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KAIST Controls the Rotation Direction of Light Without Complex New Materials
A new pathway has opened for controlling the rotation direction of light simply by changing how molecules are arranged, without having to synthesize complex new materials. Circularly polarized light is a special form of light that travels while rotating like a pinwheel either to the left or to the right. Because different rotation directions can carry different information, it is drawing attention as a key light source for next-generation displays, optical communications, and security technologies. KAIST researchers have developed a platform technology that arranges symmetric molecules into “microscopic pinwheels,” enabling circularly polarized light with a desired rotation direction.
KAIST (President Choongsik Bae) announced on August 14 that a research team led by Professor Dong Ki Yoon from the Department of Chemistry, in collaboration with researchers from Chungnam National University, Ajou University, Yonsei University, and Japan’s RIKEN, has developed a technology that spatially confines symmetric non-chiral liquid crystal molecules and applies an electric field to form micrometer-scale chiral pinwheel structures, then permanently replicates them onto polymer nanofibers.
Chirality refers to the property of an object whose mirror image cannot be perfectly superimposed on the original, like a person’s left and right hands. Chirality is a key property not only of biological molecules such as proteins and DNA, but also of optical materials used in next-generation displays, optical sensors, and optical communications.
Until now, producing chiral optical materials has generally required the complex synthesis of molecules with asymmetric structures or the addition of large amounts of chiral substances. This has made fabrication complicated, limited the range of usable materials, and made it difficult to realize chiral structures with the same handedness over a large area.
To address this challenge, the research team proposed a new approach based on the idea that “structure creates function.”
The team applied to molecules the same principle by which the same sheet of paper can form either a clockwise or counterclockwise pinwheel depending on how it is folded. They focused on the fact that even symmetric molecules can form structures with different handedness depending on how they assemble.
The researchers first induced rod-shaped molecules to self-assemble into microscopic pinwheel-like structures. They then added an extremely small amount of chiral additive, less than 1% of the total material, to guide all of the pinwheels to face the same direction. The team then successfully replicated this structure onto polymer nanofibers.
When a conventional luminescent material was coated onto this structure, circularly polarized light rotating in opposite directions was emitted depending not on the luminescent material itself, but on the direction of the pinwheel structure. Circularly polarized light is a special form of light that rotates to the left or right as it travels, and because each rotation direction can carry different information, it can be used in next-generation displays, optical communications, and anti-counterfeiting technologies.
In other words, the study showed that the properties of light can be controlled simply by changing the structure on which a light-emitting material is placed, rather than by changing the light-emitting material itself. Put simply, just as the same LEGO blocks can form completely different shapes depending on how they are assembled, the same molecules can produce different optical properties depending only on how they are arranged.
Professor Dong Ki Yoon said, “The key point of this study is that we controlled the rotation direction of light not through the complex chemical structure of chiral molecules, but only through the way molecules are arranged,” adding, “This work presents a new optical material design principle that can be applied to next-generation displays, AR and VR optical devices, polarization sensors, and optical communications without the need to develop complex new materials.”
Jeong Yeon Han, the first author and a Ph.D. candidate, explained, “In conventional approaches, left-handed and right-handed structures tended to form together, canceling out chiral properties. In this study, however, we succeeded in aligning the structures in a single direction over a large area by designing an extremely small amount of additive to select only one rotation direction.”
This study was led by Ph.D. candidate Jeong Yeon Han as the first author, and the research results were published in the international journal Nature Communications on August 05.
Paper title: Microchiral pinwheel arrays based on achiral molecules,
DOI: 10.1038/s41467-026-76089-z
Authors: Jeong Yeon Han (first author), Won Kyung Park, Byeongil Noh, Fumito Araoka, Sungwook Jung, Byeong Hak Jhun, Youngmin You, Yoonsu Park, Kyung Jin Lee*, Jung-Moo Heo*, and Dong Ki Yoon* (*corresponding authors)
This research was supported by the Technology Innovation Program of the Ministry of Trade, Industry and Energy, the InnoCORE Program of the Ministry of Science and ICT, and the National Research Foundation of Korea.
2026.08.14 View 3516 -
KAIST research team develops a forgery prevention technique using salmon DNA
The authenticity scandal that plagued the artwork “Beautiful Woman” by Kyung-ja Chun for 30 years shows how concerns about replicas can become a burden to artists, as most of them are not experts in the field of anti-counterfeiting. To solve this problem, artist-friendly physical unclonable functions (PUFs) based on optical techniques instead of electronic ones, which can be applied immediately onto artwork through brushstrokes are needed.
