Design considerations for the structural optimization of a single-mode fiber

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Abstract
Design considerations are made for the structural optimization of single-mode fibers used in high-bit-rate and long-haul transmission systems in the long-wavelength region. As the basic fiber parameters, a combination of the spot size W0and the effective cutoff wavelength λceis newly chosen, because the combination is found to suitably describe various actual index profiles which deviate from an ideal step-index profile. A procedure to specify the usable range of W0and λceis established, whereby the overall transmission-line loss in one repeater section is calculated using simple expressions for fiber intrinsic loss, excess loss in the cabling process, and splice loss, etc. The optimum values for a 400 Mbit/s transmission system operating at 1.3 μm with a repeater spacing of 20 km are obtained asW_{0} = 5.0 \pm 0.5\mum and 1.1 μm\leq\lambda_{ce}\leq 1.28 \mum taking into consideration the additional requirement for the possible use at\lambda=1.55 \mum