Anomalous Dispersion Properties Research Articles

Broadband supercontinuum generation in hollow-core photonic crystal fibers infiltrated with chloroform

The chloroform-infiltrated square lattice photonic crystal fibers (PCFs) are designed with the difference of the air hole diameters in the cladding to improve chromatic dispersion and nonlinear properties. Based on numerical simulation results, two optimal structures with flat dispersion, high nonlinear coefficient, and small confinement loss are used for supercontinuum (SC) generation. The first fiber has an all-normal dispersion regime, a nonlinear coefficient of 486.355[Formula: see text]W[Formula: see text].km[Formula: see text] generating an SC spectrum of 640.3[Formula: see text]nm within 30 dB levels at a pump wavelength of 0.945[Formula: see text][Formula: see text]m with peak power as low as 1.44[Formula: see text]kW. With anomalous dispersion properties, the second fiber gives a very broad SC spectrum of 1471.8[Formula: see text]nm within 30 dB levels at a 1.4[Formula: see text][Formula: see text]m pumping wavelength with a peak power of 20[Formula: see text]kW. All-fiber SC sources operating with low-power pump lasers can use these fibers to effectively replace glass-core fibers.

Engineering Hybrid Guided Modes in Subwavelength Uniaxial Metamaterial Waveguides

We report anomalous dispersion properties of hybrid guided modes (HGMs) and their group velocity in a subwavelength uniaxial metamaterial waveguide with metal cladding. We derive exact dispersion relations and modal fields of HGMs by solving eigenvalue equation based on basic electromagnetic field theory in detail. Numerical results show that two fundamental HGMs and two types of high-order HGMs can be excited, and their exciting conditions are clarified. In addition, such HGMs can be engineered to belong to normal dispersion or anomalous dispersion. Importantly, the HGMs may be controlled to be forward or backward, and their group velocities may be very small in a certain frequency band. These properties make such metamaterial waveguides have many potential applications in integrated optics, information storage and biosensing.

A Lattice-Boltzmann Model of Mass Transport in the Diffusion Layers of Vanadium Redox Flow Batteries

During the last years all-Vanadium Redox Flow Batteries (VRFBs) have gained attention as a way to store energy due to their high energy efficiency, long cycle life, independently tuneable power/energy size, and lack of contamination from cross-mixing of electrolytes [1]. However, in order to improve VRFBs performance, some conceptual and technological issues are still open. In particular, a properly designed geometry of flow channels and porous medium, which guarantees a uniform distribution of the reacting species all along the electrode, is still under investigation [2]. The ideal configuration aims to minimize the drag and maximize the mixing. In the present work a Lattice Boltzmann tri-dimensional multi-relaxation-time model has been used to better understand the dependence of mass and momentum transports on the porosity and carbon fiber preferential orientation in a typical VRFB porous medium. The model has been successfully validated against theoretical solutions of the Volume Averaged Navier-Stokes Equations [3]. The typical porosity used in VRFB, f=0.9±0.1, is considered in a triperiodic box (left panel of Fig. 1). The flow is driven along the x direction by a mean pressure gradient DP/Dx which imposes the Reynolds number Rep= rd p U/(m (1-f)) with U the bulk velocity, dp the fiber diameter, r and m the fluid density and dynamic viscosity, respectively. Different fiber orientations and distributions have been analyzed, from random isotropic cases to a completely oriented medium. Results show that the drag measured by the friction factor fp =(f 3/1-f)(DP/Dx)/(rU 2) is well captured by the semi-empirical Ergun formula fe=1.75+150/Rep when the medium is isotropic or preferentially oriented in directions transversal to the flow (right panel of Fig. 1). Conversely, when the medium is preferentially oriented along the flow direction the drag is appreciably reduced differing from the standard predictions. The fiber orientation also affects the mixing in the porous medium that needs to be enhanced to optimize the VRFB performance. The mass transport shows anomalous dispersion properties. Super-diffusive and sub-diffusive behaviors can be observed depending on the considered direction and fiber preferential orientation. A detailed analysis of mixing and drag properties of the porous media will be discussed in the final contribution in order to highlight the optimal configurations for VRFB.

