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 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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Acoustooptic Modulator hF hf h(f+F) / Blue Road Research Session 1, Page 27

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Blackbody Radiation Blue Road Research Session 2, Page 18

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

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

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

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

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

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

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

Etalon Finesse Blue Road Research Session 2, Page 26

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

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

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

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

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

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