1. An Introduction to Fiber Optic Sensors
Eric Udd
Blue Road Research
376 NE 219th Avenue
Gresham, Oregon 97030
(F)

2. 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

3. Fundamental Components and Concepts
Session 1 5 4 3 2
Session 6 8 7
Blue Road Research

4. Fundamental Components and Concepts
Sensor capabilities
Advantages
Historical trends
Sensor types
Fundamental components
Fiber fabrication / coupling
Light sources
Modulators
Detectors
Blue Road Research
Session 1, Page 1

5. Fiber Optic Sensor Capabilities
Rotation, acceleration
Electric and magnetic fields
Temperature and pressure
Acoustics and vibration
Strain, humidity, and viscosity
Blue Road Research
Session 1, Page 2

6. Fiber Optic Sensor Advantages
Lightweight / nonobtrusive
Passive / low power
EMI resistant
High sensitivity and bandwidth
Environmental ruggedness
Complementary to telecom / optoelectronics
Blue Road Research
Session 1, Page 3

7. Fiber Optic Sensors Historical Trends
1980
1990
2000
Few, high-priced
components, laser
diodes, microoptics
Low-cost basic components, laser diodes pigtailed, fiber beamsplitters
Low-cost complex
components, mass
produced integrated
optics
Blue Road Research
Session 1, Page 4

8. Fiber Optic Sensors Historical Trends
1980
1990
2000
Niche markets - RF temperature
Mass markets emerge - fiber gyros, medical, lab instruments, manufacturing
Fiber optic systems - fiber optic smart structures, industrial systems
Blue Road Research
Session 1, Page 5

9. Fiber Optic Sensors What’s Next?
2005
2010
2015
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
Blue Road Research
Session 1, Page 5A

10. Fiber Optic Sensors What’s Next?
2005
2010
2015
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
Blue Road Research
Session 1, Page 5B

11. Extrinsic Fiber Optic Sensors
Environmental signal
Input fiber
Output fiber
Light modulator
Blue Road Research
Session 1, Page 6

12. Intrinsic Fiber Optic Sensors
Environmental signal
Optical fiber
Blue Road Research
Session 1, Page 7

13. Fundamental Components
Optical fiber
Light sources
Beam conditioning optics
Modulators
Detectors
Blue Road Research
Session 1, Page 8

14. Total Internal Reflection
Air
Water
Bottom of pool
Blue Road Research
Session 1, Page 9

15. Optical Fiber Structure
n (clad)
n (core)
Waveguide axis
Numerical
aperture
Blue Road Research
Session 1, Page 10

16. Types of Optical Fiber Multimode step index Graded index multimode
Single mode
Polarization preserving
Polarizing
Blue Road Research
Session 1, Page 11

17. Types of Polarization Preserving Fiber
Elliptical
clad
Soft glass
side pit
Stress rod
Blue Road Research
Session 1, Page 12

18. Fiber Depolarizer Broadband input light beam
Polarization preserving fiber
sections at 45 degrees
Broadband
input light
beam
Blue Road Research
Session 1, Page 13

19. Fiber Fabrication Types
Modified chemical vapor deposition
Outside chemical vapor deposition
Vapor axial deposition
Rods in glass tube
Blue Road Research
Session 1, Page 14

20. Fiber Coupling Techniques
Fused biconical taper
Polished
Etched
Microoptic
Integrated optic
Blue Road Research
Session 1, Page 15

21. Fiber Coupling Techniques
core
clad
Blue Road Research
Session 1, Page 16

22. Light Sources Light emitting diodes Laser diodes Superradiant diodes
Fiber Lasers
Blue Road Research
Session 1, Page 17

23. Spontaneous Emission Low probability of photon interaction
Wide spectral bandwidth
High immunity to low level backscatter
Blue Road Research
Session 1, Page 18

24. Stimulated Emission High probability of photon interaction
Narrow bandwidth due to spectral selectivity of cavity
High sensitivity to low level backscatter
Blue Road Research
Session 1, Page 19

25. Superradiance High probability of photon interaction
Wide bandwidth due to spectrally nonselective cavity
Moderate sensitivity to backscatter
Blue Road Research
Session 1, Page 20

26. Surface Emitting LED - + N AlyGa1-yAs P GaAs Metal electrodes
P AlxGa1-xAs
N AlyGa1-yAs
Blue Road Research
Session 1, Page 21

27. Laser Diode and Edge Emitting LED Structures
Insulator
Metal electrode
GaAs substrate
Light emitting area
Blue Road Research
Session 1, Page 22

28. Characteristic Current/Power Curves
Blue Road Research
Session 1, Page 23

29. Fiber Lasers Pump laser diode WDM coupler Active fiber
Blue Road Research
Session 1, Page 24

30. Fiber Optic Modulators
Electrooptical
Acoustooptical
Magnetooptical
Mechanical
Blue Road Research
Session 1, Page 25

31. Electrooptic Modulator
Integrated optic waveguide
Fiber
Electrode
Blue Road Research
Session 1, Page 26

32. Acoustooptic ModulatorhF hf
h(f+F)
/
Blue Road Research
Session 1, Page 27

33. Mechanical Modulators
Constriction
Expansion
Blue Road Research
Session 1, Page 28

34. Detectors PIN photodiodes Avalanche photodiodes
Spectrally selective detectors
Blue Road Research
Session 1, Page 29

35. Summary - Basic Elements of a Fiber Optic Sensor
Light source
Beam conditioning
optics
Transducer
Modulator
Detector
Blue Road Research
Session 1, Page 30

