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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.