Sub-wavelength metal polarization gratings array used in polarization imaging

Polarization imaging is a powerful tool to observe hidden information from an observed object, for instance, degree of polarization, polarization azimuth and polarization ellipticity. According to the request of the visible light polarization imaging, a metal sub-wavelength polarization gratings array was designed based on FDTD method. And its principle was analyzed by effective medium theory. The effects of metal thickness and duty ratio on the TM and TE polarization transmission efficiency as well as the extinction ratio was analyzed by FDTD method when the grating's period is 200nm and 250nm, and the metal is Al. When the metal sub-wavelength polarization gratings array works in normal incidence, its TM transmission efficiency are more than 45%, and the extinction ratios are more than 3.5x10(3) in all visible light spectrum. Numerical results and theoretical analysis show that the designed metal sub-wavelength polarization gratings array is a polarizer with high TM polarization transmission efficiency and high extinction ratios.