For more than two decades, scientists in the field of integrated photonics have chased the same goal: fitting a powerful ultrafast laser onto a tiny chip. A new study published June 3 in the journal Nature shows that goal has now been achieved.
Researchers demonstrated that a laser on a photonic chip could deliver 1.05 nanojoules of energy in 147-femtosecond bursts. A femtosecond is one quadrillionth of a second. That output puts the chip-based laser in the same performance range as large laboratory-class ultrafast lasers that currently take up whole tabletops in labs and factories.
According to Live Science, the key to the breakthrough was not a new invention, but an old one that the field had largely ignored. The team used a laser architecture called the Mamyshev oscillator, developed in 1998 by physicist and engineer Pavel V. Mamyshev at Bell Labs. The oscillator had received little attention in photonic chip research until now.
The Mamyshev oscillator works by placing a nonlinear waveguide between two optical filters. When a high-intensity laser pulse passes through, it expands into a broader range of colors that can pass through both filters. Weaker light, which can destabilize the laser, gets blocked out. The result is a stable, high-intensity pulse that can be maintained on an extremely small chip.
Photonic chips use light rather than electricity for computing operations. They manipulate light through microscopic structures called waveguides, which are usually optical fibers or etched cavities. The chips are already used in fiber-optic communications, medical sensors, and lidar systems. But they have historically struggled with high-powered, ultrafast lasers because the light is confined to such small waveguides that it interacts strongly with itself and becomes unstable.
"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 the Swiss Federal Institute of Technology in Switzerland. "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."
Ultrafast lasers are currently used in precision manufacturing, eye surgery, biological imaging, and atomic clocks. The systems that power them are large and expensive, which limits where and how they can be used. Getting that same performance onto a chip could lead to portable diagnostic devices, affordable imaging tools, and smaller information-processing systems.
The research team says the chip-based laser competes with the output of full-scale lab systems. Whether that performance holds across a range of real-world applications remains to be tested, but the demonstration marks the first time the long-sought chip integration has been shown to work.
