2a519ccd   
   From: rrllff@yahoo.com   
      
   On May 27, 9:33 pm, Joe Gwinn  wrote:   
   >   
   > The offset spot launch was intended to reduce pulse broadening   
   > (increase fiber bandwidth), to increase the reach of gigabit fiber   
   > optic links.  The bandwidth of a fiber is expressed in   
   > Megahertz*Kilometers, the product being a constant for any fiber   
   > design.  So, if you have fiber guaranteed to carry one gigabit data 300   
   > meters, that fiber will carry ten gigabit data one tenth as far, 30   
   > meters, and so on.   
   >   
   > In the middle radii, all the helical modes take the same time to get   
   > from one end to the other.  One way to think of it is to regard a   
   > multimode fiber as a form of GRIN lens - in both cases, the refractive   
   > index profile is parabolic or nearly so.   
   >   
   > One test that is made of fiber is to collect the impulse response   
   > function as a function of the radius at which the drive spot center is   
   > located.  The drive spot diameter does not change.  Things really clean   
   > up in the middle radii, especially with fiber designed for the purpose.   
   > Such fibers have 50-micron cores and are described as being intended   
   > for laser transmitters.   
   >   
   > Joe Gwinn   
      
   This is not my field but I am also curious.  Am I correct that the   
   fibers need to be straight?  It seems that any bends in the fiber will   
   very quickly mix the modes.   
      
   http://www.richardfisher.com   
      
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