The optical fiber Thermometers is based on the creatin-on of an ideal radiator that is optically coupled to a fiber-optic transmission system (12,13) , as shown in 8.32 The temperature sensor in this system is a thin, single-cryal aluminum oxide (sapphire) fiber; a metallic coating on the tip of the fiber forms a blackbody radiating cavity, which raniates directly along the sapphire crystal fiber. The single-crystal sapphire fiber is necessary because of the high-temparatuer operation of the thermometer. The operating range of thermometer is 300 to 1900c. Signal transmission is accomplished using standard, low-tempature fiber optics. A specific wavelength band of thetransmittsd radistion is detected and measured, and these raw data are reduced to yield the temperature of the blackbody sensor.