Addressing System-Level Trimming Issues in On-Chip Nanophotonic Networks

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.