Abstract

We describe a novel grating polarizer, in which the ultrahigh spatial frequency gratings (USFG) with double duty ratio are alternately replaced on the land and groove of the diffraction grating. The USFG of the land, which is formed perpendicular to that of the groove, is fabricated by electron-beam lithography.¹ The periods of the diffraction grating and the USFG are 20 m and 0.3 m, respectively. The depth of the grating is 1.4 m. The USFG duty ratio (L&S) of the land is 3:2, and that of the groove is 2:3. The incident light normal to the device is diffracted by Raman-Nath diffraction. The refractive indices for light polarized parallel and perpendicular to the diffraction grating are different. The duty ratio and depth of the USFG are chosen such that the phase shift is 180 for one polarization direction and 0 for the other. The zero and 1st order diffraction efficiencies were 58% and 12%, respectively, for light polarized parallel to the diffraction grating, and the efficiencies were 10% and 38% for light polarized perpendicular to the grating. The resultant extinction ratios were calculated to be −7 dB for the zero order and −6 dB for the 1st order. By optimizing the fabrication condition, an extinction ratio as high as −40 dB could be obtained.

© 1990 Optical Society of America