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Entry  Wed Feb 20 10:38:46 2019, awade, DailyProgress, WOPO, Fixing 532 nm polarization linearity issues 
    Reply  Thu Feb 28 16:00:59 2019, awade, DailyProgress, WOPO, Pol launch into PM fiber 19-02-26_19-46-51_5122.jpgPMFiber.pdf19-02-28_17-52-41_5131.jpg
       Reply  Tue Mar 12 16:35:43 2019, awade, DailyProgress, WOPO, Pol launch into PM fiber 1064 nm 
          Reply  Wed Mar 13 12:44:41 2019, awade, anchal, DailyProgress, WOPO, Pol launch into PM fiber 1064 nm IMG_5149.JPG
Message ID: 2303     Entry time: Tue Mar 12 16:35:43 2019     In reply to: 2300     Reply to this: 2305  
Author: awade 
Type: DailyProgress 
Category: WOPO 
Subject: Pol launch into PM fiber 1064 nm 

I've replaced the SM fiber in the 1064 nm launch with a PM fiber (P3-1064PM-FC-5). I also moved the fiber collimator (F240APC-1064) back 2.54 cm back to give more space for a PBS cube (to check linearly of the light).  

For the 1064 nm launch it seemed to be a lot harder to find the initial alignment of the collimator using the alignment of the back propagated 650 nm fiber laser source. Here I aligned a pair of irises in the forward propagating direction and then back propagated through the PM fiber using 650 nm to get the initial​ pointing of collimator. I don't know why this is so much harder than the 532 nm case.  I suspect one of the steering mirrors is not really reflecting off the front dielectric surface.  In the end I did a bunch of systematic walking of the fiber launch mount and eventually fount the alignment.  

From 4.44 mW of input light I get 2.74 mW of light out the other end of the fiber.  This is an efficiency of 62 % which is more than enough for my needs.  I expect the HD will only need 1 mW (2 mW max), so this is fine. Getting this in coupling higher will require a bit of lens walking, not really worth it at this stage.

I had already carefully aligned the collimator orientation to put the fast axis on aligned to p-pol (wrt the table), by eye.  It seems like the launch pretty much hit the correct launch polarization on the first go.  I see little variation in the polarization when I pulse the heat on the fiber.  This is now good to go for optimizing the homodyne visible and polarization overlap output from the SQZ.

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