UC San Diego

Although it may seem mundane, we have been and we continue to face an extensive and seemingly never ending growth trend of data traffic: in terms of the increase in the number of network users, as well as the emergence of new bandwidth-hungry applications and services, and certainly driven by the unprecedented cloud computing, high-definition videos, Artificial Intelligence, and the Internet of Things. The former predicament implies that the backbone of our fixed broadband, wireless, and optical communication networks needs to be well-equipped to facilitate this evolution and accommodate the need for higher capacity systems. Specifically, the new generation 5G network’s frequency spectrum extends from several MHz to the Milimeter-wave region and supports a wide variety of signal bandwidths and carrier spacings. Through this flexible framework, the recently launched wireless network serves various users and applications. On the other hand, the coherent optical communication network is also experiencing a shift toward higher bandwidth optical signals with qaudrature amplitude modulation. The transmission of 220GBd QPSK [1] and 128GBd 16-QAM [2] optical signals have already been demonstrated and the baud rate of QAM modulation formats has increased with a pace of 12 GBd per year over the last decade[3]. The aim of this dissertion work was to investigate the utilization of hybrid optoelectronic subsystems in high capacity communication networks which may offer functionalities which are difficult, or even impossible to achieve with the existing all-electronic subsystems. In this dissertation, the hybrid optolectronic subsystems for either wireless network, or coherent optical communication network were proposed. Specifically, in these subsystems, optical and electrical components with bandwidths compatible with commercially available devices are utilized. Thus, they pave the way to the realization of more robust, cost-effective, and higher capacity communication systems. In this respect, the first experimental demonstration of a sub-GHz flat-top comb-based RF-photonic filter is reported in this dissertation. The high quality flat-top spectral shape and shape-invariant tuning of the filter center frequency was enabled by a precise higher order dispersion compensation, for the first time. Furthermore, successful retrieval of digitally modulated RF signals at different center frequencies with varying symbol rates for QPSK and 16-QAM modulation additionally verified the filter integrity. The extended experimentation clearly demonstrated that this new narrowband flat-top filter can be used as a simultaneously tunable and programmable filter at remote 5G nodes, which correspondingly relaxes the need for high-resolution ADCs. Furthermore, within the realm of fiber optic transport, we have proposed and investigated channelizer-assisted chromatic dispersion compensation in high baud rate coherent systems. Chromatic dispersion penalty is a crucial signal impairment which scales as a square of the (symbol) signal rate and will severely limit the transmission reach if not mitigated efficiently. Our findings have shown that transmission reach can be more than tripled when resorting to this physically-aided processing strategy, as opposed to the standard digital processing – only approach.