FIBEROPTIC SENSOR TECHNOLOGY HANDBOOK

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electron-hole recombination. The combining of an electron and a hole resulting in a decrease in electron energy and the production of a photon. electronically-controllable coupler. An optical element that enables other optical elements to be coupled to, or uncoupled from, each other, in accordance with an applied electrical signal. For example, two parallel slab dielectric waveguides with an optical material between them whose refractive index can be altered by application of an electronic signal, thus turning the coupling of the waveguides on or off according to the signal. electrooptic coefficient. A measure of the extent to which the refractive index changes with applied high electric field, auch as several parts per 10 thousand for applied fields of the order of 20 V/cm. Since the phase shift of a lightwave is a function of the refractive index of the transmission medium in which it is propagating, the change in index can be used to phase-modulate the lightwave by shifting its phase at a particular point along the guide, by changing propagation time to the point. electrooptic device. 1. An electronic device that uses electromagnetic radiation in the visible, infrared, or ultraviolet regions of the frequency spectrum; emits or modifies noncoherent or coherent electromagnetic radiation in these same regions; or uaes such electromagnetic radiation for its internal operation. The wavelengths handled by theae devices range from approximately 0.3 to 30 microns. 2. Electronic devices associated with light, aerving aa sources, conductors, or detectors. Synonymous with optoelectronic device. electrooptic effect. The change in the refractive index of a material when subjected to an electric field. It can be used to modulate a light beam in a mater– ial since many light propagation properties are dependent upon the refractive indices of the transmission medium in which the light travels. electrostrictive effects. The change in physical dimensions that occurs to certain materials when they are placed in an electric field. EMI. EMP. emission. See electromagnetic interference. See electromagnetic pulse. See spontaneous emission. emission of radiation. See light amplification by stimulated emiasion of radiation (laser). energy band. A specified range of energy levels that a constituent particle or component of a substance may have. The particles are uaually electrons, protons, ions, neutrons, atoms, or molecules. Some energy bands are allowable and some are unallowable for specific particles. For example, electrons of a given element at a specific temperature occupy only certain energy bands. Examples of energy bands are the higher and lower level ranges of the conduction and valence bands. energy gap. The difference in energy level between the lower limit of the conduction band and the upper limit of the valence band. energy level. The discrete precise amount of kinetic and potential energy possessed by a body, such as an orbiting electron. A quantum of energy is absorbed or radiated depending on whether an electron moves from a lower to a higher energy level or vice versa. evanescent-field coupling. Coupling between two waveguides, auch as an optical fiber or an integrated optical-circuit (IOC), in which the waveguides are held parallel to each other in the coupling region, with the evanescent waves on the outside of one of the waveguides entering the coupled waveguide, bringing some of the light energy with it into the coupled waveguide. In optical fibers and planar dielectric waveguides, close-to-core proximity or fusion is required. The evanescent field of the core modes can be made available by etching away the fiber cladding or locally modifying the refractive index. evanescent wave. In a waveguide conducting a transverse electromagnetic wave, the wave on the outside of the guide. It will radiate away at sharp bends in the guide if the radiua of the bend is less than the critical radius. It uaually has a frequency smaller than the cutoff frequency above which true propagation occurs and below which the waves decay exponentially with distance from the guide. Evanescent wavefronts of constant phase may be perpendicular or at an angle less than 90” to the surface of the guide. extrinsic fiber loss. Optical power loss in an optical fiber aplice, connector, or coupling caused by end separation, axial displacement, axial misalignment, reflection, or other external condition involved in implementation or use and subject to the control of the uaer. F Fabry-Perot interferometer. A high-resolution multiple-beam interferometer consisting of two optically flat and parallel glasa or quartz plates held a short fixed diatance apart, the adjacent aurfaces of the platea or interferometer flata being made almoat totally reflecting by a thin silver film or multilayer dielectric coating. If one plate is moved with respect to the other, interference patterns are produced. If the ends of an optical fiber are made reflective, moving one end with reapect to the other will also result in an output signal when monochromatic light is inserted into the fiber. Faraday effect. FDM. Synonym for magnetooptic effect. See frequency-division multiplexing. fiber. See graded-index fiber; low-loss fiber; multimode fiber; optical fiber; SELFOCc fiber; self-focusing optical fiber; single-mode fiber; step-index fiber; optical-fiber coating. fiber length-bandwidth product. The product of the length of an optical fiber and the spectral width of lightwavea propagating within it, usually expressed in micron-kilometers. fiber loss. See extrinsic fiber loss; intrinsic fiber loss; optical fiber loss. A-7
