Hello Lorenzo,
OptiFDTD can definitely model those structures. The only real limitation of any FDTD algorithm is the overall size of your domain relative to your source wavelength as well as your smallest feature sizes. There are additionally constraints but they are generally very specific to get into here without knowing your specific application.
We have a series of webinars located on the site (https://optiwave.com/category/resources/webinars). If you select “View entire list” (will need to login) then you can find all of the videos for OptiFDTD which should provide you with an idea of our capabilities.
Scott
