FIBEROPTIC SENSOR TECHNOLOGY HANDBOOK

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optical fiber ribbon. A rowof optical fibers laminated in a flat plastic strip. Synonymous with fiberoptic ribbon. optical fiber sensor. Synonym for fiberoptic sensor. optical integrated circuit. A synonym for integrated optical circuit. optical mixing box. A fiberoptic coupler consisting of a piece of fiberoptic material that receives several optical frequencies and that mixes them to produce dichromatic or polychrometic lightwaves for dispatch via one or more outputs for transmission elsewhere and perhaps subsequent separation into the constituent frequencies to produce the original information introduced by the modulation of each of the constituent frequencies. The mixing box usually has reflective inner surfaces, except at the ports. The lightwaves entering the box are usually a group of monochromatic waves each of a different frequency and each modulated separately. optical mixing rod. An optical mixing box that has the general shape of a right circular cylinder, usually with pigtails to serve as entrance and exit ports. optical power budget. In an optical transmission system, the distribution of the available power that is required for transmission within specified distortion limits or error rates. The distribution is usually in terms of decibels for each component of the system from source to sink. Components include the light source pigtail, connectors, cable, splices, and detector pigtail. optical power density. The optical energy per unit time transmitted by a light beam through a unit area normal to the direction of propagation or the direction of maximum power gradient, expressed in watts per square meter or joules per second-(square meter). A watt is a J/S. optical power efficiency. The ratio of the emitted electromagnetic power of an optical source to the electrical input power to the aource. optical repeater. An optical/optical, optical/electrical, or electricalloptical signal amplification and processing device. The repeater usually accepts an optical signal, converts it into an electrical signal (photodetection) amplifies it, and converts it back to an optical signal for further transmission. optical sensor. See slab dielectric optical wave- optical waveguide. guide. optics. optoacoustics. See fiberoptic sensor. See integrated optics. Synonym for acoustooptics. optoelectronic. 1. Pertaining to the conversion of optical power or energy into electrical power or energy, such as the conversion of an optical signal into an electrical signal. Also see electrooptic. 2. Synonym for electrooptic. optoelectronic device. optomagnetic. See magnetooptic. See electrooptic device, optostrain. Pertaining to the change in lightwave propagation characteristics caused by changes in waveguide parameters due to strain resulting from applied stress (tensile, compression, shear, bending, torsional or combinational stress). Synonymous with optostress. optostress. A synonym for optostrain. ordinary bend. A bend in the core of an optical fiber in which the central axis of the core may be said to have a bend with finite nonzero radius. If the radius of the bend is smaller than the critical radius, light will leak from the core as total internal reflection no longer takes place. Bending a fiber from more than to less than the critical radius can be used to modulate the light intensity or the leakage. Contrast with microbend. See combined metal oxide semicon- oxide semiconductor. ductor. parameter. — PD. P See refractive index profile parameter. See photodetector. phase detection. Obtaining an output electrical signal proportional to an input lightwave phase angle that varies with respect to a fixed reference in accordance with a baseband input signal. Often phase detection can be accomplished by conversion to amplitude detection. ?hase-lock loop. An electronic circuit that controls an oscillator so that it maintains a constant phase angle relative to a reference signal source. The system can be used in situations in which signals that are shifted in phase with respect to one another maintain a fixed or specified phase relationship. In spread-spectrum systems a phase-lock loop is used to cause an oscillator internal to the feedback loop to oscillate at an incoming carrier frequency. The feedback, or servoloop, circuit utilizes the output of a phase-sensitive detector, via a low pass filter, to control the frequency of its own reference signal. The feedback loop is damped to permit tracking of the carrier phase changes at the input, but not tracking of the modulation changes. The arrangement also provides a low noise threshold. In fiberoptic systems, a similar arrangement can be used to control the phase of a continuous or modulated lightwave carrier. phase modulation (PM). Angle modulation in which the instantaneous phase angle of an unmodulated sine wave carrier is varied proportionally in accordance with the instantaneous value of the amplitude of a modulating signal. phase velocity. The velocity with which a specific point on a sine wave (e.g., the peak value of the electric vector of an electromagnetic wave) is propagated in a material medium or in free space. This concept can only strictly be applied to a single frequency wave, such as an unmodulated carrier wave. The phase velocity is the propagation velocity of a uniform plane sinusoidal wave, given as the wavelength times the frequency of the wave. The phase A-15
