Showing papers on "Optical fiber published in 1972"

Optical power handling capacity of low loss optical fibers as determined by stimulated Raman and brillouin scattering.

Abstract: The effect of stimulated Raman and Brillouin scattering on the power handling capacity of optical fibers is considered and found to be important especially when low loss optical fibers are used. A critical power below which stimulated effects may be neglected is defined for forward and backward Raman scattering and for backward Brillouin scattering. This critical power is determined by the effective core area A, the small signal attenuation constant of the fiber alpha, and the gain coefficient for the stimulated scattering process (gamma0), by the approximate relation P(crit) approximately 20Aalpha/(gamma0). For a fiber with 20-dB/km attenuation and an area of 10(-7) cm(2)P(crit) approximately 35 mW for stimulated Brillouin scattering. For stimulated Raman scattering P(crit) is approximately two orders of magnitude higher. It is concluded that these effects must be considered in the design of optical communication systems using low loss fibers.

Coupled-Mode Theory for Optical Fibers

Abstract: A set of coupled-mode equations is derived to describe mode propagation in uniform and slightly nonuniform cylindrical optical-fiber systems. The coupling between fibers of an array made up of n identical fibers each at the vertex of a polygon and one at the center, which is not necessarily the same as its n neighbors, is determined. Examples of this array are two fibers, three fibers in a row, and a hexagonal array with a fiber in the center. Very simple expressions for the coupling coefficients are presented. Mode coupling on a lossy fiber is investigated and a simple expression for the loss of a HE11 mode is given.

Stimulated Brillouin scattering in optical fibers

Abstract: Observations of backward stimulated Brillouin scattering (SBS) in glass optical fibers are reported. Threshold for SBS has been achieved with less than 1 W of input power at 5355 A. Relaxation behavior in the SBS signal has also been observed and is attributed to finite‐cell‐length oscillation. Experimental results are compared with theory, and the implied limitation to optical fiber transmission is discussed.

Instrument for performing laser micro-surgery and diagnostic transillumination of living human tissue

Abstract: An instrument for performing delicate surgery on man is provided with a continuous wave laser source specially associated with a binocular surgical microscope. The laser source emits electromagnetic radiation at wavelengths, preferably in the visible light range but also in the near visible infrared and ultraviolet ranges, which are absorbed selectively by different types of human tissue or tissue substructures. The source is mounted on a portable base remote from the operating area, and the radiation from the laser is communicated through a flexible fiber optic conductor to the binocular surgical operating microscope which is mounted on an articulating arm extending from the base so that the microscope may be freely positioned adjacent to the patient at the operating area. The laser beam is directed onto the tissue of the patient in a path coaxial with the viewing axis of the microscope to a point in the microscope''s field of view. Controls on the microscope give the surgeon complete control of the laser beam. These include a focusing telescope for control of the laser spot size and angle of convergence of the beam, a joy stick control for moving the fiber optic tip to cause a corresponding movement in the focused laser beam on the tissue within the field of view of the microscope to allow the surgeon to precisely prescribe an incision or effect localized irradiation on that area of the patient. Transillumination of the tissues in the area of interest on the patient is possible by the direct laser beam emitted at a low-nonhazardous power level or by a second laser system which may be operated independently of the main high power surgical laser and is delivered by a hand-held sterile probe.

Intensification of Spontaneous Raman Spectra by Use of Liquid Core Optical Fibers

Abstract: Intense spontaneous Raman radiation has been obtained from C6H6 and C2Cl, by passing the focused beam from an argon ion laser (4880 A, 5 to 250 mW) through filled hollow fused quartz optical fibers having core diameters of ∼75 μm and lengths from 10 to 25 meters. Spectral intensifications by factors of ∼102 to 103 compared to conventional sample techniques have been obtained with the fiber optics method. Raman spectra were recorded with a Cary model 81 spectrophotometer by collecting the divergent radiation emitted from the end of the optical fiber at the focus of the "image slicer." However, the intensification method is general and may be employed with any double or triple monochromator by placing the fiber end near the entrance slit. For C6H6 at least 33 Raman components were observed in the 3300 > Δν> 1650 cm−1 region including shifts due to overtones and combinations, by using a slit-width of 2 cm−1 with a 15 m fiber length and a laser power of ∼130 mW. The Raman spectra from C6H6 were found to be in good agreement with those recently reported by Schrotter and Bofilias. For C2Cl4 intense spectra were also obtained using 2 cm−1 slit-widths with fiber lengths of 25 m and power levels to 250 mW. These spectra augment those obtained earlier by Wittek and indicate five newly observed Raman and infrared coincidences that in several cases may result from the breakdown of D2h selection rules. Details of the fiber optics Raman technique are described.

