Study Of Fourier Transform Hyperspectral Polarization Imaging

Fourier transform hyperspectral polarization imaging technology is a combination of space imaging,spectral measurement and polarization measurement.Four Stokes polarization vectors at each spatial position of the target can be obtained with nanometer spectral resolution.Because this technology can accurately characterize the multi-dimensional physical and chemical characteristics of the target,it is considered as a new breakthrough in the field of optical measurement.The research of this technology is of great significance and application value in the fields of remote sensing,military reconnaissance,planetary exploration,biomedicine,food safety,fine agriculture,environmental monitoring and cultural relics protection.In the process of synchronous fusion detection of spatial information,spectral information and polarization information,traditional schemes often lose the resolution in time domain,space domain or frequency domain,and it is difficult to achieve effective high-resolution measurement of highdimensional optical information.In order to achieve high-efficiency and high-resolution Stokes vector hyperspectral imaging measurement,a scheme of Fourier transform hyperspectral polarization imaging technology based on birefringent shearing interference and high-speed polarization modulation of ferroelectric liquid crystal(FLC)is proposed in this paper.The main research contents are organized as follow.The principle of birefringent shearing interference,liquid crystal polarization modulation and polarization spectrum demodulation involved in the presented method are described.On the basis of describing the system structure of Fourier transform hyperspectral polarization imaging,the model of optical path and the principle of shearing interference are discussed.Then the basic theory of spectrum and polarization measurement is described,including Fourier transform spectroscopy and Stokes polarization measurement technology.The principle of information modulation and demodulation for hyperspectral polarization measurement based on four-fold sampling is deduced.These basic principles of optical measurement can provide abundant theoretical guidance for the research of the proposed technical scheme.In order to solve the non-linear distribution of optical path difference(OPD)and the difference of total OPD of traditional birefringent interferometer,we present a compact birefringent interferometer,which consists of a shearing plate and a compensation plate.The shearing plate is used mainly to generate an OPD associated with the field of view for broadband interference.By compensating for the constant term OPD and the square term OPD of the shearing plate,the compensation plate can adjust the position of the zero-order fringe pattern and suppress the inconsistent total OPD.Formulas for the optical path difference(OPD)produced by the proposed birefringent interferometer are derived by the ray-tracing method.On the basis of the correlation between the OPD distribution and the parameters of the optical elements,the distribution characteristics of the OPD are analyzed in detail.According to the mechanism of Fourier transform spectral imaging,the theoretical relationship between the parameters of the interferometric imaging system and the design parameters is established.And then the optimal parameters combination of the birefringent shear interferometer is optimized by the design parameters.To suppress the reduction of time resolution,spatial resolution and spectral resolution introduced in the process of merging the traditional polarization modulator and hyperspectral imaging module,a high-speed polarization modulator based on FLC is proposed.Through the high-speed switching characteristic of the fast axis azimuth of FLC,the fast acquisition of all Stokes polarization vector is realized.The fast modulation mechanism of wide-band Stokes polarization information based on FLC is demonstrated.The wide-band optimization design method of liquid crystal polarization modulator is studied.According to the phase-delay characteristics of FLCs and retarders,the polarization measurement matrix of the system is derived.Under the constraint of the minimum condition number of the matrix,the optimal parameters are obtained by genetic algorithm.In order to extract the high-precision interference polarization signal in the window scanning mode,a fast method of sub-pixel interference image registration based on phase correlation method is studied.This method can improve the efficiency of image registration with the local up-sampling operation.Due to the dispersion effect of the birefringent interferometer,adopting a conventional Fourier transform directly in the spectral reconstruction process causes a deviation of the wavelength position.To solve this problem,the wavelength position of the restored spectra is corrected by the wavenumber sampling equation in optical path squeezing interferometry.A matrix calculation method based on singular value decomposition(SVD)is studied to improve the robustness of polarization measurement.The principle device of hyperspectral polarization imaging was developed according to the theoretical analysis and high-precision alignment.The wavelength calibration,radiation calibration and polarization calibration of the principle device have been completed.Using the calibrated device,the measurement experiment of broadband light source and imaging experiments are carried out.A series of experimental results which accurately indicate the spectral and polarization characteristics of the imaging target are obtained.So that the natural and military targets can be identified accurately with the proposed method.Finally,the sources of measurement error are analyzed.The results demonstrate that the proposed method offers much promise for spectropolarimetric measurement with the advantages of high efficiency and high resolution measurement of hyperspectral polarization imaging.Therefore,this method has reference significance for the development of high-dimensional information measurement.