Gap-Embedded Patch-Antenna EOM

Since the global data traffic increases every year, capacity enhancement is required for anticipating the large data traffic and bottleneck in the future. It can be solved by using high microwave frequency operation. However, they have large transmission losses in the air. It can be solved by connecting pico/femto cell through optical fiber cables. Thus, broadband wireless communication can be realized by utilizing the radio and optical networks through radio-over-fiber (ROF) technology. In the ROF technology, converters between wireless microwave and lightwave signals are required as the key devices. On of them is the converters from wireless microwave to lightwave signals. It can be composed of an antenna and optical modulator. The challenges in high-frequency microwave operation are microwave losses, substrate resonant mode, precise tuning requirement, and so on. Electro-optic modulators (EOMs) are promising for the conversion with their advantages such as high-speed operation, large bandwidth, and good linearity. Optical modulation through the Pockels effect can be obtained by applying microwave electric fields. This chapter presents and discusses in detail relating gap-embedded patch-antenna EOMs for wireless microwave-lightwave signal conversion. The devices fabricated on an EO crystal consist of patch antennas with narrow gaps at the center and optical waveguides located close to the narrow gaps. Several device structures are presented in this chapter including a gap-embedded patch-antenna EOM, an array of gap-embedded patch-antenna EOM, and meandered gap-embedded patch-antenna EOM. Additionally, performance of the devices for communication and sensing applications are also presented.