First light-based chip could signal revolution for fiber networks

A processor that uses light to communicate with other microprocessors has been fabricated for the first time. It could be the evolution of fiber networks.

First light-based chip could signal revolution for fiber networks
Glenn J. Asakawa, University of Colorado

Researchers have combined transistors and photonics in a fabricated chip for the first time. The photonics act as inputs and outputs (I/O) and let the microprocessor talk to other chips. That light-based technology could be faster and more bandwidth-friendly than wires.

The new chip is revolutionary because the photonics I/O have been made into part of the chip for the first time in a manufacturing scenario, scientists from the University of California Berkeley and the University of Colorado wrote in a letter published in Nature.

Photonics is the technology behind the detection of photons, or particles of light. It's the principal building block for fiber-optic transmission of data.


What's the big deal with photonics in chips? Well, for one thing, it's the fact that light transmits more data between microprocessors than wires.

Another issue is power density, or power related to volume. Light can transmit more power, and thus increases the transmission distance.

"Data transport across short electrical wires is limited," the letter reads.

That "creates a performance bottleneck for semiconductor microchips," the scientists added.

The chip

Transmission distance is one of the most important elements in data transmission. The further you can send data with a chunk of power, the better.

The scientists at Berkeley reckon their chip will allow data to travel further distances with less energy used, and fewer repeaters. Repeaters are needed when signals need regenerating, and they are heavy power users. Reducing the number of repeaters will improve energy consumption, the scientists say. 


Key innovations achieved in the chip design include a way to use a silicon body of a transistor to guide light with limited loss.

The group also capitalized on silicon-germanium's light-absorbing ability. Silicon-germanium is an existing element in a transistor.

Reducing power

"The advantage with optical is that with the same amount of power, you can go a few centimeters, a few meters or a few kilometers," co-lead Chen Sun, a UC Berkeley graduate at the Berkeley Wireless Research Center, said in an article on the university's website.

"For high-speed electrical links, one meter is about the limit before you need repeaters to regenerate the electrical signal, and that quickly increases the amount of power needed," Sun said.

The Berkeley optical chip uses 1.3 picojoules per bit. That's the same as using 1.3 watts of power to send a terabit of data per second, they say. The team used a receiver 10 meters away.

For a traditional electrical signal to go a kilometer, "you'd need thousands of picojoules for each bit," they explain.

Fabrication process

The group managed to get the chip manufactured too, which is one of the things they're excited about. That means the idea not simply theoretical, they reckon.

Previous attempts at integrating photonics into the same processes used to build transistorized chips have encountered difficulty getting the photonics built onto the same platform without changing the process. This often drives up manufacturing costs or leads to failures in the transistors.

This 70 million transistors and 850 photonic component chip, measuring 3-by-6-millimeters, was fabricated in a normal chip foundry. That means mass production is viable, the scientists think.

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