Showing papers on "Radiation mode published in 1996"

Optical device employing edge-coupled waveguide geometry

Abstract: An optical device for modulating or interacting with radiation guided and propagating along an optical longitudinal axis of an optical waveguide, such as, an optical fiber, has a different directional geometry compared to conventionally comparable devices such as, for example, plasmon or planar surface modulators for optical fibers. The geometry includes a nonlinear, electro-optic medium formed between two spatially disposed electrodes. The medium/electrode sandwich is aligned along the waveguide longitudinal propagating axis and extends in a radial direction from the optical waveguide core with the inner end of the medium in spatial proximity to the waveguide core for evanescent coupling with the radiation field propagating in the waveguide. An applied electric field to the spatially disposed electrodes varies the refractive index of the electro-optic medium from just below the effective refractive index of the waveguide to just above the effective refractive index waveguide to induce a lossy condition on the propagating radiation. Modulation of the applied electric field will bring about intensity modulation of the propagating radiation.

Adiabatically tapered periodic segmentation of channel waveguides for mode-size transformation and fundamental mode excitation.

Abstract: We report modeling, fabrication, and characterization of tapered waveguides, using periodically segmented annealed proton exchange in LiNbO3. For a taper transforming the 1/e full width (intensity) mode size from 6.0 μm × 4.4 μm to 2.0 μm × 1.3 μm, 0.4-dB excess loss was observed. The large, slightly elliptical mode can ease coupling to single-mode fibers and circular free-space beams. The same taper structure was used to excite a highly multimoded (13 modes) waveguide with more than 95% of the power stably launched into the lowest-order mode. This function is useful for nonlinear waveguide devices, such as difference-frequency generators, in which modes at highly disparate wavelengths interact.

Dispersion managed optical waveguide

Abstract: A single-mode optical waveguide fiber designed to limit power penalty due to four wave mixing and a method of making the waveguide is disclosed. Variations in properties, e.g., radius or refractive index, of the waveguide fiber core provide a total dispersion which varies along the length of the waveguide. The algebraic sum of products of length times total dispersion is controlled to a pre-selected value for each waveguide fiber which makes up a system link. Proper choice of total dispersion variation magnitude and sub-length results in a system link wherein a signal travels only short distances in waveguide portions having total dispersion near zero. However, the variation of the total dispersion provides a system link which has a pre-selected dispersive effect on the signal over a selected wavelength range. The dispersive effect on the signal can be chosen to be essentially zero. A number of techniques for fabricating DM fiber are also disclosed.

Optical waveguide having two or more refractive indices and method of manufacturing same

Abstract: An optical tapered waveguide for use in optical arrays is described which contains at least one inclusive structure. The inclusion may possess an abrupt refractive index interface within the body of the tapered optical waveguide or it may consist of a graded refractive index region within the tapered optical waveguide. The tapered waveguide propagates light rays via total internal reflection from the sidewalls of a tapered optical waveguide. The different refractive index of the inclusion also acts to alter the direction of the light rays passing through the waveguide. The tapered waveguide is advantageously useful in an array of waveguides for use in display devices, such as for example projection display devices, off screen display devices, and direct view displays. Such displays are used in a wide range of applications including computer terminals, airplane cockpit displays, automotive instrument panels, televisions, and other devices that provide text, grapics, or video information.

Positive dispersion optical waveguide

Abstract: A single mode optical waveguide fiber having a positive total dispersion is disclosed. The novel waveguide fiber has a core region comprising three distinct segments. Studies of this novel waveguide, wherein properties are calculated as various ones of the core region parameters are changed, show that the waveguide satisfies the requirements of a fiber in a high bit rate, long regenerator spacing system. The novel waveguide design is relatively simple to manufacture and maintains its functional properties at tight tolerances when the core region parameters are varied over a prescribed range. This high performance waveguide limits self phase modulation and four wave mixing, facilitates wavelength division multiplexing, and is compatible with optical amplifiers.

Light wavelength filtering circuit and manufacturing method thereof

Abstract: A light wavelength filtering circuit in a wavelength-division multiplexing light communication system minimizes transmission loss in the waveguide after wavelength discrimination by having a linear output waveguide added to an output end of a light wavelength discriminating element, at which a signal having a long wavelength is outputted. A curved output waveguide is added to the rear stage of the output end at which a signal having a relatively short wavelength is outputted. Hence, a radiation loss at the output waveguide at the output end is minimized, while a space between the output light waveguides is being widened. Additionally, a core layer bandgap wavelength at the output waveguide of the long wavelength signal is set to be longer than a core layer band gap wavelength in another region. Hence, a substantial light confinement is formed in a horizontal direction even in the output waveguide at the long wavelength signal side and even if the output waveguide at the long wavelength signal side is curved, and the radiation loss can be reduced.

