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One benefit of fiber optic cables popularly cited is that they are "immune" to electro-magnetic interference. [See http://services.eng.uts.edu.au/~akadi/ite/major_assignments/barber/advdisad.htm]

My (admittedly naive) question is:

How is light, being an electro-magnetic wave itself, immune to electro-magnetic interference e.g. solar flare or nuclear weapon?

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In order to meaningfully interfere with a fiber optic signal, the interfering waves would have to have close to the same frequency as the signal itself. This means that "electromagnetic interference" for fiber optics takes the form of light shined on the fiber optic cable. If a fiber optic cable is covered with an optically opaque substance (which they almost always are), then no light can get in, and hence no interference can happen.

In contrast, traditional electronic communications happen at far lower frequencies (typically in the radio/microwave band), and are thus far harder to shield. In order to properly shield a normal wire from this kind of interference, you would have to cover the wire with an insulating material with a thickness of a few times the wavelength of the interference*. For radio waves, this wavelength is in the range of cm to m, so you would need insulation several meters thick to protect the wire. This is usually impractical at best.

*This is also true for light waves; however, their wavelengths are in the hundreds of nm, so virtually any macroscopic coating on the cable would suffice.

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  • $\begingroup$ And "ionizing" radiation impact pet link here. en.m.wikipedia.org/wiki/Radiation_effects_on_optical_fibers is this off topic? Thanks. $\endgroup$ – tx1918 Aug 2 '17 at 7:54
  • $\begingroup$ I mean, yes, if you physically damage the cables, then communication will be interrupted. But this has little to do with the "electromagnetic interference" that people are usually talking about, and has more in common with slicing through a cable with a laser than causing signal interference. In addition, "interference" is usually understood to be transient, but damage to a cable from ionizing radiation is permanent. $\endgroup$ – probably_someone Aug 2 '17 at 7:55
  • $\begingroup$ But even if the fiber-optic cables weren't shielded, even similar frequencies couldn't interfere, because they couldn't get their signal propagating down the cable because the angles wouldn't be right. The signal would just cross through the cable and not interfere (unless they could get their signal into the cable at the source, but that wouldn't be considered "interference" $\endgroup$ – McKay Feb 10 at 17:53

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