In fiber optic light can travel in two forms that characterize the fiber itself : single-mode fiber and multimode fiber.
In single-mode fibre is as a straight shot: the light path is small in diameter, which makes the signal path mostly straight.
It has a diameter ranging from about 8 um to 10 um depending on the manufacturer. To use this type of fiber, a very precise source must be used which can produce a single mode of light radiation into the fiber. The index of refraction of a single mode fiber is very low because such a small core prevents the ray dispersion. This optical fiber is capable of propagation wavelengths of 1310 nm and 1550 nm, slightly attenuates the signal. It used for long distances and high bandwidth.