The field of fiber optics depends upon the total internal reflection of light rays traveling through tiny optical fibers. The fibers are so small that once the light is introduced into the fiber with an angle within the confines of the numerical aperture of the fiber, it will continue to reflect almost losslessly off the walls of the fiber and thus can travel long distances in the fiber. The branch of optics that deals with the transmission of light through transparent fibers, as in the form of pulses for the transmission of data or communications, or through fiber bundles for the transmission of images.Technology based on the use of hair-thin, transparent fibers to transmit light or infrared signals. The fibers are flexible and consist of a core of optically transparent glass or plastic, surrounded by a glass or plastic cladding that reflects the light signals back into the core. Light signals can be modulated to carry almost any other sort of signal, including sounds, electrical signals, and computer data, and a single fiber can carry hundreds of such signals simultaneously, literally at the speed of light. Signals that have weakened after travelling very long distances in the fibers can be optically pumped with lasers, amplifying them without the need to convert them into electrical signals.
Optical telecommunication is usually conducted with infrared light in the wavelength ranges of 0.8–0.9 μm or 1.3–1.6 μm—wavelengths that are efficiently generated by light-emitting diodes or semiconductor lasers and that suffer least attenuation in glass fibres. Fibrescope inspection in endoscopy or industry is conducted in the visible wavelengths, one bundle of fibres being used to illuminate the examined area with light and another bundle serving as an elongated lens for transmitting the image to the human eye or a video camera.