Post on 19-Aug-2018
Optical Waveguide Sensors: Sub-Micron to Supra-Kilometer
R. A. Lieberman
ABSTRACT
The advancement of optical waveguide technology has been driven by interplay between the development of techniques for sensing and for communications. This interplay has resulted in sensors capable of measuring physical and chemical properties at length scales comparable to entire railroad tunnels, comparable to cellular organelles, and a panoply of point sensors, distributed sensors, and sensor arrays for every length scale in between. As new waveguide-related technologies emerge, exciting new opportunities are arising to extend this range even further.
Outline • Physical Sensors
• Pressure (micrometer/millimeter)
• Temperature (millimeter/centimeter)
• Ultrasound/Strain (centimeter/meter)
• Electric Field (centimeter)
• Chemical Sensors • Biomedical (micrometer/centimeter)
• Microbiology (nanometer/micrometer)
• Environmental (centimeter/meter)
• Security (meter/kilometer)
} “nanofabricated”
Fiber-tip Fabry Perot Pressure Sensor
250 μm
FULL REFLECTOR
Fiber Optic Bragg Grating Pressure Sensor
n 1 (Core)
n 2 (Cladding)
Transmitted Light
Reflected Light, λ B
Incident Light Fiber Bragg Grating
Λ , Grating Period (100’s of nm)
2a, core diameter
λ B = 2neff ΛReflected Wavelength:
Multipoint Bragg Grating Sensor Array: 10 FBGs in 5 cm
Fiber Bragg Grating Readout • Passive spectral monitoring
• “White light” plus array waveguide grating (AWG): Wavelength is directly read by CCD array
• Narrow-band source, broadband grating: Reflected intensity depends on measurand
• Active monitoring (source/receiver tracking) • Modulated DFB laser locked to grating wavelength: “Error current” directly proportional to temperature • Strain-tuned reference grating: Wavelength matches probe wavelength
Multipoint FBG Thermometry
• Bragg grating array fabricated with intra-grating spacing < 0.5 cm
• Wavelength-keyed spatial resolution:
grating reflectivity maxima successively increase by 3 nm
• Scanned DFB laser-based readout addresses each grating sequentially
• Temperature grid measured in < 1 sec
Multipoint Temperature Response: 0.1°C Resolution
K(G,T) =dλ BdT
= 2 ΛdneffdT
+ neffdΛdT
Temperature Sensitivity
Monitoring Medical Hyperthermia Treatment
FBG Medical Diathermy Monitoring
Tiss
ue P
hant
om T
empe
ratu
re (º
C)
Fiber Optic Ultrasound Detection – 1995 Cantilever Test Assembly with Surface Mounted FBGs
A
C B
D
FBG Locations Ultrasound Source
200 kHz Detected at 4 Locations
FBG A
FBG C
FBG B
FBG D
Self- Acoustic Emission - 1999 • All structures “creak” at ultrasound frequencies when
stressed.
• This self-acoustic emissions (SAE) is composed of ultrasound pulses caused by the formation of micro-cracks.
• Increase in SAE under load is a recognized precursor to catastrophic failure.
• FOAES – The fiber optic acoustic emission sensor system – is designed to detect self-acoustic emission from structures.
Aircraft Engine Mount Fatigue Tests
Typical Time Domain Signal Under Loading Conditions
FBG Array for Guided-Wave Ultrasound Detection - 2010
• Launch ultrasound with conventional transducer at any convenient point
• Conformal array of FBG transducers maps ultrasound field over large (m2) area
• Eliminates fluid bath, custom-shaped transducers, and other inconveniences of piezoelectric pickups
612-Grating Ultrasound Receiver
FBG Ultrasound Panel DAQ System
GWUS Detected with FBG-panel in F-15 Composite Skin
(Top left) at 2 in. separation; (top center) at 3 in. separation; (top right) at 4 in. separation; (bottom left) at 5 in. separation; (bottom center) at 6 in. separation; (bottom right) at 7 in. separation.
F-15 Composite Disbond Detection Ultrasound Image acquired with a grid of 612 FBGs
Color-coded GWUS amplitude map. Red shows areas where disbonds occur in F-15 vertical stabilizer.
