FIBEROPTIC SENSOR TECHNOLOGY HANDBOOK

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1 The light-ray concept is a convenient approximate approach that may be used to introduce other important concepts such as total internal reflection and ray trapping. To extend the theory of light propagation farther, however, it is necesaary to take into account the notions that light is an electromagnetic wave phenomenon and that optical fibers are cylindrical dielectric waveguides. With these in mind it is possible to develop concepts regarding the allowed electromagnetic propagation modes of a cylindrical waveguide and to introduce the frequently encountered optical fiber waveguide V-Parameter (V-value) that must be considered when selecting a suitable fiber for a particular application. In accordance with the ray theory of light propagation, a light beam incident from below on the interface surface between two transparent media, at an angle e 1 with the interface surface behaves as shown in Fig. 2.3. When fll ia large, part of the incident beam Fig. 2.3 MEDIUM2 ! .-”’” X6; n2 k n1>n2 Reflection and refraction at the interface when a lightwave travels from a higher to a lower refractive index medium. is transmitted into the upper medium and vart is reflected. Their relative intensities depend upon the refractive indices of the two media. The refractive index of a medium is defined as the ratio of the velocity of light in a vacuum to the velocity of light in the medium. The higher the refractive index of a medium the slower light will travel in it. The refractive index of medium 1 is designated as nl and that for medium 2 as n2 as shown in Fig. 2.3. These indices alao determine the direction of the beam transmitted into medium 2, i.e., @2 in Fig. 2.3 is determined by the indexes of both media. Snell’s law of refraction of light at an interface predicts that the ratio of the cosine of the angle 131 to the cosine of the angle of t12 is equal to the ratio n2/nl which is equal to the velocity ratio v1/v2. Thus, as shown in Fig. 2.3, if light propagates in medium 1 at a lower velocity than in medium 2, the angle 01 will be greater than the angle 02 and the ray will be bent toward the interface when entering medium 2. The angle of the reflected beam is equal to the angle of the incident beam. These are an application of the well known laws (Snell’s laws) of refraction and reflection that aPPIY in ray treatments of wave phenomena. nl > n2 +’*NG) v,< V2 I \ MEOIUMI’(CORE) CASEI 01>0, CASE2 e)=ec CASE3: 01 n2. There is both a refracted and a reflected beam and, from the conservation of energy, the sum of their energies must equal the energy in the incident beam. 2-2 Fig. 2.5 A step-index optical fiber showing the critical angle, 6C for total internal reflection.
fleeted each time it is incident on the core-cladding interface so that it remains ““trapped”” in the core. This, and any other ray with f31
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: CHAPTER 2 FIBEROPTIC SENSOR COMPONE
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
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optical source of constant intensit
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in a straight section of the fiber
Page 65 and 66:
A simplified design of the cladding
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Referring once more to Fig. 5.35, i
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The path length AL traveled by ligh
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5.4.9 Fiberoptic Rotation-Rate Sens
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a modulation scheme, the output of
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Fig. 5.60 lists several sources of
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CHAPTER 6 FIBEROPTIC SENSOR ARRAYS
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method of sensor energization will
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1 The preceding discussion applied
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SIMPLEX FIBEROPTIC TRANSMITTER FIBE
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MAXIMUM ALLOWABLE RISETIME = 0.7/RN
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PROCESSING STATION TRANSMISSION wAV
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fiberoptic cable (optical cable), a
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angstrom. A unit of length equal to
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core. The central primary light-con
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diffraction. 1. The procesa by whic
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fiberoptic. Pertaining to optical f
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methods of coupling power outside t
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M Mach-Zehnder interferometer. An i
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N nanometer. One thousandth of a mi
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velocity is also the velocity at wh
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where nl and n2 are the reciprocals
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slab dielectric optical waveguide.
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v vacancy defect. In the somewhat o
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