Polymer Technology for Optical Modulators and Node Design for Flexible and High-Speed Optical Interconnects for Intra- and Inter- Data Centers

Abstract

In today's world, use of telecommunications as well as the sector itself are inextricably linked to the everyday life of man, aiming at improving his own life. To this end, recent advances in smart devices, mobile voice and data services, cloud data, large file transfer and the Internet of Things have contributed to an exponential increase in traffic requirements globally, resulting in a tripling of global IP traffic between 2015 and 2021. Consequently, these requirements have led to an increasing use of the available bandwidth of networks, in order to fully meet the increasing needs by using only optical data transmission networks, which are the only solution to serve such requirements. And this is because the satisfaction of the capacity requirements depends on two factors. Firstly, there is a dependence on the capacity of the interfaces for communication and transfer of data within the data centers, and secondly on their transfer between remote data centers, taking into account efficiency as well as low cost. Based on the current data, interfaces within data centers (DCs) use 10 and 40 Gb/s interfaces with on-off-keying (OOK) format and wavelength division multiplexing (WDM), while Ethernet switches will adopt connections 100 Gb/s, making it necessary to use high-speed optical technologies. In this context, the objective should focus on the development of integrated optical solutions that will allow simple, direct switching from 10 Gb/s data rates to 40 Gb/s and ultimately to 100 Gb/s (or even higher speeds 400 Gb/s), while reducing the physical size of the devices and power consumption to fully meet current requirements. In this general picture, it should be taken into account that peak Internet traffic times are growing faster than average online traffic, suggesting that network capacity requirements are evolving into ever greater and more dynamic, resulting in the weight in the trunk network dropping through the input/output elements (edge switches), which correspond to the interfaces between DCs. In order for data of such size to be accommodated, state-of-the-art edge switches are now equipped with multiple interfaces, each with 10, 40, 100 or even 400 Gb/s of total capacity. However, the increasing number of services very soon leads to data flows that can reach transmission rates of up to 1 Tb/s, so these interfaces need to be upgraded and support similar capacities to keep pace. Consequently, the factors currently hindering the development of ultra-high-speed transceivers of the order of 100 Gb/s and multi-flow transceivers with terabit capacities is the absence of a flexible combination of integration platforms that can make available high-performance photonic and electronic circuits for high speed with gigabit and terabit capacity. In accordance with the above-mentioned requirements and needs, this PhD dissertation is divided into two parts, namely the high-bit rate optical interfaces using optical polymers in data centers as well as corresponding flexible optical interfaces between data centers. In more detail, one part focuses on the OOK format and the use and properties of the Electro-optic (EO) polymer platform for the fabrication of integrated transmitters capable of generating optical signals at 100 Gb/s. This particular optical polymer takes precedence over the other integration optical platforms as it has an extremely fast EO response with a bandwidth> 65 GHz. On the basis of Mach-Zehnder's specific polymer device, and the adhesion of an active 90° inverted distributed feedback laser (DFB), an integrated transmitter is implemented in combination with the use of a 100 Gb/s electronic circuitry based on the InP-DHBT combining multiplexer and driver functionalities. This integrated transmitter was evaluated through lab demonstration experiments with a serial NRZ-OOK format presenting error-free operation for transmission rates up to 100 Gb/s. At the same time, the scope of this 100 Gb/s transmitter is presented within DCs and the most appropriate ring-based optic circuit architecture (ring-based optical circuit switching domain) for PODs (point-of-delivery) interfaces up to 2 km is analyzed. The second part of this PhD dissertation presents the technology of the higher order modulation formats in the optical core networks and their capabilities with the aim of providing a transmission rate of up to 1 Tb/s to meet the demands of the next-generation optical network. At the same time, the passive, low-loss integrated multi-platform integration platform is explored and hybridly integrated with InP technology to develop flexible optical transceivers that can simultaneously produce multiple optical flows that can transfer data to variable wavelength and type of modulation (m-QAM) depending on the transmission distance and the volume of signal data, further increasing the total capacity through selective its polarization state. For the first time this possibility of choosing the kind of polarization (single or dual) from an optical transceiver is given because the prevailing approach refers to the use of superchannels in integrated optical circuits. Based on the multi-flow transceivers, a flexible, colorless and directionless optical node is designed and deployed, capable of exploiting their full potential, implemented using wavelength selective switches. Due to the fact that these implementations are intended for use in future flexible high-capacity optical networks, within this thesis, a software-defined-optics platform has been developed with the aim of highlighting the full spectrum of the flexibility of this transceiver and the node, defining both its optical and electrical parameters. This system was evaluated in lab settings using advanced mQAM formats up to 28 GBd demonstrating the capabilities of the proposed flexible transceiver with error-free operation, making it necessary to meet the extremely high demands of future optical network networks.