Our novel miniature fiber-optic sensor platform capable of simultaneously detecting the amplitude and phase of an EMF in the range of 0.1 – 6 GHz is presented. It is based on an open optical platform to which various antennas can be attached and contains a radio-frequency amplifier for signal conditioning and a vertical-cavity surface-emitting laser as an electro-optic converter. The millimeter size and the full electrical isolation of the sensor allow EMF detection with minimal disturbance. We have characterized the sensor in the near field of a λ / 2 dipole, a rectangular waveguide, and a microstrip line.