36. Intensity Based and Fabry-Perot Interferometric Sensors
Session 1 5 4 3 2
Session 6 8 7
Blue Road Research

37. Closure and Vibration Sensors Based on Numerical Aperture
Blue Road Research
Session 2, Page 1

38. Closure and Vibration Sensors Based on Numerical Aperture
Flexible
mounted
mirror
Blue Road Research
Session 2, Page 2

39. Translation Sensor Based on Numerical Aperture
Input light
Collection fibers
Detectors
Blue Road Research
Session 2, Page 3

40. Rotary Position Based on Reflectance
Variable reflectance shaft
Input/output fibers
Blue Road Research
Session 2, Page 4

41. Linear Position Sensors Wavelength Division
Encoder card
Light source
WDMs
Detectors 1 3 2
Blue Road Research
Session 2, Page 5

42. Linear Position Sensors Time Division
Encoder card
Light source
Detector
Time delay loop
Blue Road Research
Session 2, Page 6

43. Critical Angle Pressure/Index of Refraction Measurement
Light input,
output
Fiber cladding
Fiber core
no outside
medium index
of refraction
Mirror
Blue Road Research
Session 2, Page 7

44. Liquid Level Sensor Based on Total Internal Reflection
Blue Road Research
Session 2, Page 8

45. Evanescence Based Sensors
Light
outputs
Light in L d
Fiber cores
Interaction length
Blue Road Research
Session 2, Page 9

46. Microbend Fiber Sensors
Light source
Detector
Microbend
transducer
Blue Road Research
Session 2, Page 10

47. Grating Based Intensity Sensor
Graded index lens
Input fiber
Output fiber
Spring
Stationary mount
Blue Road Research
Session 2, Page 11

48. Dynamic Range Limit Output Intensity Position of Grating
Blue Road Research
Session 2, Page 12

49. Dual Grating Mask, 90 Degrees Out of Phase
Region 1
Region 2
Blue Road Research
Session 2, Page 13

50. Quadrature Detection 1 2
Blue Road Research
Session 2, Page 14

51. Limitations of Intensity Based Fiber Optic Sensors
Variable loss due to connectors
Microbending losses
Macrobending losses
Mechanical losses due to creep and misalignment
Blue Road Research
Session 2, Page 15

52. Spectral Approaches
Self referenced intensity sensors based on dual wavelengths
Fiber optic sensors based on spectral response
Blackbody radiation
Absorption/fluorescence
Dispersive elements - gratings and etalons
Blue Road Research
Session 2, Page 16

53. Blackbody Sensors Blackbody Narrow band filter cavity Lens
Optical fiber
Lens
Detector
Narrow band filter
Blue Road Research
Session 2, Page 17

54. Blackbody Radiation
Blue Road Research
Session 2, Page 18

55. Variable Absorption Probes
Input fiber
Output fiber
GsAs sensor
probe
Blue Road Research
Session 2, Page 19

56. Fluorescent Probes End tip Fluorescent material Etched
Blue Road Research
Session 2, Page 20

57. Absorption/Fluorescent Systems
Spectrometer
Probe tip
Connector
Light source
Blue Road Research
Session 2, Page 21

58. Fiber Grating Laser beams Fiber Induced grating pattern
Blue Road Research
Session 2, Page 22

59. Fiber Grating System Light source Fiber gratings 1 2 Detector
Modulated reference fiber grating
Detector
Light source
Fiber gratings 1 2
Blue Road Research
Session 2, Page 23

60. Grating Based Position Sensor
Light emitting diode
Variable
grating
Lenses
Spectrometer
signal processor
Translation stage
Blue Road Research
Session 2, Page 24

61. Hybrid Etalon Based Fiber Sensors
Pressure
Temperature
Refractive index
of liquids
Multimode fibers
Blue Road Research
Session 2, Page 25

62. Etalon Finesse
Blue Road Research
Session 2, Page 26

63. Demodulators for Broadband Etalons
CCD
detector
array
Beamsplitter
filter
Divider
Detector
Blue Road Research
Session 2, Page 27

64. Fiber Etalons Intrinsic Tube Air gap Extrinsic Demodulator
Blue Road Research
Session 2, Page 28

65. Fly by Light System
Blue Road Research
Session 2, Page 28A

66. Fly by Light System-Airframe
Blue Road Research
Session 2, Page 28B

67. Fly by Light System-Engine
Blue Road Research
Session 2, Page 28C

68. Summary - Intensity and Spectrally Based Fiber Sensors
Intensity based sensors
Offer simplicity and low cost
Are subject to variable attenuation errors
Spectral techniques may be used to minimize attenuation errors
Blue Road Research
Session 2, Page 29