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Fiber Protrusion and Undercut    [Back]

                    Fiber Protrusion                                             Fiber Undercut

Fiber undercut and protrusion are shown above, both conditions are undesirable.  In order to view the differences in height from the fiber surface to the ferrule surface, you must first tilt the connector slightly.  This is done to cause the circular fringes to cross over the fiber / ferrule boundary and begin to straighten out.  To tilt the connector, turn the Tilt Dial clockwise while observing through the eyepiece.  Once you begin to feel resistance, you will notice the fringe pattern shifting. Continue turning approximately ½ turn until there are several fringes over the fiber face.  As the fringes cross over the fiber / ferrule border, they should remain straight, and not shift at all.  This can be seen in [Figure 3].  If no fringes can be seen on the fiber surface, but can be observed on the ferrule surface, then the fiber surface may be too far down to obtain fringes.  In which case the connector is unsatisfactory.  If fringes can be found on the fiber face, but not on the ferrule surface, then the fiber is protruding so far from the ferrule surface that fringes cannot be obtained.  This is also unsatisfactory.

 Undercut and protrusion can be caused by several things.  Undercut is most often caused by over polishing, and there is little that can be done to correct this.  Since the ceramic used in ferrules is so much harder than the glass fiber, the more you try to polish down the ferrule, you will also polish down the glass as well.  Protrusion can be the result of under-polishing of the fiber.  If that is the case, it can be corrected by further polishing.  However, both undercut and protrusion can also be the result of adhesive failure.  In that case, carefully examine the adhesive, its expiration date, and curing time and temperature.

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       2008 Pine Valley Precision, Inc.
       Last modified: 02/27/08