This document defines terminology, structure, and a characteristic test method of an optical current sensor using the polarimetric method. It addresses the current sensing element only and not the additional devices that are unique to each application (see 3.11). Generic specifications for fibre optic sensors are defined in IEC 61757. As the specifications of optical polarimetric fibre current sensors required by each user vary depending on the application, this document does not define the required performance values. The required performance values are defined when designing a sensor according to the specific application.