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Electronic/photonic ‘chip sandwich’ promises cooler data centers

Technology News |
By Rich Pell


Engineers at Caltech and the University of Southampton say they have designed an electronics chip integrated with a photonics chip. The result is a cohesive product capable of transmitting information at ultra-high speed while generating minimal heat.

The new design, say the researchers, could influence the future of data centers that manage very high volumes of data communication.

“Every time you are on a video call, stream a movie, or play an online video game, you’re routing data back and forth through a data center to be processed,” says Caltech graduate student Arian Hashemi Talkhooncheh (MS ’16), and lead author of a paper describing the two-chip innovation. “There are more than 2,700 data centers in the U.S. and more than 8,000 worldwide, with towers of servers stacked on top of each other to manage the load of thousands of terabytes of data going in and out every second.”

The more efficient that data center servers can be made, the less heat they will generate, and ultimately, the greater the volume of information that they will be able to manage. While data processing is done on electronic circuits, data transmission is most efficiently done using photonics. Achieving ultra-high speed in each domain is very challenging, but engineering the interface between them is even more difficult, say the researchers.

“There is a continuous demand for increasing the speed of data communication between different chips not only in data centers but also in high-performance computers,” says Azita Emami, the Andrew and Peggy Cherng Professor of Electrical Engineering and Medical Engineering, executive officer for electrical engineering, and senior author of the paper. “As the computing power of the chips scale, the communication speed can become the bottleneck, especially under stringent energy constraints.”

To address this, the researchers designed both an electronics chip and a photonics chip from the ground up and co-optimized them to work together. The process, from the initial idea to the final test in the lab, took four years to complete, with every design choice impacting both chips.

“We had to optimize the entire system all at the same time, which enabled achieving a superior power efficiency,” says Hashemi. “These two chips are literally made for each other, integrated into one another in three dimensions.”

The resulting optimized interface between the two chips allows them to transmit 100 gigabits of data per second while producing just 2.4 pico-Joules per transmitted bit. This improves the electro-optical power efficiency of the transmission by a factor of 3.6 compared to the current state-of-the-art, say the researchers. (A picojoule is one-trillionth of a Joule, which is defined as the energy released in one second by a current of 1 ampere through a resistance of 1 ohm—or about 0.24 calories.)

“As the world becomes more and more connected, and every device generates more data,” says Emami, “it is exciting to show that we can achieve such high data rates while burning a fraction of power compared to the traditional techniques.”

For more, see “A 100-Gb/s PAM4 Optical Transmitter in a 3-D-Integrated SiPh-CMOS Platform Using Segmented MOSCAP Modulators.”


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