I was recently asked if there was any negative for working on live optical fiber, and I was not sure of the answer. I imagine the answer is don't do it, but aside from specialized glasses to protect from the light, are there other dangers here?

Also if fiber is severed will both modules which were communicating continue to send light? Such that if I cut a cable I would see light out of both ends of the fiber. My first guess is there is probably some feedback required to continue sending information.

  • \$\begingroup\$ What makes you fearful of optical fibers used for communication? I've worked with optical fibers much of my life and I can't recall having this feeling cross over me. I'm still unable to understand why someone would worry so much. If the intensity is high enough and there is a risk of you looking directly into the central beam itself, you'll wear protective goggles (not unlike what welders may use if serious precautions are needed.) But I think this is a rare situation, usually a matter of research and not commercial interest. Do you expect to work in such a rare situation? \$\endgroup\$
    – jonk
    Jun 13, 2021 at 5:20
  • 1
    \$\begingroup\$ Unless the transmit and receive are using different wavelengths of light (Wavelength-Division Multiplexing), bidirectional communications actually uses two fibers, optically isolated but may be in a single jacket and generally, the plugs are double (e.g. en.wikipedia.org/wiki/Optical_fiber_connector#/media/…). \$\endgroup\$
    – DoxyLover
    Jun 13, 2021 at 6:04
  • \$\begingroup\$ @jonk lasers in your eyes = instant blindness, in the general case, and it's even scarier if the lasers are invisible. So I'd want a specific reassurance that these specific lasers are eye-safe. \$\endgroup\$
    – user253751
    Jul 22, 2021 at 13:06

1 Answer 1


The power level used in communication fibres is very low, the light coming from a cut end would not be focussed, and would usually be in the IR spectrum, so the danger to vision would be non-existent.

You can guide lasers down optical fibres for cautery or 'optical scapel' use in keyhole surgery, don't mess with these.

If a link is operating with a protocol that requires acknowledgement, then certainly lack of a reply will tell both ends the link has failed. Whether or not both ends will continue to probe the link to see whether it's been re-established will depend on the protocol.

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    \$\begingroup\$ I can't think of any protocols that would detect the link break and not try to re-establish the link (you unplugged a cable then plugged it back in). Either it will detect the break and keep probing the link or it will not detect the break and will just keep transmitting. \$\endgroup\$
    – DoxyLover
    Jun 13, 2021 at 5:59
  • \$\begingroup\$ What about fiber cables that transmit a massive amount of data, Such as internet fiber cable run through a subdivision? \$\endgroup\$
    – Feynman137
    Jun 13, 2021 at 11:59

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