Dielectric Fiber Research Articles

Infrared hollow fiber with a vitreous film as the dielectric inner coating layer

A vitreous material with an optimum reflective index of 1.41 for dielectric metallic hollow fiber is used for what is believed to be the first time. A smooth vitreous film is formed by the treatment of a hardener at room temperature by using the liquid-phase coating technique. Low-loss properties were obtained in both the infrared and visible wavelength regions, and the fibers are of high durability when sterilized. This hollow fiber is promising for use in medical applications or other harsh environments.

Analysis and optimal design of smart skin structures for buckling and free vibration

Analysis and optimal design of the smart skin, i.e., the conformal load-bearing antenna structure for buckling and free vibration are studied. The smart skin is modeled as an asymmetric composite sandwich structure which consists of different materials. In order to act as antennas or radars, a dielectric layer is embedded on the middle surface of the sandwich structure. The formulation of the smart skin model is based on the first-order shear deformation plate theory, and numerical results are obtained by the finite element method using a four-node plate element with five degrees of freedom at each node. The buckling and vibration behaviors of the smart skin are investigated with the variation of the aspect ratio, Honeycomb core thickness, area of dielectric layer and fiber angle of face sheet. Furthermore, to maximize the buckling load and the natural frequency of the smart skin, the optimal design is performed using a simple genetic algorithm.

Asymptotic formulas for calculating the decay length of linearly polarized groups in optical fibers with step-index profile

We obtain asymptotic expressions for the eigenvalue difference of the waveguide modes of an optical fiber with step-index profile. The estimation of accuracy of the formulas is presented. Relationship between the indices of the modes that form linearly polarized groups and the roots of the characteristic equation and the principal mode number is considered. Estimates for the difference between the eigenvalues and the decay length of linearly polarized groups in a perfect dielectric fiber are obtained. The results of experimental studies of the integral degree of linear polarization of the output radiation are shown for different input angles and their comparison with the theory is carried out.

Energy transfer in optical fibres

The possibility of energy transfer over long distances in the form of laser radiation propagating in dielectric optical fibres is discussed. Because nonlinear-optical phenomena in glasses prevent the transfer of high radiation powers in standard two-layer fibres, the outlook for this transfer is associated with the development of the technology of microstructure fibres with a hollow core and with further progress in the development of high-power fibre lasers.

Preparation of the Ultra‐Low Dielectric Constant Polyimide Fiber Membranes Enabled by Electrospinning

AbstractIn this article, electrospinning technique has been demonstrated for the synthesis of ultra‐low dielectric constant polyimide fiber membranes. Poly(amic acid) fiber membranes have been prepared as precursor. After the treatment of thermal imidization, ultra‐low dielectric constant polyimide fibers membranes can be obtained. The morphologies and structures of precursors and products are characterized by scanning electron microscopy (SEM), Fourier transmission infrared (FTIR) spectra, and a radio frequency (RF) impedance/capacitance material analyzer. The DK of the as‐prepared polyimide membrane ranges from 1.53 to 1.56, which could be applied in the electronic packaging industry.magnified image

Transient fields in the input coupling region of optical single-mode waveguides

We investigate numerically the optical field in the region immediately behind the input facets of dielectric step-index single-mode slab and fiber waveguides. Visualization of the intensity distributions gives insight into the formation of the fundamental mode and of radiation modes. For a more quantitative characterization we determine the amount of optical power and mode purity of the field in core vicinity as a function of propagation distance. The investigation assists in designing and optimizing waveguides being employed as modal filters, e.g. for astronomical interferometers.

Um Desenvolvimento Numérico nas Equações Dinâmicas de Sólitons em Fibras Óticas

We develop and evaluate a numerical procedure for a system of nonlinear differential equations, which describe the propagation of solitons into ideal dielectric optical fibers. This problem has analytical solutions known. The numerical solutions of the system is implemented by the finite element method, using methods of stabilization such as Streamline Upwind Petrov-Galerkin (SUPG) and Consistent Approximate Upwind (CAU). Comparing the numerical and analytical solutions, it was found that the numerical procedure adequately describes the dynamics of this system.

