Showing papers on "Optical fiber published in 1975"

Theory of Dielectric Waveguides

Abstract: Dielectric waveguides are the structures that are used to confine and guide the light in the guided-wave devices and circuits of integrated optics. This chapter is devoted to the theory of these waveguides. Other chapters of this book discuss their fabrication by such techniques as sputtering, diffusion, ion implantation or epitaxial growth. A well-known dielectric waveguide is, of course, the optical fiber which usually has a circular cross-section. In contrast, the guides of interest to integrated optics are usually planar structures such as planar films or strips. Our discussion will focus on these planar guides even though most of the fundamentals are applicable to all dielectric waveguide types.

Mode Coupling Effects in Graded-index Optical Fibers

Abstract: Mode coupling theory is applied to the study of multimode optical fibers with graded-index cores. For coupling caused by random bends in the waveguide axis, the results predict the dependence of the induced losses on the fiber's characteristics. The impulse response is determined for fibers with random bends having several different power spectra. The results are used to predict the transmitted power, the delay time, and the rms pulse width in fibers with graded-index cores.

Zero material dispersion in optical fibres

Abstract: The material dispersion of optical fibres having cores of silica or phosphosilicate glass falls to zero at a wavelength between 1.2 and 1.3µm. A considerable increase in bandwidth can be obtained, especially with an l.e.d. source, by operation in this region.

Phase-matched-stimulated four-photon mixing in silica-fiber waveguides

Abstract: Stimulated four-photon mixing has been observed in silica-fiber waveguides. Phase matching is achieved by using the dispersion of the waveguide modes to compensate for bulk dispersion. The coherence lengths can be greater than 10 m and the gains more than double the usual Raman gain.

Optical-fiber packaging and its influence on fiber straightness and loss

Abstract: Glass fibers are in general not thick enough to withstand external forces on their own without suffering axial distortion, mode coupling, and loss. Thus, plastic jackets must be carefully designed to provide effective protection. We evaluate jacket designs ranging from the mere use of soft materials to the application of multiple plastic coatings and graphite reinforcement. We compute the distortion loss as a function of dimensional variations and of lateral forces considered typical for cable packaging. The protective quality of a jacket is found to depend on a combination of stiffness and compressibility and on the fiber characteristics.

Mode conversion coefficients in optical fibers.

Abstract: A simple method has been devised for the experimental determination of mode conversion coefficients in multimode fibers and involves only the observation of the far-field output as the angle of incidence of a collimated input beam is changed. The normalized mode coupling coefficient in a liquid-core fiber is D = 3 x 10-6 rad2 / m and increases by as much as a factor of 10 when transverse pressure is applied. Values some 2 orders of magnitude larger are found in glass-core fibers. There is good agreement between the theory presented and experiment.

Microbending loss in optical fibers

Abstract: The loss induced in optical fibers by random bends in the fiber axis is studied by winding fibers under constant tension onto a drum surface that is not perfectly smooth. The tension forces the fibers to conform to slight surface irregularities, which can result in an increase in the optical loss on the order of 100 dB/km. This microbending loss may be a significant design consideration in system applications of low-loss optical fibers. Data are presented on the reduction of the effect by means of coatings and increased numerical aperture.

Calculation of Cooling Rate and Induced Stresses in Drawing of Optical Fibers

Abstract: The rate of cooling of fused-silica fibers and the generation of stress in clad fibers of fused silica and 96%-silica glass (∼125 μm OD) pulled at 1750°C were studied. Experimental cooling rates reported by previous workers were fitted using low- and high-temperature heat-transfer coefficients derived from their data. The birefringence which developed in clad fibers consisting of silica and 96%-silica glass was measured and found to change in sign as a function of the magnitude of the pulling stress. A model involving differences in viscosity (mechanical stress) as well as differences in expansion coefficient (thermal stress) is proposed to account for this behavior.

Variable optical coupler

Abstract: This invention relates to an optical waveguide switch and directional coupler providing variable coupling between two optical fibers. The coupler is fabricated in semiconductive material such as GaAs or GaAlAs. A double heterostructure is used having a higher index of refraction middle layer. Optical fibers are inserted in channels in the semiconductive material. Varying the reverse bias across the heterostructure junctions located in the material between the channels electrically changes the refractive index of the material and alters the coupling between the fibers. The device is applicable to switching in optical communication systems.

Propagation Effects in Optical Fibers

Abstract: The round dielectric waveguide exhibits a surprising variety of characteristics that are not accurately inferable from the slab model. The forceful effort of recent years has grately extended the knowledge of these structures and added new and exciting modifications. An attempt to unify these results in a simplified picture is made. Specific phenomena relevant to optical fiber design and fabrication are then brought into focus. Some of the problems discussed are cross sectional loss variations, various core index profiles and the tolerances required in their preparation, the necessary cladding thickness, directional changes, and sources of mode coupling affecting signal distortion and loss.

