Figure 2
From: Geometric metasurface enabling polarization independent beam splitting
Fabrication of the metasurface and its optical properties. (a,b) SEM image of the fabricated metasurface in the top and tilted view. The phase distribution is different in our metasurface than in the conventional metasurface beam splitter which has a one-dimensional linear phase distribution. The a-Si:H is used as the structuring material to cover visible working frequencies. inset: Geometry of the unit cell: length L = 150 nm, width W = 80 nm, height H = 300 nm, pitch P = 240 nm. (c) Comparison of the measured complex refractive indices of our a-Si:H (solid lines) and the literature value of unhydrogenated amorphous silicon58 (dotted lines). Red lines represent the refractive index while black lines show the extinction coefficient for both materials. Hydrogen impurities decrease the extinction coefficient of amorphous silicon in visible wavelengths improving the CPT. (d) The calculated transmittance spectrum of the designed unit cell. The red line represents cross-polarization while the black line shows co-polarization. The transmittance in shorter wavelength region can be improved by using low loss materials such as c-Si, TiO2 and GaN.
