A novel, to our knowledge, sapphire-fiber thermometer ranging from 20 degrees to 1800 degrees C is presented that combines the radiance detection and the fluorescent lifetime detection schemes into one system. The thermal probe is a sapphire fiber grown from the laser-heated pedestal growth method. Its end part is doped with Cr(3+) ion and coated with some radiance material to constitute a minifiber cavity. The sapphire fiber is coupled with a Y-shaped silica fiber bundle for signal transmission. Radiance and fluorescence signal processing schemes are also set up within one thermometer system. A sandwich two-band p-i-n detector is used that may respond to both the radiation and the fluorescence. Preliminary experimental results show that the thermometer is suitable for practical application with potential long-term stability and a high-temperature resolution.

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YAG crystal fibers with end Cr3+ doped have been grown by the laser heated pedestal growth method as the temperature sensor probe using fluorescence decay. The crystal fibers show good optical properties and mechanical strength and offer advantages of compact construction, high performance, and ability to withstand high temperature. The fluorescence characteristics of the Cr3+:YAG crystal fiber probe with temperature were investigated from −20to500°C. The experimental results indicate that Cr3+:YAG crystal fiber shows a monotonic relationship between the fluorescence lifetime and temperature over a wide temperature range. This fiber was found to be an excellent material to be used as fluorescence decay optical fiber temperature sensor.