A study of nano-structural effect on the polarization characteristics of metallic sub-wavelength grating polarizers in visible wavelengths

摘要

The structural effect of subwavelength gratings as the polarizer on the polarization characteristics in visible wavelengths (400-700 nm) is systematically investigated through both numerical simulation with Finite Difference Time Doman algorithm and experiments. The grating parameters such as the material, the pitch, the duty cycle, the height and the cross-sectional shape of the grating are addressed in this work. The optimized range for those parameters is worked out, based on the desired performance margin at the level of 70% transmittance and 50:1 for the extinction ratio. Polarization performance such as the transmittance over 70% and the extinction ratio above 50:1 has been experimentally demonstrated by the 200 nm pitched grating in Al with the height of 150 nm, which was fabricated by high resolution electron beam lithography in this work, guided by the simulation result. Au grating as the polarizer was also compared but ruled out in this work because of the poor performance in polarization. This work is essential in developing grating based polarizers for polarimetric detection and imaging in visible wavelengths.