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To: James Connolly who wrote (8408)	9/3/2000 2:35:33 PM
From: James Connolly	Respond to of 10309

"The cable, bent in a "U" shape, will allow signals to pass through unharmed, but the GigaBlade's receiving laser will be able to pick up light signals that "spray" from the U-turn in the fiber, Stelliga said" The idea behind the GigaBlade is quite interesting. Here's a little background on how it works from an optical point of view. Fiber optics work on the principle or phenomena of "Total internal reflection" (TIR). This means that once a ray of light is launched into a fiber the ray then bounces or zig-zags along the fiber with 100% reflectivity at the boundaries or sidewalls of the fiber. The ray therefore becomes confined or trapped within the strand of glass. Most modern fibers are so thin that a ray of light never actually gets the chance to bounce along the sidewalls of the fiber. Such fibers are called mono mode fibers, i.e , the ray has only one possible path to take, straight down the middle. However even in this case the principle of "Total internal reflection" still applies. The principle of TIR only works if the conditions are right. One way to disrupt the phenomena is to put a U-turn or bend in the fiber. If the radius of curvature is small enough then the conditions necessary for TIR start to breakdown. Put another way, a ray can make it's way around a bend with a gentle curve but once the curve becomes too sharp the light starts to escape or leak out of the sidewalls of the fiber. The trick is to find the curvature at which TIR just starts to breakdown. At this point only a small percentage of the light leaks out but the majority stays within the fiber. The light that leaks out is therefore just a weaker version of the signal within the fiber. Using this scheme the GigaBlade system is then able to read-off or monitor the packet's of data within the fiber. Put another way the GigaBlade system is effectively a kind of line tap. Some other stuff on TIR cvu.strath.ac.uk or hyperphysics.phy-astr.gsu.edu Regards JC.