Chris Craig

1.7 Gbit/in.2 gray-scale continuous-phase-change femtosecond image storage

We demonstrate high-density, multi-level crystallization of a Ge2Sb2Te5 thin film using tightly focused femtosecond laser pulses. The submicron spots with 8 distinct data storage states are written on a 1.08 μm square grid. The significant change in reflectivity of every specific state of crystallized spot allows easy optical reading and identification. As a demonstration, two gray-scale images are written into the storage medium. Our results open up potential applications in ultra-fast two-dimensional parallel cognitive computing and holography.

Refractive index and dispersion control of ultrafast laser inscribed waveguides in gallium lanthanum sulphide for near and mid-infrared applications

The powerful ultrafast laser inscription technique is used to fabricate optical waveguides in gallium lanthanum sulphide substrates. For the first time the refractive index profile and the dispersion of such ultrafast laser inscribed waveguides are experimentally measured. In addition the Zero Dispersion Wavelength of both the waveguides and bulk substrate is experimentally determined. The Zero Dispersion Wavelength was determined to be between 3.66 and 3.71 μm for the waveguides and about 3.61 μm for the bulk. This work paves the way for realizing ultrafast laser inscribed waveguide devices in gallium lanthanum sulphide glasses for near and mid-IR applications.

Engineering of composite metallic microfibers towards development of plasmonic devices for sensing applications

The paper discusses the analysis of tapered hybrid composite microfibers based on a metal-core and dielectric-cladding composite material system. Its advantages over the pure metal tips conventionally used, are the inherent enhanced environmental robustness due to inert borosilicate cladding and the capability of multiple excitation of the tapered nanowire through the length of the fiber due to the enabled total internal reflection at the borosilicate/air interface. Simulations through finite element method (FEM) have demonstrated an improved field enhancement at the tapered region of such microfibers. Furthermore, experimental results on tapering in copper based microfibers together with light coupling and propagation studies will be demonstrated revealing the potential for the development of plasmonic devices for sensing applications.

Plasmonic nanowire continuum light source

Optically pumped gold nanowire, 330 nm in diameter imbedded into silicate optical fiber produces broadband, highly collimated radiation (in the range 470-900 nm) with divergence of less than 4 mrad.

Phase engineering of tin sulphide grown by atmospheric pressure chemical vapour deposition at ambient temperature

Considerable efforts have been made in the search for new photovoltaic (PV) materials that satisfy requirements such as low toxicity, optimum energy gap, high stability as well as the ability to synthesize by a wide range of methods. Tin (II) monosulfide (SnS), a binary metal (IV-VI) compound semiconductor offers many attributes. SnS is a p-type with high optical absorption coefficient >104 cm−1 and a band gap of Eg =1.1–1.32 eV making it a favourable material for PV applications and optical devices.

Structural modification of Ga-La-S glass for a new family of chalcogenides

In this work, the effect of adding Se, Te, In, Cs, Y to gallium lanthanum sulphide glass was studied. Structural modifications to the glassy network were achieved by substitution of sulphur, gallium or lanthanum using a melt-quench method in an inert atmosphere. Optical, thermal and mechanical characterisation of the samples revealed tailorable features according to the nature and the amount of glass modifier. In particular, the addition of selenium and tellurium resulted in an extended transmission in the infrared up to 12 μm. Furthermore, for small amounts of selenium, the position of the bandgap did not change significantly, maintaining visible transmission. The addition of indium led to the formation of glasses with longer transmission in the infrared and a cut-off edge around 600nm in the UV-visible range. Over-all, the addition of these modifiers resulted in stronger materials with improved thermal stability and similar mechanical properties to original Ga-La-S glass. The outcome of this work aims to bring a new family of chalcogenide glasses for applications in the infrared and visible range.

Chalcogenide waveguides for mid-infrared biomedical sensing applications

High contrast GeTe4 channel waveguides were fabricated on silicon with a ZnSe isolation layer using the lift-off technique. Waveguiding in these channels was demonstrated in the mid-wave and long-wave infrared spectral regions. The results of numerical modelling on the optical loss with different isolation layer thicknesses are also briefly discussed.

Mid-infrared GeTe4 waveguides on silicon with a ZnSe isolation layer

GeTe4 waveguides were designed and fabricated on silicon substrates with a ZnSe isolation layer. GeTe4 has a refractive index of 3.25 at a wavelength of 9 μm and a lower refractive index isolation layer is needed to realise waveguides on silicon. Numerical modelling was carried out to calculate the thickness of the isolation layer (ZnSe, refractive index ~2.4) required to achieve low loss waveguides. For a loss between 0.1 and 1.0 dB/cm it was found that a ~ 4 μm thick ZnSe film is required at a wavelength of 9 μm. ZnSe thin films were deposited on silicon, GeTe4 waveguides were fabricated by lift-off technique and were characterised for mid-infrared waveguiding.

Chalcogenide Microfiber Photonic Synapses

Optical axons and photonic synapses implemented using chalcogenide microfibers allow the generation and propagation of photonic action potentials which give rise to the demonstration of various neuromorphic concepts.