Cables that transmits signals in form of light is

Optical Fiber:

• It is a very thin fiber made of glass and plastic having a radius of the order of a micrometer (10-6 m).
• It works on the principle of Total Internal Reflection.
• It is lightweight, fast, and useful for long-distance data and light transmission with very few losses.
• Optical fiber mostly used for communication purposes with negligible loss of energy.
• A bundle of such thin fibers forms a light pipe.

Explanation:

• The working principle of optical fibers is Total Internal Reflection.
• Each fiber consists of a core and cladding.
• The refractive index of the material of the core (μ1) is higher than that of the cladding (μ2).
• When the light is incident on one end of the fiber at a small angle, the light passes inside, undergoes repeated total internal reflections along with the fiber, and finally comes out.
• The angle of incidence is always larger than the critical angle of the core material with respect to its cladding.
• Even if the fiber is bent, the light can easily travel through along the fiber.