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Proceedings Paper

Effect Of Laser Coherence And System Design On FMCW Multiplexed Sensor System Performance
Author(s): Denise M. Francis
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Paper Abstract

United Technologies Research Center (UTRC) has investigated the Frequency-Modulated-Carrier-Wave (FMCW) technique for fiber optic displacement sensors and fiber optic multiplexed networks. There is especial interest in multiplexing techniques such as frequency-division, wavelength-division, and time-division for aerospace and industrial sensing applications. UTRC has looked at a number of these techniques for multiplexing fiber-optic sensors for engine control applications. In particular, UTRC has concentrated on coherent techniques because of the inherent sensitivity and robustness of these methods. In previous work, the FMCW technique was investigated using different lasers in a discrete optic Michelson interfeyometer, in which laser frequency chirp and coherence properties were studied. In an interferometric system, direct modulation of the laser diode with a linear ramp generates an output beat frequency. This beat frequency is proportional to the optical path length difference of the interferometer. Various schemes fo5 multiplexing fiber sensors using the FMCW technique have been suggested. The emphasis has been on increasing the sensor count through understanding the coherence and optical power requirements of the system; and minimizing the effect of cross terms by implementing various architectures and imposing restrictions on the information frequency band to be measured. This paper compares two approaches to the FMCW technique in which the effects of cross terms on the system performance is minimized by taking advantage of laser coherence properties and system design. A fiber-optic linear bus network consisting of three reflective sensors was constructed. The paper presents experimental results and analysis of the FMCW multiplexed system performance.

Paper Details

Date Published: 13 February 1990
PDF: 13 pages
Proc. SPIE 1169, Fiber Optic and Laser Sensors VII, (13 February 1990); doi: 10.1117/12.963028
Show Author Affiliations
Denise M. Francis, United Technologies Research Center (United States)

Published in SPIE Proceedings Vol. 1169:
Fiber Optic and Laser Sensors VII
Ramon P. DePaula; Eric Udd, Editor(s)

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