Showing papers on "Cladding (fiber optics) published in 1991"

Bragg grating formation and germanosilicate fiber photosensitivity

Abstract: The refractive index of germanosiicate and germano—aluminosilicate fiber can be increased by a few parts in iO toupwards of five parts in i04 by photobleaching the oxygen vacancy defect band of germania. Typically, the fiber core is exposed through the side of the cladding to UV radiation at a wavelength from 240—250 nm. Permanent phase gratings are"written" with a specified period by using a pair ofintersecting coherent beams. We have investigated the fiber photosensi-tivity by monitoring the grating reflectivity and wavelength spectrum during the exposure. The Bragg wavelength shifts asthe grating is "written" due to a small increase in the average refractive index of the core. From these measurements, onecan determine the growth and saturation characteristics of the photoinduced changes and study the effects of composition and high temperature hydrogen annealing. We have also measured the polarization sensitivity and thermal stability ofgratings and the transient and permanent changes in fiber absorption.

Epitaxial Growth of ZnMgSSe on GaAs Substrate by Molecular Beam Epitaxy

Abstract: We propose a new material, ZnMgSSe, as the cladding layer of a blue-light laser diode. Band-gap energy can be varied from 2.8 to near 4 eV, maintaining lattice-matching to a (100)GaAs substrate. The band-gap energies of MgS and MgSe (zincblende structure) are estimated to be about 4.5 eV and 3.6 eV, and the lattice constants are 5.62 A and 5.89 A, respectively. The refractive index of ZnMgSSe lattice-matched to GaAs is smaller than that of ZnSSe lattice-matched to GaAs. ZnMgSSe meets the requirements of the cladding layer of ZnSSe for fabricating the blue-light laser diode.

Optical waveguide sensor using evanescent wave excitation of fluorescent dye in sol-gel glass

Abstract: The sol-gel process for low temperature fabrication of porous glass has been used to entrap chemically-sensitive dyes for optical sensor applications. Evanescent wave excitation was used to examine the behaviour of an unclad fibre which was dipcoated with a thin layer of porous cladding within which a pH-sensitive dye was entrapped. The performance of the pH sensor is reported and the potential of the technique for distributed and integrated optic sensing is discussed.< >

Quantum efficiency enhancement of AlGaAs/GaAs quantum well infrared detectors using a waveguide with a grating coupler

Abstract: Long wavelength quantum well detectors with very high quantum efficiency, based on the coupling of radiation into an optical resonant cavity or waveguide defined by a reflection grating coupler on one side of the infrared absorbing multiquantum well stack, and an aluminum arsenide cladding layer on the other, have been fabricated and the results compared with theory. Theory shows that quantum efficiencies up to 90% may be obtained (for polarized radiation). However, experimental results indicate that the response peak becomes broadened due to spread in the grating period and therefore the maximum quantum efficiency is in practice limited to 60%, corresponding to a current responsivity of 2.1 A/W. This is 2.7 times larger than for a 45° polished edge detector with the same quantum well characteristics.

Excellent uniformity and very low (<50 A/cm2) threshold current density strained InGaAs quantum well diode lasers on GaAs substrate

Abstract: We report the growth and fabrication of InGaAs/GaAs strained quantum well (QW) lasers with a very low threshold current density, Jth, of <50 A cm−2 emitting at 0.98 μm. The lasers, 1350 μm long, had two InGaAs 80 A quantum wells in the active region and Al0.6Ga0.4As in cladding layers, and were grown on 3° off (100) towards 〈111〉A GaAs substrate. Misorienting the substrate towards 〈111〉A improves the material quality and device performance substantially for x≊0.6 in the cladding layer, but degrades it somewhat for x≊0.35. The Jth increased about 25% with decreasing x from 0.6 to 0.35 due to decreased optical confinement. Single QW stripe lasers with x=0.35 tested on a 3.0 cm×1016 μm size bar, representative of the whole 5‐cm‐diam substrate, exhibited a yield of ≳90% and an excellent spatial uniformity of Jth and emission wavelengths which were 212±4 A cm−2 and 989±1 nm, respectively.

