US 7,263,246 B1Granted

Oxygen detection using evanescent fields

AssigneeUnited States of America Department of Energy

InventorsYixiang Duan, Weenqing Cao

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Abstract

An apparatus and method for the detection of oxygen using optical fiber based evanescent light absorption. Methylene blue was immobilized using a sol-gel process on a portion of the exterior surface of an optical fiber for which the cladding has been removed, thereby forming an optical oxygen sensor. When light is directed through the optical fiber, transmitted light intensity varies as a result of changes in the absorption of evanescent light by the methylene blue in response to the oxygen concentration to which the sensor is exposed. The sensor was found to have a linear response to oxygen concentration on a semi-logarithmic scale within the oxygen concentration range between 0.6% and 20.9%, a response time and a recovery time of about 3 s, ant to exhibit good reversibility and repeatability. An increase in temperature from 21° C. to 35° C. does not affect the net absorption of the sensor.

Claims20

Dependent claims

An apparatus for detecting gaseous oxygen comprising in combination:

(a) an optical fiber having an exterior cladding, a first end and a second end, a portion of the cladding between the first end and the second end being removed from said optical fiber;
(b) a coating disposed on the portion of the surface of said optical fiber for which the cladding has been removed, said coating comprising methylene blue, whereby said methylene blue supports an intensity of evanescent radiation from said optical fiber responsive to the level of oxidation of said methylene blue;
(c) means for exposing said coating to a gas containing said gaseous oxygen;
(d) a light source for generating wavelengths of light in part absorbed by said methylene blue in accordance with the level of oxidation thereof;
(e) means for directing the selected wavelengths of light into the first end of said optical fiber;
and
(f) means for detecting the intensity of selected wavelengths of light exiting the second end of said optical fiber;
and
(g) means for analyzing the intensity of the selected wavelengths of light detected to determine the change in intensity of the evanescent radiation which is dependent upon the concentration of exposed gaseous oxygen.

6 more elements

Dependencies are inferred from the claim text.