Siemens shows 1Gbit/s over plastic fibre
Alternative to glass and copper appears in a POF of light
Siemens researchers have demonstrated a data rate of 1Gbit/s over plastic optical fibre, a speed ten times higher than is possible with current products.
Sebastian Randel, the Siemens project manager, said the team sent an IPTV signal at 1008Mbit/s over a 100m connection in the lab, without errors or any flickering on the TV screen.
The company claims this is a big breakthrough for plastic (or polymer) optical fibre - POF - a technology which proponents want to supplant glass fibres and copper wires in demanding environments such as factory and home automation.
POF's advantages include flexibility, robustness and ease of connection, all of which make it easier and therefore cheaper to handle - it can even be installed by us cack-handed end users. In particular, the optical core is much thicker than in glass fibre, so it is more tolerant of misaligned connectors, and it can be cut satisfactorily with a metal cutter, whereas glass needs a diamond cutter.
Its main disadvantage is that it has a much higher transmission loss than glass, so current POF technology tops out at 100Mbit/s - the speed of Fast Ethernet.
What the Siemens team has done is to use a different modulation scheme - in fact, it's quadrature amplitude modulation, as used in DSL and the latest Wi-Fi specs. Instead of simple binary, QAM has 256 signal states so each pulse can carry far more information, hence the ten-fold speed increase.
Its robustness means that POF cable is already used is some demanding areas, such as inside cars and high-speed trains, and of course in lighting. It is used in audio too, with connections based on the IEEE 1394 Firewire spec - like glass fibre, it is immune to electrical interference and doesn't generate noise or crosstalk.
Randel suggested that taking it to Gigabit speeds could also make it suitable for applications such as factory and medical networking, and for home LANs to support high-def IPTV.
He added though that this was just a demonstration, and said he could not quote dates or prices for possible Gigabit plastic optical fibre products. ®
Re: broken glass
Unfortunately I don't think POF will offer any enhanced robustness over glass fibre: If you bend it past the recommended bend radius then you will still encounter reflection issues. Also, whilst it might not snap as catastrophically as glass, accidentally crushing, bending, treading on a plastic fibre may result in stressing of the plastic which will make the plastic go "cloudy" in the stress area and stop it working.
Tricky: You could use QAM on fibres in general, but there's not a lot of point as in practice it would increase noise in other modulation techniques and thus not offer any benefit.
Frequency Division Multiplexing is generally used when sending lots of data over a single-mode fibre, which means that you divide the frequencies available on the fibre into many channels and send data along each one. It's analagous to how they can send several TV channels over the same bit of space between the transmitter and your TV. You have a different data stream on each channel.
QAM of Glass fibre.
Single and Multi-mode glass fibre is designed to carry digital light signals and as such has a very small core (as little as 10 micrometres in diameter). The fibre used by Siemens in this example has a vastly thicker core capable of transmitting analogue light signals, since QAM is an analogue modulation technique.
The cost of glass fibre with a core this thick would be far greater and probably not worth the effort. It also would probably not offer any great speed advantage. The distance that a signal would be able to travel before it becomes too attenuated, however, would be much greater than 100M.
I know you are presenting a simplified version, but please, you've made a rather sweeping statement by saying that QAM has 256 levels. Quadrature Amplitude Modulation can have as many amplitude/phase states in its constellation as is desired to balance phase noise vs data rate.
QAM is just a generalised description of a series of methods for modulation of data to analogue signals.