Smallest Integrated Kerr Frequency Comb Generator – ScienceDaily

A major challenge has been to make these comb sources smaller, more robust and more portable. Over the last 10 years, the use of chip-based monolithic micro-resonators for the manufacture of such combs has grown considerably. Although microresonators generating frequency combs are tiny – smaller than a human hair – they have always relied on external lasers that are often much larger, expensive and energy hungry.

Researchers at Columbia Engineering announced today in Nature that they have built a Kerr frequency comb generator that, for the first time, integrates the laser with the micro-resonator, significantly reducing the size and power requirements of the system. They designed the laser so that half of the laser cavity rests on a semiconductor waveguide section with high optical gain, while the other half rests on silicon nitride waveguides , a material with very low loss. Their results showed that they no longer needed to connect separate devices to the laboratory using fiber optics; they can now integrate everything on compact photonic chips and energy saving.

The team knew that the lower the optical loss in silicon nitride waveguides, the lower the laser power required to generate a frequency comb. "To understand how to eliminate most of the loss of silicon nitride, many students in our group have been working for years," said Michal Lipson, professor of electrical engineering at Eugene Higgins, professor of applied physics and co-leader of the team. "Last year, we demonstrated that we could reproducibly reproduce highly transparent, low-loss waveguides, which were essential in reducing the power needed to create a comb. frequency on chip, which we show in this new document. "

Micro-resonators are usually small round discs or rings made of silicon, glass or silicon nitride. Curving a ring-shaped waveguide creates an optical cavity in which light travels several times, generating a strong build-up of power. If the ring is properly designed, a single frequency pump laser input can generate a complete frequency comb in the ring. Columbia's engineering team has launched another key innovation: in extremely low loss microresonators like theirs, the light travels and accumulates such intensity that it can see a strong reflection coming back from the ring.

"We actually placed the microresonator directly on the edge of the laser cavity so that this reflection makes the ring work like one of the laser's mirrors." The reflection made it possible to keep the laser perfectly aligned. Brian Stern, lead author of the study. who led the work as a PhD student in the Lipson group. "So, rather than using a standard external laser to pump the frequency comb into a separate microresonator, we now have the freedom to design the laser so that we can make sure that the laser and the resonator interact in a way. new."

All optics are in a millimetric area and researchers say their new device is so efficient that even a common AAA battery can power it. "Its compact size and low energy requirements open the door to the development of portable frequency comb devices," says Alexander Gaeta, Professor of Applied Physics and Materials Science at Rickey, and co-leader of the team . "They could be used for ultra-precise optical clocks, for laser / LIDAR radar in autonomous cars, or for spectroscopy in order to detect biological or environmental markers." We compare the frequency combs resulting from experiments. lab-based, even portable, or even portable devices. "

The researchers plan to apply such devices in various configurations for high precision measurements and detection. In addition, they will extend these designs to exploit them in other ranges of wavelengths, such as the average infrared, where the detection of chemical and biological agents is extremely effective. In collaboration with Columbia Technology Ventures, the team has a provisional patent application and is currently studying the possibility of commercializing this device.