Flexible FBG Panel - 2012
100kHz Resonant PZT Source Measures at 100kHz excitation
Defect-Free Sample
Defect Present
Difference Response Shows Reflected Antisymmetric A0 Component
Subtraction of "Reflection Measurements on ISU Samples,Source: NDT PZT Resonant f: 100 kHz, Receiver: B-1025 Broadband
PZT Drive Frequency: 0.1 MHz, (2-01-11)"
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0 20 40 60 80 100 120 140 160
Time, μs
US
Res
pons
e, V
Reflected A0
Direct propagation of A0
Frequency Content of Responses with 100kHz excitation
Defect-Free
Again: See an increase in Lower-Frequency content of Defected sample response vs. Defect-free sample
Defect Present
Laser Ultrasound Technology (LUT) Inspection System
• Laser ultrasonics combines: • High-energy pulsed laser to excite ultrasound
• Adaptive interferometer that detects only ultrasound
Base Station
Measurement Head
Fiber Umbilical
I O Receiver
CW Probe Laser
Generation Pulsed Laser
Measurement Head
Sample
Principle of Operation: Photorefraction/Two-Wave Mixing
• Photorefractive “mirror” perfectly satisfies Bragg condition • Interferometer in quadrature for all distances until material’s frequency
response dies out (100kHz) • Result: nm-scale ultrasound vibrations faithfully be measured even in
presence of mm-scale low-frequency vibrations
LUT Laboratory System
Base station
Pulsed generation laser
Optical head and scanning hardware
Measurement Head Mounted Onto Weld Carriage
36” pipe
Real-Time Measurement of Steel Pipe Wall Thickness During Manufacturing
5m/s
0 2 4 6 8 10 12 14 16 18
Pipe Position (m)
3.8
2.8
3.0
3.2
3.4
3.6
Wal
l Th
ickn
ess
(mm
)
Measured by Laser-Based Ultrasonic System
Measured by Conventional Ultrasonic Gage
LUT Measurement Head
Liquid Crystal E-field Sensor
Millivolt Sensitivity of E Optrode Bias on linear portion of polarization curve
Bioelectric Field Optrodes
Liquid Crystal
Fiber Optic E Field Sensor Response to Cardiac Rhythm
Oscilloscope Lock-in Amplifier
Top trace – Input to the LC cell Bottom trace – Output of the photodetector
Outline
• Physical Sensors • Pressure (micrometer/millimeter)
• Temperature (millimeter/centimeter)
• Ultrasound/Strain (centimeter/meter)
• Electric Field (centimeter)
• Chemical Sensors • Biomedical (micrometer/centimeter)
• Microbiology (nanometer/micrometer)
• Environmental (centimeter/meter)
• Security (meter/kilometer)
} “nanofabricated”
Blood Chemistry Biosensors
• Oxygen partial pressure(PO2), carbon dioxide partial pressure (PCO2), and acidity (pH) change radically minutes before patient goes into shock
• Chemically sensitive optrodes undergo fluorescence quenching (for O2) or color change (for pH, CO2) when analyte changes
• Fluorescence lifetime and intensity, measured as for fluoroptic temperature sensor, and optical absorbance, measured by multi-wavelength methods, give continuous readings of critical parameters.
“Blood Gas” Optrode Evolution
Conjunctival Tissue Gas Sensor For Neonates Requirement to non-invasively
measure blood/tissue oxygenation in neonates:
Too low -> potential cerebral palsy
Too high -> retinopathy with risk of blindness
Pulse oximetry alone not sufficient
Standard lab tests cause anemia
Solution: Very thin, pliable sensor placed under infant’s eyelid monitoring tissue gases (pO2, pCO2, pH) due to contact with conjunctival capillary layer
Initial research funded by NIH; collaboration with Harbor-UCLA (Pediatric Ophthalmology and Pediatric Critical Care)
Tissue/Blood “Gas” Sensor
Schematic view of probe
Micro-Drilled Fiber Two orders of magnitude more signal than evanescent and fiber-tip designs
Oxygen Sensor Film Response
1.50E+05
1.70E+05
1.90E+05
2.10E+05
2.30E+05
2.50E+05
2.70E+05
2.90E+05
0 300 600 900 1200 1500 1800 2100 2400 2700 3000 3300
Time in seconds
Em
issi
on, a
.u.
2% 3% 5% 10% 20%
Tissue/Blood Gas Sensor
3000
3500
4000
4500
5000
5500
0.00 120.00 240.00 360.00 480.00 600.00 720.00 840.00
Elapsed Time
Inte
nsity
(cou
nts)
0
10
20
30
40
50
60
70
80
90
100
CO
2 %
Tes
t Pro
file
Cyc
le (s
imul
ated
)
Response to varying dissolved CO2 concentrations
Fully fabricated multi-analyte probe: pH, PCO2, PO2
Cell Chemistry Biosensor
• Multiple non-interacting optical waveguide cores can be formed in a probe that is less than 1 μm in diameter.
