Investigation On Subwavelength Pixelated Linear And Full Stokes Micropolarizer Array

As one of the basic attributes of light, polarization contains many characteristic information of objects. With the development of imaging technology, polarimetric imaging technology that combines polarization detection and imaging has been increasingly important in target recognition and detection. In this thesis, a pixelated linear micropolarizer array based on subwavelength double-layer metallic grating in IR band(3μm-5μm) and a pixelated full-Stokes micropolarizer array near-infrared band(1.6μm) are proposed and investigated. Based on equivalent medium theory and finite difference time domain numerical method, characteristics of polarization transmission of the devices are obtained. The main results are as follows:(1) Theory, design method and experimental fabrication of a subwavelength polarizing metallic grating have been conducted. A double-layer metallic grating with transition layer has been designed with optimized parameters using time domain finite difference numerical method. Simulation results indicate that both high TM transmission efficiency(TMT, >89%) and extinction ratio(ER, >58d B) can be simultaneously obtained with the designed double-layer metallic grating in which the tolerance of the structural parameters on the performance of the device is relaxed and the fabrication difficulty can thus be lowered. Based on the designed parameters, a pixelated double-layer multi-orientation(0°, 45°, 90° and 135°) micro-grating(period 300nm) array is fabricated with laser direct writing technique. The performance of the fabricated linear polarizer is measured in that TMT efficiency is higher than 46% and ER is higher than 23.8d B.(2) A novel pixelated full Stokes polarimetric imaging device by integrating metallic linear polarizers and metallic chiral circular polarizers on a single silicon chip is proposed and demonstrated numerically. The micro linear polarizers collect linear polarizing information of different orientations while the chiral metallic circular polarizers collect left-handed or right-handed circular polarization information so that full Stokes polarimetric imaging can be implemented on a single chip in real time. In the device, it is emphasized that the structure of the linear polarizers and the circular polarizers are compatible so that they can be fabricated on the same platform and the same process. Effects of different parameters on the performance of the circular polarizer are investigated numerically and the optimized parameters are obtained. Numerical results show that the ER of linearly polarization can reach 56 d B with TMT being 85%, and the dichroism of left-handed and right-handed circular polarization can reach 56% at a wavelength of 1.6μm.