| The transmission characteristics of light are physical phenomena of common concern.With further study,people can use different artificial photonic micro-structures to manipulate the transmission of light.As a periodic artificial micro-structure made up by materials of different refractive indexes,photonic crystals have attracted wide attention after the concept is put forward.As a light trapping structure which helps enhance light absorption,photonic crystals are one of the effective methods to enhance light absorption.Since the introduction of surface plasmons,scientists have used a variety of new photonic devices to excite surface plasmons.With the development of optical devices,more and more attention has been paid to the study of surface plasmons which have broken the diffraction limit.This paper will propose and prove by numerical simulation that silicon-based micro-nano structural films,with a given thickness of absorption layer,can significantly improve omnidirectional absorption of light in the visible range.There will be theoretical discussion on the plasmon characteristics of thin calcium films under the excitation of Kretschmann.It can be found through calculation that thin calcium films with plasmon characteristics can be used as a Fraunhofer narrow band filter.The second chapter expounds on the theoretical research methods used in this paper,with particular emphasis on the calculation of photonic crystals by plane wave expansion and on the rigorous coupled wave method.The third chapter presents a composite micro-nano structural film of silicon-based photonic crystal and metal,and proves by numerical simulation that silicon-based micro-nano structural films,with a given thickness of absorption layer,can significantly improve omnidirectional absorption of light in the visible range.A comparative study of complete silicon / metal composite films suggests that,when silicon films are of the same thickness,silicon-based micro-nano structural films can increase the absorption rate by nearly 70%.In addition,through analysis,it can be found that such silicon-based micro-structures,with omnidirectional band gaps,can provide the appropriate reflection phase shift in a wide range of spatial spectrum,making the absorption enhancement effects of silicon-based micro-nano structural films still feasible when the angle of incidence reaches.To further study the properties of silicon-based micro-nano structures,this paper will calculate the structure of energy band of silicon-based micro-nano structural films through the expansion of plane waves.By analyzing the energy band of corresponding structures and the mode field configuration,it can be found that such absorption enhancement which is not sensitive to the angle of incidence can be attributed to the special boundary light trapping effect of metal plates and truncated photonic crystals and the omnidirectional band gaps of six lattices.The fourth chapter of this thesis explores theoretically the plasmon characteristics of the calcium films of alkali metals under Kretschmann excitation.Based on surface plasmons,the absorption rate of calcium films on polarized light p can reach 100%,much higher than the absorption rate of it on polarized light s at the 422.7nm-wavelength region(corresponding to the line g of Fraunhofer).At 422.7nm-wavelength,the reflectivity of 45nm-thick calcium film on polarized light s is about 76%;when the angle of incidence is 19?,the reflectivity on polarized light p reaches the minimum value.As the narrow band filter based on the calcium film is a large solid device and is especially suitable for in-plane integration,it should be used together with the traditional calcium atomic filter.In addition,the plasma filter based on the calcium film has great potential of application in sensors with angular sensitivity and polarization sensitivity and in weak laser detection. |
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