JPS57194324A - Optical temperature measuring device - Google Patents

Abstract

PURPOSE:To eliminate the need for optical coupling while reducing the size of constitution, and to achieve high-precision temperature measurement stable with time by using a reflection type optical fiber probe sensor, and then taking the advantage that an optical fiber has a small diameter. CONSTITUTION:The end part 5 of an optical fiber 10 is arranged in an atmosphere of measurement. The end part 5 is coated as a cladding layer 3 with a transparent dielectric 3 which varies in refractive index with temperature. Light is guided into the optical fiber 10 through a beam splitter 13 and a lens 14, and then returned after being reflected by a reflective layer 4. Emitted light is guided to a photodetector 12, wherein the photodetecting element and detecting circuit detect the quantity of the light. Since the refractive index of the cladding layer 3 varies with temperature, the critical angle of total reflection at the end part 5 varies and the transmission loss of the light varies with temperature while the light goes to and returns from the end part. For this purpose, the relation between temperature and the photodetected quantity of light is found previously, so that the temperature is measured by measuring the photodetected quantity of light.