fiberoptic. Pertaining to optical fibers and the systems in which they are used, such as sensor, telemetry, and telecommunication systems. fiberoptic cable. Optical fibers incorporated into an assembly of materials that provides tensile strength, external protection, and handling properties comparable to those of coaxial cables. Fiberoptic cables (light guides) are a direct replacement for conventional coaxial cables and wire pairs. The glassbased transmission facilities occupy far less physical volume for an equivalent transmission capacity, which is a major advantage in crowded underground ducts. Manufacturing, installation, and maintenance costs are less. These advantages, with the reduced use of critical metals, such as copper, is a strong impetus for the use of fiberoptic cables. fiberoptic data link. A data link, consisting of a modulated light source, a fiberoptic cable, and a photodetector, that can handle signals in the form of a modulated lightwave. Synonymous with optical data link. fiberoptic ribbon. Synonym for optical fiber ribbon. fiberoptic (FO). 1. As first defined by Kapany in 1956, the art of the active and passive guidance of light (rays and waveguide modes) in the ultraviolet, visible, and infrared regions of the spectrum along transparent fibers through predetermined paths. 2. The technology of guidance of optical power, including rays and waveguide modes of electromagnetic waves along conductors of electromagnetic waves in the visible and near-visible region of the frequency spectrum, specifically when the optical energy is guided to another location through thin transparent strands. Techniques include conveying light or images through a particular configuration of glass or plastic fibers. Incoherent optical fibers will transmit light, as a pipe will transmit water, but not an image. Coherent optical fibers can transmit an image through small (2-12 microna diameter), clad, optical fibers that are in a fixed spatial relative position at both ends. Specialty fiberoptic combine coherent and incoherent aspects. fiberoptic sensor. A sensor in which a parameter (property, characteristic) of an optical waveguide (optical fiber), or of a lightwave propagating in an optical fiber, is varied in accordance with an input baseband signal thus modulating the lightwave in the waveguide. Synonymous with optical fiber sensor; optical sensor. Also see sensor. fiberoptic sheath. An outer protective covering placed over an optical fiber, bundle, or cable. fiberoptic splice. A nonseparable junction joining one optical conductor to another. fiber ribbon. See optical fiber ribbon. fiberscope. A receiving device consisting of an entry point, at which a bundle of optical fibers can enter, and a faceplate surface on which the entering fibers can uniformly terminate, in order to display the optical image received through the fibers. The bundle of fibers transmit a full color image that remains undisturbed when the bundle is bent. By mounting an objective lens on one end of the bundle and an eyepiece at the other, the assembly becomes a flexible fiberscope that can be used to view objects that are otherwise Inaccessible for direct viewing. The transmitter is a similar device, except that an image is focused on it for transmission. The device is used to transmit images. Also see coherent bundle. fiber sensor. See fiberoptic sensor. field coupling. See evanescent field coupling. focusing optical fiber. See self-focusing optical fiber. frequency-division multiplexing (FDM). Multiplexing in which the available transmission frequency range is divided into narrower bands, each used as a separate channel. When an optical fiber transmits more than one frequency at the same time, each frequency can be modulated with a different information-bearing signal. frequency modulation. The modulation of the frequency of an electromagnetic, elastic, sound, or other wave serving as a carrier, with another wave serving as the modulating signal, such that the frequency excursions of the carrier are proportional to a parameter of the modulating signal bearing the information to be transmitted. It is a form of angle modulation in which the instantaneous frequency of a aine wave carrier is caused to depart from the carrier frequency by an amount that is proportional to the instantaneous value of the modulating signal. Combinations of phase and frequency modulation are also considered as frequency modulation. Fresnel equations. See reflection coefficient, transmission coefficient. E!