Linfang Shen

Finite-size effects of a left-handed material slab on the image quality.

The characteristics of an imaging system formed by a left-handed material (LHM) slab of finite length are studied, and the influence of the finite length of the slab on the image quality is analyzed. Unusual phenomena such as surface bright spots and negative energy stream at the image side are observed and explained as the cavity effects of surface plasmons excited by the evanescent components of the incident field. For a thin LHM slab, the cavity effects are found rather sensitive to the length of the slab; the bright spots on the bottom surface of the slab may stretch to the image plane and degrade the image quality.

Terahertz surface plasmon polaritons on periodically corrugated metal surfaces

Based on a modal expansion of electromagnetic fields, a rigorous method for analyzing surface plasmon polaritons (SPPs) on a periodically corrugated metal surface has been formulated in this paper. This method takes into account the finite conductivity of the metal as well as higher-order modes within the grooves of the surface structure, thus is able to accurately calculate the loss of these spoof SPPs propagating along the structured surface. In the terahertz (THz) frequency range, the properties of the dispersion and loss of spoof SPPs on corrugated Al surfaces are analyzed. For spoof SPPs at THz frequencies, the strong confinement of the fields is often accompanied with considerable absorption loss, but the performance of both low-loss propagation and subwavelength field confinement for spoof SPPs can be achieved by the optimum design of surface structure.

Band structure for a one-dimensional photonic crystal containing left-handed materials

The explicit dispersion equation for a one-dimensional periodic structure with alternative layers of left-handed material (LHM) and right-handed material (RHM) is given and analyzed. Some abnormal phenomena such as spurious modes with complex frequencies, discrete modes and photon tunnelling modes are observed in the band structure. The existence of spurious modes with complex frequencies is a common problem in the calculation of the band structure for such a photonic crystal. Physical explanation and significance are given for the discrete modes (with real values of wave number) and photon tunnelling propagation modes (with imaginary wave numbers in a limited region).

High birefringence photonic crystal fiber with a complex unit cell of asymmetric elliptical air hole cladding

High birefringence induced by elliptical air hole photonic crystal fibers (EHPCFs) is analyzed numerically using the finite-element method. Statistical correlations between the birefringence and the various parameters are obtained. We found that the complex elliptical air hole is better than that of a circular one to obtain high birefringence in photonic crystal fibers. Our suggested structures can considerably enhance the birefringence in EHPCFs and show that the birefringence can be as high as 1.1294 x 10(-2), which is higher than the birefringence obtained from conventional step-index fiber (5 x 10(-4)), circular air holes PCF (3.7 x 10(-3)), and elliptical hollow PCF (2.35 x 10(-3)).

High-Order Modes of Spoof Surface Plasmon Polaritons on Periodically Corrugated Metal Surfaces

High-order modes of spoof surface plasmon polaritons (SPPs) on the periodically corrugated metal surfaces are investigated theoretically with the modal expansion method. An analytical expression for the condition of existence of high-order modes is presented. The properties of high-order modes such as dispersion and fleld pattern are analyzed detailedly, from which it seems that the propagation of spoof SPPs along the corrugated metal surface is mainly based on the coupling between the open groove cavities.

Surface modes at the interfaces between isotropic media and indefinite media.

Characteristics of surface modes at the interface between an isotropic medium and an indefinite medium that has a dispersion relation of hyperbolic form are studied. Four cases for the isotropic medium, including normal, left-handed, magnetic (with negative permeability), and metallic media, are considered. The conditions for the existence of surface modes in each case are analyzed in detail, and the results are expressed explicitly, indicating that the existence of surface modes is determined by the nature of the indefinite medium as well as the orientation of the boundary surface of this anisotropic medium. The energy flows associated with the surface modes are also discussed.

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.

Wedge mode of spoof surface plasmon polaritons at terahertz frequencies

Surface plasmon polaritons (SPPs) propagating along a structure consisting of a single row of metallic wedges periodically protruding out of a planar metallic surface are investigated theoretically. It is shown that such a structure can sustain a mode of spoof SPPs in the terahertz region, whose fields are highly confined in the transverse plane. The guiding mode in the structure possesses excellent properties such as good modal shape, large propagation length, and low bending loss, making it a promising candidate for routing terahertz radiation in highly integrated circuits.

Analysis for the convergence problem of the plane-wave expansion method for photonic crystals

The convergence feature of two types of plane-wave expansion methods commonly used for photonic crystals is analyzed. It is shown that the reason for the slow convergence of these plane-wave expansion methods is not the slow convergence of the Fourier series for the permittivity profile of the photonic crystal but the inappropriate formulation of the eigenproblem. A new formulation of the eigenproblem is presented to improve the convergence in the one-dimensional case.

A novel directional coupler utilizing a left-handed material

A novel directional coupler with a left-handed material (LHM) layer between two single-mode (SM) waveguides of usual material is introduced. The coupling system is analyzed with the supermode theory. It is shown that such an LHM layer of finite length can shorten significantly the coupling length for the two SM waveguides. An LHM layer with two slowly tapered ends is used to avoid the reflection loss at the ends.