RSoft Enewsletter

August 2017

Silicon Photonics for Data Center Switches: Schematic- Driven Simulation and Mask Generation for an AIM PDK-Based 4x4 Benes Switch

The growth in intra-datacenter traffic is rapidly outpacing the growth in long-haul and inter-datacenter connectivity segments due to a gradual migration of storage, virtualization, and computing to the cloud. The Cisco global cloud index [1] estimates that by 2020, global cloud IP traffic will account for more than 92% of total datacenter traffic.

For efficient distributed computing and storage, effective interconnectivity and switching fabrics between servers are required so that application layers can assign parallel tasks to distributed servers with minimal overhead and disruption. From the switching perspective, this translates to having a scalable switching fabric with faster switching speeds ("low latency"), dense port count ("high radix"), lower footprint ("higher port density" measured in Gbps/mm2), and higher power efficiency (lower pJ/bit). Current switch architectures are difficult to scale from the bandwidth and port-count perspective due to electrical signaling limitations. This is where silicon photonics can play a vital role, which explains the immense amount of interest lately in various integrated photonic technologies, including silicon photonic microring modulator based switches [2-4].

This article is based on a published experimental work [5] utilizing a single micro-ring-based switching element to provide 2x2 functionality. Input 1 is routed to port 2 or port 1, depending on the state (cross or bar, respectively) of the switch as shown in Figure 1.

Figure 1. Cross and bar states of a single silicon photonic micro-ring-based 2x2 switch from [5]

Figure 1. Cross and bar states of a single silicon photonic micro-ring-based 2x2 switch from [5]

The switching element in Figure 1 can be scaled to a high-radix switch fabric. As an example, a 4x4 Benes switch is shown in Figure 2.

Figure 2. 4x4 Benes topology [5] using six 2x2 switching elements from Figure 1

Figure 2. 4x4 Benes topology [5] using six 2x2 switching elements from Figure 1

The Benes architecture has the advantage of being able to realize any static permutation ("non-blocking") of connectivity, and has fewer waveguide crossovers compared to a cross-bar architecture [6].

The rest of this article describes an OptSim Circuit flow [7] for designing the 4x4 Benes switch in Figure 2, from schematic entry to performance simulation and mask generation. We use the AIM Photonics PDK [8] for this case study. A typical migration path from idea to fabrication is shown in Figure 3.

Figure 3. A high-level view of the steps involved in moving from an idea to its PIC realization

Figure 3. A high-level view of the steps involved in moving from an idea to its PIC realization

The OptSim Circuit topology in Figure 4 simulates switching performance of the 4x4 Benes switch created from the AIM PDK elements, implemented as a hierarchical compound component labeled "AIM 4x4 Benes Switch". The routed signal at one of the port outputs is shown in the top right inset.

Figure 4. OptSim Circuit setup for testing a 4x4 Benes switch using the AIM PDK. A routed signal is shown in the inset.

Figure 4. OptSim Circuit setup for testing a 4x4 Benes switch using the AIM PDK. A routed signal is shown in the inset.

The detailed schematic of the 4x4 Benes architecture in Figure 2 using six 2x2 silicon photonic micro-ring modulator based switching elements is shown in Figure 5. 

Figure 5. OptSim Circuit schematic of the AIM PDK-based 4x4 silicon photonic Benes switch

Figure 5. OptSim Circuit schematic of the AIM PDK-based 4x4 silicon photonic Benes switch

Once the OptSim Circuit simulation results are verified to match the desired performance objectives for the switch, the next step is the creation of a PhoeniX OptoDesigner [9] layout for the schematic in Figure 5. OptSim Circuit has a utility (which is accessed via the "Utilities" menu of the OptSim Circuit GUI) to create the layout, which can be further modified within OptoDesigner. Figure 6 depicts the layout, which can be exported as a GDS II mask for the AIM Photonics foundry at SUNY-Poly.

Figure 6. OptSim Circuit schematic of the AIM PDK-based 4x4 silicon photonic Benes switch (left) and layout in PhoeniX Software OptoDesigner (right)

Figure 6. OptSim Circuit schematic of the AIM PDK-based 4x4 silicon photonic Benes switch (left) and layout in PhoeniX Software OptoDesigner (right)

For more information, please contact rsoft_support@synopsys.com.

References

1. https://www.cisco.com/c/en/us/solutions/collateral/service-provider/visual-networking-index-vni/mobile-white-paper-c11-520862.html

2. Dessislava, N., et al., “Scaling silicon photonic switch fabrics for data center interconnection networks,” Optics Express, vol. 23, no. 2, January 2015.

3. Ashkan Seyedi, M., et al., “Crosstalk analysis of ring resonator switches for all-optical routing,” Optics Express, vol. 24, no. 11, May 2016.

4. Seok T. J., et al., “High density optical packaging of high radix silicon photonic switches,” Paper # Th5D7, Proc. OFC 2017.

5. Li, Q., et al., “Single microring-based 2x2 silicon photonic crossbar switches,” IEEE Photonics Technology Letters, vol. 27, no. 18, September 15, 2015.

6. Papadimitriou G., et al., “Optical switching: switch fabrics, techniques, and architectures,” Journal of Lightwave Technology, vol. 21, no. 2, February 2003.

7. https://www.synopsys.com/optical-solutions/e-news/rsoft/2017_apr.html

8. https://news.synopsys.com/2016-12-07-Synopsys-Releases-Version-2016-12-of-the-RSoft-Photonic-System-Design-Suite

9. http://www.phoenixbv.com/product.php?prodid=50010466&submenu=dfa&prdgrpID=24&prodname=Synopsys%20PDA-Link

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