Rare earth element-doped optical waveguide and process for producing the same

Abstract: A core waveguide having a substantially rectangular cross section, with the width thereof greater than the thickness thereof, is provided in a cladding formed on a substrate, and a rare earth element-doped layer is provided in the core waveguide along the waveguiding direction of the waveguide. With the width of the core waveguide set greater than the thickness of the core waveguide, good optical confinement in the width direction of the waveguide is obtained, which enables light to be absorbed by the rare earth element-doped layer efficiently and concentratedly. It is thereby possible to achieve a marked improvement in the excitation efficiency of excitation power. Thus, an enhanced excitation efficiency is achieved with less addition of a rare earth element, and a high-gain optical amplification waveguide free of concentration extinction is provided.

Heterostructure laser with lattice mismatch

Abstract: Semiconductor heterostructure lasers having at least one lattice mismatched strain layer in the cladding proximate to the active region. Indium or phosphorus may be added in high concentration to form the strain layers. The strain layers may be spaced somewhat apart from the active region or may be adjacent to the active region. In either case, the strain layers decrease transparency current and increase differential gain.

General solutions for stress-induced polarization in optical fibers

Abstract: General solutions of thermal stresses and material birefringence in polarization-maintaining optical fibers are presented. The solutions give the stresses and birefringence at every point in the cross section of various fibers. The fundamental solution of the stress field is constructed by using the complex variable method in elasticity. When the cores, inner claddings, or stress-inducing regions are ellipses, circles, or bow-tie shapes, exact closed-form solutions can be found. The average core birefringence and center core birefringence of elliptical core, elliptical cladding, twin core, Panda, and bow-tie fibers are calculated and compared. Among these fibers, the bow-tie fiber shows the highest birefringence. >

Thermal properties of etched-well surface-emitting semiconductor lasers

Abstract: A comprehensive two-dimensional model for analysis of thermal effects in etched-well vertical-cavity surface-emitting lasers is presented. A self-consistent solution for the electrical and thermal processes is obtained numerically. Joule heating is shown to play a key role in thermal behavior of these devices. Substantial mismatch between current density and optical field profiles can be remedied by proper doping of top cladding layer. A simple way to control the sign and strength of thermal waveguiding is suggested. Consequences for large-scale two-dimensional integration are indicated. >

Optical waveguide comprising Bragg grating coupling means

Abstract: Disclosed are planar waveguides comprising substantially polarization-independent Bragg gratings. A preferred embodiment of the invention comprises a Si body with a silica lower cladding layer thereon, and a phosphorus P-doped silica core on the lower cladding. Appropriate periodic recessed features are etched into the core, and phophorus P- and B-doped silica upper cladding is deposited over the core. The dopant concentrations are adjusted such that the refractive index difference between core and upper cladding is small (0.35-1.45×10-2), and such that the flow temperature of the upper cladding material is lower than that of the core material. In another preferred embodiment a thin layer of Si3 Nx (x˜4) is conformally deposited over the core after the grating etch, and the upper cladding material is deposited onto the Si3 Nx layer. Bragg devices according to the invention are advantageously used in Integrated Optical Circuits (IOCs), e.g. in IOCs used in WDM optical communication systems.

High-power mode-selective optical fiber laser

Abstract: An optical fiber includes a multimode primary core having an index or refraction N1 and doped with a material providing optical gain; the cladding surrounding the core having an index of refraction N2 ; and a secondary core doped with an absorbent material for providing optical loss in unwanted modes.

Plasma waveguide: A concept to transfer electromagnetic energy in space

Abstract: This paper studies the possibility of using a laser‐generated ‘‘plasma waveguide’’ to transfer electromagnetic (EM) energy. The plasma waveguide is a cylindrical vacuum core surrounded by a plasma cladding. The analysis shows that guided‐mode fields do exist inside the core. Like a general dielectric waveguide, the plasma waveguide is characterized by a ‘‘normalized frequency parameter’’ (also called the V number). Although the permittivity of the plasma varies strongly with frequency, the V number surprisingly remains constant over the entire frequency range. Because of this property, the frequency dependence of the plasma waveguide is different; it has a wider high‐frequency response than the general dielectric waveguide. The EM pulse can propagate in the plasma waveguide at close to the speed of light and keep its profile and shape unchanged. When the V number is smaller than 2.4048 (the first root of the zero‐order Bessel function), only the single HE11 mode exists in the plasma waveguide. Unlike the ...

