Cross-Layer Optimization Framework for Integrated Optical Switches in Data Centers
The advancement of silicon photonics promises integrated optical switches to provide high-bandwidth, low-latency and low-power communications in data centers. An optical switch’s loss limits its scale and affects the energy efficiency of the switch system. In this work, we present CLOSO, a cross-layer optimization framework, based on not only photonic device models at the physical layer but also optical switch models at the fabric layer. With the proposed framework, optimal losses of optical switches can be evaluated efficiently, and the corresponding losses and design parameters of photonic devices can be obtained. Using CLOSO, we optimize four categories of integrated optical switches, Crossbar, PILOSS, DRAGON and FODON, and compare them regarding their optimal worst-case loss with variation of the switch scale and data rate of signals. Furthermore, system-level evaluations of the optimized optical switches are performed, demonstrating a significant improve- ment of energy efficiency from the cross-layer optimization. For instance, CLOSO helps to reduce the energy consumption of a 64-port DRAGON and FODON to as low as 6 pJ/bit and that of a 128-port DRAGON and FODON to as low as 10 pJ/bit. The investigation of 128-port switches also shows the necessity of adaptive power control on lasers for high-radix integrated optical switches. Through quantitative analyses and comparisons, CLOSO shows the capability of facilitating initial design exploration of optical switches and paves the way to fair evaluations and comparisons of switch systems in data centers.
This project is still under further development. If you would like to try the framework, please feel free to contact us.
This project is still under further development. If you would like to try the framework, please feel free to contact us.
High-Radix Non-Blocking Integrated Optical Switching Fabric for Data Centers
To accomplish high-bandwidth and low-latency communications among tens or even hundreds of nodes with low power consumption, dual radial and angular grating optical network (DRAGON), a new integrated high-radix strictly nonblocking optical switching fabric, is proposed in this paper. The topology and routing algorithms of DRAGON are discussed, and a formal proof for the strictly nonblocking property is presented. With the loss model developed, we show DRAGON has significantly lower worst-case loss as well as average loss compared with other widely studied integrated nonblocking switching fabrics. In addition, our crosstalk analysis also suggests a lower crosstalk of DRAGON. For example, for 32 wavelength division multiplexing channels, both the worst-case loss and average loss of 180 × 180 DRAGON are around 20 dB lower than crossbar of the same size, and 28 dB lower than 128 × 128 Benes. Furthermore, due to the strictly nonblocking property, DRAGON has advantages of smaller communication latency and larger throughput compared with Benes̆ switching fabric.
Low-Loss High-Radix Integrated Optical Switch Networks for Software-Defined Servers
Software-defined servers provide high flexibility and customizablility with low power consumption. To satisfy the ultrahigh bandwidth requirement of the interconnection of these servers, integrated optical switch networks, based on the recent development of silicon photonics, are promising candidates. In this study, we present a family of floorplan optimized delta optical networks (FODONs) with the proposed stage switches. Both the analytical approximation and the loss model based on the exhaustive search approach are developed to evaluate the loss parameters in the networks. The optimization of the stage switch radix is conducted as well. Results show that when 32 WDM channels are employed, the worst-case loss of the 1024 × 1024 FODON with 4 × 4 stage switches is only 26 dB, which is 95, 63, 37 dB less than Benes, Fat-tree, and Baseline networks of the same size, respectively. Furthermore, the average loss and the cost of hardware resources of FODONs are much lower than other networks.
Modeling and Analysis of Add-drop Racetrack Microresonator and Thermal Tuning
Add-drop microresonator has become one of the most promising candidates to be switching elements in optical network on-chip. To describe characteristics of MR, analytical models based on both coupled-mode theory and transfer matrix method have been developed in this paper. All the parameters in these models are obtained from the field equation with effective index method approximation. Among them, the wavelength dependence of coupling coefficient of MR has been analyzed specifically. Moreover, the thermal tuning of MR has also been modeled not only to decide an appropriate temperature difference between on and off state but also to estimate the tuning speed.