Posted by
Zdenek Svindrych-2 on
URL: http://confocal-microscopy-list.275.s1.nabble.com/Laser-beam-sharing-via-multi-mode-fibers-tp7584037p7584053.html
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Hi Kyle,
if you plan to use the fiber output for microscope illumination, you either
need a uniform far-field angular distribution (for Kohler illumination) or a
uniform intensity at the fiber end facet (for critical illumination). I have
tried many tricks to get uniform output from a multimode fiber (e.g. weak
rotating diffusers, shaking coupling lens, shaking the fiber), but it never
worked perfectly (at least in the critical illumination mode, 50 um step
index fiber).
However, there are commercial fiber shakers, e.g. Borealis (Spectral Applied
Research, later bought by Andor, now part of Oxford Instruments) that works
really great, as you can appreciate in Vutara superresolution microscopes
and the new Andor spinning disc systems.
There are no pointing stability issues with multimode fibers, the output
beam (or speckle pattern) is always within the NA of the fiber, though the
pattern changes randomly with time. Just try to focus your laser into a
piece of mm fiber, it's a few USD investment. Or just shine your laser into
a liquid light guide that you find laying around, that might give you an
idea how seriously compromised the uniformity might be...
Good luck!
zdenek
---------- Původní zpráva ----------
Od: Kyle Douglass <
[hidden email]>
Komu:
[hidden email]
Datum: 31. 7. 2015 2:43:22
Předmět: Re: Laser beam sharing via multi-mode fibers
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Thanks for the feedback, everyone. I appreciate the help quite a lot.
One thing that is still not clear to me, though, is whether and how the
direction of the laser beam may be affected at the output coupler due to
fiber vibrations. As mentioned by a few others, the speckled intensity
profile at the fiber's output face is going to be randomly modulated as
the fiber vibrates. From my college days, I seem to recall that spatial
mode fluctuations are linked to pointing stability
(
http://www.rp-photonics.com/beam_pointing_fluctuations.html) in laser
cavities. Could vibrations of the fiber result in something similar,
whereby the laser leaving the fiber points in random directions with
time? Or would this effect likely be too small to matter for aligning
the beam at the second microscope?
I have an idea that this will not be a serious issue, but I am wondering
if anyone can comment before I invest the time in doing this.
Thanks again everyone!
Kyle
On 07/30/2015 06:18 PM, Craig Brideau wrote:
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>
> Depending on how straight the run between the rooms is, you might be able
> to run a beam tube across the hallway in the ceiling and do it free space
> with a periscope. This would save you the headaches of fiber coupling and
> reduce any long-term stability issues. I'm guessing you are not up for
that
> level of 'infrastructure modification' though, so the multimode fiber may
> be the way to go. Try to match the design wavelength of your optics as
best
> as you can to the wavelength of your laser. Assuming you have a
> monochromatic source, you can get away with simpler, cheaper optics by
> using single-wavelength components. If your laser is a common wavelength
> these should be easy to get.
>
> Craig
>
> On Thu, Jul 30, 2015 at 9:59 AM, João Lagarto <
[hidden email]> wrote:
>
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>>
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>>
>> Hi Kyle,
>> I don't know if this is a problem for you but in case you have a pulsed
>> laser, the fibre will also cause temporal dispersion of the pulses. This
>> may be a problem for time-critical applications such as FLIM.
>> João
>>
>>
>> Às 08:25 de 30/07/2015, Kyle Douglass escreveu:
>>
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>>> To join, leave or search the confocal microscopy listserv, go to:
>>>
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy>>> Post images on
http://www.imgur.com and include the link in your
posting.
>>> *****
>>>
>>> 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.iohttp://leb.epfl.ch"