Development of a 2D metamaterial that preferentially emits broadband circularly-polarized (CP) infrared radiation is hindered by the fact that orthogonal electric-field components are uncorrelated at the surface of the thermal emitter, a consequence of the fluctuation-dissipation theorem. We achieve broadband CP thermal emission by fabricating a meanderline quarter-wave retarder on a transparent thermal-isolation layer. Behind this isolation layer, in thermal contact with the emitter, is a wire-grid polarizer. Along with an unavoidable linear polarized radiation characteristic from the meanderline, we measured a degree of circular polarization (DOCP) of 28%, averaged over the 8-to 12 μm band.
A meanderline wave retarder is a unique type of frequency-selective-surface (FSS) that enables a change in the state of optical polarization. The principles of operation are very similar to a typical crystalline waveplate, such that the artificially structured meanderline array has both 'slow' and 'fast' axes that provide a phase offset between two orthogonal wave components. In this paper, we study the behavior and response of multilayered meanderline quarter-wave retarders designed for operation at 10.6 mum wavelength (28.28 THz). It will be shown that meanderline quarter-wave plates with more than a single layer exhibit improved transmission throughput at infrared frequencies due to impedance matching, similar to a multilayer optical film coating. Numerical data, both from simulations and measurements, are presented to validate this claim.
We present a novel reflective quarter-wave plate comprised of subwavelength meanderline elements. The device is operational over the long-wave infrared (LWIR) spectrum, with significant spectral and angular bandwidths. Power reflection is approximately 70% over the majority of the LWIR. Efficient conversion from a 45° linear polarization state into circular polarization is demonstrated from finite-element electromagnetic simulations and from broadband polarimetric measurements.
Anti-reflection (AR) coatings on plastic substrates have been extensively investigated with the development of large-area LCD and LED displays. A robust AR coating on plastics requires strong adhesion to the substrate, precise thickness and refractive index, and abrasion resistance. In this paper, abrasion-resistant AR coatings were fabricated on polycarbonate substrates using the layer-by-layer spraying deposition of poly(allylamine hydrochloride) (PAH) and silica nanoparticles. The adhesion between the substrates and coatings was enhanced by treating the polycarbonate surfaces with aminopropyltrimethoxylsilane (APTS). The porous low-refractive-index PAH/silica-nanoparticles multilayers were constructed by the layer-by-layer spraying of PAH and silica-nanoparticles aqueous solutions onto the functionalized substrates. The subsequent treatment of the porous coatings with tetrahydroxylsilane leads to stable abrasion-resistant AR coatings. The resultant AR coatings can reduce the reflection from 5 to 0.3%. The reported technique provides a cost-effective method for large-scale production of AR coatings on plastic substrates.
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