JPS643548A - Slight differential heat measuring instrument by optical fiber interferometer - Google Patents

Abstract

PURPOSE:To enable temp. measurement with high sensitivity by winding optical fibers respectively on containers contg. a standard material and material to be measured and measuring the phase difference of the two beams of the light past the winding parts. CONSTITUTION:The light radiated from a laser light source 3 enters the optical fiber from a branch 2 and is propagated by being divided to branches 4, 6 via a coupler 1. The light is transmitted through a PZT cylinder 10 and the container 5 contg. the standard material in the branch 4 and is reflected at the front end thereof. A driving voltage of a sinusoidal wave is applied to the electrode of the cylinder 10 to modulate the phase of the light passing the optical fiber. The light is transmitted through the container 7 contg. the material to be measured in the branch 6 and is reflected at the front end. The reflected beams of the light of the branch 4, 6 are projected via a branch 8 to a photodetector 9 by which the beams of the light are subjected to homodyne detection. The AC component of this detected output has the repeating waveform based on the driving frequency of the cylinder 10 and generates the phase change corresponding to the phase difference occurring in the temp. difference between the containers 5 and 7. This phase change is detected by a pseudo heterodyne detection circuit 11. The slight temp. change of about 10<-5> deg.C is thus measured.