Full-wave modeling of generalized double ridge waveguide T-Junctions

Abstract: A rigorous technique for full wave modeling of the generalized double ridge waveguide T-junction has been developed. Eigenmodes in each ridge waveguide region are obtained using mode-matching technique. Based on the eigenmode expansion method, combining the cascading procedure and computation of the magnetic fields of each mode at the shorted ports, the generalized admittance matrices and scattering matrices of all three ports are obtained. The method is general and very efficient. The accuracy and versatility of the method are verified through several numerical examples. The computed dominant mode's S-parameters are compared with that by finite element method (HFSS) and shown to be in good agreement.

Single mode optical waveguide having large effective area

Abstract: A single mode optical waveguide having large effective area is disclosed. The large effective area is achieved by using a segmented core profile design which includes at least one segment, or a part of one segment, having a refractive index less than the minimum refractive index of the clad layer. The large effective area serves to reduce or eliminate detrimental non-linear optical waveguide effects which limit regenerator spacing and bit rate. The large effective area is achieved while maintaining bend resistance at least as good as that of standard step index single mode waveguide fiber.

Control of dispersion in an optical waveguide

Abstract: Disclosed is a single mode optical waveguide fiber having periodic perturbations (2) in the core to provide a birefringence which mixes the polarization modes of launched ligth. In addition, pertubations (4) are introduced into the core which serve to manage total dispersion. The total dispersion of preselected segments (6, 8) of the waveguide are caused to change sign so that the sum of products, total dispersion times length (13, 15), algebraically add to a preselected value. The two distinct core perturbation types serve to control both polarization mode dispersion and total dispersion. Methods for making the subject waveguide are also discussed.

Antireflection-coated angled facet design

Abstract: New and accurate semianalytical expressions, based on the free-space radiation mode method, are derived for the reflectivity of a polarised guided mode of a slab waveguide incident on a multicoated laser facet at an arbitrary angle. Solutions may be obtained simply and with minimum computational effort. Results presented confirm that the coated angled facet can reduce the guided-mode reflectivity to near zero for both polarisations. The far-field radiation pattern is also significantly modified by angling the waveguide to the facet.

Dispersion compensation based on dual-mode optical fiber with inhomogeneous profile core

Abstract: It is well known that the first higher order mode of optical fibers exhibits large negative waveguide dispersion by operating close to its cutoff wavelength. By using this dispersion, the positive dispersion in conventional 1.3 /spl mu/m zero dispersion optical fibers for 1.55 /spl mu/m signal light can be compensated. In this paper, we focus on the dispersion compensation technique using the first higher order mode in a dual-mode optical fiber, which supports both the fundamental LP/sub 01/ and first higher order LP/sub 11/ modes. Numerical calculations show that the waveguide dispersion of the first higher order mode is very sensitive to the refractive-index profile of optical fibers. In addition, it is demonstrated that a directional coupler composed of a single-mode fiber and a dual-mode fiber operates as a mode converter, which converts the signal light from the LP/sub 01/ mode to the LP/sub 11/ mode.

TE-TM mode converter in a poled-polymer waveguide

Abstract: A novel active TE-TM mode converter in a poled electrooptic polymer waveguide is demonstrated. The mode converter utilizes a 45/spl deg/-off poling configuration, which can be obtained by arranging upper- and lower-stripe poling electrodes with a proper lateral displacement. The mode-conversion properties and electrooptic effect are demonstrated by using a vector-beam propagation method in a buried channel-type waveguide. Applications to integrated polymer-waveguide devices are also suggested.

Planar silica-glass optical waveguides with thermally induced lateral mode confinement

Abstract: A new type of planar silica-glass optical waveguide is proposed utilizing the thermo-optic effect of glass. The vertical mode-field confinement is defined by the core slab sandwiched between the upper and lower claddings while the lateral confinement is achieved due to localized increase of refractive index induced by the thin-film heater placed on the upper cladding. An analytical expression of the steady-state temperature distribution across the waveguide cross-section is derived and the induced mode-field characteristics are analyzed by solving the vector-wave equation using the mode-matching method. Mode propagation losses due to the metallic heater and the leakage into the silicon substrate are both calculated. The bending loss of this thermally induced waveguide is also analyzed for future device implementation using this waveguide.

