RE: Patch cable showing no core
by TechGuy on Fri, Jul 11 2008 9:46 AM
There are several factors that can affect whether or not the core of a fiber can be seen in a microscope. The best way to ensure that the core isvisible is through core illumination, shining visible white light into the opposite end of the fiber being inspected. In many cases, this occurs without trying, if the opposite end is open to the air. If the fiber is connected to equipment (please don't use a handheld optical microscope to inspect live fibers...), or if the cable is relatively long, there may not be enough light ini the core to make it visible. Other factors that can affect this are the illumination style of the scope, coaxial illumination bounces light directly off the face of the connector, which may or may not allow the core to be seen, while oblique illumination bounces the light off the connector face at an angle, which will show the core easily due to the light bouncing off of the different purities of glass differently. While that may make oblique lighting sound like the way to go, there are trade-off's to that as well. Since the light is shining on the endface at angle, scratches, pits, chips and other defects can appear larger than they really are due to shadows being cast across the endface.
The polish of the connector can affect the core visibility as well. The polishing process can affect the core and cladding slightly differently depending on the process being used. All in all, the only way to be sure you can see the core is by illumination from the opposite end.
