On Topology Optimization Strategies for Ultra-Compact High Contrast Grating Design

We describe a design methodology for optimizing an ultra-compact
$3\mu$
m long circular high contrast grating (HCG) reflector. A multi-stage optimization process involving parameter optimization (PO) followed by seeded topology optimization (TO) is demonstrated to design a device with performance better than that achieved with PO or TO alone. The device is designed for a foundry process and offers reflection commensurate with waveguide-based Bragg gratings with a significantly higher bandwidth in an ultra-compact footprint. A peak reflectance of 98.9 % was simulated centered at 1569 nm with a minimum reflectance of 97.9 % over C-band.