How Fiber Carries Data With Light

Fiber-optic cable carries data as pulses of light instead of electrical signals on copper. A laser or LED flashes light on and off (or modulates it) to represent the ones and zeros of digital data, and a detector at the far end reads the flashes back into data. Because light travels through glass with very little loss, fiber reaches far greater speeds and distances than copper.

A fiber strand has a layered structure:

• Core — the ultra-thin glass center that carries the light.
• Cladding — glass around the core that reflects light back inward.
• Buffer and jacket — protective coatings outside.

The core and cladding are made of glass with slightly different properties, and this difference is what keeps the light bouncing along the core.