IV. CONCLUSIONS We evaluated the frequency response of our optical-fibermounted electric-field probe at frequencies from 20 kHz to 180 GHz. The frequency response is flat within a 6-dB range at frequencies from 100 kHz to 10 GHz except for the frequency response due to the piezo-electric effect and the sensitivity increases at frequencies higher than 20 GHz. In the calculation, the electric field at the center of the CdTe crystal increased because of the RF resonance inside the crystal at frequencies higher than 100 GHz. Reducing the crystal thickness should shift the resonance to a higher frequency and thereby improve the flat frequency response. The resonance frequency of 300 GHz corresponds to crystal thickness of around 0.2 mm, which decreases the sensitivity to a fifth. The organic crystal, 4dimethylamino-N-methyl-4-stilbazollium tosylate (DAST), is promising for overcoming these drawbacks because of its high EO coefficient and low permittivity [15]. In transient electrostatic discharge measurements, electric-field mapping, and near-field antenna measuremnets, the optical electric-field probe provides the useful information for the deterioration diagnosis and the lifetime prognosis of electric circuits, devices, and antennas. These applications of the optical electric-field probe are regarded as promising ways for sowing the seeds of
evolution in electric-field measurements for antenna measurement, EMC, and EMI.