Study of structural effects on the polarization characteristics of subwavelength metallic gratings in short infrared wavelengths

Abstract

Applications of subwavelength grating based-polarizers for polarimetric detections are being hindered due to the limited extinction ratio. In this work, the structural effect, including the line edge roughness (LER), of the gratings on the polarizing characteristics was studied by both numerical simulations using finite difference and time domain (FDTD) method and experiments, aiming to figure out the optimal grating profile for achieving high transmittance as well as high extinction ratio. Two different configurations of the gratings, one is dual layer Au lines and the other is parabolic shaped Al lines on structured spin-on-carbon (SOC) films were systematically studied and compared. Nanofabrication of the gratings by electron beam lithography without lift-off process were conducted and optical measurements of their polarization properties demonstrate superior performance of the developed polarizers. The origin of the structural effect was explained by the local surface plasmonic modes, existing in the nano-slits in metallic gratings, which is instructive for further enhancement of the polarization performance.