Invasiveness of an Optical Magnetic Field Probe Consisting of a Loop Antenna Element and an Electro-Optic Crystal

Abstract

When probes are positioned close to a device being tested, the electromagnetic field distribution is inevitably changed to some extent. The change affects the measurement accuracy and the operation of devices. In order to perform magnetic near-field measurement with high accuracy in the GHz frequency range, we are developing an optical magnetic field probe that consists of a loop antenna element and an LiNbO₃ crystal. In this paper, the invasiveness of the optical magnetic field probe was quantitatively evaluated by experiment and FDTD method simulation. The undesired output caused by electric field is substantially suppressed owing to the symmetrical structure of the probe. The disturbance of the surrounding electromagnetic field is reduced by eliminating the metallic cable and consisting of a few metallic elements. The influence on operation of the device is comparatively small when the probe is positioned close to the device. This study indicated that the optical magnetic field probe is less invasive and suitable for an accurate measurement.