Standard single-mode fibre attenuation can be modelled as the sum of Rayleigh scattering

PHYSICS · Multi-part · Fermi University Physics · Optics & Photonics · Beams, resonators and guided-wave photonics · Beams, resonators and guided-wave photonics

What an Instrument Can See, Ch The optical constants of a medium

Problem

Standard single-mode fibre attenuation can be modelled as the sum of Rayleigh scattering,

0.8/\lambda^4

dB per kilometre, and an infrared absorption tail,

7.81\times10^{11}\,e^{-48.48/\lambda}

dB per kilometre, with

\lambda

in micrometres in both terms. A link is operated at

\lambda = 1.310\ \mu\mathrm{m}

, which is close to this fibre's zero-dispersion wavelength, so dispersion-induced pulse spreading may be neglected there. The system has a total loss budget of

28\ \mathrm{dB}

between transmitter and receiver, with no other loss mechanism. ((a)) Estimate the total attenuation of the fibre at

1.310\ \mu\mathrm{m}

from the two mechanisms given. ((b)) Estimate the loss-limited reach of the link. ((c)) Explain briefly why, unlike a link operated at 1550 nm, dispersion is not expected to set the reach here.

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