KAIST Develops Chip-Scale Microcomputer Technology
22 GHz repetition rate, 2.6 femtosecond timing jitter
Simultaneous generation of optical pulse trains is possible


A joint research team led by Professor Lee Han-seok of the Department of Physics and Professor Kim Jeong-won of the Department of Mechanical Engineering at the Korea Advanced Institute of Science and Technology (KAIST) announced on the 17th that they have developed a technology to periodically generate pulse signals with very low noise using a silica microresonator.

This technology can generate optical pulse trains with a high repetition rate of 22 GHz and a low timing jitter of 2.6 femtoseconds (385 trillionths of a second) from a 3 mm diameter chip. Therefore, it is expected to be utilized in the development of sampling clocks for ultra-high-speed, wideband analog-to-digital converters (ADCs) or ultra-low-noise microwave signal sources for 5G and 6G communications.

Mode-locked lasers, which generate optical pulses with pulse widths on the femtosecond (quadrillionths of a second) scale, are used as important light sources in basic science. Recently, research is being conducted on microcomb technology, which generates femtosecond pulses using chip-scale microresonator devices rather than laser equipment. While conventional mode-locked lasers have repetition rates of around 100 MHz, microcombs have repetition rates of over tens of GHz, more than 100 times higher.

Microcombs are theoretically expected to achieve extremely low timing errors, on the order of 1 femtosecond. Previously, measurement limitations prevented accurate measurement of this performance, nor did they allow for optimization of noise performance.

This research was possible by combining the on-chip microresonator fabrication technology with a very high Q factor (quality factor) of over 100 million, owned by Professor Lee Han-seok's team, with the pulse-to-pulse timing measurement technology with a resolution of 100 attoseconds (one quadrillionth of a second) owned by Professor Kim Jeong-won's team.

The joint research team was able to measure the time error between pulses using timing measurement technology that is more than 100 times more precise than existing technology, and by using the results to find the optimal operating conditions for the microresonator, they were able to improve the noise performance of the microcomb.

Professor Lee Han-seok stated, "We are currently researching new optical device configuration techniques to further improve pulse generation efficiency and noise performance." Professor Kim Jeong-won also stated, "We are conducting follow-up research to utilize the developed technology as a K-band microwave signal source with extremely low phase noise and as a sampling clock for ultra-high-speed ADCs."