1. Applications of the Fiber Optic Sagnac Interferometer
Session 1 5 4 3 2
Session 6 8 7
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2. Sagnac Interferometer
Part I
Rotation Sensing
Part II
Quasi-Static and Time Varying Sensing
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Session 3, Page 1

3. Rotation Sensor Characteristics
Rate Gyro
 = KV
 = Rotation rate
K = Scale factor
V = Output signal
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4. Definition of Terms
Rate integration gyro - Integrates angular rate to get angular output
Fixed bias - Output rotation rate with zero input rotation rate
Bias drift - Change in output rate over time (temperature, wear, etc.)
Scale factor - Linearity and hysteresis
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5. Rotation Sensor Performance Factors
Sensitivity
Lowest measurable rotation rate
Spectral noise characteristics
Dynamic range
Turn on time
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6. The Sagnac Effect cw path: 2R+ RL/c ccw path: 2R - RL/c
Net path difference: 2RL/c
ZR = 2RL/(c)
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7. The Sagnac Effect ZFcw = (Fo+F)(Ln/c) ZFccw = FoLn/c ZF = FLn/c
Setting ZR = ZF
Renders F = 2R/n F
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8. Fiber Optic Gyro Competition
Mechanical Gyros
Advantages
Established industrial base
Disadvantages
Bearing wear
Start-up time
Reliability
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9. Fiber Optic Gyro Competition
Ring Laser Gyros
Advantages
Established industrial base
Replaced mechanical gyros for navigation
Disadvantages
Mechanical dither
Ultraclean vacuum tube technology
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10. Fiber Optic Gyro Tradeoffs
All solid state
Packing flexibility
Potentially very long lifetimes
Small size
Low cost
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11. Ring Laser Gyro Assembly
Anode
Cathode
Partially transparent
mirror
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12. Ring Laser Gyro Readout Optics
cw beam
ccw beam
Rolling fringe
pattern
Split
detector
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13. Ring Laser Lock In Zone
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14. Open Loop Fiber Optic Gyro
Detector
Light source
Polarizer
Fiber optic loop
Modulator
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15. Detection Signals
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16. Open Loop Fiber Optic Gyro Output
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17. Closed Loop Fiber Optic Gyro
Detector
Light source
Polarizer
Fiber optic coil
Modulator
Frequency
shifter
Oscillator
Integrator
VCO
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18. Scale Factor Open loop fiber gyro  = ZR[c/2RL]
Closed loop fiber gyro
 = F(n/2R)
Dependence on wavelength
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19. Correction of Scale Factor
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20. First Closed Loop Fiber Optic Gyro
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21. First Solid State Fiber Optic Gyro
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22. 2.5” 1980 Fiber Optic Gyro
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23. 1982 Oil Drilling FOG
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24. 1983 Closed Loop FOGs
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25. First Honeywell Production FOG
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26. Litton (NG) FOG IMU
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27. The Open Loop Fiber Optic Gyro Marketplace
Automobiles and trucks
Pointing and tracking
Robot navigation
Aircraft attitude control
Short range air navigation
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28. The Closed Loop Fiber Optic Gyro Marketplace
Medium to long range aircraft
Spacecraft
Missiles
Launch vehicles
Platforms making rapid turns
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29. FOG Manufacturers Hitachi Closed loop automotive and low cost FOGs
Delivered over supports high end automobiles like Lexus navigators, thousands of units per year
Japan Aviation Electronics
Intermediate grade FOGs for Japan self-defense force, variety of commercial applications, soccer field grass cutters, cleaning robots, mini-crop spraying helicopters…
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30. FOG Manufacturers (continued)
Honeywell
Supplies 3 axis FOG navigator for German Dornier commuter aircraft, 777 back up navigator
Leader in commercial aircraft navigation and space based FOG
Northrup
3 axis closed loop AHRS units with deg/hr performance to full military specifications
Working on full navigation grade 0.01 deg/hr FOGs targets competing with Honeywell on commercial aircraft
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31. FOG Manufacturers (continued)
Mitsubishi Precision Company
Flight tested first space based FOG on Feb. 22, 1990 aboard S rocket
Makes both open and closed loop FOGs
Photonetics
Closed loop 0.1 deg/hr FOGs to support ship navigation
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32. Estimated FOG Market Size
$50,000,000
$100,000,000
$150,000,000
Combination of commercial and military/government funded markets
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33. Fiber Optic Gyro References
S. Ezekiel and H.J. Arditty, Editors, “Fiber Optic Rotation Sensors”, Springer-Verlag, New York, 1982.
E. Udd, Editor, “Fiber Optic Gyros: 10th Anniversary Conference”, SPIE Proc., Vol. 719, 1986.
R.B. Smith, Editor, “Selected Papers on Fiber Optic Gyros”, SPIE Milestone Series, Vol. MS 8, 1989.
