Investigation on Basic Characteristics of Optical Current Transducer Applying Optical Heterodyning Technique

Abstract

In this paper, the possibility of optical current transducers applying the optical heterodyning method is investigated. From results of experiments, the following advantages were confirmed regarding the characteristics of the current detection system using the method. [A]: Stability to signal level changes. [B]: Wide dynamic range of measurement.
However, in the experiments, it was also found that measurement errors appear due to cross-talk between the polarization components of the dual frequency light used. Study was conducted on countermeasures in case of generation of cross-talk at light insertion to polarization maintaining fiber for transmission. From the study, it became known that it is effective to make the state of incident light linearly and orthogonally polarized.
It was also observed that modulation depths of the beat signals change as time elapses. By experiments and analysis, it became clear that the undesirable phenomenon is related to the coherence of light. As a countermeasure, compensating the optical path length difference between normal polarization modes of the polarization maintaining fiber was proposed. Effect of the method was confirmed experimentally.