Federico Forni. Photo | Bart van Overbeeke

Home Stretch | WiFi via a plastic optical fiber

Where is the best WiFi coverage often found at home? Not in the bedroom where you want it, but in the meter cupboard. While this could be resolved by giving each room its own WiFi box, that would be a costly solution. Now the Italian PhD candidate Federico Forni has succeeded in sending the WiFi signal through a cheap plastic fiber: a significant step towards achieving fast, affordable WiFi in every corner of the house.

With the growing number of mobile devices per household, the gulf is widening between the internet speed promised by providers and the user's own experience. All these devices drink from the same WiFi well, and what's more that well is often located in some remote corner of the house, like the meter cupboard. Add to that the disruptive influence of the neighbors' own WiFi, and for many households another three or so WiFi points wouldn't be an extravagance.


“At airports and in other public spaces it's often the case that WiFi ‘transceivers’ are installed at various sites in the complex,” tells PhD candidate Federico Forni. “But for households this isn't affordable; you need either pretty valuable electronics at all the end points, or a glass fiber connection between the connection point - which may be in the meter cupboard - and the site where you want good reception.”

And glass fiber is not only expensive to install, it is also very fragile. “Laying it is a job that requires a fair bit of expertise; because the alignment has to be very exact you need a special connector to link the fiber to the connection point. You also have to handle it extremely carefully because it is very fragile material.” Then again, the disadvantage of the ‘good old’ copper cable is that you can't send a radio WiFi signal through it, so at the end of the line you've still got to install a box containing relatively complex (read: expensive) electronics to handle the conversion to WiFi. And you're doing that at various places, which means the costs can really start to mount up.


But there is an alternative. In theory plastic fibers can replace glass fibers, as Forni has proved with his doctoral research. “Plastic fibers have a much lower capacity than glass fiber, but unlike copper wire high enough to convey a WiFi signal together with the signals for your wired internet connection, tv, etcetera. And in the near future, one would probably like to add transmission of the 4G data signal for your mobile phone as well.” Not that everything just fell into place. Forni's valuable contribution was to succeed in manipulating the WiFi signal such that at 2.4 gigahertz it was still strong enough at the end of a 50-meter plastic fiber. “The bandwidth of the plastic fiber is in principle roughly 1 gigahertz. This means that much of the strength of a signal of 2.4 gigahertz is lost in transmission. However, I found a way to boost that signal as much as possible.”


So much so that he got an excellent WiFi signal at the end of 50 meters of plastic fiber; long enough for anyone not living in a palace. In cooperation with TNO in The Hague, Forni also tested his method in combination with a box that converts the ‘4G-in-a-cable’ into a wireless signal. "Its range was tested up to twelve meters, enough for a large lounge. It turned out that everything worked perfectly, from video streaming to making a call on Skype.”

The result of Forni’s work will not, unfortunately, be on sale in stores tomorrow. First of all, someone in the Electro-Optical Communications group will carry forward the Italian's work, aiming to convert his inventions into a handy prototype. “After that, industry will have to pick it up,” says Forni. His own next step is to take a well-earned vacation, before he starts looking for a job in the region.

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