Hollow Dielectric Waveguide Research Articles

Analysis of mode structure in hollow dielectric waveguide fibers.

In this paper, we analyze the electromagnetic mode structure of an OmniGuide fiber-a hollow dielectric waveguide in which light is confined by a large index-contrast omnidirectional dielectric mirror. In particular, we find that the modes in an OmniGuide fiber are similar to those in a hollow metallic waveguide in their symmetries, cutoff frequencies, and dispersion relations. We show that the differences can be predicted by a model based on a single parameter-the phase shift upon reflection from the dielectric mirror. The analogy to the metal waveguide extends to the transmission properties, resulting in the identification of the TE01 mode as the lowest-loss mode of the OmniGuide fiber.

Extinction and scattering of a guided beam in a hollow dielectric waveguide.

We present a theoretical approach to the problem of mode scattering by a spherical object that is placed inside a circular dielectric waveguide. This approach is based on the separation-of-variables method for each subsystem, namely, the spherical inclusion and the circular dielectric cylinder, and on the concept of the generalized recursive T-matrix algorithm for multilayered structures. We apply the technique to the backward and the forward scattering of a quasi-optical beam in the form of the fundamental HE11 mode by a sphere inside a circular hollow dielectric waveguide. The results calculated for the perfectly conducting spherical objects inside the circular hollow dielectric waveguide are compared with corresponding measured data of the backward-and the forward-scattering characteristics at the 4-mm wave band.

Quasi-optical waveguide modeling method and microcompact scattering range for the millimeter and submillimeter wave bands

The possibility of using the quasi-optical waveguide modeling (QWM) method in the near millimeter and submillimeter ranges of the electromagnetic spectrum for a study of the backward and forward scattering amplitude and phase characteristics of physical objects or scaled models is discussed in the paper. The method is realized with the aid of a quasi-optical waveguide microcompact range (MCR). The microwave part of MCR is based on the regular section of a hollow dielectric waveguide (HDW) and corresponding quasi-optical components. The results of measurements of backward and forward scattering characteristics for a number of standard objects in the 4-mm wavelength band are presented.

An Optimum Sectional Waveguide Taper for Quasioptical Transmission Lines

The paper considers an optimum sectional waveguide taper (OSWT) which at a shortest length of the transition region provides nearly adiabatic propagation of the fundamental mode between circular, widely different in diameter quasioptical transmission lines of class “hollow dielectric waveguide” (HDW). Derived as a consequence of coaxial circular-horn sections, the OSWT offers all the advantages of a simple geometry and lends itself to simple fabrication techniques. The relationships among the critical geometrical parameters and the loss calculation formulae are presented. The comparison studies show that even at a few sections, the OSWT is almost as good in performance as the parabolic taper, but the OSWT is much better from a mechanical viewpoint. And compared to the ordinary linear taper, the OSWT allows essential cut in length and loss with the broadbandness kept. The HDW-based four-sectional OSWT has been fabricated and tested in a quite broad wave range 2,5-8 mm. The testing results lend a good support to the analytical formulae lying at the basis of the design software.

Design of Optimum Sectional Tapers for Quasioptical Waveguide Circuits

The paper considers an optimum sectional taper (OST) which at a shortest length of the transition region provides nearly adiabatic propagation of the fundamental mode between circular, widely different in diameter quasioptical transmission lines of class "hollow dielectric waveguide". Derived as a series of coaxial circular-horn sections, the OST offers all the advantages of a simple geometry, primarily the ease in manufacture. The relationships among the critical geometrical parameters and the insertion loss calculation formulae are presented. The comparison studies show that the OST keeps the broad band ness of the ordinary linear taper but it allows much shorter length and lower loss. And even at a few sections, the OST is almost as good in performance as the ideal parabolic taper.

Ray representation of the electromagnetic field in a circular hollow dielectric waveguide used as a facility for scattering measurements

A new ray representation of electromagnetic field inside a quasi-optical structure in the form of a circular hollow dielectric waveguide (HDW) is suggested, which permits, among other things, estimating the dimensions of the measurement area for the free-space scattering characteristics of an object that can be measured in the millimeter- and submillimeter-wave regions by putting the object into a circular HDW.

