• Researcher Associate at KAIST
• Research interest:
Ultra-fast Photonics
- Daejeon, South Korea
- Email
- Google Scholar
• Researcher Associate at KAIST
• Research interest:
Ultra-fast Photonics
- Daejeon, South Korea
- Email
- Google Scholar
Stabilizing a frequency comb to an ultra-stable optical frequency reference requires a multitude of optoelectronic peripherals that have to operate under strict ambient control. We propose an utmost case of frequency comb-to-comb stabilization made through a 1.3 km free-space optical (FSO) link by coherent transfer of two separate comb lines along with a feedback suppression control of atmospheric phase noise. The FSO link offers a transfer stability of 1.7×10–15 at 0.1 s averaging, while transporting the mater comb’s stability of 1.2×10–15 at 1.0 s over the entire spectrum of the slave comb.
The usefulness of the remote comb-to-comb stabilization proposed in this research was corroborated by implementing molecular absorption spectroscopy and microwave generation by utilizing slave comb. Our remote comb-to-comb stabilization is intended to expedite diverse long-distance ground-to-ground or ground-to-satellite applications; as demonstrated here for broad-band molecule spectroscopy over a 6 THz bandwidth as well as ultra-stable microwaves generation with phase noise of -80 dBc Hz–1 at 1 Hz.
The research above is being presented in conference paper as an co-author, and is now accepted in NATURE｜LIGHT: SCIENCE & APPLICATIONS
DOI: https://doi.org/10.1038/s41377-022-00940-3
Maintaining a stable optical beam path and quality is essential for various photonic applications such as metrology, timing and clock, and telecommunication. While seamless and high-quality connectivity determines the performance of the achievements, naturally propagating optical beam inevitably encounters spatial and temporal noises. Here, we propose a combined feedback system based on three different techniques: pointing, acquisition, tracking (PAT), wavefront compensation, and phase noise compensation. Acquiring a stable beam position with the PAT system, beam quality is enhanced with the feedback systems followed. The combined feedback system is evaluated under imitated atmospheric turbulent conditions, verifying its performance even under harsh environments.
Randomly fluctuated beam spot is accumulated within Ø < 55 μm, 99.5% diminished fluctuation. Furthermore, the Zernike coefficient of wavefront compensated up to 96% of distortion simultaneously. With such result, we verified our optical feedback system can be utilized to facilitate diverse photonic applications from micro to macro scale
1. Ultra-precision Photonics based on Femtosecond Lasers – National Scientist Project
National Research Foundation of Korea - (2020-Present)
◦ Development of free-space optical frequency transfer link system
◦ Stabilization of ultra-stable light source referenced to a high-finesse cavity
2. Development of Ultra-precision Optical Time/frequency Transfer over Long Free-space based on Optical Frequency Comb
National Research Foundation of Korea - (2020-Present)
◦ Design of phase compensation system for time/frequency transfer
3. Space Communications with Multi-Mission Low-Earth-Orbit Satellite Constellations
Korea Institute of Science & Technology - (2022-Present)
◦ Free-space channel design for optical communication system
4. Fast and Precise 3D Inspection for Heterogeneous Semiconductor Packaging
INTEKPLUS Company, Korea - (2021-Present)
◦ Design of multi-wavelength interferometry system for rapid/high-precision measurement
5. Frequency-comb-referenced Multi-DOF Absolute Distance Measurement for Precision Control of Real-time Stage’s Position and Attitude
National Research Foundation of Korea - (2020-Present)
◦ Development of ultra-precision positioning system based on dual-comb technique
Measurements of electrical properties, such as resistivity, of thin films allow characterizations of the microstructures and damages of the material. The 4-point measurement has typically been used to measure the resistivity with high precision, but a wafer scale mapping of resistivity using this technique require hours of measurement time. In this work, we utilize the Electric Impedance Tomography (EIT) to map out resistivity distribution of thin films on a 4-inch wafer. Compare to the 4-point measurement scheme, resistance mapping with the EIT can decrease the measurement time from hours to seconds without losing the accuracy significantly. We demonstrate that the technique successfully identifies structural and damage information of the thin films.
