Fiber-optic evanescent-wave methane-gas sensor using optical absorption for the 3392-μm line of a He–Ne laser
Abstract
Gas sensing using evanescent waves of optical fibers is investigated. Methane gas is detected by means of its strong optical absorption of the 3.392-micron line of a He-Ne laser. A single fiber is used as both a sensor and an optical transmission line. The sensor has a small diameter, ranging from 1.8 to 7 microns, made by heating and expanding a part of a step-index silica fiber. An evanescent wave of 5 to 40 percent of the total propagating power is generated outside the fiber. When a sensor fiber of 1.8-micron diameter and 10-mm length is used, the minimum detectable concentration of methane is less than the lowest explosive limit of 5 percent.
- Publication:
-
Optics Letters
- Pub Date:
- June 1987
- DOI:
- 10.1364/OL.12.000437
- Bibcode:
- 1987OptL...12..437T
- Keywords:
-
- Evanescence;
- Fiber Optics;
- Gas Detectors;
- Helium-Neon Lasers;
- Absorption Spectroscopy;
- Methane;
- Molecular Spectra;
- Nondestructive Tests;
- Optical Fibers;
- Transmittance;
- Instrumentation and Photography