FIBEROPTIC SENSOR TECHNOLOGY HANDBOOK

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Fig. 2.28 FURNACE— PREFORM — n II THICKNESS GAGE — - - - JACKETING UNIT z+ P DRYING FURNACE —-----r!l II + TAKEUP DRUM - 6) ~> ‘ The double-crucible optical fiber drawing system. In principle, the double-crucible process has the advantage that it may be used to draw continuous fibers of any desired length. Unfortunately, because the core and cladding glasses must be contained and heated within the crucibles, it is difficult to maintain the very high purity levels required to yield the very low-loss fibers. A much different procedure for producing extremely low-losa fibers was developed during the early and middle 1970’a. Though several variations of the same approach are being used by manufacturer, they all are based on the production of glass fiber using a vapor-phase oxidation (VPO) process. 2.2.2.2 The Inside Vapor-Phase Oxidation (IVPO) Process The inside vapor-phase oxidation process (IVPO) is shown in Fig. 2.29. Vapors of various metal SiCl 4 J. GeC14 Q r MIXING MANIFOLD AND FLOW CONTROLLER SILICA BAIT TUBE ‘+== BURNER H2+02TORCH 1 shown in Fig. 2.29. In each case, the halides are introduced into the mixing manifold by means of a vapor distillation process. For example, high purity oxygen may be bubbled through the liquid silicon tetrachloride (SiC14)”and germanium tetrachloride (GeC14). This process reduces the level of impurities in the halide vapors that are fed into the reaction tube. Heat is applied to the outside of the tube using a movable hydrogen-oxygen torch. This leads to oxidation of the metal halides, yielding a precipitate of very fine glass particles (soot) that builds up on the walls of the bait tube. The tube is mounted in a glass-working lathe and continuously rotated during the oxidation process so that the precipitate deposits uniformly around the inner circumference of the tube, as shown in Fig. 2.30. BAIT TUBE / REACTANTS _ SOOT FORMATION_ (METAL HALIDES+ 02) SINTERED GLASS TRAVERSINiG BURNER EXHAUST :) u’ SOOT DEPOSIT Fig. 2.30 The inside vapor-phase oxidation (IVPO) process for producing optical fibers. After P. Schultz, Appl. Opt. Q, 3684 (1979) The traversing burner not only provides the heat required to oxidize the various metal halide vapors but also transforms the porous soot deposit into thin sintered glass layers that are built up as the burner slowly traverses back and forth along the length of the bait tube. By controlling the concentration of the various reactants fed into the bait tube it ia possible to build up layers of Si02 glass with any desired level of doping. These will eventually form the cladding and the core of fibers that may be drawn from the resulting glass boule (preform) that is produced in this process. Several other steps are carried out before the tube is ready for fiber drawing. These are show in Fig. 2.31. After the cladding and core glasses are depoaited, the tube is heated so that under surface Fig. 2.29 i)He The vapor-phase oxidation (VPO) process for producing optical fiber preforms. halides are mixed with oxygen and helium to desired highly-controlled concentration levels and fed into a hollow silica cylinder (bait tube). The chlorides of silicon and germanium exist as liquids at atmospheric pressure and room temperature, while those of phosphorus and boron must be stored under high pressure, as 2-14 SUSSTRATE TUBE CLADDING DEPOSITED CORE DEPOSITED COLLAPSED PREFORM Fig. 2.31 c1 Q+ ,- d I / FIBER DRAWING ‘1 ~ÿÿÿÿÿÿÿÿÿÿÿ @ /; SUBSTRATE REMOVED DRAWING gjjj/p”FIBER 1// THIN LAYER DEPOSITED ‘, // —u (3” oc’? FIBER ORAWING Stages in the processing of preforms in production of optical fibers. the