Apparatus for generating light pulse train

Abstract: The ends of a length of optical fiber are coupled to each other to form a closed loop so that light wave may propagate freely through the looped optical fiber. At one or more portions of the looped path of light are provided the sections through which the loop is optically coupled to external equipments. A light pulse is injected through the sections into the loop fiber and a part of it is taken out through the sections each time it completes a cycle of travel through the loop fiber, so that a light pulse train with pulses equidistantly appearing on the time base can be obtained.

Panoramic rear viewing system

Abstract: A panoramic rear viewing system for an automotive vehicle includes plural fiber optic bundles having input ends mounted behind lenses in swivel mounts at various positions around the periphery of the roof of the vehicle for viewing in adjoining rearward azimuthal sectors. The output ends of the fiber optic bundles are located in a side by side array behind a similar array of magnifying lenses within view of the driver for combining the sector images carried by the bundles into a panoramic view.

Single-crystal fiber optical devices: A Nd:YAG fiber laser

Abstract: Single−crystal fibers of Nd:YAG have been grown in diameters as small as, but not limited to, 50 μm by a pedestal growth (modified zone melting) technique. Room−temperature cw laser operation has been achieved with 0.5−1−cm−long samples. The method is directly applicable to the growth of single−crystal fibers of various materials for devices covering a wide range of applications, especially for optical communications.

Method and apparatus for splicing optical fibers

Abstract: A method and apparatus are described for permanently splicing glass optical fibers. The fibers are aligned colinearly, and their endfaces are brought into contact. An electrical arc discharge is generated at the junction between the fibers and is moved along the junction to ensure complete fusing of the fiber endfaces. Best results are obtained by first applying only enough heat to the fiber junction to cause the fibers to adhere to each other without forming a good optical connection, and thereafter, increasing the arc current to a value sufficient to cause complete fusion of the fiber endfaces.

Keyboard using optical switching

Abstract: The invention relates to keyboard devices using optical switching and includes novel light distribution means to multiple fiber optics, switching means between fiber optics, and collection means from multiple fiber optics to a single point.

Raman Spectral Characterization of Pure and Doped Fused Silica Optical Fibers

Abstract: The utility of Raman spectroscopy as a means of characterizing the properties of pure and doped fused silica has been investigated. Laser-Raman spectra were obtained by forward scattering from solid optical fibers ~35 to 85 m in length using 514.5 nm excitation with an "image slicer" and a Cary model 81 instrument. Clad and unclad fibers of fused silica and doped fibers having SiO2-GeO2 and SiO2-GeO2-B2O2 cores were examined. Raman spectra were also obtained from bulk samples of glasses, including pure GeO2, pure B2O3, and various compositions of SiO2-GeO2, SiO2-B2O3, and SiO2-GeO2-B2O3. The addition of dopants to fused silica was found to alter the Raman spectrum both by the appearance of new bands, roughly proportional to dopant concentration and not common either to the fused silica or to the dopant alone, and by the marked alteration of other Raman bands, which is indicative of changes in the local intermolecular order. Thus, addition of GeO2 produces new Raman bands at ~675 and ~1000 cm−1; and of B2O3, new bands at ~940 and ~1350 cm−1. Addition of GeO2 and/or B2O3 weakens the relatively sharp Raman lines near 485 and 600 cm−1 (and a similar but small effect was also noted with increasing OH content). GeO2 and B2O3 together also produce observable narrowing of the broad intense 440 cm−1 Raman contour. These spectral effects are interpreted, respectively, in terms of a decrease in the concentrations of [Equation] and [Equation] defects produced by dopant addition and of a concomitant reordering of the silica structure. Raman spectroscopy thus appears to be a useful optical technique for elucidating the properties of dopants that have been especially chosen for good optical transmission and hence are not easily detectable by absorption measurements.

Refractive index profile of a graded index fiber: measurement by a reflection method.

Abstract: Several methods that measure the refractive index pro­ file of a graded index fiber have been reported: for examFig. 1. The off-axis ray's path in an inhomogeneous medium. ple, an interferometric method, a far-field pattern meth­ od, and an electron beam microprobe method. This Let­ ter reports a simple and accurate reflection method. The reflected power from the surface of the sample is di­ rectly related to the refractive index of the sample. In the case of normal incidence, the reflectivity R is given as

Formation of a Spherical Lens at Optical Fiber Ends with a CO(2) Laser.

Abstract: A study was made of the use of a CO(2) laser for producing a hemispherical lens at the end of a fiber. When the fiber end is heated to the softening points of the material, it tends to become spherical in shape due to surface tension. A one-dimensional heat conduction model for the fiber can reasonably predict the required laser power for a given pulse length to produce lenses on fibers made of various kinds of materials. A He-Ne laser beam was coupled into a fiber to investigate the properties of the spherical lens. We also observed that such lens can couple light from a source into the fiber, can be used for imaging, and can focus enough laser intensity for machining various materials.

Polarization optics of index-gradient optical waveguide fibers.

