Showing papers on "Optical fiber published in 1973"

Image formation using self-imaging techniques*

Abstract: Two situations in which self-imaging techniques can be applied to advantage are presented: the pinhole-array camera and transmission through an optical fiber. The experimental procedure and results are presented for the case of a pinhole array illuminated with an extended incoherent object distribution. In the Fresnel-image planes, more images are formed than there are pinholes in the array, which is in contrast to the case of the pinhole-array camera. An optical fiber or thin film working in the kaleidoscope mode may form an image, provided that its length fulfills the self-imaging condition.

Neodymium‐doped silica lasers in end‐pumped fiber geometry

Abstract: Fused SiO2 has been used as a new noncrystalline host for the fabrication of two types of neodymium‐doped room‐temperature lasers, one of which operates at 1.06‐μm and the other at 1.08‐μm wavelength. The lasers have the geometry of clad optical fibers, with active cores as small as 15‐μm diameter by 1‐cm length. They are end pumped at 0.590 and 0.5145 μm with a pulsed dye laser and an argon ion laser, respectively. Thresholds as low as 1–2 mW of absorbed pump power in a 40‐μm‐diam core have been obtained, and eventual pumping with high‐radiance semiconductor optical sources appears feasible.

Research toward optical-fiber transmission systems

Abstract: The fundementals of optical fiber transmission systems including the fiber transmission medium, sources suitable for use as a carrier, modulation and detection techniques, and some system design considerations are reviewed. The advent of low-loss optical fibers brings new dimensions to optical communication prospects. Fibers may soon be used much as wire pairs of coaxial cable are now used in communication systems. Transmission losses as low as 2 dB/km have been achieved. Experimental repeaters for fiber systems with 10-9error rate at about 300-Mb/s pulse rate have been reported. Fiber cabling and splicing are among the problems requiring new ideas in order to make feasible an operable system.

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.

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.

Light coupling from a stripe-geometry GaAs diode laser into an optical fiber with spherical end

Abstract: The acceptance angle of a fiber is increased remarkably by forming the fiber end spherically. It was demonstrated with light coupling into a fused‐silica‐core glass fiber from a mesa‐stripe‐geometry GaAs diode laser. The coupling efficiency increased in this way is observed to be 5.2 times as high as that of a previous method. The proper design of a fiber in this manner will lead to a light coupling efficiency higher than 90%.

Power transfer between optical fibers

Abstract: Previous papers have treated power transfer between HE11, TE01, and TM01 modes propagating on identical cylindrical fibers. Here we extend the theory to include power transfer between modes of any order propagating on uniform circular fibers of different radii and dielectric constant. A simple analytical expression for the coupling coefficient is derived. The error in using the decoupled two-mode form of the coupled-mode equations is determined. Examples are given to illustrate the extension of the two-fiber results to arrays of fibers with different properties. All results are presented in a dimensionless form applicable to circularly cylindrical fibers of arbitrary physical parameters.

Method and means for splicing arrays of optical fibers

Abstract: Multiple linear arrays of optical fiber cable are aligned and spliced by use of a thin rigid chip with a large number of closely spaced parallel longitudinal fiber-receiving grooves having a uniform cross section. An array splice is built by stacking successive layers of chips and linearly arrayed fibers. A termination is prepared from the foregoing by end grinding or the like. Two ends so prepared are then brought together and aligned by one or two aligning modules having grooves which are mating opposite to those of the chip. The system achieves relatively precise and reliable axial alignment for corresponding fibers of the two prepared terminations.

Optical fiber end preparation for low-loss splices

Abstract: Cables made from brittle materials like glass require new techniques of end preparation for the purpose of splicing, especially if such splices are to be made in the field. We report here on a method of breaking fibers in a way which invariably produces flat and perpendicular end faces. We explain the underlying theory and derive optimal parameters that permit the design of a simple breaking tool. Experiments with a tool of this kind show that the tolerances for successful fracture are not critical. Laboratory splices of multimode fibers prepared by this method exhibited losses of less than 1 percent (0.04 dB) when joined in index-matching fluid.

B.S.T.J. brief: A new optical fiber

Abstract: Currently there is strong interest in optical fibers for use as a transmission medium, analogous to the use of coaxial or wire pairs in the low-frequency region. Most work is devoted to a fiber structure consisting of a central glass core surrounded by a cylindrical glass cladding having a slightly lower index of refraction. This in turn requires that the chemical composition of the core glass differs from that of the cladding glass, leading to undesired effects at the core-cladding interface and perhaps limiting the minimum fiber losses achievable.

