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 Tue Apr 24 11:31:59 2018, gautam, Configuration, ALS, Proposed changes to EX fiber coupling Tue Apr 24 18:54:15 2018, gautam, Configuration, ALS, Proposed changes to EX fiber coupling Wed Apr 25 19:09:37 2018, gautam, Configuration, ALS, New look EX Fiber coupling Thu Apr 26 11:24:50 2018, gautam, Configuration, ALS, New look EX Fiber coupling - pol stability Thu Apr 26 18:58:21 2018, Bruce, Configuration, ALS, New look EX Fiber coupling - pol stability Fri Apr 27 01:36:02 2018, gautam, Configuration, ALS, IR ALS noise performance Wed May 2 21:39:33 2018, gautam, Configuration, ALS, IR ALS for EY Fri May 4 21:17:57 2018, gautam, Configuration, ALS, BeathMouth pulled out of PSL table Tue May 8 00:40:51 2018, gautam, Configuration, ALS, BeathMouth pulled out of PSL table Thu May 24 19:41:28 2018, gautam, Configuration, ALS, BeathMouth reinstalled on PSL table Thu May 24 13:06:17 2018, gautam, Configuration, ALS, DFD noises Thu May 24 20:31:03 2018, gautam, Configuration, ALS, DFD noises
Message ID: 13824     Entry time: Tue May 8 00:40:51 2018     In reply to: 13817     Reply to this: 13889
 Author: gautam Type: Configuration Category: ALS Subject: BeathMouth pulled out of PSL table

Summary:

I did some more BeatMouth characterization. My primary objective was to do a power budget. Specifically, to measure the insertion loss of the mating sleeves and of the fiber beam splitters. All power numbers quoted in this elog are measured with the fiber power meter. Main takeaways:

• Measured insertion loss of all mating sleeves, which are ADAFCPMB2, are in agreement with the < 1dB spec. 1 dB in power is ~20%.
• But there is large variance in the above number, between different supposedly identical connectors.
• Measured insertion loss from input port to coupled ports of the fiber beamsplitters are slightly larger than spec (~3.5dB), when measured after mating the fiber beamsplitter (which has Hi1060 flex fiber) and PM980 fiber (which is what brings light to the BeatMouth).
• But measured insertion loss when mating is between Hi1060 flex fiber ends is more in line with the expected value of ~3.5dB.
• Isolation of fiber beam splitters seems to match the spec of >55dB.

Results:

• I used the fiber bringing 416uW of IR light from EY for this test.
• Insertion loss was measured by injecting the fiber light at one port and measuring the transmitted power at various other ports.
• In order to couple the fiber power meter across a single mating sleeve, I used a short (~1m) patch cable from newport (F-SY-C-1FCA). Technically, this is single mode fiber with the correct type of connector, FC/APC, but is not PM.
• See Attachment #2 for the labeling of the connectors which is how I refer to them in the table below.
• Lest there be confusion, I use the definition of insertion loss  $\mathrm{Insertion ~loss [dB] }=10\mathrm{log_{10}}(\frac{P_{in}}{P_{out}})$.
Mating Sleeve # Insertion loss [dB]
1 0.38
2 0.65
3 0.71
4 0.43
5 0.95
6 0.79
7 0.5

Remarks / Questions:

1. Is there any way to systematically reduce the insertion loss? Like getting a better mating part?
2. Question for the fiber experts: How do we deal with the unused port of the beam-splitters? Right now, they are just capped. But as you can see in Attachment #1, the caps certainly don't block all the light. What are the implications of back-scattered light into the fiber on the ALS noise? I guess the beamsplitter itself has the spec'd 55dB directivity, so do we not care about this?
 Attachment 1: IMG_6986.JPG  894 kB  Uploaded Tue May 8 02:08:21 2018
 Attachment 2: IMG_6987.JPG  2.561 MB  Uploaded Thu May 24 18:47:26 2018
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