Background-noise reduction in the infrared fiber optic thermometry

Infrared optical fibers have been desired in the remote sensing fields to extend the measurement spectral range. Thermometry is one of those fields in which the use of infrared fibers has been studied most keenly. Although many papers on the fiber optic thermometers have been published, only a few sensors are actually used in industrial or medical measurements. One reason for their low popularity is the measurement error that is caused, for example, by fiber bending or by surrounding temperature change. In particular, thermal emission by the fiber affects the measurement accuracy, since the fiber probe is usually inserted into a warm or hot environment. The change in fiber temperature causes a change in the background thermal emission, leading to sensor signal drift. The drift can be reduced in high-temperature measurements (>200/spl deg/C), since the short-wavelength radiation of the high-temperature object can be separated from the long-wavelength radiation of the low-temperature fiber. However, the surrounding temperature yields a serious effect on the low-temperature measurement (<200/spl deg/C) in which radiation around 10 /spl mu/m wavelength has to be measured. In this work, we used a small, rugged, and heat-resistant infrared modulator to conduct drift-free fiber optic thermometry.