IBM demos first fully integrated monolithic silicon photonics chip

IBM logoAt a conference in the US, IBM has demonstrated what it claims to be the first fully integrated wavelength multiplexed silicon photonics chip. This is a big step towards commercial computer chips that support both electrical and optical circuits on the same chip package, and ultimately the same die. Optical interconnects and networks can offer much higher bandwidth than their copper counterparts, while consuming less energy—two factors that are rather beneficial as the Internet grows and centralised computing resources continue to swell.

Engineers have long known that fibre-optic links are more desirable than copper wires for shuttling data around—the available bandwidth is higher, the distances that signals can be squirted over are longer, and energy consumption is lower. On the other hand, when it comes to actually doing stuff with that data, electronics are where it's at. This dichotomy has resulted in a very pronounced split between optical and electrical technologies: optics are used for networking between computers, but inside the chassis it's electronics all the way.

This approach has worked well so far, but as bandwidth and energy requirements continue to soar, research labs around the world have been looking at ways of bringing the optics ever closer to the electronics. The first step is to bring optical channels onto the motherboard, then onto the chip package, and ultimately onto the die so that electrical and optical pathways run side-by-side at a nanometer scale.

IBM demos first fully integrated monolithic silicon photonics chip

IBM's latest nanophotonic chip belongs to the second category: it can be placed on the same package as an electronic chip, bringing the electro-optical conversion a lot closer to the logic. It's important to note that the lasers themselves are still being produced off-chip, and brought into the nanophotonic chip through the "laser input ports" that you can see in the diagram above. Once the chip has been fed some lasers, there are four receive and transmit ports, each capable of transporting data at 25 gigabits per second, which are bundled up into 100Gbps channels via wavelength multiplexing.

That's just this chip, though; IBM says that, in theory, its technology could allow for chips with up to eight channels. 800Gbps from a single optical transceiver would be pretty impressive.

For now, IBM is targeting its silicon photonics technology at data centre and HPC settings, where bandwidth can be a bottleneck. IBM says it has successfully demoed its new photonic chips in a "datacenter interconnect" setup that could push 100Gbps over a range of up to 2 kilometres (1.24 miles). If IBM can produce nanophotonic transceivers capable of 800Gbps—and confirm there actually is a significant reduction in power consumption from moving the photonics closer to the electronics—then the company's technology could compare very favourably against standards such as 40Gbps and 100Gbps Ethernet, and the being-discussed 400Gbps/1Tbps Ethernet standard.

The next step, according to IBM, is to get the lasers on-package using III-V semiconductors. From there, next step (which won't happen quickly) will be to get the lasers, waveguides, photodiodes, and other optical gubbins right onto the processor die itself, alongside the copper wires and transistors.

One the most impressive facets of IBM's new chip is that it's fabricated on a fairly standard 90nm CMOS process. One of the larger barriers to the adoption of electro-optical computing, or indeed any novel method of computing, is whether it slots tidily into existing manufacturing processes: when you're a company like Intel with billions of dollars sunk into capital equipment, you ideally want to stick to tools, materials, and processes that you already know a lot about. If IBM's nanophotonic technology wasn't built on a monolithic CMOS process, the odds of it being commercialised would be much lower.

Source: Ars Technica

Tags: IBM, technologies

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