Plasmonic micropolarizers for full Stokes vector imaging
2012
Polarimetric imaging using micropolarizers integrated on focal plane arrays has previously been limited to the linear
components of the Stokes vector because of the lack of an effective structure with selectivity to circular polarization. We
discuss a plasmonic micropolarizing filter that can be tuned for linear or circular polarization as well as wavelength
selectivity from blue to infrared (IR) through simple changes in its horizontal geometry. The filter consists of a patterned
metal film with an aperture in a central cavity that is surrounded by gratings that couple to incoming light. The aperture
and gratings are covered with a transparent dielectric layer to form a surface plasmon slab waveguide. A metal cap
covers the aperture and forms a metal-insulator-metal (MIM) waveguide. Structures with linear apertures and gratings
provide sensitivity to linear polarization, while structures with circular apertures and spiral gratings give circular
polarization selectivity. Plasmonic TM modes are transmitted down the MIM waveguide while the TE modes are cut off
due to the sub-wavelength dielectric thickness, providing the potential for extremely high extinction ratios. Experimental
results are presented for micropolarizers fabricated on glass or directly into the Ohmic contact metallization of silicon
photodiodes. Extinction ratios for linear polarization larger than 3000 have been measured.
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