Jin-Jei Wu

Realization of tightly confined channel plasmon polaritons at low frequencies

Subwavelength guiding of channel plasmon polaritons (CPPs) is realized by a properly structured metallic groove at frequencies far below the plasma frequency of metal. Compared with CPPs at visible frequencies, more versatile physical mechanisms can be introduced in these CPPs by surface patterning, so that they can exhibit superior features as visible CPPs, while eliminating the potential drawbacks of the latter. Such designer CPPs are explained physically with the effective-index method and verified experimentally in the microwave regime.

Subwavelength Microwave Guiding by a Periodically Corrugated Metal Wire

The guiding properties of a periodically corrugated metal wire at microwave frequencies are studied theoretically. The outer radius of the corrugated wire is of subwavelength size, and it seems difficult for spoof surface plasmon polaritons (SPPs) in the wire to be confined highly, even if the set of the geometric parameters of the wire structure is optimized. However, if the grooves of the corrugated wire are filled with a dielectric with high permittivity, the strong field confinement of spoof SPPs can be achieved even at frequencies smaller than the asymptotic frequency, for which the SPP losses are quite low. It is also shown that for this type of wire structure, the subwavelength microwave guiding is available for a certain frequency range.

Band-rejection fiber filter and fiber sensor based on a Bragg fiber of transversal resonant structure.

We propose a novel band-rejection fiber filter based on a Bragg fiber of transversal resonant structure, which can also be used as a fiber sensor. Defect layers are introduced in the periodic high/low index structure in the cladding of the Bragg fiber. Coupling between the core mode and the defect mode results in large confinement loss for some resonant wavelengths inside the band gap of the Bragg fiber. A segment of the Bragg fiber of transversal resonant structure can be used as a band-rejection fiber filter, whose characteristics are mainly determined by the defect layer. The loss peak wavelength of the Bragg fiber is dependent on the refractive index and the thickness of the defect layer which indicates its applications of refractive index and strain sensing.

THE OPTICAL PROPERTIES OF BRAGG FIBER WITH A FIBER CORE OF 2-DIMENSION ELLIPTICAL-HOLE PHOTONIC CRYSTAL STRUCTURE

The optical properties of birefringent Bragg flber with a flber core of 2-dimension (2D) elliptical-hole photonic crystal structure has been studied. Elliptical air holes are introduced into the flber core to form a normal 2D photonic crystal structure with a hole pitch (center-to-center distance between the air holes) much smaller than the operation wavelength of the Bragg flber. The elliptical-hole photonic crystal structure acts as an anisotropic medium with difierent efiective indices for transmission light of difierent polarization, which inevitably results in high birefringence (up to the order of magnitude of 0.01) of the Bragg flber. The proposed Bragg flber possesses difierent band- gaps for difierently polarized mode. Besides the periodic alternating layers of high/low refractive indices, the bandwidth of the band-gap is also dependent on the efiective index of the flber core, which can be controlled by the area of the elliptical air holes.

Complete trapping of electromagnetic radiation using surface magnetoplasmons

Because the dispersion properties of surface magnetoplasmons (SMPs) in a magnetized plasmonic material closely depend on its cladding dielectric, it is possible to completely trap SMPs in a system consisting of a plasmonic material with cladding of a dielectric heterostructure. By using a semiconductor, our finite element simulation (performed using the software COMSOL) shows that terahertz one-way SMPs in such a system can be completely trapped at the interface of the heterostructure and hence, a focused subwavelength-scale hotspot with dramatically enhanced field is generated. Moreover, a one-way SMP pulse in this system can also be completely trapped, and the wave packet can be compressed into a stable hotspot on the subwavelength scale.

Anisotropic medium with parabolic dispersion

A layered metamaterial which is predicted by the effective medium theory to be an anisotropic medium with partial zero permittivities is analyzed carefully. It is shown that such a material has a dispersion relation in parabolic form, which is quite different from the known ones. This material may be viewed as a homogeneous medium but is spatially dispersive strongly. The structured medium may support either forward wave or backward wave, depending on the magnitude of the wave vector. Moreover, it is demonstrated that this medium with parabolic dispersion is especially suitable for the transmission of Gaussian beam with subwavelength width.

One-Way Propagation and Complete Trapping of Terahertz Radiations in All-Dielectric Systems

Surface magnetoplasmons (SMPs) in the three-layer structure of semiconductor, dielectric, and photonic crystal (PhC) are theoretically investigated. The PhC portion in the structure is designed properly so that its band gap covers the one-way propagation range of SMPs. In such an all-dielectric system, robust one-way propagation is available for SMPs at terahertz frequencies, and SMP band gap also occurs due to the PhC effect. With the use of a heterostructure of dielectric layer in the all-dielectric system, two different approaches for trapping terahertz radiation are proposed and verified by numerical simulations.

Terahertz Plasmonic Microcavity with High Quality Factor and Ultrasmall Mode Volume

In this paper, the characteristics of a novel terahertz plasmonic microcavity consisting of a circular hole and a coaxial (metallic) cylindrical core machined on a planar metal surface is theoretically investigated. It is shown that such a structure can sustain plasmonic modes, whose resonant wavelengths are much larger than the hole diameter and fields tightly localized within the cavity. For this cavity, both high quality factor and ultrasmall mode volume can be achieved in the terahertz range. As this type of microcavity is particularly compatible with planar technology, it has promising applications in the miniaturization and integration of terahertz optical components.

Variation in the Absolute Photonic Band Gap of Rods Ranging from Square to Octagonal in Square Lattices

The band structures and field patterns of dielectric rods in square lattices are calculated using the plane-wave method. The rods with various cross-sectional shapes from square to octagonal at a fixed filling-factor are constructed to assess the geometry effect of photonic crystals to their band gap properties. Analytical results indicate that the corner profiles of rods significantly affect the E- and H-polarization bands in resonance frequency and field distribution. The absolute photonic band gap is closed in the square lattice when square dielectric rods are replaced with octagonal dielectric rods.