Ring vs. Bus: a Theoretical and Experimental Comparison of Photonic Integrated NoC

Abstract

Silicon photonics enables the fabrication of photonic integrated circuits with high bandwidth density, making it suitable for computercom applications. In multicore computing systems, the communications between cores and memory can be supported by optical networks-on-chip (NoC) realized with photonic integrated circuits (PIC). While different optical NoC topologies have been proposed in the past, only few NoC were fabricated and tested. This paper aims at comparing the performance of two PIC NoC with a bus and a ring topology. First, a framework is presented for passing from the theoretical analysis of silicon photonics basic building blocks like waveguides and microrings, to the PIC design and to the NoC performance derivation, using the scattering matrix method. Based on this framework, the two NoC topologies are simulated, designed, fabricated in silicon photonics, and experimentally characterized for comparison. Spectral performance validates the theoretical model with minor deviations due to the fabrication inaccuracies and limitations. Bit error rate performance at 10 Gb/s demonstrates the capability of simultaneous transmissions in both topologies with limited or negligible crosstalk. Moreover, ring NoC is shown to slightly outperform the bus NoC thanks to the filtering properties of the central microring.