I know for some backbone comms technologies (SDH, maybe?) there has to be some sort of carrier signal at all times. I think this is probably true for fibre as w

I know for some backbone comms technologies (SDH, maybe?) there has to be some sort of carrier signal at all times. I think this is probably true for fibre as well, it's never truly dark. So maybe the bandwidth being there should be used for something useful? (I purposely ignore the processing power required at the other end to serve you the images ;-)