Measurement of the refractive index of liquids at 1.3 and 1.5 micron using a fibre optic Fresnel ratio meter

A fibre optic technique based on the Fresnel reflection from the fibre tip is used for measurements of the refractive indices of various liquids at wavelengths of 1310 and 1551 nm. Reflection signals from liquid–fibre interface are compared with reflection signals from air–fibre interface to obtain the refractive index. Values of refractive indices for distilled water measured by this technique compare very well with known values at both wavelengths only if the fibre effective waveguide index is used. Applying the double-pulse measurement technique, it is shown that a measurement resolution of about 2.5 × 10 −5 can be achieved.