Modeling of radar scattering conditions inside a circular hollow dielectric waveguide

A new ray representation of electromagnetic field inside a quasi — optical structure in the form of a circular hollow dielectric waveguide is suggested and confirms the possibility for the unusual application of such a waveguide as an off-beat microanechoic chamber for electromagnetic modeling in the near millimeter and submillimeter wave regions.

A spherical scatterer inside a circular hollow dielectric waveguide

A theoretical investigation is presented of scattering characteristics of a perfectly conducting spherical object placed inside a quasi-optical transmission line of the millimeter and submillimeter waves in the form of a circular hollow dielectric waveguide (HDW). From the analytical expressions obtained, backscattering and extinction cross sections of this object are derived via the excitation coefficient of the dominantHE 11 mode of the circular HDW and the HDW geometrical parameters. The agreement of the results with the corresponding data for the scattering of a plane homogeneous wave is shown.

APPLIED RADIOPHYSICSA Hollow Dielectric Waveguide as a Field Former in Quasioptical- Waveguide Modeling of Electromagnetic Scattering

In the present paper, a hollow dielectric waveguide (HDW) is theoretically considered as a field former to be employed in the laboratory investigations of the scattering characteristics of physical objects or their scaled models by the method of quasioptical-waveguide modeling (QWM) in the near-millimetric /submillimetric wave range. The field quality criteria developed for the HDW-enclosed operation volume yield the easy and sufficiently accurate for practical purposes analytical relations which allow the designer to select optimum HDW parameters controlling the desired field characteristics within the operation volume. Applying the minimization criterion to longitudinal variations of the field in the operation volume reveals that a quasioptical forming structure of the HDW type admits a far greater extent of the operation volume as compared with free space. This opens the way to measure very extended scatterers through their scaled models which may be as long as hundreds and even thousands of the wavelengths.

Field distribution in He-Ne waveguide lasers

In a waveguide laser, the laser light is guided in a hollow dielectric waveguide which also serves to confine the discharge. In this paper we study the radial distribution of the resonant field progressive components for such a laser, both theoretically and experimentally. To compute the resonant field distribution, we use a numerical method based on a field expansion in terms of a set of Bessel functions.

Method for radar cross section measurements in millimeter and submillimeter wave regions

We present a new method for electromagnetic modeling radar scattering processes. In this method we use a quasi-optical waveguide of the type of "hollow dielectric waveguide" as a fundamental component of radar cross section (RCS) instrumentation systems. Such waveguide structure produces required target-illuminating quasiplane wave and suppresses unwanted waves as well as transmits the legitimate signal from test object, mounted inside this waveguide, to the reception zone. Presented method is especially effective one in millimeter and submillimeter wave regions, in particular, for investigation RCS of targets with small reflectivity.

Quasi-optical unidirectional ferrite devices

The questions concerning design and study of quasi-optical (QO) ferrite unidirectional devices, based on two types of transmission line, namely hollow dielectric beamguide (HDB) and squire metal-dielectric waveguide (MDW) were considered.

Attenuation, modal, and polarization properties of n < 1, hollow dielectric waveguides

The attenuation coefficients for hollow sapphire and lead-based, oxide glass waveguides are calculated using an approximate formalism from Marcatili and Schmeltzer [Bell Syst. Tech. J. 43, 1783-1809 (1964)]. These results are compared with an exact calculation, and the agreement is found to be excellent for bore diameters greater than 100 µm. Although the hollow lead glass waveguides have measured losses in agreement with theory, the hollow sapphire waveguides have losses greater than those calculated for the lowest-order mode. This excess loss is due to roughness of the inner surface of the sapphire. The hollow dielectric waveguides are also shown to preserve polarization and the single mode as do some of the hollow metallic waveguides.

Waveguide beam splitters and recombiners based on multimode propagation phenomena

Novel waveguide beam splitters and recombiners based on multimode propagation phenomena in hollow step-index waveguides are predicted and demonstrated. The splitter designs are based on symmetrically feeding the fundamental-mode field from a square cross-section waveguide, 2a × 2a, into a multimode rectangular guide, 2a × 2b (b > a). As a result of multimode superposition phenomena, unique transverse-field patterns representing different-order multiway splitting of the input field occur at predictable positions along the rectangular-guide axis. The predictions are verified experimentally at 10.6 μm with hollow dielectric waveguides but are considered to be more widely applicable.

