FIBEROPTIC SENSOR TECHNOLOGY HANDBOOK

More documents

Recommendations

Info

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

isotropic material. A substance that exhibits the same property when tested along an axis in any direction. For example, a dielectric material with the same permittivity to electric fields, a glass with the same refractive index for a lightwave, or the same conductivity to electric currents, in all directions. jacket. See heterojunction; homojunction; p-n junc- junction. tion. See bundle jacket; cable jacket. J K Kerr cell. A substance, usually a liquid, whose refractive index change is proportional to the square of an applied electric field. If the substance is configured to be part of an optical path, the cell can provide a means of modulating the light in the optical path. L lasing. A phenomenon occurring when resonant frequency controlled energy is coupled to a specially prepared material, such as a uniformly-doped semiconductor crystal that has free-moving or highly mobile loosely-coupled electrons. AS a result of resonance and the imparting of energy by collision or close approach, electrons are raised to highly excited energy states, which, when they move to lower states, cause quanta of high-energy electromagnetic radiation to be released as coherent lightwaves. This action takes place in a laser. LED. length. See light emitting diode. See coherence length. length-bandwidth product. product. See fiber length-bandwidth light. See coherent light; incoherent light; polarized light. light amplification by stimulated emission of radiation (lasers). A coherent-light generator in which molecules of certain substances absorb incident electromagnetic energy at specific frequencies, store the energy for short periods in higher energy-band levels and then release the energy, upon their return to the lower energy levels, in the form of light at particular frequencies in extremely narrow frequency bands. The release of energy can be controlled in time and direction so as to generate an intense highly directional narrow beam of electromagnetic energy that is coherent, i.e., the electromagnetic fields at every point in the beam are uniquely and specifically definable. Diode lasers and heliumneon lasers make use of a resonant cavity that is pumped to high energy levels to cause Population inversion and lasing action. rate, and the same operational current densities, but without lasing action. The high current densities of thousands of amperes per square centimeter often cause catastrophic and graceful degradation. Compared to the laser diode, the LED possesses greater simplicity, tolerance, and ruggedness, and about 10 times the spectral width. Typical peak spectral power output for a gallium arsenide LED occurs at 0.910 pm (microns), with a spectrum about 0.005 pm wide. An aluminum arsenide LED operates at 0.820 pm at a 10-MHz-wide spectrum. Both operate at roughly l-mW spectral power output and a 50-mA driving current. lightfield sensor. Synonymous with brightfield sensor. light pipe. 1. An optical element that conducts light from one place to another, such as an optical fiber or slab-dielectric waveguide. 2. A hollow tube with a reflecting inner wall that guides lightwaves in its hollow center. 3. An optical fiber. light ray. A line perpendicular to the wave-front of a lightwave indicating its direction of propagation and representing the lightwave itself. light source. A device that produces or emits lightwaves, such as a light-emitting diode, a laser, or a lamp. linear medium. An electromagnetic wave transmission medium with constitutive parameters, such as electric permittivity, magnetic permeability, and electric conductivity (and hence refractive index), that remain constant under the influence of applied electric and magnetic fields. For example, in the relations B=uH, D=cE, andJ=uE, thep, e, a nd u are constant at a given point even though the fields are changing. link. See data link; fiberoptic data link. lock 100P. w“ See phase-lock loop. See phase-lock loop. loss. See coupling loss; extrinsic fiber loss; insertion loss; intrinsic fiber 10SS; microbending 10SS; optical fiber loss; refractive-index-profile mismatch loss. low-loss fiber. AII optical fiber having a low energy loss, due to all causes, per unit length of fiber, usually measured in decibels/kilometer at a specified wavelength. Low-loss is usually considered to be below 20 dB/km. In low-loss fiber, attenuation of a propagating wave is caused primarily by scattering due to metal ions, by absorption due to water in the OH radical form, and by Rayleigh scattering. Low-loss fiber attenuation rates are approaching 0.01 dB/km. luminous intensity. The ratio of the luminous flux emitted by a light source, or an element of the source, in an infinitesimally small cone about the given direction, to the solid angle of that cone, i.e., luminous flux emitted per unit solid angle. light-emitting diode (LED). A diode that operates sim - ilar to a laser diode, with the same total output power level, the same output limiting modulation A-II
M Mach-Zehnder interferometer. An interferometer in which an electromagnetic wave is split, each half traveling around half a loop in opposite directions, one via a beam splitter and a fixed mirror, the other via a movable mirror and a beam splitter, both halves being recombined at a photodetector where their relative phase can reinforce or cancel. The moveable mirror modulates the resultant intensity at the photodetector. magnetooptic. Pertaining to the control of lightwaves by means of magnetic fields, for example by rotating the magnetic polarization of a lightwave and thus achieving polarization modulation or by cementing or coating ferromagnetic material on the outside of a fiber and using the magnetostrictive effect to alter the length of a fiber in the sensing arm of an interferometer thus obtaining a method of converting magnetic field variations to light intensity variations. Synonymous with optomagnetic magnetooptic effect. The rotation of the polarization plane of lightwaves in a transmission medium brought about when subjecting