Crossing-aware channel routing for photonic waveguides

Silicon photonics technology is progressing at a rapid pace. Despite greatly expanded manufacturing capability, physical design of integrated optical circuits currently lacks the level of automation found in VLSI design. A key component of integrated optic design is waveguide routing; however, unlike VLSI, where signal nets are routed with metal layers and vias, photonic waveguides are fabricated in planar substrates. For many applications, our studies show that the waveguide routing problem can be formulated as planar channel routing. Signal losses become a major factor due to the insertion losses of planar waveguide crossings. Channel routing must therefore take into account these losses. This paper investigates methods for adapting traditional VLSI channel routing techniques for integrated optics - specifically, a technique based on left-edge-style track assignment. We show how incorporating waveguide crossing constraints into the underlying constraint model affects the routing solution, and describe the necessary modifications and extensions to the routing technique to properly exploit optical technology. We implement the channel router, describe the experimental results, and compare the cost of solutions with respect to waveguide crossings, corresponding to signal loss, and channel height.