Principles and simulation of spectropolarimetirc imaging technique based on static dual intensity-modulated Fourier transform
Authors: Yu Hui  , Zhang Rui  , Li Ke-Wu  , Xue Rui  , Wang Zhi-Bin  ,   School of Science, North University of China, Taiyuan 030051, China;,   School of Information and Communication Engineering, North University of China, Taiyuan 030051, China;,   Engineering and Technology Research Center of Shanxi Province for Opto-electric Information and Instrument, Taiyuan 030051, China;,   Key Laboratory of Electronic Measurement Technology, North University of China, Taiyuan 030051, China
Published: December 2020

Traditional imaging spectropolarimetry generally requires slit, moving parts, electrically tunable devices, or the use of micropolarized arrays. Furthermore, the acquired raw data are a physical superposition of interferogram and image. Given their complicated structure, poor seismic capacity, low detection sensitivity, and heavy computations with approximation in spectral reconstruction, meeting the needs for applications in aviation, remote sensing, and field detection is difficult. To overcome these drawbacks, a new spectropolarimetric imaging technique based on static dual intensity-modulated Fourier transform is presented. The system consists of a front telescopic system, two phase retarders, a linear polarizer, a Wollaston prism, a Savart polariscope, a linear analyzer, a reimaging system, and a charge-coupled device (CCD) array detector. The incident light is modulated through a module of polarization spectrum modulation, which consists of the retarders and the polarizer. The Wollaston prism splits the modulated incident light into two equal intensities, orthogonally polarized components with a small divergent angle. After passing through the interference module, which is composed of the Savart polariscope and the analyzer, then the reimaging system, two full-polarization interferograms, which are the superposition of background images and interference fringes, are recorded simultaneously on a single CCD. The pure target image and the pure interference fringes can be simply achieved from the summation or the difference of the two interferograms. Spectral and complete polarization information can be acquired by using the Fourier transform of the pure interference fringes. The principle and the configuration of the system are described here in this paper. The reconstruction processes of the target image and the full Stokes polarization spectra are theoretically analyzed and mathematically simulated. The results show that the system can availably separate background image from interference fringes of the target, achieving high-precision spectral reconstruction and effective extraction of the complete polarization information. Compared with the features of existing instruments, one of the salient features of the described model is to use the dual-intensity modulation, which can avoid mutual interference between the image and the fringes from the hardware and is conducive to the extraction of pure interference fringes with high signal-tonoise ratio (SNR). With this feature, the inadequacies on traditional spectral reconstruction, such as large computation, heavy data processing, and low accuracy of acquired information, are overcome. Moreover, the entrance slit in the front telescopic system is removed, which greatly increases the transmittance and flux of the incident light and improves the SNR of the interferogram. The modified Savart polariscope is used in the interference module. Its transverse shearsplitting principle further enlarges the field of view and increases the spectral resolution of the straight fringes. Thus, this design has the advantages of good stability, high spectrum, high sensitivity, large SNR, high-precision information reconstruction, and low-complexity data processing, as well as simultaneous detection of image, spectrum, and complete polarization information. This work will provide an important theoretical basis and practical instruction for developing new spectropolarimetric imaging technique and its engineering applications.