The Korea Research Institute of Standards and Science (KRISS) announced on the 4th that it has developed a length measurement system with precision at the limit allowed by quantum physics. With precision at a world-class level and sufficiently simple to operate in outdoor environments, it is expected to be utilized as a 'standard' for next-generation length measurement.
Currently, the most accurate length measuring device is the 'length measurement standard' that serves as a reference for 1 meter (m). Length measurement standards operated by KRISS and representative institutions from various countries utilize short-wavelength laser interferometers that measure length by employing the interference pattern created when two beams of light meet. The short-wavelength laser has a very uniform distribution of wavelength like a ruler with closely spaced markings, enabling precise measurements at the 1-10 nm (nanometer, one-billionth of a meter) level. However, the narrow wavelength range of short-wavelength lasers significantly limits the lengths that can be measured at one time.
In contrast, absolute length measurement systems have lower precision but can measure long distances at once. They primarily measure length by emitting light (pulses) toward the measurement target from a reference point and calculating the time it takes for the light to return. The measurement method is relatively simple, allowing for miniaturization of the equipment, and can quickly measure long distances, making it widely used in various industrial fields. However, the measurement precision of existing absolute length measurement systems had a limit of μm (micrometer, one-millionth of a meter).
The KRISS length shape measurement group succeeded in enhancing the precision of the absolute length measurement system to the level of length measurement standards by using an 'optical frequency comb interferometer.' The researchers devised a method to apply the optical frequency comb interferometer to the absolute length measurement system. The optical frequency comb is a bundle of light composed of thousands of frequencies arranged at regular intervals, like piano keys. Unlike the light sources used in existing interferometers, the optical frequency comb has a broad wavelength range, while its wavelengths are arranged at very consistent intervals, enabling precise measurement of long distances at once.
The 'optical frequency comb spectrometer-based absolute length measurement system' developed by the research team possesses both the precision of a length measurement standard and the simplicity of an absolute length measurement system. The system's precision is 0.34 nm, which is the highest level among existing equipment and at the limit achievable in quantum physics. Its measurement speed is 25 μs (microsecond, one-millionth of a second), making it fast and simple enough to operate in outdoor environments, which is expected to significantly enhance the precision of length measurement in Korea's advanced industrial fields.
The research team plans to continue follow-up studies to evaluate the measurement uncertainty of the developed system and improve its performance so that it can be registered as the next-generation length measurement standard.
Jang Yoon-soo, a senior researcher in the length shape measurement group, noted, "The competitiveness of future industries such as artificial intelligence (AI) semiconductors and quantum technologies depends on accurately measuring and controlling distances at the nanometer level," adding, "This achievement will serve as an opportunity for Korea to position itself as a leading country proposing the next-generation length standard."
The results of this research were published in the international academic journal 'Laser&Photonics Review' in June.
References
Laser&Photonics Review (2025), DOI: https://doi.org/10.1002/lpor.202401995