Light-Speed Computing: Hertz Fellow Rajeev Ram Leading the Surge toward Photonic Microprocessors

February 24, 2016

Imagine computers running at the speed of light. Now stop imagining them, because they’re almost here.

Hertz Fellow and MIT electrical engineering professor Rajeev Ram has been working on the next generation of computing for the past decade. Last year, he was part of a group of researchers that announced a breakthrough that could change computers forever: a microprocessor that uses light, instead of electricity, to send and receive information.

Working with UC Berkeley and University of Colorado Boulder (CU Boulder) engineers who built a new type of multi-core microprocessor, Ram’s Physical Optics and Electronics Group at MIT used existing electronic materials and processes to create optical devices--waveguides, wavelength filters, modulators and detectors--packing them on the microchip alongside electronic components. The result was a 3 by 6 millimeter, light-enabled microprocessor combining 70 million transistors with 850 optical input-output components, proving that low-power yet ultrafast high performance photonic computing was possible.

“The approach was a radical one,” Ram said. “We basically re-used the various materials used to make transistors and made every optical function out of them. In my mind, it’s like MacGyver, you’re taking all these parts that are used to make a transistor and seeing if you can make an optical network out of them.”

The breakthrough device was described in the journal Nature on December 24, showing the chip had a bandwidth of 300 gigabits per second per square millimeter, about 10-50 times greater than existing electrical microprocessors.

Light-based integrated circuits, Ram said, could solve a problem that has plagued computing in recent years, especially with the explosion of cloud-based systems and big data analytics; while transistors and microprocessors have improved dramatically, Ram said, interconnect bandwidth simply hasn’t kept up pace.

“There are fundamental limitations to using electrical wires as the only means for communicating from chip to chip,” Ram said. “In simulations we found photonics could drop the amount of energy required to communicate information by about a factor of 100. For the same amount of power, you could communicate 100 times more data and unclog this interconnect bottleneck that’s developed over the past decade.”

Rajeev Ram Photonic Microprocessor
Image Courtesy of Glenn J. Asakawa
"Single-chip microprocessor with integrated optical communications. Two-processor cores (blue), 1 MB of on-chip RAM (orange) are integrated with multi-wavelength optical communication (between green bands).”

The light-based microprocessor is the culmination of a decade of funding and support from the Defense Advanced Research Projects Agency (DARPA), which recruited Ram and a colleague at Berkeley, Vladimir Stojanovic, to investigate the potential for photonic computers. While both men were skeptical at first, now that the concept has been proven to work, the next phase is to commercialize it.

Last year, students at MIT, UC Berkeley and CU Boulder spun off a company, AyarLabs (formerly Optibit), that won the MIT Clean Energy Prize in 2015. With Ram serving on the company’s board, AyarLabs has startup incubators in Silicon Valley and is looking for investors.

Ram envisions the first applications of photonic microprocessors in large data centers, in big data arenas such as molecular scale manipulation and gene sequencing, and eventually, becoming the brains behind quantum computing.

“It’s a new capability, so it feels there should be a way to leverage that for commercial success,” Ram said. “Now that you have this ability to take a multibillion dollar factory and start producing optical components out of them, you could imagine using this infrastructure for many applications.”

Ram has a long background in researching the merging of light and electronics. Born in England, he moved with his parents to Brooklyn at the age of 7 before settling in Bakersfield, California. He attended Caltech intending to become a computer scientist, but fell in love with quantum mechanics. At UC Santa Barbara, where he earned his PhD, Ram worked on quantum optics and proposed Bose-Einstein condensates using semiconductors (devices now known as polariton lasers). The work was funded by his Hertz Fellowship and is currently being pursued by a number of groups all over the world.

In 2010, Ram became a program director for a new Department of Energy agency called ARPAe, where he oversaw projects aimed at modernizing the electricity grid. In his 2 ½ years there, he created the Agile Delivery of Electrical Power Technology (ADEPT), Solar ADEPT (part of President Obama’s Sunshot Initiative), and Green Electricity Network Integration (GENI).

Ram also has lead research into thermally-pumped light-emitting diodes (LEDs), in 2012 demonstrating LED lights could absorb heat from the environment and put out more optical power than the electrical power they take in.

At MIT, Ram’s next focus is on building a scalable quantum computer by integrating microelectronics with trapped ion-based computing. Over the next year, Ram’s group will be working on a larger-scale demonstration of next generation photonic microprocessors and attempting to utilize them into experimental quantum systems.

“It’s challenging but we’re hopeful,” Ram said. “It takes a lot of faith to keep working on a problem for a decade, but when things work, it's all worth it.”

To contact Hertz Fellow Rajeev Ram regarding his research: