Research On The Characteristics Of Reflectors With Broad Band In Visible Region Based On Guided-mode Resonance Grating

The combination of diffraction optics and micro-nano electronic technology makes the diffraction optics theory research method more and more complete and continuous improvement makes the application of diffraction devices more and more widely. In the future, the diffractive optical elements will advanced towards micro-nano optoelectronic and the subwavelength structure. Subwavelength grating is one of the most widely used devices.Subwavelength grating due to its grating period is smaller than the wavelength of incident light, so there is only the zero-order diffraction wave exist, which makes the calculation process simple and the diffraction efficiency high. Owing to the special diffraction characteristics of subwavelength grating, it has a lot of optical functions that many traditional optical devices can not be achieved. With the features such as high diffraction efficiency, narrow band and sensitivity to the parameters, subwavelength grating can be used to design a narrowband filter. And the subwavelength coupler because of its no special requirements for structure also has a wide range of applications. Recently, it’s been proved theoretically that the subwavelength grating can also get broadband and the reflectivity is close to 100%. The interactions between multiple resonance peaks yields the wideband reflection.In this paper, we use the rigorous coupled wave analysis method to simulate and analyze the diffraction characteristics of stacked subwavelength grating.A subwavelength guided-mode resonant grating reflector with wide band in visible light band is designed. The main contents and contributions of this work are summarized as follow:1. Briefly described the development of diffractive optics and introduced the classification of diffraction grating and its application.2. In this paper, we introduced the effective-medium theory（EMT）. The principle of rigorous coupled wave analysis（RCWA） and derivation process is described in detail.3. Analyzed the resonance characteristics of the TiO₂ and SiO₂ stacked grating with different parameters such as grating period, fill factor, layer thickness and incident angle by using RCWA. As we can see, the period is mainly effect on the position of the broadband, and the fill factor mainly effect on width of the resonance. The effect of the thickness of the SiO₂ layer is not obvious, and the thickness of the TiO₂ layer is very obvious. Finally,Particle swarm optimization algorithm is used to optimize the structure of the grating.4. A reflector with wideband reflection spectrum in the visible band based on grating stacked structure is proposed. Optimize the stacked grating formed by three different high refractive index materials（TiO₂,Si C,Si） with SiO₂.The reflection bandwidth of TiO₂ and SiO₂ grating can reach more than 50 nm.SiC and SiO₂ grating can achieve reflection bandwidth above 100 nm. Si and SiO₂ stacked grating can achieve more than 150 nm grating bandwidth. Finally, the influence of three different refractive index material and the number of layers on the reflection characteristics of wide spectrum is analyzed by using the theory of guided-mode resonance. The higher of the index difference, the wider bandwidth and better angle insensitivity.