Spectral losses of unclad vitreous silica and soda-lime-silicate fibers

Abstract: Spectral transmission losses of unclad optical fibers drawn from various types of commercial vitreous silica and of soda-lime-silicate glasses were measured in the wavelength range between 0.5 and 1.12 µm. The automated technique employed was both convenient to use and sensitive enough to measure losses of 6 dB/km, i.e., 75% loss per km, with an estimated accuracy of ±2 dB/km. Bulk-loss measurements performed with calorimetric and bridge-type techniques were in good agreement with the fiber-loss measurements.

Graded-index optical fiber

Abstract: A graded index, multimode optical waveguide. The waveguide is characterized by a graded profile region, followed by an abrupt drop in index, then a region of constant index. At predetermined intervals, the fiber is modified to have a conventional graded index profile to suppress unwanted modes propagating along the guide.

Pulse dispersion and refractive-index profiles of some low-noise multimode optical fibers

Abstract: The refractive-index profile and impulse response of three low-loss multimode optical fibers have been measured. Pulse dispersion of about 1.5 ns or less was observed in two of the fibers, each 1 km long.

Separable optical fiber connector and the method of manufacturing the same

Abstract: A separable optical fiber connector and method for manufacturing the connector are disclosed. The end portion of a thermoplastic coated optical fiber is inserted into an axial through hole in a terminal member. The through hole includes a first portion of a relatively large diameter equal to the diameter of the thermoplastic-coated optical fiber. The axial through hole tapers down to a narrow-diameter second portion which has a diameter equal to that of the optical fiber without the thermoplastic coating. The fiber is heated to remove the thermoplastic coating from the fiber, and the end of the fiber from which the coating is thus removed is inserted into the narrow-diameter second portion of the through hole. The protruding end of the fiber is then fixed to the end surface of the terminal member and is polished.

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.

Optical scanner utilizing organ arrays of optical fibers

Abstract: An organ array comprises a plurality of optical fibers each cut to a different length with the differences between functionally adjacent (i.e., lengthwise consecutive) fibers being uniform. The fibers are arranged in a bundle so that one set of ends of the fibers is terminated in an input plane and the opposite set of ends is terminated in an output plane. Described are several embodiments utilizing the organ array including a passive spatial scanner, optical memory systems, an image converter, an optical sampling oscilloscope, and an x-y coordinate locater.

Termination for fiber optic bundle

Abstract: Cladding is etched from the end portions of the fibers which form a fiber optic bundle, and the etched end portions are supported to form a bundle termination having reduced crosssectional area and increased packing fraction since the ratio of the fiber core area to the bundle area increases. The light emission and collection efficiency of the bundle termination therefore increases.

Simple, low-loss joints between single-mode optical fibers

Abstract: Low-loss joints between single-mode optical fibers have been made without microscopic alignment, without fusing the tips, and without monitoring the transmitted power while the joints are assembled. The fibers are tightly held in an embossed groove; an index-matching liquid is added. Average power coupling efficiencies close to 90 percent in the red and to 85 percent in the infrared have been obtained. Mediocre end faces are acceptable. Realistic discrepancies between the fiber cladding diameters (slightly in excess of twice the core diameter) do not deteriorate the results.

The length dependence of pulse spreading in the CGW-Bell-10 optical fiber

Abstract: Previous measurements of pulse broadening in the CGW-Bell-10 optical fiber showed very low dispersion ( 550 m) which are of practical significance.

Low‐loss silica core‐borosilicate clad fiber optical waveguide

Abstract: A low‐loss fiber optical waveguide has been constructed having a pure fused silica core of 40‐μm diameter and a chemical‐vapor‐deposited cladding layer of borosilicate glass 15–20 μm thick. This core‐clad structure has an outer jacket of fused silica which serves to strengthen and protect the waveguide. Fabrication procedures and evaluation techniques are described. One fiber has been found to have a minimum optical attenuation of 13 dB/km at a wavelength of 0.7 μm. In the range 0.8–1.1 μm, where optical communications appear most promising, the attenuation varies between 18 and 22 dB/km with the exception of the OH absorption peak at 0.95 μm.