tension it collapses to eliminate the remaining center hole. In order to obtain various desired physical properties, fibers can be drawn either without removing the substrate tube, after removing the substrate tube, or after a final layer of glass haa been deposited on the outside of the collapsed preform, as shown in Fig. 2.31. In the drawing process, the boule is placed in an induction furnace and fibers are drawn and coated in almost exactly the same manner as in the double-crucible technique that was shown in Fig. 2.28. 2.2.2.3 The Outside Vapor-Phase Oxidation (OVPO) Process Preforms also are made by precipitating soot on the outside of a rod that is turned in a glaas-working lathe, as shown in Fig. 2.32a. In the outside vapor (a) SOOT DEPOSITION g“’+ww’””’ 4—.—... (b) PREFORM SISTERING o:,::.#.:~C:DING >0 INDEX n (c) FISER DRAWING Fig. 2.32 The outside vapor-phase oxidation (OVPO) process for producing optical fibers. After P. Schultz, Appl. Opt. l&, 3684 (1979). phase oxidation (OVPO) process, the core material is deposited first and then the cladding is deposited on the outside, just in the IVPO process described earlier. The amount of doping may be continuously varied during the core material deposition process. It is thus poasible to produce preforms for graded-index fibers, as well as for step-index fibers, as shown in the example of refractive index versus radial displacement curve at the extreme upper right in Fig. 2.32. The refractive index of the porous material deposited on the center bait rod decreases monotonically out to what will correspond to the core-cladding interface, and then it remains constant to the outer surface of the porous cylindrical shell. fed to the burners, a porous preform with the desired radial variation of refractive index is built up, beginning at the end of the silica rod. The rod is slowly pulled vertically upward as deposition continues at a constant rate at the lower end of the porous preform. The porous section then passes through a concentric heater ring that collapses and sinters the porous section to form a clear glass rod with the desired radial refractive index profile. The entire process is carried out inaide a reaction chamber with a carefully controlled inert atmosphere to reduce the level of impurities. The VAD process permits the production of large preforms capable of yielding single pieces of fiber over 100 km long. The optical quality of current VAD fibers is very high. Data on attenuation rates versus wavelength for VAD and IVPO fibers is shown in Fig. 2.34. The IVPO process produces a fiber with a relatively large attenuation rates peak at 1.4 pm and smaller peaks in the vicinity of 1.23 pm and 0.94 Um. These are due to the vibrational mode absorption lines of the OH- radical. In the VAD process, the OH- radical contamination is reduced substantially by careful drying during the preform fabrication process thus eliminating these attenuation peaks. -.. (’ ;=> STARTING SILICA ROD }! T & SiC14+BBr3 f--l II TRANSPARENT PREFORM $!!$ . -- -— -. CARBONHEATER ‘..-=-, .,.. .,,,,,,.,,, =.. 1’ I l.. t I : POROIJS PREFORM + I ,.. I % ~%-.+’ ‘\ FINE GLASS PARTICLES ~~• QOxy-HyDROGEN BURNERS SiC14+GeC14+PC13 Fig. 2.33 The vapor axial deposition (VAD) process for producing optical fibers. After P. Schultz, Appl. Opt. l&, 3684 (19791 Thus, preform fabrication by the OVPO process is a multistage procedure, including center bait rod removal, followed by porous preform sintering and the collapsing of the central hole, either prior to or during the fiber drawing process. Aa in the IVPO process, the deposition process is carried out on a glass-working lathe. Thus, the preforms produced by both processes have a limited size so that usually fiber lengths from 10 to 20 kilometers may be drawn from a single preform. 2.2.2.4 The Vapor Axial Deposition (VAD) Process Length limitations are overcome in the vapor axial deposition (VAD) process that is ahown in Fig. 2.33. Core and cladding glass particles ejected from oxygen-hydrogen burners are deposited longitudinally and radially on to the end of a silica rod. By carefully controlling the concentration of the metal halides 2-15 Fig. 2.34 0.8 1.0 12 1,4 1.6 1.8 WAVELENGTH (pm) The variation of attenuation as a function of wavelength in optical fibers produced by the vapor axial deposition (VAD) and the inside vapor-phase oxidation (IVPO) processes.
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: : 1.5 z o GeOz 0 ~ =1.49 u w > ~1.4
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 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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