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Entry  Mon Sep 19 23:19:40 2011, Keiko, Update, IOO, AM modulation mistery 
    Reply  Tue Sep 20 23:01:37 2011, Keiko, Update, IOO, AM modulation mistery 
       Reply  Wed Sep 21 16:44:18 2011, Keiko, Update, IOO, AM modulation mistery P9210138.JPGP92101381.jpg
          Reply  Wed Sep 21 17:42:35 2011, rana, Update, IOO, AM modulation misery 
             Reply  Wed Sep 21 18:53:03 2011, Keiko, Update, IOO, AM modulation misery AM0.pngAMratio1.pngAMratio50.png
                Reply  Wed Sep 21 21:13:35 2011, rana, Update, IOO, AM modulation misery 
                   Reply  Thu Sep 22 17:29:42 2011, Keiko, Update, IOO, AM modulation mistery AMmod0MICH.pngAMmod1e-1MICH.pngAMmod0SRCL.pngAMmod3e-3SRCL.pngAMmod3e-3SRCL-AS55I.png
                      Reply  Sat Sep 24 09:55:42 2011, Keiko, Update, IOO, AM modulation mistery 
Message ID: 5491     Entry time: Tue Sep 20 23:01:37 2011     In reply to: 5472     Reply to this: 5502
Author: Keiko 
Type: Update 
Category: IOO 
Subject: AM modulation mistery 

Keiko, Suresh

AM modulations are still there ... the mechanical design for the stages, RF cables, and connections are not good and affecting the alignment.

I write the activity in the time series this time - Because we suspect the slight EOM misalignment to the beam produces the unwanted AM sidebands, we tried to align the EOM as much as possible. First I aligned the EOM tilt aligner so that the maximum power goes through. I found that about 5% power was dumped by EOM. After adjusting the alignment, the AM modulation seemed be much better and stable, however, it came up after about 20 mins. They grew up up to about -40dBm, while the noise floor is -60 dBm (when AM is minimised, with DC power of 8V by PDA225 photodetector).

We changed the EOM stage (below the tilt aligner) from a small plate to a large plate, so that the EOM base can be more stable. The EOM stands on the pile of several black plate. There was a gap below the tilt aligner because of a small plate.  So we swapped the small plate to large plate to eliminate the springly gap. However it didn't make any difference - it is the current status and there is still AM modulations right now.

During above activities, we leaned that the main cause of the EOM misalignment may be the RF cables and the resonator box connected to the EOM. They are connected to the EOM by an SMA adaptor, not any soft cables. It is very likely applying some  torc force to the EOM box. The resonator box is almost hunging from the EOM case and just your slight touch changes EOM alinment quite a bit and AM mod becomes large. 

I will replace the SMA connector between the resonator box and EOM to be a soft cable, so that the box doesn't hung from EOM tomorrow. Also, I will measure the AM mod depth so that we compare with the PM mod depth.



 Keiko, Anamaria

We started to investigate the AM modulation mistery again. Checking just after the EOM, there are AM modulation about -45dBm. Even if we adjust the HWP just before the EOM, AM components grow up in 5 mins. This is the same situation as before. Only the difference from before is that we don't have PBS and HWP between the EOM and the monitor PD. So we have a simpler setup this time.

We will try to align the pockells cell alignment tomorrow daytime, as it may be a problem when the crystal and the beam are not well parallel. This adjustment has been done before and it didn't improve AM level at that time.


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