Optical waveguide light source

Abstract: A source of optical wave energy for an optical transmission system. One end of an optical fiber having a thin, elongated core of laser material is so aligned with an end of an optical waveguide that coherent light generated in the core is coupled to the optical waveguide. A first transparent cladding layer is disposed upon the surface of the core, and a second thin transparent cladding layer is disposed upon the surface of the first layer. The refractive index of the first layer is less than that of the core and greater than that of the second layer. A solid state source of incoherent light is disposed immediately adjacent to that end of the optical fiber which is opposite the optical waveguide. Light from the solid state source is coupled into the optical fiber and is propagated longitudinally therethrough. Coherent light is generated by the core of laser material as it absorbs incoherent light propagating through the optical fiber.

Method of forming optical waveguide fibers

Abstract: A method of forming an optical waveguide by first forming a coating of glass with a predetermined index of refraction on the outside peripheral wall surface of a glass cylinder having a different predetermined index of refraction. The glass cylinder and glass coating combination is then heated and drawn to reduce the cross-sectional area and form a clad optical fiber where the core is formed from the glass cylinder and the cladding is formed from the glass coating.

Power coupling from GaAs injection lasers into optical fibers

Abstract: Measurements have been made to determine the efficiency of coupling light from GaAs injection lasers (λ = 9000 A) of stripe geometry into the cores of optical fibers. Laser light was coupled into a fiber across a small air gap which separated the laser from the fiber. The power coupling efficiency was calculated by extrapolating the lasing light power emitted at the end of a short length of fiber back to its input tip and comparing it with the total laser beam power. Experiments were performed with several diffused junction (DJ) lasers and with low-threshold double-heterostructure (DH) lasers having stripes formed by proton bombardment or oxide masking. The beam profile, scanned in its near and far field region, was approximately Gaussian. The beam dimensions at the surface of the laser were estimated from far field measurements and were used to predict the coupling efficiency of single-mode and multimode fibers. Power coupling efficiencies of about 70 percent were measured for DJ lasers feeding 10-µm multimode fibers. A coupling efficiency of 25 percent, almost identical to the theoretical estimate, was achieved with a DH laser having a 1-µm × 13-µm proton-bombarded stripe, feeding the 3.2-µm core of a single-mode fiber. The coupling efficiency was greater than 40 percent when a DJ laser fed the same fiber. A cylindrical lens is proposed to increase the power coupling perpendicular to the junction plane. Permanent self-supporting couplers were made by applying epoxy between structures which supported the fiber and the laser.

Pulse propagation in multimode dielectric waveguides

Abstract: Using coupled power equations to describe the average performance of a multimode waveguide with random coupling, it is shown that a Gaussian input pulse remains approximately Gaussian with a pulse width that increases proportionally to the square root of the length of the waveguide. The proportionality factor is determined for the model of a slab waveguide. Since coupling between guided modes of necessity causes coupling of some of the guided modes to radiation modes, radiation losses are un-avoidable. A desired improvement in pulse distortion that is accomplished by coupling the guided modes intentionally to each other must be paid for by a certain loss penalty. This loss penalty is also evaluated for the special case of the slab waveguide model. Pulse dispersion improvement can be achieved by providing intentional roughness of the core-cladding interface of the dielectric waveguide. The “power spectrum” of the core-cladding interface function must be designed very carefully in order to minimize the radiation loss penalty that accompanies any attempt to reduce pulse dispersion. The dependence of the loss penalty on the shape of the “power spectrum” of the core-cladding interface function is studied in this paper. Design criteria for the improvement of multimode pulse dispersion are given based on the slab waveguide model. The connection between the slab waveguide model and the round optical fiber is pointed out.