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34. Fiber Optic Gyro References (continued)
S. Ezekiel and E. Udd, “Fiber Optic Gyros: 15th Anniversary Conference”, SPIE Proc., Vol. 1585, 1991.
H. Lefevre, “The Fiber Optic Gyroscope”, Artech House, 1993.
W.K. Burns, Editor, “Optical Rotation Sensing”, Academic Press, 1994.
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35. Part II
Quasi-Static and Time Varying Sensing Using the Fiber Optic Sagnac Interferometer
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36. Time Varying Environmental Effects-Acoustics
Detector
Light source
Center
Acoustic
Wave
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37. Optimized Fiber Coil Configurations
Variable
coating
Shielded
Fiber
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38. Effects of Shielding/Position
Induced phase shift
unshielded coil
shielded coil
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39. Time Varying Effects Fiber Coil Length L dy y Response of Fiber G(y,P)
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40. Example Cases I. G(y,P) = A = Constant, R[P(t)] = 0
II. G(y,P) = 0, 0<y<L/2
G(y,P) = A = Constant, L/2<y<L,
R[P(t)] = AnL2/4c]dP/dt
for P = Bsin(t)
R[P(t)] = [ABnL2/4c] sin(t)
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41. Quasi-Static Sensing-Strain
Detector
Light source
Frequency
shifter
Fo+F Fo
Polarizer
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42. Quasi-Static Sensing ZF = F(Ln/c) Suppose ZF = Constant
0 = dF(Ln/c)+FdL(n/c)
dF/F = -dL/L
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43. Sagnac Strain Sensor Cabling
Detector
Light source
Frequency
shifter
Fiber cable
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44. Earth Movement Detection System
Fault line
Fiber cables
Earth
movement
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45. Monitoring Oil Platform Motion
Fiber optic strain sensor
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46. Stress on Power Lines Fiber strain sensor surrounded
by conductive cable elements
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47. Distributed Sagnac Sensors
Changing modes from time varying to quasi-static
Interlaced Sagnac loops
Combination of the Sagnac and Mach-Zehnder interferometers
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48. Changing Mode Distributed Sensor
Detector
Light source
Frequency
shifter
Polarizer
Fo+F Fo
Switches
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49. Interlaced Sagnac Loops
Detector, 1
Light source, 1
Detector, 2
Light source, 2
Position I
WDMs
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50. Sagnac/Mach-Zehnder Light source, 1 Sagnac Detector, 1 Mach-Zehnder
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51. Detection of Leaks in Pressurized tanks
Sagnac
distributed sensor
Fiber coil
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52. Coherence Length L1 L2 Light source Detector Blue Road Research
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53. Basic Sagnac Interferometer Secure Communication System
Detector
Light source
Data
out
Receiver
Transmitter
Phase
modulator
Data in
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54. Basic Intrusion Scenario
Detector
Light source
Data
out
Receiver
Transmitter
Phase
modulator
Data in LA LB
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55. References for Part II Acoustic Sensors
E. Udd, “Fiber Optic Acoustic Sensors Based on the Sagnac Interferometer”, SPIE Proc., Vol. 425, p. 90, 1983.
K. Krakenes and K. Blotekjaer, “Sagnac Interferometer for Underwater Sound Detection: Noise Properties”, Optics Letters, Vol. 14, p. 1152, 1989.
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56. References for Part II (continued)
Strain Sensors
R.J. Michal, E. Udd, and J.P. Theriault, “Derivative Fiber Optic Sensors Based on the Phase Nulling Optical Gyro”, SPIE Proc., Vol. 719, p. 150, 1986.
E. Udd, R. Blom, D. Tralli, E. Saaski and R. Dokka, “Application of the Sagnac Interferometer Based Strain Sensor to an Earth Movement Detection System”, SPIE Proc., Vol. 2191, 1994.
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57. References for Part II (continued)
Spectrometers and Scale Factor
E. Udd, “Usage of Dispersive Effects for Scale Factor Correction in the Fiber Optic Gyro, SPIE Proc., Vol. 1585, p. 255, 1991.
