Easiest opto-isolator is to epoxy the sfp into the socket, and then fill the rx port on the critical side with epoxy, and then just run one fiber. The epoxy may

Easiest opto-isolator is to epoxy the sfp into the socket, and then fill the rx port on the critical side with epoxy, and then just run one fiber. The epoxy may seem excessive, especially if the sfp dies and you have to swap a whole nic, but it makes people stop and think.