Distributed Chemical Sensing Utilising Evanescent Wave Interactions

Kvasnik, Frank; McGrath, A. D.

doi:10.1117/12.963175

Cited by 21 publications

(12 citation statements)

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“…The studies presented here were carried out with the goal of identifying the experimental conditions that allow for the read out of large sensor arrays. Compared to a one-ber scheme, 7,8 the two-ber scheme offers considerably more exibility for signal optimization since the parameters of the two bers can be chosen separately and the berjunction geometry can be adjusted.…”

Section: Resultsmentioning

confidence: 99%

“…This problem is overcome by doping the uorophores into the ber cladding where they interact with guided light m odes in the ber core via the evanescent eld. 7,8 Another restriction when applying the OTDR technique to uorescent sensors is the limited spatial reso-lution along the ber that comes about due to the relatively long uorescence lifetimes of the uorophores (on the order of 10 ns, compared to scattering processes that occur on a picosecond timescale). We have recently shown 9,10 that by introducing a second ber that acts as an optical delay line, the spatial resolution attainable along the original ber can be reduced from the limit imposed by the uorescence lifetime (on the order of meters) to within fractions of a millimeter.…”

Section: Introductionmentioning

confidence: 99%

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Fluorescent Fiber-Optic Sensor Arrays Probed Utilizing Evanescent Fiber-Fiber Coupling

et al. 2001

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Optical-fiber sensors that use fluorescent probes located in the fiber cladding are of great interest for monitoring physical and chemical properties in their environment. The interrogation of a fluorophore with a short laser pulse propagating through the fiber core allows for the measurement of the location of the fluorophore by measuring the time delay between the exciting pulse and the returning fluorescence pulse. The spatial resolution of such an array of fluorescent sensors is limited since a minimum separation of the fluorophores is required to resolve returning light pulses. For many applications a closer spacing of sensor regions is desirable, particularly for fibers prepared by using our recently introduced one-dimensional combinatorial chemistry method [A. W. Schwabacher et al., J. Am. Chem. Soc. 121, 8669 (1999)]. This method allows for efficient preparation of large, diverse, and densely packed linear arrays of sensors. We demonstrate that by using a second fiber as an optical delay line, the minimum spacing between adjacent sensor regions can be well below the fluorescence lifetime limit. Since the coupling between the two fibers is evanescent, the attenuation of the excitation pulse is low, making long arrays of sensor regions feasible. Moreover, we identify the conditions that allow for the optical readout of long arrays of sensors.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Fluorescent Fiber-Optic Sensor Arrays Probed Utilizing Evanescent Fiber-Fiber Coupling

et al. 2001

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“…(the difference occurs as a result of the difference in phase changes between the two polarisations when a ray undergoes total internal reflection). This in turn means, according to equation (2), that the penetration depths of the evanescent fields for the two polarisations will be significantly different as illustrated in Fig.5 where the Th mode has a penetration depth of 154nm while the TM mode has a depth of 196nm for = 1.33Rm. When a contaminant (assumed non-absorbing) layer begins to form on the surface, the two polarisation modes "see" different relative amounts of species and contaminant.…”

Section: Compensation For Contaminationmentioning

confidence: 96%

<title>Improvement in the performance of evanescent wave chemical sensors by special waveguide structures</title>

et al. 1991

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Evanescent wave sensors based on single mode waveguides are attractive but have rather low sensitivities for gaseous species and suffer degradation from surface contaminants. We propose the use of a thin, high-index loading film on a silica waveguide to enhance the field strength at the guide surface and to correct measurements for surface contamination by launching the two polarisation modes. Resonant structures also enhance sensitivities when matched to the absorption characteristics of a gas.

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“…td . (4) For a fiber that is uniformly clad over its entire length with a silicone polymer coating that enriches HC compounds this provides a simple manner for distinguishing between response signals from different fiber zones that contact the HC analyte.…”

Section: Distributed Sensing: Spatial Resolution By Time Resolved Detmentioning

confidence: 99%

<title>Optical fiber sensors for the distributed measurement of hydrocarbons</title>

Buerck

Sensfelder

1999

Chemical, Biochemical, and Environmental Fiber Sensors X

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Truly distributed sensing systems for nonpolar hydrocarbons are described that are built from a chemically sensitive polymer-clad silica fiber adapted to different optical time domain reflectometer (OTDR) setups. OTDR measurements allow to locate and detect chemicals by measuring the time delay between short light pulses entering the fiber and discrete changes in the backscatter signals that are caused by chemical effects in the fiber cladding. The light guiding properties of the fiber are affected by the enrichment of chemicals in the cladding through the evanescent wave. Such arrangements are developed to monitor hydrocarbon leakage from spatially extended technical installations or contaminated areas.Data are presented on the distributed sensing of fluorescent polynuclear aromatic hydrocarbons (PAH) that can be located by combining the fiber with an OTDR setup and a pulsed UV laser light source. This setup allows spatially resolved sensing of PMIs, e.g. fluoranthene, in the low micrograms-per-liter concentration range. However, due to the strong aUenuation ofthe UV excitation light in the fiber, the maximum fiber length is limited to about 100 m. Much longer sensing lengths are possible if OTDR measurements are performed in the near-infrared spectral range. First data on the distributed sensing of chlorinated hydrocarbons (CHCs) with a commercially available mini-OTDR adapted to a sensing fiber of nearly one kilometer length are described. Here, a laser diode emiUing at the 850-nm telecommunication wavelength was applied to locate the CHCs by analyzing the step drop (light loss) in the backscatter signal that is caused by refractive index changes in the silicone cladding induced by analyte enrichment.

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Distributed Chemical Sensing Utilising Evanescent Wave Interactions

Cited by 21 publications

References 0 publications

Fluorescent Fiber-Optic Sensor Arrays Probed Utilizing Evanescent Fiber-Fiber Coupling

Fluorescent Fiber-Optic Sensor Arrays Probed Utilizing Evanescent Fiber-Fiber Coupling

<title>Improvement in the performance of evanescent wave chemical sensors by special waveguide structures</title>

<title>Optical fiber sensors for the distributed measurement of hydrocarbons</title>

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