Stacked subwavelength gratings as circular polarization filters

We have stacked subwavelength gratings (SWGs) on a single substrate to crea te 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 operat ion over the 3.5-5.0-mum wavelength range. The fabricated silicon broadband QWP exhibited a phase retardance of 82-97 degrees across this wavelength r ange. Two stacked structures are presented, each with a different wire grid polarizer fabricated on an organic planarization layer (SU-8) that is depo sited on a QWP grating. Transmittance measurements of the first structure w hen illuminated with nominally right- and left-circularly polarized light i ndicate a circular extinction ratio (CER) limited by the low linear extinct ion ratio of the polarizer. Use of a wire grid polarizer with a higher exti nct ratio led to a stacked SWG structure that demonstrated CERs of 10-45 ac ross the 3.5-5.0-mum wavelength range. (C) 2001 Optical Society of America.