Single-mode mid-infrared silver halide planar waveguides

Abstract: A single-mode silver halide symmetric step-index planar waveguide for 10.6 μm is described. We fabricate the waveguide from extruded multimode silver halide fiber by pressing the fiber between metal plates while heating. The device is therefore automatically pigtailed to a fiber, which could ease the difficulties of coupling light into it. We achieved single-mode confinement by suitably adjusting the refractive index of the core and the cladding and by reducing the core thickness to 30 μm. The output radiation from the planar waveguide was measured to confirm single-mode confinement. Silver halide single-mode waveguides for the mid-infrared can be used to enhance sensitivity in fiber-optic evanescent-wave infrared spectroscopy measurements or for the development of mid-infrared single-mode lasers and interferometers.

Optical fiber waveguide

Abstract: Optical waveguide of the type comprising a core (10) presenting a refractive index (n1), maximal at least at its center; an optical cladding (20) involving core (10) and presenting a refractive index (n2) constant along its diametral extension and lower than the maximum refractive index (n1) of core (10) and further including a region defined by at least a stress-relieving intermediate portion (30) disposed between core (10) and the optical cladding (20), said intermediate portion presenting: a refractive index (n3), maximal along its diametral extension, at the maximum equal to the refractive index (n1) of core (10) and at least equal to refractive index (n2) of optical cladding (20), so as to provide an increase in the cutoff wavelength; a thermal expansion coefficient and a viscosity adequate to reduce the internal stress levels at least in core (10) of the optical waveguide to values which permit the obtention of acceptable attenuation and chromatic dispersion for a wavelength region.

LSM and LSE mode dielectric waveguide having propagating and non-propagating regions

Abstract: A dielectric waveguide has a dielectric member disposed between a pair of parallel conductor flat surfaces, such that a propagating region and a non-propagating region are formed. The spacing between the conductor flat surfaces in the non-propagating region is determined to be smaller than that in the propagating region. The above-mentioned spacings and the dielectric constant of the dielectric member are determined such that the cut-off frequency of the LSM 01 mode propagating through the propagating region is lower than the cut-off frequency of the LSE 01 mode and that electromagnetic waves of both the LSM 01 mode and the LSE 01 mode are cut-off in the non-propagating region, so that any transmission loss attributable to a mode conversion between the LSM 01 mode and LSE 01 mode occurring at, for example, a bend of the waveguide is eliminated so as to facilitate production of the waveguide having a desired bend angle and radius of curvature.

Mode competition and control in free electron lasers with one and two dimensional Bragg resonators

Abstract: We present a time domain analysis of the transverse mode dynamics which occur in FEL oscillators using oversize microwave cavities. It is shown that both traditional one-dimensional and novel two-dimensional Bragg cavities can produce radiation at a single frequency with a one-mode azimuthal distribution, which corresponds to spatial synchronization of the electromagnetic radiation. In one-dimensional system, electronic mode selection occurs via nonlinear mode competition. In contrast, electrodynamic mode selection occurs in two-dimensional Bragg cavities, resulting in the production of a single azimuthally-symmetric mode after the linear stage of evolution. The two-dimensional Bragg cavity is shown to retain its selectivity when its radius greatly exceeds the radiation wavelength.

Optical device with composite passive and tapered active waveguide regions

Abstract: A semiconductor optical device, for example a laser, has a composite optical waveguide including a tapered, MQW active waveguide in optical contact with a substantially planar, passive waveguide. The fundamental optical mode supported by the composite waveguide varies along the length of the composite waveguide so that, in a laser, the laser mode is enlarged and is a better match to single mode optical fiber. A method for making such semiconductor optical devices is also disclosed.

Waveguide-type optical device coupling structure with circular rods

Abstract: A waveguide-type optical device is constituted by an optical waveguide circular rod inside which an optical waveguide device is fixed and supported, an optical fiber circular rod inside which the end of an optical fiber is fixed and supported and a circular sleeve from both ends of which these optical waveguide circular rod and optical fiber circular rod are fitted. An optical waveguide and an optical fiber can be readily aligned by forming the circular rod in a circle so that one optical waveguide in an optical waveguide device is located in the center and the circular rod in a circle so that one optical fiber is located in the center. Another optical waveguide and another optical fiber can be readily aligned by setting a position in the peripheral direction and fitting both the circular rods and to the circular sleeve. An optical fiber and an optical waveguide device can be readily connected.

Fiber optic mode scrambler

Abstract: The present invention is an optical transmission system comprising an optical source, a first lens and a second lens, a multimode optical waveguide, and a phase-only filter. The optical source generates an optical signal having a predetermined wavelength which is received by the first lens. The signal is then sent from the first lens through the phase-only filter and then to the second lens. The second lens then focuses the signal into the multimode optical waveguide. The multimode optical waveguide has predetermined dimensions and has multiple modes. The phase-only filter excites a plurality of modes in the optical waveguide to approximate equilibrium modal power distribution as the optical signal is received into the optical waveguide.

