Fiber optics, branch of physics based on the transmission of light pulses along hair- thin glass fibers. Fiber optics is used in telecommunications; information is coded as a series of light pulses and thus can be transmitted over distances of up to 100 mi (160 km). There are 2 types of optical fibers: single-mode and multi-mode. Single-mode fibers are used for long-distance transmissions and require the use of a laser as a light source, while multi-mode fibers can use more types of light sources but cannot be used over long distances. Fiber optics is also used in instruments like the gastroscope, allowing physicians to view internal body parts without performing surgery, and aiding in surgery.