This paper describes the overview of special issue on new high-speed photonic devices and their applications, edited by Prof. Hiroshi Murata at Mie University. The topics of this issue cover high speed electro-optic polymer modulators, antenna-coupled electrode electro-optic modulators for 5G systems, evaluation of radiation resistance of onboard components for future coherent optical satellite communications, optical fiber technologies for future power grid, and radio-over-fiber technologies for mobile communication systems, aircraft surveillance systems, and public infrastructures such as high-speed railway systems.

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Analog radio-over-fiber (A-RoF) technologies, including intermediate frequency-over-fiber (IFoF) schemes, have attracted much attention for future mobile fronthaul (MFH) links because they simplify the equipment deployed in wireless antenna sites and transmit wireless signals on an optical fiber with high spectral efficiency; these advantages will be strongly required in future mobile services. In this paper, we present MFH architecture consisting of broadband and narrowband IFoF links by combining analog and digital signal processing for IF channel extractions and frequency conversions. In addition, we show experimental results that verify the effectiveness of parallel intensity and phase modulators as a broadband IFoF transmitter to compensate the influence of dispersion-induced RF power fading on wireless signals and the above MFH architecture. We also review recent research activities related to A-RoF and IFoF technologies for MFH and 5G mobile services.

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Recent progress of highly efficient and high-speed electro-optic (EO) modulator technology has received intensive research attentions in microwave photonics and fiber-optic networks. In particular, EO polymer modulators open up a variety of opportunities for realizing unique wideband modulation beyond 100 Gbaud signaling. We demonstrate 100 Gbit/s NRZ and 112 Gbit/s PAM4 modulations. The polymer is performed on the silicon waveguide modular toward possible hybrid silicon and polymer photonic platform.

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Seamless convergence between radio and optical fiber networks is indispensable for achieving such advanced radio access schemes as 5th generation (5G) mobile communication systems. Radio-over-fiber (RoF) technology is a promising solution to efficiently convert radio signals into optical signals in a physical layer and vice versa. RoF systems have already been installed as compensation for radio dead zones on metro subway lines, mountain areas, high-rise buildings, and so on. The advantages of the RoF are based on a low loss feature of optical fibers, the broad bandwidth capacity of the optical signals, and low immunity to existing radio services due to the encapsulation of radio signals into optical carriers. In this paper, we introduce RoF technology following millimeter-wave and terahertz-wave signal generation empowered by a photonics technique and its application to such public infrastructure as high-speed railway and radio-relay systems.

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Optical coherent technology has been attractive for realizing optical satellite communication, optical beam-former and photonic payload in the future. The radiation resistant test of onboard components was also evaluated as the change of the optical output power, optical spectra and optical frequency noise before and after proton irradiation. As a result, there was no performance degradation due to an aluminum shield with thickness of 4 mm against the proton irradiation corresponding to 15 years of geostationary satellite orbit.

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In this paper, we introduce several owned-operated communication networks for the operation, protection and maintenance of power grids. Communication networks mainly consist of optical fiber and fixed microwave radio to provide high reliability with low latency. After introducing studies of the lightning protection of microwave radio station and multipoint sensing data acquisition systems using optical fiber power transmission and radio-over-fiber (RoF) techniques, we discuss a desired communication network in future power grids.

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Although radar is an important component of aircraft surveillance systems used in air traffic control, its performance parameters such as data refresh rate, which depends on antenna rotation period or position estimation accuracy, do not satisfy the requirements for high density operation. Multilateration utilizing hyperbolic positioning is a newly proposed surveillance system that is said to have better performance than conventional radar systems. We applied Radio over Fiber to a multilateration system and achieved improved performances. We confirmed our evaluation results in an actual airport environment.

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Antenna-coupled electrode electro-optic (EO) modulators operating in the 28-GHz band were analyzed, designed, and fabricated for applications to next generation (5G) mobile wireless communication systems and to the precise antenna measurement systems. By scrutinizing antenna-coupled electrodes with 3-D field analysis software, an electric field enhancement factor of approximately 8000 times the irradiated wireless 28-GHz field was obtained for optical modulation, which enables a compact wireless-optical signal convertor without an external power supply. We fabricated our designed EO modulator using a 50-μm-thick z-cut LiNbO3 crystal film and a 250-μm-thick SiO2 glass base substrate, and successfully demonstrated signal conversion characteristics from the 28-GHz band wireless to optical signals in the experiment.

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