Direct near-field antenna testing via non-perturbing photonic probe

Discusses a new photonic sensor for the microwave and millimeter-wave range. The probe is a silicon optical microsensor made of an interferometric Fabry-Perot microcavity, directly connected to a fiber optic for remote interrogation. When exposed to an EM field, the power dissipated in the semiconductor-sensing element induces the heating, and in turn, a change of the refractive index of the silicon by thermo-optic effect. This variation induces a modulation of the probing light intensity reflected by the interferometric cavity. The characterization of a nonoptimized prototype in the frequency range 2-18 GHz was carried out, and resolutions going well beyond those characterizing other nonperturbing sensors operating at the same frequency range were measured. A theoretical analysis, giving results in good agreement with experiments, was also carried out, showing the sensor capability to detect signals up to 100 GHz and the possibility of significantly increasing the sensitivity in optimized designs. In the communication, new preliminary results concerning the application of the proposed class of probes to indoor near-field antenna characterization are presented. In particular, the results we report have been carried out with a prototype realized starting from a 280-μm-thick Si wafer