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Speeding and Splitting Optic Communication

Two separate developments, both emerging in January 2007, when combined offer fundamental improvements to speed, reliability, and cost of fibre-optic communications systems.

Optic Fibre networks are most definitely the way forwards. Suffering far less latency than electronic circuits, nearly immune to interference, and with terabytes of bandwidth potentiate on every single fibre, these networks are essential for transferring the gigabytes of data from every user, for the full-immersion worlds of the future, and for the eventual sensor network.

In the past few years, technological strides have miniaturised photonic devices, integrating many of them onto a single chip. This has promoted advances in cheaper manufacturing, smaller footprints, and higher performance. Modern photonic devices share the same materials as electrical systems, paving the way toward integrating photonics and electronics on the same chip.

However, there are still many bottlenecks and crimps, preventing data from running at anywhere near its maximum potential.

There are many reasons for this. Fibre optics cause random polarisations of light that can lead to weakened or garbled signals down sufficient fibre. Specialist photonic structures have to be created, to accommodate different possible polarisations, and this complex architecture, and redundancy slows down the maximum speed of the fibre, as well as increasing cost.

As fibre optics have to have a repeater station every kilometre or so, a way to radically increase data throughput and diminish costs is very welcome.

The situation is worse with modern devices at the microscale - a few hundred atoms across. In devices at the microscale, the outputs change depending on if the waves are oriented vertically or horizontally. This means the devices tend to only process certain polarisations, which means half the bandwidth is discarded.

Researchers at MIT's Research Laboratory of Electronics think they have developed an answer. They have developed a totally different paradigm, Instead of building separate devices for different light polarisations, they have created a polarisation rotator, a device which takes any signals that enter it vertically, into horizontally polarised light. As it leaves horizontal light alone, it enables the entire datastream to be processed horizontally, tremendously simplifying the device structure.

First, the device splits light into its horizontally and vertically polarised components, directing these into separate channels. Then it gradually rotates the vertically polarised light to make it horizontal. At this point, the light in both channels has the same polarisation. Both channels are then processed in parallel, using identical structures, utilising all the bandwidth and with no signal degradation.

After processing the second of the channels is fed through an inverted polarisation rotator, which translates the signal from horizontal to vertical. The two streams are then combined, to continue their journey, or fed into further processing.

Optical CPUs

Modern computer systems are electronic. They function on electric signals travelling through wire. Due to friction, this is far slower than optical communication, and the friction between the electron flow and the wiring, produces intense levels of heat that requires case fans, heat sinks and air conditioning to deal with.

Intel is working on a way to deal with all the heat and power consumption issues at once - by replacing electrical signals with photonic. A photonic computer would have none of the heat discharge issues, use less power, and be much faster than traditional electronics. It has also however, been long considered a pipedream.

Intel has now developed a significant milestone towards that, a milestone that may revolutionise fibre communication on its own. The team has demonstrated a record-breaking silicon modulator that can encode data at a rate of 30 gigabits per second which is near enough as makes no difference, as fast as similar modulators currently in use that use exotic materials. Historically, photonic devices such as modulators and lasers have been made of exotic, costly semiconductors such as indium phosphide.

Considering that three years ago, the fastest silicon modulator in existence - by the same team - operated at one gigabit per second, it will likely not be long before these cheap modulators out perform their exotic brethren.

A silicon modulator that can operate at these speeds, says Mario Paniccia, Intel research fellow and director of the Silicon Photonics Technology Lab, could make it possible to design faster computers that include photonic chips. In addition, Paniccia says, it could be part of an all-silicon photonic chip that might be used in fiber optic networks. Since silicon devices are easy to mass-produce and relatively inexpensive, the chips could replace more expensive network hardware, reducing the cost of bandwidth.


MIT Photonic Rotators:

Swift Silicon Modulators

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