Research On Far-Infrared Enhanced Optical Absorption Structures Based On Surface Plasmon Resonances

In recent years,the enhanced optical absorption in metallic nanostructures based on surface plasmon resonances have been widely used in various fields such as,military photodetectors sensing and surface-enhanced Raman spectroscopy,with the rapid developing of the research on surface plasmons.The application of surface plasmon to the design and development of new infrared detectors is one of the important research directions.Infrared detector based on surface plasmon resonance can be applied to various military systems such as infrared alarm system,small unmanned aerial vehicle reconnaissance,precision guidance,night vision,thermal imaging aiming,fire control and individual combat.And to improve the absorption efficiency of the absorption layer of the infrared detector is an important way to improve the performance of the detector.In order to obtain an efficient far-infrared absorption structure,the metallic grating structures with dielectrie film were studied to achieve the enhanced optical absorption of far-infrared by the methods as theoretical modeling,numerical simulation and analytic calculation.Besides,the properties of the enhanced optical absorption in metallic grating structures were investigated and the mechanism of the enhanced optical absorption was explained.Furthermore,the metallic grating structures with dielectric film were fabricated by micro-fabrication technology.And the enhanced absorption of far-infrared was demonstrated by measuring the reflection spectra of the metallic grating structures.The main research contents and innovative result are as follows:1.In order to realize the enhanced optical absorption of far-infrared,the four region grating structure as air/metallic grating/dielectric film/air was designed.The absorption efficiency of far-infrared in the grating structures were simulated by rigorous coupled wave analysis.The perfect optical absorption with the absorption efficiency more than 95%was achieved of normal TM-polarized far-infrared with the wavelength from 8 ?m to 12 ?m by optimizing the grating structure parameters.Furthermore,the basic properties of the enhanced optical absorption in grating structures were clarified by studying the influence of the structure parameters on the absorption spectra.And the perfect absorption grating structure and the fabrication window were provided for the specific wavelength of far-infrared.2.The analytical method of grating structure was proposed and a serial of analytical formula were offered for the metallic grating structure with dielectric film.And the correctness of the analytical formula is verified by comparing the absorption dispersion of grating structure calculated by the analytical formula and finite differential time domain method.The analytical formula present the relations between the grating structure parameters and the reflection,transmission and absorption efficiency,which can be used as method reference for the investigation on the properties of one-dimensional metallic gratings.3.The properties of the enhanced optical absorption in metallic grating structures with dielectric film were investigated and three fundamental modes of enhanced optical absorption were proposed as the surface plasmon polarizations on both surfaces of grating,the Fabry-Perot cavity modes in the slits and the quasi waveguide modes in the film.And the effects of three fundamental modes on enhanced optical absorption in grating structure were also explained.The air/grating lattice modes play a negative role on the enhanced optical absorption because the surface lattice modes short out the input surface and lead to high reflectance.Contrarily,the grating/film lattice?Fabry-Perot cavity modes in the slits and quasi waveguide modes in the film all enhance the absorption.The quasi waveguide modes in the film play a key role on the enhanced absorption and introduce new absorption resonance peaks and new energy band distortions.All absorption curves with the absorption efficiency more than 50%are related with one quasi waveguide mode.4.Three analytical sufficient and necessary conditions for the perfect absorption were provided as phase(?21,24u2)=2n?,phase(?24)=2n? and ?14,0 =0 for the metallic grating structure with dielectric film.The analytical sufficient and necessary conditions of the perfect optical absorption provide an efficient tool to understand and design the perfect optical absorber structures.Besides,the electric field amplitude distributions and energy loss distributions were investigated and analyzed in order to deeper understand the mechanism of the perfect optical absorption.The three resonant modes of enhanced optical absorption were explained according to the electric field amplitude distributions and energy loss distributions,which demonstrate the accuracy of the fundamental mode analysis based on the analytical formula.5.The grating structures with dielectric film were fabricated by UV-LIGA,and the process was designed based on UV-LIGA.An excellent gold plating solution and its compound method were provided with multiple experiments.SOI metallic grating structure was proposed to resolve the supporting issue of dielectric film,which can also realize the perfect absorption of far-infrared.The SOI metallic grating structures were fabricated successfully and its reflection spectra were characterized with intelligent Fourier transform infrared spectroscopy.The enhanced optical absorption in grating structures with dielectric film was demonstrated by comparing the experimental measurements and the simulation results.The findings of the research in this thesis can not only provide significant data and reference for the research of the mechanism of the enhanced optical absorption in grating structures,but also afford an efficient tool to understand and design the perfect optical absorber structures.Furthermore,an efficient far-infrared absorption structure was also provided for the design and implementation of new infrared detector with high detection sensitivity,which has important military significance and application value.