Light in the cloud: Photonic innovation for data centers

The widespread adoption of new cloud computing services, streamed entertainment, online gaming and social networking means that there is more data being transferred around the world now than ever before, and the amount is always increasing. On the global information highway, data centers act as traffic controllers that receive and direct thousands of requests for information and services every second. Data centers are large banks of information storage and servers that organize and control this data. A combination of software and hardware is used to connect and direct traffic between massive populations of servers and computers around the world.

Silicon photonic components such as this demultiplexer are enabling components for emerging data center photonics. Credit: National Research Council of Canada

Silicon photonic components such as this demultiplexer are enabling components for emerging data center photonics. Credit: National Research Council of Canada

Initially, these connections were all switched electronically, through large amounts of copper wiring. However, as cloud traffic continues to grow and with it the burden on data centers, this electronic switching presents issues of speed, space constraints, and an immense use of electric power. When internet users perform actions like search queries and streaming videos, these requests need to be properly directed, and an increase in the amount of data flow means that more controls are required to manage the information traveling through centers across the globe. To handle increasing congestion, the data centers are under pressure to increase their data capacity while operating within the constraints of sustainable cost and available power.

To solve these problems, the industry has increasingly switched to use light, rather than electronics, to channel information through its data centers. With photonics, a combination of lasers, integrated photonic chips and fibre optic cables can be used by data centers for faster communications, lower power consumption and smaller devices that are easy to mass produce. Silicon photonics involves the use of tiny chips (the size of a spec of confetti) built onto a ‘wafer’ of silicon, which is a natural semiconductor. This greatly reduces the cost of manufacturing, as it erases the need to assemble many small parts by hand –including filters, optical modulators and detectors – into the transceiver. Instead, using a process called complementary metal-oxide semiconductor (commonly referred to as CMOS) that is used to make microelectronic chips, manufacturers can print or etch thousands of photonic devices on a single chip, and mass produce them on silicon wafers.

To see further improvement in speed and space usage, data centers are adopting a technology borrowed from long distance telecommunications called wavelength division multiplexing (WDM) to carry multiple signals at various wavelengths. Because WDM transceivers allow for a combination of different data streams within the same fiber, you can carry much more information at the same time with fewer optical cables required. Although helping to alleviate pressure on data centers, these new photonic components still have a lot of room for improvement in size, performance, and even temperature control.

At the National Research Council of Canada (NRC), we and our industry partners are collaborating to create new photonic components technologies to make the data center systems run more effectively and more efficiently.

Photonic integration with advanced light sources

In employing the WDM technology, a component called a multiplexer which combines several light streams into one path is at its core. Current commercial systems often still use multiplexers in stand-along modules. At NRC we have developed silicon photonic multiplexers that are the size of a grain of sand, and provide high spectral performance and low transmission loss. Of course these multiplexers are meant to be integrated with other components on chip. NRC has a long history of expertise in the WDM technology based on several material platforms, and we have set up design capabilities that can be quickly adapted to meet client requirements. We continue to refine device designs and invent new configurations to meet the industry’s emerging needs.

As silicon does not produce light, lasers made of III-V semiconductors are often used as light sources to integrate with the silicon photonics platform. Light on the chip eventually needs to be channelled to an optical fiber for transport across the data center. Highly efficient coupling of light between the laser or the fiber and the silicon chip is of paramount importance in reducing energy loss. To do this, we are working on making a laser that is integration-ready, in that it is specifically designed and tailored for easy integration. We have also developed light couplers on silicon chips based on our own subwavelength grating (SWG) technology. These couplers enable more than 90 percent of the light to go through the coupling process, which is record-setting performance. Apart from using single wavelength lasers, NRC has developed quantum dot lasers which can emit several different wavelengths from a single chip. In this configuration, only a single interface is required to pass through several data streams, greatly reducing the packaging effort and cost.

For a data center and its users, this added data capacity means that there is less lag time when accessing or uploading information. Data center operations would cost less, and there would be more room for capacity growth due to the compactness of the components.

The Canadian Photonic Fabrication Centre offers advanced semiconductor laser design and fabrication services. Credit: National Research Council of Canada.

The Canadian Photonic Fabrication Centre offers advanced semiconductor laser design and fabrication services. Credit: National Research Council of Canada.

Reducing power consumption

One of the greatest challenges for data centers to overcome is the massive power usage required to run operations. One data center can use enough electricity to power 180,000 homes (1). Often, these centers are built beside rivers to access more direct power. The construction and operation of hydropower dams significantly affects natural river systems as well as wildlife populations. Reducing the demand on power consumption represents significant financial and environmental benefits,  allowing data center operators to be better corporate citizens while cutting costs.

The servers and switches consume a lot of power to run. By making the components smaller, making each part more efficient, and through on-chip integration of multiple functions, great energy saving can be achieved. When using multiple chips is necessary, reducing the light loss at the junction and reducing the number of connections are key. These are areas NRC is already addressing.

Even with these advancements, there will still be a lot of heat generated by the processors and electronics. A significant amount of power is used to keep equipment and components at the correct temperatures to work according to their design. Although the use of photonics cuts down the amount of power used for cooling, temperature control is still needed. Almost all photonic devices’ properties change with temperature, and these potential changes can greatly affect their performance. NRC is working on ways to reduce this dependency on thermal controls so devices can run over a wider temperature range, and eventually without temperature control at all. This work involves innovation in the design of the photonic components, as well as the introduction of new materials.

To feed the growing hunger for information, data centers have been required to rapidly innovate and adopt new technologies. Although carrying data using light rather than electricity is a significant game-changer, on-going work is needed to make photonic solutions more compact, efficient, and easy to manufacture to ensure their continued penetration within the data center market. The benefits of harnessing the power of light not only further the bottom line of the data center operators, but also provide benefits both environmentally and to end-users.

To learn more about NRC’s expertise in photonics, visit the NRC website.

Notes

1 – Walsh, Bryan. “The Surprisingly Large Energy Footprint of the Digital Economy.” TIME Inc., 14 Aug. 2013.


APC team bio picThe NRC Advanced Photonic Components (APC) program team works with Canadian and international photonics companies and research organizations to create the basic building blocks of the optical communication system: the semiconductor light sources, photodetectors and photonic integrated circuit chips that transmit, process, and detect the data flowing through the global communication network. The team is composed of researchers and engineers who are internationally recognized leaders in III-V and silicon photonics design, fabrication and material science. The APC program also operates the Canadian Photonic Fabrication Centre (CPFC), one of the worlds most advanced foundries for fabricating III-V semiconductor photonic components.  The team helps partners to develop new products from first prototype development cycles all the way through to production runs.

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