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.
We present a study of optical transmission in the visible and
near-infrared regimes through subwavelength apertures in gold
films. Samples consisting of single, ~100 nm wide, 50 micron long, linear apertures, centered between two finite grating structures, were prepared using electron-beam lithography with
subsequent broad-beam argon-ion milling. The period and number of
the corrugations that make up the grating structures was constant,
while the distance between the gratings on each side of the
aperture was varied. Spectrally resolved far-field transmission
measurements were obtained for normal incidence with a
spectrometer-coupled optical microscope configured for
transmission measurements. Transmission through these structures
was significantly enhanced relative to an isolated aperture at
resonant wavelengths for transverse magnetic polarized incident
light, in agreement with the literature. Wavelengths where the
transmission was suppressed relative to an isolated aperture were
also observed. The wavelengths of maximum transmission and of
suppression were found to depend on the spacing between the
grating arrays and the aperture. Measured spectra were consistent
with modeled results and can be interpreted in terms of the
interference between the incident light and surface plasmon
polaritons (SPP) as well as cavity resonances of the SPPs.
Enhanced transmission through structures consisting of linear gratings surrounding a single subwavelength aperture in an opaque gold film is modeled using a commercial finite element model (FEM). The stability of the FEM and boundary conditions are discussed, and different field visualizations are explored to gain insight into field behavior. The results from the FEM were compared with experimental results, yielding excellent agreement. This lends confidence that the FEM is giving an accurate representation of the field behavior around the structure. The FEM was then used to examine how transmission enhancement depends on geometric properties of the structure and to gain insight into the mechanisms of transmission enhancement.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.