What is optical fiber?

Optical fiber consists of an area called core, which confines a light, and one called clad, which reflects it.

While confined in the core, the light is reflected by the clad to go onward. Optical fiber composed of plastic core and clad plastic is called plastic optical fiber (APF or POF), and that composed of quartz glass core and plastic clad is called plastic clad quartz optical fiber (PCF), and that composed of quartz glass core and quartz clad is called quartz optical fiber, respectively.