Thermally-diffused expanded core fibres for low-loss and inexpensive photonic components

Abstract: A technique is presented to locally expand the mode-field diameter of singlemode fibres. This can rapidly diffuse germanium ions into the core of silica fibres without deforming the cladding. The mode-field diameter broadens 20 μm after 5–l0 min of heating. Low-loss and inexpensive fibre-to-fibre and fibre-to-device connections are realised using the thermally-diffused expanded core fibre.

Surface polaritons in cylindrical optical fibers

Abstract: The properties of the polariton modes associated with a resonance in the dielectric function of an optical fiber are derived. Particular attention is given to the surface polaritons, whose energy densities and power flows are concentrated close to the interface of the fiber core and its cladding. The results are illustrated with a range of dispersion curves for the two most important cases, when the fiber dielectric function has the reststrahl and plasma forms. General expressions are given and illustrated graphically for the power flow and the power density. It is shown numerically that the energy velocity, or group velocity, can have opposite sign to the phase velocity of the surface polariton.

Gaussian and equivalent-step-index approximations for nonlinear waveguides

Abstract: The field of the fundamental waveguide mode, when it propagates at extremely high intensities or when the core or cladding material has a large nonlinear coefficient, may be quite significantly distorted from that of the corresponding linear mode. We derive a variational formulation of the scalar wave equation for waveguides with arbitrary nonlinearity in the core and show that this formulation can be used to find simple, but accurate, analytical approximations for these nonlinear fields. In particular, we find Gaussian and equivalent-step-index approximations for a variety of planar waveguide and optical-fiber structures and show how they can be used to calculate quantities such as the effective area and group-velocity dispersion.

Ferroelectric-domain inversion induced by SiO2 cladding for LiNbO3 waveguide SHG

Abstract: It was found that, by heating an LiNbO 3 crystal with SiO 2 cladding on the +z face, ferroelectric-domain inversion is induced under the cladding. The inversion method offers high reproducibility and is suitable for fabrication of quasiphase-matching waveguide SHG devices. A prototype device was fabricated and SHG was demonstrated using a CW-YAG laser

Method of making polarization retaining fiber

Abstract: A method of making an optical fiber having an oblong core comprising the steps of depositing layers of core glass particles and cladding glass particles on an enlarged mandrel, removing the mandrel to form a tubular porous preform, consolidating the porous preform to form a dense glass preform, evacuating the central hole of the dense glass preform while stretching that preform to collapse the central hole thereof and form a flattened rod, applying cladding material to the rod, and drawing the resultant composite to form an optical fiber. To facilitate the flat collapse of the central hole of the dense glass preform and to cause the core to have a large aspect ratio, the inside diameter-to-outside diameter ratio of the dense glass preform should be within the range of 0.3 to 0.9. For preferred core and cladding glasses, this ratio should be between 0.5 and 0.6. Also, the mandrel diameter should be at least 12 mm, and it is preferably between 25 mm and 50 mm.

Formation of polymer channel waveguides by excimer laser ablation and method of making same

Abstract: This invention provides polymeric chanel waveguides which are formed by means of an excimer laser photoablation procedure. The smooth-wall channel waveguides polymeric medium is in combination with polymeric cladding layers to form a laminated matrix. The polymers in the waveguiding medium and the cladding layers of the laminated matrix have side chains which exhibit second order nonlinear optical susceptibility, and which can be molecularly oriented by an electric field.

Plastic optical fibers

Abstract: There is provided a plastic optical fiber capable of exhibiting good light transmitting characteristics even at high temperatures, which comprises a core layer, a cladding layer, and a protective layer as basic consititutional units, wherein the protective layer has a heat distortion temperature [HDT] of at least 120° C., a thickness of at least 10 μm, and a cross-sectional area of at least 0.07 times the sum of cross-sectional areas of the core and cladding layers. There is also provided such a plastic optical fiber good in high-temperature light transmitting characteristics, which comprises a core layer, a cladding layer, and a protective layer as basic constitutional units and has a plastic coating layer having a silane-crosslinked structure provided as an outer layer thereof, wherein the protective layer has a heat distortion temperature [HDT] of at least 120° C., a thickness of at least 10 μm, and a cross-sectional area of at least 0.07 times the sum of cross-sectional areas of the core and cladding layers.

