The optical fiber thermometer is based on the creation of an ideal radiator that is optically coupled to
a fiber-optic transmission system (12, 13), as shown in Figure 8.32. The temperature sensor in this
system is a thin, single-crystal aluminum oxide (sapphire) fiber; a metallic coating on the tip of
the fiber forms a blackbody radiating cavity, which radiates directly along the sapphire crystal fiber.
The single-crystal sapphire fiber is necessary because of the high-temperature operation of the