XRing: A Crosstalk-Aware Synthesis Method for Wavelength-Routed Optical Ring Routers

Wavelength-routed optical networks-on-chip (WR-ONoCs) are well-known for supporting high-bandwidth communications with low power and latency. Among all WRONoC routers, optical ring routers have attracted great research interest thanks to their simple structure, which looks like concentric cycles formed by waveguides. Current ring routers are designed manually. When the number of network nodes increases or the position of network nodes changes, it can be difficult to manually determine the optimal design options. Besides, current ring routers face two problems. First, some signal paths in the routers can be very long and suffer high insertion loss; second, to connect the network nodes to off-chip lasers, waveguides in the power distribution network (PDN) have to intersect with the ring waveguides, which causes additional insertion loss and crosstalk noise. In this work, we propose XRing, which is the first design automation method to automatically synthesize optical ring routers based on the number and position of network nodes. In particular, XRing optimizes the waveguide connections between the network nodes with a mathematical modelling method. To reduce insertion loss and crosstalk noise, XRing constructs efficient shortcuts between the network nodes that suffer long signal paths and creates openings on ring waveguides so that the PDN can easily access the network nodes without causing waveguide crossings. The experimental results show that XRing outperforms other WRONoC routers in reducing insertion loss and crosstalk noise. In particular, more than 98% of signals in XRing do not suffer first-order crosstalk noise, which significantly enhances the signal quality.