optical fiber. Optical fibers are frequently used in public and enterprise networks when the distance between the communication devices is larger than one kilometer. There are two main types of optical fibers : multimode and monomode. Multimode is much cheaper than monomode fiber because a LED can be used to send a signal over a multimode fiber while a monomode fiber must be driven by a laser. Due to the differentmodesofpropagationoflight, monomodefibersarelimitedtodistancesofafewkilometerswhile multimodefiberscanbeusedoverdistancesgreaterthanseveraltensofkilometers. Inbothcases,repeaters can be used to regenerate the optical signal at one endpoint of a fiber to send it over another fiber.