The term "optical nose" refers to a fiber-optic chemical sensor of a type that has been proposed to enable distributed measurement of the concentrations of volatile compounds. Optical noses should not be confused with electronic noses, which are single-point sensors based on chemical-induced variations of the electrical resistances of carbon-black/polymer composite films. Optical noses could enable rapid measurement of gas mixtures (e.g., volatile compounds in air) at multiple sensing locations along their lengths, which could be of the order of kilometers. Optical noses could function well in locations where audio- and radio-frequency electromagnetic interference renders electronic noses ineffective. Moreover, it may be easier to fabricate optical noses than to fabricate electronic noses because it would not be necessary to handle carbon black.

Volatile Compounds in the Air would give rise to local variations in the index of refraction at sensing locations along an optical fiber. The locations and magnitudes of these variations would be measured by use of optical time-domain reflectometry.
An optical nose (see figure) would include a commercially available hand-held optical time-domain reflectometer (OTDR) and a fiber-optic transducer, which would typically be prepared as follows: An optical fiber would be coated with a polymer that swells when it absorbs a volatile compound. The outer surface of the polymer would be coated with a gas-impermeable film. At designated sensing locations along the optical fiber, the impermeable film would be removed in patterns to form half-circumference, millimeter-wide notches through which gases could enter the polymer.

The absorption of one or more volatile compounds through the notch at a given sensing location would give rise to asymmetric swelling of the polymer; the asymmetric swelling would engender shear stress which, in turn, would cause local variation in the index of refraction of the fiber. (Optionally, the notches could extend the full circumference, in which case the swelling and the resulting shear-stress pattern would be symmetric. However, the asymmetric configuration is preferred because the shear stress and the associated change in the index of refraction would be greater.)

The OTDR would launch picosecond laser pulses into the optical fiber at one end. The index-of-refraction variations associated with the presence of volatile compounds at the notches would cause part of the incident laser light to be reflected. The OTDR would make time-resolved measurements of the intensity of the reflected laser light. For a given reflected pulse, the location of the corresponding sensing notch could be inferred from the measured round-trip pulse travel time.

It should be possible to construct arrays of optical noses for discrimination among different volatile compounds. Each fiber-optic transducer in such an array would be coated with a different polymer, which would be chosen so that the index-of-refraction response of this transducer to different volatile compounds of interest would differ from the corresponding responses of the other transducers. For automated or semiautomated operation, the readouts of all the transducers in the array could be digitized, then processed by principal-component-analysis and pattern-recognition algorithms to discriminate the volatile compounds of interest.

This work was done by Adrian Ponce and Dmitri Kossakovski of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp  under the Physical Sciences category.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to

Technology Reporting Office
JPL
Mail Stop 249-103
4800 Oak Grove Drive
Pasadena, CA 91109
(818) 354-2240

Refer to NPO-21105, volume and number of this NASA Tech Briefs issue, and the page number.

Topics:
Chemicals Fabrication Fiber optics Fibers Gases Lasers Manufacturing processes Optics Physical Sciences Polymers Sensors and actuators
This Brief includes a Technical Support Package (TSP).
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Fiber-Optic Transducers for Distributed Sensing of Volatiles: An Optical Nose

(reference NPO-21105) is currently available for download from the TSP library.

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    NASA Tech Briefs Magazine

    This article first appeared in the June, 2001 issue of NASA Tech Briefs Magazine (Vol. 25 No. 6).

    Read more articles from the archives here.

    Overview

    The document is a technical support package prepared under the sponsorship of the National Aeronautics and Space Administration (NASA) and focuses on the development of fiber-optic transducers for distributed sensing of volatiles, referred to as "An Optical Nose." Authored by inventors Adrian Ponce and Dmitri A Kossakovski, the report is part of the NASA Tech Brief, Vol. 25, No. 6, dated June 1, 2001, and is associated with the Jet Propulsion Laboratory (JPL) at the California Institute of Technology.

    The primary objective of this technology is to create a distributed sensor capable of monitoring volatile chemicals in the atmosphere with high spatial resolution. This capability is crucial for applications that require the detection of gas mixtures over large areas, where traditional sensors may be limited in effectiveness. The document outlines the solution provided by the optical nose, emphasizing its potential to enhance environmental monitoring, safety, and various scientific applications.

    The report includes a detailed description and explanation of the technology, highlighting its innovative approach to sensing. The use of fiber-optic transducers allows for the detection of chemical compounds with improved sensitivity and accuracy. This technology could be particularly beneficial in fields such as environmental science, industrial safety, and even space exploration, where precise measurements of atmospheric conditions are essential.

    Additionally, the document includes a notice stating that the information contained within is not guaranteed to be free from privately owned rights and does not imply any endorsement of specific commercial products or services by the U.S. Government or JPL. It emphasizes that the work was conducted under a contract with NASA, reinforcing the collaborative nature of the research.

    Overall, the document serves as a comprehensive overview of the advancements in fiber-optic sensing technology, showcasing its potential applications and the innovative work being done at JPL. It highlights the importance of developing new sensing technologies to address the challenges of monitoring volatile compounds in various environments, ultimately contributing to enhanced safety and scientific understanding.