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Device quality InAs/InGaAs multiple quantum well (MQW) structures were grown on InP substrates by metalorganic vapor phase epitaxy (MOVPE) and applied to lasers emitting at wavelengths longer than 2 mum. InAs/InGaAs MQWs with flat interfaces were obtained by adjusting the growth temperature between 460 degC and 510 degC. The photoluminescence peak wavelength of the MQWs increases from 1.93 to 2.47 mum as the thickness of InAs quantum wells increases from 2 to 7 nm. The structural and optical properties remained almost unchanged even after annealing at 620 degC. For 40-mu m-wide stripe broad-area lasers with 5-nm-thick InAs quantum wells, a lasing wavelength longer than 2.3 mum and an output power higher than 10 mW were achieved under continuous-wave operation at a temperature of 25 degC. These results indicate that InAs/InGaAs MQW structures grown by MOVPE are very useful for the active region of 2 mum wavelength lasers. [ABSTRACT FROM PUBLISHER]

The recent paper is devoted to design, manufacturing and testing the permanent magnet system to be used for Positron Emission Tomography (PET) cyclotron. The using permanent magnet material instead of copper coils allows essential electric power savings during PET cyclotron operation, though it comes to some increasing construction cost. The main problem why until now permanent magnets were not used for PET cyclotron magnet system is huge magnetic force, making cyclotron assembling/disassembling and isochronous magnetic field adjustment very difficult. For presented magnet system that problem is solved by applying rotating system providing the magnetic field switch-off (reduction to practically zero level inside working aperture). It makes assembling and adjustment easy at force free conditions. The main parameters of permanent magnet system are as follows: the average field is 1.4 T, pole radius is 375 mm and weight is 900 kg. As it shown in paper the magnetic properties of constructed permanent magnet system does satisfy to specification for magnet system of typical 10 MeV cyclotron for PET radioisotope production. [ABSTRACT FROM AUTHOR]

We have investigated the relationship between current distribution and transport AC losses in coaxial multi-layer HTS transmission cables and clarified that the same layer current in conducting layers can reduce the transport AC losses effectively. It can be, however, considered that magnetization losses are much larger than the transport AC losses in a large transport current. Therefore, we analytically investigated effective current and magnetic field distributions for reducing total AC losses in an HTS transmission cable with a large transport current. The total AC losses in the case of the same applied magnetic field in the conducting layers were much smaller than those of the same layer current in the conducting layers. This result means that inhomogeneous current distribution is more effective for reducing the total AC losses than homogeneous current distribution. The total AC losses decreased with the electrical insulation thickness between the conducting and shielding layers; the electrical insulation thickness is one of the important parameters in terms of reducing the total AC losses. [ABSTRACT FROM AUTHOR]

A nonlinear Mach-Zehnder interferometer based on photonic-crystal waveguides is proposed and modeled by using rigorous finite-element-based numerical scheme. Guided modes of nonlinear photonic-crystal waveguides are investigated to determine a length of nonlinear arm and a switching power, and further, intensity-dependent switching characteristics of the nonlinear Mach-Zehnder interferometer, for the first time, as far as the authors know, are demonstrated. Effects of saturable nonlinearity and two-photon absorption (TPA) on switching characteristics are also taken into account. [ABSTRACT FROM PUBLISHER]

A finite-element method (FEM) is newly formulated for the modal analysis of nonlinear periodic optical waveguides. In order to treat periodicity in the propagation direction, periodic boundary conditions are imposed on the envelope of electromagnetic fields. The validity of this method is verified by way of numerical examples of a PC waveguide composed of nonlinear dielectric pillars placed on square array in the cladding region. Furthermore, the present method is applied to various nonlinear photonic crystal waveguide structures for exploring appropriate structures to enhance the nonlinearity and their nonlinear modal properties are presented, including coupled-resonator optical waveguides. [ABSTRACT FROM PUBLISHER]

The time evolution of a pulse-excited charge qubit in a semiconductor double quantum dot is investigated. All-electrical initialization and coherent gate control of the system are achieved, and coherent charge oscillation is observed through the transport measurements. The oscillation frequency and decoherence time T2 are estimated by fitting the transport data with a simple model. Possible decoherence mechanisms in a charge qubit system are pointed out and discussed in detail. [ABSTRACT FROM PUBLISHER]