A Plastic Optical Fiber ADSL box


In most homes today the internet connection is provided by ADSL, which has a lot of electromagnetic emissions from the wire, from the modem and from the filter that is needed for the analog phone.

A good way to stop this electromagnetic radiation from going into the computer, monitor and other user interface peripherals is to use a connection based on fiber optic. In particular we can use Plastic Optical Fiber which is easy to install.

However, near the ADSL line we still have a lot of things: the ADSL modem, the ADSL filter, a phone wire from the filter to the modem, another phone wire from the filter to the analog phone, and then the POF media converter, the power adapter of the POF converter, the Cat5 patch between the modem and the POF converter, the power adapter of the modem.

All these devices and cables emit a lot of electromagnetic radiation, which may be ignored if the devices are placed in a separate room, but can be a serious problem if the devices are in the same room where people work and live, so all these devices must be arranged into a suitable metal enclosure that can shield most of the EM radiation.

Ideally, we should have a small box which provided all these functions: ADSL modem, ADSL filter, conversion to fiber optic, power supply, all in the same box. Such a device is not available on the market and who knows if and when some industry will make it. Now the trend is wireless Internet everywhere, which is just the opposite of people's health.

The conversion between the Ethernet signals and the optical fiber signals wouldn't be necessary if the router had integrated processors for the optical fiber signals, but this requires a deep restructuring of the electronics of the router, which takes much time and investments.

The industries are starting to provide devices to connect a POF based local area network to an external internet connection based on glass optical fiber, the so called Fiber To The Home (FTTH), but fiber optic to the home is still a luxury, it is spreading very slowly, and it is also still quite expensive.

After all, the typical ADSL connections, based on the same copper wires of the analog phone, provide a communication speed that is enough for working purposes, and also for some entertainment.

So in practice it is still useful to consider a hybrid system, composed by a home network made of plastic optical fiber connected to a copper based ADSL by means of an ADSL modem, or by an ADSL modem-router for up to 4 independent computers.

Small computer network on Plastic Optical Fiber with ADSL POF box
Fig.1 Small computer network on Plastic Optical Fiber with ADSL POF box

We have designed various systems using products currently available on the market, and selecting the less expensive options.

It is possible to make such box with an ADSL modem that has just one LAN port, using one POF media converter only, but given that the cost of the modem-router is relatively low, we consider directly a solution with 4 independent connections, provided by an ADSL modem which is also a LAN router. The box could contain just the number of POF converters that are really needed but it could be designed to host up to 4 converters.

A first design of this thing is just a simple enclosure that contains all the devices as they are provided today, with no modifications. The devices are just arranged into the enclosure, and each device gets the electric power from its own power adapter. The power adapters are attached to a multiple socket placed inside the enclosure, and since the switch of the multiple socket remains inside the box we add another switch on the enclosure, to open and close the AC power of all devices.

But having many power adapters on the same socket creates quite a lot electromagnetic noise into the mains, and this is a problem for small offices and homes. The switching mode power adapters generate also an EM radiation that can be a problem. So we have to abandon the original power adapters and replace them with a custom power supply. The power supply may have to have two outputs, one for the ADSL modem and one for the POF converters. If these two groups of devices use the same DC voltage we can put them in parallel on the same power supply output, otherwise the power supply must provide two different voltages.

This power supply must be capable of filtering the high frequency electromagnetic noise generated by the modem and the converters or else this EM noise would pass into the mains. Generally a good filtered AC connector is enough to reduce the noise to a level that is not a problem for the rest of the home. If that is not enough then another type of AC filter must be used.

If we want to connect more than one computer to the Internet through the same ADSL we have to use a network router. There are already ADSL modems that are also routers, for example with 4 ports, but such a modem-router would require as many POF converters as the computers connected to the router. Unfortunately there isn't any POF router available on the market at this moment, there are just POF switches, which aren't routers. The switch gets a standard LAN cable and distributes it to a number of POF destinations. A switch must be connected to a router to have effectively independent internet access on each computer. However, for just 4 ports the price of a POF switch is higher than the total cost of POF converters, so for this project it is convenient to use several POF converters.

System schematic of an ADSL to POF converter
Fig.2 System schematic of an ADSL to POF converter

If a POF switch is available, or if we want to connect more than 4 computers, even if the ADSL may be not enough for them when used simultaneously, then the system would be as follows:

System schematic of an ADSL to POF converter with POF switch
Fig.3 System schematic of an ADSL to POF converter with POF switch

To minimize the electromagnetic radiation escaping from the box we should make the POF cables pass through small holes on the enclosure. For the phone input line and output line, we should provide RJ11 sockets. For the AC power, the box should have a standard AC connector, like those of computers or monitors.

Detailed project

We have designed an ADSL to POF box with 4 ports, adjusting the internal layout and selecting the components to reduce the electromagnetic emissions, while providing also robustness and easiness of use. We have finished the construction of the first piece for our local network and we are currently refining some details. If you would like to build one by yourself, or if you think that this could be a product to invest in, you can contact us by email or leaving a message here.

Related pages

Conclusions about Plastic Optical Fiber
Overview of Plastic Optical Fiber
Plastic Optical Fiber to stop radiation from ADSL
Plastic Optical Fiber page list