Patent ID: 8830585

Claim:
A polarization filter comprising: an optical element of configured to transmit incident light having a particular polarization direction mainly by 0-order transmission and configured to diffract incident light having a polarization direction perpendicular to the particular polarization direction, the optical element including: a periodic structure having a period equal to or greater than the wavelength of the incident light, wherein the periodic structure includes first and second subwavelength concave-convex structures formed perpendicularly adjacent to each other in each period of the periodic structure, the first and the second subwavelength concave-convex structures having a period less than the wavelength of the incident light; wherein a filling factor of the first subwavelength concave-convex structures and a filling factor of the second subwavelength concave-convex structures are determined such that the first and the second subwavelength concave-convex structures have the same effective refraction index with respect to the incident light having the particular polarization direction, and wherein the filling factor of the first subwavelength concave-convex structures is different from the filling factor of the second subwavelength concave-convex structures, and a groove depth of the first subwavelength concave-convex structures and a groove depth of the second subwavelength concave-convex structures are determined such that the first and the second subwavelength concave-convex structures have a phase difference π with respect to the incident light having the polarization direction perpendicular to the particular polarization direction, and wherein the groove depth of the first subwavelength concave-convex structures is the same as the groove depth of the second subwavelength concave-convex structures; wherein the polarization filter includes Ta 2 O 5 and a glass substrate, the Ta 2 O 5 being located on the glass substrate, and wherein the first and the second subwavelength concave-convex structures are located in the Ta 7 O 5 .