22 research outputs found
Robust optical delay lines via topological protection
Phenomena associated with topological properties of physical systems are
naturally robust against perturbations. This robustness is exemplified by
quantized conductance and edge state transport in the quantum Hall and quantum
spin Hall effects. Here we show how exploiting topological properties of
optical systems can be used to implement robust photonic devices. We
demonstrate how quantum spin Hall Hamiltonians can be created with linear
optical elements using a network of coupled resonator optical waveguides (CROW)
in two dimensions. We find that key features of quantum Hall systems, including
the characteristic Hofstadter butterfly and robust edge state transport, can be
obtained in such systems. As a specific application, we show that the
topological protection can be used to dramatically improve the performance of
optical delay lines and to overcome limitations related to disorder in photonic
technologies.Comment: 9 pages, 5 figures + 12 pages of supplementary informatio
Ultrafast Laser Inscription of High-Performance Mid-Infrared Waveguides in Chalcogenide Glass
International audienceWe present the realization of mid-infrared waveguide by ultrafast laser inscription technique in a chalco-genide glass. Our approach is based on multicore waveguide that consists in an alignment on a mesh of positive refractive index channels placed parallel to each other. Two different meshes are investigated with different refractive index contrasts between the channel and the glass matrix. A detailed analysis of the performances at a wavelength of 4.5 mu m shows propagation losses of 0.20 +/- 0.05 dB/cm and coupling efficiencies higher than 60%
Ultrafast Laser Inscription of High-Performance Mid-Infrared Waveguides in Chalcogenide Glass
Potentiometric Chemical Sensors Based on Metal Halide Doped Chalcogenide Glasses for Sodium Detection
Chalcogenide glasses are widely used as sensitive membranes in the chemical sensors for heavy metal ions detection. The lack of research work on sodium ion-selective electrodes (Na+-ISEs) based on chalcogenide glasses is due to the high hygroscopicity of alkali dopes chalcogenides. However, sodium halide doped Ga2S3-GeS2 glasses are more chemically stable in water and could be used as Na+-sensitive membranes for the ISEs. In this work we have studied the physico-chemical properties of mixed cation (AgI)x(NaI)30-x(Ga2S3)26(GeS2)44 chalcogenide glasses (where x = 0, 7.5, 15, 22.5 and 30 mol.% AgI) using density, DSC, and conductivity measurements. The mixed cation effect with shallow conductivity and glass transition temperature minimum was found for silver fraction r = Ag/(Na + Ag) ≈ 0.5. Silver addition decreases the moisture resistance of the glasses. Only (AgI)22.5(NaI)7.5(Ga2S3)26(GeS2)44 composition was suitable for chemical sensors application, contrary to the single cation sodium halide doped Ga2S3-GeS2 glasses, where 15 mol.% sodium-halide-containing vitreous alloys are stable in water solutions. The analytical parameters of (NaCl)15(Ga2S3)23(GeS2)62; (NaI)15(Ga2S3)23(GeS2)62 and (AgI)22.5(NaI)7.5(Ga2S3)26(GeS2)44 glass compositions as active membranes in Na+-ISEs were investigated, including detection limit, sensitivity, linearity, ionic selectivity (in the presence of K+, Mg2+, Ca2+, Ba2+, and Zn2+ interfering cations), reproducibility and optimal pH-range
Chemically-invariant percolation in silver thioarsenate glasses and two ion-transport regimes over 5 orders of magnitude in Ag content
International audienceIonic conductivity σi measurements of AgY−As2S3 (Y = Br, I) glasses, covering 13 orders of magnitude in σi(x) over 5 orders of magnitude in silver content x, confirm two drastically different ion transport regimes in silver halide thioarsenate glasses. As expected, the ionic conductivity in the critical percolation domain, 20 ppm 7-10 at.% Ag, and the difference in σi(x) between AgI- and Ag2S-As2S3 glasses approaches 4 orders of magnitude. Random distribution of silver in the critical percolation domain, shown by DFT modeling of neutron and high-energy x-ray diffraction data, is a key of the observed conductivity invariance. When silver cation leaves the residence site and travels throughout the glass network, characterized by the average Ag-Ag separation distance of 12 Å or more, the memory of its original chemical form (sulfide or halide) vanishes rapidly with increasing the mean square displacement. A non-random silver distribution in the modifier controlled region implying formation of preferential conduction pathways via direct contacts of edge- and corner-sharing silver chalcogenide or chalcohalide polyhedra rules out this possibility. Chemically-invariant ionic conductivity seems to be a common feature of any disordered system with random distribution of mobile ions having similar size of charge carriers
Wastewater treatment by cyclodextrin polymers and noble metal/mesoporous TiO<sub>2</sub> photocatalysts
New membrane material for thallium (I)-selective sensors based on arsenic sulfide glasses
New membrane materials were studied for thallium (I)-selective chemical sensors based on chalcogenide glasses in the TlI-Ag2S-As2S3 system. Using these studies on the radioactive tracers diffusion (108mAg и 204Tl) and electrical conductivity, an ionic conductivity of σion = 10−7 Ohm−1 cm−1 (20 °C) was found for the glass composition 27%TlI-20%Ag2S-53%As2S3. This composition of chalcogenide glass was selected as a membrane material for the Tl-selective chemical sensor displaying a value of the electrode function of 57 mV/pTl and a detection limit of 3 × 10−6 mol l−1
Drastic Connectivity Change in High Refractive Index Lanthanum Niobate Glasses
The
highly ionic, high refractive index La<sub>2</sub>O<sub>3</sub>–Nb<sub>2</sub>O<sub>5</sub> system has a La-rich glass forming
region and another Nb-rich glass forming region. The La-rich and Nb-rich
regions have markedly different structural and physical properties.
Structural analyses using diffraction and spectroscopic measurements
combined with structural modeling show that the Nb-rich glass, which
has unusually high oxygen packing density, is a network of distorted
NbO<sub><i>n</i></sub> polyhedra with mainly corner-sharing,
and LaO<sub><i>x</i></sub> polyhedra with both corner-sharing
and edge-sharing. Contrastingly, in the La-rich glass, small-sized
symmetrical NbO<sub><i>n</i></sub> polyhedra with a large
amount of edge-sharing are inhomogenously distributed in the network
of LaO<sub><i>x</i></sub> polyhedra. The drastic connectivity
change of cation–oxygen polyhedra and the dense oxygen packing
due to edge-sharing polyhedra contravene long-established rules of
oxide glass formation. These results raise the possibility that novel
higher refractive index with lower wavelength dispersion glasses,
which contain highly ionic heavy elements at the lower left in the
periodic table, may be synthesized