIM)technology can achieve full Stokes vector and spectral information snapshot imaging of target object optical signals,improving the amount and accuracy of data for obtaining target optical information.It has broad application prospects in various fields such as aerospace,national defense,military,agriculture,forestry,and animal husbandry;Equipped with polarization remote sensing payload of small and mediumsized unmanned aerial vehicles,it has the advantages of flexibility,long range,and can meet the application needs of obtaining polarization spectral remote sensing data of ground object targets in most environments.It is one of the development directions of future aviation multi-source remote sensing.However,the existing polarization spectral imaging systems currently have problems such as narrow working spectral range and small field of view angle,which cannot meet the requirements of airborne remote sensing detection for work efficiency,wide working band,and large angle polarization imaging.Therefore,this article completes the following work from the perspectives of application indicators,system optical scheme design,and engineering implementation:Firstly,the development status of polarization spectral imaging technology at home and abroad was investigated,and the relevant theories of polarization spectral imaging technology were elaborated.The modulation principle,restoration method,and thickness design of multi-level bands of intensity modulation polarization spectral imaging technology were analyzed in detail,providing theoretical basis and technical guidance for subsequent optical system design work.Secondly,based on the application requirements of a certain airborne polarization imaging spectrometer,a detailed analysis of the indicator parameters,optical system structure selection,and detailed design of the polarization imaging spectrometer were completed.To meet the requirements of a large field of view,wide spectral range,and low polarization sensitivity of the system,a transmissive front telescope group is designed and selected;In order to meet the requirement in the PSIM module that the angle of incidence of the multi-stage wave plate is less than 5 °,an anti telephoto structure is adopted for the design of the telescope objective,and the integration design of the pre telescope system and the post spectrometer system is considered,so that the polarization spectrometer telescope objective system reaches the centroid of the image;A method for selecting achromatic glass based on band division Abbe number variation was proposed based on achromatic theory to address the problem of large color difference in large field of view and wide spectral transmission systems.Based on this,the optical design of the front telescope system was completed.The results show that the primary color difference of the system has been effectively balanced and corrected, and the color focal shift is less than twice the focal depth.Good imaging with an Fnumber of 4 and an MTF value above 0.4 at a cut-off frequency of 55lp/mm has been achieved,meeting the application requirements.The splitting method of the post spectrometer system is achieved by using a convex grating.Considering the long slit and wide band of the system,a correction lens correction structure is introduced to reduce the spectral line distortion and bending of the system.The design results are comprehensively evaluated using point plots,optical transfer functions,and other methods.The results show that the spectrometer system has good imaging performance,and the spectral line distortion is less than 5% pixels,which makes the Spectral resolution meet the index requirements of polarization spectral restoration resolution.Finally,the integrated optimization design was carried out after docking the front telescope system with the rear spectral splitting system.The polarization effect of the weak polarization components in the system was analyzed using polarization ray tracing method,and the polarization preserving optimization of the optical system was carried out.The overall performance of the system was evaluated using optical transfer function MTF,point plots,aberration curves,etc.The polarization effect analysis and evaluation of the polarization imaging spectrometer were carried out to complete the tolerance of the system Engineering research on stray light and temperature adaptability analysis.The final results show that the Spectral resolution of the system is 1.5 nm,the diattenuation at the central wavelength is reduced by 37%,the retardance is reduced by61%,and the polarization maintaining effect is significant.The MTF value is higher than 0.4 at the cut-off frequency,the RMS size is less than one pixel,the image illumination uniformity is greater than 0.8,and the edge field distortion is less than 12%.The optical system has excellent image quality.This design result can be used as an optical model for the development of a prototype of polarization spectral imaging principle with a wide field of view and spectral range.