• Near-field optical effect is used to photopolymerize
optrodes at the ends of each sub-wavelength core. • The resulting “nanoprobe” can simultaneously
measure oxygen, pH, and metabolytes in vivo in single cells.
Nanoscale Fiber Optic Biosensor
Fiber Optic Nano-Biosensor
Photomicrograph (length approx. 100 μm)
•Optical fiber tapered to 100 nm •“Sensor bead” optically formed at tip of fiber – multiple channels •Fluorescence of sensor beads depends on local chemical environment
Multi-Core Chemical “Nanoprobe”
Central fiber end
One of six outer fiber ends
Sensor Core
Isolation Member
Three-Function Optochemical Nanoprobes
Dye-doped polymer sensing site
Three Sensor Channels in Subcellular Dimensions
Channel#1: Calcium Green; Channel #2: Texas Red; Channel #3: No Dye
Fiber Optic “Life Detector”
• Most living cells share common biochemical pathways for energy production, storage, and transport
• Spectral properties of the proteins involved in these pathways are similar
• Straightforward remote fiber spectroscopy, coupled with sophisticated spectral processing algorithms, can identify living cells, whether in biofilms, in tissue samples, or in vivo.
Fiber Optic Sensor for Tissue Viability/ Biofilm Detection
NAD/NADH Fluorescence Detected
UV Excited Planktonic Bacterial Fluorescence Captured by Fiber Optic Probe
00.0020.0040.0060.008
0.010.0120.0140.016
400 450 500 550 600
Wavelength, nm
Nor
mal
ized
Flu
ores
cenc
e In
tens
ity0th Order Dilution (1:1)
1st Order Dilution (1:10)
2nd Order Dilution (1:100)
3rd Order Dilution (1:1,000)
BioProbe Live/Dead Differentiation
Maximum Response of Biofilms on Polycarbonate Coupons Using Bioprobe
0
1000
2000
3000
4000
biofilm 1 (g=0.45) biofilm 2 (g=0.35) biofilm 3 (g=0.45)samples
Opt
ical
Sig
nal (
mV)
live samples
killed samples
Colorimetric Detection • Immobilize hydrogen-sensitive indicator in optically transparent medium • Indicator/matrix reversibly changes color in presence of H2 • Intensity of light transmitted through matrix depends upon hydrogen concentration • Intrinsically safe, electrically inert, wide temperature range, works in absence of O2
Optical Waveguide Hydrogen Sensing
Optical Sensor Formats
Integrated Optic Waveguide: Indicator imbedded in waveguides fabricated on optical chip. Multiple channels improve performance.
Optrode: Indicator immobilized in porous glass. Sensors can be packaged with electronics or remotely addressed through fibers.
Distributed Sensing Fiber: Indicator coated on entire length of sensing fiber. Wide area continuous coverage with a single cable.
Optical Fibers
Braids
Cable core
Hydrogen Safety Sensor Prototype
Hardware Package Evolution
2011 2012
Sensor Repeatability/ Reversibility Validated
Optrode response to 0.2; 1.0; 2.0%, of hydrogen at IOS
Optrode response to 0.22, 1.08 and 2.15% of hydrogen at U.S. Dep’t of Energy
H2 Partial Pressure (atm)
0.000 0.005 0.010 0.015 0.020 0.025 0.030
Signa
l/ZV
0.5
0.6
0.7
0.8
0.9
1.0
1.1
Calibration Curve at P = 0.8, 1.0 and 1.2 atm (NREL)Calibration Curve at P = 1.0 atm (IOS Lab)
Time / min
0 100 200 300 400
Sign
al /
Cou
nts
24000
26000
28000
30000
32000
34000
36000
38000
8000 10000 12000 14000 16000 18000
Sig
nal /
Cou
nts
16000
18000
20000
22000
24000
26000
28000
30000
•Optical signals self-consistent within 2% •Optical signals at NREL within 2% of IOS signals
Hydrogen Sensor Alarm Algorithm Detail
0.2% H2
0.2% H2
0.4% H21% H2
2% H2
OFF
OFF
Optrodes Have High Sensitivity and Rapid Alarm Capability
H2 (%) Detection Time (s)*
4.0 3
2.0 3
1.0 3
0.5 3
0.1 10
0.05 10
0.02 30
0.01 120
Response Time (T90) at Various Hydrogen Levels
*RH = 45%; P = 1 atm.; T = 23 ºC; Flow Rate = 1.0 L/min.
