实现高纯度偏振转化的等离激元几何相位型超表面器件

Plasmonic geometric metasurfaces for high-purity polarization conversion

等离激元型超表面由金属型周期性二维亚波长人工微结构组成,能改变波前来实现光的多方位调控;目前,等离激元型超表面的透射光中,其正交偏振的纯度较低,即同时存在目标光和背景光.为此提出了一种基于带有矩形孔的金膜等离激元型超表面来实现圆偏振光的高纯度转化.利用时域有限差分法(FDTD),优化矩形孔的几何尺寸,在偏振转换效率大于10%的情况下,透射光中的理论偏振纯度约为99.5%,且该结构对膜厚的宽容度较大,有利于器件在全息、透镜和光栅方面的实用化.

Plasmonic metasurfaces are made up of metallic artificial micro-structures with two-dimensional subwavelength periods,which can realize full control of light via tailoring the wavefronts.Currently,the purity of cross-polarization for transmissive plasmonic metasurfaces is low,leaving that both the signal(cross-polarization)and background(co-polarization)light exist in the transmitted light.Here,a rectangle-hole-based plasmonic metasurface made in a gold film was proposed to realize high-purity conversion of circular polarization.By using the finite-difference time-domain(FDTD)method,the dimension of the rectangle hole was optimized numerically to obtain the theoretical polarization purity of 99.5%in the transmitted light meanwhile maintain the total conversion efficiency larger than 10%.In addition,such a structure has good tolerance to the thickness of film,which benefit its practical applications such as holograms,lenses and gratings.