Microwave Electric-Field Mapping Using Optical-Fiber-Mounted Electro-Optic Probes

A microwave electric-field mapping system based on electro-optic sampling has been developed using micromachined gallium arsenide crystals mounted on gradient-index lenses and single-mode optical fibers. Three orthogonal polarization components of the electric field are distinguished, and two-dimensional field images are obtained by scanning the fiber-based probes in a plane above the device under test. Because the probes are simple dielectrics and require no metal or electrodes to extract the electric field amplitude and phase, they are uniquely useful in the imaging of the aperture-plane region of antennas and arrays, where they provide complete information on radiated, guided, and evanescent waves. Due to the high level of versatility afforded by the optical-fiber coupling, this diagnostic testing can be extended not only to open, guided-wave structures, but also to shielded microwave circuits and packages.