Re: Laser beam sharing via multi-mode fibers

Posted by Michael Giacomelli on
URL: http://confocal-microscopy-list.275.s1.nabble.com/Laser-beam-sharing-via-multi-mode-fibers-tp7584037p7584042.html

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I agree with George that a beam splitter is a better solution (power
permitting).  I have done this with a single mode fiber and had to
adjust the coupling every week or so due to drift.  With multimode you
will be much less sensitive to this (in proportion to the core size),
but larger cores may result in you losing power anyway due to the
larger output core diameter.  If you do go with the flip mirror, I'd
recommend having the deflected beam go into the microscope rather than
the fiber.

As for your second question, vibration can have some small effect on
light propagating through fibers with more than one mode as any
bending of the fiber will alter the distribution of power between
modes.  Probably though if you are routing this fiber through a
ceiling you'll end up randomizing the mode distribution fairly well
anyway so it shouldn't matter too much.

Mike

On Thu, Jul 30, 2015 at 3:25 AM, Kyle Douglass <[hidden email]> wrote:

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>
> Hello everyone,
>
> In my lab we have two microscope setups in two different rooms separated by
> a hallway between them. One of our microscopes has a free-space laser that
> must remain in place; however, I would like to use this laser with the
> microscope located in the other room while maintaining its ability to be
> used with its current microscope. Both microscopes accept free-space beams
> as inputs for fluorescence microscopy in an epi-illumination geometry.
>
> I am considering the following solution: introduce a flipper mirror before
> the fixed laser to allow me to switch between a path that would send the
> beam into its current microscope and another path that would couple the beam
> into a long multi-mode fiber. I would then run the fiber above the ceiling
> panels between the labs and onto the table of the other setup, where the
> output light would be collimated and introduced like normal into the other
> microscope. I do not require a single-mode beam for the second microscope.
> In fact, I am proposing to use a multi-mode beam to achieve a better power
> coupling efficiency into the fiber and to prevent burning the fiber cladding
> by allowing for larger focal spot sizes when coupling. I also am not
> concerned about the speckle on the sample since I am averaging over multiple
> speckle patterns during the acquisition of a single frame.
>
> My primary concern is the stability of the input and output couplers. The
> microscopes are used by people with little optics experience and this
> solution must be as easy as possible to switch between the two paths.
> Ideally, the only action required would be to flip the mirror up or down
> (after the initial alignment, of course).
>
> Here are my questions:
> 1. Has anyone tried such an approach with satisfactory results and would be
> willing to comment?
> 2. Would vibration of the fiber significantly affect its propagation
> direction upon leaving the output coupler?
> 3. Would a "standard" flipper mirror or magnetic mount have sufficient
> return accuracy to avoid having to adjust the input coupler alignment every
> time we switched between microscopes?
> 4. Is there another obvious solution I am missing?
>
> Thanks for the responses!
> Kyle
>
> --
> Kyle M. Douglass, PhD
> Post-doctoral researcher
> The Laboratory of Experimental Biophysics
> EPFL, Lausanne, Switzerland
> http://kmdouglass.github.io
> http://leb.epfl.ch