Analysis of modal dispersion in plastic optical fibres with a W-shaped refractive index

The effect of the refractive index valley at the core-cladding boundary on the optimum index profile in W-shaped plastic optical fibres is investigated in this paper. For this purpose, we derived the analytical expression that allows us to calculate the temporal broadening due to different rays taking different amounts of time to propagate through the fibre. Finally, we carried out computational analysis to investigate the dependence of modal dispersion on the depth of the index valley ρ and of the index exponent q. Results show that the modal dispersion is strongly dependent on the depth of the index valley. We concluded that, for the case NA=0.24 and ρ=1.5, the index exponent q=1.96 minimizes pulse dispersion.