FIBEROPTIC SENSOR TECHNOLOGY HANDBOOK

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$Course Material\Efficiently Coding Communication Protocols in C++ ...$

c cable. 1. A jacketed bundle or jacketed fiber in a form that can be terminated. 2. A group of conductors that are bound together, usually with a protective sheath, a strength member, and insulation between individual conductors and for the entire group. See fiberoptic cable. cable jacket. The outer protective covering applied over the internal cable elements. carrier. 1. In communications, a wave, pulse train, or other signal suitable for modulation by an information-bearing signal to be transmitted over a communication system. 2. h unmodulated emission. A carrier is usually a sinusoidal wave, a recurring series of pulses, or a direct-current (DC) signal. See charge carrier. cavity. See resonant cavity. charge carrier. tin atomic or molecular particle that possesses an electric charge and is capable of moving under the influence of an electric or magnetic field. For example, an electron, a hole, or an ion. cladding. An optical transparent material, with a refractive index lower than that of the core, placed over or outside the core material of an optical waveguide that serves to reflect or refract lightwaves in order to confine them to the core. The cladding also serves to protect the core. cladding mode stripper. 1. A material applied to optical fiber cladding to allow light energy being transmitted in the cladding to leave the cladding of the fiber. 2. A piece of optical material or an optical component that can support only certain electromagnetic wave propagation modes. In particular, it does not support the propagation modes in the cladding of a cladded optical fiber, slab dielectric waveguide, or integrated optical circuit. The stripper effectively removes the cladding modes without disturbing the core-supported propagation modes. close-confinement junction. A synonym for single heterojunction. CMos. coating. See combined metal oxide semiconductor. See optical fiber coating. coherence length. The coherence time of a light beam multiplied by the velocity of the light, namely (1/cAv)c = l/Av. AI.SO see coherence time. coherence time. In beam of light propagating in a vacuum, the time obtained from the expression l/cAv, where c is the velocity of light in a vacuum, v is the reciprocal of the wavelength, and Avis the variation or spread of v over time for the beam. In material media, the c is replaced by c/n, where n is the refractive index. Also see coherence length. coherent bundle. A bundle of optical fibers in which the spatial coordinates of each fiber are the same or bear the same spatial relationship to each other at the two ends of the bundle. Synonymous with aligned bundle. coherent light. Light of which all parameters are predictable and correlated at any point in time or space, particularly over an area in a plane perpendicular to the direction of propagation or over time at a particular point in space. Contrast with incoherent light. collection angle. Synonym for acceptance angle. combined metal oxide semiconductor. A metal oxide semiconductor that consists of both positively-doped and negatively-doped material. common-mode. 1. Pertaining to any uncompensated combination of generator or receiver ground potential difference (voltage), generator common return offset voltage, and longitudinally-coupled peak random noise voltage measured between the receiver circuit ground and receiver cable with the generator ends of the cable short-circuited to ground. 2. The algebraic mean of the two voltages appearing at the receiver input terminals with respect to the receiver circuit ground. 3. Pertaining to the relative optical intensity fluctuations between two coherent electromagnetic (light) waves. common-mode rejection ratio (CMRR). The ratio of the common-mode interference voltage or optical intensity at the input of a circuit to the interference voltage or optical intensity at the output of the circuit. conduction band. In a semiconductor, the range of electron energy, higher than that of the valence band, possessed by electrons sufficient to make them free to move from atom to atom. When they leave the valence band, they are free to move under the influence of an applied electric field and thus they constitute an electric current. conductor. 1. In fiberoptic, a transparent medium that is capable of transmitting or conveying lightwaves a useful distance. 2. In electric circuits, a material that readily permits a flow of electrons through itself upon application of an electric field. Electrical conductors include copper, aluminum, lead, gold, silver, and platinum. The conductivity is specified by: J = aE, where J is the current density in amperes/square meter for S1 units, E is the applied electric field in volts/meter, and o is the conductivity in reciprocal ohms/meter. Also see dielectric. Contrast with insulator. connector. In fiberoptic, a device that permits the coupling of signals from one optical fiber or cable to another. connector insertion loss. The power loss sustained by a transmission medium, such as a wire, coaxial cable, optical fiber cable, or integrated optical circuit component, due to the Insertion of a connector between two elements, which would not occur if the media were continuous without the connector i.e., if there were no reflected, absorbed, dispersed, or scattered power. controllable coupler. coupler. See electronically controllable A-3
