4 research outputs found
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Graphene Modulators for Silicon Photonic Optical Links
The backbone of today’s society is the transfer of information. Next-generation data network infrastructures need to support Tb/s data rates. Existing optical fibre communication networks cannot support Tb/s data transmission without consuming an unsustainable amount of power. Optical transceivers send and receive information encoded in light, relying on electro-optic modulators to convert the electrical data signal into the optical domain, and photodetectors to convert the optical signal back into the electrical domain. Power consumption can be reduced by using efficient and compact modulators and photodetectors to integrate the optics closer to the electronics and thus minimise the losses of electrical interconnect at high frequencies. Si photonics technology offers a cost-effective solution for fabricating integrated photonic circuits by combining electronic and photonic components in the same circuit by using existing CMOS technology. This thesis focuses on the development of a scalable graphene-based platform for integrated photonics, and specifically on the electrooptic modulator. I have focused on a double single-layer graphene modulator design in three different configurations that can be used for different types of optical links. This includes a graphene-based electro-absorption modulator, ring resonator modulator, and Mach-Zehnder modulator. The double-layer structure enables the absorption and phase of an optical carrier signal to be electrostatically controlled without the need for doped waveguides. This is the most efficient graphene-based phase modulator to-date with an extracted VπL ∼ 0.12 V·cm, which is ∼ 2 times better than the lowest reported graphene phase modulator. As well as showing very efficient phase modulation, the graphene phase modulator is capable of being operated in the transparency regime where graphene becomes transparent to absorption via interband transitions. Operating in the transparency regime means that the graphene phase modulator is capable of pure phase modulation which is a desirable property for complex modulation formats. Benefiting from efficient phase modulation, the graphene ring resonator modulator has demonstrated an FOM(EA) ∼ 4.48, ∼ 2 times better than the highest currently reported for graphene-based modulators. These results represent a step towards the development of a future graphene-based platform for efficient and compact modulators and photodetectors needed for next-generation optical links
Optical Wireless Data Center Networks
Bandwidth and computation-intensive Big Data applications in disciplines like social media, bio- and nano-informatics, Internet-of-Things (IoT), and real-time analytics, are pushing existing access and core (backbone) networks as well as Data Center Networks (DCNs) to their limits. Next generation DCNs must support continuously increasing network traffic while satisfying minimum performance requirements of latency, reliability, flexibility and scalability. Therefore, a larger number of cables (i.e., copper-cables and fiber optics) may be required in conventional wired DCNs. In addition to limiting the possible topologies, large number of cables may result into design and development problems related to wire ducting and maintenance, heat dissipation, and power consumption.
To address the cabling complexity in wired DCNs, we propose OWCells, a class of optical wireless cellular data center network architectures in which fixed line of sight (LOS) optical wireless communication (OWC) links are used to connect the racks arranged in regular polygonal topologies. We present the OWCell DCN architecture, develop its theoretical underpinnings, and investigate routing protocols and OWC transceiver design. To realize a fully wireless DCN, servers in racks must also be connected using OWC links. There is, however, a difficulty of connecting multiple adjacent network components, such as servers in a rack, using point-to-point LOS links. To overcome this problem, we propose and validate the feasibility of an FSO-Bus to connect multiple adjacent network components using NLOS point-to-point OWC links. Finally, to complete the design of the OWC transceiver, we develop a new class of strictly and rearrangeably non-blocking multicast optical switches in which multicast is performed efficiently at the physical optical (lower) layer rather than upper layers (e.g., application layer).
Advisors: Jitender S. Deogun and Dennis R. Alexande