-Fl” See energy gap. G geometric spreading. In a wave propagating in a transmission medium in which there are no sources, the decrease in power density as a function of distance in the direction of propagation. As a curved wavefront, such as for divergent electromagnetic waves, moves in the direction of propagation, the available power at one point must be spread over a larger area at the next point in space; e.g., a point source of light has its light energy spread over larger and larger spherical surfaces as the distance from the source increases. graded-index fiber. An optical fiber witb a variable refractive index that is a function of the radial distance from the fiber axis, the refractive index getting progressively lower away from the axis. This characteristic causes the light rays to be continually refocused by refraction in~o the core. As a result, there is a designed continuous change in refractive index between the core and cladding along a fiber diameter. Synonymous with gradient-index fiber. gradient-index fiber. A synonym for graded-index fiber. A-8
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FIBEROPTIC SENSOR TECHNOLOGY HANDBO
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FOREWORD THE FIBEROPTIC SENSOR TECH
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4.2 Phase 4.2.1 4.2.2 4.2.3 4.2.4 4
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CHAPTER 1 INTRODUCTION 1.1 BACKGROU
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CHAPTER 2 FIBEROPTIC SENSOR COMPONE
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fleeted each time it is incident on
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6=0 REFERENCE PLANE that propagate
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in the right center of Fig. 2.13. T
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The vertical height of the various
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60 40 20 10.C ~8 x z 6 n u 4 % c 62
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: 1.5 z o GeOz 0 ~ =1.49 u w > ~1.4
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tension it collapses to eliminate t
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MAXIMUM TENSILE STRENGTH (GN/m2 = l
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mately a 0.5 electron-volt increase
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I in one portion of the recombinati
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crated electron-hole paira that are
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sink fiber. Likewise angular misali
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fused together. The ends are bent a
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A laboratory beam splitter set-up u
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aged multichannel unit. High-streng
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CHAPTER 4 LIGHTWAVES IN FIBEROPTIC
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tor addition indefinitely, as indic
Page 45 and 46: modes. Since at point (a) the two e
Page 47 and 48: as a number of wavelengths. An expr
Page 49 and 50: 100 meters of fiber, length changes
Page 51 and 52: the aingle-sideband phaae noiae int
Page 53 and 54: sets up periodic spatial fluctuatio
Page 55 and 56: ient configuration in the lower rig
Page 57 and 58: sors or a pressure gradient sensor.
Page 59 and 60: nickel H. = 3.6 oersteds and for a
Page 61 and 62: optical source of constant intensit
Page 63 and 64: in a straight section of the fiber
Page 65 and 66: A simplified design of the cladding
Page 67 and 68: Referring once more to Fig. 5.35, i
Page 69 and 70: The path length AL traveled by ligh
Page 71 and 72: 5.4.9 Fiberoptic Rotation-Rate Sens
Page 73 and 74: a modulation scheme, the output of
Page 75 and 76: Fig. 5.60 lists several sources of
Page 77 and 78: CHAPTER 6 FIBEROPTIC SENSOR ARRAYS
Page 79 and 80: method of sensor energization will
Page 81 and 82: 1 The preceding discussion applied
Page 83 and 84: SIMPLEX FIBEROPTIC TRANSMITTER FIBE
Page 85 and 86: MAXIMUM ALLOWABLE RISETIME = 0.7/RN
Page 87 and 88: PROCESSING STATION TRANSMISSION wAV
Page 89 and 90: fiberoptic cable (optical cable), a
Page 91 and 92: angstrom. A unit of length equal to
Page 93 and 94: core. The central primary light-con
Page 95: diffraction. 1. The procesa by whic
Page 99 and 100: methods of coupling power outside t
Page 101 and 102: M Mach-Zehnder interferometer. An i
Page 103 and 104: N nanometer. One thousandth of a mi
Page 105 and 106: velocity is also the velocity at wh
Page 107 and 108: where nl and n2 are the reciprocals
Page 109 and 110: slab dielectric optical waveguide.
Page 111 and 112: v vacancy defect. In the somewhat o
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FIBEROPTIC SENSOR TECHNOLOGY HANDBOOK

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