Showing papers on "Cladding (fiber optics) published in 1985"

Method for producing glass preform for optical fiber

Abstract: A rod-in-tube method for producing a glass preform for use in the fabrication of an optical fiber, which comprises steps of inserting a glass rod (13) as a core material in a glass tube (12) as a cladding material, fusing and closing one end of the cladding material, filling a gap between the core and cladding materials with an atmosphere containing at least one gaseous halogen-containing compound and then heating the core and cladding materials at a temperature not lower than 1,900°C to collapse the gap between them and to fuse them together, from which glass preform, an optical fiber with low attenuation of light transmission is fabricated.

Optical fiber coupler with tunable coupling ratio and method of making

Abstract: An optical coupler for single mode optical signals having a tunable (variable) coupling ratio, and a method of fabricating the coupler. A pair of virtually identical optical fibers are fused together at a narrowed waist region, each fiber being formed of a core and cladding, each being tapered toward the waist in such a manner as to ensure adiabatic propagation of light in the structure. An optical signal carried by one fiber first passes through a decreasing taper region and then passes through an increasing taper region of one or the other fiber (or both). The decreasing taper rate of the input portion of one fiber is such that the optical signal radiates out of the core (where V=1 locally) and into the cladding, as it approaches the waist. The increasing taper rates of the output portions of the two fibers are such that a predetermined coupling ratio is obtained. The coupler is bent in the region of the waist whereby a coupling ratio can be selected between the incoming fiber portions having the decreasing taper and the outgoing fibers having increasing tapers.

Color Centers in Glass Optical Fiber Waveguides

Abstract: Color centers formed in the core and cladding of optical fiber waveguides by exposure to nuclear radiation can greatly increase the attenuation in the infrared spectral region of interest for optical communications. The radiation-induced paramagnetic defect centers in pure silica, silica doped with Ge, P, or B, and heavy metal fluoride glasses have been identified and thoroughly characterized by electron spin resonance (ESR) techniques. This paper will review the results of recent studies of color centers in optical fiber waveguide materials and their Identification via correlations of the radiation-induced optical absorptions and defect centers elucidated by ESR.

Nonlinear guided waves in saturable nonlinear media.

Abstract: The behavior of nonlinear waves guided by a film configuration with a nonlinear cladding is investigated. The intensity-dependent dielectric function of the cladding is characterized by saturation effects. The field patterns that arise are discussed, and the dispersion relations are derived. Several dispersion curves are plotted. The results are compared with those familiar from nonlinear guided-wave propagation along configurations with Kerr-like cladding dielectric functions.

Measurement of the core proximity in polished fiber substrates and couplers.

Abstract: We report recent developments in a technique to measure the thickness of cladding remaining on polished single-mode fiber substrates. This technique relies on the measurement of the throughput attenuation resulting when a drop of liquid of appropriate refractive index is placed on the substrate. Applications to fiber couplers and other all-fiber devices are described.

Properties of InxGa1−xAs‐GaAs strained‐layer quantum‐well‐heterostructure injection lasers

Abstract: Some of the properties of InxGa1−xAs‐GaAs strained‐layer quantum‐well‐heterostructure (SL‐QWH) injection lasers are described. The laser structures are grown by molecular beam epitaxy on n+ GaAs substrates. Following the growth of a 0.5‐μm n+ GaAs buffer layer, a 2‐μm Al0.45Ga0.55As n‐type cladding layer is grown. Next an undoped active region is grown, consisting of ∼1600 A of GaAs with three ∼40‐A In0.35Ga0.65As quantum wells separated by two ∼30‐A GaAs barrier layers. Following the active region, a 2‐μm Al0.45Ga0.65As p‐type cladding layer and a 0.5‐μm p+ GaAs cap layer are grown. Broad‐area SL‐QWH lasers operate under pulsed conditions at room temperature with threshold current densities as low as 465 A/cm2. The operating wavelength is near 1 μm. Lasers have operated for up to 1000 h with less than 25% increase in current density to maintain a constant output of 2 mW/facet. Data are also presented describing the temperature dependence of threshold current density. Values of T0 between 80 and 103 K are...

Improvement of Radiation Resistance of Pure Silica Core Fibers by Hydrogen Treatment

Abstract: A pure silica core fiber with glass cladding is known to produce larger absorption in the visible wavelength region under γ-ray irradiation than a similar fiber with silicone cladding. This absorption is a serious problem, especially in image-guiding fibers used in radiation environments such as in nuclear power plants. The absorption is attributed to the formation of defect centers such as non-bridging oxygen hole centers and E' centers induced by bond scission. A new and simple method of hydrogen treatment to improve the radiation resistance of an optical fiber with a pure silica core has been proposed. Post-treatment by this method can significantly reduce existing radiation-induced absorption, while preliminary treatment can suppress the increase of the radiation-induced absorption.

