| 摘要 |
PURPOSE:To obtain a sensor which is easily manufactured and has superior characteristics by providing an optical fiber which has a slantingly cut end surface and a specular surface, a photodetector, a laser light source wavelength control part, etc. CONSTITUTION:Light which is emitted by a laser light source 1, passed through a half-mirror 2 and an optical fiber 3, and reflected totally by the end surface 4 cut at an angle close to the critical angle travels backward through the forward traveling path from the specular surface 4a to reach the photodetector 6. Here, the wavelength of the light source 1 is brought under feed-back control so that the mean photodetection level of the detector 6 is invariably constant. Then, a circumferential medium varies in refractive index like a sine wave with an ultrasonic wave 5, so the sine-curve variation in the photodetection level is averaged by a level averaging circuit 21 and compared by a comparator 22 with a reference signal 23 and a control signal 25 from a control signal generator 24 is controlled with the difference to control a current applied to the light source 1, thereby determining its oscillation wavelength. Consequently, variation in scale factor due to the condition change of measurement environment can be suppressed and quantitative measuring operation becomes possible. Further, the manufacture accuracy of the slanting cutting of an optical fiber head part can be relaxed.
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