Abstract: An investigation of the polarization optical properties of index-gradient glass fibers confirmed the applicability of the linear birefringent model to fibers of this type. The phase retardation (delta(s) = 58 degrees /cm) is homogeneously distributed along the whole length of the fiber. The depolarization occurring when the incident polarization angle coincides with the fast (or slow) axis of the fiber is negligibly small. The measuring technique employed allows the phase retardation between the wave components in the privileged directions within the fiber to be determined as a function of the temperature (Deltadelta(s)/DeltaT = 0.09 degrees /K cm). As the fiber is twisted the polarization vector rotates synchronously with the twisted endface of the fiber.

Fiber optic phased array antenna system for RF transmission

Abstract: A system for providing the plural variable phase RF signals required to control the beam pointing angle of a phased array A light energy source (shown as a laser generator) is modulated by an RF signal and fed to a plurality of channels in parallel Each of the said channels corresponds to one radiating element of the phased array and each channel includes as many selectively employed fiber optic delay lines of different lengths as are required to generate the discrete phases required at the corresponding antenna (radiator) element of the array A commutating programmer controls the selection of individual radiating element phases for each successive beam pointing position

Arbitrarily shaped inhomogeneous optical fiber or integrated optical waveguides

Abstract: Using the finite element technique, a numerical method is devloped so that one may obtain the propagation characteristics of optical waves along guiding structures whose cores may be of arbitrary cross‐sectional shape and whose material media may be inhomogeneous in more than one transverse direction. Several specific examples are given and the results are compared with those obtained by other exact or approximate methods. Very close agreement was found. The method developed here can easily be applied to many important problems dealing with practical optical fiber or integrated optical waveguides whose cross‐sectional index of refraction distribution may be quite arbitrary.

Multi-core optical communications fiber

Abstract: Methods and apparatus are disclosed for providing a multipath optical communications system within a single fiber. One embodiment comprises a concentric multi-core optical fiber having an inner core for transmitting information and an outer core for transmitting a security signal. Attempted access to the inner core causes a decrease in the security signal intensity alerting the operator to the attempted intrusion.

Nondestructive refractive‐index profile measurements of clad optical fibers

Abstract: An interferometric method in conjunction with Abel inversion is used to precisely measure the index of refraction profile of clad optical fibers without perturbing them. The sample is immersed in index‐matching fluid, so that fiber index variations cause only small phase shifts for rays propagating perpendicular to the axis, making interferometric methods applicable.

Fiber reinforced optical fiber cable

Abstract: A room temperature vulcanizable silicone rubber having a high coefficient of thermal expansion is provided at the interface between an optical fiber and a surrounding fiber reinforced resin shell in a cable construction. The surrounding rubber because of high coefficient thermal expansion shrinks more than the optical fiber or the resin shell during the manufacture operation. This relieves radial compressive loads on the optical fiber and prevents the distortion of the optical fiber by the surrounding fiber reinforced shell in manufacture and use. As a consequence, light transmission qualities are not impaired.

New coupling method for GaAs-laser--fibre coupling

Abstract: A new method for coupling a diode laser to an optical fibre is described. This uses a cylindrical glass fibre as a focusing element. Optical feedback from the fibre endface has been found to have an influence on the laser output power. As a result, the light power launched into a single-mode fibre was higher than that obtainable from the laser during normal operation.

Solar energy apparatus

Abstract: A solar energy apparatus for gathering and transmitting solar radiation to an energy storage area. Wide-angle lens apparatus is used to focus solar radiation on an end of an optical fiber bundle. The other end of the optical fiber bundle is placed in the energy storage area and has a radiating device attached thereto to more efficiently remove the solar energy from the optical fiber bundles. A heat sink is advantageously utilized as a storage means for the solar energy thus gathered and transmitted.

Surface-wave radiation loss from curved dielectric slabs and fibers

Abstract: A newly developed systematic procedure to calculate the real and imaginary parts of the change in propagation constant of a surface-wave mode on a curved open waveguide of general cross section is used here to determine these quantifies for the TE modes of an asymmetric slab waveguide and for all the modes of an optical fiber. Comparison of these results with the existing literature points up the care which must be taken in making approximations in this problem, since errors of significant factors in the radiation loss have been made in previous work.

Sheathed optical fiber element and cable

Abstract: One or more optical fibers are loosely enclosed in a tubular plastic sheath so as to be slidable with respect to the sheath. The fibers may be longer than the length of the corresponding surrounding sheath. The sheathed fibers are wound around a core and covered with a further sheath to form a cable. In the process, the optical fiber is treated with an anti-adhesive material before the sheath is extruded thereover and during the subsequent processing the sheath, which has a length greater than the length of the enclosed fiber, either because of its temperature or because of mechanical stretching, is allowed to contract while in non-slidable relation with the fiber, thereby providing a fiber length greater than that of the sheath.

Measuring method for the refractive index profile of optical glass fibres

Abstract: A new method for measuring the refractive index profile of optical glass fibres is described. This simply monitors the reflection of a focused laser beam from a polished fibre end face. Detailed tests on the accuracy and resolution of the method are described and the index profiles of several fibres are given as an example of its feasibility.