An introduction to fiber optic sensors
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An Introduction to Fiber Optic Sensors. Eric Udd Blue Road Research 376 NE 219 th Avenue Gresham, Oregon 97030 503-667-7772 (F) 503-667-7880 www.blueroadresearch.com. Outline. Session 1 - Fundamental Components and Concepts

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An introduction to fiber optic sensors

An Introduction to Fiber Optic Sensors

Eric Udd

Blue Road Research

376 NE 219th Avenue

Gresham, Oregon 97030

503-667-7772

(F) 503-667-7880

www.blueroadresearch.com


Outline

Outline

  • Session 1 -Fundamental Components and Concepts

  • Session 2 -Intensity Based and Fabry-Perot Interferometric Sensors

  • Session 3 -Applications of the Fiber Optic Sagnac Interferometer

  • Session 4 -The Mach-Zehnder and Michelson Interferometers and Multiplexing

  • Session 5 -Fiber Optic Smart Structures for Natural, Civil, and Aerospace Applications

  • Session 6 - Fiber Optic Grating Sensors and Applications


An introduction to fiber optic sensors

Session

6

Session

8

Session

7

Session

1

Session

5

Session

4

Session

3

Session

2

Fundamental Components and Concepts

Blue Road Research


Fundamental components and concepts

Fundamental Components and Concepts

Blue Road Research

Session 1, Page 1

  • Sensor capabilities

  • Advantages

  • Historical trends

  • Sensor types

  • Fundamental components

  • Fiber fabrication / coupling

  • Light sources

  • Modulators

  • Detectors


Fiber optic sensor capabilities

Fiber Optic Sensor Capabilities

Blue Road Research

Session 1, Page 2

  • Rotation, acceleration

  • Electric and magnetic fields

  • Temperature and pressure

  • Acoustics and vibration

  • Strain, humidity, and viscosity


Fiber optic sensor advantages

Fiber Optic Sensor Advantages

Blue Road Research

Session 1, Page 3

  • Lightweight / nonobtrusive

  • Passive / low power

  • EMI resistant

  • High sensitivity and bandwidth

  • Environmental ruggedness

  • Complementary to telecom / optoelectronics


Fiber optic sensors historical trends

Fiber Optic Sensors Historical Trends

1980

1990

2000

Blue Road Research

Session 1, Page 4

Few, high-priced

components, laser

diodes, microoptics

Low-cost basic components, laser diodes pigtailed, fiber beamsplitters

Low-cost complex

components, mass

produced integrated

optics


Fiber optic sensors historical trends1

Fiber Optic Sensors Historical Trends

1980

1990

2000

Blue Road Research

Session 1, Page 5

Niche markets - RF temperature

Mass markets emerge - fiber gyros, medical, lab instruments, manufacturing

Fiber optic systems - fiber optic smart structures, industrial systems


Fiber optic sensors what s next

Fiber Optic Sensors What’s Next?

2005

2010

2015

Blue Road Research

Session 1, Page 5A

Fiber optic health and structural monitoring systems on about 100 bridges, aerospace SHM technology moves toward level 6

Hundreds of civil structure installations, aerospace fiber optic SHM moves to level 8 and 9 with initial deployments

Fiber optic SHM systems are mandated on new civil and aerospace structures


Fiber optic sensors what s next1

Fiber Optic Sensors What’s Next?

2005

2010

2015

Blue Road Research

Session 1, Page 5B

Oil and gas deployments start to appear

Hundreds of oil and gas wells uses downhole fiber optic sensor systems, platforms begin to use fiber optic SHM systems

Thousands of systems are deployed for many high value oil and gas wells, fiber optic SHM mandated on some oil platforms


Extrinsic fiber optic sensors

Extrinsic Fiber Optic Sensors

Light modulator

Input fiber

Output fiber

Environmental signal

Blue Road Research

Session 1, Page 6


Intrinsic fiber optic sensors

Intrinsic Fiber Optic Sensors

Optical fiber

Environmental signal

Blue Road Research

Session 1, Page 7


Fundamental components

Fundamental Components

Blue Road Research

Session 1, Page 8

  • Optical fiber

  • Light sources

  • Beam conditioning optics

  • Modulators

  • Detectors


Total internal reflection

Total Internal Reflection

Air

Water

Bottom of pool

Blue Road Research

Session 1, Page 9


Optical fiber structure

Optical Fiber Structure

Numerical

aperture

n (clad)

n (core)

