Anomalous Dispersion Characteristics Research Articles

Anomalous Dispersion Characteristics of Periodic Substrate Integrated Waveguides From Microwave to Terahertz

This paper presents the anomalous dispersion characteristic of a periodic substrate integrated waveguide (SIW) with results obtained by a rigorous formulation using the hybrid generalized scattering matrix (GSM) and finite-element method (FEM), showing two types of anomalous modal behaviors, namely: 1) ${\rm TM}_{0}$ surface wave leakage in connection to the near cutoff transverse resonance of a rectangular waveguide section alternating with either microstrip or parallel sections and 2) complex modes inside the lowest ${\rm TE}_{01}$ -like propagating zone. A rigorous limiting case study of the SIW via spacing approaching less than 10% of via diameter validated the proposed hybrid GSM/FEM formulation and enabled the detailed description of various types of modes, namely, propagating ${\rm TE}_{01}$ -like, a pair of complex modes, and above the stopband regimes, respectively. Convergence analysis and comparisons to the existing literature were carried out to validate the proposed method in addition to the limiting case study. Measured results of the CMOS prototypes validate the theoretical prediction from 325 to 450 GHz and confirm the accuracy of the proposed method.

Atomic torsional modal analysis for high-resolution proteins.

We introduce a formulation for normal mode analyses of globular proteins that significantly improves on an earlier one-parameter formulation [M. M. Tirion, Phys. Rev. Lett. 77, 1905 (1996)] that characterized the slow modes associated with protein data bank structures. Here we develop that empirical potential function that is minimized at the outset to include two features essential to reproduce the eigenspectra and associated density of states in the 0 to 300cm-1 frequency range, not merely the slow modes. First, introduction of preferred dihedral-angle configurations via use of torsional stiffness constants eliminates anomalous dispersion characteristics due to insufficiently bound surface side chains and helps fix the spectrum thin tail frequencies (100-300cm-1). Second, we take into account the atomic identities and the distance of separation of all pairwise interactions, improving the spectrum distribution in the 20 to 300cm-1 range. With these modifications, not only does the spectrum reproduce that of full atomic potentials, but we obtain stable reliable eigenmodes for the slow modes and over a wide range of frequencies.

TO CONTROL THE PROPAGATION CHARACTERISTIC OF ONE-DIMENSIONAL PLASMA PHOTONIC CRYSTAL USING EXPONENTIALLY GRADED DIELECTRIC MATERIAL

The efiect of exponentially graded material on the modal dispersion characteristics, group velocity and efiective group index as well as phase index of refraction of a binary One-Dimensional Plasma Photonic Crystals (1D-PPCs) has been studied. The dispersion relation is derived by solving Maxwell's equations and using the transfer matrix method. The anomalous dispersion characteristics are observed for difierent values of selection parameters. The introduction of graded dielectric layers in 1D-PPCs provides additional parameters for controlling the propagation characteristics of 1D-PPCs. Also, the band gap is shown to become larger with the increase of plasma frequency and plasma width. Hence the structure having plasma and exponentially graded dielectric layer in unit cell is more useful for controlling and tuning of the plasma functioning devices than the structure having plasma and homogeneous dielectric layer in one unit cell.

Broadband negative refraction with a crossed wire mesh

It is demonstrated that a structured material formed by nonconnected crossed metallic wires may enable negative refraction over a wide frequency range. This phenomenon is a consequence of the anomalous dispersion characteristics of the material, particularly of the fact that the isofrequency contours are hyperbolic. These properties rely on the nonlocal response of the crossed wire mesh, and establish a different paradigm for obtaining negative refraction without left-handed materials.

Ultrahigh enhancement in absolute and relative rotation sensing using fast and slow light

We describe a resonator-based optical gyroscope whose sensitivity for measuring absolute rotation is enhanced via use of the anomalous dispersion characteristic of superluminal light propagation. The enhancement is given by the inverse of the group index, saturating to a bound determined by the group velocity dispersion. We also show how the offsetting effect of the concomitant broadening of the resonator linewidth may be circumvented by using an active cavity. For realistic conditions, the enhancement factor is as high as ${10}^{6}$. We also show how normal dispersion used for slow light can enhance relative rotation sensing in a specially designed Sagnac interferometer, with the enhancement given by the slowing factor.

