Tomas,
Simple, optical uses a red light through a clear plastic (or glass) thing and uses the red light to pass signals though to the PC / Amiga etc.
Laser's basically uses a laser, obviously, (such as you would find on a CD drive) and works in a similar way but is known to be even more accurate and doesn't beam any light apart from a real tiny red dot which you would only make out by looking straight inside from a certain angle.
I'd Google or Wiki it for better more accurate detail.