In-line single-mode fiber optic multiplexer/demultiplexer

Abstract: A single mode fiber optic multiplexer/demultiplexer has first and second optical fibers, each having an input and an output end. The first and second optical fibers are single mode fibers each having a core of a predetermined diameter and a cladding about the core of a predetermined diameter. Along a predetermined length two fibers are placed in juxtaposition and the claddings are fused together to form a fiber optic coupler. Previous to being fused, the claddings are reduced by etching. The coupling of the fiber optic device is such that a first light having a first predetermined wavelength and a second light having a second predetermined wavelength enter together on an input of one of the fibers and are substantially split such that substantially only the first light will appear on an output of one of the fibers and substantially only a second light will appear on an output of the other fiber. When the first and second lights enter on the input end of the first and second fibers, the novel device combines the first and second lights onto one of the output ends of the fibers. In this configuration the device operates as a multiplexer. A method of fabricating the multiplexer/demultiplexer is disclosed.

Single mode, single polarization optical fiber with accessible guiding region and method of forming directional coupler using same

Abstract: An optical fiber comprising a core and cladding having different refractive indices and forming a single-mode guiding region, the core having a non-circular cross-section defining two transverse orthogonal axes which, in combination with the different refractive indices, permit the de-coupling of waves polarized along the axes. The guiding region is located sufficiently close to the surface of the fiber along a selected length of the fiber, to allow coupling to a guided wave. The outer surface of the fiber has a non-circular cross-section with a predetermined geometric relationship to the guiding region and the orthogonal transverse axes so that the location of the guiding region and the orientation of the axes can be ascertained from the geometry of the outer surface.

Fiber optic coupler and method

Abstract: A low loss fiber optic coupler is fabricated by forming a coupler preform having a plurality of spaced glass cores extending longitudinally through a matrix of glass having a refractive index lower than that of the cores. The coupler preform is formed by inserting a plurality of coated optical fiber preform rods (26,27,28) into an aperture (20) extending axially through an elongated boule (21) of relatively etchable matrix glass. The cladding portion (35) of the rods, which is relatively etch-resistant, is coated with a layer of etchable glass (36). The coupler preform is heated and stretched to form a glass rod (43) which is then severed into a plurality of units (45; 49). Heat is applied to the central region (66) of each unit, and the central region is elongated and tapered inwardly. When an end of the unit is immersed in acid, the matrix glass dissolves, thereby leaving the unit cores and surrounding etch-resistant cladding glass protruding from the newly formed endface of the unit.

Mode-hopping noise in index-guided semiconductor lasers and its reduction by saturable absorbers

Abstract: Mode-hopping noise in index-guided semiconductor lasers is investigated. It is found that random switching between lasing modes and output power differences in those modes cause mode-hopping noise. An effective method to suppress such mode-hopping noise is proposed. High Te doping to an n-type GaAlAs cladding layer completely suppresses the noise. Te in GaAlAs forms a DX center that acts as a saturable absorber. This property stabilizes the laser mode and prevents mode competition. The minimum loss difference between lasing and nonlasing modes to suppress mode-hopping noise is also discussed.

Controllable optical waveguide

Abstract: A controllable optical waveguide includes a core through which light can propagate and cladding around the core, at least one of the core and cladding having plural portions made of a material having a refractive index which varies in response to an applied electric field. A plurality of electrode pairs are arranged so as to each be able to apply an electric field to a respective one of the portions of the material in a manner effecting a change in its refractive index. Each electrode pair includes two electrodes which each have a plurality of fingers, the fingers of one electrode of each pair being interdigitated with those of the other electrode of the pair. As the electric field produced by a given electrode pair varies, the refractive index of the corresponding portion of the material varies in a manner causing the waveguide to retain light or to allow light to escape through such portion.

Polarization locked optical fiber and method

Abstract: A polarization locked optical fiber having a fiber core suspended by a thin cladding web within a tube with a prestress acting along the web to fixedly polarize the core. Preferably, the tube and web are glass materials having different thermal characteristics to provide a built-in stress upon drawing of the web and tube assembly. In the preferred method, an optical fiber preform is machined to a rectangular form and drawn within an enclosing tube to provide the stressed web arrangement.

High-birefringence polarizing fiber with flat cladding

Abstract: This paper presents the theoretical and experimental investigations on polarization characteristics of PANDA fiber with flat cladding. It is theoretically shown that the modal birefringence in the flat-clad fiber is almost the same as that in the circular-clad fiber. The flat-clad PANDA fiber has been fabricated by grinding off the preform cladding on the opposite faces and then drawing with a low furnace temperature. The modal birefringence of the fiber is B = 5.9 \times 10^{-4} and the separation of the bending loss edges for the two polarization modes is \Delta\upsilon = 0.51 in the normalized frequency. The polarizing region can be tuned from 1.3 to 1.56 μm by varying the fiber-bending diameter from 3.5 to 4.5 cm. A 1.5-m length of polarizing fiber exhibits extinction ratios of 44.9 and 44.4 dB with insertion losses for the guided mode of 0.25 and 0.41 dB at 1.3 and 1.56 μm, respectively.