the medium to a magnetic field (Faraday rotation). The effect can be used to modulate the light beam in a material, since many properties, such as conducting velocities, reflection and transmission coefficients at interfaces, acceptance angles, critical anglea, and transmission modes, are dependent upon the direction of propagation at interfaces in the media in which the light travels. The amount of rotation is given by: A = aHL where a is a constant, H is the magnetic field strength, and L is the propagation distance. The magnetic field is in the direction of propagation of the lightwave. Also, by coating or cementing ferroelectric material to a fiber, the magnetostrictive effect can be used to alter the length of a fiber in the sensing arm of an interferometer, thua obtaining a method of converting magnetic field variations to light intensity variationa. Synonymous with Faraday effect. magnetooptic modulator. A modulator that makes use of the magnetooptic effect to modulate a lightwave carrier. magnetostriction. The phenomenon exhibited by some materials in which dimensional changes occur when the material is subjected to a magnetic field, usually becoming longer in the direction of the applied field. The effect can be used to launch a shock or sound wave each time the field is applied or changed, possibly giving rise to phonons that could influence energy levels in the atoms of certain materials such as semiconductors and lasers and thereby serve as a modulation method. Along with photon or electric field excitation, the phonon energy could provide threshold energy to cause electron energy level transitions, causing photon absorption or emission. The effect can also be used to change the physical dimensions of an optical fiber that is wrapped around or cemented to or jacketed by, a magnetostrictive (ferromagnetic) material and thus modulate a light beam in the fiber. margin. See power margin. material dispersion. 1. The variation in the refractive index of a transmission medium as a function of wavelength, in optical transmission media used in optical waveguides; e.g., optical fibers, slab dielectric waveguides, and integrated optical circuits. Material dispersion contributes to group- -delay distortion, along with waveguide-delay distortion and multimode group-delay spread, i.e., the spreading of a pulse. 2. The part of the total dispersion of an electromagnetic pulse in a waveguide caused by the changes in properties of the material with which the waveguide, such as an optical fiber is made, due to changes in frequency. As wavelength increasea, and frequency decreases, material dispersion decreases. At high frequencies, the rapid interactions of the electromagnetic field with the waveguide material (optical fiber) renders the refractive index even more dependent upon frequency. Maxwell’s equations. A group of basic equations, in either integral or differential form, that (1) describe the relationships between the properties of electric and magnetic fields, their sources, and the behavior of these fielda at material media interfaces; (2) express the relations among electric and magnetic fields that vary in space and time in material media and free space; and (3) are fundamental to the propagation of electromagnetic waves in material media and free space. The equations are the basis for deriving the wave equation that expresses the electric and magnetic field vectors in a propagating electromagnetic wave in a transmission medium such as a lightwave in an optical fiber. Maxwell’s equations in differential form are: vx E = -aBlat v. H = J + aD/3t V. B=O V“ D=o where E, H, B, and D are the electric field intensity, the magnetic field intensity, the magnetic flux density, and the electric flux density (electric displacement) vectors, respectively, J is the electric current density, and pis the electric charge density, the v is the “del- space derivative operator, expressing differentiation with respect to all distance coordinates, the VX being the curl and the v - being the divergence. The partial derivatives are with respect to time. These equations are Used in conjunction with the constitutive relations to obtain useful practical results given actual sources of charge and current in real media. These are only valid when the field and current vectors are single-valued, bounded, continuous functions of poaition and time, and have continuous derivatives. medium. See homogeneous medium; linear medium; sourcefree medium; transmission medium. meridional ray. In an optical fiber, a light ray that passes through the central axis of the fiber, is internally reflected, and is confined to a single plane, called the meridian plane. Also see skew ray. metal oxide semiconductor. A semiconductor composed of doped metal oxide, such as silicon oxide (Si02). See combined metal oxide semiconductor. A-12
Page 1 and 2:
FIBEROPTIC SENSOR TECHNOLOGY HANDBO
Page 3 and 4:
FOREWORD THE FIBEROPTIC SENSOR TECH
Page 5 and 6:
4.2 Phase 4.2.1 4.2.2 4.2.3 4.2.4 4
Page 7 and 8:
CHAPTER 1 INTRODUCTION 1.1 BACKGROU
Page 9 and 10:
CHAPTER 2 FIBEROPTIC SENSOR COMPONE
Page 11 and 12:
fleeted each time it is incident on
Page 13 and 14:
6=0 REFERENCE PLANE that propagate
Page 15 and 16:
in the right center of Fig. 2.13. T
Page 17 and 18:
The vertical height of the various
Page 19 and 20:
60 40 20 10.C ~8 x z 6 n u 4 % c 62
Page 21 and 22:
: 1.5 z o GeOz 0 ~ =1.49 u w > ~1.4
Page 23 and 24:
tension it collapses to eliminate t
Page 25 and 26:
MAXIMUM TENSILE STRENGTH (GN/m2 = l
Page 27 and 28:
mately a 0.5 electron-volt increase
Page 29 and 30:
I in one portion of the recombinati
Page 31 and 32:
crated electron-hole paira that are
Page 33 and 34:
sink fiber. Likewise angular misali
Page 35 and 36:
fused together. The ends are bent a
Page 37 and 38:
A laboratory beam splitter set-up u
Page 39 and 40:
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 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: methods of coupling power outside t
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
show all

FIBEROPTIC SENSOR TECHNOLOGY HANDBOOK

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?