Research Of The Applications Of The High-index Contrast Gratings

Recently, a novel type of planar optics has emerged using subwavelength gratings with a large refractive index contrast, herein referred to as high-index contrast gratings(HCGs). HCGs are not only tiny and simple in structure, compatible with standard microfabrication processes, but also possess many extraordinary properties, such as polarization control and broadband high-reflectivity. Therefore, it has been widely researched and applied. We would like to introduce three applications of HCGs in this paper and we use silicon as the high index material.First, we present a simple but practical method to design a periodic grating coupler with fully etched slots. Strong reflection between the grating and the waveguide is avoided by adding an antireflection interface. Theoretical coupling efficiency up to 43% is demonstrated.Second, we designed two types of reflectors using HCGs——one is with bars of different height and the other is with bars of different depth, which exhibit identical high focusing abilities at normal incidence with TE-polarized plane wave. It turns out that they both achieve a full-width-half-maximum(FWHM) of 0.9 ?m at the focal plane, which is fairly close to diffraction limit. And their reflectance is as high as 94% and 91% respectively.Third, we introduce a planar, high focusing ability, low loss lens using HCGs. After a plane wave passes through the 21.7 ?m wide HCG lens, it is focused 9.51 ?m below the lens, resulting an NA of 0.75.