This is a clean single mode test cable. The light spot in the
center is the 9 micron fiber core. The grey circle is the 125 micron cladding
that surrounds the core.
The following pictures are single mode fibers in Comm 6 that connect to the machine room.
These fibers are single mode strands in room 6 that connect to ISB.
This is a dirty multimode jumper that was lying around. The lack of definition of the nominal 62 micron core is evidence that this is a graded (graduated) index fiber.