Showing papers on "Radiation mode published in 1976"

Optical waveguide refractive index profiles determined from measurement of mode indices: a simple analysis.

Abstract: The WKB approximation is used to derive simple equations that predict the shape of the index profile from measured mode indices of a planar optical waveguide. This nondestructive test is a useful tool in the study of diffused guides. The index profile is assumed either to decrease monotonically from the surface or to be symmetrical in the case of a buried guide. The approximation uses straight line segments to connect the measured points. Results are compared with mathematical solutions for exponential, Fermi, and step distributions and with other independent experimental observations of the profile in a nickel-diffused LiNbO(3) guide.

Frequency selective interwaveguide coupler

Abstract: The coupler consists of an intermediate finite length waveguide located between a first and at least one second waveguide with the refractive index of the intermediate waveguide being greater than the refractive indices of the other waveguides. The intermediate waveguide further includes a structure which either in a fixed manner as by a surface relief, or in a controlled manner--as by electro-optic or acousto-optic perturbation, produces modes of propagation in the intermediate waveguide for a preselected frequency, such that energy may be coupled to or from the waveguides to the intermediate waveguide by mode matching and this energy may be converted from one mode to another in the intermediate waveguide.

Radiation and propagation of a surface‐wave mode on a curved open waveguide of arbitrary cross section

Abstract: A general scheme for calculating the change (both the real part and the imaginary part) of the propagation constant of a surface-wave mode on a general open waveguide structure is presented. By carefully keeping track of lower-order terms in the analysis, it is shown how approximations commonly made in other analyses can result in quite significant errors in the determination of the radiation loss. The resulting formulas require knowledge only of the fields and propagation constant of the corresponding straight waveguide mode, and the value of the radius of curvature of the waveguide axis. As a simple example, the curvature loss of a Goubau line is calculated.

Optical waveguide loaded with high refractive-index strip film

Abstract: Mode propagation and field distribution in a strip-loaded waveguide are analyzed for the case where the refractive index of the loading film is higher than that of the waveguide. It is found that the propagation constant is remarkably changed by loading the film with the thickness around the cutoff. As a result, the effect of the optical energy confinement below the strip film is large compared with the previously proposed case where the low-index film is loaded, and the use of the high refractive-index film as the loading strip is very attractive for constructing a three-dimensional waveguide structure.

Method and apparatus for introducing geometrical perturbations in optical fiber waveguides

Abstract: The present invention relates to method and apparatus for fabricating multimode optical fiber waveguides having reduced modal dispersion as a result of deliberate enhancement of mode coupling in the waveguide. The axial alignment and/or the diameter of an optical fiber waveguide is varied by means of one or more modulated heat sources, such as, for example, a microflame jet or CO 2 laser, directed against the fiber waveguide. By controlling the modulation of the heat source, the spatial distribution of the geometrical perturbation pattern can be controlled, thereby producing controlled mode coupling in the fiber waveguide.

Coupled‐mode theory of Raman amplification in lossless optical fibers

Abstract: Raman amplification in weakly guiding optical fibers is investigated for the two cases of weak and strong mode coupling. Use is made of the statistical ensemble of similar fibers introduced by Marcuse for studying mode coupling in optical waveguides. In the weak‐coupling case, the Stokes powers of different modes increase independently, and the gain of each mode depends on the initial poewrs of all laser modes. In the strong‐coupling case, power equipartition between Stokes modes takes place throughout the fibers, and the common gain is the average of the individual mode gains.

Thin film magneto-optic mode converters

Abstract: Mode conversion of optical signals in thin film optical devices is obtained in a region of Faraday effect magnetic material waveguide by providing a periodic structure in which alternate half cycles have the magnetization parallel to the propagation direction to turn on the Faraday effect to induce mode conversion and in which the intervening half cycles have the magnetization perpendicular to the propagation direction to turn off the Faraday effect to prevent mode conversion. Stripe domains are preferably used to turn the Faraday effect off. Non-reciprocal mode conversion is obtained by optically coupling an anisotropic crystal to the waveguide to provide a quantity of mode conversion equal to that provided by the Faraday effect.

Mode conversion losses of randomly bent, singly and doubly clad waveguides for single mode transmission

Abstract: Mode conversion effects take place when a dielectric optical guide is bent and its curvature varies along the guide. This paper considers and compares such conversion losses of singly and doubly clad slabs (adopted as analogs of corresponding fibers) for single mode transmission. It is shown that the conversion loss of a W-type slab is much smaller than that of a singly clad slab, provided that the beamwidths of both guides are equal. This property is the consequence of the wider mode spacing of the W-guide.

