A repeaterless undersea optical link operates at 1550 nm on single-mode fibre with an…

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

Optics and Photonics, Ch Optical fibres in communication and endoscopy

Problem

A repeaterless undersea optical link operates at 1550 nm on single-mode fibre with an attenuation of

0.20

dB km

^{-1}

. The transmitter launches

+3

dBm into the fibre, and the receiver at the far end can detect signals down to

-34

dBm; a power in dBm is

10\log_{10}

of the power in milliwatts, so the difference of two dBm figures is a power ratio in decibels. Estimate the greatest unrepeated length of this fibre the link can use, assuming fibre attenuation is the only loss in the budget.

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