The Research On High-accuracy Hyper-spectral Full-polarization Imaging Based On Acousto-optic And Liquid Crystal Variable Retarder

Hyper-spectral full-polarization imaging is a technology of obtaining the information on spectrum,polarization and space simultaneously.Therefore,the hyper-spectral full-polarization imaging detection technology has a great application prospect in fields of space exploration,remote sensing,environmental detection,biomedicine,chemical analysis,industry & agriculture and astronomy.The paper proposes a hyper-spectral full-polarization imaging detection method based on acousto-optic tunable filter(AOTF)and liquid crystal variable retarder(LCVR).The AOTF is used as a spectral element,and the LCVR is used as a polarization modulation element.Various factors of studying the system measurement and their correction method are the important scientific problems that must be solved and are also the key to high-accuracy measurement.In particular,the AOTF diffraction spreading leads to loss of resolution.Different incident angle leads to uneven spectral distribution in an image and inaccurate polarization measurements.The AOTF spectral drift causes a drop in accuracy in wide temperature range conditions,and the chromatic aberration of optical system design results in poor image quality.In this paper,factors affecting the system measurement accuracy are analyzed theoretically based on the AOTF and double LCVRs,and correction strategies are proposed.Two hyper-spectral full-polarization imaging prototypes(visible and near-infrared)have been designed.Firstly,the hyper-spectral full-polarization imaging principle is studied based on the AOTF and double LCVRs.The measurement principle is derived in detail.All four elements of Stokes parameters S=[I,Q,U,V]T are measured.The effects of the polarization measurement are analyzed and simulated due to phase retardation deviation.The principle verification experiment of the spectral polarization measurement is constructed.And the feasibility is verified.Secondly,factors affecting the system measurement accuracy are studied,and correction strategies are proposed.Theoretical derivation: the fundamental reason of the AOTF spectral spread is the spread of acoustic wave angles.And the Domain Estimation-Recursive Correction algorithm is proposed to solve this problem.The experimental results show that the proposed algorithm is effective.The unevenspectral distribution in an image is analyzed and corrected.The corresponding relationship between the incident angle and the wavelength at the pixel of the area array detector is obtained by theoretical analysis and experimentation.The experimental results show that the modified spectral measurement error than traditional AOTF spectral imaging measurement error reduced an order of magnitude.The spectrum is corrected by non-linear fitting of experimental data.The influence of incident angle on polarization measurement is studied and corrected.In order to solve AOTF temperature-drift problem,the wavelength temperature-drift correction methods have been proposed by changing drive frequency of the ultrasonic.Thirdly,the wide spectral achromatic optical systems are designed to be suitable for the use in spectral polarization imaging systems.To meet the needs of the above correction strategy,an improved imaging optical system is designed.The front optical system compresses the target field of view within ±3 o,and this is to fit the AOTF field of view angle.The area array detector is placed at the focal point of the rear imaging lens.The overall optical systems are optimized by Zemax simulation software,so that they achieve the purpose of achromatic.This eliminates the need for focusing and enables clear imaging at different wavelengths.And the achromatic and imaging quality of the optical system are verified by experiment.Finally,two hyper-spectral full-polarization imaging prototypes(visible and near-infrared)have been designed.According to characteristics of each band component.The respective prototypes are organized.The 110 spectral channels can be detected in the visible range,and the 70 spectral channels can be detected in the near infrared range.The spectral full-polarization imaging verification experiments are performed by the polarizers and wave plates.Combined with the polarization characteristics of the sky,the prototypes are tested in the field to verify their feasibility and practicability.