Stacked subwavelength gratings for imaging polarimetry

The stacking of subwavelength gratings (SWG) in an integrated structure is presented for an application in imaging polarimetry. Imaging polarimetry extends the capability of conventional imaging by providing polarization information about a scene, in addition to variations in intensity. In this dissertation, a novel approach is introduced to develop a real-time imaging polarimeter. Subwavelength gratings are implemented as linear and circular polarization filters that are directly mounted onto the focal plane array of an infrared (IR) camera. Wire grid polarizers are used as linear polarization filters. The stacked structure, consisting of a wire grid polarizer and a form birefringent quarter-wave plate (QWP), implements the circular polarization filter and is the focus of this dissertation.; Initial investigations of the development of the individual SWG components and their integration are presented. Rigorous Coupled Wave Analysis (RCWA) was used to design the SWG structures. A broadband form birefringent quarter-wave plate for the 3.5 to 5 mum wavelength range was designed as a grating structure patterned directly into the substrate. Two fabrication methods for the wire grid polarizer were investigated. A 0.5 mum period polarizer was patterned by interference lithography. A 1 mum period polarizer was patterned by contact printing.; The stacking of the subwavelength grating structures was analyzed using the Jones Matrix calculus and a new RCWA method (developed by fellow graduate student Jianhua Jiang). Stacked SWG's were fabricated as large area (1.3 cm x 1.3 cm) filters and as a 256 x 256 array of small aperture (15 mum x 15 mum) pixels. Two stack designs were investigated, referred to as Stack I and Stack II. Stack I consisted of the 0.5 mum period polarizer and the form birefringent QWP. Stack II consisted of the I mum grid period polarizer and the form birefringent QWP. Simulation and measured results are presented to compare the cases of samples with and without AR-coating for the large area filters. The fabrication and optical testing of the small aperture SWG stacks which implement the circular polarization filters of the imaging polarimeter are presented.