“The capability to run large-scale physical simulations using the mature and approximation free FDTD method gives us a new level of confidence at tape-out.”
— Yi Zhang, PIC lead at Rockley
Rockley embraces the ever-growing trend towards increased complexity for photonics circuits. Many effects integral to the operation of the circuit still need to be considered during design and verification, such as stray light interference or impacts of nonuniform temperature or stress fields in the photonic integrated circuit (PIC).
To date, conventional engineering know-how has provided engineers with a way to work through a solution to generate layouts. This approach is no longer practical as layout complexity grows, necessitating large-scale physical simulations of the entire photonic circuit. The growing cost of fabricating and packaging today’s devices and raising time-to-market demands warrant efforts to improve verification. The impact of letting design errors slip through the cracks is significant. If a fault makes it to silicon, the cost of a re-spin will be expensive. More importantly, the increased time to market can have an immeasurable impact on market share and brand reputation.
Rockley considered several HPC solutions to accelerate large-scale simulations, but in the end, the company decided to go with a CPU based cloud solution on Amazon Web Services (AWS) powered by Lumerical’s FDTD. This decision was driven by the accuracy and runtime performance of Lumerical’s FDTD coupled with its amenability to HPC computing, as well as the cost-effective flexibility of Amazon’s cloud solution.
Rockley conducted multiple 2D and 3D single time-domain simulations for devices A and B (Figures 1 and 2, respectively) thus allowing for the extraction of high-resolution spectra. The scale of the simulations was significant for FDTD given the size of the designs, with the layout of device B being approximately 6 mm2. EC2 was used to run simulations on up to 16 cutting-edge Xeon Platinum processor-based servers, distributing each job across 576 cores. A variety of hardware configurations was explored, enabling Rockley to choose the optimal configuration for their business and engineering needs. In some cases, spot pricing was used to realize 80-90% discounts over on-demand rates.
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