Pulse broadening in multimode optical fibres with large Δn/n: numerical results

The r.m.s. impulse response width of germania doped fibres having power-law profiles at the carrier wavelength is evaluated with the help of a numerical method and measured values of dn/dλ. For Δn/n≈0.02, our result exceeds by more than one order of magnitude that obtained from an analytical formula based on the assumption that n dn/dλ varies linearly with n². The optimum profiles are found to differ very significantly from power-law profiles. Our numerical technique is based on scalar-ray optics. It is applicable to any fibre having a large V-number and a smooth profile.