Development of an ultra-precision time-of-flight sensor
Prof. Jungwon Kim's research team of the Department of Mechanical Engineering has developed ultra-precision time-of-flight sensor technology that uses a pulsed laser and electro-optic sampling methods for distance measurement.
This new TOF sensor technology makes it possible to precisely measure a difference in position as small as 180 picometers (1/5.5 billion m), i.e., even smaller than the size of two hydrogen atoms combined, within 1/200 seconds. As a new source technology, it is expected to overcome the performance of existing high-performance distance measuring technologies.
The results of the present study were published in Nature Photonics, an international journal, on February 10, with Yongjin Na, a Ph. D. student, as the first author. (Paper title: Ultrafast, sub-nanometre-precision and multi-functional time-of-flight detection).
Laser-based distance measuring technologies are currently used not only in various industrial fields, such as LiDAR and semiconductors used in security and autonomous driving applications, but also as core technologies in a variety of other fields, such as detecting earthquakes, gravitational waves, and other natural phenomena.
Improvement in distance measurement resolution, speed, and range will not only enhance the performance of existing application technologies but also enable the measurement of new physical phenomena that were once impossible to measure.
The existing high-performance measuring technologies are largely divided into two groups. The existing TOF technology allows for a large measurement range of more than one meter, but its resolution performance is accordingly poor. In contrast, interferometer technology provides high-resolution performance at the nanometer level, but its measurement range is as narrow as several micrometers. Also, both methods share the same disadvantage that the measuring speed is slow.
To overcome these limitations, the research team proposed a TOF sensor that works in a completely different way from existing methods. They attempted to use an electro-optic sampling method to measure the time difference between the light pulse that was generated by the pulsed laser and the current pulse generated by the light diode.
Here, the time difference between the light pulse and the current pulse was so small, e.g., 100 attoseconds (one byllionth seconds), that it was possible to accurately measure any distance difference of several nanometers at high speed.
Also, the current pulse length was as long as tens of picoseconds, and thus the measurement range can be at the millimeter level or higher. Likewise, the researchers were able to overcome the respective limitations of both existing technologies at the same time, i.e., the poor resolution performance of the existing TOF technology and the narrow measurement range of the interferometer technology.
The research team demonstrated high-resolution three-dimensional shaping technology using this new TOF technology and implemented high-precision strain sensors that can be used to measure microscopic displacements, as in seismic wave and volcanic activity measurement.
They also demonstrated the feasibility of the technology to real-time measure the position of an object that moves at a speed of 100Mhz (corresponding to 100 million vibrations per second) in a nanometer resolution based on its advantage that a high resolution can be implemented even in ultra-high-speed measurement.
The research team expected that it would be possible to realize a multi-point, multi-functional complex sensor system that uses a single laser source and optical fiber links in a smart factory-like environment by utilizing the advantage of the technology that the TOF of multiple points that are far apart from one another can be precisely measured at the same time.
Prof. Kim said, “Our future study will focus on using this technology to make it possible to real-time measure and characterize complex and fast dynamic phenomena that have never been identified using existing technologies, such as non-linear motions in microelectronic devices.”
This research was supported by the Research Support Program for Mid-career Researchers of the National Research Foundation of Korea.