Signal detection and delay equalization in optical fiber transmission systems

Abstract: A stripper at the end of an optical fiber selectively couples propagating signal components out of the fiber at characteristic angles A linear array of photodetectors selectively responds to each of the coupled signal components or to groups of such components When used simply as a mode or as a frequency separator, the detected signals are separately coupled to different output circuits In a detector-equalizer embodiment, the signals, suitably delayed relative to each other, are coupled to a common output circuit

Method of splicing optical fibers

Abstract: Apparatus, and a method of splicing optical fibers which includes placing the fibers in a V-shaped groove, slipping a pliable, metallic sleeve over the fiber ends, and then crimping the sleeve, thereby simultaneously aligning and mechanically securing the two fibers.

Material dispersion in optical fiber waveguides.

Abstract: In weakly guiding dielectric (glass) fiber waveguides the factors governing the envelope delay distortion of optical signals can be separated conveniently into material and waveguide contributions. By making use of the fact that the normal dispersion of the index-of-refraction of glasses accurately fits a single oscillator Sellmeier equation, simple relations of general validity are obtained for the material contribution to the group delay and frequency dependence of the group delay in dielectric fiber waveguides. Using these results expressions are obtained for the material contribution to the information bandwidth of fiber optic waveguides excited by wideband sources (light emitting diodes) and narrow band sources (lasers). It is shown that in single mode guides the bandwidth limitation imposed by material dispersion is negligible, while in multimode guides the difference in group delay of higher order modes imposes the most severe bandwidth limitation.

Optical fiber splicing device and technique

Abstract: OPTICAL FIDER SPLICING DEVICE AND TECHNIQUE Abstract of the Disclosure A method and an apparatus are described for joining together single optical fibers under adverse environmental conditions. The fibers are aligned collinearly in a hollow sleeve, a quantity of low melting point transparent thermoplastic is inserted in the sleeve at the junction of the two fibers and heat is applied to melt the thermoplastic causing it to flow around the aligned ends thereby producing an optically efficient bond when the heat source is removed. - i -

Optical transmission loss in liquid-core hollow fibers

Abstract: Multimode optical fibers consisting of glass cladding and liquid core have been constructed. For a cladding index of refraction of 1.52 and a core of bromobenzene, index of 1.560, a loss of 0.140 dB/m has been measured over lengths of about 50 m. The loss measured with incoherent light is higher due to the presence of higher order modes. Strong absorption in the near infrared occurs in narrow wavebands associated with overtones of the C-H fundamental vibration frequency.

Acousto-optic underwater detector

Abstract: A low frequency or pressure-gradient hydrophone comprising an optical reflector experiencing displacements responsive to acoustic waves. A beam light from a light source is carried by a first group of fiber optics guides and is incident upon the optical reflector. The light reflected from the reflector is carried by a second group of fiber optics guides to a light detector. Any displacements of the reflector due to pressure gradient due to acoustic waves impinging on the opposite sides of the reflector are detected by changes in intensity of reflected light from the light source.

New low-loss liquid-core fibre waveguide

Abstract: Low-loss liquid-core fibre-optical waveguides having a transmission loss of 10 dB/km has been made using commercially available glass tubing. The loss is less than 20 dB/km over a wavelength range of greater than 0.8-1.1 μm, and, at the semiconductor laser wavelength of 0.9 μm, has a value of 14 dB/km. This is the first low-loss fibre to be made using glass.

Coaxial diode mount for use with fiber optic light guide

Abstract: A conventional single lead connector is modified to house a light emitting or light detecting device. A first end of the connector is adapted to connect with a current or voltage driving source while the opposite end of the connector receives a fiber optic light guide. In the instance where the connector houses a light emitting device such as a diode, an electrical signal is applied to the diode through conductors in the connector. Resulting light from the diode is transmitted along the fiber optic to a remote detector. If a light detecting device is housed by the conductor, a reversal of light-electrical signal transmission occurs.

