Editorial Feature

Nanophotonics in Computing

In December 2012, IBM became the first to develop silicon nanophotonics technology that integrates optical and electrical components on a single chip, produced with standard 90nm semiconductor techniques. The technology uses light rather than electrical signals to rapidly transfer large volumes of data, for example between supercomputers, large data-centers or computer chips. The technology features various silicon nanophotonic components that include photodetectors, ultra-compact wavelength-division multiplexers, high-performance digital and analog CMOS circuitry and modulators.

This novel technology allows single-chip optical communication transceivers to be manufactured using a standard CMOS foundry, thus avoiding the need for assembling multiple parts or expensive factory re-tooling. Also, it is capable of introducing many parallel optical data streams into a single fiber with the help of compact on-chip wavelength-division multiplexing devices. Furthermore, the use of standard semiconductor manufacturing technology will in turn reduce the cost of traditional interconnects.

Cross-sectional view of a hybrid electronic-photonic processor chip.

Cross-sectional view of a hybrid electronic-photonic processor chip. Image Credits: IBM Newsroom.

The Promise of Photonic Computing

The modern world is built on computers - as they become crucial to more and more areas of life, we are placing ever greater demands on the technology. There are unavoidable limits to the performance of silicon-based electronics which we are on track to hit very soon. Photonics is one of the key ways that researchers in the semiconductor industry hope to avoid this limit.

Whilst photonic chips may not be a complete replacement for their silicon counterparts for quite some time, hybrid devices using silicon for computation and photonics for communication could provide a speed boost which will lead to a fresh spike in computing performance. Allowing data to flow between processors and between machines at the speed of light will reduce latencies, making better use of our existing high-speed processor cores and increasing the overall speed at which computers operate.

The key to integrated photonic chips has been the development of nanoscale photonic components, such as ring resonators, which are analagous to electronic transistors. For the last decade or so, research groups around the world have been incrementally improving these components, so that they are now compact enough to integrate with silicon chips, and can be manufactured using similar fabrication methods, permitting commercial applications of photonic computing to begin.

The first uses of this hybrid technology will most likely be in high-capacity data centres, where data transfer latency is crucial to performance, and in high-end multicore processors in supercomputers, to permit faster communication between the cores. As with other advances in computing technology, this will then trickle down into speciality desktop computers, then to laptops and mobile devices over the following few years as the technology becomes more mature.

A multicore chip with silicon photonic components directing data traffic between the cores.

A multicore chip with silicon photonic components directing data traffic between the cores. Image Credits: IBM Newsroom.

IBM’s Research Road to Nanophotonic Computing

IBM has developed several novel scalable nanophotonic technologies that rapidly increase communication between computers. In 2005, IBM introduced an integrated photonic circuit that reduces the light signal speed and controls the speed with an application of electric current. This achievement was a major breakthrough in the development of silicon chips integrated with electric and photonic components. Following this, in 2006, the company demonstrated a compact optical buffer that enables super computers to achieve better performance with the use of optical interconnects. An ultra-compact and low-power silicon optical modulator capable of converting electrical signals into light pulses was introduced by the company in 2007.

Further, IBM unveiled a silicon broadband optical switch along with another key component in 2008, which enable on-chip optical interconnects. This paved the way for IBM scientists to make an important advancement in 2009 with respect to communication of computer chips. The company’s recent development involves the introduction of a new technology in 2010 for dense integration of optical and electrical devices on a single silicon chip so that the computer chips communicated to each other using light pulses rather than electrical signals.

Other Recent Developments

Some of the important advancements in the field of nanophotonic computing were presented by the researchers at the University of Pennsylvania recently. They modeled the first all-optical photonic switches using cadmium sulfide nanowires and combined all the switches to form a logic gate to perform computation. The fact that the cadmium sulfide nanowires exhibit strong light-matter coupling for light manipulation enabled them to create this innovative model that is crucial for the advancement of nanophotonic circuits. The logic gate thus developed overwhelms the existing bulk and energy-consuming mechanisms of nanophotonic circuits for controlling light flow.

Another novel technology created by the Penn State researchers involves the combination of transformation optics and metamaterials for developing miniaturized optical device designs employed in chip-based optical integrated circuits. The researchers emphasized that the transformation optics capable of performing simple, diverse functions can be integrated to form complex photonic systems used for optical sensing, computing, imaging and communications. On the other hand, the novel technology uses graded index metamaterial structures like patterned air holes on a silicon-on-insulator platform for providing wider bandwidth without losses.

Sources and Further Reading

Will Soutter

Written by

Will Soutter

Will has a B.Sc. in Chemistry from the University of Durham, and a M.Sc. in Green Chemistry from the University of York. Naturally, Will is our resident Chemistry expert but, a love of science and the internet makes Will the all-rounder of the team. In his spare time Will likes to play the drums, cook and brew cider.

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