Research On Optical Mechanism Of Bionic Moth-eye Antireflection Microstructure

Moth-eye outer surface is covered by regular array of hexagonal protuberances, the scale of the micro-nano structures is smaller than the visible wavelengths, thus the waves unable to identify the micro-nano structures. The micro-nano structure layer can be equivalent to a continuous gradient refractive index cover along the depth direction. It can restrain the reflection which caused by the refractive index saltation, therefore the moth-eye has a very low reflectivity. Furthermore, bionic moth-eye microstructures array can keep high antireflection performance at a wide incidence angle and a wide spectrum, and the structure is stabile, so it has wide application prospects in a variety fields.In the thesis, we firstly introduce and summarize the electromagnetic wave vector diffraction theory of subwavelength microstructure array, and then discuss the numerical calculation implementation process based on Rigorous Coupled Wave Analysis Methods of diffraction efficiency in one-dimensional grating and the two-dimensional grating is mainly discussed. Based on the Rayleigh expansion of diffraction grating, the evanescent conditions of each diffraction order wave are derived, and the polarization characteristics are analyzed.According to the analysis, polarization splitter with three split modes which can split the polarization beams to different diffraction orders based on one dimensional grating are presented, including reflective, trans-reflective, and transmissive types. The finite difference time domain(FDTD) method is applied to simulate and analyze the spectral characteristics and manufacturing tolerances of different splitters. It offers a new idea for polarizer.Based on the rigorous coupled wave analysis method, a program is coded to simulate and analyze the diffraction characteristics of microstructure array by numerical computation,particularly focuses on relations between the reflectivity and the parameters such as wavelengths, microstructure array periods, depths, microstructure diameters, contour shapes.Furthermore, the antireflection spectral band width and the structure size tolerance are alse be analyzed to provide a theoretical basis and design method for micro-nano structures array design and manufacture. The analysis reveals that the ratio of the array period and the operating wavelength directly affect the anti-reflection characteristics of the microstructure array, and associated with the evanescent critical angle of higher order diffraction wave. The conical taper coefficient is introduced to unify the expression of cylindrical, truncated cone,and conical microstructures continuum, thus indicating the principles and rules of the structural parameters. Then the effects on antireflective performance caused by edge etching passivation is analyzed.According to the numerical simulation results, microstructure arrays with shapes ofcylindrical, round hole, conical, Gaussian surface, parabolic surface are designed. The binary exposure technology, laser direct writing technology, wet etching technology, reactive ion etching and electron beam exposure technology are enrolled to fabricate "moth eye" antireflective micro-nano structures arrays with different cell shapes on infrared material and quartz glass(JGS1). Different process methods are used to analyze the applicable range and advantages and disadvantages. Through a large number of experiments, the influences on the etching rate and the microstructure morphology by process parameters, including etching gas flow, work pressure and radio frequency power, is researched. The atomic force microscope(AFM), thermal field emission scanning electron microscope(SEM) and ZYGO white light interferometer are applied to measurements and characterize the microstructure morphology.The reflectivity and transmissivity of the microstructure arrays are measured by infrared imaging spectrometer and UV-visible spectrophotometer. The results certificate the effectiveness and feasibility of the microstructure parameters design methods and fabrication process.