Blue Road Research Applications of the Fiber Optic Sagnac Interferometer Blue Road Research Session 6 Session 8 Session 7 Session 1 Session 5 Session 4

Blue Road Research

Applications of the Fiber Optic Sagnac Interferometer

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Session6

Session8

Session7

Session1

Session5

Session4

Session3

Session2

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Sagnac Interferometer

Blue Road Research Session 3, Page 1

Part I

Rotation Sensing

Part II

Quasi-Static and Time Varying Sensing

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Rotation Sensor Characteristics


Rate Gyro

= KV

= Rotation rate

K = Scale factor

V = Output signal

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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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Rotation Sensor Performance Factors


• Sensitivity» Lowest measurable rotation rate

• Spectral noise characteristics

• Dynamic range

• Turn on time

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The Sagnac Effect


R

cwccwcw path: 2R+ RL/c

ccw path: 2R - RL/c

Net path difference: 2RL/c

ZR = 2RL/(c)

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The Sagnac Effect


cwccw

ZFcw = (Fo+F)(Ln/c)

ZFccw = FoLn/c

ZF = FLn/c

Setting ZR = ZFRenders F = 2R/n

F

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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


Anode

Cathode

Partially transparentmirror

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Ring Laser Gyro Readout Optics


cw beam ccw beam

Rolling fringe pattern

Splitdetector

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Ring Laser Lock In Zone


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Open Loop Fiber Optic Gyro


Detector

Light sourcePolarizer

Fiber optic loop

Modulator

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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


Detector

Light sourcePolarizer

Fiber optic coil

Modulator

Frequency shifter

Oscillator

IntegratorVCO

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Scale Factor


Open loop fiber gyro

= ZR[c/2RL]

Closed loop fiber gyro

= F(n/2R)

Dependence on wavelength

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Correction of Scale Factor


-F F

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First Closed Loop Fiber Optic Gyro

Blue Road Research Session 3, Page 18A

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First Solid State Fiber Optic Gyro

Blue Road Research Session 3, Page 18B

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2.5” 1980 Fiber Optic Gyro

Blue Road Research Session 3, Page 18C

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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


Detector

Light source

Center

AcousticWave

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Optimized Fiber Coil Configurations


Variablecoating

ShieldedFiber

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Effects of Shielding/Position


Induced phase shift unshielded coil

Induced phase shiftshielded coil

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Time Varying Effects


dyyFiber Coil Length L

Response of Fiber G(y,P)

..y n

c

.( )L y n

cd

d tP

R( )P( )t d

0

L

y.G( ),y Pd

d t.P

.( ).2 y L n

c

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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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Quasi-Static Sensing-Strain


Detector

Light source

Frequency shifter

Fo+F

FoPolarizer

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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


Detector

Light source

Frequency shifter

Fiber cable

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Earth Movement Detection System


Fault line

Fiber cables

Earthmovement

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Monitoring Oil Platform Motion


Fiber optic strain sensor

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Stress on Power Lines


Fiber strain sensor surroundedby conductive cable elements

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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


Detector

Light source

Frequency shifter

Polarizer

Fo+F

Fo

Switches

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Interlaced Sagnac Loops


Detector, 1

Light source, 1

Detector, 2

Light source, 2

Position

I

WDMs

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Sagnac/Mach-Zehnder


Detector, 1

Light source, 1

Sagnac

Mach-Zehnder

Detector, 2Light source, 2

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Detection of Leaks in Pressurized tanks


Sagnac distributed sensor

Fiber coil

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Coherence Length


L1

L2

Light source Detector

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Basic Sagnac Interferometer Secure Communication System


Detector

Light source

Data out

Receiver Transmitter

Phasemodulator

Data in

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Basic Intrusion Scenario


Detector

Light source

Data out

Receiver Transmitter

Phasemodulator

Data in

LA LB

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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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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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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

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Session6

Session8

Session7

Session1

Session5

Session4

Session3

Session2

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Interference requirements:

Polarization state of two beams identical

Path length difference < Coherence length:

Interferometer Basics

nL nL2

cLL

Detector

2

sin2 1010 IIIIID

Light Source

Detector

Light Source

2

cL

Mach-Zehnder Michelson

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Flexible Geometries, High Sensitivity