Anomalous dispersion properties of TM waves in subwavelength metallic waveguides loaded by uniaxial metamaterials

Abstract Dispersion properties of transverse magnetic (TM) waves in a subwavelength metallic waveguide loaded by uniaxial metamaterials are investigated, based on two kinds of uniaxial metamaterials with different orientations of optical axis. The numerical results show that the existence of fundamental TM 0 mode and high-order TM modes in the waveguide system is dependent on the orientation of optical axis. In addition, their anomalous dispersion properties are clarified. When the orientation of optical axis is selected properly, there are two branches of dispersion curves for each high-order mode—one is normal dispersion and another belongs to anomalous dispersion, showing a transition from a backward wave to a forward one with the increase of working frequency. Moreover, the group velocity and energy flow distribution for TM 1 mode are also demonstrated. These properties may have potential applications in optical information storage, integrated optics and nanophotonic devices.

Anomalous dispersion and group velocity properties in subwavelength uniaxial metamaterial waveguide with metal cladding

We investigate propagation behavior of electromagnetic waves in a slab uniaxial metamaterial waveguide with metal cladding and discuss the dispersion relation, group velocity and energy flux distribution of transverse electric guided modes in two kinds of uniaxial metamaterial waveguides with different orientations of optical axis in detail. The numerical results show that there exist anomalous dispersion properties such as backward modes existing in low-frequency range, and the group velocity can be negative or approach zero. If the orientation of optical axis is selected properly, each guided mode has two dispersion curves—one is normal dispersion and another belongs to anomalous dispersion and shows a transition from a backward mode to a forward one with the angular frequency increasing. In addition, the condition of the existence of cutoff frequency is clarified. These properties may have potential applications in optical information storage, optical communication, integrated optics and nanophotonic devices.

Anomalous dispersion properties of an atomic medium with a closed excitation contour

This paper examines the refractive index dispersion in an atomic medium with a closed excitation contour. The refractive index as a function of the algebraic sum of the phases of excitation fields (Φ) and Rabi frequencies is shown to have a maximum for Φ ≤ π/4. A frequency range is found near the maximum where an increase in refractive index is accompanied by amplification of one of the optical fields.

Photonic band mixing in linear chains of optically coupled microspheres

The paper deals with optical excitations arising in a one-dimensional chain of identical spheres due to optical coupling of whispering gallery modes (WGM). The band structure of these excitations depends significantly on the intermixing between WGMs characterized by different values of angular quantum number, l. We develop a general theory of the photonic band structure of these excitations taking these effects into account and applied it to several cases of recent experimental interest. In the case of bands originating from WGMs with the angular quantum number of the same parity, the calculated dispersion laws are in good qualitative agreement with recent experiment results. Bands resulting from hybridization of excitations resulting from whispering gallery modes with different parity of l exhibits anomalous dispersion properties characterized by a gap in the allowed values of wave numbers and divergence of group velocity.

Plasmonic Band Gaps and Trapped Plasmons on Nanostructured Metal Surfaces

Nanostructured metal surfaces comprised of periodically arranged spherical voids are grown by electrochemical deposition through a self-assembled template. Detailed measurements of the angle- and orientation-dependent reflectivity reveal the spectral dispersion, from which we identify the presence of both delocalized Bragg and localized Mie plasmons. These couple strongly producing bonding and antibonding mixed plasmons with anomalous dispersion properties. Appropriate plasmon engineering of the void morphology selects the plasmon spatial and spectral positions, allowing these plasmonic crystal films to be optimized for a wide range of sensing applications.

Dispersion And Gas Flow Effects In The Ring Laser Gyro

The effects of dispersion and gas flow on the operation of the ring laser gyro are summarized. The theory is shown to predict a dimple in the anomalous dispersion properties of the atomic transition. Experiments were carried out using a 43.4 cm and 21.7 cm visible laser gyro. Scale factor and nullshift results showed consistency and confirmed the existence of the dimple. The peak-peak relative magnitude of the scale factor dimple was found to be approximately 25 x 10-6. Gas flow was varied by unbalancing the discharge currents in the two legs of the laser gyro. A nullshift sensitivity of 0.0066 deg/hr/mamp of unbalance was found. Analysis of the data showed the nullshift sensitivity to velocity flow to be 4.4 deg/hr/cm/sec of velocity unbalance.