velocity is also the velocity at which an observer would have to move to make the wave characteristics appear to remain constant in phase in a given medium. The phase velocity in a given medium is equal to the velocity of propagation of the wave divided by the refractive index of the medium when the wave is an electromagnetic wave. It is not the velocity of electromagnetic energy propagation, although it may be higher than the velocity of light in free space. For a given frequency, the wavelength is less in material media than in free space when electromagnetic waves are involved. In nondispersive media, the phase velocity and the group velocity are equal. Also see group velocity. photodetector (PD). A device that is capable of extracting information from a lightwave by producing an electrical output signal from an optical input signal. yhoton. A quantum of electromagnetic energy. The energy of a photon is hf, where h is Planck’s constant, and f is the frequency of the radiation. ylane of polarization. See polarization plane. p-n junction. In a semiconductor (solid-state) device, the interface between semiconducting ~terial that has been doped positively, i.e., with an impurity material that produces holes (acceptor sites) on one side of the interface, and material that produces relatively free electrons (donor sites) on the other side. The junction is usually assumed to be abrupt, or linearly graded in its transition region across the interface. Pockel cell. A material, usually a crystal, whose refractive index change is linearly proportional to a change in an applied electric field, the material being configured so as to be part of another system, such as an optical path. The cell thus provides a means of modulating the light in the optical path. polarimetric sensor. In fiberoptic, a sensor in which a baseband input signal alters the polarization of a lightwave in an optical fiber or the output intensity is varied by a process of polarization selection. polarization. The direction of the electric field vector of an electromagnetic wave, such as a lightwave. It is the property of a radiated electromagnetic wave that describes the time-varying direction and amplitude of the electric field vector, that, together with the magnetic field vector, makes up the wave. It is specifically illustrated by the figure that is traced in space as a function of time by the extremity (tip) of the vector that represents the electric field with its base at a fixed point in space, as observed along the direction of propagation. In general, for a plane polarized wave, the figure is elliptical and it is traced in a clockwise or counterclockwise sense. Circular polarization and linear polarization are obtained when the ellipse becomes a circle or a straight line, respectively. Clockwise sense rotation of the electric field vector is designated right-hand polarization, and counterclockwise sense rotation is designated left-hand polarization. Sense of rotation is obtained by viewing the rotating electric field vector while facing in the direction of propagation. The direction of propagation is the forward direction of a right-hand screw obtained when the electric vector is rotated through the smaller angle into the magnetic vector, A-16 the direction of propagation being perpendicular to both fields, namely, the direction of the Poynting vector. polarization diversity. 1. Pertaining to the ability to change the direction of polarization of an electromagnetic wave, usually at the source of radiation, by changing the direction of the polarization plane, the horizontal or vertical polarization, i.e., the polarization angle with respect to a fixed reference or the linear, circular, elliptical, or helical polarization. 2. Pertaining to two or more types of polarization. 3. Any method of diversity transmission and reception in which the same information signal is transmitted and received simultaneously on orthogonally polarized waves with fade-independent propagation characteristics. Also see diversity reception. polarization modulation. The modulation of an electromagnetic wave in such a manner that the polarization of the carier wave, such as the direction of polarization of the electric and magnetic fields, or their relative phasing, to produce changes in polarization angle in linear, circular, or elliptical polarization, is varied according to a characteristic of an information-bearing input signal, such as a pulseor-no-pulse digital signal. In optical fibers or other waveguides, polarization shifts that are made in accordance with an input signal variation are a practical means of modulation. polarization multiplexing. Multiplexing accomplished by using two mor more lightwave polarization modes in the same transmission medium at the same time with the same frequency. Each polarization mode would constitute a separate channel. polarization plane. In a transverse, or ordinary, electromagnetic (TEM) wave, the plane defined by the electric and magnetic field vectors of the wave; i.e., both field vectors at a point lie in, and therefore define, the polarization plane. The direction of propagation, or power flow, of the wave is perpendicular to both the electric and magnetic field vectors at the point, i.e., perpendicular to the polarization plane at that point. The wavefront lies in the polarization plane. The Poynting vector, ExH, is perpendicular to the polarization plane. polarized light. A light beam whose electric vector vibrates in a direction that doea not change, unless the propagation direction changes; i.e., it is in a plane perpendicular to the direction of propagation. If the time-varying electric vector can be broken into two perpendicular components that have equal amplitude and that differ in phase by 1/4 wavelength, the light is said to be circularly polarized. Circular polarization is obtained whenever the phaae difference between the two perpendicular components is any odd, integral number of quarter wavelengths. If the electric vector is resolvable into two perpendicular components of unlike amplitudes and differing in phase by values other than O, 1/4, 1/2, 3/4, 1, etc., wavelengths, the light beam is said to be elliptically polarized. population inversion. A redistribution of energy levels in a population of elements such that, instead of having more atoms with lower-energy-level electrona, there are fewer atoms with higher-energy-level electrona. That ia, an increaae in the total number of electrons in the higher excited states occurs at the expense of the energy in the electrons in the
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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
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modes. Since at point (a) the two e
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as a number of wavelengths. An expr
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100 meters of fiber, length changes
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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 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: N nanometer. One thousandth of a mi
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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