Laser to optical fiber coupling

Abstract: An optical fiber is coupled along an edge of a rectangular GaAs injection laser. A circulatory mode of light reflection is established between the four side walls of the laser at an angle of incidence which provides a narrow rectangular strip of light. The fiber is positioned transversely at one reflection point or corner of the light path. A narrow rectangular metal strip contact on one face of the laser confines current to the desired path. A reflective coating on an end of the fiber may provide a unidirectional optical source. Other variations include an optical amplifier for a light input source and an optical coupler from an input fiber to an output fiber.

Gallium arsenide laser fiber coupling

Abstract: The coupling of an injection laser diode into an optical fiber is improved by a short resonating length of fiber. A partially reflective layer is positioned at the remote end of the resonator section and a highly reflective layer with an aperture slit and anti-reflection layer in the slit are disposed at the laser end. A circulatory laser mode can also be improved using a resonator section with a matching interference layer at the coupling point. A rectangular contact strip confines current to the desired circulating area. Another variation includes two different coupling points with one more tightly coupled than the other for circulating light in one direction.

Fiber optics distance converting technique

Abstract: According to an illustrative embodiment of the invention, a technique is described for producing signals varying as a function of the distance of a surface relative to a reference face, comprising transmitting a beam of coherent light to an admitting end of a fiber optic bundle to transmit light to a reflecting surface opposite an emitting end of the bundle. A fiber optic receiver bundle having at least one receiving end for picking up light reflected by the surface is provided for transmitting a flux of reflected light to produce a signal related to this relative distance by a linear relationship over a certain range of variation of such distance. Such range may be varied by varying the angle of incidence of the coherent light beam on the admitting end. The receiving end may be transversely separated from the emitting end by an amount selected in accordance with a desired angle of incidence and a predetermined range. For the purpose of measuring the thickness of transparent bodies as measured by the distance between an outer and an inner face thereof opposite the emitting end, first and second respective receiving ends are provided such that light reflected by the inner face cannot be picked up by the first receiving end and vice-versa. A simple technique for determining the effects of variations of reflectivity of a light reflecting surface is also disclosed.

Method for splicing optical films

Abstract: An arrangement of optical fibers, apparatus and method for splicing same are described. The fiber arrangement comprises a plurality of fibers secured to a ribbon-like tape. The fiber segments to be spliced are mounted on the slidable holders of a splicer such that each of the fibers of one segment are aligned approximately coaxially with a fiber on the other segment. The individual fibers are then cut, as required; moved into position; more accurately aligned by mechanical means; and then bonded together by the application of either heat or a bonding material of suitable refractive index. In one arrangement, accurate alignment of the fibers is obtained by means of a grooved cover plate which is placed over the adjacent ends of the fibers and left in position until the bonding step is completed. Various means for mounting the fiber segments in the splicer and for strengthening the splice are disclosed. A modified splicer for liquid core fibers is also described.

Method of forming an economic optical waveguide fiber

Abstract: A METHOD OF FORMING AN OPTICAL WAVEGUIDE BY FIRST FORMING A COATING OF GLASS ON THE INSIDE WALL OF A GLASS TUBE, THE GLASS TUBE AND THE FIRST COATING BEING OF SUBSTANTIALLY SIMILAR MATERIAL. THEREAFTER, A SECOND COATING OF GLASS IS APPLIED TO THE INSIDE WALL OF THE GLASS TUBE OVER THE FIRST COATING, SAID SECOND COATING HAVING A PRESELECTED DIFFERENT INDEX OF REFRACTION FROM THAT OF THE FIRST COATING. THE GLASS TUBE AND COATING COMBINATION IS THEREAFTER DRAWN TO REDUCE THE CROSS-SECTIONAL AREA AND TO COLLAPSE THE SECOND AND INNER COATING OF GLASS TO FORM A FIBER HAVING A SOLID CROSS-SECTIONAL AREA. THE COLLAPSED INNER COATING FORMS THE FIBER CORE AND THE FIRST COATING FORMS THE CLADDING FOR THE FIBER WHILE THE EXTERIOR GLASS TUBE PROVIDES STRUCTURAL STRENGTH FOR THE FIBER. D R A W I N G

Coupling of lasers to optical fibres

Abstract: A laser is coupled to an optical fibre by coupling the laser beam to a planar waveguide, and coupling the waveguide to the fibre. Particularly the laser beam is coupled to the planar waveguide by a grating. For ease in obtaining and maintaining good alignment between waveguide and fibre core, the fibre is positioned in a groove in a support member. Crystallographic etching a Vee groove gives a simple and effective way of forming the groove in the support member.