Anomalous behaviour in a Bragg reflection waveguide

A novel asymmetric Bragg reflection waveguide (BRW) showing anomalous dispersion characteristic is presented. The abnormal behaviour of increase of modal effective index with wavelength is primarily caused by the changes taking place in the imaginary part of the Bloch wavevector, in the periodic stratified cladding. The phase velocity and the group velocity dispersion characteristics for the waveguide have also been analyzed. Such an anomalous behaviour can find applications in the design of integrated optical devices.

Wavelength demultiplexer consisting of Photonic crystal superprism and superlens

We propose a novel compact wavelength demultiplexer, for which two functions arising from the anomalous dispersion characteristics of photonic crystals are combined. One is the superprism that exhibits large angular dispersion and expansion of light beam. The other is the superlens used for the focusing of the expanded light beam. Theoretically, a high resolution of 0.4 nm will be realized in the 1.55 ?m wavelength range with device areas of 0.2 and 2.0 mm2, respectively, for available bandwidths of 3 and 35 nm. Also, a low insertion loss of less than 1 dB is expected by the optimization of input and output ends of the photonic crystals. The demultiplexing function is clearly demonstrated in finite-difference timedomain simulation.

A theoretical analysis of the propagation properties of the twisted-wire pair running above a ground plane

Electromagnetic coupling between neighboring circuits can be mitigated using twisted-wire pairs (TWP). However, the presence of twisting provokes an alteration of the wave propagation parameters of the wire pair itself. The periodicity arising from conductor twisting gives rise to frequency-domain standing-wave effects that may dramatically alter the system propagation properties as compared to those concerned with the untwisted case. This paper deals with the analysis of the propagation properties of a three-conductor nonuniform transmission-line system comprising a TWP running above a conducting plane. In particular, we show that important stop bands with anomalous dispersion characteristics occur for frequencies such that the twist period gets close to one half wavelength. A simplified abrupt-twist model for the TWP, together with an averaging technique, is used in order to derive closed-form analytical results for the wave propagation parameters of the three-conductor system. This model, despite its simplicity, conveys the key ideas necessary for a good understanding of the propagation properties of the helical-type TWP configuration.

Broad-band and extremely flat super-continuum generation via optical parametric gain extended spectrally by fourth-order dispersion in anomalous-dispersion-flattened fibers

Broad-band and extremely flat super-continuum (SC) generation phenomenon was found out in propagation of sub-100 fs and pJ optical pulse along very short anomalous-dispersion-flattened fibers (0.6/spl sim/3.4 m). In contrast to the usual SC cases, fiber-optic anomalous-dispersion characteristics are essential. Results of numerical and experimental analyzes suggest that its origin stays in the broad-band optical parametric gain generation whose spectrum is extended by fourth-order dispersion characteristics. The remarkable features of SC spectra are (1) excellent static flatness of /spl plusmn/1 dB over 150 nm (or /spl plusmn/0.5 dB over 100 nm) and (2) asymmetric spectral expansion toward the shorter wavelength side overwhelming S-band.

The disordered solid phases of potassium cyanide

Molecular dynamics calculations have been carried out for the orientationally disordered phases of solid potassium cyanide. It has been found that the properties of the simulated crystal are very sensitive to the assumed charge distribution of the cyanide ion and that there is a strong correlation between the static and dynamic consequences of assumptions about the form of the interionic potential. Results are reported for the orientational distribution of the cyanide ions and for time correlation functions relevant to polarised Raman and inelastic neutron scattering experiments. The anomalous dispersion characteristic of transverse acoustic phonons in phase I is shown to be reproducible, but no single model has been found that will account for all the existing experimental data.

Dispersion cancellation using optical-fiber filters

The anomalous dispersion characteristic of recently reported [Opt. Lett. 5, 476 (1980)] optical-fiber filters is proposed for use in equalization of material dispersion in optical-communication (OC) links employing single-mode fibers. Calculations show that, under appropriate circumstances, a fiber filter of length shorter than 2 cm can equalize dispersion from an OC link about 1 km long.