K. Knight

Metamaterial electro-optic switch of nanoscale thickness

NanoBioScience Lab, Istituto Italiano di Tecnologia, Via Morego 30, I16163 Genova, Italy andBIONEM Lab, University of Magna Graecia, viale Europa, I88100 Catanzaro, Italy(Dated: December 21, 2009)Combining metamaterials with functional media brings a new dimension to their performance.Here we demonstrate substantial resonance frequency tuning in a photonic metamaterial hybridizedwith an electrically/optically switchable chalcogenide glass. The transition between amorphousand crystalline forms brings about a 10% shift in the near-infrared resonance wavelength of anasymmetric split-ring array, providing transmission modulation functionality with a contrast ratioof 4:1 in a device of sub-wavelength thickness.We demonstrate an innovative concept for nanoscale electro-optic switching. It exploits the frequency shift of a narrow-band Fano resonance mode in a plasmonic planar metamaterial induced by a change in the dielectric properties of an adjacent chalcogenide glass layer. An electrically stimulated transition between amorphous and crystalline forms of the glass brings about a 150 nm shift in the near-infrared resonance providing transmission modulation with a contrast ratio of 4:1 in a device of subwavelength thickness.

Deposition and Characterization of CVD-Grown Ge-Sb Thin Film Device for Phase-Change Memory Application

Germanium antimony (Ge-Sb) thin films with tuneable compositions have been fabricated on SiO2/Si, borosilicate glass, and quartz glass substrates by chemical vapour deposition (CVD). Deposition takes place at atmospheric pressure using metal chloride precursors at reaction temperatures between 750 and 875 °C. The compositions and structures of these thin films have been characterized by micro-Raman, scanning electron microscope (SEM) with energy dispersive X-ray analysis (EDX), and X-ray diffraction (XRD) techniques. A prototype Ge-Sb thin film phase-change memory device has been fabricated and reversible threshold and phase change switching demonstrated electrically, with a threshold voltage of 2.2 - 2.5 V. These CVD-grown Ge-Sb films show promise for applications such as phase change memory and optical, electronic and plasmonic switching.

Chalcogenide Glass Metamaterial Optical Switch

The technology behind rewritable optical disks offers a new switching paradigm for metamaterials. A switch comprising resonant plasmonic metamaterial and electro-optic chalcogenide glass layers provides 75% optical transmission modulation in a device of sub-wavelength thickness.

Focused ion beam etched ring-resonator in CVD-grown Ge-Sb-S thin films

Focused ion beam technique has been applied to fabricate ring resonators in Ge-Sb-S thin films for optoelectronic applications. The CVD-grown Ge-Sb-S thin films have been characterizatezed by micro-Raman, scanning electron microscopy, energy dispersive X-ray analysis and UV-VIS-NIR spectroscopy and the properties of the resonator are being assessed.

Toward compact optical waveguide devices for active infrared applications

The infrared (IR) spectrum is of significant importance in many defence applications including free-space communication, thermal imaging and chemical sensing. The materials used in these applications must exhibit a number of suitable properties including mid-IR transparency, rare-earth solubility and low optical loss. When moving towards miniaturised optical devices one tends to adopt the concepts introduced by integrated optics; multiple devices operating harmoniously on a single photonic chip. Our work focuses on the use of a laser to directly write into a novel chalcogenide glass to engineer optical waveguide devices. Our material of choice is gallium lanthanum sulphide (Ga:La:S) glass, an exceptional vitreous chalcogenide material possessing these aforementioned properties as well as a broad range of other properties. These Ga:La:S glasses have a wide transmission window between 0.5 to 10 μm. Furthermore, these low-phonon energy glasses have a high transition temperature (Tg = 560°C), high refractive index, the highest reported non-linearity in a glass, excellent rare-earth solubility with well documented near-mid IR spectroscopic properties. We report on low loss single-mode active channel waveguides in Ga:La:S glass engineered through direct laser writing (λ= 244 nm). We discuss laser operation at 1.075 µm (neodymium) and IR emission at 1.55, 2.02 and 2.74 µm (erbium) from these waveguides.