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The thermohaline circulation of the ocean results primarily from downwelling at sites in the Nordic and Labrador Seas and upwelling throughout the rest of the ocean. The latter is often described as being due to breaking internal waves. Here we reconcile the difference between theoretical and observed estimates of vertical mixing in the deep ocean by presenting a revised view of the thermohaline circulation, which allows for additional upwelling in the Southern Ocean and the separation of the North Atlantic Deep Water cell from the Antarctic Bottom Water cell. The changes also mean that much less wind and tidal energy needs to be dissipated in the deep ocean than was originally thought.
Relief Bragg gratings were imprinted by 248 nm interferometric excimer laser ablation on potassium ion-exchanged channel waveguides in BK-7 glass overlaid with a thin high-index InOx film. Using five pulses of energy density 60 mJ/cm2, a spectral transmittance notch of depth 66% and FWHM<0.1 nm was obtained at 1547 nm in the TE polarization for a waveguide having a nominal width of 8 µm and a 135-nm-thick InOx overlayer. In waveguides coated with 100 nm InOx, with widths increasing from 3 to 8 µm, the reflection wavelength shifted by 0.12 nm/µm and the reflectivity increased monotonically.
A new technique for UV direct writing of Bragg gratings in planar silica is presented. In this method the Bragg gratings and the channels are defined simultaneously, conferring advantages in flexibility of design and grating performance. Photosensitive germanium-doped silica-on-silicon produced by flame hydrolysis deposition was used.
The fabrication and operation of robust integrated optical refractometers, suitable for precise measurements of small changes without ambiguity over a wide range of refractive indices, is described. The design primarily uses an optical fibre coupled dual-sensitivity integrated optical Mach–Zehnder interferometer (MZI) sensor chip incorporating 3×3 directional coupler combiners and internal referencing. High-index tantalum pentoxide (Ta2O5) films were deposited on the waveguide surface in order to increase sensitivity and measurements of their response to liquid analyte index have been carried out by passing aqueous sucrose solutions over the sensor surface. These devices are intended for application as high-sensitivity multi-purpose chemical sensors and bio-sensors.
The thermal diffusion of Nd^3+ and Gd^3+ ions in YVO_4 is characterized, yielding diffusion rates of 7X10^-19 and 44X10^-19 m^2s^-1, respectively, at 1400°C and activation energies of 5.3X10^-19 and 2.9X10^-19 J, respectively, for diffusion along the c axis. The fluorescence properties of the Nd^3+ -diffused YVO_4 agree well with those of bulk doped materials. The formation of a planar optical waveguide was also observed for one of the Nd^3+ -diffused samples. This characterization is a significant first step toward fabrication of waveguide lasers and amplifiers in this important laser material.
The measurement of surface charge is an important parameter for evaluating the electrical performance of high voltage insulation materials. The method proposed allows on line mwurement of charge and can generate two-dimensional images that represent the charge behaviour on the surface of the material under test. The measurement system utilises Pockels effect by using a wafer of bismuth silicon oxide (BSO) as the sensing element. This method allows non-destructive measurements since no direct electric signal or component interferes with the surface charge. Unlike conventional surface charge measurement systems, this approach can dynamically observe and simultaneously quantify surface charge. This allows the surface charge distribution under the influence of a time varying electric field to be studied. The system?s accuracy and sensitivi...
Microstructured optical fibers are of increasing interest since they offer unique optical properties and design flexibility that cannot be achieved in conventional forms of fiber. We review structural features, fabrication, optical properties and potential applications of index-guiding holey optical fibers. The state-of-the-art is presented for both silica and compound glass holey fibers.
Spin and population dynamics of photoexcited carriers in GaAs/AlGaAs and InGaAs/InP quantum wells is investigated from 5K to 300K, revealing transition between excitonic and free carrier spin-relaxation at intermediate temperatures. Localisation is found to prolong spin relaxation of excitons by two orders of magnitude.
The dielectric strength is believed to limit the second-order nonlinearity induced by poling. We propose a simple method that allows the measurement of the dielectric strength of alkali-rich glasses in-situ.
Lasers based on planar optical waveguides have recently generated interest for use as high-average-power sources, due to a combination of attractive features including high optical gain, good thermal-power handling and compatibility with the geometry of high-power diode pump sources [1,2]. However, high-power diode pumping of monolithic plane-plane waveguide cavities generally leads to multi-mode output. One possible route to controlling the spatial output of such devices is through the use of tapered waveguides [3]. For devices of a few centimetres in length, adiabatic expansion can be achieved up to widths of a few hundred microns. This leads to structures compatible with end-pumping by broad-stripe diodes or, for higher power, side-pumping by diode bars. The latter route requires a very strong absorption of the diode emission, as th...
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