Coupling of modes in bent biconically tapered single-mode fibers

Abstract: Biconically tapered single-mode fibers are fabricated by heating a single-mode fiber while applying tension. As a result of this tapering, cladding modes are excited in the tapered region of the fiber where the V parameter of the fiber goes down below 1.0. These cladding modes couple to one another, leading to fluctuations of the optical throughput. Since the index difference between the cladding and the external medium is rather high ( approximately 0.5), the cladding modes will be of the exact type, namely, TE, TM, HE, and EH modes. The coupling of these modes in the tapered region is analyzed using the exact mode formalism when the tapered region is bent. The theoretical results agree very well with experimental results obtained on bent tapers which show strong fluctuations of the optical power as a function of the bending angle. >

Optical fiber having enhanced bend resistance

Abstract: An optical fiber (22) of this invention is suitable for use in tethered vehicle. The optical fiber has a W-shaped refractive index configuration and is characterized by a Δ of at least 0.9% and a cutoff wavelength of less than 1500 nm. Further, the refractive index configuration is such that a core (30) is characterized by a relatively high value of Δ + . The value of Δ + is at least 0.6% for a single window of operation, whereas for a dual window it is 0.9%. Also, the refractive index configuration of the optical fiber is characterized by a depressed inner cladding portion (32) which has a Δ - of 0.3% and an outer radius about equal to the product of 2.5 and the radius of the core.

Single-mode fiber microlens with controllable spot size

Abstract: A novel method for fabricating microlenses on tapered single-mode fibers is shown to be able to control the lens spot size. The fiber cladding is first symmetrically tapered by etching it with an evaporating ammonium bifluoride solution. A hemispheric lens is then melted on the taper tip with a CO2 laser. The lens can reduce the fiber mode radius to 40% of its original value. A theoretical calculation of the focused spot size agrees well

Guided-wave optical circuit and method for adjusting a characteristic thereof

Abstract: A method for adjusting a characteristic of a guided-wave optical circuit which includes one or more waveguides formed by a substrate, a cladding layer (7, 8) formed on the substrate (9), and a core portion having one or more cores (1, 2) embedded in the cladding layer. The method is carried out by producing a reversible thermal hysteresis phenomenon, after the cladding layer and core portion have been formed. The thermal hysteresis phenomenon is produced in a thermal hysteresis produced region (7a or 13 or 1, 2) preselected so as to include at least a portion of the cladding layer and/or the core portion, thereby adjusting a refractive index difference between the cladding layer and the core portion. To produce a reversible thermal hysteresis phenomenon, the following steps are carried out: raising the temperature of the thermal hysteresis produced region to a predetermined temperature; maintaining the predetermined temperature of the thermal hysteresis produced region for a predetermined time period; and cooling the thermal hysteresis produced region at a predetermined cooling rate. At least one of the values of the predetermined temperature, predetermined time period, and predetermined cooling rate is controlled so that the refractive index difference between the cladding layer and the core portion is adjusted to a desired value, thereby adjusting the characteristic of the guided-wave optical circuit.

Surface emission type semiconductor laser

Abstract: In order to manufacture a surface emission type semiconductor laser, a plurality of semiconductor layers including a multilayered semiconductor mirror, a cladding layer, an active layer and other layers are sequentially formed on a substrate through the organic metal vapor growth method. A photoresist mask is then formed on the semiconductor layers. At least the cladding layer in the semiconductor layers is anisotropically etched by the use of the photoresist mask. At least one column-like portion is thus formed to have sidewalls extending perpendicular to the substrate and to guide the light in a direction perpendicular to the substrate. Thereafter, a buried layer including a single layer formed therein at an area covering at least the sidewalls of the column-like portion is formed around the column-like portion. A multilayered dielectric mirror is deposited in the column-like portion on the light exit end thereof. The multilayered dielectric mirror is disposed at the light exit port of a light exit side electrode. To increase the reflectivity below the light exit side electrode, a multilayered semiconductor mirror may be formed in the column-like portion at a position nearer the light exit side than the cladding layer.