Incoherent illumination of an optical fiber

Abstract: The power of the trapped modes on a semi-infinite optical fiber illuminated by an incoherent source is determined. All possible modes are excited, each with approximately the same power when V → ∞, V=2πρ{n12−n22}1/2/λ, where ρ is the fiber radius, λ the wavelength of light in vacuum, and n1, n2 are the refractive indices of the fiber and its surround, respectively. A ray-optical interpretation is given for the summed power of the modes. For V = ∞, the power corresponds to that found from classical geometric optics, treating all rays as if they are meridional. This result is independent of the degree of coherence of the source. The per cent error of meridional ray optics is 100/V when V is large. The total power within the fiber is the combined power of the trapped modes and the radiation field. In the limit V = ∞, the total power within the fiber at any position z along its axis is that given by classical geometric optics, i.e., that found by tracing all rays, skew and meridional. At the point z = ∞ for arbitrary V, the total power is that due to the trapped modes only.

The impulse response of an optical fiber with parabolic index profile

Abstract: To the paraxial approximation there is no difference in the group delay of the modes of a parabolic index fiber. However, the wave optics treatment of the infinitely extended parabolic index medium predicts a slight difference in the group delay of the various modes. This result is used in this paper to predict the shape and width of the impulse response function of a parabolic index fiber with finite radius.

Effect of misalignments on coupling efficiency of single-mode optical fiber butt joints

Abstract: Analysis and computations made here, corroborated by experiment, determine the effects of axial displacement and angular misalignment on the power coupled between butt-joined, single-mode optical fibers. The absolute accuracy with which fibers must be joined on-centers is reduced for fibers with relatively smaller core; the angular accuracy is increased.

Fiber optic system

Abstract: An optical magnifying device employing fiber optics. When functioning as a microscope, the object plane is defined by and divided into sub-areas by the input termini of many coherent fiber bundles. Each output terminal of each bundle is provided with an objective lens which projects onto an image plane. When used as a microfiche reader, a first magnifying stage is provided, and this (first) image is in turn further magnified in the same manner. Microfiche characters of 2 micron size may be resolved by the entire system.

Optical fiber transmission medium

Abstract: An optical fiber ribbon structure is formed by enveloping a plurality of optical fibers with a predetermined spacing between two laminate elements spaced in parallel array. Once formed, either element can be peeled back from the other end from the fibers to expose fibers for subsequent splicing. The forming process embodies the fibers equally in each laminate, forming semicircular grooves in each. These become guide channels for splicing.

Mode excitation in a multimode optical-fibre waveguide

Abstract: For normal incidence of a Gaussian beam on a multimode optical fibre, theory predicts that only HE1m, modes are excited, and this is confirmed experimentally for a liquid-core fibre of normalised frequency v = 125. Discrete-mode propagation is observed, indicating that the amount of mode conversion due to fibre imperfections is thus very small.

Fused‐silica‐core glass fiber as a low‐loss optical waveguide

Abstract: A new type of glass fiber is discussed. The core of the fiber is pure fused silica, and the cladding is a high‐silica‐content glass. This type of glass fiber has potentially the lowest attenuation of light propagation. A light attenuation of approximately 20 dB/km was measured at a 632.8‐nm wavelength in the preliminary work.

Butt-joined optical fibers

Abstract: In order to minimize electromagnetic radiation losses in optical fibers (especially single-mode fibers) at the locations where the fibers are joined together as by butt-joining, such optical fibers are constructed with a reduced diameter at the joint locations. The reduced dimaeters of the fibers at the locations of joining (''''joints'''') cause an increase in the diameter of the cross section of electromagnetic field at these locations. Thereby, electromagnetic radiation losses due to lateral misalignments at joint locations in optical fibers are reduced.

Multi-component flow probe

Abstract: A multi-component flow probe for determining the characteristics, such as the presence of voids, in heavily loaded multi-component flows, either columnar or in rotating fluidized beds, is provided by using a wedge-shaped fiber optic rod transmitting light into the flow and detecting the light reflected by the flow through an adjacent wedge-shaped fiber optic rod. The wedge of the rod points upstream the general flow direction. The angle and shape of the point of the wedge of the fiber rods are relatively critical.

Fabrication of microlenses

Abstract: Photolithographic techniques are employed to fabricate hemispherical or semicylindrical microlenses on the end surfaces of optical fibers. The power coupling efficiency between junction lasers and fibers is thereby significantly increased.