The new "light ruler" will bring about major changes in optical clocks, telescopes and communication technologies

[ Instrument R&D of Instrument Network ] Just like the meter ruler uses hundreds of graduation lines to accurately measure the distance, the laser frequency comb has hundreds of evenly distributed and well-defined frequencies, which can be used to accurately measure the color of light waves. Evenly spaced frequencies are similar to comb teeth, hence the name laser frequency comb. It enables a new generation of atomic clocks, greatly increasing the number of signals passing through optical fibers, and by identifying small frequency changes in starlight to find hidden planets.

Scientists from the National Institute of Standards and Technology (NIST) and the University of California, Santa Barbara (UCSB) have collaborated to develop a new type of "microcomb" on the chip, by enhancing and expanding the capabilities of these micro devices Promote the progress of time frequency measurement technology.

The core of this frequency microcomb is an optical microresonator. The width of this ring device is about the thickness of a human hair. The light from the external laser forms high intensity around it. Microcombs made of glass or silicon nitride usually require an amplifier for external lasers, making the comb itself complicated, difficult to handle, and extremely expensive to produce.

Researchers at NIST and UCSB have shown that if a semiconductor aluminum gallium arsenide is used to make a microcomb, it will have two important characteristics: this frequency comb operates at very low power and therefore does not require an amplifier; at the same time, it can produce an ultra-stable frequency, which It is the ability to accurately measure frequency using a microchip comb as a sensitive tool. This research belongs to the "NIST on Chip" project.

The researchers believe that the microcomb technology can help engineers and scientists make accurate optical frequency measurements outside the laboratory. In addition, microcombs can be mass-produced through nano-manufacturing techniques similar to those used to manufacture microelectronic products.

UCSB scientists have developed a microresonator made of aluminum gallium arsenide. The frequency comb made with this microresonator only needs one percent of the power of the device made of other materials. At the same time, the NIST team placed the microresonator at a temperature 4 degrees below absolute zero to detect the device. Low temperature experiments show that the interaction between the heat generated by the laser and the circulating light in the microresonator is the only obstacle that causes the device to generate the required high stable frequency.

At low temperatures, the research team proved that it can reach the so-called "soliton state", that is, in this state, a single light pulse does not change its shape, frequency or circulation speed within the microresonator. With such an soliton, all the teeth of the frequency comb are in phase with each other and can be used as a scale to measure the frequencies used in optical clocks, frequency synthesis, or laser ranging.

The researchers published the results in the Journal of Laser and Photonics Review published in June 2020.