Fiber optic patch cord means that both ends of the optical cable
are equipped with connector plugs to realize the active connection
of the optical path; one end with a plug is called a pigtail. Fiber
optic patch cords are similar to coaxial cables, but without the
mesh shield. In the center is the glass core for light propagation.
In a multimode fiber, the diameter of the core is 50 μm to 65 μm,
roughly equivalent to the thickness of a human hair. The
single-mode fiber core has a diameter of 9 μm. The core is
surrounded by a glass jacket with a lower refractive index than the
core to keep the fiber inside the core. On the outside is a thin
plastic jacket to protect the envelope.