Multiconstituent optical fiber

Abstract: Silica-based optical fiber comprising at least a core and a cladding surrounding the core, both core and cladding material produced by a vapor phase deposition process. The core and/or the cladding comprise at least two substituents, one chosen from Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, and the 4f-type rare earths (the "modifiers"), and the other chosen from B, Al, Ga, In, P, As, and Sb (the "homogenizers"). The maximum concentration of the substituents in the fiber is such that 3<(n 1 M+n 2 H)/H<20, preferably<10, where n 1 and n 2 are the valences of the modifier and the homogenizer, respectively, and M and H are the concentration, in mole %, of modifier and homogenizer, respectively. Fiber according to the invention comprises at least 50, frequently more than 80% by weight, SiO 2 , and further has a maximum modifier concentration of at least 0.2 mole %, preferably at least 1 mole %. The presence of homogenizer frequently permits achievement of modifier concentrations that lead to phase separation or crystallization in prior art fibers. Disclosed is also a method for producing optical fiber, the method comprising forming a metal halide complex having a relatively high vapor pressure.

Finite-element analysis of optical fibres with iterative treatment of the infinite 2-D space

Abstract: A finite-element method is formulated for determining the propagation characteristics of weakly guiding fibres. An iterative process is developed for eliminating the variables in the infinite cladding of the fibre. The final algebraic eigenvalue equation to be solved does not therefore involve any variables in the cladding. Numerical examples show that the method is very accurate and efficient in the whole guiding range of frequency.

Channel add/drop filter-coupler

Abstract: A channel add/drop filter-coupler includes two single-mode optical fibers that have different refractive index profiles. Each optical fiber has a propagation constant that is a function of frequency. A portion of the cladding of each fiber is removed to form a planar surface on each fiber. A plurality of channels is formed in one or both of the planar surfaces. The channels are spaced with a predetermined channel period that is inversely proportional to the difference between the propagation constants of the two fibers of the filter-coupler at the desired center frequency of the filter-coupler. The filter-coupler is completed by joining the two fibers at the planar surfaces. The coupling of the filter-coupler may be tuned by moving one fiber longitudinally, angularly, or, preferably, laterally with respect to the other fiber. Furthermore, the filter response of the filter-coupler is advantageously shaped by varying the location of the channels within the predetermined channel periods or by varying the depth or the width of the channels.

Single mode optical fiber

Abstract: A single mode optical fiber of stepped index of refraction. Both core and cladding are fabricated of pure fused silica doped with a small base percentage of fluorine to substantially eliminate hydroxyl ions and reduce viscosity. In addition to the base amount of fluorine, the cladding contains a further amount for lowering its index of refraction relative to that of the core and for further reducing viscosity.

Method for producing glass preform for single mode optical fiber

Abstract: A method for producing a glass preform for a single mode optical fiber comprising a core and a cladding, which method comprises depositing fine glass particle of a glass raw material on a periphery of a cylindrical seed member having a smooth and clean outer surface by flame hydrolysis to form a soot of the fine glass material, pulling out the seed member from the soot, inserting a core glass rod in a hollow portion of the soot and dehydrating and sintering a complex of a core rod and a cladding to produce a glass preform from which a single mode optical fiber having low attenuation of light transmission, particularly due to absorption by hydroxyl groups can be drawn.

Tuned-port twin biconical-taper fiber splitters: fabrication from dissimilar low-mode-number fibers.

Abstract: Fused biconical-fiber splitters have been fabricated from dissimilar low-mode-number optical fibers. Through selective etching of the cladding diameters of the two fibers forming the splitter, the amount of energy transferred between the fibers can be controlled. A tuned condition characterized by low insertion loss and strong optical coupling between modes of the fibers forming the splitter has been demonstrated. In the detuned condition an asymmetry in the coupling between fibers has been observed.

Spectral properties of strongly coupled 1.5 &#181;m DFB laser diodes

Abstract: Spectral measurements of strongly coupled DFB lasers operating at 1.5 μm are presented. The magnitude of the coupling coefficient k in these devices was determined to be 80 cm-1for lasers with \lambda = 1.12 \mu m cladding layers and 160 cm-1for devices with \lambda = 1.3 \mu m cladding layers. These values for k are believed to be the largest reported for 1.5 μm DFB lasers. CW spectral linewidths as low as 10 MHz at 15 mW output power were obtained, and the linewidth was observed to vary approximately as the inverse of the device length cubed. Spectral measurements performed under 2 Gbit/s direct modulation exhibited a side mode suppression ratio of >38 dB. The effects of transient wavelength chirping were also investigated in detail and the maximum wavelength deviation was found to be ≃1.5 A.

