Optical fibers can be divided broadly into two types according to the way in which they transmit optical signals. One type, known as single-mode fiber, has a thin core with a diameter of about 10 microns, and allows light pulses to propagate in only one mode. The other type, multimode fiber, has a thick core of about 50 microns in diameter, and permits the propagation of multiple light pulses of differing angles of reflection. However, in multimode fiber the distance at which signals can propagate differs according to the angle of reflection, resulting in disparities in the arrival time of signals. As such, multimode fibers are used mainly for low- and medium-capacity transmission over relatively short distances. Most optical fiber in use today is single-mode fiber that enables high speed, high capacity transmission.