@lritter The pen is either an optical transmission module or the end of an optical fibre connected to one. In normal operation, electrical signals get converted to pulses of near infra-red light (usually 1310 nm or 1550 nm) and that white bit at the right would be clamped against a matching bit on an optical fibre, which will carry the signal for (wild guess based on the power here) a few hundred miles. At the far end the much-attenuated light will get converted back to electrical signals.

@lritter A fibre-optics panel is a bunch of these mounted next to each other, into which you plug fibres. Some of these fibres will be going across the room, and have low-power transmitters on them. Some will be going a long way. If those long-distance fibres have been unplugged, the connector they should be plugged into can be emitting literally eye-searing invisible radiation.

@tienelle ahhh! now i get it. so this signal would likely be transmittable over a very long distance since its power is so high, hence even under attenuation by inverse squared distance (through a reflective fiber cable though), it would be unlikely to degrade below ambient noise levels