Inverse-designed silicon nitride reflectors

Reflectors play a pivotal role in silicon photonics since they are used in a wide range of applications, including attenuators, filters, and lasers. This Letter presents six silicon nitride reflectors implemented using the inverse design technique. They vary in footprint, ranging from 4 µm × 3 µm to 4 µm × 8 µm. The smaller device has an average simulated reflectivity of −1.5 dB, whereas the larger one exhibits an average reflectivity of −0.09 dB within the 1530 to 1625 nm range. The latter also presents a 1-dB bandwidth of 172 nm, spanning from 1508 to 1680 nm. Despite their resemblance to circular gratings, these devices are more intricate and compact, particularly due to their non-intuitive features near the input waveguide, which include rough holes and teeth. The roughness of these features significantly contributes to the performance of the devices. The reflectors were fabricated on a silicon nitride multi-project wafer (MPW) through a streamlined process involving only a single etching step. The 4 µm × 8 µm reflector demonstrates a remarkably high reflectivity of −0.26±0.11 dB across the 1530 to 1600 nm range, rendering it suitable for high-quality factor cavities with direct applications in lasers and optical communications.