Method of measuring the dispersion in multimode optical fibers

A description is given of an apparatus and method for measuring the transmission characteristics of glass optical fibers, enabling the broadening of $10^{-9}-10^{-10}$ sec pulses to be determined with an accuracy of $5\cdot10^{-12}$ sec. The results are given of measurements of the pulse shape at the output of a multimode fiber having an M-shaped refractive index profile under different conditions of matching the fiber to the source and radiation detector. It is shown that three mode groups propagate in the investigated fiber. This leads to a splitting of a single input radiation pulse into three output pulses, separated in time, when all the modes are excited at the fiber input and the length of the fiber is less than its mode-excitation length.