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Proceedings Paper

Real-time simultaneous temperature and strain measurements at cryogenic temperatures in an optical fiber
Author(s): Scott Mahar; Jihong Geng; Joel Schultz; Joseph Minervini; Shibin Jiang; Peter Titus; Makoto Takayasu; Chen-yu Gung; Wenyan Tian; Arturo Chavez-Pirson
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Paper Abstract

A novel fiber optic sensor has been developed to be used in superconducting magnets for fusion reactors and other large cable-in-conduit superconductor (CICC) magnet applications. These large superconducting magnets need a diagnostic that can measure the temperature and strain throughout the magnet in real-time, which was not possible until now. Simultaneous temperature and strain measurements at cryogenic temperatures have been demonstrated, using spontaneous Brillouin scattering in an optical fiber. Using an extremely narrow (100 Hz) linewidth Brillouin laser with very low noise as a frequency shifted local oscillator, the frequency shift of spontaneous Brillouin scattered light was measured using heterodyne detection. A pulsed laser was used to probe the fiber using Optical Time Domain Reflectometry (OTDR) to determine spatial resolution. The spontaneous Brillouin frequency shift and linewidth as a function of temperature agree with previous literature on stimulated Brillouin scattering data from room temperature down to 4 K. For the first time, the spontaneous Brillouin frequency shift, linewidth, and intensity as a function of strain have been measured down to 4 K. Analyzing the frequency spectrum of the scattered light after an FFT gives the Brillouin frequency shift, linewidth, and intensity of the scattered light. 65,000 pulses, with 53 ns pulse widths, were averaged in under one second, providing a 5 meter spatial resolution along a fiber that was about 100 m long. Measuring these three parameters allow the simultaneous determination of temperature and strain in real-time throughout a fiber with a spatial resolution on the order of several meters.

Paper Details

Date Published: 25 August 2008
PDF: 12 pages
Proc. SPIE 7087, Remote Sensing System Engineering, 70870I (25 August 2008); doi: 10.1117/12.791913
Show Author Affiliations
Scott Mahar, Massachusetts Institute of Technology (United States)
Jihong Geng, NP Photonics (United States)
Joel Schultz, Massachusetts Institute of Technology (United States)
Joseph Minervini, Massachusetts Institute of Technology (United States)
Shibin Jiang, NP Photonics (United States)
Peter Titus, Massachusetts Institute of Technology (United States)
Makoto Takayasu, Massachusetts Institute of Technology (United States)
Chen-yu Gung, Massachusetts Institute of Technology (United States)
Wenyan Tian, NP Photonics (United States)
Arturo Chavez-Pirson, NP Photonics (United States)


Published in SPIE Proceedings Vol. 7087:
Remote Sensing System Engineering
Philip E. Ardanuy; Jeffery J. Puschell, Editor(s)

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