An optical fiber ( optical fibre) is a flexible, transparent fiber made of a pure glass (silica) not much wider than a human hair. It functions as a waveguide, or “light pipe”, to transmit light between the two ends of the fiber.The field of applied science and engineering concerned with the design and application of optical fibers is known as fiber optics. Optical fibers are widely used in fiber-optic communications, which permits transmission over longer distances and at higher bandwidths(data rates) than other forms of communication. Fibers are used instead of metal wires because signals travel along them with less loss and are also immune to EMI(Electro Magnetic Interference). Fibers are also used for illumination, and are wrapped in bundles so they can be used to carry images, thus allowing viewing in tight spaces. Specially designed fibers are used for a variety of other applications, including sensors and fiber lasers.
The yellow cables are Single Mode Fibers and the orange and blue cables are Multi-Mode fibers
Optical fibers typically include a transparent core surrounded by a transparent cladding material with a lower index of refraction. Light is kept in the core by total internal reflection. This causes the fiber to act as a wave guide. Fibers that support many propagation paths or transverse modesare called Multi-mode fibers(MMF), while those that only support a single mode are called Single-mode fibers(SMF). Multi-mode fibers generally have a larger core diameter, and are used for short-distance communication links and for applications where high power must be transmitted. Single-mode fibers are used for most communication links longer than 1,050 meters (3,440 ft).