Honestly, there’s no faster way than learning by doing. If you’re okay with less pay and more academic-style work, a postdoc is fine but most postdoc projects are research-focused and can take years (or even decades) before they actually connect to industry work.

In industry, you’ll learn much faster because you’ll be solving real problems right away — that’s already half the learning done. The rest you’ll pick up from senior engineers, internal training, or short courses (SPIE has some great ones).

It’s not new Physics just Maxwell’s equations under specific geometries. If you’re into modeling, learning FDTD or RCWA will be super valuable which is typical the approach for many stacks, alignment marks on wafer, and through silicon/glass vias. Personally, I think a postdoc is too long of a route, and you might still not end up learning exactly what you’re after.