Dispersion engineering with inverse design (Conference Presentation)

Slow light photonic crystal waveguides (PCW) are a promising tool for optical signal processing as well as integrated optical devices that require strong light-matter interactions, such as modulators or non-linear devices. However, the low group velocity that characterizes these PCWs is typically accompanied by a large group velocity dispersion (GVD), and a low coupling efficiency. Improving both these properties for a large bandwidth forms the design challenge of most optical devices that rely on PCWs. In this work, we use inverse design methods to, firstly, design slow light PWCs with a large group index-bandwidth product (GBP), and secondly, to design couplers for the PCW, i.e. a mode converter, which couples a ridge waveguide to the PCW, and a grating coupler, which couples free space light directly to the PCW slow light mode. Both couplers are optimized for the PCW’s low group velocity dispersion bandwidth. Unlike pre-existing work, we perform the PCW optimization in full 3D simulations which result in more accurate and fully fabricable devices. The high degrees of freedom associated with inverse design makes it an effective method for these problems and, as such, an essential design tool to optimize future PCW applications.