Optical star coupler

Abstract: The ends of tapered optical waveguides are focused onto one another by means of a graded index rod lens. The tapered tips are connected to the end faces of the lens. The coupling conditions are improved by taking into account the cladding modes emerging from the tapered portions.

Polarization-selective fiber directional coupler

Abstract: A directional coupler has been made which exhibits a 9-dB polarization selectivity. One-half of the coupler is polished parallel and the other half perpendicular to the elliptical stress cladding of a high-birefringence fiber. Measurements on the coupler and on the fiber suggest a procedure for improving the selectivity.

Cladding materials for optical fibers

Abstract: This invention provides a cladding material for an optical fiber, said cladding material having a structural unit represented by the formula ##STR1## wherein R1 represents chain hydrocarbon group having 1 to 5 carbon atoms or cyclic hydrocarbon group having 3 to 6 carbon atoms and optionally substituted with lower alkyl group having 1 to 6 carbon atoms.

Method for making self-aligning optical fiber with accessible guiding region

Abstract: A method of making an optical fiber, comprising the steps of forming an optical preform having a core and a cladding with different refractive indices, the core being offset from the geometric center of the preform and having a non-circular cross-section defining two transverse orthogonal axes, the core having a longer transverse dimension along one of the orthogonal axes than along the other of the axes for guiding two fundamental modes, which, in combination with the different refractive indices, permits the de-coupling of waves polarized along the axes, the outer surface of the preform having a non-circular cross-section forming an indexing surface with a predetermined geometric relationship to the core and the orthogonal transverse axes so that the location of the core and the orientation of the axes can be ascertained from the geometry of the outer surface, and drawing an optical fiber from the preform with the drawing rate and the temperature of the preform being controlled to produce a fiber with a cross-sectional geometry similar to that of the preform.

Clad superlattice semiconductor laser

Abstract: A clad superlattice semiconductor laser is fabricated utilizing Impurity Induced Disordering (IID) techniques that provides (1) reduction of free carrier absorption in the optical cavity and (2) the ability to selectively vary the amount of index guiding in the optical waveguide independent of the properties of the electron confining multiquantum well structure. The clad superlattice semiconductor laser provides for the novel inclusion of a superlattice in a cladding layer or region of the laser structure. An effective index waveguide can be realized by selectively disordering the cladding superlattice in regions adjacent to the formed index guide type optical cavity, as long as the superlattice is designed so that the established optical mode significantly overlaps with the disordered superlattice cladding regions, i.e., the evanescent wave propagating in the laser cavity overlaps into regions of the disordered superlattice.

A review of zircaloy fuel cladding behavior in a loss-of-coolant accident

Abstract: The paper reviews the state-of-the-art experimental work performed in several countries with respect to the acceptance criteria established for emergency core cooling (ECC) in a loss-of-coolant accident (LOCA) of light water reactors (LWRs). It covers in detail oxidation, embrittlement, plastic deformation and coolability of deformed rod bundles. The main test results are discussed on the basis of research work performed at the Karlsruhe Nuclear Research Center (KfK) within the framework of the Nuclear Safety Project (PNS) and reference is made to test data obtained in other countries. The conclusion reached in the paper is that the major mechanisms and consequences of oxidation, deformation and emergency core cooling are sufficiently investigated in order to provide a reliable data base for safety assessments and licensing of LWRs. All test data prove that the ECC-criteria are conservative and that the coolability of an LWR and the public safety can be maintained in a LOCA. Ein Uberblick Uber das Zircaloy-HUllrohrverhalten beim KUhlmittelverlust stör fall

Low-loss single-mode optical couplers

Abstract: The fabrication of very-low-loss single-mode optical-fibre couplers is described. The biconical fusion method has been used to investigate three types of single-mode fibre (i.e. depressed cladding, matched cladding and raised cladding), and losses of less than 0.05 dB have been obtained. Experimental evidence also shows that power transfer in the biconical fusion coupler cannot be supported by evanescent wave coupling between the cores of the fibres. The fabrication of polished-type couplers is also described for fixed and mechanically tunable output power splitting ratio couplers. Typically losses of less than 0.2 dB are possible.

Biconical taper coaxial coupler filter

Abstract: The wavelength-dependent transmission characteristics of biconical tapers fabricated from single-mode fibres of depressed cladding are examined. The wavelength response is found to be oscillatory with large modulation depths. We describe here a simple fabrication technique which produces narrow passband filters of low loss and high extinction ratio (>30dB).