Brian Siller, Ryan Matz, and Helen Waechter Recent Progress in Developing a Commercial Fiber-Loop...
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Brian Siller, Ryan Matz, and Helen Waechter Recent Progress in Developing a Commercial Fiber-Loop Cavity Ring-Down System International Symposium on Molecular
Brian Siller, Ryan Matz, and Helen Waechter Recent Progress in
Developing a Commercial Fiber-Loop Cavity Ring-Down System
International Symposium on Molecular Spectroscopy 2014
Slide 2
Overview Introduction to Tiger Optics CRDS platforms Fiber-loop
CRDS Ideal for Liquids Principles of operation Features and
benefits Target applications Experimental Setups and Results
Sensing element types Sampling systems Conclusions and Outlook
Slide 3
Versatility of CW-CRDS: Major Platforms Mirrors FibersPrisms
Continuous-Wave Cavity Ring-Down Spectroscopy
Slide 4
Fiber-Loop Background Primary inventors circa 2001 Kevin
Lehmann (fiber loop, tapers) Peter Loock (fiber loop, gap in loop)
Markus Sigrist (gold-coated fiber ends as mirrors) Anthony OKeefe
(fiber Bragg gratings as mirrors) Brian Culshaw (fiber amplifier in
fiber loop) Initial applications Chemical, biological sensing
(absorption and refractive index) Strain sensing, temperature
sensing (C.J. Wang)
Slide 5
Fundamentals of Fiber-loop CRDS Optical cavity is fiber loop
Measure ring-down times as with mirror cavities Sensing element
allows light to interact with sample Sensing Elements Couplers
Slide 6
Features and Benefits of Fiber-Loop CRDS Measures very small
volumes of liquid samples (~L) Requires very little space Low cost
of components Handles turbid or absorbing matrices, bubbles, and
particles Withstands harsh environments Temperatures ranging from
-270 to 600C Harsh chemical solutions
Slide 7
Potential Fiber-Loop Applications Cryogenic liquid purity: NSF
Small Business Innovation Research (SBIR) grant Process Monitoring:
Wet-etching solutions and cleaning baths, liquid chemical streams,
micro-reactors Quality Monitoring: Contaminants in chemicals,
composition of mixtures Composition of biomedical and biochemical
samples
Slide 8
Fiber-Loop = Broadband Cavity Limited only by the transparency
range of fiber and fiber components Fiber-loop offers a versatile
platform: Laser at a single wavelength (single analyte) Multiple
lasers at different wavelengths (multiple analytes) Broadband light
source (spectra of complex mixtures)
Slide 9
Fiber-Loop Sensor Element Types Standard fiber Light mostly
confined to the core Small amount of light extends into cladding No
evanescent field outside the cladding Fiber sensing elements
Majority of the light is confined in the fiber core and cladding A
small amount of light extends outside of the fiber Cladding Core n
core > n cladding Tapered Side-polished Core-only
Slide 10
Experimental Setup: Side-polished Fibers Two fiber couplers
(99:1) for coupling light in and out Fiber-loop length: 2km Static
sample monitor or use in flow system Side-polished region
Slide 11
Results: Side-polished Fibers Flow system with fast response
time:
Slide 12
Experimental Setup: Tapers Much more fragile than side-polished
fibers Mounted on ceramic support structures Only used for static
sample measurement Taper Waist Human Hair
Slide 13
Results: Tapers Sensitivity ~0.3% H 2 O in D 2 O Usefulness
limited by fringing Transmission [dB] Wavelength [nm]
Slide 14
Experimental Setup: Core-only Fiber Multimode fiber used for
loop, core diameter = 100 m Sensing element length: 0.1 to 2 meters
Tested both with fiber-loop and single-pass with spectrometer Long
sensing element: potential for very low detection limits, e.g. for
cryogenic liquid contaminants Splice of 100/125 m step-index fiber
to 100 m core-only fiber
Slide 15
Preliminary Results: Core-only Fiber Spectrometer shows ice
absorption peak Very small shift in ring-down time when inserting
sensing element into liquid nitrogen Liquid Nitrogen Air
Spectrometer Signal: Single pass through core-only fiber
Slide 16
Summary Side-polished fiber Sensitivity not as good as tapers
(1% H 2 O in ethanol) Much more robust than tapers Tapers Good
sensitivity (0.3% H 2 O in D 2 O) Fragility and fringing limit
usefulness in commercial system Core-only fiber Longest sensing
elements; potentially highest sensitivity Currently too lossy for
sensitive detection Ideal for cryogenic liquids Optimization
continues for commercial use