I would definitely recommend doing optics as a specialization not the main field. While its growing, its a very nitch field and the employment pool is not as large as the main enginering fields (EE, ME, SW).

I'm a mechanical engineer with a specialization in optics. Having both fields has helped me do better design, but also when optical work is done, I can then move onto the mechanics of things. Helps with finding jobs as you can now target either or.