Opt. Express 20, 1308–1319 (2012)

Credit: © 2012 OSA

Complete Stokes vector imaging is a challenge because of the difficulty in fabricating micropolarizing structures that are sensitive to circular polarization. However, recent work by Kate Bachman and colleagues from Colorado in the USA suggests that this won't be a problem any longer. The researchers demonstrated that a spiral plasmonic antenna with a high circular polarization selectivity allows the transmission of one circular polarization state while blocking the opposite circular state. They formed the antenna by first nesting Archimedean spiral gratings in a silicon-dioxide-coated gold film. They then formed a cavity by cutting out the gold region in the centre of the spiral grating to the same depth as the grating grooves, and covering the aperture in a gold cap. Incident light couples to surface plasmons travelling towards the central aperture. The spectral bandwidth, efficiency and extinction ratio of the device, which operates in the visible and near-infrared regimes, can be tuned by changing the antenna's geometric parameters. The researchers also fabricated an array of spiral antennas to form a circular dichroic metamaterial, which can be used as a circular dichroic thin-film filter compatible with very-large-scale integration.