User:Anthony Salvagno/Notebook/Research/2010/08/18/Fiber Optic Fun
The past few days I've been lacking in the note department but let me summarize what we've done and what we've seen.
- We imaged the AOM onto the QPD and managed to get the drift to a minimum. We didn't eliminate it, but we did get it to what I deem to be a manageable amount. Is the problem fixed? No. But we did get some promising results.
- We had to do it with a lens. When there was no lens on the QPD, there was almost no change in drift. When we put a lens on the QPD we were able to determine where was the appropriate location for the QPD.
- That leads us to believe that spot size plays a factor. We haven't done any tests to determine to what extent, but with a lens the spot size is small because we are focusing the beam onto the QPD. Without the lens we have pur collimated beam with a diameter ~1-2mm depending on where our QPD is. It was in this range that we would get very large drifts.
Today we are trying to couple the laser to a fiber and are shining the fiber directly on the QPD. It is difficult to tell if we are getting any light in the fiber and right now we aren't getting much. Starting with 500mW power gives us an output of ~1mW which is no good. We decided to try it anyways to see what happened.
- QPD causes some sort of drift when SUM signal is less than 1V. That was an interesting effect.
- We tested AOM drift and it had none when it went through the fiber. We tested it by moving the lens in front of the fiber up and down which should change where the laser spot is. We would see a change in SUM signal meaning less power was getting through, but no shift in X/Y position. So any drift before the fiber would not be translated to the QPD.
- We got a super crisp clean beam with next to no noise on the QPD. That was nice to see.