Team led by Professor Lee Seung-woo, develops the core optical elements of an AR Display
Paper published in Advanced Functional Materials.
The team developed a technique to produce faster than had been ever achieved before a ‘multidirectional diffraction grating’, which also featured the highest degree of integration.

The team led by Professor Lee Seung-woo (KU-KIST Graduate School of Converging Science and Technology / Department of Integrative Energy Engineering, College of Engineering) developed a method of manufacturing a 'multidirectional diffraction grating', the core optical element of AR displays, in record-breaking time and featuring the highest integration available.

The results of this study were published in Advanced Functional Materials (Impact Factor: 16.836), a world-renowned journal at 6 pm on April 29, Korea local time.
- Author information: Lim Yong-jun (first author, Integrated Master’s and Doctoral program of Korea University), Kang Byung-soo (co-author, Korea University), Lee Seung-woo (corresponding author, Korea University)
- Paper title: Photo-Transformable Gratings for Augmented Reality
- Publication: Advanced Functional Materials (published online on April 29, 2021, https://onlinelibrary.wiley.com/doi/full/10.1002/adfm.202100839)
 (2021년 04월 29일 online published, https://onlinelibrary.wiley.com/doi/full/10.1002/adfm.202100839)

Diffraction gratings have been widely used for 3D hologram reproduction. The concept of diffraction, which was first proposed by C. Huygens in the 1690s and quantitatively understood in Fourier Optics in the 1900s, allows the recording of not only the intensity but also the phase information of light. Therefore, it has been indispensable for the recording and reproduction of 3D stereoscopic images.

After the first recorded diffraction grating in the 1890s, hologram reproduction was generalized by D. Gabor in the 1940s, and recently, with the rise of the importance of Augmented Reality (AR) and Virtual Reality (VR) technologies, diffraction gratings have been attracting attention once again. In particular, they are a key optical element in commercialized AR displays, such as Microsoft's HoloLens. In order for AR Display users to perceive a stereoscopic image with a wide viewing angle, the diffraction grating must be pixelated to have multidirectionality and be integrated at high density. For this purpose, *optical (EUV) lithography, which is an established semiconductor process, has been widely used, but this manufacturing process takes too long, the yield is too low, and the degree of integration has not reached 100%. These drawbacks have resulted in the excessively high production costs of AR displays, such as the HoloLens, and consumer-unfriendly high sales prices.
* Optical (EUV) Lithography: This refers to the semiconductor manufacturing process that has recently become an issue due to Japanese semiconductor export regulations. When a photoresist coat is formed and is then irradiated by patterned light, only the part that received or, alternatively, did not receive the light is selectively etched, allowing the semiconductor material to be selectively etched using this as a masking technique.

Professor Lee Seung-woo's team developed a new diffraction grating capable of shape transformation and proposed a new method that is up to 108 times faster than the existing semiconductor process and capable of 100% integration. The shape of the diffraction grating could be freely changed with only hologram printing and without requiring any chemical etching process, the core process of lithography. The process succeeded in integrating the multidirectional grating pixels at 100% density, and the process time was reduced to 20 to 30 minutes rather than the tens of hours required by conventional optical lithography. In addition, varied holograms were able to be successfully reproduced with respect to direction (chameleon holograms).

This technology can lead to the popularization of optical AR technology by significantly increasing the productivity of AR displays such as HoloLenses, and it is expected to contribute to user convenience by greatly reducing the volumes of AR displays. Based on this technology, the team plans to conduct research into integrating and miniaturizing wearable optical AR devices.