Distributed Sensing
E. Udd, “Sagnac Distributed Sensor Concepts”, SPIE Proc. 1586, p. 46, 1991.
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58. References for Part II (continued)
Secure Communication
E. Udd, “Secure Communication System”, U.S. Patent 5,223,967, June29, 1993.
E. Udd, “Secure Communication System, U.S. Patent 5,274,488, December 28, 1993.
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59. The Mach-Zehnder and Michelson Interferometers and Multiplexing
Session 1 5 4 3 2
Session 6 8 7
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60. Interferometer Basics
Mach-Zehnder
Michelson
Light Source
Light Source
Detector
Detector
Interference requirements:
Polarization state of two beams identical
Path length difference < Coherence length:

61. Flexible Geometries, High Sensitivity
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62. Basic Elements of the Mach-Zehnder Interferometer
Light source / coupler module
Homodyne demodulator
Transducer
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63. Grating Based Homodyne Demodulator
Dual input fibers
Grin lens
Interference
pattern
Split photomasked detector,
sine and cosine outputs
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64. Quadrature Demodulation Electronics
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65. The Signal Fading Problem
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66. Active Feedback Light source / coupler module Amplifier/integrator
Transducer
Coupler
Amplifier/integrator
Detectors
Modulator
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67. 3 by 3 Coupler 120 degree offsets between outputs Light source 1 2 3
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68. Phase Generated Carrier
Light source L1 L2 
Current driver
, 2
Output
F(L1-L2)n/c
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69. The Michelson Interferometer
Light source
Coupler L1 L2
Mirrors
Detector
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70. SMARTEC Strain Sensors
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71. SMARTEC Strain Sensors (continued)
Coupleur
Photo-
LED
1300nm
A/D m
Ampli PC
Internal
Mirrors
Structure under test
Portable PC
diode
filtre
Mirror
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72. Coatings Secondary compliant Primary coating Glass fiber Pressure
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73. Compliant Mandrels Optical fiber Pressure Blue Road Research
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74. Transducer Materials Acoustics Magnetic fields Electric fields
Nylon
Magnetic fields
MetGlass, Nickel
Electric fields
PVF
Seismic/Vibration
Soft rubber
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75. Transducer Geometries
Hollow mandrel
Strip
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76. Seismic/Vibration Sensor
Fiber coil
Soft rubber
mandrel
Seismic
mass
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77. Serial Layout
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78. Seismograph Layout Seismograph recorders Line arrays Transmitter
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79. Multiplexing Techniques
Time division
Frequency division
Wavelength
Coherence
Polarization
Spatial
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80. Time Division Multiplexing
Light source
Signal processing
electronics
Detector
Microbend
fiber
attachment
Pipe joints
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81. Frequency Division Multiplexing
Light source F1 F2 F3
Detector L1 L2 L3 L
Frequency chirped
light source
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82. Wavelength Division Multiplexing
Light source 1 2 3 4
Wavelength division
multiplexer/detectors
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83. Signal falls exponentially to zero when
Coherence Length L1 L2
Light source
Detector
Signal falls exponentially to zero when
|L1-L2|>Lc
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84. Coherence Multiplexing
Light source L
Detector 2
Detector 1
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85. Polarization Multiplexing
Light source
Detector 1
Detector 2
Polarizing
beamsplitter
Evanescent sensors
Polarization states
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86. Spatial Multiplexing S1 1 S1(1),S3(2) S2 Light sources S3
Detectors
Unbalanced interferometers
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87. Extensions of Spatial Multiplexing1 2 3 J
Sources 11 J1 1K JK 1 3 2 K
Detectors
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88. Distributed Fiber Sensors
Optical time domain reflectometers
Rayleigh
Raman
Brillouin
Fluorescence
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89. Raman Scattering
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90. Brillouin Scattering Incident laser wavelength Brillouin lines
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91. Summary Mach-Zehnder and Michelson interferometers
High sensitivity
Excellent multiplexing potential
Distributed sensors may be used to cover wide areas with less sensitivity
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92. Fiber Optic Smart Structures for Natural, Civil, and Aerospace Applications
Session 1 5 4 3 2
Session 6 8 7
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93. Fiber Optic Smart Structures
Part I
Fundamental concepts and technology
Part II
Applications
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94. Access to Space/Rockets
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95. Space Platforms
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96. Transport Aircraft SHM
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97. Transport Aircraft SHM
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98. Military Aircraft SHM
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99. Aspects of Fiber Optic Smart Structures
Smart manufacturing
Nondestructive testing
Health and damage assessment
Control systems
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100. Advantages of Fiber Optic Sensors for Smart Structures
Lightweight/nonobtrusive
All passive
EMI resistant
Environmental ruggedness
Multiplexing potential
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101. Fiber Optic Smart Structure System
Composite panel
with multiplexed
fiber sensors
Fiber optic link to
actuator system
Control system
-Performance
-Health
Optical/
Electronic
Processor
Environmental effect
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102. Fiber Optic Smart Structure System Technology
Fiber/material issues
Fiber optic sensors
Multiplexing
Signal processing
System architecture
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103. Fiber/Material Issues
Fiber coatings
Ingress/egress
Connectors
Wide range of materials
Carbon epoxy, polyimides
Aluminum, titanium
Ceramics, carbon-carbon
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104. Fibers Embedded in Carbon Epoxy
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105. Polyimide Coating in Thermoplastic
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106. Fibers in Titanium Metal Matrix
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107. Fiber Optic Sensors-Issues
Parameters to be sensed
Strain, temperature, viscosity, etc.
