Transfer data with multiple light colors simultaneously

June 29, 2023

(Nanowerk News) Data centers and high-performance computers running artificial intelligence programs, such as large language models, are not limited by the sheer computing power of the individual nodes. It’s another issue — the amount of data they can transfer between nodes — that underlies the “bandwidth bottleneck” that currently limits the performance and scalability of these systems.

The nodes in this system can be separated by more than one kilometer. Because metallic cables dissipate electrical signals as heat while transferring data at high speeds, these systems transfer data over fiber-optic cables. Unfortunately, a lot of energy is wasted in the process of converting electrical data to optical data (and back again) as signals are sent from one node to another.

In a study published in Nature Photonics (“Massively scalable Kerr comb-based silicon photonic link”), researchers at Columbia Engineering demonstrated an energy-efficient method for transferring larger amounts of data over fiber-optic cables connecting nodes. This new technology improves upon previous attempts to transmit multiple signals simultaneously over the same fiber-optic cable. Instead of using a different laser to generate each wavelength of light, the new chip requires only one laser to generate hundreds of different wavelengths of light that can simultaneously transfer independent streams of data. Photonic integrated chip for a penny. (Image: Light Wave Research Laboratory, Columbia Engineering)

Simpler and energy efficient data transfer method

Millimeter-scale systems use a technique called wavelength-division multiplexing (WDM) and a device called a Kerr frequency comb that takes a single color of light at the input and creates many new colors of light at the output. The critical Kerr frequency comb developed by Michal Lipson, Higgins Professor of Electrical Engineering and Professor of Applied Physics, and Alexander Gaeta, David M. Rickey Professor of Applied Physics and Materials Science and Professor of Electrical Engineering, allows researchers to transmit clear signals through different wavelengths of light. separate and proper, with space in between.

“We realized that this device was an ideal source for optical communications, where one could encode independent channels of information at each color of light and propagate it over a single optical fiber,” said senior author Keren Bergman, Charles Batchelor Professor of Electrical Engineering in Columbia Engineering, in where he also serves as faculty director at the Columbia Nano Initiative. This breakthrough allows systems to transfer exponentially more data without using proportionally more energy.

The team miniaturized all of the optical components onto chips roughly a few millimeters on each edge to generate light, encoded it with electrical data, and then converted the optical data back into electrical signals at the target node. They devised a new photonic circuit architecture that allows each channel to be individually encoded with data while having minimal interference with neighboring channels. That means the signals sent in any color of light don’t get messed up and it’s hard for the receiver to interpret and convert them back into electronic data.

“In this way, our approach is much more compact and energy efficient than comparable approaches,” said the study’s lead author Anthony Rizzo, who carried out the work while a PhD student in Bergman’s lab and is now a research scientist at US Air. Directorate of Information Research Laboratory Forces. “It’s also cheaper and easier to scale because silicon nitride comb generation chips can be fabricated in standard CMOS castings used to make microelectronics chips rather than in expensive custom III-V foundries.” The photonic emitting chip is mounted on a printed circuit board with electrical and fiber-optic connections The photonic emitting chip is mounted on a printed circuit board with electrical and fiber-optic connections. (Image: Light Wave Research Laboratory, Columbia Engineering)

The compact nature of these chips allows them to directly interact with computer electronic chips, greatly reducing total energy consumption because electrical data signals only need to travel within millimeters rather than tens of centimeters.

Bergman notes, “What this work demonstrates is a viable path toward both dramatically reducing system energy consumption while increasing computing power by an order of magnitude, enabling artificial intelligence applications to continue to grow at exponential rates with minimal environmental impact.”

The exciting results paved the way for real-world implementation

In the experiment, the researchers managed to transmit 16 gigabits per second per wavelength for 32 different wavelengths of light with a total single fiber bandwidth of 512 Gb/s with an error of less than one bit out of one trillion bits of data transmitted. This is a very high level of speed and efficiency. The silicon chip that transmits data measures just 4mm x 1mm, while the chip that receives optical signals and converts them into electrical signals measures just 3mm x 1mm—both of which are smaller than a human fingernail.

“While we used 32 wavelength channels in our proof-of-principle demonstration, our architecture can be adapted to accommodate more than 100 channels, which is well within the range of standard Kerr comb designs,” added Rizzo.

These chips can be fabricated using the same facilities used to manufacture microelectronic chips found in standard consumer laptops or cell phones, providing a direct path to volume scaling and real-world deployment.

The next step in this research is to integrate photonics with chip-scale drive and control electronics to further downsize the system.

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