Showing papers on "Radiation mode published in 1973"

Fundamental optical attenuation limits in the liquid and glassy state with application to fiber optical waveguide materials

Abstract: Fundamental optical scattering and absorption mechanisms have been identified which limit light transmission in fiber optical waveguide materials. These mechanisms, which are intimately associated with the random structure in the liquid and glassy state, are described and then used as a basis for comparing fiber optical waveguide materials. It is concluded that pure fused silica is a preferred waveguide material, having ultimate total losses of 1.2 dB/km at the Nd : YAG laser wavelength of 1.06 μ, 3.0 dB/km at the GaxAl1−xAs emission wavelength of approximately 0.8 μ, and 4.8 dB/km at the GaP : Zn, O emission wavelength centered at 0.7 μ.

Mode guidance parallel to the junction plane of double-heterostructure GaAs lasers

Abstract: We investigate the origins of mode confinement, parallel to the junction plane, of stripe‐geometry double‐heterostructure GaAs injection lasers. Based upon the kind of control of the mode extent by the stripe width, we establish a distinction between two types of lasing mode guidance; (i) well‐behaved, where a single mode substantially fills the entire active region, and (ii) filamentary, where the mode size is much smaller than the width of the active region and its location is random. For low‐order well‐behaved modes, it is shown, at least in principle, that gain alone (no refractive index effects are required) can explain not only the confinement but also the approximate waveguide dimensions for which leakage losses, connected with the penetration of the mode into the regions outside the active guide, become important. When only this postulated gain‐guiding prevails in the case of higher‐order modes, we find that their spatial character is markedly different from the Hermite‐Gaussian distributions which have been seen for GaAs lasers. The introduction of a positive incremental index, which may reasonably be associated with the gain and/or with a thermal mechanism, restores agreement with observation. If any incremental index within the active region is negative, then although there is a defocusing effect, confinement may still be maintained by the gain. In the case of filamentary lasing we analyze four focusing mechanisms; two are connected with local built‐in gain (loss) and refractive index variations, while two are current dependent and are related to the saturation of gain‐associated refractive index and the free carrier effect. While all four processes appear to be reasonable candidates for providing the necessary confinement in filamentary lasing, the latter two simultaneously violate a condition necessary for stability of a filament. We conclude that imperfections in lasers are likely to be related to filamentary lasing and that such behavior may not be intrinsic to such devices.

Coupled mode theory of round optical fibers

Abstract: This paper presents a comprehensive theory of mode coupling in optical fibers with imperfections. The paper begins with the derivation of a general coupled wave theory based on the modes of the ideal fiber. The general theory is applied to a simplified description of guided and radiation modes of the fiber that is valid for small core-cladding index differences. The simplified theory results in expressions for the coupling coefficients that are nearly as simple as those of the slab waveguide. As an example, the theory is applied to the calculation of radiation losses caused by pure core diameter changes and by elliptical deformations of the fiber core.

Method of filtering modes in optical waveguides

Abstract: Modes are filtered in an optical waveguide by selecting and providing a periodic variation, such as a surface corrugation or a refractive index variation, in a filter region in the waveguide. The filter region diverts light in an unwanted mode from the propagation axis by scattering or reflection. Both planar waveguide filters and fiber-optic filters are disclosed.

Two different mode interactions in an electron tube with a Fabry—Perot resonator—The Ledatron

Abstract: An electron tube with a Fabry-Perot resonator for the generation of millimeter and submillimeter waves, the Ledatron, has been investigated both theoretically and experimentally. Two different mode interactions, Fabry-Perot mode and surface wave mode, were predicted and found to exist. These two modes can be separated by proper selection of the mirror spacing of the Fabry-Perot resonator in the tube. These two mode oscillations have different characteristics. In the case of the Fabry-Perot mode, the oscillating frequency is tuned mainly by variation of the mirror spacing, that is, mechanical tuning is predominant. On the other hand, in the case of the surface wave mode, electronic tuning predominates. For gratings of the same physical size, the surface wave mode oscillator needs a larger electron accelerating voltage than the Fabry-Perot mode oscillator in order to obtain the same wavelength. The experimental results are in good agreement with our theory of operation.

Periodic dielectric waveguide filter

Abstract: An optical waveguide comprising either a substrate coated with a layer of optic material or a clad optic fiber. A periodic variation in the index of refraction of either: (1) the substrate and/or the optical layer, or (2) the core and/or cladding of the optic fiber, is introduced so that unwanted frequency components present in the optical signal passing through the waveguide are eliminated. The waveguide may be employed as a band-pass or a band-stop filter, or for phase-matching purposes. Various means are disclosed for altering the periodicity of the index of refraction to thereby tune the device.

Nonreciprocal waveguide mode converter

Abstract: An optical waveguide which provides coupling between waveguide modes dependent upon the direction of propagation. The device comprises a sandwich of an anisotropic material, a neutral material and a magneto-optic material. Such a system may be used as an isolator or circulator in integrated optical circuits.

Mutual Coupling Between Parallel-Plate Waveguides

Abstract: The radiation field and mutual coupling between two identical parallel-plate waveguides having the same axis of symmetry are investigated. Jones' method of formulation is applied and a modified Wiener-Hopf equation is obtained. Expressions for the radiated field in free space, reflected field in the exciting waveguide, and transmitted field in the coupled waveguide are obtained and the reflected and transmitted fields are expressed in terms of waveguide modes. The reflection coefficient for each mode is represented by three terms, two of which are due to reflections at the open end of the exciting waveguide and are constant along the waveguide. The third term is the contribution from the field scattered by the open end of the coupled waveguide and decays along the waveguide according to the radiation condition. Similarly, the transmission coefficient of each mode is represented by three terms, two of which decay along the coupled waveguide and the third one is constant. The radiation field is also divided into three terms. One of them is due to the radiation from the open end of the exciting waveguide and the other two are the contribution of multiple interactions between the two waveguides. Computed results for the reflection and transmission coefficients and the radiation field are shown for TE/sub 0,1/ excitation and various separation distance of the waveguides. The results for the reflection and transmission coefficients are oscillating functions of period /spl pi/, and approach gradually the well-known final values of a single excited wavegnide.

Optical waveguide linear modulator array

Abstract: An optical waveguide linear modulator array comprising an optical waveguide having an input coupler and an output coupler The waveguide or substrate is formed of electrooptical material with different shaped electrodes secured thereto An electrical field applied between the electrodes modulates the radiation passing through the waveguide so that the radiation may be phase shifted or shaped into desired outputs

Broadband waveguide with means for suppressing te {11 {11 mode

Abstract: A rectangular waveguide dimensioned to propagate the TE10 mode includes at each end of the waveguide terminations for terminating the TE20 mode comprising slotted tapered ridges with lossy cavities closing the slots.

Magnetic bubble detection using waveguide fiber optics

Abstract: A magnetic bubble domain was detected optically by the Faraday effect using a single‐mode optical waveguide structure and a photomultiplier. The light source was a 20‐mW He–Ne laser. The optical waveguide having a 5‐μ core diameter was placed 5 μ from a garnet film which supported 8‐μ bubble domains; the bubble motion was produced by the action of a conducting gold strip evaporated onto the garnet film. It is suggested that detection of bubble domains of the order of 1 μ could be made by the method with the appropriate waveguide with no loss of signal.