Inverse-Designed Photonic Crystal Devices for Optical Beam Steering.

The ability of photonic crystal waveguides (PCWs) to confine and slow down light makes them an effective component to enhance the performance of many photonic devices, such as optical modulators, optical sensors and optical phased arrays (OPAs). However, the integration of PCWs in photonic applications comes with various design challenges, most notably, engineering the PCW mode dispersion and efficiently coupling to the modes of the PCW. Here, we solve these challenges through the use of inverse design methodologies. The dispersion relation of even and odd mode PCWs are engineered for a group index of 25 over a bandwidth of 20nm and 12nm, respectively. For both PCW designs, we create strip waveguide couplers, as well as free space grating couplers. The transmission of optical delay devices constructed with the strip waveguide converters are experimentally characterized and, using the PCW grating couplers, the group index of both PCWs is measured. Finally, radiative losses are introduced to our PCW designs while maintaining the dispersion relation of the original PCW. With these loss and dispersion engineered PCWs, alongside the strip waveguide couplers, we construct OPAs with different radiative strength. The OPAs are experimentally characterized and shown to steer a light beam up to 20{\deg} in a 20nm bandwidth. The devices in this work illustrate how inverse design methods can enable the use of PCWs in future LiDAR systems, optical communication, and sensing applications.