Method of manufacture for shielded flat electrical cable

Abstract: A method of manufacturing shielded flat cable comprising a plurality of tape form conductors, arranged in a horizontal plane, and in parallel fashion, and insulation cladding which covers the surfaces of the conductors and is unitary in structure, and using a cladding cable which is formed by the placing of a tear-away wire, comprising materials having a greater physical strength than the insulation cladding, between at least one of the plurality of the conductors and the insulation cladding covering this conductor, in which, in the exposure of a conductor which is overlaid by the tear-away wire, the tear-away wire, along with the area of the insulation cladding which overlays this tear-away wire, is pulled in an angled direction with respect to the surface, and after this a shield layer comprising conductive materials and having a tape form is laid on the surface of the cladding cable and the shield layer is brought into electrical contact with the exposed conductor.

Apparatus and method of forming optical waveguides on metalized substrates

Abstract: An integrated opto-electrical circuit is described. An apparatus and method are disclosed whereby planar optical waveguides are formed on Al2O3, other ceramics, silicon, silica, and other glass substrates (10) that are thin film wired (20). An interface coating of silicon or silicon dioxide (30) is applied to a surface of the thin film wired substrates (10) using a low temperature deposition process such as sputtering or chemical vapor deposition. Glass cladding (40) and core layers (46) are deposited onto the thin film coating. With this invention, channel waveguides and integrated optical circuits can be formed on a common substrate with electronic IC chips.

Low index of refraction optical fiber with tubular core and/or cladding

Abstract: An optical fiber having an index of refraction less than that conventionally available. The low index of refraction fiber 10 of the present invention includes a fiber core 20 of a first index of refraction. The fiber core 20 circumscribes a longitudinal axis, and is surrounded by a cladding layer 30 having a second index of refraction less than the first index of refraction. Included within the cladding layer 30 are a plurality of tube structures 40 arranged about the fiber core 20. The tube structures 40 create a plurality of channels 42 within the cladding layer 20, thereby engendering a low index of refraction therein.

Radiation-emitting semiconductor device and method of manufacturing such a semiconductor device

Abstract: Radiation-emitting semiconductor diodes in the form of a laser diode or an LED form important components in information processing systems. There is a particular demand for diodes emitting in the visible range of the spectrum and having a high admissible operating temperature. A radiation-emitting diode comprising a semiconductor body with a semiconductor substrate on which a lower cladding layer, an active layer, and an upper cladding layer are present, the active layer and the two cladding layers each comprising different semiconductor materials which form a mixed crystal, partly fulfill the above requirements. According to the invention, such a diode is characterized in that the mixed crystal of the active layer is more strongly ordered than that of the two cladding layers. This makes the difference in bandgap between these layers greater than in the known diode. The diode thus has a comparatively high T o value and accordingly a high maximum operating temperature. The invention also relates to a method of manfuacturing such a diode. In this method, a difference in the degree of ordering between the active layer and the cladding layers is achieved through a change in the growing temperature or in the ratio of the quantities of the offered elements during providing of the semiconductor layers. Thus diodes - for example in the InGaP/InAlGaP material system - with the required characteristics are obtained.

Smooth-wall polymeric channel and rib waveguides exhibiting low optical loss

Abstract: This invention provides process embodiments for fabricating polymeric channel or rib optical waveguides. An invention optical waveguide has a channel or rib structure which has a polymer thin film smooth-wall lining on its surfaces to minimize optical loss by scattering of propagating wave energy. The smooth-wall channel waveguide polymeric medium is in combination with polymeric cladding thin films to form a laminated matrix. The polymers in the waveguiding medium and the lining and cladding thin films of the laminated matrix preferably have side chains which exhibit second order nonlinear optical susceptibility, and which can be molecularly oriented by an electric field.

Coherent infrared fiber image bundle

Abstract: Coherent infrared (IR) image bundle was developed for the delivery of the IR thermal image. The fiber employed was the As2S3 glass core of 65 μm diam and Teflon (perfluoronated ethylene propylene) cladding of 75 μm diam, which has the transmission range in the wavelength region between 1 and 7 μm. Two kinds of bundles of 100 cm long were prepared, which consisted of 1550 fibers (NPB75‐1550) and of 8400 fibers (NPB75‐8400). The IR imaging system was constructed by coupling the bundle to an IR television camera. The performance of the system was investigated by detecting the thermal image of an operating LSI package.