A design of real-time unipath polarization imaging system based on Wollaston prism

Abstract

A real-time polarization imaging system employing the Wollaston prism and a single charge-coupled device(CCD) chip covering a wavelength range of 400 nm-650 nm is proposed to avoid the false polarization information from dynamic scenes in non-real-time polarization detection imaging method. An architecture consisting of telescope lens, collimation lens, Wollaston prism, the imaging lens and a single CCD chip is employed in the system. The telescope lens is used to focus the incoming light on an intermediate image. And after collimation, the beam is angularly separated by the Wollaston prism. Two beams corresponding to ordinary light and extraordinary light are subsequently focused on the CCD plane via the imaging lens. The telescope lens is designed to have a telecentric structure in the imaging space, and the invert of which is used as the collimation lens, the completely symmetrical structure design is used to reduce the influence of aberrations. More abundant details from this system can be obtained by using matched image post-processing strategy, which is beneficial to high-quality target detection with enhanced working distance and improved environment adaptability. After joint-designing and optimization, the system modulation transfer function (MTF) value at cut-off frequency is higher than 0.55, and the root-mean-square (RMS) radius of the system is less than 5.3 m, which is smaller than the pixel size of the CCD detector. Additionally, the lateral chromatic aberration of the system is much smaller than the diameter of airy disk, and the absolute values of all kinds of aberrations are kept smaller than 0.02 at the same time. The calculation results show that all the aberrations are mostly corrected. The system imaging is numerically modeled and analyzed, and it is demonstrated that two intensity images with perpendicular polarization states appear adjacently on the CCD plane simultaneously in the imaging simulation. One image is formed with the fraction of the backscattered light polarized parallelly to the incident light, and the other with light polarized orthogonally to the incidence, indicating that the expected design is accomplished. Compared with the traditional amplitude-split polarization imaging system, the proposed real-time polarization imaging system shows that the improved performance for real-time detection with promoted power efficiency, spatial resolution, and the light crosstalk in focal plane is well handled. Moreover, the joint design of the whole system can compensate for the distortion aberration in the vertical direction of the CCD detector, which means that a further improvement of image quality can be expected. The proposed system has a promising perspective in the fields of underwater imaging detection, astronomical observation, remote sensing, biological tissues inspection, and environmental monitoring.