Waveguide axis

Blue Road Research

Session 1, Page 10


Types of optical fiber

Types of Optical Fiber

Blue Road Research

Session 1, Page 11

  • Multimode step index

  • Graded index multimode

  • Single mode

  • Polarization preserving

  • Polarizing


Types of polarization preserving fiber

Types of Polarization Preserving Fiber

Blue Road Research

Session 1, Page 12

Elliptical

clad

Soft glass

side pit

Stress rod


Fiber depolarizer

Fiber Depolarizer

Broadband

input light

beam

Polarization preserving fiber

sections at 45 degrees

Blue Road Research

Session 1, Page 13


Fiber fabrication types

Fiber Fabrication Types

Blue Road Research

Session 1, Page 14

  • Modified chemical vapor deposition

  • Outside chemical vapor deposition

  • Vapor axial deposition

  • Rods in glass tube


Fiber coupling techniques

Fiber Coupling Techniques

Blue Road Research

Session 1, Page 15

  • Fused biconical taper

  • Polished

  • Etched

  • Microoptic

  • Integrated optic


Fiber coupling techniques1

Fiber Coupling Techniques

clad

core

Blue Road Research

Session 1, Page 16


Light sources

Light Sources

Blue Road Research

Session 1, Page 17

  • Light emitting diodes

  • Laser diodes

  • Superradiant diodes

  • Fiber Lasers


Spontaneous emission

Spontaneous Emission

Blue Road Research

Session 1, Page 18

  • Low probability of photon interaction

  • Wide spectral bandwidth

  • High immunity to low level backscatter


Stimulated emission

Stimulated Emission

Blue Road Research

Session 1, Page 19

  • High probability of photon interaction

  • Narrow bandwidth due to spectral selectivity of cavity

  • High sensitivity to low level backscatter


Superradiance

Superradiance

Blue Road Research

Session 1, Page 20

  • High probability of photon interaction

  • Wide bandwidth due to spectrally nonselective cavity

  • Moderate sensitivity to backscatter


Surface emitting led

Surface Emitting LED

-

-

N AlyGa1-yAs

P GaAs

Metal electrodes

P AlxGa1-xAs

+

Blue Road Research

Session 1, Page 21


Laser diode and edge emitting led structures

Laser Diode and Edge Emitting LED Structures

Metal electrode

Insulator

GaAs substrate

Light emitting area

Metal electrode

Blue Road Research

Session 1, Page 22


Characteristic current power curves

Characteristic Current/Power Curves

Blue Road Research

Session 1, Page 23


Fiber lasers

Fiber Lasers

Pump laser diode

WDM coupler

Active fiber

Blue Road Research

Session 1, Page 24


Fiber optic modulators

Fiber Optic Modulators

Blue Road Research

Session 1, Page 25

  • Electrooptical

  • Acoustooptical

  • Magnetooptical

  • Mechanical


Electrooptic modulator

Electrooptic Modulator

Electrode

Fiber

Integrated optic waveguide

Blue Road Research

Session 1, Page 26


Acoustooptic modulator

Acoustooptic Modulator

hf

h(f+F)

