The performance (bandwidth, sensitivity, and spatial resolution) of a fiber edge magnetooptic (FEMO) probe developed for observing three-dimensional magnetic-field distributions was evaluated. A gigahertz bandwidth was achieved without any magnetic bias by using the magnetization rotation in a magnetooptic crystal. The ferromagnetic resonance restricted the observation bandwidth to around 10 GHz. Precise adjustment of the polarization and efficient use of the optical amplifier enhanced the magnetic field sensitivity, enabling an electric current of less than 0.05 mA to be detected. The concept of"sensitive volume"was used to measure the spatial resolution in three-dimensional space; reducing the sensitive volume improved the spatial resolution. Magnetic fields above a microwave patch antenna and around a 10-µm-class circuit board were observed using FEMO probes. The FEMO probe should thus be effective for evaluating microwave and miniature circuits.
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