Journal
IEEE SENSORS JOURNAL
Volume 11, Issue 5, Pages 1178-1183Publisher
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/JSEN.2010.2087323
Keywords
Fiber-optic sensor; interferometric measurement; lensed-fiber; photonic crystal fiber (PCF); refractive index (RI) measurement; spectral domain interferometry
Funding
- Korean government: (MEST) [R01-2007-000-20821-0]
- NCRC (MEST) [R15-2008-006-02002-0]
- National Research Council of Science & Technology (NST), Republic of Korea [D31200] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
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We report a fiber-optic sensor for measuring the refractive index (RI) of a liquid sample. The sensing probe is constructed from an extrinsic cavity formed by a micromirror and a lensed photonic crystal fiber (PCF) tip. We show that PCF lens with an unconventionally large radius of curvature is bifunctional; an effective reflector as well as a collimator and thus suitable for realizing long single-arm interferometers, with a cavity length of the order of few mm. A sensing head suitable for measuring the refractive index (RI) of liquids is constructed by encapsulating the bifunctional lens tip and a micromirror in a glass tube. A hole is made in the glass-tube to allow free-flow of the liquid sample in-and-out of the cavity. The cavity length was about 1 mm. The group index of the liquid samples is obtained from the Fourier peak position of the interference signal measured in wavelength with optical spectrometer. The RIs of distilled water, acetone and ethanol (at 829 nm, 20 degrees C) were measured to be 1.32822, 1.35416, and 1.35715, respectively. The resolution of the sensor was analytically found to be 2.6 x 10(-5) and the response was experimentally shown to be linear.
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