Fiber optics work by using total internal reflection to guide light through thin glass or plastic fibers. Light entering the fiber at angles greater than the critical angle reflects off the fiber walls, bouncing along the fiber without escaping. Learn about their core and cladding structure, single‑mode vs multi‑mode fibers, and why optical communication powers our digital world. An optical fiber is comprised of a light-carrying core in the center, surrounded by a cladding that acts to traps light in the. Total internal reflection occurs when light traveling through a denser medium (core) strikes the boundary with a less dense medium (cladding) at an angle greater than the Instead of refracting out, the light is completely reflected back into the core, ensuring continuous transmission over long. Optical fibers operate on the principle of total internal reflection, which keeps the light in the fiber core and guides it down the length of the fiber.