基于通道调制的宽波段全偏振同时成像技术研究

Polarimetric Imaging has rapidly developed in recent years, and become a well recognized technique in remote sensing as a powerful tool for object detection and identification with preferable accuracy. However, in conventional imaging polarimeters, polarization analyzing optics such as, rotating polarization elements, electrically controllable and micro polarization components are typically used. These apparatuses generally suffer from vibration, heat generation, and poor temporal registration for rapidly changing scenes especially for remote sensing applications on moving platforms. In this program, a novel method for simultaneous measurement of complete polarimetric image in wide band is proposed. With specially aligned birefringent retarders and beamsplitters, different spatial phase factors are modulated on four Stokes parameters of the incident light. And then interfere. Because of the Fourier transform properties, the four Stokes parameters are divided into several independent channels in the frequency domain. Thus the complete polarization information can be obtained with a single snapshot. The bandwidth of the system is extended by compensating the wavelength items of the phase factors with birefringent diffractive elements. Key points of this program are focused on the mechanisms of the simultaneous modulation of the spatial phase factors, spatial-frequency domain transform and channels separation, and bandwidth extension, Light propagation in the key birefringent elements of the system, and the improving method of the detection accuracy, signal to noise ration of the system. This research gives a new way for simultaneous measurement of complete polarimetric image in wide band, and provides fundamental principle for the development of new space born polarimetric imaging sensors.

本项目针对目前偏振成像技术受探测原理限制，须机械旋转/电控调制或微型偏光元件阵列，稳定性差、抗振能力差、装调困难，无法探测动态目标，只能获取线偏振或窄波段全偏振信息等问题，从信息光学角度重新审视偏振成像，提出通道调制宽波段全偏振同时成像新方法。利用双折射晶体元件将不同的空间位相因子分别同时调制到代表入射光全偏振信息的4个Stokes参量上，并发生干涉，利用干涉数学上的傅里叶变换特性和空间位相因子频移性质，实现空域-频域转换，使各Stokes参量在频域上分离为数个独立通道，同时引入偏振衍射元件补偿各空间位相因子波长相关项，实现宽波段全偏振图像信息的同时获取。深入研究空间位相因子同时调制、空-频域转换与通道分离、波段扩展机理，核心双折射晶体元件光传输特性及其对成像质量的影响，系统偏振测量精度、信噪比优化等问题。增加系统偏振信息探测量、扩展工作波段范围，为宽波段全偏振同时成像开拓新的技术途径。

偏振成像技术是近年发展起来的新型光学遥感探测技术，世界各国非常重视偏振成像技术研究，发展了电控位相调制、分振幅、分焦平面等多种偏振成像方法。然而，随着空间光学遥感任务的日趋复杂，对地遥感、深空探索、军事侦察等任务需求的不断提高，现有偏振成像技术已很难满足未来发展要求。为此，项目提出并开展了基于通道调制的宽波段全偏振同时成像技术研究，旨在发展一种无运动/电控调制部件，能够同时获取目标全部偏振信息的宽波段全偏振成像技术。在项目研究期内，项目组在国际上首次提出了基于通道调制的宽波段全偏振同时成像方法，建立了探测及波段宽度扩展机理模型，给出了干涉-衍射波段补偿参数匹配关系；利用波法线追迹研究了双Wollaston棱镜偏振分束器内部光传输特性及其对干涉条纹的影响、系统视场角的限制；研究了偏振分束器、衍射元件、检偏器等偏振透过率及衍射效率等对系统光学效率、干涉调制度的影响；搭建了双Sagnac-grating干涉快照式宽波段全偏振成像原理样机，实现了400-700nm波段全偏振图像信息的快照式同时获取，实验测试Stokes参量S1、S2、S3测量精度分别为1.69%、3.65%和3.54%，部分成果在国际光学类著名期刊Optics Express上发表，并被选为Editor’s Pick论文。上述研究为宽波段全偏振同时成像提供新的技术途径；提高了仪器探测效率，为具有高空间分辨率、高灵敏度、高稳定度、实时探测等优点的新型空间光学遥感器开发提供基础理论与技术支持；增加了圆偏振成像能力，可扩展空间光学遥感设备工作范围，为地球资源普查（矿产、水资源、土壤与植被等），环境灾害预报与监测（海面浮冰、水涝灾害、沙尘暴等），大气气溶胶、卷云、冰晶云的探测，大气与水体污染（雾霾、海面溢油等）监测，深空探测与天体物理研究，军事侦察等领域提供新的信息获取手段。