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The existence of a left-handed ͑LH͒ transmission band in a bulk composite metamaterial ͑CMM͒ around 100 GHz is demonstrated experimentally. The CMM consists of stacked planar glass layers on which periodic patterns of micron-scale metallic wires and split-ring resonators are fabricated. The LH nature of the CMM band is proved by comparing the transmission spectra of individual CMM components. Theoretical investigation of the CMM by transmission simulations and an inversion scheme for the retrieval of the effective permeability and permittivity functions supports the existence of LH behavior.

Cataloged from PDF version of article.Planar chiral structures may provide asymmetric transmission for circularly polarized optical waves at normal incidence if the structures are anisotropic and lossy, but the role of loss has not yet been clarified. Here, a typical planar chiral structure is studied, and the mechanism of asymmetric transmission is analyzed. It is demonstrated for the first time that asymmetric transmission can be manipulated by changing the anisotropy of loss. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The authors report high performance solar-blind photodetectors with reproducible avalanche gain as high as 1560 under ultraviolet illumination. The solar-blind photodetectors have a sharp cutoff around 276 nm. The dark currents of the 40 m diameter devices are measured to be lower than 8 fA for bias voltages up to 20 V. The responsivity of the photodetectors is 0.13 A / W at 272 nm under 20 V reverse bias. The thermally limited detectivity is calculated as D * = 1.4 ϫ 10 14 cm Hz 1/2 W −1 for a 40 m diameter device.The recent developments in high Al-content Al x Ga 1−x N material growth technology made it possible to fabricate high performance solar-blind photodetectors operating in the ultraviolet ͑UV͒ spectral region with improved receiver sensitivity, low noise, low dark current density, and high speed. 1-3 AlGaN-based Schottky, p-i-n, and metalsemiconductor-metal photodetectors with very high performances have already been demonstrated. 4,5 The UV-filtering nature of the atmospheric ozone molecules blocks the solar radiation to reach the earth's surface for wavelengths shorter than 280 nm. In this case, UV photodetectors with cutoff wavelengths around 280 nm, which are also called solarblind detectors, can detect very weak UV signals under intense background radiation. These devices have important applications including missile plume detection, chemical/ biological agent sensing, flame alarms, covert space-to-space and submarine communications, ozone-layer monitoring, and gas detection. Due to their high responsivity ͑Ͼ600 A / W͒, high speed, high cathode gain ͑on the order of a million͒, and low dark current properties, photomultiplier tubes ͑PMTs͒ are frequently used in such applications. However, PMTs are very expensive and bulky. Besides, they require a cooling system, and they have high operation voltages in excess of 1000 V. To achieve solar-blind detection, PMTs should also be integrated with complex and expensive filters. In order to avoid these disadvantages, high performance solid-state UV photodetectors with high internal gain are needed. 6 Wide band-gap semiconductor photodetectors, such as Al x Ga 1−x N with x = 0.4, are ideal candidates for this purpose. These devices are intrinsically solar blind, in which no additional filters are needed, they have low noise, 7 and fast response times. 8 The lack of high internal gain has been the major limitation for the usage of AlGaN photodetectors for applications that require high sensitivity detectors. There have been several theoretical research work that examined the avalanche effect in GaN and AlGaN-based structures. 9-11 Experimental work on both GaN ͑Refs. 12-18͒ and AlGaNbased ͑Refs. 4, 19, and 20͒ avalanche photodiodes ͑APDs͒ were also reported. However, reproducible high gain in AlGaN-based APDs is still a major limitation. In this letter, we report the realization of solar-blind AlGaN-based avalanche photodetectors with reproducible high avalanche gain.The epitaxial structure of the avalanche photodetector is designed for solar-blind operation w...

Fabrication and experimental characterization of a broadband quarter-wave plate, which is based on two-dimensional and binary silicon high-contrast gratings, are reported. The quarter-wave plate feature is achieved by the utilization of a regime, in which the proposed grating structure exhibits nearly total and approximately equal transmission of transverse electric and transverse magnetic waves with a phase difference of approximately π/2. The numerical and experimental results suggest a percent bandwidth of 42% and 33%, respectively, if the operation regime is defined as the range for which the conversion efficiency is higher than 0.9. A compact circular polarizer can be implemented by combining the grating with a linear polarizer.