Hwang Jehwan, Ku Zahyun, Jeon Jiyeon, Kim Yeongho, Kim Deok-Kee, Kim Eun Kyu, Lee Sang Jun
Interdisciplinary Materials Measurement Institute, Korea Research Institute of Standards and Science, Daejeon 34113, Korea.
Department of Physics and Research Institute for Convergence of Basic Sciences, Hanyang University, Seoul 04763, Korea.
Sensors (Basel). 2020 Sep 20;20(18):5382. doi: 10.3390/s20185382.
Infrared (IR) polarimetric imaging has attracted attention as a promising technology in many fields. Generally, superpixels consisting of linear polarizer elements at different angles plus IR imaging array are used to obtain the polarized target signature by using the detected polarization-sensitive intensities. However, the spatial arrangement of superpixels across the imaging array may lead to an incorrect polarimetric signature of a target, due to the range of angles from which the incident radiation can be collected by the detector. In this article, we demonstrate the effect of the incident angle on the polarization performance of an alternative structure where a dielectric layer is inserted between the nanoimprinted subwavelength grating layers. The well-designed spacer creates the Fabry-Perot cavity resonance, and thereby, the intensity of transverse-magnetic I-polarized light transmitted through two metal grating layers is increased as compared with a single-layer metal grating, whereas transverse-electric (TE)-transmitted light intensity is decreased. TM-transmittance and polarization extinction ratio (PER) of normally incident light of wavelength 4.5 μm are obtained with 0.49 and 132, respectively, as the performance of the stacked subwavelength gratings. The relative change of the PERs for nanoimprint-lithographically fabricated double-layer grating samples that are less than 6% at an angle of incidence up to 25°, as compared to the normal incidence. Our work can pave the way for practical and efficient polarization-sensitive elements, which are useful for many IR polarimetric imaging applications.
红外（IR）偏振成像作为一项在众多领域颇具前景的技术已受到关注。通常，由不同角度的线性偏振器元件加上红外成像阵列组成的超像素，通过利用检测到的偏振敏感强度来获取偏振目标特征。然而，由于探测器能够收集入射辐射的角度范围，成像阵列上超像素的空间排列可能会导致目标的偏振特征不正确。在本文中，我们展示了入射角对一种替代结构偏振性能的影响，该结构在纳米压印亚波长光栅层之间插入了一个介电层。精心设计的间隔层产生了法布里 - 珀罗腔共振，因此，与单层金属光栅相比，透过两个金属光栅层的横向磁I偏振光的强度增加，而横向电（TE）透射光强度降低。作为堆叠亚波长光栅的性能，波长为4.5μm的垂直入射光的TM透过率和偏振消光比（PER）分别为0.49和132。与垂直入射相比，纳米压印光刻制造的双层光栅样品在入射角高达25°时PER的相对变化小于6%。我们的工作可为实用且高效的偏振敏感元件铺平道路，这些元件对许多红外偏振成像应用都很有用。
