Hi all, I'm mostly trying to pick the right fiber collimation/ coupler to get   
   a laser beam (or other source maybe) into a fiber.  Fiber is multi mode 63 um   
   diameter core, NA= 0.27.  The laser source is ~800nm.  I was looking at these   
   on thorlabs   
   https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=944&pn=F220FC-780   
   (You'll have to scroll down.)   
      
   Do I want to pick a coupler with a lens that matches the NA of the fiber to   
   get the most light into the fiber?   
      
   Does the beam diameter tell me the maximum beam size that will make it into   
   the fiber?   
   (Sorry for the rather simple questions.)   
      
   George H.   
      
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