Characteristics of sapphire fiber connected with ruby sensor head for the fiber-optic thermometer applications

The fiber-optic thermometer probe, in which the sapphire fiber was connected mechanically with the ruby sensor head, has been fabricated and the performances of the probes are evaluated as compared with those using the silica fiber. The value of photoluminescence (PL) lifetime and its temperature coefficients for the ruby sensor head with sapphire fiber (t = 3.9 ms and -9.9 mus/K) were slightly different from those using the silica fiber (tau = 4.2 ms and - 10.9 mus/K), even if the same ruby sensor head was used. These differences are found to be caused by the background PL due to residual impurities and/or defects in the sapphire fibers, which vary with the growth techniques of the fibers. The influence of the PL from the sapphire fiber on the temperature measurements can be reduced successfully using a modified lifetime calculation based on the curve fitting of the PL decay with double exponential equation. By using a modified lifetime calculation, the ruby sensor head with sapphire fiber can be used in the temperature measurement ranging from 270 to 670 K with +/-1.5 K accuracy. (C) 2002 Elsevier Science B.V. All rights reserved.