Design And Fabrication Of Pixelated Nanoscale Gratings With Multi-orientations

With the development of nano technology,great progress has been made in nanophotonic science and technology,in which miniaturization and integration as well as functional extension and efficiency improvement of photonics devices can be realized.Polarimetric imaging technology that combines polarization detection and imaging has been increasingly important in target recognition and detection.In this thesis,a pixelated linear micro polarizer array based on subwavelength double-layer metallic grating in IR band(3?m-5?m)is proposed and investigated both theoretically and experimentally.Based on equivalent medium theory and finite difference time domain numerical method,characteristics of polarization transmission of the devices are obtained and experimental verification of the device is performed.The main results are as follows:(1)Theory and design method 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,>90%)and extinction ratio(ER,>60dB)can be simultaneously obtained with the designed double-layer metallic grating in which not only the TM transmission,but also the extinction ratio can be improved,and furthermore,no ion etching process is needed for the formation of metallic gratings.In addition,the tolerance of the structural parameters on the performance of the device in the double-layer metallic grating is relaxed when compared with conventional single layer metallic gratings and the fabrication difficulty can thus be lowered.(2)A pixelated double-layer multi-orientation(0°,45°,90° and 135°)micro-grating(period 280nm)array with a scale of 3203256 is fabricated with plasma enhanced chemical vapor deposition(PECVD),electron beam lithography(EBL),inductively coupled plasma-reactive ion etching(ICP-RIE)and E-beam evaporator.A measurement setup for the polarization behavior is built,and the performance of the fabricated linear polarizer is measured in that TMT efficiency is higher than 80% and ER is higher than 40 dB.The physical mechanism and possible reasons of the inconsistency between the experimental data and the simulation results are discussed and analyzed and the possible improved method is proposed.(3)Application of nano-imprint in high-efficient and high-yield fabrication of the proposed pixelated nanoscale gratings with multi-orientations is explored.Electron beam exposure lithography(EBL)and inductively coupled ion etching(ICP)were used to fabricate highly reusable silicon templates for nano-imprinting.of multi-oriented pixel nano-grating for high efficiency and success rate.Feasibility of fabricating the device by nano-imprinting technique is preliminarily verified.