EO Sensing for 5G Antenna Characterization

Electro-optic (EO) sensing is a mature technique where visualization of electromagnetic waves must be minimally invasive. The fully dielectric nature of EO materials associated with photonics provides numerous advantages over conventional electrical methods. EO probes can measure fast electric fields up to the terahertz frequency associated with ultrafast optical sources. The probes measure extreme levels of an intense electric field up to the MV/m scale without damage or saturation. They can also be implemented with a ceramic ferrule pigtailed with polyimide optical fibers so as to take measurements even in boiling oil. Such robustness of these probes against high power and temperature levels can facilitate field measurements in harsh environments with, for instance, plasma or electrostatic discharges. The probes can be miniaturized on the optical-fiber scale, thus allowing extremely fine resolutions down to the mode-field diameter of a fiber. Among these unique features of EO probes, low invasiveness is the most distinguished merit for microwave sensing. In this chapter, we present a minimally invasive EO probing system that is specialized for millimeter-wave 5G antenna measurements. Two types of EO probes are presented, as well as a commercial-grade control unit. Practical techniques to enhance the stability of the field measurement system and the visualization of the measurement are also discussed. Finally, visualized electric field images of horn, open-ended waveguide, and phased array antennas operating on the millimeter-wave frequency for 5G communication are presented.