i don't know... i mean it's an exercise where i have to design this circuit... i told you everything i know... i don't know anything about lasers... what i know and have studied is especially operational amplifier and its applications (comparator, filters, etc)... then modulations and demodulations (ask psk fsk ook dpsk and so on...)
i have to suggest a circuit with a photocell that has to send to 200m a signal that ranges between those values... moreover it has to be a series of pulses... at the end i have to suggest a data trasmission... that's all...