Design and fabrication of sub-wavelength metal polarization gratings used in polarization imaging

Abstract

This paper designs a sub-wavelength metal polarization gratings array composing two orthogonal micro polarization gratings as one unit. Effects of different metal materials and grating profile on the TM and TE polarization transmittance as well as the extinction ratio are analyzed by the Finite Difference Time Domain (FDTD) method. Based on the requirement of the visible light polarization imaging and the resolution of the holographic lithography, we obtain the best parameters for the grating: period is 250nm, Al thickness is 260nm, and duty cycle is 0.4, the transmittance is higher than 45% and extinction ratio is higher than 100. Then, the sub-wavelength metal polarization gratings have been fabricated by two methods: the holographic - ion beam etching - Al oblique deposition or the holographic - reactive ion etch (RIE) - ion beam etching. Preliminary results indicate the polarization information has been obtained. A prototype metal polarization gratings array will be fabricated in late 2011.