We have seen that the problems of electromagnetic emissions from Plastic Optical Fiber devices are due to the interface between the computer and the POF cable.
The ideal way to connect a plastic optical fiber to a desktop computer would be having a suitable electronic board inside the computer, with only optical connectors on the back side of the computer case. This avoids the electromagnetic emissions of the optical transmitter and receiver, which would be inside the computer case. This avoids also the additional external power supply needed by the transmitter/receiver, and the piece of Cat5 or other cable from the computer to the external converter.
For laptops and other devices that cannot host an extension card, there are external converters, which have to be attached to the device by means of a piece of network cable with RJ45 connectors, and the converter has also an external power adapter.
The external POF converters have the Cat5 patch cable which connects the standard network port of the converter with the standard network port of the computer. This cable has some electromagnetic emissions. Maybe the circuits of the transmitter and receiver put less power into the network cable when the cable is short, however this may depend on the exact design of the converter. If this piece of network cable is not so short however there are noticeable electromagnetic emissions.
The small power adapters have also a bad effect on other devices attached to the mains. This effect is stronger if the power adapter and the other device are attached to the same socket, but it is still present if the other device is on another socket. For example the electromagnetic noise generated by a small power adapter attached to a wall socket can appear into a LED desk lamp if the lamp hasn't a filter capable of blocking that noise. Maybe the electromagnetic noise created by the power adapter into the mains can be partially stopped with a suitable electronic filter. The power adapter should be attached to a movable socket outlet, and the movable socket outlet should have an embedded filter, or there should be a filter between the plug and the wall socket. These power adapters emit also some electromagnetic radiation directly into space.
There are POF converters that use an USB port of the computer, so they don't have a separate power adapter. These converters have a quite short USB cable and so they have less electromagnetic emissions than the POF converters based on RJ45 connection, but they are still worse than the internal POF network card.
There is also a POF converter that is inserted directly into a wall socket. This product is designed in such a way that the wall socket is not blocked by the converter, another plug can be inserted into the converter, while the converter gets the power from the wall socket. This type of converter doesn't have the little but terrible power adapter because the power adapter is embedded into it, so the emissions due to the power supply circuits are much lower. The problem of these wall mounted devices is that they use a Cat5 cable to reach the computer, and this cable has lots of electromagnetic emissions, and it attached on the back side of the computer near the cables of the computer peripherals.