A Study On Polarization Elements Of The Sub-wavelength Structure In Infrared Broadband

With the development of science and technology,the infrared detection and imaging technology is also improving.The traditional infrared detection technology applies the specific radiation intensity information of the object to distinguish it from the background and is recognized.Currently,the recognition ability and accuracy of this technology are very high.However,the traditional infrared detection technology will no longer be applicable in the case of complex background,such as the existence of noise sources with the same radiation information around the tested object.According to Kirchhoff Theory,objects will produce specific polarization information when they radiate electromagnetic waves.Therefore,when utilizing a polarization device to detect objects with the same radiation intensity,it can be distinguished according to the difference of the polarization information.The application of the polarization technology can enrich the information of the tested target and improve the recognition ability of the system.Therefore,the infrared polarization imaging detection technology has become a research hotspot in recent years.The sub-wavelength metal wire-grid polarization element possesses the advantages of s-mall size,wide range of working band,and large incident angle,which is especially suitable for the integrated optical circuit.In this way,it is of great significance to develop the metal wire-grid polarization elements so as to promote the development of infrared detection technology.At present,domestic and foreign researches on metal wire-grid polarization elements mainly focus on the design and improvement of the wire-grid structure,the manufacturing process of the wire-grid,the application and expansion of the device,etc.There are not many studies on the performance of the wire-grid substrates.In the optical system,the closer the refractive index of the substrate and air is,the higher the transmission efficiency of light is,and the better the performance of the device is.However,such substrates do not exist in practice.In order to solve this difficulty,the multi-layer antireflection film structure can be designed on the substrate,so that the effective refractive index after their combination is close to the theoretical value.At this time,the polarization performance of the element can be greatly improved by applying it to the design and preparation of the wire-grid polarization structure.This dissertation designed and prepared a single layer metal Al wire-grid polarization element with multi-layer antireflection film on the Si substrate and medium wave infrared3-5 ?m band.Firstly,the polarization elements without dielectric layer were optimized according to the Effective Medium Theory and the Rigorous Coupled Wave Theory,and the Finite-difference Time-domain method was applied to simulate the influence of various wire-grid parameters on polarization performance.Subsequently,according to the film design theory,the multi-layer antireflection film structure was designed on the substrate,and the influence of antireflection film on polarization performance was simulated and analyzed.For the wire-grid structure of the metal Al,p(the design parameter period)is 300 nm,h(height)is 100 nm,and f(duty ratio)is 0.5.In this dissertation,the optimized wire-gate structure was prepared by combining lithography with film technology.By optimizing the film process,the surface quality and environmental resistance of the antireflection film were improved;the lithography process was optimized to improve the accuracy of the metal wire-grid structure.The Fourier infrared spectrometer with a built-in polarizer built in the laboratory was applied to perform spectral testing on the polarization element,and the scanning electron microscope and the atomic force microscope were employed to detect the microstructure of the element.The actual and theoretical aspects of the prepared elements were compared,and TFCalc software and FDTD software were applied to inversely analyze the influence from the optical constants of the film material and the error of the wire grid structure on the polarization performance so as to further optimize the preparation process.The test results reveal as follows: for the prepared metal wire-grid polarization from 3 ?m band to 5 ?m band,the average transmittance of TM waves was 89.1%,and the average transmittance of TE waves was 0.6%;the extinction ratio was 21.7 d B.