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.
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These fibers are single mode strands in room 6 that connect to ISB.

isb-01
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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.