Response time < 5 sec. at 10% Lower Flammable Limit
Humidity/Temperature Effects
H2 %
0 1 2 3 4 5
Sign
al/Z
V
0.75
0.80
0.85
0.90
0.95
1.00
1.05RH 10%RH 20%RH 40%RH 75%
H2 %
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Sign
al/Z
V
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1T = 10 οCT = 20 οCT = 30 οCT = 50 οC
• Excellent response at all RH levels • Reproducible effect
• Good response at all temperatures • Reproducible effect
Fibers fabricated specifically for chemical detection “The cable IS the sensor!”
• CO2
• Water • H2S • NH3
• pH
• Cl2
• HCl • HCN • H2
• Relative Humidity • Etc..
Distributed Intrinsic Chemical Agent Sensing and Transmission (DICAST)®
DICAST® is a registered trademark of Intelligent Optical Systems
The DICAST® Paradigm
• LINEAR sensor, not a “point sensor” • Sensor cables respond to target chemical anywhere
over sensor length • Cables contain arrays of optical fibers, each
intrinsically sensitive to a particular chemical agent
• Dosimetric response • Longer exposure yields larger signals • “Integrates” concentration over time • Reversible (concentration) response also possible
Operational Features • Installation
• Continuous cable • Seamless sensing – absolutely no gaps in coverage over entire cable length
• Serpentine deployment can provide “blanket” coverage
• Concatenated segments • Sensor fiber segments interspersed with communication-grade cable
• Extends coverage range – replaces point sensor array
• Optoelectronic detection • “Alarm-style”
• Alerts user if even a single meter of cable is exposed to 10%IDLH/LCT50
• Self-referenced lock-in detection gives high sensitivity and stray light immunity
• Position-resolved • Locates chemically exposed section with 10 cm resolution
• Self-referenced optical time domain reflectometry differentiates between chemical and physical changes in fiber cable
DICAST® Sensor Principle: Chemically-Induced “Cladding Light Loss”
So S1 n1
n2 Fiber core
Fiber cladding
Chemical agent
• Interaction of chemical agent with indicator in cladding changes optical properties
• Light propagating through sensor fiber is affected by changes in exposed region
Indicator Molecules
DICAST fibers use a step-index polymer clad silica core (PCS) fiber structure Cladding material characteristics:
Polymer: • Index < 1.458 • Good adhesion to glass • Good abrasion resistance • Low moisture permeability • Suitable for high-speed fiber draw • Good host for chemical indicator
Coated fiber
Uncoated fiber
The Key: Chemically Sensitive Polymers
Indicator System: • Colorimetric response to analyte • Reversible response to analyte • No response to other substances • Narrow-band optical absorbance • Suitable for high-speed fiber draw • High stability in target environment
Sensor Fiber Performance (HCN) Fibers respond faster to higher concentrations
TEST031805-1
-5
-4
-3
-2
-1
0
1
0 60 120 180 240 300 360 420 480 540 600
Exposure Time (sec.)
Sens
or S
igna
l (dB
/m)
50ppm50ppm5ppm5ppm5ppm
Chemical Exposure Begins
Test exposure: Response of one fiber in cable to H2S--Signal vs. Reference
• Different wavelengths used to interrogate the same fiber allow self-referencing
• Signal wavelength (light blue) reacts immediately to H2S exposure
• Reference wavelength (purple) practically unaffected by exposure
• Allows alarm algorithm to compensate for non-specific effects (temperature, mechanical stress etc.)
