Silicon-photonic links are projected to replace the electrical links for global on-chip communications in future manycore systems. The use of off-chip laser sources to drive these silicon-photonic links can lead to higher link losses, thermal mismatch between laser source and on-chip photonic devices, and packaging challenges. Therefore, on-chip laser sources are being evaluated as candidates to drive the on-chip photonic links. In this paper, we first explore the power, efficiency and temperature tradeoffs associated with an on-chip laser source. Using a 3D stacked system that integrates a manycore chip with the optical devices and laser sources, we explore the design space for laser source sharing (among waveguides) and placement to minimize laser power by simultaneously considering the network bandwidth requirements, thermal constraints, and physical layout constraints. As part of this exploration we consider Clos and crossbar logical topologies, U-shaped and W-shaped physical layouts, and various sharing/placement strategies: locally-placed dedicated laser sources for waveguides, locally-placed shared laser sources, and shared laser sources placed remotely along the chip edges. Our analysis shows that logical topology, physical layout, and photonic device losses strongly drive the laser source sharing and placement choices to minimize laser power.
An optical multi microring network-on-chip (MMR NoC) is proposed and evaluated through numerical simulations. The network architecture consists of a central resonating microring with local microrings connected to the input/output ports. A mathematical model based on the transfer matrix method is used to assess the MMR NoC performance and to analyze the fabrication tolerances. Results show that the proposed architecture exhibits a limited coherent crosstalk with a bandwidth suitable for 10 Gb/s signals, and it is robust to coupling ratio variations and ring radii fabrication inaccuracies.
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