With the breakthrough of optical chips, photonic chips will realize faster and more energy-saving artificial intelligence programs.

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Photonic integrated link driven by Kerr frequency comb. Source: Light Wave Research Laboratory/Columbia Project.

Data centers and high-performance computers running artificial intelligence programs (such as large-scale language models) are not limited by the absolute computing power of their nodes. This is another problem-the amount of data they can transmit between nodes-which is the basis of the "bandwidth bottleneck" that currently limits the performance and expansion of these systems.

Nodes in these systems can be more than one kilometer apart. Because metal wires emit electrical signals in the form of heat when transmitting data at high speed, these systems transmit data through optical fiber cables. Unfortunately, when signals are sent from one node to another, a lot of energy is wasted in the process of converting electrical data into optical data (and back again).

In a study published in Nature Photonics, researchers from Columbia Institute of Technology demonstrated an energy-saving method, which can transmit a large amount of data through optical fiber cables connecting nodes. This new technology improves the previous attempt to transmit multiple signals simultaneously through the same optical fiber cable. Instead of using different lasers to generate light of each wavelength, the new chip only needs one laser to generate hundreds of different wavelengths of light, which can transmit independent data streams at the same time.

Simpler and more energy-saving data transmission method

Millimeter-scale systems use a technology called wavelength division multiplexing (WDM) and a device called Kerr frequency comb. These devices acquire light of a single color at the input end and generate light of many new colors at the output end. The critical Kerr frequency comb, developed by Michal Lipson, professor of electrical engineering and professor of applied physics at Higgins, and Alexander Gaeta, professor of applied physics and materials science and professor of electrical engineering at David M. Rickey, allows researchers to send clear signals through individual and precise optical wavelengths, with space between them.

Photonic integrated chip is placed on a dime. Source: Light Wave Research Laboratory/Columbia Project.

"We realize that these devices are ideal sources of optical communication, and people can encode independent information channels on each color of light and spread them through an optical fiber," said Keren Bergman, a senior author, who is Charles Batchelor, a professor of electrical engineering at Columbia Institute of Technology, and the academic director of Columbia Nano Project. This breakthrough can make the system transmit more data exponentially without using more energy in proportion.

The team miniaturized all optical components to chips with each edge about several millimeters, which were used to generate light, encode it with electrical data, and then convert the optical data back to the electrical signal of the target node. They have designed a novel photonic circuit architecture, which allows each channel to encode data separately, and at the same time, the interference to adjacent channels is minimal. This means that the signals sent with each color of light will not be confused, and the receiver will not have difficulty in interpreting and converting back to electronic data.

"In this way, our method is more compact and energy-saving than similar methods," said Anthony Rizzo, the lead author of the study, who did this work as a doctoral student at Bergman Laboratory and is now a research scientist at the Information Council of the US Air Force Research Laboratory. "It is also cheaper and easier to expand, because the silicon nitride comb foundry can be manufactured in a standard CMOS foundry for manufacturing microelectronic chips, rather than in an expensive dedicated III-V foundry.

The compact characteristics of these chips enable them to directly interface with computer electronic chips, which greatly reduces the total energy consumption, because electrical data signals only need to travel to millimeters instead of tens of centimeters.

Bergman pointed out, "This work shows that this is a feasible way, which can not only greatly reduce the energy consumption of the system, but also improve the computing power by several orders of magnitude, so that the application of artificial intelligence will continue to grow exponentially, and at the same time, it will have the least impact on the environment.

The exciting results paved the way for actual deployment.

In the experiment, the researchers managed to transmit 16 gigabits per second for 32 different wavelengths of light, with a total single fiber bandwidth of 512 Gb/s, and the error was less than one bit in the one trillion transmitted data. These are incredibly high levels of speed and efficiency. The silicon chip for transmitting data is only 4mm x 1mm in size, while the chip for receiving optical signals and converting them into electrical signals is only 3mm x 1mm in size, both of which are smaller than human nails.

Schematic diagram of decomposed data center based on Kerr frequency comb driving silicon photonic link. Source: Light Wave Research Laboratory/Columbia Project.

"Although we used 32 wavelength channels in the proof-of-principle demonstration, our architecture can be expanded to accommodate more than 100 channels, which is completely within the scope of standard Kerr comb design," Rizzo added.

These chips can be manufactured by the same facilities as microelectronic chips in standard consumer laptops or mobile phones, thus providing a direct way for volume expansion and practical deployment.

The next step of this research is to integrate photonics with chip-level drive and control electronics to further miniaturize the system.

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Original title: "Optical Chip Breakthrough! Photonic chip will realize faster and more energy-saving artificial intelligence program.

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