Physicists Finally Figured Out How to Fit an Ultrafast Pulsing Laser onto a Microscopic Computer Chip

An overlooked laser design could make ultrafast optics smaller and cheaper.

Ultrafast lasers are the heavy artillery of modern optics. Their intense, rapid pulses power eye surgeries, precision manufacturing, and the world’s most accurate atomic clocks. But these revolutionary tools have always suffered from glaring physical drawbacks. They are massive, costly, and typically require entire laboratory tables to function.

Now, a team of scientists in Switzerland has squeezed much of that power onto a single, tiny photonic chip. The implication is clear: ultrafast lasers will soon be ready to become portable instruments.

The researchers at EPFL report that their chip-based ultrafast laser produces 1.05 nanojoules of energy in pulses that can be compressed to 147 femtoseconds. A femtosecond is one quadrillionth of a second. That exceeds the performance of previous photonic-chip ultrafast sources by more than two orders of magnitude and begins to rival fiber-based laboratory systems.

A Tiny Chip With an Old Idea Inside

The team did not invent a brand-new laser principle. Instead, it revisited an older design called the Mamyshev oscillator, an architecture long known in fiber lasers but largely overlooked in integrated photonics.

“For more than twenty years, a high-pulse-energy femtosecond laser on chip was widely regarded as a holy grail of integrated photonics,” said Tobias Kippenberg, a photonics professor at EPFL.

“Our result shows that it is not only possible, but that it can be achieved with a surprisingly elegant architecture that the integrated-photonics community had overlooked.”

A photonic chip guides light through tiny channels called waveguides. The problem is that squeezing powerful laser pulses into such narrow paths can make the light unstable. The Mamyshev design solves part of that problem by using two optical filters. Strong pulses broaden into a wider spread of colors and pass through. Weak, destabilizing light does not broaden enough and gets filtered out.

“This design is especially attractive because it does not require any component that is difficult to make on this erbium-doped silicon nitride chip,” said Zheru Qiu, a co-leading author.

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The laser cavity itself is 42 centimeters long, but the researchers folded it into a spiral on a 2-centimeter-by-1.1-centimeter chip. In prototype form, 26 separate mode-locked lasers fit on one chip, and the authors report more than 300 laser cavities per wafer.

Big Power, Tiny Footprint

Ultrafast lasers do not simply flash quickly. When their pulses repeat with extreme regularity, they can form optical frequency combs, often described as rulers for light. NIST says these combs measure exact light frequencies and connect optical waves to radio and microwave technologies used in clocks, communications and computing. The technique helped earn the 2005 Nobel Prize in Physics.

The EPFL device also generated a broad “supercontinuum” of light, spanning 736 to 2,331 nanometers, without extra amplification. Such broad light sources can support spectroscopy and optical coherence tomography, a medical imaging technique used, for example, in the eye.

The researchers then used the chip laser to drive a terahertz time-domain spectroscopy system. Terahertz radiation sits between microwaves and infrared light; it can pass through many materials, does not ionize tissue and can reveal molecular signatures. In the experiment, the system reached a 5-terahertz bandwidth and a 90-decibel dynamic range. It measured the thickness of a silicon wafer and distinguished lactose powder from flour by detecting a characteristic absorption feature near 0.53 terahertz.

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Ultrafast lasers on chips can be used for checking hidden defects in materials, identifying chemicals without contact, monitoring pollutants or building smaller precision instruments.

The work is not yet a pocket laser though. The experiment still used external pump lasers and separate testing equipment. Future versions would need tighter integration, lower cost packaging and real-world robustness. But the key barrier — getting high-energy femtosecond pulses from an integrated photonic platform — looks less immovable than it did.

“With kilowatt-level peak powers, the chip can drive demanding applications that have long depended on large, expensive laboratory lasers,” Qiu said.

The findings were reported in the journal Nature.