Numerical evaluation of the impulse response of multimode optical fibers

A numerical technique based on ray optics is presented that provides the impulse response of multimode optical fibers having arbitrary smooth index profiles and arbitrary material dispersion. The variation of dn/dλ₀ as a function of n when the dopant concentration varies is obtained from Fleming⁽¹⁾ measurements on bulk samples. This technique is applied to germania-doped multimode fibers with power-law profiles and various values of Δ ≡ Δn/n Previous results⁽²⁾ are shown to be invalid when Δ ≳ 0.005. By successive approximations, optimum profiles that minimize the impulse response widths for quasi-monochromatic sources are found. For these optimum profiles, the quasi-monochromatic root-mean-square (rms) impulse response width is found to be of the order of 150 Δ²nsec/km, in agreement with a recent analytical result.⁽³⁾