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I am new to the fiber-optic communication systems, and in reading some relevant papers, I faced to the term "span length" (such as long-span link) which I cannot distinguish it from the length of the cable.

For example in one of the figures, it has depicted a quantity for various spaning lengths vs. the length of the cable.

Can anyone explain what is the "span length" of a fiber-optic link? I surfed the internet, but did not get any answer.

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    \$\begingroup\$ could you add a reference to "some relevant papers" \$\endgroup\$ – Marcus Müller Apr 15 '17 at 21:20
  • \$\begingroup\$ sure, for example see figure 4 of the following paper: \$\endgroup\$ – CLAUDE Apr 15 '17 at 21:22
  • \$\begingroup\$ osapublishing.org/DirectPDFAccess/… \$\endgroup\$ – CLAUDE Apr 15 '17 at 21:22
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Fibre optic cables are fairly lossy. As such a signal can only be transmitted so far down a piece of "glass" before they must be received by a transceiver or relay device that decodes the optical signal, regenerates it and transmits it out again. This is a span.

The "cable length" itself could go from north America to Europe. A span may be only a kilometer.

ADDITION: That does not only apply to fibre-optics though. Any high frequency communication system, other than point to point micro-wave, needs the same "pass-the-bucket" handling.

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  • \$\begingroup\$ Point-to-point microwave does have the same problem... \$\endgroup\$ – immibis Jun 13 '17 at 11:00
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In this context, a span is the cable length between two amplifying stations.

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