0
0.2
0.4
0.6
0.8
1
1.2
0 200 400 600 800 1000 1200 1400 1600
Time [sec]
Val
ue
Gas OnFiber 2--visible (Signal)Fiber 2--IR (Reference)
Test exposure: Response of all fibers in cable to H2S—Signal wavelength only
• Signal wavelength shown for all fibers in cable
• Response from all fibers to exposure event provides unique “fingerprint”
• Alarm algorithm can use response trained pattern to identify individual threat
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 200 400 600 800 1000 1200 1400 1600
Time [sec]
Valu
e
Gas OnFiber 1 SignalFiber 2 SignalFiber 3 SignalFiber 4 Signal
Test exposure: Response of all fibers in cable to HCN and Cl2—Signal wavelength only
• Broad-spectrum fiber provides instantaneous warning
• Response from all fibers to exposure event provides unique “fingerprint”
• Alarm algorithm can use response trained pattern to identify individual threat
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 200 400 600 800 1000 1200 1400 1600 1800
Time [sec]
Valu
e
Gas OnFiber 1 SignalFiber 2 SignalFiber 3 SignalFiber 4 Signal
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 200 400 600 800 1000 1200
Time [sec]
Valu
e
Gas OnFiber 1 SignalFiber 2 SignalFiber 3 SignalFiber 4 Signal
HCN Cl2
DICAST® Rapid Alarm Optoelectronics
• Proprietary system architecture
• Proprietary circuit designs
• Commercial off-the-shelf components
0 10 20 30 40
trans
mis
sion
(cou
nts)
365
370
375
380
385
390
Reference Signal: 805 nmRaw Sensor Signal: 580 nm
Time (min)
0 10 20 30 40
trans
mis
sion
(cou
nts)
370
375
380
385
390
395
Compensated Signal
0.0 % CO2
0.5% CO2
1.0% CO2
3.0% CO2
6.0% CO2
Wavelengths far from the absorbance of the indicator dye are unaffected or minimally affected by the presence of the analyte, which enables the system to be self-referenced
Sensor Signal Compensation
Zone-by-Zone Deployment
• Sensor cable • Parallel sensor fiber loops
• Fed by commercial fiber
• Continuous coverage
• Can be “diced out” as short sensor cable sections joined by long conventional cable sections
• Readout • One channel per segment
• Zones monitored in real time
• Alarm triggered upon change in λ1 intensity without change in λ2
1.25 dB/m 20 meters (x4)
0 dBm
-10 dBm -35 dBm 316 nW (x4)
Silicon PIN
DICAST® System HCN Response County Regional Airport, Nov. 29, 2006
Position-Resolved DICAST®
Visible OTDR
• Principle: time-of-flight determines location sensed
• System provides user with plot of chemical concentration versus location
Position-Resolved Deployment
• Sensor cable • Single-ended sensor segments • Fed by commercial fiber • Continuous coverage • “Diced” into discontinuous segments
• Readout • Entire cable read”in real time • Optical absorbance plotted as a
function of length • Self-referenced: use of two
wavelengths minimizes false alarms • Chemical incursion localized within 10
cm
Before Exposure
4 m Exposed to Chlorine
DICAST® Applications • Environmental Monitoring
• Carbon dioxide sequestration reservoir integrity
• Groundwater contamination by halogenated hydrocarbons
• Critical Asset Protection • High-value buildings (airports, rail stations, subways, containers…)
• Transportation assets (Airplanes, trains)
• Industrial Monitoring • Pipeline leaks
• Fugitive emissions
• First Response to Chemical Events • Site characterization: Serpentine deployment over entire suspected area
• Containment verification: “Tripwire” perimeter around contaminated area
• Corrosion Monitoring • Moisture/humidity
• pH/corrosion byproducts
DICAST® Sensor Cables
• Analyte-permeable sheath • Lets ambient chemicals in to
react with fibers • Provides rugged protection
against shear stress
• Multi-fiber “core” • Grooves allow air unimpeded
access • Embedded stiffening member
adds ruggedness
DICAST® Beta Sites
DICAST® Field Deployments – 2005 - 2008
TC&C Dev3
0
0.5
1
1.5
2
2.5
3
1300 1400 1500 1600 1700 1800 1900 2000 2100
Time (Sec)
DC (V
olts
)
ExtPD2DCExtPD1DCSignal2DCSignal1DCExtPD4DCExtPD3DCSignal4DCSignal3DC
DICAST Sensor Fiber Exposure at Beta Test Site (25 PPM H2S)
Gas Flow Initiated
Controlled-Release CO2 Field Trials: 2013
CO2 Injection Well
CO2 Sensor Cable Wells
Sampling Wells
TEST PROTOCOL: Controlled release of
CO2 into ground “Grabbed sample”
measurements of CO2 transported 20m through soil
Continuous
recording of response of DICAST sensor fibers installed between release and sampling wells
Preliminary Field Trial Results
Time (hours)
0 50 100 150 200 250 300
CO
2 sat
urat
ion
(%)
0
20
40
60
80
100
120Pure CO2 is injected in the aquifer
DICAST® Sensor Fiber Response to Injected CO2 – Single-zone readout –
Submicron to Supra-Kilometer
Dye-doped polymer sensing site
Optical Waveguide Sensors are Here!