Subwavelength imaging by a dielectric-tube photonic crystal

In contrast to previous two-dimensional coated photonic crystals, in this paper we propose a left-handed one that is made of dielectric tubes arranged in a close-packed hexagonal lattice. Without metallic cores, this structure is low-loss and convenient to fabricate. Negative refraction and its resulting focusing are investigated by dispersion characteristic analysis and numerical simulation of the field pattern. With proper modification at the interface, the image is improved. With better isotropy than that with noncircular rods, planoconcave lenses made by dielectric tubes focus a Gaussian beam exactly at R//n - 1/.

Core size scaling of helical-core optical fibres

The mode-area, scaling properties of helical-core optical fibres are numerically studied and the limit of core size for achievable single-mode operation is explored. By appropriate design, helical-core fibres can operate in a single mode with possible scaling up to 300 mu m in core diameter with numerical aperture 0.1.

Subwavelength imaging with two symmetrical interfaces by dielectric-tube photonic crystals

As distinct from coated photonic crystals, in this paper we propose a novel one that is made of dielectric tubes arranged in a close-packet square lattice. Without metallic cores, this structure is low-loss and convenient to fabricate. A left-handed frequency region is found in the second band by dispersion characteristic analysis. Without inactive modes for the transverse electric mode, negative refraction and subwavelength imaging are demonstrated by the finite-difference time-domain simulations with two symmetrical interfaces, i.e. Gamma X and Gamma M.

Spin-helical Dirac states in graphene induced by polar-substrate surfaces with giant spin-orbit interaction: a new platform for spintronics

Spintronics, or spin electronics, is aimed at efficient control and manipulation of spin degrees of freedom in electron systems. To comply with demands of nowaday spintronics, the studies of electron systems hosting giant spin-orbit-split electron states have become one of the most important problems providing us with a basis for desirable spintronics devices. In construction of such devices, it is also tempting to involve graphene, which has attracted great attention because of its unique and remarkable electronic properties and was recognized as a viable replacement for silicon in electronics. In this case, a challenging goal is to lift spin degeneracy of graphene Dirac states. Here, we propose a novel pathway to achieve this goal by means of coupling of graphene and polar-substrate surface states with giant Rashba-type spin-splitting. We theoretically demonstrate it by constructing the graphene@BiTeCl system, which appears to possess spin-helical graphene Dirac states caused by the strong interaction of Dirac and Rashba electrons. We anticipate that our findings will stimulate rapid growth in theoretical and experimental investigations of graphene Dirac states with real spin-momentum locking, which can revolutionize the graphene spintronics and become a reliable base for prospective spintronics applications.

Conductance calculation of a long tube with equilateral triangle cross section

Using the stratified gas flow model for calculating the conductance of long tubes with constant cross section, an analytical expression for calculating the conductance of along tube with equilateral triangle cross section has been derived. The formula given is applicable to the full pressure range. A minimum in the conductance in the intermediate flow state is shown. 2002 American vacuum Society.

Self-Similarity and helical symmetry in vortex generator flow simulations

According to experimental observations, the vortices generated by vortex generators have previously been observed to be self-similar for both the axial (u(z)) and azimuthal (u(circle minus)) velocity profiles. Further, the measured vortices have been observed to obey the criteria for helical symmetry. This is a powerful result, since it reduces the highly complex flow to merely four parameters. In the present work, corresponding computer simulations using Reynolds-Averaged Navier-Stokes equations have been carried out and compared to the experimental observations. The main objective of this study is to investigate how well the simulations can reproduce the physics of the flow and if the same analytical model can be applied. Using this model, parametric studies can be significantly reduced and, further, reliable simulations can substantially reduce the costs of the parametric studies themselves.