Optical Fiber Patch Cord/Cable is similar to coaxial cable, except that there is no mesh shielding layer. In the center is the glass core through which light propagates. 

In a multimode fiber, the diameter of the core is 50μm~65μm, which is roughly equivalent to the thickness of a human hair. The single-mode fiber core has a diameter of 8 μm to 10 μm. 

The core is surrounded by a glass envelope with a lower refractive index than the core to keep the optical fiber in the core. On the outside is a thin plastic jacket to protect the envelope.