Mode mixing with reduced losses in parabolic-index fibers

Abstract: We present design criteria for the construction of a modified parabolic-index fiber with intentional mode coupling. Mode coupling serves the purpose of reducing multimode pulse dispersion and is accomplished by introducing carefully designed index fluctuations into the fiber core or by controlled “random” bends of the fiber axis. Radiation losses due to mode coupling can be minimized by terminating the parabolic-index fiber core in an abrupt index discontinuity. The additional modes introduced by this step must be filtered out by periodic mode filters that consist of parabolic-index fiber sections without the refractive-index step.

Routine characterisation of single-mode fibres

Abstract: In single-mode fibres, the core diameter and refractive-index difference between core and cladding may be found from the widths of (a) the halfpower points and (b) the first minimum of the far-field radiation. The technique has been used to study the effect of heat treatment.

RF coupling and mode conversions at the lower hybrid resonance

Abstract: A thorough analytical study is conducted of linear mode conversion near lower hybrid resonance in a one-dimensional weakly inhomogeneous plasma. The analysis is based on the cold-, warm- and hot-plasma approximations depending on the ratio of the ion Larmor radius to the perpendicular wavelength. Mode conversion is found to take place in two different locations. An appropriate differential equation is derived to describe the electric field in each of the mode conversion regions. A complete conversion of a long wavelength mode to a short wavelength mode is confirmed in both regions. The energy coupled into the plasma and the surface impedance of the plasma are computed for slow-wave excitations.

A partially reflecting metal cladding: its effect on the modes of dielectric optical waveguides

Abstract: If the metal cladding of a dielectric optical waveguide is sufficiently thin to be only partially reflecting, then the waveguide modes differ from those of the conventional metal-clad waveguide. The TE modes are little affected by a variation in the metal thickness but the TM modes change considerably due to a coupling between the waveguide modes and the surface plasma waves supported by both the metal: dielectric interfaces and the metal film. It is the refractive index of the dielectric cladding which is remote from the guiding core that determines whether the lowest order TM mode is the TM0 or TM1 mode. This dielectric cladding also strongly influences the attenuation of the TM modes and, if the guide supports a TM0 mode, then the attenuation of the TM modes far from cut-off are an order of magnitude higher than that of the corresponding modes when the guide cannot support a TM0 mode. If the guide can support a TM0 mode then its dimensions can be chosen such that it will support the TEN and TMN modes with equal phase velocities. A lossless approximation is used to develop an expression which will specify the required guide dimensions directly and parametric plots of these dimensions are discussed.

Scattering from a localized inhomogeneity in a cladded fiber optical waveguide. 1:radiation loss.

Abstract: An exact analysis using the Green’s function formulation of the problem of scattering from a localized inhomogeneity inside a cladded fiber optical waveguide is carried out. The analysis yields radiation loss that agrees well with that evaluated from the infinite-medium approximation. However, the spatial distribution of the radiation loss, i.e., the radiation pattern, differs markedly from that predicted by the infinite-medium approximation. The same analysis also permits the study of mode conversion due to scattering to be reported separately.

Numerical solution for nonreciprocal inhomogeneous waveguide interface

Abstract: Mode matching is used to analyse the interface between a reciprocal homogeneous waveguide and a nonreciprocal inhomogeneous waveguide. The configuration used for the nonreciprocal structure is that of the twin-slab ferrite-loaded waveguide. The investigation is restricted to symmetrical E-plane loading, and to lossless structures in which only one mode may propagate. Based on the analysis, the interface and the nonreciprocal waveguide are described by relatively simple equivalent transmission circuits. In these circuits, unique equivalent transmission-line characteristic admittances are defined for the nonreciprocal waveguide. Results show that although the phase coefficients in the two directions of propagation can be very different, the equivalent characteristic admittances are nearly the same. Measurements on a practical version of the twin-slab configuration yield similar results. It is also noted that the energy stored, which is associated with the inhomogeneous interface, does not depend solely on the type of modes excited, in contrast to the case of (reciprocal) dielectric loading.

