Digital optical fiber point sensor for high-temperature measurement

The development and performance of a high-temperature optical fiber point sensor based on fluorescence decay time of a chromium-doped material are reported. The device exploits a novel digital signal processing scheme for decay time measurement. It is based on a modified phase-sensitive-detection technique with the phase locked to a fixed value and the modulation frequency tracking the measured decay time. The sensor was calibrated in the temperature range from -25 to 500°C with a 0.1°C resolution. Remarkable features are the system immunity to fluorescent intensity losses and the long-term stability, showing a maximum drift of 0.3°C over more than 600 h