Showing papers on "Photonic-crystal fiber published in 1974"

Scattering from side-illuminated clad glass fibers for determination of fiber parameters

Abstract: The theoretical characteristics of the scattered-light pattern from a clad glass fiber illuminated by a laser beam perpendicular to its axis agree closely with results of experimental measurements of the scattered light. A simplified geometric ray-tracing technique shows that for fibers with medium and small core sizes, specific angle ranges of the scattering pattern provide determinations of fiber diameter independent of core parameters. Measurements of the fringe modulation give relatively sensitive determinations of core diameter. Light scattering is a useful technique for determining the diameters of both clad and unclad fiber. Total-diameter determinations have accuracies of ±0.2 μm and core diameters, ±0.5 μm for 0.02 refractive-index difference between core and cladding.

Hyperbolic type optical fiber lens coupler for coupling the fiber to an optical line source

Abstract: The angular profiles of optical radiation emitted by certain conventional optical sources, such as a semiconductor P-N junction laser, are similar to those of optical line sources. In order to increase the optical coupling efficiency from such optical line sources to an optical fiber, the input end of the fiber is shaped essentially into the form of a hyperbolic cylindrical lens by first forming a flat wedge at this end of the fiber and then finishing the wedge to the desired essentially hyperbolic cylindrical surface. This finishing can be accomplished by either a flame (heat) type polishing or a mechanical (fine abrasive) type polishing.

Refractive Index and Diameter Determinations of Step Index Optical Fibers and Preforms

Abstract: A new method to determine the index of refraction in combination with the diameter of the cores of step-index optical fibers and preforms is presented. The technique is based on an analysis of the backscattered light when a beam from a cw laser impinges transversely upon the fiber or preform. A geometrical-optics analysis shows that, under appropriate assumptions, a combination of the refractive indexes and the radii of the core and cladding can be determined from unique characteristics of the backscattered radiation pattern. The theory is compared to experimental observations with excellent agreement.

Method for measuring the parameters of optical fibers

Abstract: Parameters of a clad optical fiber are measured by irradiating the fiber with a laser beam to generate a scattering pattern. Measurements are made of fringes and modulations in the scattering pattern and these measurements are translated into such parameters as core and fiber diameter.

Laser Drawing of Optical Fibers

Abstract: A system consisting of a cw CO2 laser and an ellipsoidal reflector was developed in order to draw fused silica fibers from bulk material. The system was used to obtain unclad fused silica fibers (Suprasil 2) having a total transmission loss of less than 100 dB/km at 6328 A. Preforms (rod in tube) have also been drawn to fibers of long lengths with diameters as small as 10 μm and variations within 5%. Analysis of the fiber drawing process established relations that allow determination of the design parameters for fiber drawing systems. Experimental results are given that support these relationships.

Method of making optical fiber with porous cladding

Abstract: Improving the light-transmitting efficiency of a clad lightconducting fiber by minimizing core-cladding interfacial defects. Elongated open channels extending longitudinally of the fiber are formed within the cladding to cushion the expansion of gases existing and/or created along the fiber core-cladding interface during fabrication of the fiber.

Borosilicate clad fused silica core fiber optical waveguide with low transmission loss prepared by a high-efficiency process

Abstract: A method for making fused silica core‐borosilicate clad optical fiber waveguides is described. The process involves the growth of a needlelike layer of borosilicate glass onto the surface of a commercially available high‐purity fused silica rod by an efficient flame reaction of boron and silicon hydrides with oxygen. The needlelike layer is subsequently heat treated at relatively low temperature to form a homogeneous bubble‐free glass with a smooth surface. It is then covered with a thin protective jacket of silica and drawn into a fiber. These fibers have attenuation coefficients only slightly greater than the bulk loss of the fused silica core materials. Over the Al1−xGaxAs injection laser wavelength range, 0.82–0.88 μm, the loss is 5 dB/km, while at the YAG : Nd laser wavelength, 1.06 μm, it is 3 dB/km. The process appears to be attractive for the economical manufacture of low‐loss fibers due to its simplicity and high chemical conversion efficiency.

Propagation characteristics of multimode fibers with graded core index

Abstract: Bending loss and impulse response of multimode fibers with graded-index core have been studied. A multimode fiber which has a large index difference is profitable because of low loss in bends. Impulse response of the fiber in which all of the possible modes are excited with the same intensity depends remarkably on the fourth-order term of the index profile. A small value of mode delay of 0.15 ns/km is estimated to be obtainable in a fiber having an optimum index profile and index difference ratio of 0.05 using incoherent light.

Fiber distributed feedback laser

Abstract: Utilizing round optical fibers as communication channels in optical communication networks presents the problem of obtaining a high efficiency coupling between the optical fiber and the laser. A laser is made an integral part of the optical fiber channel by either diffusing active material into the optical fiber or surrounding the optical fiber with the active material. Oscillation within the active medium to produce lasing action is established by grating the optical fiber so that distributed feedback occurs.

A simple two‐fiber optical displacement sensor

Abstract: An optical displacement sensor is described in which only a pair of large‐diameter fibers is used rather than a branched bundle of many small‐diameter fibers. The basic idea of the two‐fiber sensor is that the axes of the fibers are at an angle to one another at the sensor face, rather than parallel as is the case for the many‐fiber configuration. The sensitivity of this two‐fiber sensor is approximately the same as the most sensitive configuration of the many‐fiber sensor.

