We have stacked subwavelength gratings (SWGs) on a single substrate to create a compact, integrated circular polarization filter. The SWGs consist of a wire grid polarizer and a broadband form-birefringent quarter-wave plate (QWP). Rigorous coupled-wave analysis was used to design the QWP for operation over the 3.5–5.0-μm wavelength range. The fabricated silicon broadband QWP exhibited a phase retardance of 82–97° across this wavelength range. Two stacked structures are presented, each with a different wire grid polarizer fabricated on an organic planarization layer (SU-8) that is deposited on a QWP grating. Transmittance measurements of the first structure when illuminated with nominally right- and left-circularly polarized light indicate a circular extinction ratio (CER) limited by the low linear extinction ratio of the polarizer. Use of a wire grid polarizer with a higher extinct ratio led to a stacked SWG structure that demonstrated CERs of 10–45 across the 3.5–5.0-μm wavelength range.
© 2001 Optical Society of America
(050.1950) Diffraction and gratings : Diffraction gratings
(230.5440) Optical devices : Polarization-selective devices
(260.1440) Physical optics : Birefringence
(260.5430) Physical optics : Polarization
Panfilo C. Deguzman and Gregory P. Nordin, "Stacked Subwavelength Gratings as Circular Polarization Filters," Appl. Opt. 40, 5731-5737 (2001)