The core of a conventional optical fiber is the part of the fiber that guides the light. The core is surrounded by a medium with a lower index of refraction, typically a cladding of a different glass, or plastic. Light. A fiber optic is made of five main parts, labeled in the animation and summary image of Video 1. The numerical aperture. This post will unravel the mystery of fiber optics by exploring their three main layers— core, cladding, and coating —to show you why they're so essential for lightning-fast connections. In the 1960s, due to the advancement of technology and the growth of communication demands, people began to seek new communication technologies.