Image by Pete Linforth from Pixabay


The CONCORDA Consortium is pleased to invite you to the PhD defense of Alvaro Morales Vicente, from the Eindhoven University of Technology (one of the project’s partners). The work is based also on CONCORDA’s implementation and results.

Title: Towards Optical Beamforming Systems on-Chip for Millimeter Wave Wireless Communications

Date : Monday, December 7th 2020

Time: 11-12 am

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Summary of the PhD defense:

The advent of the multimedia mobile era has driven a steady and enormous increase in the Internet protocol (IP) wireless traffic, which has been successively managed by past and current wireless communications standards. As this trend continues, new paradigms must be investigated to accommodate future wireless capacity demands, reaching more than 275 exabytes per month in 2022, according to previsions. The development of more efficient and powerful signal sources and detectors in the millimeter wave (mmWave) (30 – 300 GHz) and sub-terahertz (0.1 – 1 THz) domains make these spectrum regions suitable for implementing ultra-high capacity wireless links because of the available bandwidth. The fundamental limitation of mmWave wireless communications is the inherent high propagation loss due to the increasing free-space path loss, atmospheric absorption, and diffraction, among other factors. Thereby, high-gain directive antennas with the ability to steer the radiation beam are required to enable point-to-point mmWave wireless interfaces. Conventional electronic-based signal generation and phase-shifting approaches, which have been widely used in the microwave domain, limit the achievable modulation bandwidth in the mmWave domain. Alternatively, photonic techniques allow the broadband generation and manipulation of high-frequency signals.

This work experimentally investigates photonics-based mmWave systems for wireless communications, showcasing the potential of this approach to implement the future high-capacity wireless technology and proposing a series of innovative concepts. While multiple topics are covered, the contributions can be essentially classified into two areas. First, analog radio-over-fiber (A-RoF) systems, based on optical heterodyning, are studied as the prime candidate to realize wireless access networks at mmWave frequencies. The broadband nature of the optical domain, the integration into already deployed optical distribution networks, and the mmWave signal generation by optical heterodyning are some of the main features supporting this choice. Thus, mmWave wireless links become not only the interface with the end-users, but they can also extend the reach of optical fibers with wireless fronthaul connections. The reported experimental demonstrations examine some relevant aspects to achieve the practical realization of high-speed low latency access networks, such as the bidirectionality, physical layer confidentiality, and beamforming. In particular, optical true-time delay (OTTD) beamforming is investigated as the solution to implement broadband beam steering in A-RoF links. The beamforming network is centralized, and the delayed copies of the signals are transmitted through different cores of a multi-core fiber (MCF) that distributes the signals and maintains the temporal relations.

Second, the design of a small-footprint transmitter system based on a photonic integrated circuit (PIC) and an array of photoconductive antennas (PCAs) is reported. Such a system is suitable for multi-Gb/s short-range wireless communications with a wide tuning range in the wireless carrier. The pic splits an optical signal into four different copies and sets the true-time delay configuration of the mmWave signal by continuously tuning the group delay with optical ring resonators (ORRs). Then, the optical signals are converted into the mmWave domain and radiated into the free-space by an array of terahertz (THz) PCAs on-chip. Finally, the mmWave radiation is efficiently coupled to the free-space by an array of dielectric rod waveguide (DRW) antennas made in silicon. The tremendous potential of THz optoelectronic technology for highly-tunable ultra-broadband communications was also experimentally addressed in a mmWave heterodyne transmission experiment. The link was demonstrated in continuous wave operation with an intermediate frequency of 3.7 GHz over an extensive range, between 80 GHz and 320 GHz. A successful data transmission was achieved at 80 GHz, 120 GHz, and 160 GHz carrier frequencies without essential changes in the setup.

The results obtained after completing this project and the discussions included in the dissertation and the published articles represent a notable step towards realizing a small-footprint, broadband transceiver for future ultra-high capacity short-range wireless communications in the mmWave and sub-THz bands. This work is part of the ‘Convergence of Electronics and Photonics Technologies for Enabling Terahertz Applications (CELTA)’ project, funded by the Horizon 2020 research and innovation program of the European Union.