Transmission characteristics of long spliced graded-index optical fibers at 1.27µm

Transmission characteristics of graded-index fibers at 1.27 μm are investigated. Bandwidth measurements are made in the frequency domain by using a CW GaInAsP laser diode modulated by a sinusoidal signal. For a germanium pbosphosilicate fiber, the optimum index profile at 1.27 μm is determined as 1.98. It is shown that optimum profile at 0.83 μm is 2.08 and there exists a large profile dispersion effect: for example, the experimental maximum 3-dB bandwidth at 1.27 μm decreases to one-third at 0.83 μm. Length dependence of bandwidth is investigated for 48 km long spliced graded-index fibers at 1.27 μm. It is verified that using a simplified transmission model in which mode conversion is assumed at splicing points, the bandwidths of long spliced fibers are predicted with satisfactory accuracy in terms of unit fiber transfer functions.