A new technique of full polarization hyperspectral imaging based on acousto-optic tunable filter and liquid crystal variable retarder

Abstract

In order to achieve all Stokes parameters of spectral image with high spectral resolution, high spatial resolution, high polarization accuracy, high signal-to-noise ratio and good stability, taking into account the orthogonal characteristic of ±1 order diffraction light which diffracts from a acousto-optic tunable filter (AOTF), a new technique of full polarization hyperspectral imaging is presented. It uses one AOTF to diffract the incident light, one liquid crystal variable retarder (LCVR) to modulate the light retardation, and two CCDs to image the ±1 order diffraction light, respectively. According to the Muller matrixes of all optical elements in the system, the basic working principle of the new technique is that LCVR sequentially provides the retardation 2π, 1.5π, π and 0.5π for each spectral channel, so the CCD obtains corresponding images. After analyzing these images, the all Stokes parameters are obtained; the precision of this system for polarization imaging is determined mainly by polarization modulation device LCVR. Considering the azimuth of LCVR fast axis and retardation precision at the same time, it is unveiled that LCVR has no effect on the accuracy of the first Stokes parameter, and the relative errors of other latter 3 Stokes parameters are less than 0.064%, 0.31% and 3.97%; then, our prototype system is used to do the outdoor experiments in a summer sunny morning, images data for 26 spectral channels with spectral bandwidth of 10 nm, which are from 450 nm to 700 nm, are acquired, the imaging quality is very fine. Firstly, LCVR are not assembled in our prototype system, and AOTF works in the sweeping frequency mode. The spectrum from each CCD proves that the diffraction efficiency of AOTF ± 1 order diffraction light is not completely the same, and the difference must be considered in polarized image processing. Then another experiment is done after LCVR has been assembled. The image data of the incident light of 600 nm are taken for example to discuss its all Stokes parameters in detail. The results show that the principle of the new technique is correct and the new scheme is feasible. This study provides a new theory and implementation scheme for the polarization spectral imaging technology.