On May 23, a KAIST research team led by Professor Dong Ki Yoon in the Department of Chemistry revealed the development of a proprietary technology for security and certification using random patterns that occur during the self-assembly of soft materials.
With the development of the Internet of Things in recent years, various electronic devices and services can now be connected to the internet and carry out new innovative functions. However, counterfeiting technologies that infringe on individuals’ privacy have also entered the marketplace.
The technique developed by the research team involves random and spontaneous patterns that naturally occur during the self-assembly of two different types of soft materials, which can be used in the same way as human fingerprints for non-replicable security. This is very significant in that even non-experts in the field of security can construct anti-counterfeiting systems through simple actions like drawing a picture.
The team developed two unique methods. The first method uses liquid crystals. When liquid crystals become trapped in patterned substrates, they induce the symmetrical destruction of the structure and create a maze-like topology (Figure 1). The research team defined the pathways open to the right as 0 (blue), and those open to the left as 1 (red), and confirmed that the structure could be converted into a digital code composed of 0’s and 1’s that can serve as a type of fingerprint through object recognition using machine learning. This groundbreaking technique can be utilized by non-experts, as it does not require complex semiconductor patterns that are required by existing technology, and can be observed through the level of resolution of a smartphone camera. In particular, this technique can reconstruct information more easily than conventional methods that use semiconductor chips.
< Figure 1. Security technology using the maze made up of magnetically-assembled structures formed on a substrate patterned with liquid crystal materials. >
The second method uses DNA extracted from salmon. The DNA can be dissolved in water and applied with a brush to induce bulking instability, which forms random patterns similar to a zebra’s stripes. Here, the patterns create ridge endings and bifurcation, which are characteristics in fingerprints, and these can also be digitalized into 0’s and 1’s through machine learning. The research team applied conventional fingerprint recognition technology to this patterning technique and demonstrated its use as an artificial fingerprint. This method can be easily carried out using a brush, and the solution can be mixed into various colors and used as a new security ink.
< Figure 2. Technology to produce security ink using DNA polymers extracted from salmon >
This new security technology developed by the research team uses only simple organic materials and requires basic manufacturing processes, making it possible to enhance security at a low cost. In addition, users can produce patterns in the shapes and sizes they want, and even if the patterns are made in the same way, their randomness makes each individual pattern different. This provides high levels of security and gives the technique enhanced marketability.
Professor Dong Ki Yoon said, “These studies have taken the randomness that naturally occurs during self-assembly to create non-replicable patterns that can act like human fingerprints.” He added, “These ideas will be the cornerstone of technology that applies the many randomities that exist in nature to security systems.”
The two studies were published in the journal Advanced Materials under the titles “1Planar Spin Glass with Topologically-Protected Mazes in the Liquid Crystal Targeting for Reconfigurable Micro Security Media” and “2Paintable Physical Unclonable Function Using DNA” on May 6 and 5, respectively.
Author Information: 1Geonhyeong Park, Yun-Seok Choi, S. Joon Kwon*, and Dong Ki Yoon*/ 2Soon Mo Park†, Geonhyeong Park†, Dong Ki Yoon*: †co-first authors, *corresponding author
This research was funded by the Center for Multiscale Chiral Architectures and supported by the Ministry of Science and ICT-Korea Research Foundation, BRIDGE Convergent Research and Development Program, the Running Together Project, and the Samsung Future Technology Development Program.
< Figure 1-1. A scene from the schematic animation of the process of Blues (0) and Reds (1) forming the PUF by exploring the maze. From "Planar Spin Glass with Topologically-Protected Mazes in the Liquid Crystal Targeting for Reconfigurable Micro Security Media" by Geonhyeong Park, Yun-Seok Choi, S. Joon Kwon, Dong Ki Yoon. https://doi.org/10.1002/adma.202303077 >
< Figure 2-1. A schematic diagram of the formation of digital fingerprints formed using the DNA ink. From "Paintable Physical Unclonable Function Using DNA" by Soon Mo Park, Geonhyeong Park, Dong Ki Yoon. https://doi.org/10.1002/adma.202302135 >
2023.06.08 View 18115 -
Success in Real-Time Observation of the Formation Process of Topological Solitons, a Core Technology for Next-Generation Information Transfer
< From left) Geonhyeong Park (Ph.D. Candidate), Yun-Seok Choi (Ph.D.), Professor Dong Ki Yoon, and Changjae Lee (Ph.D. Candidate) of the Department of Chemistry >
Professor Dong Ki Yoon's research team in the Department of Chemistry at KAIST announced on the 11th that they have succeeded in controlling the formation of topological solitons in a regular, large-area manner through the self-assembly of chiral liquid crystal materials and observing their formation process in real-time.
