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How to eliminate the polarization effects in Sagnac interferometer based sensor?

I want to build a distributed vibration sensor using sagnac interferometer. how to eliminate the adverse polarization effects? some prior works utilized two polarization controllers ,one after the laser source and the other before the PD. I want to know exactly how they works and is there any other scheme?

Another question. If i just compose a single loop using a laser source , a detector , a 2*2 coupler and SM fiber, what will i see from the detector? The two counter-propagating waves have a pi/2*2=pi phase shift cause one of them passed across the coupler twice. Is it means that all light will go back to the source?

Thank you!

Reply to
zcx83
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Hi, you can eliminate pz effects completely using a polarization maintaining fiber and polarization maintaining couplers, although this is a somewht expensive option. If you chose so, make sure you have a polarized probe light. You have to couple this light then to one of the polarization-maintaining axes of the fiber.

You description of the loop is not quite clear, although it seems you described so-called Sagnac loop mirror. That mirror will reflect all light to the input port, provided that a coupler have exact 50:50 coupling ratio.

Reply to
m4svosm

Thank you very much! I now know that the loop i madeup several days ago is exactly the so- called "fiber loop mirror". So that's why i needed a very big amplification coefficient to get a better signal display on the oscillograph. Actually i have no PM fiber so i have to find some else schemes to instead. Some patents by E.Udd said that using a polarization scrambling element in the loop can reduce the polarization induced noise in the system. I 'm going to find some related papers of other refrences to make a full view and understand of this. And some other distributed vibration sensing methods with the ability of locating of the disturbance also under my consideration.

Reply to
Chengxian.Zhang

There's considerable useful understanding to be gained by digging into the history of what I first called the "antiresonant ring" concept (and which others then pointed out to me was a Sagnac interferometer), as applied to multiple different applications in ordinary lasers, pre-fiber optics, which in turn had its own pre-history in microwave waveguides, including "Magic Tees" and related waveguide concepts, e.g.

AES, "An antiresonant ring interferometer for coupled laser cavities, laser output coupling, mode locking, and cavity dumping," IEEE J. Quantum Electron. QE-9, 247--250, Feb 1973.

AES, "Laser system with an antiresonant optical ring," U.S. Patent #3,869,210 (1975).

Send me an email and I'll send or post online an annotated list of 30 or

40 subsequent publications by me and (mostly) by others on this general topic.
Reply to
AES

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