Ultrafast lasers—devices that fire pulses lasting mere femtoseconds (quadrillionths of a second)—have revolutionized everything from precision eye surgery to optical atomic clocks. They've also been the size of laboratory tables.
A team at EPFL in Switzerland has just shrunk them to the size of a photonic chip.
The breakthrough, published in Nature, delivers pulses of 147 femtoseconds with 1.05 nanojoules of energy—performance comparable to traditional tabletop systems, but in a package that could eventually fit in a smartphone.
"This design is far less susceptible to these problems, making it particularly well suited for integrated photonic devices," explains Zheru Qiu, one of the co-leading authors.
The "holy grail" they achieved was implementing a Mamyshev oscillator—a laser architecture that had been theoretically ideal for chip-scale integration for over two decades but remained stubbornly difficult to build.
Here's why it works: photonic chips confine light in tiny waveguides, which creates intense nonlinear effects. In most laser designs, those nonlinear effects destabilize the system. The Mamyshev oscillator uses those nonlinear effects as a feature, not a bug.
The design places a nonlinear waveguide between two optical filters. Intense pulses broaden across the spectrum and pass through both filters, while weaker light gets blocked. The system naturally selects only the strongest pulses, creating a self-stabilizing ultrafast laser that thrives in the exact environment that breaks other architectures.
Led by Professor Tobias Kippenberg at EPFL's Institute of Electrical and Microengineering, with collaboration from Helmholtz-Zentrum Dresden-Rossendorf, the team validated that the theoretical elegance actually translates to working hardware.
So what becomes possible when you can put femtosecond lasers in portable devices?
Current applications of ultrafast lasers include precision manufacturing (drilling holes in turbine blades without thermal damage), (sculpting corneas with sub-micrometer precision), and optical frequency combs—the Nobel Prize-winning technology that powers the world's most accurate atomic clocks.
