Error Induced by the Optical Path of a High Accuracy and High Bandwidth Optical Current Measurement System

Birefringence and optical losses in the optical sensor head of a Faraday effect based, high accuracy and high bandwidth current measurement system lead to changes of the polarisation state and orientation. These changes, if not properly determined and calibrated, lead to systematic measurement errors. Therefore, a calibration method for the optical current measurement system focusing on pulse current applications is proposed. The procedure is based on a zero-current measurement and a full (Stokes) polarimeter. It determines the full polarisation state and orientation of a beam propagating through the optical system. The calibration method then allows to determine the parasitic linear birefringence caused by any subsequent optical element in the system. Eventually, an error analysis characterising the potential error reduction by the proposed calibration method is conducted. Further, the additionally introduced error sources caused by the full polarimeter approach are characterised.