What is a photonic integrated circuit?

11 October 2011 |

How photonic integrated circuits (PICs) can support optical networks.

Global service providers are facing increasing demands for bandwidth, much of which is being driven by video, mobile and cloud-based services. This is illustrated by the fact that in the UK, streaming from BBC iPlayer already comprises 7% of peak downstream traffic; while in the US, video streaming from Netflix alone accounts for nearly a quarter of all bytes transferred at peak times.

Network planners around the globe are faced with the task of ensuring that they can meet this demand but, just as importantly, do it at a lower cost per bit so they can turn an increased profit from this demand. Carriers tackle this issue using a variety of methods, but one approach that has been adopted by companies such as Interoute, Telefónica, Deutsche Telekom, Level 3 and Global Crossing is to base their optical networks on the photonic integrated circuit (PIC).

What benefits can PICs bring to networks?

PICs can enable carriers to operate a digital optical network which helps eliminate planning errors and ease operations. As opposed to an analogue optical network, which may require a team of physicists and engineers to keep it running, photonic integration introduces the simplicity of a switch or even an IP router, allowing operators to run larger networks with smaller teams.

While more challenging to build than microprocessors, multiple devices and functions can be integrated onto a single PIC, therefore reducing the number of optical components and offering a potential capex saving.

What technology is used in a PIC?

Conceptually, a PIC is very similar to an electronic integrated circuit. While the latter integrates many transistors, capacitors and resistors, a PIC integrates hundreds of discrete optical components and miniaturises them onto an integrated circuit. This can carry up to 500 gigabits of internet traffic on a chip no bigger than a fingernail. In the future, it is estimated that this capacity could be extended further, to a terabit and beyond.

The concept was first proven in the electronics domain by placing thousands of transistors onto silicon, which helped to drive the microprocessor industry. It has since developed to enable the computing power found in today’s smartphones. PIC-based optical systems are therefore designed to be more reliable than discrete optical equipment – in a similar fashion to how microprocessor-based PCs are more reliable than computers that were built with valves for transistors.

How can PICs help increase capacity on networks?

A lot of today’s optical fibre in the ground was built for a maximum speed of 10Gbps circuits. But with the popular uptake of HD and 3D technology, higher data rate transmission is needed in the near future. Using a technique known as coherent detection, photonic integration can give service providers the opportunity to squeeze many multiples of that maximum speed down the same ‘pipe’.

Coherent detection uses the same technique that an FM radio uses to extract one radio station from the dozens that may be transmitting all around it, and can allow 40Gbps and 100Gbps circuits  to operate over the same or even greater fibre distances as 10G, using less sophisticated modulation.

Electronic bandwidth management is also required to create maximum efficiency from today’s networks, particularly by deploying optical transport networking (OTN) switching throughout the network. This combination of operational scaling and bandwidth efficiency could prove essential at a time when some carriers may be running short of capacity on key routes. By making the optics smaller and less power hungry, PICs can allow sophisticated bandwidth management to be deployed throughout the network.

What is the future for PIC technology?

In the short term, photonic integration could help carriers scale up to 40Gbps and 100Gbps circuit-based networks.

However, the next generation of future photonic integrated networks may even see the creation of  500Gbps ‘super-channels’, upgradeable to 1Tbps super-channels and yielding up to 24Tbps per fibre. This potentially massive increase in capacity could help prepare network infrastructure for any levels of demand in the future.

Contact: Infinera
For further information, contact Geoff Bennett, product director at Infinera: