Compact optical oxygen sensors with self-calibration capabilities are undergoing development. A sensor of this type features a single-chip, integrated-optic design implemented by photolithographic fabrication of optical waveguides in a photosensitive porous glass. The porosity serves as both a matrix for retention of an oxygensensitive fluorescent indicator chemical and a medium for diffusion of oxygen to the chemical from the ambient air to be monitored. Each sensor includes at least one such waveguide exposed to the atmosphere and at least one covered with metal for isolation from the atmosphere. The covered one serves as a reference channel. In operation, the concentration of oxygen is deduced from the intensity and lifetime of the fluorescence in the exposed channel, with the help of calibration data acquired via the reference channel. Because the sensory chemical is placed directly in and throughout the cross section of the light path, approximately 99 percent of the light in the waveguide is available for interaction with the chemical, in contradistinction to only about 1 percent of the light in an optical sensor that utilizes evanescentwave coupling. Hence, a sensor of this type is significantly more sensitive.

This work was done by Edgar A. Mendoza and Robert A. Lieberman of Physical Optics Corp. and Intelligent Optical Systems, Inc. for Johnson Space Center. For further information, contact:

Physical Optics Corp.
20600 Gramercy Place, Building 100
Torrance CA 90501-1821
Telephone No.: (310) 320-3088

Refer to MSC-23085

NASA Tech Briefs Magazine

This article first appeared in the July, 2004 issue of NASA Tech Briefs Magazine.

Read more articles from the archives here.