Dessislava Nikolova
silicon photonics ~ optical networks ~ photonics systems design ~ optical switches
Silicon Photonic Switch Fabrics
High radix, low latency, energy efficient optical switches are essential to sustain the rapid growth in aggregate bandwidth requirements in data centers and high performance computers. Higher port count switches not only permit to interconnect more hosts directly but they also allow more compact topologies involving less links and switches to interconnect large networks. The proposed switch is fully non-blocking, has path independent insertion loss, low crosstalk and is straightforward to control. We further analyze this architecture and compare it to other common switching architectures for varying underlying technologies and radices, showing that the proposed architecture favorably scales to very large port counts when considering both crosstalk and architectural footprint. Separating a switch fabric into functional building blocks via multiple photonic integrated circuits offers the advantage of piece-wise manufacturing, packaging, and assembly, potentially reducing the number of optical I/O and electrical contacts on a single die.
Reference:
A scalable modular architecture for a fully non-blocking silicon photonic switch fabric, Dessislava Nikolova*, David M. Calhoun*, Yang Liu, Sébastien Rumley, Ari Novack, Tom Baehr-Jones, Michael Hochberg, Keren Bergman, to appear in Nature Microsystems & Nanoengineering
Starting with detailed device models which I have developed and experimentally verified, I analyzed the scalability of silicon photonic microring based switch fabrics with the widely used Benes topology. I was able to estimate the crosstalk and losses of a single chip switch fabric. This allowed me to determine the achievable port count and bandwidth density for these switch fabrics. The surprising conclusion of this was work was that the on-chip waveguide crossings contribute significantly to the scaling of a two dimensional switch fabric.
References:
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Scaling Silicon Photonic Switch Fabrics for Data Centre Interconnection Networks, D. Nikolova, S. Rumley, D. Calhoun, Q. Li, R. Hendry, P. Samadi, K. Bergman, Optics Express 23(2), 1159-1175 (2015)
2D switch fabric from double microring switching elements with Benes topology ; top left inset shows picture from a fabricated device; top right - schematics of the operation of the switching element; right inset - picture of a on-chip waveguide crossing; bottom - miltiple crossings model.
Silicon Photonic Interconnects for Rack-to-Rack Communication
Vision for optically interconnected racks enabled by silicon photonic microring modulators and filters
The silicon photonic technology is still young and only recently emerging for commercial systems adoption. Optical interconnects based on silicon photonic devices have the potential to deliver huge amount of bandwidth at low energy and cost. Understanding the capacity limits of these interconnect is of vast importance. In this paper, we present a design and modeling approach for obtaining the maximum achievable aggregate bandwidth in a silicon photonic link with microring modulators and filters. It is based on a uniquely comprehensive modeling platform for efficiently exploring the design space of silicon photonic interconnects, from the physical layer to the link-level analysis. We concentrate our efforts on microring-resonator-based links, as they have the lowest footprint among the current most developed silicon photonic interconnect devices. Furthermore we derived the optimal device parameters. We obtained an upper bound on the maximum aggregate throughput achievable with a microring-based silicon photonic link. This is of paramount importance for link designers, informs device designer for optimal parameters and also can allow comparison with other existing and future devices.
References:
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Comprehensive Design Space Exploration of Silicon Photonic Interconnects, M. Bahadori, S. Rumley, D. Nikolova, and K. Bergman, in press, Journal of Lightwave Technology
Packet Scheduling over Multiple Channels
When hundred thousands of flows are competing for the same switch output, scalable, low complexity scheduling algorithm are needed to ensure low latency and fairness. In wire-line access networks where the infrastructure is shared by relatively low number of users achieving high utilization but at the same time guaranteeing stringent quality of service has led to the use of multiple channels over the same cable/fiber. I proposed the input and output queuing concepts for scheduling a single user transmission simultaneously over multiple channels. I also analyzed and implemented the bonded deficit round robin algorithm which realizes these concept and demonstrated that it can guarantee strict quality of service requirements even when the channels use varying bit rates.
References:
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Bonded Deficit Round Robin: packet scheduling algorithms for networks with channel bonding, D. Nikolova and C. Blondia, Computer Networks 55 (2011), pp. 3503-3516
Output queuing where the packets are scheduled for transmission on a given channel mmediatelly upon arrival
Input queuing where the packets are buffered in common queue and scheduled for transmission owhen a channel becomes free
The realization of silicon photonic devices is made possible due to the confinement of light in nanometer structures. Another example of tight confinement of the light field are surface plasmons-polaritons which are coupled light-electron plasma waves, propagating at the interface between a dielectric and conducting material. They are extremely sensitive to the dielectric properties of the materials which makes them very interesting also for sensing applications and have given rise to the field of plasmonics. The combination of plasmonics with magneto-optical materials is particularly interesting because it introduces a nanoscale interaction between light felds and magnetisation, hence opening up the possibility of using either one of these fields to control the other. My particular contribution in this area was to derive the influence of magnetization on the light propagation in plasmonic waveguides. I was able to demonstrate how the magnetic field can be used to switch dipole emission on and off and to spatially direct the light out of a plasmonic cavity. This raises the novel possibility of using magnetic fields to control light propagation in nanostructures and using light to sense the magnetic properties in nanoscale domains.
References:
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Switching and propagation of magneto-plasmon-polaritons in magnetic slot waveguides and cavities, D. Nikolova and A. Fisher, Physical Review B 88 (12), 125136 (2013)
On-Off Switching with Magnetic Field
Magnetic switching of the dipole emission in an 80 nm thick cavity of ferromagnetic dielectric surround by silver