A lab accident prompts engineers to develop a chip that fires a powerful rainbow-colored laser beam. This could help data centers better manage the proliferation of artificial intelligence (AI) data.
The new photonics chip contains an industrial-grade laser light source combined with a precisely engineered optical circuit that shapes and stabilizes the light before splitting it into multiple evenly spaced colors.
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Creating this rainbow effect, called a frequency comb, typically requires large and expensive lasers and amplifiers. But while researchers were working on ways to improve lidar (light detection and ranging) technology, they stumbled on how to pack this powerful photonics technology into a single tiny chip.
Lidar uses laser pulses to measure distance based on the time it takes for the laser pulse to reach an object and reflect back. While trying to create a more powerful laser that could capture detailed data from far away, the team noticed that the chip splits light into multiple colors.
What is a frequency comb?
A frequency comb is a type of laser light that consists of multiple colors or frequencies evenly spaced across the light spectrum. When plotted on a spectrogram, these frequencies appear as spikes that resemble comb teeth.
The peak of each “teeth” represents a stable, precisely defined wavelength that can convey information independently of other “teeth”. The wavelengths are both frequency and phase locked, meaning their peaks are perfectly aligned, so they do not interfere with each other. This allows multiple data streams to travel in parallel over a single optical channel, such as a fiber optic cable.
Scientists discovered the effect by accident and devised a way to recreate it intentionally and controllably. They also packed the technology into a silicon chip, allowing light to travel through waveguides just a few micrometers wide. One micrometer (1 µm) is 1/1000th of a millimeter (0.0001 cm), or about 1/100th the width of a human hair.
The research team published their findings in the journal Nature Photonics on October 7th. The breakthrough is especially important at a time when AI is increasingly putting a strain on data center infrastructure, the researchers said.
“Data centers are creating tremendous demand for powerful, efficient light sources that contain many wavelengths,” study co-author Andres Gil-Molina, principal engineer at Xscape Photonics and former research fellow at Columbia Engineering, said in a statement.
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“The technology we developed takes a very powerful laser and converts it into dozens of clean, high-power channels on a chip. This means racks of individual lasers can be replaced with one compact device, reducing costs, saving space, and opening the door to faster, more energy-efficient systems.”
rainbow on chip
To create a frequency comb on a chip, researchers needed to find a high-power laser that could be squeezed into a compact photonic circuit. They ultimately settled on multimode laser diodes, which are widely used in medical equipment and laser cutting tools.
Although multimode laser diodes can produce a powerful beam of laser light, the beam is “messy,” meaning researchers need to refine and find ways to stabilize the light to make it practical, the researchers said in the study.
They accomplished this using a technique called self-injection locking. This involves integrating a cavity into the chip that returns a small portion of the light to the laser. This filters and stabilizes the light, creating a powerful and stable beam.
Once stabilized, the chip splits the laser beam into polychromatic frequency combs. The result is a small yet efficient photonics device that combines the power of industrial lasers with the precision needed for data transmission and sensing applications, the scientists added.
Beyond data centers, this new chip could enable portable spectrometers, ultra-high precision optical clocks, compact quantum devices, and even advanced LIDAR systems.
“This is about bringing a laboratory-grade light source into a real-world device,” said Gil Molina. “If we can make it powerful, efficient and small enough, we can put it almost anywhere.”
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