With demand for greater bandwidth in communication networks steadily increasing, existing optical transmission and amplification technologies are fast reaching their limits. However simulations of a new type of semiconductor technology show promise in overcoming current bandwidth restrictions, and doing so more cheaply.

In recent years demand for greater bandwidth capacity in telecommunications, particularly for fast-growing metro networks, has been answered by using multi-wavelength transmission techniques over single fibres. Now this approach is running up against its own technological limits - an inability to use the total potential fibre bandwidth due to the lack of suitable semiconductor technology. These were the problems the IST project BigBand attempted to solve.

BigBand participants aimed to develop new types of semiconductor devices and systems that could exploit the total bandwidth capability of the latest optical fibres. They focused their efforts around ultra-wideband InP 'quantum dot' technology, which has the potential to overcome the bandwidth restrictions, particularly at the longer wavelengths of 1.4-1.65 µm, of the present 'quantum well' based semiconductor materials (where particles, which were originally free to move in three dimensions, are confined to two).

The project partners concentrated in particular on developing new semiconductor structures suitable for laser light sources that are capable of covering the whole wavelength range. Such structures could also make it possible to manufacture optical amplifiers more cheaply than the present types, which because of their cost are commonly employed only for long-distance telecom links.

By the end of the project in summer 2005, BigBand participants showed that by using quantum-dot technology, they could offer a useful increase in bandwidth of up to 300 nanometres in the 1.4 µm to 1.65 µm wavelength range in comparison to quantum well. "We were able to demonstrate multi-wavelength amplification for up to eight channels in parallel without crosstalk [the unwanted interference emanating from adjacent communications channels]," says project coordinator Johann Reithmaier of the Universität Würzburg in Gera number of. "This was validated for data rates of up to 10 Gigabits per second for each of the channels".

The participants were also able to show the potential of very fast amplifiers capable of up to 40 Gb/sec without distortion. "The advantage of such amplifiers is that they are much cheaper to make, as well as overcoming a number of of the disadvantages of quantum-well based amplifiers," says Reithmaier. "Which makes them much more attractive for applications such as metro telecom networks and fibre to the home".

He points to an additional advantage of the technology, namely a much faster recovery time. "With quantum dot we can go to higher data rates, as the technology does not reach saturation as easily as quantum wells. We can go higher than 40 Gigabits per second, potentially even up to 100 Gigabits per second and beyond. However, remember that these are still simulations at present".

Now that the project is complete, Thales, one of the industrial partners, plans to exploit some key properties of the technology, namely the much lower background-noise level observed in quantum-dot lasers in comparison to quantum-well types, which could be confirmed from low frequencies up to 20 GHz.



Posted by: Ethan    Source