New method makes microcombs ten times more efficient

Laser frequency combs can measure frequencies with revolutionary precision and are considered the most disruptive technological advance in the field since the birth of the laser. Simply put, a microcomb is like a ruler made of light. The principle is based on a laser sending photons that circulate inside a small cavity, a so-called microresonator, where the light is divided into a wide range of frequencies. These frequencies are precisely positioned in relation to each other, like the markings on a ruler. Thus, a new kind of light source can be created consisting of hundreds -- or even thousands -- of frequencies, like lasers beaming in unison.

Since virtually all optical measurements are connected to light frequencies, the microcomb has a multitude of applications -- from calibrating instruments that measure signals at light-year distances in space in the search for exoplanets, to identifying and keeping track of our health via the air we exhale.

Unprecedented, ground-breaking efficiency

Up to now, a fundamental problem with microcombs has been that their efficiency was too weak to produce a wider technological impact on society. The conversion efficiency between the laser and the microcomb was too weak, meaning that only a fraction of the power contained in the laser beam was usable. But now, a Chalmers research team has successfully developed a method to increase the effect of the microcomb's laser beams tenfold.

"We've developed a new method that breaks what was previously thought to be a fundamental limit for optical conversion efficiency. Our method increases the laser power of the soliton microcomb by ten times and raises its efficiency from around 1 percent to over 50 percent," says Victor Torres Company, Professor of Photonics at Chalmers.

The new method uses two microresonators, as opposed to just one. They form a unique ensemble with properties that are greater than the sum of its parts. One of the resonators enables the light coming from the laser to couple with the other resonator; rather like impedance matching in electronics.

"The new microcombs have transformative potential because they make high-performance laser technology available to many more markets. For example, frequency combs could be used in lidar modules for autonomous driving, or in GPS satellites and environmental sensing drones, or in data centres to enable bandwidth-intensive AI apps," says Torres Company.