Is there a way to reduce the amplitude of a light wave to half its value in one case and do nothing in the other cases? Three Cases: Case A: Light amplitude input is 2 - reduce to 1 on output (cut in half) Case B: Light amplitude input is 1 - output is 1 (do nothing/pass through) Case C: Light amplitude input is 0 - output is 0 I would like to design a hi-speed device that would allow this to occur. By hi-speed I mean instantaneous or without converting to/from any electronics. I can almost envison a possibility where you have some kind of photon absorbing medium that doesnt kick in until a certain intensity is reached. Does anyone have any insight or could point me into a(ny) direction with this?