Rigorous analysis of an embedded optical waveguide is tried by applying the mode-matching method, which is based on the Rayleigh expansion theorem and the mode -matching technique, by which the boundary conditions are matched in the sense of least squares. In conclusion, a high degree of accuracy is realised, and detailed propagation characteristics are obtained not only on the dispersion relation but also on the field distribution, comparing with the results by Marcatili's approximate method. The problem of single-mode transmission in the embedded waveguide is also discussed.
The design of an improved TM010-mode cavity for measuring the microwave breakdown characteristics of gases is discussed. The evaluation of the field distribution within the cavity, which contains an axially placed quartz tube and deformable end-wall diaphragm, is described. The operation of the cavity is tested using helium gas. The breakdown characteristic of the helium-oxygen mixture used in diving is measured as a function of pressure.
The purpose of the paper is to present a hybrid-mode analysis for obtaining dispersion characteristics of a broadside-coupled microstrip line. A characteristic equation for a propagation constant is derived via Galerkin's method in the Fourier-transform domain. It is shown that the dependence of the solution on the basis functions is small. Computed effective dielectric constants in the low-frequency region agree well with other investigators' numerical results, which are based upon the quasi-TEM method. Finally, dispersion characteristics, which are important in practical design, are demonstrated.
An expression for the input impedance seen by the coaxial line feeding a rectangular patch radiator is derived, taking the effect of wall admittance, conductor and dielectric losses into account. The real part of wall admittance of the patch radiator is determined from the angular spectrum of plane waves in the visible region of the wave-number plane, and its imaginary part is determined from the electric and magnetic energy stored in the region of the fringe field close to the radiating edges of the patch radiator. The electric field inside the patch radiator required for the analysis is expressed as a superposition of its resonant modes, the coefficients of which are determined in terms of wall admittance, surface impedance of the conducting boundary and amplitude of the exciting current. A comparison of the computed results with the available experimental data and theoretical results obtained by others is presented.
The large service integrated optical broadband communications system of the Heinrich-Hertz-Institut in Berlin, Germany has run a long-duration test during the last two years. The paper deals with the experiences gained during this long-time operation, reports on corresponding measurements of the optical components, bit-error rates and phase jitter, as well as measurements of the analogue optical subscriber line, and, finally, reviews the system's concept.
The theory of the resonant circular cavity loaded by many concentric dielectric tubes is developed, yielding the resonant frequency, the Q-factor and the field distribution for every mode. The theory is checked against experimental results and the application to atomic frequency standards is discussed.
An analytical solution for a circular waveguide bifurcation with incident TE11- and TM11-modes is presented using the residue calculus method. It is shown how the coupling between the TE1n- and TM1n-modes can be taken into account by expressing the coupling factor as a contour integral, which is the key step enabling the residue calculus method to be applied. Graphical results for the scattering matrix parameters of the junction are given for a range of waveguide radii of interest in the design of dual-mode coaxial prime focus feeds for paraboloidal antennas.
We demonstrate a novel optical waveguide interferometric modulator/switch in glass, which uses the thermo-optic (TO) effect based on the temperature dependence of refractive index. The TO modulation and switching characteristics are discussed experimentally. In particular, TO switching of the order of 50 μs was successfully obtained under an overdriven operation.
A method for the inclusion of higher-order evanescent modes in planar periodic structures is presented. The approach utilises the wave matrix method that is extended to account for the nonpropagating orders. As an example, the case of two closely spaced singly periodic gratings is demonstrated. In order to produce suitable data concerning reflection and transmission matrices, an integral equation formulation is used to describe the scattering behaviour of the grating. The application of the theory is intended for the design of multilayer dichroic surfaces.
An approximate model for high Qfactor wide-gap re-entrant cavity resonators is presented which is suitable for evaluating the performance of units capable of operation in the 900 MHz and 1500 MHz bands. The model is used to estimate the unloaded Q-factor and temperature stability. Theory and practice are compared.
The paper reports optical and current-triggered bistable switching of twin-stripe lasers. External light sources have been used to trigger the bistable switching directly, and the twin-stripe laser has been used in optical flip-flop configuration. The mechanisms causing the observed bistable switching have been investigated. The switching is believed to be associated with a change in the dominant waveguiding mechanism from self focusing to gain guiding, as the mode is observed to switch from a central self-focused mode to a gain-guided one crossing from one side of the laser at one facet to the other side at the opposite facet. The direction in which the crossing occurs is critically dependent on bias and may allow a tristable device to be developed. A simple theoretical model is reported to confirm the above hypotheses.
