Special optical fiber has been invented not a long time ago. It is used in cables and wires to transport information across large distances. It is essentially an extremely thin thread of glass. The cable with such material does not experience energy losses like metal wires do. The major improvement of optical fiber is that it’s not affected by any electromagnetic interference. But since optical fiber operates with different types of signals, they require special equipment for maintenance and repair. Specialized light sources are used to test such optical fiber cables. They emit light with a wavelength we cannot see and transfer the signal along the cable, measuring the amount of time the signal travels and other parameters required for performing an examination. These light sources can adjust the wavelength of light they emit, so they can be used with different types of cables and perform various types of tests.