Delay distortion in weakly guiding optical fibers due to elliptic deformation of the boundary

Abstract: The delay distortion in glass fiber optical waveguides due to small elliptical deformations of the cross section is calculated. Simple approximations are given for the case of small differences in index of refraction between core and cladding (weak guidance). Since the delay distortion is quadratically dependent on the index difference it is found that it is generally possible to keep it negligible by judiciously choosing the guide parameters.

Picosecond pulse distortion in optical fibers

Abstract: Low-loss glass fibers are a prospective transmission medium for optical communication systems. To study their dispersion characteristics, we investigated the propagation of short optical pulses in up to 10 m of cladded fiber. The pulses, 7 ps long and 6 THz in spectral width, were derived from a mode-locked Nd:glass laser by frequency doubling (0.53-μm wavelength). We measured the broadened pulses emerging from the fiber by a sampling technique that employed an optical Kerr shutter of 10 ps gating time. The fiber had a core diameter of 11 μm and an index difference of 1 percent between core and cladding. The loss was about 1.8 dB/m. Our measurements showed satisfactory agreement with a theory that takes material dispersion and mode dispersion into account and assumes strong attenuation of the high-order modes in the particular fiber tested. At the end of 10 m, the 7-ps pulse reached a width of 110 ps, haft of which can be accounted for by material dispersion. When we extrapolate these results to practical systems, we conclude that pulses from a light-emitting diode transmitted through a fiber with the above design would broaden by at least 2.6 ns/km (because of material dispersion), and possibly by as much as 33 ns/km, if all modes were excited and reached the detector with comparable attenuation and negligible coupling.

Power loss on optical fibers

Abstract: The power loss, due to material absorption from an HE 11 mode propagating on an optical fiber, is derived and approximations are introduced which simplify its calculation. The attenuation constant of the HE 11 mode, for fibers with a small index of refraction difference between the core and the cladding, is shown to be equal to the known (measured) loss of the material in bulk multiplied by the fraction of modal power flowing through the lossy region.

Smoke detecting device utilizing optical fibers

Abstract: A smoke detecting device utilizing optical fibers is composed of a required number of optical fibers arranged in series alignment with gaps provided therebetween, a light source introducing light rays through one end of the first of the serially arranged optical fiber to the interior thereof, a photo-electric transducer for receiving light rays passed through the optical fibers and delivered from the end of the last of the serially arranged optical fiber to convert the amount of light thus received into an electric quantity, and a discriminating circuit which produces a predetermined electric signal for indicating the detection of fire whenever the variation of the electric quantity thus obtained exceeds a preset value, whereby any variation in the amount of light due to the intervention of smoke into the gaps between the optical fibers is detected electrically thereby to obtain an electric signal.

Transmission loss of tetrachloroethylene-filled liquid-core-fibre light guide

Abstract: The attenuation of a tetrachloroethylene-filled liquid-core light guide has been measured for wavelengths between 600 and 1600 nm. A number of peaks appear in the curve, and some of these are identified with the effects of residual water. Attenuation troughs appear at 1090, 1205 and 1280 nm where, in each case, the attenuation is less than 8 dB/km.

Method utilizing an optical fiber raman cell

Abstract: A long length of liquid-core optical fiber is employed as a Raman cell, wherein the fiber core contains the material whose Raman spectrum is to be analyzed. Spectral intensifications of from 102 to 103 times greater than that obtained by conventional means are realized, using very small sample volumes. Optimum fiber lengths are disclosed.