Re: fiber optic question

I'm just starting to dabble in this direction myself, my plan is to use a laser collimating lens or ball lens to couple the beam into a commercial patch cord (though i might end up making the cables myself - getting sutiable finish on lengths of fibre is an expensive art it seems) - I'm going for a single mode fc/apc (fibre coupler/angled phsysical contact) to maintain coherence and limit end reflections - these are available from many suppliers, who rate their fibres down to 325 or 250 nm as custom jobs (the reputation is that UV lasers don't go through fibres - seems to work ok on my leica confocal, which I've just successfully hitched up to a replacement non-leica-supplied laser). 

FC/APC adapters are also available (these are just empty receptacles that the patch cord will mate with reproducibly), the lens goes between the beam and the adpater. micropostioners (or custom plate steerers a la laser high reflector mirror mounts) will be needed to ensure that a: the end of the fibre is at the focal point of the lens, and B: the laser enters the fibre @90 degrees).	The sprung plate with three screws used on the Enterprise beam-splitting periscope may be adequate for this, along with some careful nudging, you'd have to try and err.

The positioning needs to be very precise, and rigid - the core of the fibre is in the order of 5 to 8 microns diameter for single mode fibres (I'm going to compare 50 micron multimode with single mode to see how bad multimode fibres might be - it would certainly ease alignment to do so, if it works, I'll see how 1mm plastic goes, not holding out much hope there tho:))

Once you've got the set up to launch the beam into the fibre, you need something similar at the other end to re-collimate it - the laser leaves the fibre over an angle governed by it's numerical aperture and the refractive indices of the fibre and the medium the beam is entering (if you're using index matching gel to directly couple to quartz, you might not need this), again, you could use a converging lens of the right strength to directly focus it on your target, or you could focus it down then extend the waist with a diverging lens (maybe:))

I found using an fc/apc pigtail (ie a connector with a short length of bare-ended fibre) coiled tightly to make a "mode filter" helped the intial lens/adapter alignment to launch the laser into the fibre, then I fitted the leica fibre, unhooked it from the confocal head, aimed it at a paper target and fine-tuned the focus, then hooked it back into the head and adjusted the focus/orientation to that.  The mode filter helped a great deal: rough alignment can be had with the fibre held straight, but some of the light is carried by the cladding once this is peaked, you coil the fibre, and the cladding-carried light leaks out, while the core light doesn't, so you re-tweak the alignment to get full power again, and bingo.

If you have a workshop, you should be able to make/buy all the gear you need for maybe 200 dollars (plus workshop costs), if you need to buy micropositioners, you'll find these are 200-400 dollars each, but micrometer barrels are a mere 8 dollars so if you can get the workshop to use these and make some sledges, again the costs should be pretty low, designs for angular positioners can be found in sam's laser faq's (mirror steering plates)


If you're going to have the laser trailing around, you'll need a steel armoured cable for safety and reliability, though plain plastic buffered should be fine if you run it through conduit - if you're going for off-the-shelf cable, make sure it's able to carry 488nm without significant loss, many are optimised to telecoms laser wavelengths (800nm ish and 1300 nm ish)

Ray

ps the only suppliers I've got are european, if you have difficulty finding suppliers of one-off ball lenses, patch cords, positioners etc, let me know and I'll forward them to you
  ----- Original Message ----- 
  From: WThrondset@genencor.com 
  To: Cytometry Mailing List 
  Sent: Wednesday, March 30, 2005 9:03 PM
  Subject: fiber optic question



  Hello, 

  This is more of a laser/hardware question - but I know some of you out there have experience with this.  I have a flow cytometer with an Enterprise laser (Coherent) that emits both UV and 488.   I'd like to use a fiber optic cable to deliver the 488 beam to another instrument approximately 200 ft away from the laser.  Does anyone know what type of fiber I'd need or how to determine this? 

  Thanks very much, 

  Bill Throndset
  Senior Research Associate
  Genencor International
  925 Page Mill Road
  Palo Alto, CA 94304


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