半波片角度失配对通道调制型偏振成像效果的影响及补偿

通道调制型偏振成像系统能够实时地对目标进行全偏振成像,是当前偏振成像领域的研究热点之一.基于萨瓦板的通道调制型偏振仪中半波片的光轴方向对成像结果的准确性有较大的影响.本文分析了半波片失配角的大小对探测器采集到的光强分布的影响,得到了二者之间的表达式,根据该表达式提出通过测量半波片失配角对系统进行定标并利用测得的半波片失配角对偏振成像的解调结果进行修正和补偿的方法.计算机仿真结果显示失配角为0.5?时,S1,S2和S3的解调结果准确度在经过修正补偿后分别提高了0.06%,3.49%和3.49%.表明该方法能够较好地对解调出的偏振斯托克斯参数图像进行补偿,得到更精确的成像结果,对提高通道调制型偏振成像的质量具有重要的意义.

Effect of half wave plate angle mismatch on channel modulating imaging result and its compensation

Polarization imaging technology is a powerful tool in remote sensing, bioscience, or other scientific areas science, and it can extract the polarization information of target effectively. As a novel polarization imaging technology, the channel modulating polarization imaging has been widely investigated in recent years, owing to its prominent advantages of compact, snapshot and full-Stokes acquirable. In the polarization imaging system based on Savart Plate, a half wave plate with its optical axis at an angle of 22.5° is used to rotate the vibration direction of each incident light to ± 45°. Thus, the amplitude of the light could be equally divided by the second Savart Plate polariscope. Finally, the different components of light will interfere with each other on the focal plane and the target polarization information will be modulated in the interference pattern. Since the intensity distribution of interference pattern is sensitive to the orientation of the half wave plate, a small mismatch angle of half wave plate will lead to a wrong polarization image. In order to solve this problem, we investigate the relationship between the mismatch angle and the image intensity grabbed by focal plane array (FPA) and propose an error eliminating method to improve the accuracy of polarization imaging. We analyze how the mismatch angle α affects the light intensity and deduce the expression of the image obtained by the FPA. According to the expression, the raw image we grabbed directly by the FPA is a superposition of the modulated Stokes images with different carrier frequencies. Compared with the ideal expression, the expression we obtained shows that the channels of Stokes parameter S₁ and S_2,3 each contain a constant factor which is related to the mismatch angle α. On the basis of this expression, we propose a method to measure the mismatch angle by imaging a target twice, one is behind a polarizer that is oriented at 0° and the other at 45°. Then we can calibrate the system by calculating the mismatch angle through the demodulated images. To image a target with the calibrated system, we just demodulate the raw image obtained by the FPA and then divide the reconstructed stokes images by the constant factor which is determined by α. For a mismatch angle of 0.5°, a computer simulation is conducted. The result shows that through the compensation method, the accuracies of S₁, S₂ and S₃ can be increased by 0.06%, 3.49% and 3.49%, respectively.