Crossing-Aware Channel Routing for Integrated Optics

Increasing scope and applications of integrated optics necessitates the development of automated techniques for physical design of optical systems. A key area of integrated optic design is waveguide routing, which currently lacks the level of automation found in VLSI design. Unlike VLSI, where signal nets are routed with metal layers and vias, integrated optics is a planar technology and lacks the inherent signal restoration capabilities of static-CMOS. Waveguides suffer signal loss due to planar (perpendicular) waveguide crossings and also from sharp bends. Therefore, in contrast to area or wire length, signal loss minimization - as a function of waveguide crossings and bends - is a primary objective of any routing solution. Our studies show that waveguide routing problems can be suitably formulated as planar channel routing. This paper investigates channel routing for integrated optical waveguides fabricated in a planar substrate. We present routing techniques where crossings, bends, and area are accounted for in an integrated solution. Two distinct channel routing techniques are presented: 1) a new channel router based on net sorting and utilizing non-Manhattan routing grids and 2) a router based on crossing-aware graph-constrained track assignment that also exploits waveguide curves to improve track utilization. Both techniques are crossing-minimal, and are also constrained suitably to reduce bend loss and area. We compare and evaluate the performance of our channel routers on a number of optical design benchmarks.