A series circuit includes a sensor located in the alternating field and a Faraday rotator in a constant magnetic field is used for measuring magnetic fields. The circuit is driven by a reflection arrangement. The temp. dependent offset drift in the Faraday rotator is used for temp. compensation of the measurement signal. Alternatively, the sensor itself generates the offset drift. Linearly polarised light is reflected through the series circuit and travels in the reverse direction. The measurement light is then split into two and converted into electrical intensity signals. The electrical signals include all the frequency components of the variable magnetic field.