Vectorial modeling of near-field imaging with uncoated fiber probes: transfer function and resolving power

Using exact 3D vectorial simulations of radiation coupling into uncoated dielectric fiber probes, we calculate amplitude transfer functions for conical single-mode fiber tips at the light wavelength of 633 nm. The coupling efficiency of glass fiber tips is determined in a wide range of spatial frequencies of the incident radiation for opening angles varying from 30 degrees to 120 degrees . The resolution in near-field imaging with these tips is considered for field distributions limited in both direct and spatial-frequency space. The characteristics of the transfer functions describing the relation between probed optical fields and near-field images are analyzed in detail. The importance of utilizing a perfectly sharp tip is also examined.

A study of neutron and gamma radiation effects on transmission of various types of glasses, optical coatings, cemented optics and fiber

A study of radiation effects on various types of glasses, dielectric optical coatings, cemented optics and fiber was undertaken with a view to select them for extreme radiation environments. Samples were exposed to different radiation doses in the Pakistan Research Reactor-I (PARR-I) for neutron and Cobalt 60 source for gamma irradiation. Transmissions were measured before and after irradiation. The dielectric coatings were subjected to additional tests (adhesion, abrasion and humidity, etc.) as per MIL-M-13508C and MIL-C-675C. All 15 glasses studied showed varying amounts of transmission loss as expected, with negligible degradation for three types. Recovery of transmissions with time/ageing was also studied, with more or less complete recovery with temperature annealing. A faster bleaching of darkened/brown glasses was achieved by using UV lamps or UV laser. The dielectric coatings (HR, AR) and one of the two commercial optical cements showed excellent resistance to neutrons and gamma radiations, and could be good candidates for the fabrication and utilization of optical components in extreme radiation environments. The data allowed several Chinese glasses to be studied for the first time.

Towards dispersion relations for tapered core dielectric elliptical fibers

The paper presents an analytical investigation of the electromagnetic wave propagation in a tapered core dielectric elliptical step-index fiber. Implementing Maxwell's equations in elliptical coordinates, field components are deduced that essentially incorporate Mathieu and the modified Mathieu functions. Finally, the characteristic dispersion equations are developed for even and odd modes supported by the fiber.

Towards the Dispersion Characteristics of Tapered Core Dielectric Optical Fibers

Using Maxwell's field equations, an analytical investigation is presented of the modal characteristics for a step-index plastic clad tapered optical fiber operating in the infrared region of the electro-magnetic spectrum. Following rigorous analytical approach, dispersion relations are developed, and a study is presented of the fiber characteristics for different lower order modes. The cutoff situation is also discussed. Attention is also paid to the characteristics of dispersion curves for the tapered fiber under consideration by taking into account the different possible modes. Results are compared with conventional optical fibers in terms of dispersion characteristics.

Electromagnetic characteristics of frequency selective fabric composites

Frequency selective fabric composites that transmit microwaves in certain frequency bands are proposed. The composites consist of carbon fibres and low-loss dielectric fibres that together build periodic patterns. Unlike existing metallic frequency selective surfaces, the frequency selective fabric composite with additional load-carrying capability showed an amount of transmission near a resonance frequency.

Eigenvalue and field equations of three-layered uniaxial fibers and their applications to the characteristics of long-period fiber gratings with applied axial strain

By using the Debye potentials, the exact eigenvalue equations and the corresponding field distributions of the core and cladding modes for three-layered, radially stratified, and dielectric uniaxial optical fibers are derived completely; the modes include TE, TM, and hybrid HE/EH modes. The strain characteristics of long-period fiber gratings' (LPFGs') with applied axial strain are investigated theoretically by studying three-layered uniaxial optical fibers. When uniform axial strain is applied to fiber, the core, and inner and outer cladding become uniaxial crystal optically; that is, the optical axes are parallel to the fiber's axis. Analytic expressions of the strain sensitivities of LPFGs are derived. The analysis reveals that the strain sensitivities of LPFGs based on various cladding modes, including the shift value and direction of the resonance wavelength, differ greatly.

