Millimeter-wave and Terahertz Reconfigurable Radio-over-Fiber Systems

The bandwidth of wireless networks needs to grow exponentially over the next decade, due to an increasingly interconnected and smart environment, driven by cloud applications operating on mobile devices. Low-cost, compact and broadband wireless transceivers operating over different frequency bands will be required. The current WiFi (low)frequency bands do not have enough capacity and wireless communication needs to move to the millimeterwavelength or sub-terahertz range. Furthermore, millimeter-wavelength links offer a flexibility solution for non-incumbent operators to lay down fiber-like capacity links when deploying fiber is not an option. Radio-over-Fiber (RoF) technologies have evolved from a blue sky academic topic in the 90s to a main driver within the current quest for the 5th generation mobile systems (5G). A twist in RoF technologies is that it has found along the way niches in areas non purely related to communication technologies (ICT) applications: distribution of highly pure clock signals for radio telescopes, photonic-based coherent radar and fiber optic sensing. It is however in the communication arena where RoF seems to be able to provide a technological edge; RoF techniques based on photonic technologies enable to generate, transport and radiate in a straight forward manner microwave and millimeter wave signals. Although electronic technologies are able to sustain an increase in frequency from a technology point of view, with current developments hitting the Terahertz regime, the complexity of fabrication and to integrate this solutions have to compete with the off-the-shelf solutions provided by RoF technologies. Technologically though, reconfigurable Radio-over-Fiber networks require a co-design effort involving tunable lasers, digital signal processing, high speed modulators and photodiodes and optical switching technologies. Furthermore, reconfigurability is key as future networks are expected to be malleable. An overview on the state-of-the-art and current efforts towards optical components enabling photonic reconfigurability and experiments demonstrating such feature will be given during the presentation.