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Excerpt from: Kuang-An Chang, Ho-Joon Lim and Chin B Su, “A fibre optic Fresnel ratio meter for
measurements of solute concentration and refractive index change in fluids”, Meas. Sci. Technol. 13
(2002) 1962–1965.
Here, we introduce a new normalization technique that greatly enhances resolution when applied to
conventional fibre optic reflectometry that is based on Fresnel reflection from the fibre tip. The
overall technique provides accuracy, simplicity, near non-invasiveness because of the small
dimension of the optical fibre, high spatial resolution of less than 10 µm and almost unlimited
temporal resolution.
Figure 1. The experimental setup for concentrationmeasurement. The light source is a 1.3 µm wavelength
multi-longitudinal diode laser.
Figure 2. Two typical pairs of reflectance pulses from the fluid–fibre and air–fibre interfaces for 0 and 3%
salt concentrations.
O-SING Issue 3 Page 9 of 12 AUGUST 26, 2004
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