Dear @voglerv

Indeed, nested parameter sweep and optimization tab will be useful for small tweaks in geometry and not for designing a cavity from scratch. The best approach will be to use literature to come up with the design theory.

In my best knowledge, a good approach is to focus on bandstructures and simulate periodic structure to find the bandgaps (in your case you want a large bandgap at ~1.56um). The periodic array section will act as the mirror part of PC. Then gradually tapering the hole size to build the cavity section. There should be plenty of papers and ideas on how you need to taper the hole size. For example, this paper was really good for designing 1D PC cavity (https://arxiv.org/abs/1108.2675) and you should be able to find similar papers that discusses the geometry for hexagonal PC cavities.

Please note that designing a high-Q PC cavity is generally challenging and will take time. Once you come up with some initial design, you can perform weep and use optimization tab to modify geometry to support high-Q devices. You also need to make sure that your devices is robust to fabrication imperfections if you are planning to measure their response experimentally.

I hope this was helpful.