Magneto-optical sensors

The principle underlying magneto-optics is the Faraday effect. It describes the rotation of the plane of polarization of linearly polarized light passing through a transparent medium subjected to a magnetic stray field parallel to the direction of propagation of the light wave. If the light now passes through a magneto-optical medium to which a magnetic field is applied parallel to the direction of propagation of the light, it splits into two oppositely rotating, circularly polarized waves.

A phase shift now occurs for the two partial waves because they have different refractive indices and propagation velocities. Their frequency stays the same. This shift causes the polarization plane to rotate. When the circularly polarized partial waves emerge, absorption causes the creation of a common elliptically polarized wave. The different angles of rotation as a function of the magnetic field strength result in differences in contrast on the sensor, which can be evaluated optically. This achieves direct real-time visualization of static magnetic fields over the entire sensor area. The micrometer-thin MO layer provides the highest possible lateral resolution, depending on the optical system used.

The MO sensors are already standardly equipped with a mirror and an anti-scratch layer, making direct use in reflection mode possible.