The coupling between the different guided modes of an integrated-optic waveguide grating filter is analysed. A numerical method based on a finite-difference scheme for the solution of this coupling problem in the case of normal incidence is presented. This allows one to study the influence of the grating profile on the coupling between guided or radiated waves. The exact numerical results are compared with approximate formulas for the coupling coefficient.
The paper considers the radiation patterns of both single- and dual-offset reflector antennas excited by an array feed in which mutual coupling effects have been fully included. For the single-offset reflector antenna, the crosspolar pattern is dominated by the geometry of the configuration, but for a dual-offset reflector, whose geometry has been optimised to give low crosspolarisation, mutual coupling in the array becomes a dominant factor in influencing crosspolarisation. The influence of feed displacement is also reported. It is found that the change in crosspolar level is marked only for the optimised dual reflector. Then for small displacements mutual-coupling effects dominate, but for large displacements they can be neglected.
A directional coupler switch having an extinction ratio better than 35 dB has been fabricated using Ti-indiffused waveguides. Detailed measurements of voltage, wavelength and temperature response and of the mode intensity profile are given. A computer model which allows inaccuracies in fabrication to be included is presented, with results relating extinction ratio to waveguide separation angle and mode confinement.
A planar helix, constituted of a pair of unidirectionally conducting screens conducting in different directions, is suggested as a slow-wave structure for application in a travelling-wave tube (TWT). Circuit parameters, such as interaction impedance and space-charge parameter, are derived for the suggested planar-helix TWT. Computed results for the planar helix indicate a performance comparable with that of its circular helix counterpart. Also, the change in interaction impedance and the dispersion characteristics of the planar helix, are considered in the presence of dielectric substrates and a metal shield. Results are obtained for a few different possible configurations of the planar helix on dielectric substrates with or without a metal shield. The phase velocity and interaction impedance reduce, both as the substrate thickness increases and as the metal shields are brought closer to the planar helix. However, the resulting degradation in the characteristics of the structure with commonly used substrate materials, for example alumina and beryllia, is less severe than in the case of the circular helix.
The results of the theoretical analysis of modal fields and radiation characteristics of the microstrip ring antenna are presented. Radiation patterns for the different modes are derived from the fringing fields at the inner and outer peripheries of the ring. Theoretical patterns are compared with experimental results at 1.8 GHz. The analyses show that the TM1m-modes (m = 2, 4, 6, ¿¿) are suitable for broadband boresight antennas while TM1m-modes (m = 1,3,¿¿) may be used for narrowband boresight antennas.
A monolithic optoelectronic integrated circuit (OEIC) including a laser diode, photomonitor and driving and detecting circuits has been fabricated on a semi-insulating GaAs substrate. The OEIC has a horizontal integrating structure which is suitable for realising high-density multifunctional devices. The fabricating process and the static and dynamic characteristics of the optical and electronic elements are described. The preliminary results of the co-operative operation of the laser and its driving circuit are also presented.
In the paper a derivation of the rough-surface reflection coefficient for the coherent reflected field is given. The result obtained assumes a plane wavefront incident on a Gaussian collection of sinusoidal surface waves with uniform phase distribution. The theoretical results obtained is compared with experimental data. In addition, the probability density function of sea-wave elevations is obtained.
Numerical results are presented for regular polygonal coaxial transmission line, a class of TEM transmission line with outer circular conductor, using an eigenfunction approach. A successive integration method in conjunction with the collocation or point-matching technique is utilised for boundary condition satisfaction. Highly accurate results are obtained with just a few terms in the solution, and they are in good agreement with those available in the literature. Results for equilateral triangular cross-section are presented for the first time.
The lack of satisfactory passive connectors, of standardisation in fibre-optic devices and the unidirectional light transmission employed in most fibre links prohibits the direct translation of networking techniques from the better developed wire or cable systems. A point-to-point network with nodes connected in an arbitrary fashion can provide an ideal solution to these problems while maintaining high network reliability and permitting easy reconfiguration, but has associated problems in the routing of the data. A possible solution is to use the flood routing technique as proposed by Neff and Senzig in their Anarchy network. Unfortunately, this network exhibits very low channel utilisation and has packet looping problems. In the paper we discuss methods of removing the looping problem and then propose a modified Anarchy flood routing (MAFR) protocol, for which a simplified performance analysis and simulation studies indicate that better network performance can be achieved with little additional hardware. However, we believe that a hybrid flood routing scheme (HFR) involving MAFR and a virtual circuit approach will produce a better system.
