Powerful and precise multi-color lasers now fit on a single chip

(Press-News.org) A few years ago, researchers in Michal Lipson’s lab noticed something remarkable. 

They were working on a project to improve LiDAR, a technology that uses lightwaves to measure distance. The lab was designing high-power chips that could produce brighter beams of light. 

“As we sent more and more power through the chip, we noticed that it was creating what we call a frequency comb,” says Andres Gil-Molina, a former postdoctoral researcher in Lipson’s lab. 

A frequency comb is a special type of light that contains many colors lined up next to each other in an orderly pattern, kind of like a rainbow. Dozens of colors — or frequencies of light — shine brightly, while the gaps between them remain dark. When you look at a frequency comb on a spectrogram, these bright frequencies appear as spikes, or teeth on a comb. This offers the tremendous opportunity of sending dozens of streams of data simultaneously. Because the different colors of light don’t interfere with each other, each tooth acts as its own channel. 

Today, creating a powerful frequency comb requires large and expensive lasers and amplifiers. In their new paper in Nature Photonics, Lipson, Eugene Higgins Professor of Electrical Engineering and professor of Applied Physics, and her collaborators show how to do the same thing on a single chip. 

“Data centers have created tremendous demand for powerful and efficient sources of light that contain many wavelengths,” says Gil-Molina, who is now a principal engineer at Xscape Photonics. “The technology we’ve developed takes a very powerful laser and turns it into dozens of clean, high-power channels on a chip. That means you can replace racks of individual lasers with one compact device, cutting cost, saving space, and opening the door to much faster, more energy-efficient systems.”

“This research marks another milestone in our mission to advance silicon photonics,” Lipson said. “As this technology becomes increasingly central to critical infrastructure and our daily lives, this type of progress is essential to ensuring that data centers are as efficient as possible.”

Cleaning up messy light  The breakthrough started with a simple question: What’s the most powerful laser we can put on a chip?

The team chose a type called a multimode laser diode, which is used widely in applications like medical devices and laser cutting tools. These lasers can produce enormous amounts of light, but the beam is “messy,” which makes it hard to use for precise applications.

Integrating such a laser into a silicon photonics chip, where the light pathways are just a few microns — even hundreds of nanometers — wide, required careful engineering. 

“We used something called a locking mechanism to purify this powerful but very noisy source of light,” Gil-Molina says. The method relies on silicon photonics to reshape and clean up the laser’s output, producing a much cleaner, more stable beam, a property scientists call high coherence.

Once the light is purified, the chip’s nonlinear optical properties take over, splitting that single powerful beam into dozens of evenly spaced colors, a defining feature of a frequency comb. The result is a compact, high-efficiency light source that combines the raw power of an industrial laser with the precision and stability needed for advanced communications and sensing.

Why it matters now The timing for this breakthrough is no accident. With the explosive growth of artificial intelligence, the infrastructure inside data centers is straining to move information fast enough, for example, between processors and memory. State-of-the-art data centers are already using fiber optic links to transport data, but most of these still rely on single-wavelength lasers.

Frequency combs change that. Instead of one beam carrying one data stream, dozens of beams can run in parallel through the same fiber. That’s the principle behind wavelength-division multiplexing (WDM), the technology that turned the internet into a global high-speed network in the late 1990s.

By making high-power, multi-wavelength combs small enough to fit directly on a chip, Lipson’s team has made it possible to bring this capability into the most compact, cost-sensitive parts of modern computing systems. Beyond data centers, the same chips could enable portable spectrometers, ultra-precise optical clocks, compact quantum devices, and even advanced LiDAR systems.

“This is about bringing lab-grade light sources into real-world devices,” says Gil-Molina. “If you can make them powerful, efficient, and small enough, you can put them almost anywhere.”

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