Multipurpose carbon fiber sensor design for analysis and monitoring of the resin transfer molding of polymer composites

The resin transfer molding (RTM) process is taking an ever-growing place among the manufacturing technologies of polymer composite parts because of its numerous advantages. However, consistent production of high-quality parts is difficult to achieve and requires better understanding of the process and good control of the raw materials. Part-to-part variations are inevitable as a result of uncarefully controlled molding environments and unidentifiable or undetected disturbances that cannot be completely eliminated or accounted for. Despite of many efforts to understand and model the fundamental physical and chemical behavior of materials during processing, there is no reliable system able of predicting the optimum processing parameters to manufacture high-quality parts in a productive way. In this context, this work aims to develop systems allowing the monitoring of the whole RTM process (from preforming to resin curing) and that are reliable, cheap, and easy to use on production line. We have chosen to investigate the potential of the electric and dielectric carbon fiber sensors, which have already proved to be suitable for in service damage monitoring and preventive maintenance without any integration issues. However, the development of the continuous electric sensor has been limited by the polarization of the resin under the direct current. The flow front and the cure monitoring of the resin has been achieved with the dielectric sensor, energized by an alternative current preventing the polarization. Additionally, the ability of this carbon fiber sensor to evaluate the thickness of dry reinforcements and to measure online the actual unsaturated permeability of reinforcements has been demonstrated. POLYM. COMPOS., 26:717–730, 2005. © 2005 Society of Plastics Engineers

Capillary Plasma Formation by a Laser

A plane parallel laser beam, incident on a cylindrical dielectric fiber perpendicular to the axis of the fiber, focuses to small dimension as it approaches the axis. The focusing effect is enhanced by nonlinear self-focusing in the dielectric. For a given radius of the fiber one requires a specific laser intensity for which the beam focuses on the axis. In the axial region, however, the high intensity of the laser leads to tunnel ionization and optical breakdown of the dielectric, causing electron–hole pair production and plasma formation in the form of capillary. The plasma tends to self-defocus the laser.

Comment on “Low level plasma formation in a carbon velvet cesium iodide coated cathode” [Phys. Plasmas 11, 1680 (2004)

First Page

Metal wires for terahertz wave guiding

Sources and systems for far-infrared or terahertz (1 THz = 10(12) Hz) radiation have received extensive attention in recent years, with applications in sensing, imaging and spectroscopy. Terahertz radiation bridges the gap between the microwave and optical regimes, and offers significant scientific and technological potential in many fields. However, waveguiding in this intermediate spectral region still remains a challenge. Neither conventional metal waveguides for microwave radiation, nor dielectric fibres for visible and near-infrared radiation can be used to guide terahertz waves over a long distance, owing to the high loss from the finite conductivity of metals or the high absorption coefficient of dielectric materials in this spectral range. Furthermore, the extensive use of broadband pulses in the terahertz regime imposes an additional constraint of low dispersion, which is necessary for compatibility with spectroscopic applications. Here we show how a simple waveguide, namely a bare metal wire, can be used to transport terahertz pulses with virtually no dispersion, low attenuation, and with remarkable structural simplicity. As an example of this new waveguiding structure, we demonstrate an endoscope for terahertz pulses.

A multi-channel optical fibre thermometer

As part of a project aimed at identifying unsatisfactory temperature distributions within foods heated in microwave ovens, a multi-channel optical fibre temperature system based on fluorescence thermometry has been developed. The system consists of a digital fluorescence lifetime thermometer, a 12-channel optical fibre multiplexer and a set of fully dielectric optical fibre probes. A custom analog-to-digital signal processing (A–DSP) for fluorescence lifetime detection was developed and special probes, suitable for microwave oven applications, were constructed. The multi-channel thermometer was calibrated by comparison against a platinum resistance thermometer traceable to ITS-90 in the temperature range 0–150 °C. The system affords a temperature repeatability to within 0.3 °C, with 0.5 s response time. Overall system performance and probe calibration are reported. Examples of temperature distribution measurements within food analogues heated in microwave ovens are reported, as well.

On a new approach to generate spatial optical soliton in dielectric fibers

In this Letter, we describe a new and simple approach for modulating the electromagnetic wave and propagating it in a dielectric medium in the form of self-guided soliton by considering the torque developed between the induced dipoles in the medium and the external electromagnetic field without taking into account the nonlinear Kerr effect.

Response to the “comments on the analysis of a weakly guiding doubly clad dielectric optical fiber with an annular core”

Response to the “comments on the analysis of a weakly guiding doubly clad dielectric optical fiber with an annular core”