Zjs log: Difference between revisions

* '''Added a new passive fast feedback branch that goes directly to the laser diode.''' I talked to Larry yesterday about our issues trying to feedback through the laser driver. He said that that's problematic for same two reasons we had been suspecting: ground/noise issues and the fact the laser driver mod input has very high gain, so you need very low noise. He suggested a fast feedback branch directly to the diode and sketched out a little circuit. I implemented something like it. Turns out we had a lot of little discarded fast feedback boxes lying around so i cannibalized one of those used the layout suggested by Larry. His circuit is nice and simple and passive, so we also don't have to worry about powering it. I stuck it inline immediately before the laser. As for an error signal pick-off, i added one inside the lockbox, picking off inside the fast feedback branch, immediately after the first op-amp buffer. This makes it so the phase is correct, and not inverted relative to the slow feedback branch. I didn't disconnect the existing fast feedback but left it in place. We could try sending that directly to he diode as well.