Method and apparatus for driving an optical waveguide with conherent radiation

Abstract: A method and apparatus for driving an optical waveguide with a coherent source of radiation. The apparatus includes means for providing a relatively high level of continuous wave (cw) coherent optical/infrared radiation in a closed waveguide, preferably traveling in one direction, means for scattering the optical radiation out of the closed waveguide, and means for collecting the scattered radiation in an adjacent waveguide for transmission to distant points. The cw coherent radiation is preferably generated within a single-frequency traveling-wave multi-turn Nd: YAG laser. A first waveguide is coupled at the ends to form a multi-turn laser or a closed loop system. The scattering means includes means for impressing a microwave modulating signal onto the first waveguide at the Bragg angle which serves to set up an effective optical grating within the first waveguide for scattering the laser beam. The second or output waveguide is positioned with respect to the scattered beam for intercepting same to travel along its optical axis. In a preferred embodiment, the second waveguide is potted in a parallel relationship with the first waveguide and includes an inclined end surface for redirecting the scattered radiation along its optical axis.

Multimode light waveguide for information transmission - has stepped core giving properties of gradient waveguide

Abstract: The waveguide consists of a tubular sheath which is surrounded by a core which has a refractive index higher than the refractive index of the sheath. The core consists of at least two homogenous concentric zones of light-conducting solid material, each having a different refractive index. The radius of the inner core zone is pref. as small as possible in comparison with the thickness of the outer core zone (n). This ensures that the transmittable bit rate is greater by a factor of at least 3/2 than that of a conventional multimode waveguide whose core is not stepped.

E-Type Modes in Cylindrical Dielectric Waveguides with Periodic Boundary Perturbations

Abstract: A genered method for the analysis of the effects of periodic boundary perturbations on E-type modes of dielectric waveguides (DW's) is presented. The method is applied to hollow cylindrical dielectric wavegtside (HCDW), and numerical solutions for surface wave and radiation mode intensities are given.

Multi-wavelength Determination of Single-mode Optical Waveguide Parameters

Abstract: Single-mode optical waveguide parameters, the refractive index and thickness, can be determined from the measurements of the propagation constants at multiple wavelengths. The dispersion curve and the guide thickness obtained by a two-mode method are compared with those determined by a three-wavelength and a six-wavelength technique using both symmetric and unsymmetric optical waveguides as examples.

E-Type Modes in Cylindrical Dielectric Waveguides with Periodic Boundary Perturbations (Short Papers)

Abstract: A general method for the analysis of the effects of periodic boundary perturbations on E-type modes of dielectric waveguides (DW's) is presented. The method is applied to hollow cylindrical dielectric waveguide (HCDW), and numerical solutions for surface wave and radiation mode intensities are given.

Mobile body*s location detecting system

Abstract: PURPOSE:To detect location of a mobile body by the use of low frequency, which has no radiation mode, of leakage coaxial cable laid along the travelling route of the mobile body.

Experimental Study on the Wave Mode in Elastic Cylindrical Rod

Abstract: Experimental study on the high frequency elastic wave mode propagating in a long circular aluminum rod was executed using new devices. A four terminals type piezo-electric transducer was used to observe the phase of vibration of each mode at the end of the rod and to classify directly the wave modes. Experimental results are as follows. Good coincidence between the theoretical group velocity and the experimental propagating velocity in each mode is obtained within the experimental errors. The mode coupling phenomenon is observed at the critical frequency, and also observed in the condition of the F2 mode type impulse. The directions of the neutral surface of vibration in the F1 modes are different from each other. The directions in the F1(2) mode and the F1(3) mode are perpendicular and parallel to the direction in the F1(1) mode respectively, and each direction does not change with a change of frequency.

Investigation of a dielectric waveguide with a variable refractive-index discontinuity at the boundary

Abstract: A description is given of a light modulator in which radiation travels along a waveguide and is modulated by variation of the refractive-index discontinuity at the boundary between the waveguide and an electrooptic material. A derivation is given of the dependence of the depth of modulation of the radiation on the change in the refractive index and the number of reflections at the waveguide boundary. It is shown that this method makes it possible to increase significantly the modulation frequency.

Mode Interaction Scheme Applied to Alternate Mode Patterns of a He–Ne Laser in Axial Magnetic Fields

Abstract: The stabilization of alternately strong and weak mode patterns of the 6328 A light from a Brewster window He-Ne laser in an increasing axial magnetic field is studied. One of the necessary conditions for the appearance of this pattern is newly discovered; that is, the Zeeman splitting has to be nearly equal to an odd-number times the adjacent mode separation. This condition is deduced from a mode interaction scheme involving four kinds of interactions. The interaction between Zeeman components and mode interactions in a standing-wave resonator laser are represented by a parallelogram, and the effect of Brewster windows and the adjacent mode interactions are represented by interactions between parallelograms. This scheme is formulated in order to calculate the mode intensities numerically and a good agreement with the observations is obtained.