/

hF

Blue Road Research

Session 1, Page 27


Mechanical modulators

Mechanical Modulators

Expansion

Blue Road Research

Session 1, Page 28

Constriction


Detectors

Detectors

Blue Road Research

Session 1, Page 29

  • PIN photodiodes

  • Avalanche photodiodes

  • Spectrally selective detectors


Summary basic elements of a fiber optic sensor

Summary - Basic Elements of a Fiber Optic Sensor

Beam conditioning

optics

Modulator

Light source

Transducer

Detector

Blue Road Research

Session 1, Page 30


An introduction to fiber optic sensors

Session

6

Session

8

Session

7

Session

1

Session

5

Session

4

Session

3

Session

2

Intensity Based and Fabry-Perot Interferometric Sensors

Blue Road Research


Closure and vibration sensors based on numerical aperture

Closure and Vibration Sensors Based on Numerical Aperture

d

Blue Road Research

Session 2, Page 1


Closure and vibration sensors based on numerical aperture1

Closure and Vibration Sensors Based on Numerical Aperture

Flexible

mounted

mirror

Blue Road Research

Session 2, Page 2


Translation sensor based on numerical aperture

Translation Sensor Based on Numerical Aperture

Detectors

Input light

Collection fibers

Blue Road Research

Session 2, Page 3


Rotary position based on reflectance

Rotary Position Based on Reflectance

Variable reflectance shaft

Input/output fibers

Blue Road Research

Session 2, Page 4


Linear position sensors wavelength division

Linear Position Sensors Wavelength Division

Encoder card

1

2

3

WDMs

Light source

Detectors

1

2

3

Blue Road Research

Session 2, Page 5


Linear position sensors time division

Linear Position SensorsTime Division

Encoder card

Light source

Time delay loop

Detector

Blue Road Research

Session 2, Page 6


Critical angle pressure index of refraction measurement

Critical Angle Pressure/Index of Refraction Measurement

Fiber core

no outside

medium index

of refraction

Mirror

Light input,

output

Fiber cladding

Blue Road Research

Session 2, Page 7


Liquid level sensor based on total internal reflection

Liquid Level Sensor Based on Total Internal Reflection

Liquid

Blue Road Research

Session 2, Page 8


Evanescence based sensors

Evanescence Based Sensors

Interaction length

L

Light in

d

Light

outputs

Fiber cores

Blue Road Research

Session 2, Page 9


Microbend fiber sensors

Microbend Fiber Sensors

Light source

Microbend

transducer

Detector

Blue Road Research

Session 2, Page 10


Grating based intensity sensor

Grating Based Intensity Sensor

Stationary mount

Graded index lens

Output fiber

Input fiber

Spring

Blue Road Research

Session 2, Page 11


Dynamic range limit

Dynamic Range Limit

Output Intensity

Position of Grating

Blue Road Research

Session 2, Page 12


Dual grating mask 90 degrees out of phase

Dual Grating Mask, 90 Degrees Out of Phase

Region 1

Region 2

Blue Road Research

Session 2, Page 13


Quadrature detection

Quadrature Detection

2

1

2

1

Blue Road Research

Session 2, Page 14


Limitations of intensity based fiber optic sensors

Limitations of Intensity Based Fiber Optic Sensors

Blue Road Research

Session 2, Page 15

  • Variable loss due to connectors

  • Microbending losses

  • Macrobending losses

  • Mechanical losses due to creep and misalignment


Spectral approaches

Spectral Approaches

Blue Road Research

Session 2, Page 16

  • Self referenced intensity sensors based on dual wavelengths

  • Fiber optic sensors based on spectral response

    • Blackbody radiation

    • Absorption/fluorescence

    • Dispersive elements - gratings and etalons


Blackbody sensors

Blackbody Sensors

Blackbody

cavity

Narrow band filter

Lens

Optical fiber

Detector

Blue Road Research

Session 2, Page 17


Blackbody radiation

Blackbody Radiation

Blue Road Research

Session 2, Page 18


Variable absorption probes

Variable Absorption Probes

Input fiber

GsAs sensor

probe

Output fiber

Blue Road Research

Session 2, Page 19


Fluorescent probes

Fluorescent Probes

End tip

Fluorescent material

Etched

Blue Road Research

Session 2, Page 20


Absorption fluorescent systems

Absorption/Fluorescent Systems

Connector

Probe tip

Light source

Spectrometer

Blue Road Research

Session 2, Page 21


Fiber grating

Fiber Grating

Laser beams

Fiber

Induced

grating

pattern

Blue Road Research

Session 2, Page 22


Fiber grating system

Fiber Grating System

Light source

Fiber gratings

1

2

Detector

Modulated reference fiber grating

Blue Road Research

Session 2, Page 23


Grating based position sensor

Grating Based Position Sensor

Translation stage

Variable

grating

Lenses

Light emitting diode

Spectrometer

signal processor

Blue Road Research

Session 2, Page 24


Hybrid etalon based fiber sensors

Hybrid Etalon Based Fiber Sensors

Multimode fibers

Pressure

Temperature

Refractive index

of liquids

Blue Road Research

Session 2, Page 25


Etalon finesse

Etalon Finesse

Blue Road Research

Session 2, Page 26


Demodulators for broadband etalons

Demodulators for Broadband Etalons

CCD

detector

array

Beamsplitter

filter

Detector

Divider

Blue Road Research

Session 2, Page 27


Fiber etalons

Fiber Etalons

Intrinsic

Tube

Air gap

Extrinsic

Demodulator

Blue Road Research

Session 2, Page 28


Fly by light system

Fly by Light System

Blue Road Research

Session 2, Page 28A


Fly by light system airframe

Fly by Light System-Airframe

Blue Road Research

Session 2, Page 28B


Fly by light system engine

Fly by Light System-Engine

Blue Road Research

Session 2, Page 28C


Summary intensity and spectrally based fiber sensors

Summary - Intensity and Spectrally Based Fiber Sensors

Blue Road Research

Session 2, Page 29

  • Intensity based sensors

    • Offer simplicity and low cost

    • Are subject to variable attenuation errors

  • Spectral techniques may be used to minimize attenuation errors


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