In this paper we review recent design methodologies for fully dielectric electro-optic sensors that have applications in non-destructive evaluation (NDE) of devices and materials that radiate, guide, or otherwise may be impacted by microwave fields. In many practical NDE situations, fiber-coupled-sensor configurations are preferred due to their advantages over free-space bulk sensors in terms of optical alignment, spatial resolution, and especially, a low degree of field invasiveness. We propose and review five distinct types of fiber-coupled electro-optic sensor probes. The design guidelines for each probe type and their performances in absolute electric-field measurements are compared and summarized.

In this paper, we first demonstrate a metasurface that offers spectral filter performances not yet reported for a single-layer metasurface because of the limited number of geometric parameters. The configuration of the metasurface is determined by a conformational space annealing algorithm, which is a key toward being able to design for a desired frequency, bandwidth, and response type for various wireless communication devices, including the fifth-generation (5G) millimeter-wave communication devices. As a proof-of-concept, we fabricate a very thin (50 μm) single-layer metasurface combined with a 5G antenna array to experimentally demonstrate high frequency-selectivity with stable frequency responses with oblique incidences and polarizations. The gain of the 4 × 4 patch antenna array with the metasurface bandpass filter was reduced by only 0.48 dB compared with that of the 4 × 4 patch antenna array itself at 27.5 GHz, whereas the gain of the 4 × 4 patch antenna array with the metasurface bandstop was reduced by 20 dB compared with that of the 4 × 4 patch antenna array itself at 28.5 GHz.

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Enhancements of the modulation depth in an electro-optic sensing application, through optimization of the modulation sidebands in both an electro-optic modulator and a microcavity electro-optic probe, have been investigated. The principles and methods of optimizing the operational bias points for the devices are described from the point of view of both an electro-optic modulator and probe, and their different optimum characteristics for signal-modulation depth, due to their huge scale gap, are presented. We use an optical-heterodyne receiver employing a fast modulator along with the electro-optic sensing technique to achieve high-frequency microwave electric field mapping. The practical limitations to sensitivity enhancement, solutions for compensating distortion, and combined optimization conditions for both electro-optic modulation and sensing are presented by exploring the evolution of field-mapping distributions.

An integrated electro-optic (EO) sensor and its dedicated control system for intense electromagnetic pulse measurements are designed and implemented. The sensor performance, specifically the sensitivity, dynamic range, linearity, and bandwidth, is evaluated. For optimal measurements of intense electromagnetic pulses representing an electronic threat, a technique to optimize the sensitivity of the integrated EO sensors is presented. The sensors measure pulses with rise time of 2–3 ns and duration of 23–26 ns, and electric field strength up to 50 kV/m, thus meeting the requirement of MIL-STD-461G RS105 radiated susceptibility test for transient electromagnetic field such as nuclear electromagnetic pulses.

Visualizing the electromagnetic field transformation inside a microwave mode conversion region has been considered to be only realizable by simulation studies. For the first time, we present a comprehensive experimental observation of the electric field transformation occurring inside a metallic waveguide TE₀₁-to-TE₀₂ mode converter. An efficient electro-optic (EO) probe and its associated probing system were used for measuring the electric field pattern in the external near-field region as well as in the internal and penetrated region of the mode converter. Utilizing the optically measured field patterns at the aperture of the mode converter, the conversion performance from the TE₀₁ mode to the TE₀₂ mode can be also evaluated. Experimentally measured field patterns near the apertures show excellent agreement with simulation data. The mode conversion to the next higher-order mode (TE₀₁ to TE₀₂) was experimentally demonstrated with phase-stabilized and field-animated post processing. The presented in situ endoscopic photonic measurement technique for the field evolution inside a semi-enclosed structure could be used for visually inspecting manufacturing errors in fabricated structures, and could be of great interest for research on higher-order mode formation and transmission.