The tiny fiber is encased in a plastic sheath that allows it to bend without breaking. Typically, a transmitter at one end of the fiber uses a light emitting diode (LED) or a laser beam to transmit a light pulse to the fiber, and a receiver at the other end of the fiber uses a light-sensitive element to detect the pulse.

In daily life, optical fibers are used for long-distance information transmission because the loss of light in optical fibers is much lower than that of electricity in electrical wires.

The terms optical fiber and cable are often confused. Most optical fibers must be covered with several layers of protective structure before they can be used, and the covered cable is called an optical cable. The protective layer and insulation layer of the optical fiber protect the optical fiber from damage caused by the surrounding environment, such as water, fire, and electric shock.

Fiber optic cable is divided into: cable skin, aramid filament, buffer layer and fiber. Fiber optic cables are similar to coaxial cables, except that there is no mesh shielding. In the center is a glass core through which light travels. [1]

In a multimode fiber, the diameter of the core is 50μm and 62.5μm, which is roughly the thickness of a human hair. The diameter of single-mode fiber core is 8μm~10μm, and 9/125μm is commonly used. The core is surrounded by a glass envelope with a lower refractive index than the core, commonly known as the cladding, which keeps light inside the core. On top of that is a thin plastic coat, or coating, to protect the cladding. Optical fibers are usually bundled and protected by a shell. The core is a double-layered concentric cylinder, usually made of quartz glass, with a small cross-sectional area. It is brittle and easy to break, so an additional protective layer is needed.

Description: 9/125μm refers to the fiber core is 9μm, the cladding is 125μm, 9/125μm is an important feature of single-mode fiber, 50/125μm refers to the fiber core is 50μm, the cladding is 125μm, 50/125μm is an important feature of multi-mode fiber.