FIBEROPTIC SENSOR TECHNOLOGY HANDBOOK

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Two cables manufactured in Japan by SUMITOMO for underground and indoor telecommunication applications are shown in Figs. 3.26a and 3.26b, respectively. In the cable designed for underground installations a set of four multimode fibers, separated by plastic strings are spaced uniformly around a cushioned central strength member and surrounded first by a cushioning sheath and then a second high-strength outer polyethylene jacket. This cable has an outer diameter of only 18 millimeters. The multifiber cable designed for indoor test is even smaller. As shown in Fig. 3.25b, it has an outer polyvinylchloride (PVC) jacket only 8 mm in outer diameter, and an inner cushioning sheath that surrounds a set of plastic-jacketed graded-index optical fibers. used, especially for relatively short-run applications where microbend losses introduced by cabling are not excessive. For low-loss long-run applications, unique designs aimed at eliminating random bending and the effects of cabling and environmental disturbances have been developed that are capable of preventing the addition of more than 1 or 2 dB/km to the original optical power losses in the uncabled optical fibers. Discussions of fiberoptic cable risetime budgets, power budgets, bussing schemes, design parameters, environmental factors, and their use in connection with fiberoptic sensor arrays and telemetry systems is given in Chapter 6. PLASTIC STR PLASTIC TAPE ISmmOD ~ PESHEATH mO.D STRENGTHM A. underground CABLE B. INDOOR CABLE Fig. 3.26 Two fiberoptic cables produced by SUMITOMO of Japan. A somewhat different cable design is employed by HITACHI to reduce losses induced by cabling and installation. As shown in Fig. 3.27, channels are formed in the outer periphery of a plastic spacer that is reinforced with a central high-strength metal or plastic tension member. The individual plastic-jacketed optical fibers, and copper wires if some are required, fit loosely in the channels and are held in by a thin outer sheath. Thus, each fiber is well isolated from both external and internal stress. CU WIRE 16mm SPACER \ O.D NONMETALLIC CABLE co MPOUNDCASLE Fig. 3.27 A fiberoptic cable produced by HITACHI of Japan. 3.3.3 Summary From the above brief discussion of current fiberoptic cabling procedures, it should be clear that in some cases conventional cabling techniques are being 3-9
CHAPTER 4 LIGHTWAVES IN FIBEROPTIC SENSORS 4.1 INTERFEROMRTRIC FIBEROPTIC 4.1.1 Intensity Interferometry 4.1.1.1 Basic Principles SENSORS The basic transduction mechanism employed in many fiberoptic sensors now being developed is the phase modulation of coherent light propagating through a section of singlemode fiber by the action of the energy field that is to be detected. The techniques of optical interferometry may be used to detect these phase shifts in lightwaves. These techniques allow for the extremely high sensitivity that is achievable with the various types of interferometric fiberoptic sensors. Until recently, optical interferometry has been a research tool used in laboratories rather than an applied or operational technique. With the development of low- 10SS singlemode optical fibers, subminiature aolidstate laser light sources, photodetectors, and other related purely optical and electrooptical devices, it is now possible to construct practical interferometric-type devices for use in operational systems. Fiberoptic sensors have the potential to revolutionize sensor technology. mirror is less than the coherence length of the laser, the two beams transmitted to the detector can be made to interfere with one another. The detector output will go from a maximum to a minimum and back to a maximum each time the movable mirror is displaced by one half the optical wavelength. With this technique, it is ossible to detect mirror displacements as small as 10- ? urn, e.g. 0.63 x 10-13 m, for a He-Ne laser red light. LASER SPLITTER TRANSDUCER Four different interferometric configurations currently are being employed in fiberoptic aensors. These are the Michelson, the Mach-Zehnder, the Sagnac, and the Fabry-Perot configurations. It is convenient to review their operation in terms of a nonconventional schematic arrangement using airpaths and bulk optical components before considering how they may be constructed with optical fiber elements. There is one important aspect that these interferometric sensors have in common. In each one, the output beam from an optical source is split into two or more portions. After traveling along different paths, these separate beams are recombined and allowed to actuate a photosensitive detector. 4.1.1.2 The Michelson Interferometer The basic principle is illustrated first in Fig. 4.1 for the case of an air path Michelson interferometer. The beam splitter is shown as a partiallyreflective, partially-transmissive mirror. It sends one portion of the output beam from the laser upward to the fixed mirror where it is reflected back to the beam splitter, where it is then partially transmitted to the optical detector and partially reflected back toward the laaer. The other portion of the laser output beam passes through the beam aplitter, 1S reflected from the movable mirror to be partially reflected to the optical detector and partially transmitted back toward the laser. If the difference in the the path lengths back and forth to the fixed mirror and to the movable 4-1 4.1.1.3 The Mach-Zehnder Interferometer The Mach-Zehnder interferometer configuration is shown in Fig. 4.2. The laser output beam is split Fig. 4.2 BEAM w Fig. 4.1 The principle of the Michelson interferometer. “’’R’- 1 BEAM SPLITTER LASER I “ ‘ 1 , , MOVABLE The principle of the Mack-Zehnder interferometer. by the lower beam splitter. After traveling the upper and lower optical paths the two beams are recombined so that they may interfere with each other at the optical detector. This arrangement may also be employed to
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: aged multichannel unit. High-streng
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 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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