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GARY PICKRELL, ANBO WANG, BRIAN SCOTT, ZHIHAO YU
D E P A R T M E N T O F M A T E R I A L S S C I E N C E & C E N T E R F O R P H O T O N I C S T E C H N O L O G Y
V I R G I N I A T E C H , B L A C K S B U R G , VA 2 4 0 6 1P I C K R E L L @ V T . E D U
Novel Optical Fibers for High Temperature
In-Situ Miniaturized Gas Sensors (DE-FC26-05NT42441)
NETL CrossCutting Review Meeting
Motivation
Gas Species Sensor for harsh environments Coal Gasification products Advanced power generation
Gas species determination Process optimization Process fault/Failure identification
Scope of Work
Scope: The objective of the proposed program is to develop novel
modified fiber-based materials for miniaturized optical sensors for in-situ detection of a wide range of gaseous species at high temperatures and in harsh environments.
Background: Technical Approach
Transmission of light is not 100% Loss from impurities Loss from evanescent field Loss due to direct absorption
The Evanescent field is a portion of the EM field that extends beyond the core/cladding boundary
The interaction between the evanescent field or injected light and a gas provides an absorption spectra
This spectra is specific to the gas
I
RR-CoreR-Core
Evanescent
field
1520 1525 1530 1535 1540 1545 1550 1555 1560 1565 1570-40
-35
-30
-25
-20
-15
-10
Wavelength (nm)
Tran
smis
sion
(dB
)
Sample 550Y 700-50
Transmission in airTransmission with acetylene blow on
Background: Technical Approach
Design is fabricated by A spinodally phase separating
cladding glass Produces a 3-D interconnected
cladding Porosity has a radial
orientation Porosity connects the fiber
surface to the core
core
Radial oriented pores
Porous cladding
Solid core
Background: Porous Glass
Porous glass are made from phase separable glass compositions Article is made desired
shape Article is annealed Annealing induces phase
separation so two interconnected phases are present
One of the phases is removed
Porous skeleton remains with a 3-D interconnected porosity
Background: Prior Work
Two part structure Cladding glass- Porous glass
Core glass- solid borosilicate glass
Hollow core Pore size range
10-30 nm avg. Range tunable 4 nm to 100 nm
Sapphire Photonic Crystal Sapphire bundle based
optical structure
Background: Prior Work
Sensing ~ 1 second response time Stable up 500° C
1520 1525 1530 1535 1540 1545 1550 1555 1560 1565 1570-40
-35
-30
-25
-20
-15
-10
-5
0
WAVELENGTH(nm)
TRA
NS
MIS
SIO
N(d
B)
FIBER TRANSMISSION
1520 1525 1530 1535 1540 1545-32
-31
-30
-29
-28
-27
-26
-25
WAVELENGTH(nm)
TRA
NS
MIS
SIO
N(d
B)
ABSORPTION PEAKS OF ACETYLENE
Lead in Fiber Lead out Fiber
Fiber Stage
Gas outletPorous clad optical fiber
Current Tasks
Sapphire Photonic Crystal Fiber (SPCF) gas sensor Fabrication Sapphire bonding Testing
Porous Glass Optical Fiber Gas Sensor Sensor integration in optical system Transmission Loss reduction Gas sensing sensitivity and resolution characterization Field test prototype
Long wavelength laser system development
Center Gap Sensor
Center gap between highly polished sapphire fibers enables measurement of gas absorption peaks
Center fibers and gap held in place using six surrounding fibers in hexagonal formation
Center Gap Sensor Construction
Sensor is assembled using tapering funnels and platinum wire
Sensor Bonding- Center Gap Design
Bonding colloid is applied to areas outside of the gap area Fired at 1600°C for 12-72 hours to encourage diffusion
bonding
Colloidal particles infiltrate fibers, forming strong bond
Sapphire bundle gas sensor
• Diameter of the outer sapphire fibers is 70µm and center sapphire fiber is 50µm
• Air cavity = 10mm
Sapphire bundle with different gas concentration
3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6
x 104
-1
-0.5
0
0.5
1
1.5
2
2.5
3
Nor
mal
ized
Vol
tage
Gas absorption in sapphire bundle
100%50%25%10%
• Wavelength at 1530.4nm
3.55 3.555 3.56 3.565 3.57 3.575 3.58 3.585 3.59 3.595
x 104
0.55
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
Nor
mal
ized
Vol
tage
Gas absorption in sapphire bundle
100%50%25%10%
New sapphire bundle with FC connector
• Sapphire bundle sensor with (a) FC connectors and (b) splicing points (Both air cavity=1cm)
• Transmitted power of the sapphire bundle with FC connector has two orders of magnitude stronger than one with splicing point
• Sapphire bundle with FC connector has less modal noise
Long Wavelength SystemWhy the mid-infrared?
4 4.1 4.2 4.3 4.40
1
2
3
4x 10‐18
Wavelength (m)
Line
stre
ngth
(cm
2 cm
‐1)
Optical Spectrum of CO2
The mid-infrared, or mid-IR, is a portion of the electromagnetic spectrum spanning wavelengths between 3-15μm
The Long Wavelength System operates between 4-4.42μm
This range falls inside a transparent atmospheric window where light transmits well
This is also where chemical compounds exhibit fundamental vibrational modes
Optical spectrum measurements are used to observe the effects of these modes to both uniquely identify & quantify chemical compounds, e.g. CO2, CO, N2O, SO3
Direct absorption detection technique
Main advantage is simplicity
Light passes through a gas cell that contains the chemical for detection
Light interacts with the chemical as it traverses a porous silica or sapphire waveguide
Light intensity values are recorded for different wavelengths
These values form an absorption spectrum from which the gas is both identifiable chemically and quantifiable in terms of concentration
Laser DetectorGas
Cell WaveguideChemical for Detection
PC
CO25.3%
Signal ProcessingIdentifying and quantifying gases
The detection technique provides an absorption spectrum that appears as multiple dips across a slowly varying background
To understand the significance of these dips requires some signal processing that assigns numbers to their magnitudes & wavelength positions
Mathematical techniques such as correlation are used to relate these numbers to the identity of a specific gas
Measurements of unknown concentrations can be determined by comparison versus data of known concentrations
CO25.3%
Porous Glass Sensor Joining Techniques
Trial methods Fusion Splicing CO2 laser bonding Ceramic adhesive
Trial evaluation Transmission Bond stability
Best method CO2 laser bonding
Before bonding
After Bonding
Porous Glass Sensor
Transmission improvement Gold coating sensor interior Increased boundary
reflection Reduced loss
Nano- Porous Glass capillary tube wall
Sub micron Gold coating layer
Signal Improvement Methods
Gold plating of inner surface of glass prior to leeching.
Porous gold coating obtained on surface.
High variation, so many samples needed to obtain best results.
Plated using commercially available electroless solutions
Alternative Structures
Ordered tube arrays using vycor to obtain Photonic Crystal Fiber Structure.
Tubes stacked from pulled fibers using machined mold
Pulled using mini draw tower.
Very sensitive to heat profile of furnace.
Potential Packaging Design Two
potential designs
Provide protection to the fragile nature of the glass.
Future work
Testing of SPCF gas Optical properties Gas sensing capability
Continuing evaluation of LW system Long wavelength system gas sensing demonstration
Sensitivity measurement of SPCF and porous glass sensors
Construction of porous glass gas sensor prototype Porous glass photonic crystal fiber prototype
Thank you
Questions?
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