Optical Voltage Sensors Based on Integrated Optical Polarization-Rotated Reflection Interferometry

Optical voltage sensors based on reflection interferometry of two orthogonal polarizations have been demonstrated by using a polymeric integrated optic device, in which a thermooptic phase modulator, a polarization converter, and a polarizer are integrated on a single chip. The sensing probe for electric field measurement was prepared by assembling an LiTaO₃ electrooptic crystal along with a polarization maintaining collimator, a Faraday rotator, and a dielectric mirror. Spectral bandwidth of the light source was optimized to be 16.5 nm in order to provide low noise and good extinction ratio in the reflection interferometry. For an applied voltage of 60 Hz, 4 kV_pp, the sensor exhibited linear response with a phase retardation sensitivity of 0.5°/kV.

I. Introduction

Optical voltage sensors (OVSs) offer significant advantages over their electrical counterparts in many aspects, especially in measuring high electric fields. In electrical voltage sensors, oil or gas that is used for insulation leads to the issue of environmental contamination, and their large volume and weight due to the parts made of copper, ceramic, and iron result in difficulty in installation and maintenance [1], [2]. Moreover, the saturation of magnetic susceptibility of the iron core degrades the sensor life time and limits the linear response range, and the thermal heating caused by the surge current can lead to an accidental explosion of the sensor [3]. In contrast, OVSs are immune to the electromagnetic interference which introduces large signal noise in electrical sensors. In optical sensor, the sensing signal is delivered through the optical fiber without any galvanic connection, so that no insulation is required concerning the electrical breakdown. The optical sensor has much wider dynamic range and frequency bandwidth, which enables the measurement of surge current, and has much smaller volume for facilitating the installation and maintenance [4], [5].