Parasitic direct currents in our alternating-current power grid affect the operation of power transformers. In this work, we present a fiber-optic current sensor system designed for the long-term monitoring of such direct currents, especially those arising from solar activity. The sensor demonstrator allows remote data access and sensor operation and was deployed at an electrical substation. For the first time, we show measurements of such currents on single phases of the power grid.

We present an automated, contactless method to map thin film thickness and stress across microelectromechanical systems (MEMS) wafers. Using white light interferometry on cantilevers and step profiles, we extract both mean and gradient stress with orientation sensitivity. Applied to six thin films, the approach reveals process-dependent variations, offering a reliable tool for evaluating and comparing MEMS materials and fabrication methods.