Coupler for coupling optical energy transmitted by optical fiber to optical waveguide and method of manufacture

Abstract: A coupler for coupling optical energy transmitted by optical fibers to a thin-film optical waveguide and a method of manufacture. In the method an optical fiber is sandwiched between a pair of substrates and the substrates and fiber are bonded together with a suitable material. The bonded product is then cut to provide a surface including a cross section of the fiber. After polishing this surface a thin-film optical waveguide is then provided on the surface including the fiber end. The cutting angle is chosen such that, in the assembled coupler, the exit angle with respect to the waveguide surface is greater than the critical angle of the guide material. In this fashion the optical energy coupled from fiber to guide is trapped in the guide. The apparatus includes an optical fiber in a substrate with a cross section of the fiber in the surface of the substrate with a thin-film optical waveguide overlying the substrate surface. To insure the coupled optical energy is trapped in the guide the angle between the fiber axis in the substrate and the guide surface is greater than the critical angle for the guide material.

Integrating Sphere for Measuring Scattering Loss in Optical Fiber Waveguides

Abstract: An integrating sphere for light scattered from fused silica optical fiber waveguides that is relatively simple to construct and easy to use is described. The novel feature is the use of a solid sphere of fused silica to facilitate coupling the scattered light out of the fiber cladding into the detector. The fiber is inserted into a slot in the sphere, and glycerine is used to index match between the fiber and sphere. The sphere is coated with high reflectivity barium sulfate, and a silicon photodiode detects the radiation in the sphere. The construction, operation, and performance tests on the sphere are described.

Radiation Effects in Fiber Optic Waveguides.

Abstract: : A comprehensive review is presented on the effects of ionizing radiation on the performance of fiber optic cables, and on the materials used for fabrication of optical fibers. This includes a summary of the permanent and transient radiation-induced losses in optical transmission of state of the art fibers, a detailed discussion of the mechanisms responsible for the losses observed, and a report on inhouse materials development to achieve radiation hardened fiber optic glasses.

Some Materials Problems in the Design of Glass Fiber Optical Waveguides

Abstract: By coating a thin (d = 1–100 μ), transparent glass fiber with a second glass of lower refractive index, practical optical waveguides can be produced. Such fiber optic composites have been used for many years. A communication system utilizing these glass fibers as the transmission medium is attractive because of the high frequency (large capacity) employed and their small size. However, because of the very high degree of optical transparency required in a system of any reasonable length, the normal problems encountered in producing classical fiber optic devices are greatly magnified.

Variation of refractive index with wavelength in fused silica optical fibers and preforms

Abstract: The variation of the refractive index of an unclad fused silica fiber and the preform from which it was pulled was determined over the wavelength range 0.5–1.1 μm, in 0.025‐μm steps. The index is determined from an analysis of the backscattered radiation produced when light from an appropriately filtered xenon‐arc source impinges transversely upon the fiber or preform. The variation of the index of refraction of the fiber follows those of the preform and published values for bulk fused silica material to within 2 parts in 10−4, with the exception of two points at 0.65 and 0.95 μm.

Process for producing a gas tight light transmitting optical fiber plate

Abstract: A process for producing a gas tight light transmitting optical fiber plate comprising arranging the optical fibers or bundles of the optical fibers in a die, heating and compressing the optical fibers at a temperature of between the transition point of the glass of the optical fibers and the softening point of the glass of the optical fibers thereby to weld the optical fibers together, and maintaining the welded optical fibers within that temperature range at a pressure higher than the pressure during the heating period which is sufficient to cause the shrinkage of voids by the surface tension of the optical fibers.

Partially cladded triangular-cored glass optical fibers and lasers*

Abstract: Optical fibers that possess the characteristics of both conventional cladded fibers and of a new type of fiber have been drawn and evaluated The core has an equilateral triangular cross section with slightly bulging curved sides The rounded vertices are in contact with the inside of the cladding tube of lower refractive index Most of ther periphery of the core is surrounded by air The cavity-like waveguide modes of this new type of fiber can be described as due to skew rays being reflected systematically from the glass–to–air interfaces as they propagate along the fiber Near-field and far-field radiation patterns have been photographed and are presented A new type of laser based on these cavity-like waveguide modes is proposed, in which the triangular core is made of a material (eg, neodymium-doped glass, YAG, etc) that can be optically pumped The normal mode of operation of the laser consists of six diverging, spatially separated output beams; it can be optically pumped axially from both ends simultaneously, while being pumped from the sides

Photon Counting with Fiber-Optic Coupled Scintillators

Abstract: By coupling a scintillation crystal to a photomultiplier with fiber optics, one can place the detector in areas not normally accessible to a crystal-photomultiplier combination. Although fiber optics provide a flexible optical coupling, serious light losses cause about a factor of 10 reduction in the light intensity reaching the photomultiplier. Most of the light loss is due to the small acceptance angle of the fiber optics with transmission losses and crystal aperture losses playing secondary roles. Attention to the design and to the selection of the crystals and fiber optics help to optimize the light collection efficiency. The light losses lower the scintillation intensity from low-energy (10 to 40 keV) radiation into the region where photomultiplier noise becomes important (3.5 - 18 photoelectron equivalents). This noise consists of Cerenkov events, faceplate scintillations, electroluminescence, afterpulses and thermionic emissions. For effective low background counting this noise must be reduced. A combination of pulse-shape discrimination, magnetically limiting the photocathode area and shielding were effective in reducing the background rate from 513±3 counts/minute to 10.0±0.5 counts/minute in the energy range from 6.5 to 40 keV. By coincidence counting, in the same energy region, a background rate of 1.60±0.28 counts/minute was obtained.

Propagation of a semiconductor laser pulse in an optical fiber

Abstract: Frequency modulation of the optical carrier, due to heating a p-n junction, is a characteristic feature of the injection laser radiation. This feature is allowed for in a calculation of the distortion of a pulse generated by such a laser and traveling in an optical fiber characterized by frequency dispersion. The optimal parameters of the fiber, corresponding to the maximum narrowing of the pulse, are determined.