Gauge length
Number of sensors per string
Fiber/sensor diameter
Dynamic range/sensitivity
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108. References for Part I
Fiber Optic Sensors: An Introduction for Engineers and Scientists, Edited by Eric Udd, Wiley, 1991 (Chapter 14).
SPIE - The International Optical Engineering Society Proceedings, Volumes on Fiber Optic Sensors and Smart Structures (call for current catalogue ).
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109. Applications of Fiber Optic Smart Structures
Part II
Applications of Fiber Optic Smart Structures
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110. Smart Manufacturing Composite part Autoclave Temperature
sensor demodulator
Composite part
Autoclave
Degree of
cure monitor
(Fluorescence)
Autoclave controller
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111. Nondestructive Evaluation
Fiber optic sensor
acoustic demodulator
Pulsed laser
External acoustic source
Composite part
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112. Damage Assessment in Composite Panel
Light sources
Detectors
Damage site
Beamsplitters
Microbend
sensitive fiber
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113. Monitoring Bond Line Fixed structure Bond area Detector Light source
Tension
Fixed structure
Detector
Bond area
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114. Embedded Fiber Sensors for a Large Structure
Large numbers
Thousands to tens of thousands
Cost
System must be a small fraction of platform cost
Must add substantial value
Safety, reliability, maintainability
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115. Overall Architecture First layer Second layer Distributed sensors
Localize damage
Measure ambient conditions
Second layer
Multiplexed discrete sensors
Reconfigurable
Detailed assessment
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116. First Layer Coverage
Low cost distributed sensors or long gauge length sensor networks
Low to medium accuracy
Temperature distribution
Acoustics
Wide area strain changes
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117. First Layer Coverage Candidates
Blackbody sensor - networks
Microbend sensor - networks
Distributed sensors
Rayleigh
Raman
Brillouin
Fluorescence
Interleaved interferometric
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118. Second Layer Coverage Discrete, high performance sensor arrays
Detailed damage/health assessment of designated area
Reconfigurable to minimize processing requirements
Redundant
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119. Second Layer Sensor Criteria
Single Point of Ingress/Egress
Amplitude independence
Compatible with in-line multiplexing
Low cost and manufacturable
No larger than fiber diameter
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120. Second Layer Sensor Candidates
Fabry-Perot etalons
Fiber gratings
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121. Modular Architecture Sensor string Data formatter Optical
Vehicle health
management bus
Subsystem signal
processor
Demodulator
Data formatter
and transmitter
Optical
switch
Fiber
optic
link
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122. Avionics Example Display Distribution system Processor Pilot
Avionics bus
Vehicle health management bus
Distribution
system
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123. Civil Structures Buildings Police, fire, Bridges maintenance
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124. Natural Structures Geophysical fault line monitors
Earth movement around oil platforms
Strain induced by earth movement on high voltage lines
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125. Manufacturing Environmental Control Water and air chemistry
Process control
Oven temperature, pressure
Valve position, liquid levels
Flow rate
Health monitoring
Vibration
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126. Medicine Chemistry of the blood Internal inspection Power delivery
Oxygen content
Dosage levels
Internal inspection
Blood vessels
Intestines
Stomach
Power delivery
Potential for artificial limbs, nerves
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127. References for Part II
Fiber Optic Sensors: An Introduction for Engineers and Scientists, Edited by Eric Udd, Wiley, 1991.
Eric Udd, “Fiber Optic Smart Structures”, Chapter 14.
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