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Proceedings Paper

Optically demodulated interferometric sensor system
Author(s): Alan D. Kersey; Michael J. Marrone; Kee Pun Koo; Anthony D. Dandridge
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Paper Abstract

We demonstrate the feasibility of optically demodulating and processing the output produced by an interferometric fiber sensor. A technique for providing the time filtering of an optical signal in the optical domain based on the use of a doped fiber section is reported. Optical processing is a field which offers enormous potential for rapid, parallel processing of information, and is an area which will continue to experience significant growth over the coming years. Optical sensors have a natural inherent compatibility with this form of processing, which could be utilized to great advantage for processesing the data from large arrays of sensors. Many forms of fiber optic sensor, however, produce an optical output which does not vary in a uniform fashion with the measurand field, and consequently require a linearization circuit. or 'demodulator' to provide a linear transfer function before a signal could be converted back to the optical domain and operated on by an optical processor. This is particularly true with interferometric fiber sensors which exhibit a cosine squared transfer function. To demodulate this form of output, a range of demodulation schemes have been developed, such as active phase tracking homodyne [1], phase generated carrier (PGC) passive homodyne [2], and synthetic heterodyne [3J. These techniques allow the detection of measurand-induced phase shifts down to the irad/'JHz level over a wide range of frequencies with high linearity and wide dynamic range. Certain forms of interferometric sensors designed for low frequency measurands, such as magnetometers and electhc field sensors, require the additional demodulation of a 'dither' induced phase carrier signal which is modulated by the DC and low frequency measurand information. In such systems, the overall demodulation process requires several electronic processing blocks after photodetection of the interferometer signal. In applications where arrays of such sensors are of interest, a significant amount of electronics may be required to fully demodulate the sensor outputs. We have examined the practicality of using optical techniques to perform much of the demodulation process, and in this paper demonstrate the feasibility of this concept.

Paper Details

Date Published: 14 September 1994
PDF: 4 pages
Proc. SPIE 2360, Tenth International Conference on Optical Fibre Sensors, (14 September 1994); doi: 10.1117/12.185070
Show Author Affiliations
Alan D. Kersey, Naval Research Lab. (United States)
Michael J. Marrone, Naval Research Lab. (United States)
Kee Pun Koo, Naval Research Lab. (United States)
Anthony D. Dandridge, Naval Research Lab. (United States)

Published in SPIE Proceedings Vol. 2360:
Tenth International Conference on Optical Fibre Sensors
Brian Culshaw; Julian D. C. Jones, Editor(s)

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