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The ac losses of high critical-temperature superconducting (HTS) wires are numerically calculated by means of a finite element method (FEM), which is formulated with a self magnetic field due to an induced current as unknown. The numerical model is straight HTS wires carrying an alternating transport current in an external ac magnetic field perpendicular to the wire axis. In this situation, the electromagnetic field around the wires is given by two-dimensional (2D) Maxwell's equations. It is also assumed that the transport property is represented by either the critical state model or the power-law model, in which the electric field is proportional to the power of the current density. The obtained losses are compared with conventional theoretical curves in several simple geometries.

A directional coupler switch structure capable of short switching length and wide bandwidth is proposed. The switching length and bandwidth have a trade-off relationship in conventional directional coupler switches. Dispersion curves that avoid this trade-off are derived, and a two-dimensional photonic crystal structure that achieves these dispersion curves is presented. Numerical calculations show that the switching length of the proposed structure is 7.1% of that for the conventional structure, while the bandwidth is 2.17 times larger.

We have theoretically investigated two-dimensional photonic crystal (2D PC) L1–L21 cavities with low-refractive-index (low-n) material cladding using the 3D finite-difference time domain method assisted by group theory in the time domain. We investigated various optical properties of 2D PC L-type cavities including resonant frequency, modal symmetry, Q factor, modal volume, real-space distribution, wavevector-space distribution and resonant wavevector condition. The resonant modes in 2D PC L-type cavities are Bloch-like resonant modes. As the size of the cavity increases, the fundamental resonant mode changes from the Fabry–Perot (FP)-like resonant mode to the distributed-feedback (DFB)-like resonant mode with the envelope of the half-cycle sine window. The DFB-like resonant mode can suppress the radiation loss in the vertical direction. The DFB-like resonant mode can achieve a high Q factor (Q > 105) in a small cavity (L < 10 µm). The DFB-like resonant mode is the intrinsic resonant mode in 2D PC L-type cavities, and it is naturally formed without fine tuning. These results show the high potential of 2D PC L-type cavities with low-n material cladding.

Articles you may be interested inGrowth by molecular beam epitaxy of self-assembled InAs quantum dots on InAlAs and InGaAs lattice-matched to InPPhotoluminescence properties of self-assembled InAs quantum dots grown on InP substrates by solid source molecular beam epitaxy

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We have reported the effects of using an As 2 source and gradient composition-strain reducing laser (GC-SRL) to fabricate InAs quantum dot (QD) structures. The coalescence of the coherent QDs was reduced under the As 2 source. We have realized high density (8.0 × 10 10 cm −2 per sheet) measured by SEM and high uniformity (full-width at half-maximum: 23 meV measured by photoluminescence at room temperature) QDs using an As 2 source and the GC-SRL technique. Further, we have demonstrated ninestack QD lasers with high-density and high-uniformity QDs for the first time. We achieved a large modal gain of 54 cm −1 at a ground state emission of beyond 1.3-µm. A very low threshold current can be realized by a quantum effect for further equalization of QDs. We believe that the method of fabricating this QD laser with high density, high uniformity, and high modal gain will qualify as a novel technique.Index Terms-1.3-µm quantum dot (QD) laser, As 2 source, gradient composition-strain reducing laser (GC-SRL), high-density QD, high modal gain.