Page 1 of 1

AGITATOR FOR OPTICAL FIBER.

PostPosted: Sun Aug 12, 2018 11:04 am
by Joan Guarro Flo
Hello,

After the great and good solutions expossed by Andrew Smith, Christian Buil and others , I show the results to my agitator for optical fiber.

Here can see its operation, https://www.youtube.com/watch?v=F_klNTh ... e=youtu.be

It is very possible that the results can be improved. But I think that them are acceptable.

I leave here two graphics wiht Vega's results.

You'll already give me your opinion.

Regards, Joan.

Re: AGITATOR FOR OPTICAL FIBER.

PostPosted: Sun Aug 12, 2018 12:47 pm
by Paolo Berardi
Dear Joan, I'm no expert on optical fibre but I can see a big improvement regarding the modal noise. I think you did a great job.

Have a nice observations with the "new" equipment!
Paolo

PS: watching it while working is impressive!

Re: AGITATOR FOR OPTICAL FIBER.

PostPosted: Sun Aug 12, 2018 2:42 pm
by Andrew Smith
Joan, excellent results. Your design is magnificent and a joy to watch.
Regards Andrew

Re: AGITATOR FOR OPTICAL FIBER.

PostPosted: Sun Aug 12, 2018 4:25 pm
by Christian Buil
Excellent Joan ! We can clearly see the importance of the fiber shaking. A large majority of fiber linked spectrograph users under evaluate this aspect while the potential gain is very high ...

Christian

Re: AGITATOR FOR OPTICAL FIBER.

PostPosted: Sun Aug 12, 2018 4:33 pm
by Olivier GARDE
Hi Joan,

Great...

Did you try different speed rotation ?

Olivier

Re: AGITATOR FOR OPTICAL FIBER.

PostPosted: Mon Aug 13, 2018 6:33 pm
by Joan Guarro Flo
Thanks to all, for your support.

I still have the question, if I can do something to improve the results .. I will make modifications.

I think for now, the result is acceptable ...

Olivier, the rotation speed is fixed, one lap every 5 seconds. The question is, if I vary the rotation speed, will I improve the final result? How did I do it?

Joan.

Re: AGITATOR FOR OPTICAL FIBER.

PostPosted: Mon Aug 13, 2018 8:37 pm
by Andrew Smith
Hi Joan, I think Christian's paper "Modal noise in fibre-coupled spectrographs" gives a good method of testing fibre agitators. If you look at the far field image projected onto a CCD camera you want it to be smooth with a sampling time less than a typical exposure.

The key, from the papers I have read, is to excite as many modes as possible by using chaotic motion over a given sampling period. I suspect your design will achieve this but the measurement Christian advises will give a definitive answer.

One area I found an issue was that while spectra via the telescope were fine with my agitator, fibre fed calibration spectra were not. This was because the calibration fibre and the injection system were introducing model noise which I had to eliminate.

Regards Andrew

Re: AGITATOR FOR OPTICAL FIBER.

PostPosted: Mon Aug 13, 2018 8:37 pm
by Olivier GARDE
Joan Guarro Flo wrote:Olivier, the rotation speed is fixed, one lap every 5 seconds. The question is, if I vary the rotation speed, will I improve the final result? How did I do it?

Joan.


Did you find any relation between rotation speed vs reducing noise ?

Re: AGITATOR FOR OPTICAL FIBER.

PostPosted: Wed Aug 15, 2018 9:51 am
by Joan Guarro Flo
Many thanks Andrew, for your considerations, certainly, how you say, that have to take some precaution for resolve this problem.

Hi Olivier, I don't know if I doing the things correctly, but I tried the five seconds rotation becouse it has two rotation for a exposure time to bright stars. Really I'm guided for my intuition I don't know how mathematics.

Friendly, Joan.

Re: AGITATOR FOR OPTICAL FIBER.

PostPosted: Thu Aug 16, 2018 7:19 pm
by Joan Guarro Flo
Hi,

Another dramatic example of "modal noise".

Now I'm going to do a new a agitator for the LINX spectrograph.

Regards, Joan.