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Entry  Tue Jun 11 19:25:58 2019, aaron, Configuration, BHD, Reviving the single OMC BHD design? singleOMC.pdf
    Reply  Fri Jun 21 19:22:40 2019, Koji, Configuration, BHD, Reviving the single OMC BHD design? 
Message ID: 14664     Entry time: Tue Jun 11 19:25:58 2019     Reply to this: 14685
Author: aaron 
Type: Configuration 
Category: BHD 
Subject: Reviving the single OMC BHD design? 

I drew out some idea of how we might use a single OMC to clean both paths of the BHD after mixing, without being susceptible to polarization-dependent effects within the OMC. Basically, can we send the two legs of the BHD into the OMC counterpropagating. I've attached a diagram.

I think one issue would be scattered light, since any backscatter directly couples into the counterpropagating mode, and thus directly to the PD. However, unless the polarization of the scattered light rotates it would not scatter back to the IFO. And, since the LO and signal mix before the OMC, this scattered light would not directly add phase noise.

Maybe more problematic would be that if the rejection at the PBS (or the polarization rotation) isn't perfect, light from the LO directly couples into the dark port. Can we get away with a Faraday isolator before the OMC? 

Diagram attached.

Attachment 1: singleOMC.pdf  280 kB  Uploaded Tue Jun 11 20:38:23 2019  | Hide | Hide all
singleOMC.pdf
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