Applications of the Fiber Optic Sagnac Interferometer

1
Applications of the Fiber Optic Sagnac
Interferometer
Blue Road Research
2
Sagnac Interferometer

• Part I
• Rotation Sensing
• Part II
• Quasi-Static and Time Varying Sensing

3
Rotation Sensor Characteristics

• Rate Gyro
• ? KV
• ? Rotation rate
• K Scale factor
• V Output signal

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

5
Rotation Sensor Performance Factors

• Sensitivity
• Lowest measurable rotation rate
• Spectral noise characteristics
• Dynamic range
• Turn on time

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The Sagnac Effect
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The Sagnac Effect
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Fiber Optic Gyro Competition

• Mechanical Gyros
• Advantages
• Established industrial base
• Disadvantages
• Bearing wear
• Start-up time
• Reliability

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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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Fiber Optic Gyro Tradeoffs

• All solid state
• Packing flexibility
• Potentially very long lifetimes
• Small size
• Low cost

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Ring Laser Gyro Assembly
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Ring Laser Gyro Readout Optics
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Ring Laser Lock In Zone
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Open Loop Fiber Optic Gyro
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Detection Signals
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Open Loop Fiber Optic Gyro Output
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Closed Loop Fiber Optic Gyro
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Scale Factor
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Correction of Scale Factor
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First Closed Loop Fiber Optic Gyro
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First Solid State Fiber Optic Gyro
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2.5 1980 Fiber Optic Gyro
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1982 Oil Drilling FOG
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1983 Closed Loop FOGs
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First Honeywell Production FOG
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Litton (NG) FOG IMU
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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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The Closed Loop Fiber Optic Gyro Marketplace

• Medium to long range aircraft
• Spacecraft
• Missiles
• Launch vehicles
• Platforms making rapid turns

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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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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 0.1-1.0 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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FOG Manufacturers (continued)

• Mitsubishi Precision Company
• Flight tested first space based FOG on Feb. 22,
  1990 aboard S-520-11 rocket
• Makes both open and closed loop FOGs
• Photonetics
• Closed loop 0.1 deg/hr FOGs to support ship
  navigation

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Estimated FOG Market Size

• 1995 - 50,000,000
• 2000 - 100,000,000
• 2005 - 150,000,000
• Combination of commercial and military/government
  funded markets

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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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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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Part II

• Quasi-Static and Time Varying Sensing Using the
  Fiber Optic Sagnac Interferometer

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Time Varying Environmental Effects-Acoustics
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Optimized Fiber Coil Configurations
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Effects of Shielding/Position
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Time Varying Effects
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Example Cases
I. G(y,P) A Constant, RP(t) 0 II.
G(y,P) 0, 0ltyltL/2 G(y,P) A Constant,
L/2ltyltL, RP(t) AnL2/4cdP/dt for P
Bsin(?t) RP(t) ABnL2/4c ?sin(?t)
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Quasi-Static Sensing-Strain
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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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Sagnac Strain Sensor Cabling
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Earth Movement Detection System
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Monitoring Oil Platform Motion
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Stress on Power Lines
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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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Changing Mode Distributed Sensor
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Interlaced Sagnac Loops
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Sagnac/Mach-Zehnder
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Detection of Leaks in Pressurized tanks
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Coherence Length
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Basic Sagnac Interferometer Secure Communication
System
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Basic Intrusion Scenario
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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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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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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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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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The Mach-Zehnder and Michelson Interferometers
and Multiplexing
Blue Road Research
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Interferometer Basics
Mach-Zehnder
Michelson
Light Source
Light Source
Detector
Detector
Interference requirements Polarization state of
two beams identical Path length difference lt
Coherence length
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Flexible Geometries, High Sensitivity
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Basic Elements of the Mach-Zehnder Interferometer
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Grating Based Homodyne Demodulator
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Quadrature Demodulation Electronics
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The Signal Fading Problem
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Active Feedback
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3 by 3 Coupler
Light source
1
2
3
120 degree offsets between outputs
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Phase Generated Carrier
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The Michelson Interferometer
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SMARTEC Strain Sensors
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SMARTEC Strain Sensors (continued)
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Coatings
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Compliant Mandrels
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Transducer Materials

• Acoustics
• Nylon
• Magnetic fields
• MetGlass, Nickel
• Electric fields
• PVF
• Seismic/Vibration
• Soft rubber

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Transducer Geometries
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Seismic/Vibration Sensor
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Serial Layout
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Seismograph Layout
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Multiplexing Techniques

• Time division
• Frequency division
• Wavelength
• Coherence
• Polarization
• Spatial

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Time Division Multiplexing
Light source
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Frequency Division Multiplexing
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Wavelength Division Multiplexing
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Coherence Length
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Coherence Multiplexing
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Polarization Multiplexing
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Spatial Multiplexing
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Extensions of Spatial Multiplexing
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Distributed Fiber Sensors

• Optical time domain reflectometers
• Rayleigh
• Raman
• Brillouin
• Fluorescence

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Raman Scattering
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Brillouin Scattering
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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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Fiber Optic Smart Structures for Natural, Civil,
and Aerospace Applications
Blue Road Research
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Fiber Optic Smart Structures

• Part I
• Fundamental concepts and technology
• Part II
• Applications

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Access to Space/Rockets
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Space Platforms
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Transport Aircraft SHM
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Transport Aircraft SHM
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Military Aircraft SHM
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Aspects of Fiber Optic Smart Structures

• Smart manufacturing
• Nondestructive testing
• Health and damage assessment
• Control systems

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Advantages of Fiber Optic Sensors for Smart
Structures

• Lightweight/nonobtrusive
• All passive
• EMI resistant
• Environmental ruggedness
• Multiplexing potential

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Fiber Optic Smart Structure System
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Fiber Optic Smart Structure System Technology

• Fiber/material issues
• Fiber optic sensors
• Multiplexing
• Signal processing
• System architecture

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Fiber/Material Issues

• Fiber coatings
• Ingress/egress
• Connectors
• Wide range of materials
• Carbon epoxy, polyimides
• Aluminum, titanium
• Ceramics, carbon-carbon

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Fibers Embedded in Carbon Epoxy
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Polyimide Coating in Thermoplastic
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Fibers in Titanium Metal Matrix
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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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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 206-676-3290).

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Part II

• Applications of Fiber Optic Smart Structures

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Smart Manufacturing
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Nondestructive Evaluation
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Damage Assessment in Composite Panel
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Monitoring Bond Line
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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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Overall Architecture

• First layer
• Distributed sensors
• Localize damage
• Measure ambient conditions
• Second layer
• Multiplexed discrete sensors
• Reconfigurable
• Detailed assessment

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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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First Layer Coverage Candidates

• Blackbody sensor - networks
• Microbend sensor - networks
• Distributed sensors
• Rayleigh
• Raman
• Brillouin
• Fluorescence
• Interleaved interferometric

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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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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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Second Layer Sensor Candidates

• Fabry-Perot etalons
• Fiber gratings

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Modular Architecture
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Avionics Example
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Civil Structures
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Natural Structures

• Geophysical fault line monitors
• Earth movement around oil platforms
• Strain induced by earth movement on high voltage
  lines

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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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Medicine

• Chemistry of the blood
• Oxygen content
• Dosage levels
• Internal inspection
• Blood vessels
• Intestines
• Stomach
• Power delivery
• Potential for artificial limbs, nerves

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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.