A soliton refers to a phenomenon where a specific wave persists without dissipating through interaction with its surroundings. In particular, even when a wave is transmitted over long distances, it retains its unique information until it reaches the desired destination. Therefore, in today's digital society, which is susceptible to hacking, solitons are highly anticipated to be the core of future communication due to their inherent high stability. Furthermore, topological solitons created using organic liquid crystal molecules are expected to be utilized as next-generation anti-counterfeiting devices and memory elements due to their unique spin directionality.
Professor Yoon's team specifically revealed the formation process of topological solitons in this study, which had not been observable in real-time under mild conditions such as room temperature until now. This was made possible by using self-assembling chiral liquid crystal materials in a confined space created by air pillars.
This research, in which Geonhyeong Park (Ph.D. Candidate, Department of Chemistry) and Dr. Ahram Suh participated as co-first authors, and Dr. Yun-Seok Choi and Changjae Lee (Ph.D. Candidate) from the same group also participated, was published online in the international journal 'Advanced Materials' on June 5th and is scheduled to be featured as the back cover of the July issue. (Paper title: "Fabrication of Arrays of Topological Solitons in Patterned Chiral Liquid Crystals for Real-Time Observation of Morphogenesis")
< Figure 1. Schematic diagram of the research>
< Figure 2. Real-time observation of topological soliton formation using liquid crystals>
In this study, Professor Yoon's team implemented topological soliton structures at approximately 30 degrees Celsius, similar to room temperature, using chiral (asymmetric) liquid crystal materials instead of the conventional liquid crystal molecules widely used as core materials in liquid crystal displays (LCDs). Generally, complex equipment is required to control the formation of topological solitons, and their formation time is very short, which has hindered research into their formation process until now.
To achieve regular formation and control of topological solitons formed by chiral liquid crystal molecules, Professor Yoon's team precisely controlled a combination of vertical alignment layers, which can orient molecules vertically, and air pillars. Specifically, they prepared concave patterns based on circular silicon material, several micrometers (one-millionth of a meter) in size, coated with a vertical alignment layer, and a glass substrate. By adjusting the gap to several micrometers and injecting chiral liquid crystal material, air pillars were spontaneously formed on the concave patterns. Subsequently, the liquid crystal molecules were vertically aligned on all substrates, inevitably causing regular distortions between the substrates, and between the substrate and the air pillars, thus developing a system where chiral molecular structures, i.e., topological solitons, could be formed.
The key to the formation and control of topological solitons lies in controlling the thermal phase transition to occur regularly as desired when cooling from the isotropic phase temperature (approximately 40 degrees Celsius) to the liquid crystal phase temperature (approximately 30 degrees Celsius), where the liquid crystal material near the air pillars is cooler than the liquid crystal material between the glass substrate and the silicon patterned parts. This is consistent with the everyday wisdom of eating steamed eggs from a 'Ttukbaegi' (earthen pot) by starting from the relatively cooler part exposed to the air (near the air pillars) rather than the hot pot part (silicon or glass substrate part).
Through real-time analysis, the research team elucidated that topological defects are formed by the naturally formed air pillars through controlled thermal phase transition, and topological solitons are formed only at the locations of these defects. This analysis technique has the potential for application in various fields, including the interpretation of topological soliton formation found in other physical phenomena such as skyrmion particles in electromagnetism.
< Figure 3. Snapshots during the formation process of regularly arranged topological solitons>
Professor Dong Ki Yoon stated, "General topological solitons are known to be highly stable, capable only of generation or annihilation. Through the results of this research, we can understand the formation process of solitons in more detail, and they can be used as spintronics application technology, considered a next-generation semiconductor device for storing and recording information."
This research was conducted in collaboration with Professor Ivan Smalyukh's laboratory at the University of Colorado, Department of Physics, and was supported by the Multiscale Chiral Structures Research Center and strategic projects of the National Research Foundation of Korea under the Ministry of Science and ICT.
2022.07.11 View 6721