Tolerating process variations in nanophotonic on-chip networks

Nanophontonic networks, a potential candidate for future networks on-chip, have been challenged for their reliability due to several device-level limitations. One of the main issues is that fabrication errors (a.k.a. process variations) can cause devices to malfunction, rendering communication unreliable. For example, microring resonator, a preferred optical modulator device, may not resonate at the designated wavelength under process variations (PV), leading to communication errors and bandwidth loss. This paper proposes a series of solutions to the wavelength drifting problem of microrings and subsequent bandwidth loss problem of an optical network, due to PV. The objective is to maximize network bandwidth through proper arrangement among microrings and wavelengths with minimum power requirement. Our arrangement, called “MinTrim”, solves this problem using simple integer linear programming, adding supplementary microrings and allowing flexible assignment of wavelengths to network nodes as long as the resulting network presents maximal bandwidth. Each step is shown to improve bandwidth provisioning with lower power requirement. Evaluations on a sample network show that a baseline network could lose more than 40% bandwidth due to PV. Such loss can be recovered by MinTrim to produce a network with 98.4% working bandwidth. In addition, the power required in arranging microrings is 39% lower than the baseline. Therefore, MinTrim provides an efficient PV-tolerant solution to improving the reliability of on-chip phontonics.