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Basic Elements of the Mach-Zehnder Interferometer


Light source / coupler module

Homodyne demodulator

Transducer

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Grating Based Homodyne Demodulator


Dual input fibers

Grin lens

Interferencepattern

Split photomasked detector,sine and cosine outputs

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Quadrature Demodulation Electronics


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The Signal Fading Problem


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Active Feedback


Light source / coupler module

Transducer

Coupler

Amplifier/integrator

Detectors

Modulator

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3 by 3 Coupler


1

2

3

Light source

120 degree offsets between outputs

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Phase Generated Carrier


Light source

L1

L2

Current driver

, 2

OutputF(L1-L2)n/c

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The Michelson Interferometer


Light sourceCoupler

L1

L2

Mirrors

Detector

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SMARTEC Strain Sensors


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SMARTEC Strain Sensors (continued)


Coupleur

Photo- LED1300nm

A/D

Ampli

PC

LED1300nm

A/D

Ampli

PCInternal

LED1300nm

Mirr

ors

Structure under test Coupleur

Portable PC

diode

A/D

filtre Ampli

Mirror

Internal PC

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Coatings


Glass fiber

Secondary compliantcoating

Primarycoating

Pressure

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Compliant Mandrels


Pressure

Optical fiber

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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


Hollow mandrel

Strip

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Seismic/Vibration Sensor


Fiber coil

Soft rubbermandrel

Seismicmass

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Serial Layout


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Seismograph Layout


Line arrays

Seismograph recorders

Transmitter

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Multiplexing Techniques


• Time division

• Frequency division

• Wavelength

• Coherence

• Polarization

• Spatial

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Time Division Multiplexing


Light source

Signal processingelectronics

Detector

Microbendfiberattachment

Pipe joints

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Frequency Division Multiplexing


Light source

F1

F2

F3

Detector

L1 L2 L3

L L L

Frequency chirpedlight source

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Wavelength Division Multiplexing


Light source

1

2

34

2 3 4

1

Wavelength divisionmultiplexer/detectors

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Coherence Length


L1

L2

Light source Detector

Signal falls exponentially to zero when

|L1-L2|>Lc

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Coherence Multiplexing


L1 L2Light source

L L

L

L

L1

L2

Detector 2

Detector 1

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Polarization Multiplexing


Light source

Detector 1

Detector 2

Polarizing beamsplitter

Evanescent sensors

Polarization states

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Spatial Multiplexing


Light sources

S1

S4

S3

S2

1

2

S1(1),S3(2)

S2(1),S4(2)

DetectorsUnbalanced interferometers

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Extensions of Spatial Multiplexing


1

2

3

J

Sou

rces

11

J1

1K

JK

1 32 KDetectors

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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


Wavelength

Brillouinlines

Incident laser wavelength

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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

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Session6

Session8

Session7

Session1

Session5

Session4

Session3

Session2

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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

Blue Road Research Session 5, Page 2D

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Military Aircraft SHM

Blue Road Research Session 5, Page 2E

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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


Composite panelwith multiplexedfiber sensors

Fiber optic link toactuator system

Control system-Performance-Health

Optical/ElectronicProcessor

Environmental effect

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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


Temperaturesensor demodulator

Composite partAutoclave

Degree ofcure monitor(Fluorescence)

Autoclave controller

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Nondestructive Evaluation


Fiber optic sensor acoustic demodulator

Pulsed laser

External acoustic source

Composite part

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Damage Assessment in Composite Panel


Light sources

Detectors

Damage site

Beamsplitters

Microbend sensitive fiber

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Monitoring Bond Line


Light source

Tension

Fixed structure

Detector

Bond area

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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


Sensor string

Vehicle healthmanagement bus

Subsystem signalprocessor

Demodulator

Data formatterand transmitter

Optical switch

Fiberopticlink

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Avionics Example


Pilot

Display

Processor

Avionics bus

Vehicle health management bus

Distributionsystem

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Civil Structures


Buildings

Police, fire,maintenance

Bridges

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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.

Documents

Blue Road Research Applications of the Fiber Optic Sagnac Interferometer Blue Road Research Session 6 Session 8 Session 7 Session 1 Session 5 Session 4