Photonic devices built by standard CMOS process

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At the Optical Fiber Communication (OFC) Conference and Exposition that will take place in San Francisco from 9 to 13 March, a team of engineers will present research demonstrating that low power photonic devices can be fabricated using standard chip-making processes. The use of a standard manufacturing method will shorten the commercialisation of photonics technology, and will enable the development of photonic chip-to-chip communication links that have a higher energy efficiency and bandwidth density than electronics.

There has been an exponential rise in computing power over the last few decades, and as computing power rises, so does the amount of energy needed to operate the machine. ‘It's gotten to the point where it takes too much energy and that limits your computational power,’ said Mark Wade of the University of Colorado, Boulder, who will present his team’s work at OFC.

A solution lies in photonics, which researchers anticipate will be at least 10 times more energy efficient than electronics. Chip-to-chip communication links using these photonic devices could have at least 10 times higher bandwidth density, meaning they can transmit more information using a smaller amount of space. This is because different optical signals can share the same optical wire, whereas sending multiple electrical signals either requires multiple electronic wires or schemes that require more chip space and energy.

But so far, Wade explains, photonic devices used in chip-to-chip communication have been primarily custom-built using specialised methods, limiting their commercial applicability.

The two new devices – a modulator and a tunable filter – were built using a standard IBM advanced Complementary Metal-Oxide Semiconductor (CMOS) process – the same process used to build commercially available chips, including ones found in Sony's Playstation 3 and also in the IBM Watson supercomputer that won the America quiz show Jeopardy! in 2011.

The team has also demonstrated that the devices are as energy-efficient as existing electronic devices: ‘As far as we know, we're the first ones to get silicon photonics natively integrated into an advanced CMOS process and to achieve energy efficiencies that are very competitive with electronics,’ Wade said. His co-authors include researchers from the Massachusetts Institute of Technology (MIT) and the University of California, Berkeley.

The ability to produce high-performing photonic devices using the CMOS process means chip designers will not have to be specialists to design photonic devices, Wade explained, which will hopefully accelerate the commercialisation of photonic technology. ‘IBM’s CMOS process has already been commercially proven to make high-quality microelectronics products,’ he said.

The two devices built by the researchers are key components for the communication link between a computer's central processing unit and its memory. A modulator converts electrical signals into optical signals. A tunable filter can pick out light signals of particular frequencies, allowing it to select a signal from multiple frequencies, each of which carries data. Used in conjunction with a photodetector, the filter converts optical signals to electrical signals.

‘This is a really nice first step for silicon photonics to take over some areas of technology, where electronics has really dominated, and to start building complex electronic/photonic systems that require dense integration,’ Wade added.

The presentation titled ‘Energy-efficient active photonics in a zero-change, state-of-the-art CMOS process’, will take place Tuesday, 11 March in the Moscone Center, San Francisco.