Study On Surface Plasmon Resonance Sensor Based On Nano Metallic Surface-relief Gratings

With the development of nanotechnology and the rise of plasmonics, the study of the interaction between light and metal micro/nano structure has become a hot subject in recent years. The metallic gratings with the period on the same order of wavelength are a basic structure that is employed in the research of the interaction between light and periodic metallic structure. In this paper, by using rigorous coupled wave analysis (RCWA), the surface plasmon resonance (SPR) sensors and polarizers based on nano metallic surface-relief gratings are analyzed.The main research works are as follows:Firstly, based on numerical simulation and theoretical analysis, the influences of the grating period, grating height, the refractive index of incident medium and different metal materials on the resonant properties are analyzed and explained in the scheme of excitation of surface plasmon polaritons (SPPs) using a metallic grating; a novel grating-coupled SPR sensor with Al-Au bimetallic layer is proposed, and the refractive index sensitivity of the SPR sensor is predicted to be 187.2 degree per refractive index units (°/RIU), the full width at half maximum (FWHM) of the resonant absorption peaks is 0.93°. In addition, the shift of resonance angle as the refractive index of the medium surrounding the metal surface varied is completely linear, and the correlation coefficient is 0.99828 according to linear regression analyses.Secondly, based on the scheme of excitation of SPPs using a prism coupler and the attenuated total refection method, the principle of resonant coupling surface plasmon wave to radiation modes by use of gratings is investigated, the influences of the grating height, grating period and the thickness of metal layer on coupled efficiency are analyzed. A peak coupling efficiency of 74.57% is obtained by use of a dielectric grating with optimized structural parameters, the configuration allows TM-polarized light to be transmitted and TE-polarized light to be reflected, the extinction ratio for radiation modes and reflection modes are 30dB and 42.2dB respectively. The configuration can be used as a transmission-type SPR sensor because the resonance condition is highly sensitive to the variations of the medium surrounding the metal surface, and the properties of the sensor with the dielectric gratings and metallic gratings are investigated respectively. In addition, a method to enhance the sensitivity of the transmission-type SPR sensor by use of low refractive index prism is proposed.Thirdly, we propose a SPPs excitation scheme based on continuous film metallic gratings, in which the prism coupling method and grating coupling method are combined. The properties of surface plasmon resonance are analyzed in condition of small period grating and large period grating respectively, and the physical interpretation related to the results is provided according to theoretical analysis. The sensitivity enhancement of SPR sensor with continuous film metallic gratings is investigated. When the period of gratings is comparatively large, the method of double dips is adopted in order to enhance the sensitivity of SPR sensor. It is found that the refractive index sensitivity of the SPR sensor is predicted to be 153.23°/RIU, and the shift of resonance angle as the refractive index of the medium surrounding the metal surface varied is completely linear, and the correlation coefficient is 0.99997 according to linear regression analyses.Finally, based on the effect of form-birefringence of subwavelength metallic gratings, an Aluminum wire-grid polarizer for visible wavelengths is proposed, and the theoretical research shows that aluminum wire-grid polarizer has high transmission coefficient and extinction ratio over the visible spectrum, as well as uniform performance with wide variations in the angle of incidence. In addition, the influences of the fabrication error of gratings and the oxide layers coated on the wire on the polarization properties are analyzed. It is shown that the small fabrication errors do not have a significant effect on the polarization properties of wire-grid polarizer, and the polarizer with oxide layers coating on the wires still provides high performance.