Direct imaging of optical interference in erbium-doped Al2O3 waveguides

Abstract: Interference of 1.48-μm light in multimode interference waveguides is made visible by imaging green and infrared upconversion luminescence from Er3+ ions dispersed in the waveguide. A two-dimensional mode density image can be derived from the data and agrees well with mode calculations for this structure. This new technique provides an interesting tool for the study of optical mode distributions in complicated waveguide structures and photonic band-gap materials.

Optical fiber and integrated optic lasers with enhanced output power

Abstract: The invention describes a method of single-transverse-mode generation for waveguide lasers of various kinds having a large cross section of their active core and thus providing a possibility of efficient pump of the active core region This results in a laser beam with enhanced power and high spatial quality for high efficiency coupling to standard single-mode optical fiber networks It is found that a multimode waveguide having a central dip of special shape in the refractive index profile of its core is able to guide a higher order mode with sharp central peak of its field carrying the considerable part on the mode energy and whose width is well compatible with the width of the fundamental mode of standard single-mode fibers The useful properties of this higher order mode can be employed to provide the single-transverse-mode regime of generation in optical fiber lasers, integrated optical micro-lasers and various semiconductor laser sources

Polarization mode coupled single mode waveguide

Abstract: A single mode optical waveguide having reduced polarization mode dispersion and a method of making such a waveguide is disclosed. Perturbations (6, 8) are introduced into the waveguide core (4) to couple power between the two polarization modes. A model calculation shows that the perturbation length may be of the order of the correlation length. The inventive waveguide is robust in that polarization mode dispersion is reduced even if perturbations (6, 8) are impressed on the fiber after manufacture.

A gratingless wavelength stabilized semiconductor laser

Abstract: A single frequency laser structure is obtained by coupling a high order mode of a semiconductor waveguide to a low index polymer waveguide. The device does not require a grating or regrowth, emits in a mode compatible with optical fibers, and may be immune to catastrophic mirror damage. The epilayers of the semiconductor waveguide use quarterwave reflectors to support a mode with a low enough effective index to phase match to the polymer waveguide. The coupling between the two waveguides is highly frequency selective and therefore stabilizes the wavelength. Preliminary structures emit in a single longitudinal and spatial mode, have 30 dB of sidemode suppression, and emit about 6 mW into a fiber compatible mode.

Free space radiation mode analysis of rectangular dielectric waveguides

Abstract: The free space radiation mode (FSRM) method is used to provide a new closed-form transcendental equation for the scalar mode propagation constant of a uniformly buried rectangular dielectric waveguide. Results are readily and rapidly obtained and are shown to be very accurate over the range of practical interest.

Method and apparatus for photobleaching patterns in irradiated optical waveguides

Abstract: A method and apparatus for photobleaching predetermined patterns in an opal waveguide. The apparatus irradiates the optical waveguide generally held in a fixture. The irradiation includes a selected region or regions of the optical waveguide or the entire optical waveguide. The radiation interacts with radiation sensitive constituents in the optical waveguide to induce a light transmission loss. After the irradiation is completed, the optical waveguide is allowed to age whereby the light transmission recovers to an equilibrium less value. Light beams photobleach predetermined patterns into the previously irradiated region or regions. The patterns may take the form of Bragg gratings in the waveguide.

Compound waveguide lasers and optical parametric oscillators

Abstract: A new family of lasers and optical parametric oscillators is based on efficient frequency conversion or doubling in multimode compound optical waveguides. These waveguides exploit specific useful properties of their higher order modes while providing good compatibility with single-mode optical fibers. A mode engineering approach is applied to construct a compound waveguide structure (1, 2) that supports a higher order mode (6) having a sharp peak in its field. This sharp peak simplifies selection of this mode (6) by efficient coupling of its radiation into a single-mode fiber (8). The lasers and optical parametric oscillators employ wavelength selective properties of this mode field configuration and its unique ability to support efficient frequency conversion and doubling.

Low order multimode generation in hollow glass waveguides

Abstract: A mode mixing caused by localised stress in hollow core waveguides is investigated. It is shown that a hollow glass waveguide with a thick glass wall very effectively suppresses low order mode generation resulting from stress, and that a cable made with a thick wall glass waveguide produces a good spatial output mode.

Single Local Mode Propagation through Ion-Exchanged Waveguide Elements with Quasi-Abrupt Transitions

Abstract: An effective adiabatic condition is derived in order to obtain a single local mode operation regime in integrated devices formed by waveguide elements with quasi-abrupt boundaries. An ion-exchange process, producing this type of graded index transition, is presented in a such a way that many difficulties of both fabrication and design of waveguide elements can be overcome.