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Optical Engineering

Free-space input and output coupling to an embedded fiber optic strain sensor: dual-ended interrogation via transmission
Author(s): Liang Qiu; Keith W. Goossen; Dirk Heider; Daniel J. O'Brien; Eric D. Wetzel
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Paper Abstract

In this paper, we report a novel method of free-space passive optical coupling to completely embedded, transmission-based fiber Bragg grating (FBG) sensors. Fiber optic sensors (FOS's) have attracted intense research and commercial interest. A major challenge in implementing embedded FOS's, however, is improving upon the cumbersome and fragile ingress/egress techniques commonly used for bringing the sensing light into and out of the structures. In this paper, we successfully couple free-space light into and out of an embedded FBG sensor, without the use of physical connectorization. This coupling is enabled by splicing a multimode fiber (MMF) to a single mode fiber Bragg grating (SMFBG), and using hand polishing to integrate 45° mirrors onto the ingress and egress points of the MMF and SMFBG, respectively. We determine the total loss of the system to be 23 dB, which is considerably better than previous studies that did not use this hand polishing technique. We also demonstrate the application of this free-space coupling technique to strain measurement with a maximum strain of about 2000 µ&Vegr;. With this approach, no "pigtailing" of optical fibers is needed, and the FBG sensors can be completely embedded inside the structures, greatly increasing system simplicity and robustness.

Paper Details

Date Published: 1 September 2011
PDF: 15 pages
Opt. Eng. 50(9) 094403 doi: 10.1117/1.3625414
Published in: Optical Engineering Volume 50, Issue 9
Show Author Affiliations
Liang Qiu, Univ. of Delaware (United States)
Keith W. Goossen, Univ. of Delaware (United States)
Dirk Heider, Univ. of Delaware (United States)
Daniel J. O'Brien, U.S. Army Research Lab. (United States)
Eric D. Wetzel, U.S. Army Research Lab. (United States)

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