The basic building block of on-chip nanophotonic interconnects is the microring resonator [14], and these resonators change their resonant wavelengths due to variations in temperature -a problem that can be addressed using a technique called "trimming", which involves correcting the drift via heating and/or current injection. Thus far system researchers have modeled trimming as a per ring fixed cost. In this work we show that at the system level using a fixed cost model is inappropriate -our simulations demonstrate that the cost of heating has a non-linear relationship with the number of rings, and also that current injection can lead to thermal runaway. We show that a very narrow Temperature Control Window (TCW) must be maintained in order for the network to work as desired. However, by exploiting the group drift property of co-located rings, it is possible to create a sliding window scheme which can increase the TCW. We also show that partially athermal rings can alleviate but not eliminate the problem.
This paper proposes, simulates and experimentally demonstrate an optical interconnect architecture for large-scale computing systems. The proposed architecture, H-LION (Hierarchical Lightwave Optical Interconnect Network), leverages wavelength routing in arrayed waveguide grating routers (AWGRs), and computing nodes (or servers) with embedded routers and wavelength-specific optical I/Os. Within the racks and clusters, the interconnect topology is hierarchical all-to-all exploiting passive AWGRs. For the inter cluster communication, the proposed architecture exploits a flat and distributed Thin-CLOS topology based on AWGR-based optical switches. H-LION can scale beyond 100,000 nodes while guaranteeing up to 1.83× saving in number of inter-rack cables, and up to 1.5× saving in number of inter-rack switches, when comparing to a legacy 3-tier Fat Tree network. Network simulation results show a system-wide network throughput reaching as high as 90% of the total possible capacity in case of synthetic traffic with uniform random distribution. Experiments show 97% intra-cluster throughput for uniform random traffic, and error-free inter-cluster communication at 10 Gb/s.
This paper analyzes the scalability in arrayed waveguide grating router (AWGR)-based interconnect architectures and demonstrates active AWGR-based switching using a distributed control plane. First, the paper analyses an all-to-all single AWGR passive interconnection with N nodes and proposes a new architecture that overcomes the scalability limitation given by wavelength registration and crosstalk, by introducing multiples of smaller AWGRs (W × W ) operating on a fewer number of wavelengths (W < N). Second, this paper demonstrates active AWGR switching with a distributed control plane, to be used when the size of the interconnection network makes the all-to-all approach using passive AWGRs impractical. In particular, an active AWGR-based TONAK switch is introduced. TONAK combines an all-optical NACK technique, which removes the need for electrical buffers at the switch input/output ports, and a TOKEN technique, which enables a distributed all-optical arbiter to handle packet contention. The experimental validation and performance study of the AWGR-based TONAK switch is presented, demonstrating the feasibility of the TONAK solution and the high throughput and low average packet latency for an up to 75% offered load.
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