Modeling of a linear array of hollow dielectric square waveguide CO/sub 2/ lasers phase coupled by Talbot effect

The author develops the theory and numerically analyzes the capability of a linear array of hollow dielectric square waveguide CO/sub 2/ lasers phase coupled by the Talbot effect. The author used a Rigrod-like analysis for computing the power supplied by the phased array versus the insertion losses induced by both the filling factor and the finite number of lasers. The result is compared to the one obtained with an identical device in incoherent mode. This makes it possible to define a coupling efficiency. An arrangement able to improve this coupling efficiency using a three-mirror cavity is presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

APPLICATIONS OF SUBMILLIMETER WAVEGUIDE TO LASER-MODE SELECTION AND NONLINEAR OPTICS

Use of submillimeter waveguide for laser transverse mode control, four-wave parametric frequency conversion, ultrafast broadband radiation generation and optical pulse shortening are presented. This paper begins with a general introduction to the applications of submillimeter waveguide to laser physics and nonlinear optics. Transverse mode selection by using an intracavity capillary is then described. Nonlinear optical frequency conversion in gas-filled hollow dielectric and hollow metallic waveguide structures is discussed. Applications of submillimeter liquid-core fiber to stimulated scattering, ultrafast broadband radiation generation and optical pulse shortening are presented, and transient stimulated Rayleigh-Kerr scattering is proposed to explain the observations of these nonlinear optical processes. It is shown that the unique characterization of high usable pump power and high power emission of submillimeter waveguides makes the waveguide structures ideal for high-power, high-energy laser physics and nonlinear optics.

Mode structure of hollow dielectric waveguide lasers

The mode structure of hollow dielectric waveguide lasers with free space sections and flat mirrors is studied theoretically and experimentally. The study covers the fundamental mode and the three most important higher order modes, and graphs are given which identify regions of high mode discrimination in the parameter space. Calculated coupling losses are verified experimentally by detailed studies of the output power of CO2 lasers as a function of resonator geometry. The intensity profile inside and outside the resonator is calculated, and the profile outside the resonator is compared with experiments for the fundamental mode as well as for the higher order modes. It is shown that in general the fundamental mode is non-Gaussian, and that drastically different output characteristics are obtained for different choice of output plane. The paper identifies design criteria for obtaining single line and single mode oscillation over a wide tuning range, even in the densest region of the CO2 laser line spectrum, and this is exemplified by a spectroscopic application.

Transmission losses and mode-selection characteristics of a curved hollow dielectric waveguide with a rough surface

The effects of surface roughness and axial bends of a hollow dielectric waveguide on transmission of 10.6-μm CO2 waveguide laser radiation are measured. An analytical expression for various waveguide modes has been obtained in the beam approximation for calculating the value of the transmission of a real waveguide. This expression takes into account both Fresnel losses and radiation scattering due to the roughness. It is shown that the efficiency of selecting transverse modes from the waveguide laser is diminished with an increase in the bending radius and the waveguide diameter and also with a decrease in the radiation wavelength.

Linear array of self-focusing CO/sub 2/ waveguide lasers

A novel design is described for a phase-coupled linear array of hollow dielectric waveguide lasers using self-focusing waveguides. An analytical form of the eigenmodes of such an array has been worked out. Tests on a small linear array of RF-excited CO/sub 2/ lasers are reported that demonstrate very fair agreement between theoretical computations and experimental results. Experimental results are also given on the coupling between the modes of the individual guides.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Guidance and concentration of radiation by a hollow dielectric waveguide

A planar hollow dielectric waveguide is investigated in analogy with a quantum mechanical problem of two potential wells. Resonances are distinguished in the continuous part of the spectrum. The resonances correspond to radiation modes which concentrate in the central hole of the waveguide. These modes may find applications in confinement of concentrated laser beams and construction of long resonators for free electron lasers.