Light travels down a fiber optic cable by bouncing off the walls of the cable repeatedly. The core is the middle of the cable and the glass. Photons travel in waves through the inner core of the fiber. Because this core region has higher refractive index (i. Note that in some countries, including the UK, fiber optics is spelled "fibre optics. First, the light-carrying core. Each component – or cylindrical layer – of the optical fiber cable serves a specific purpose in the efficient.