core. The central primary light-conducting region of a material medium, such as an optical fiber, the refractive index of which must be higher than that of its cladding in order for the lightwaves to be totally reflected or refracted. Most of the optical power is in the core. coupler. In optical transmission aystems, a component used to interconnect two or more optical fibera. Also see connector; bulk coupler; electronic&llycontrollable coupler; reflective star-coupler; 3-dB coupler. coupling. The connection, attachment, or binding of optical elements, electric circuit elementa, electric and magnetic fields, propagation modes, or electromagnetic wave component, such as surface waves and evanescent waves, to internal waves in waveguides, dielectric slabs, or other interdependent associations and interactions of events and materials in a system. For example, two optical fibers or certain elements in an integrated optical circuit may be coupled together in some manner to preserve signal continuity. See evanescent field coupling. coupling coefficient. Synonym for coupling ratio. coupling efficiency. In fiberoptic transmission, the ratio of the optical power on one side of an interface to the optical power on the other side. For example, the ratio of the power developed by a light aource to the power accepted by a bundle of fibers, or the power received at the end of a bundle of fibers to the power that impinges on a photodetector. For light sources with emitting areas larger than fiber core diameters, the product of fiber numerical aperture (N.A.) and core diameter is a good indicator of maximum coupling efficiency. For other sources, such as small laser diodes with emitting areas small than the fiber core diameter, the N.A. alone is a relevant indicator of coupling efficiency, usually expresaed as a percentage. critical angle. The angle, with the normal, at which an electromagnetic wave incident upon an interface surface between two dielectric media, at which total reflection of the incident ray first occurs as the incident angle with the normal to the incident aurface is increased from zero, and beyond which total internal reflection continues to occur although with increased attenuation at a rate determined not only by the electromagnetic parameters of the transmission medium, but also by the frequency and the incidence angle. The wave is guided along the reflecting surface with no average transport of energy into the second medium, and the intensity of the reflected wave is exactly equal to the intensity of the incident wave. The wave in an optical fiber will be confined to the fiber for all incidence angles greater than the critical angle. The critical angle is given by sin ec = (~2/~1) 1/2 where 9C is the critical angle and Cz and c1 are the permittivities of the transmitted (outside) and incident medium (inside), respectively, and where El is always greater than =2; e.g. , the case for an optical fiber (conducting a wave), and air. In terms of refractive indices, the critical angle is the incidence angle from a denser medium, at an interface between the denser and less dense medium, at which all of the light is refracted along the interface, i.e., the angle of refraction is 90°. When the critical angle is exceeded, the light is totally reflected back into the denaer medium. The critical angle varies with the refractive indices of the two media with the relationship, sin Oc = n2/nl, where n2 is the index of refraction of the less dense medium, nl is the refractive index of the denser medium, and 9C is the critical angle, as above. In terms of total internal reflection in an optical fiber, the critical angle is the smallest angle made by a meridional ray in an optical fiber that can be totally reflected from the innermost interface and thus determines the maximum acceptance angle at which a meridional ray can be accepted for transmission along a fiber. Also see total internal reflection. critical radius. The largest radius of curvature of an optical fiber, containing an axially propagated electromagnetic wave, at which the field outside the fiber still detaches itself from the fiber and radiates into space because the phase-front velocity must increase to maintain a proper relationship with the guided wave inside the fiber. Thia velocity cannot exceed the velocity of light, aa the wavefront sweeps around the outside of the curved fiber. This causes attenuation due to a radiation loss. The field outside the fiber decays exponentially in a direction transverse to the direction of propagation. It is the radius of curvature of an optical fiber at which there is an appreciable propagation mode conversion loss, due to the abruptness of the transition from straight to curved. For a radius of curvature greater than the critical value, the fields behave essentially as in a straight guide. For radii smaller than the critical value, considerable mode conversion takea place. coupling loss. In a fiberoptic coupling, the optical power loss caused by the coupling itself, a loss that would not occur if the optical fiber were continuous without the coupling. coupling ratio. The ratio of power on the output side of a coupling to the power on the input side. The coupling ratio is always less than unity. Synonymous with coupling coefficient. Also see 3-dB coupler. A-4 D dark current. ~’e current that flows in a photodetector when there is no radiant energy or luminous flux incident upon its aensitive surface, i.e., when there is total darkness. Dark current generally increaaea with increaaed temperature for most photodetectors. For example, in a photoemissive photodetector, the dark current is given by: Id = AT2eq’$lkT where A is the surface area constant, T is the absolute temperature, q is the electron charge, $ ia the work function of the photoemisaive surface material, and k is Boltzmann’s constant. darkfield sensor. In fiberoptic, a sensor in which the optical power tapped and modulated by the sensor is a small fraction of the total optical power fed to or available to the sensor. Contrast with brightfield sensor. data. Representation of facts, concepts, or instructions in a manner suitable for communication, interpretation, or processing by human, manual, semiautomatic, or fully-automatic means. The characters used as data may assume any form or pattern to which meaning may be assigned in order to represent infor-
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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
Page 41 and 42: CHAPTER 4 LIGHTWAVES IN FIBEROPTIC
Page 43 and 44: 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: angstrom. A unit of length equal to
Page 95 and 96: diffraction. 1. The procesa by whic
Page 97 and 98: fiberoptic. Pertaining to optical f
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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