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Tunable fiber ring laser absorption spectroscopic sensors for gas detection
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Paper Abstract

Fiber-optic gas sensing techniques are commonly based on the recognition of a wide range of chemical species from characteristic absorption, fluorescence or Raman-scattering spectra signatures. By tuning over the vibrational lines of species in the path of laser beam, tunable diode laser gas sensors measure signal spectroscopic intensity, gas concentration, and other properties. However, they have limitations of bulk architecture, small change of signal on top of large background, and low sensitivity of direct absorption. Here we report the fabrication and optical measurements of tunable Er-doped fiber ring laser absorption spectroscopic sensor featuring a gas cell that is a segment of photonic crystal fiber (PCF) with a long-period grating (LPG) inscribed. The tunable laser beam is coupled into the cladding of the PCF by the LPG where the gas in air holes absorbs light. The light travels along the PCF cladding and reflects at the end of the fiber where a silver film is coated as a mirror at one end facet. The light propagates back within cladding and passes through the gas one more time thus increasing the interaction length. This light is finally recoupled into the fiber core for intensity measurement. The proposed fiber gas sensors have been experimentally used for ammonia (NH3) concentration detection. They show excellent sensitivity and selectivity, and are minimally affected by temperature and/or humidity changes. The sensors using PCF-LPG gas cell are simple to fabricate, cost-effective, and are deployed for a variety of applications not possible using conventional optical fibers.

Paper Details

Date Published: 19 April 2013
PDF: 9 pages
Proc. SPIE 8692, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2013, 869213 (19 April 2013); doi: 10.1117/12.2001325
Show Author Affiliations
Shijie Zheng, Northwestern Univ. (United States)
Yinian Zhu, Northwestern Univ. (United States)
Sridhar Krishnaswamy, Northwestern Univ. (United States)

Published in SPIE Proceedings Vol. 8692:
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2013
Jerome Peter Lynch; Chung-Bang Yun; Kon-Well Wang, Editor(s)

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