I need to combine two DC voltages to scan and lock a laser. The scanning will be 0-100 V and the locking will be performed with a small correcting voltage, +/- 1 V. Both of these will be fed into a PZT driver. My advisor suggested using an opto isolator, however I am not sure how that would work unless there are opto isolators that exist with two LEDs and one detector. Also, I am unsure how that would work with the negative voltages. Any help would be really appreciated, as a chemist I only have a general physics knowledge of electronics.