VOLTAGE SENSOR

PURPOSE:To obtain a voltage sensor which is superior in safety and maintenance and measures a variance of voltage with a high precision, by forming the cavity layer of a band-pass filter consisting of optical multilayered films with materials which has a high element sensitivity to voltage such as a PLZT or the like. CONSTITUTION:A cavity layer 2 of the band-pass filter consisting of optical multilayered films has lambda/2 thickness, and TiO2 layers H1-H6 and SiO2 layers L1-L4 have lambda/4 thickness. The cavity layer 2 is formed with a material having a high element sensitivity to voltage, for example, a material such as a PLZT where variance of reflective index due to electric field is large. Meanwhile, the light from a light source 5 is made incident on this voltage sensor 1 through an optical fiber 7 and a lens 9, and the light emitted from the voltage sensor 1 is made incident on a photodetector 6 through a lens 10 and an optical fiber 8. At this time, since the refractive index of the cavity layer 2 of the voltage sensor 1 is changed by an electric field and the transmission loss is changed in accordance with this change when the voltage of a high-voltage transmission line 3 is changed, this change of the transmission loss is detected by a photodetector 6.