A chromatically addressed optical fibre sensor for non-contact temperature monitoring

A non-contact, optical fibre based temperature probe is described with potential applications in hostile environments where contact between the sensing element and the fibre tips may not be possible nor desirable. This enables the sensor addressing fibres to be located outside the hostile environment so, for instance, removing the need for high temperature tolerant fibres and providing a cost effective sensing solution. The probe is based upon the wavelength shift of the spectral absorption edge of semiconductor materials, the shift being addressed by chromatic modulation methodologies. Relevant aspects of the chromatic modulation methodology and the physical basis of the temperature shift in absorption spectra are briefly reviewed. Theoretical and experimental results for the performance of various differently configured chromatic monitoring systems in conjunction with a temperature sensitive element are described. The use of chromatic monitoring is shown to be advantageous when addressing such broad wavelength modulating sensors yielding a resolution of 0.5%. covering the temperature range 20-250 degrees C, It is also shown that care is needed in choosing appropriate photo diode detectors so that the chromatic system's output is immune to unavoidable thermal hysteresis effects associated with the fibre tips. (C) 1999 Elsevier Science S.A. All rights reserved.