Fiber optic components offer a competitive implementation for applications exploiting the millimeter-wave and THz regimes due to their capability for implementing broadband, compact, and cost-effective systems. In this paper, an outline of the latest technology developments and applications of fiber-optic-based technologies for the generation, transmission, and processing of high-frequency radio signals is provided. 1. Introduction Optical fiber is an outstanding transmission medium which revolutionized data communications due to its unique combination of low loss and wide bandwidth [1]. Although originally targeted at long-distance communications, fiber optic technology has been applied to a wide range of fields, among them access networks, data centers, sensing, fiber lasers, illumination, imaging, and so forth. Another important, yet initially unforeseen, application for fiber optic technology was the interaction between optics and microwaves for applications such as radar, communications, warfare systems, and instrumentation. This area has become known as microwave photonics [2–6] and includes the photonic generation and distribution, processing, and monitoring of microwave signals, as well as photonic-assisted analog-to-digital conversion, to cite its main topics. Features such as the low loss and wide bandwidth of fiber optic technology can be exploited to provide functions and capabilities to microwave systems that are very complex or even not implementable when carried out directly in the microwave domain. These advantageous characteristics are especially relevant when high frequency signals are considered given current limitations in the generation, processing, and distribution of millimeter- and submillimeter-wave signals. The millimeter-wave region of the electromagnetic spectrum (Figure 1), also called the extremely high frequency range, (EHF), corresponds to radiofrequencies from 30？GHz to 300？GHz (i.e., wavelengths from 10？mm to 1？mm). The high frequency of the signals in this band as well as their propagation characteristics makes them useful for a variety of applications. However, the difficulty in generating and detecting signals as well as atmospheric attenuation in this band limits current applications. Existing applications include data transmission (high-bit rate wireless access networks), and radar (mainly benefiting from the beam width achievable with small antennas in applications such as short range automotive radars at 77？GHz as well as in scientific, military, security controls, and range and speed measurement for industrial
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