SNU researchers develop holographic AR display with enhanced realism via occlusion effect

Seoul National University College of Engineering announced that a research team led by Professor Jae-Hyeung Park from the Department of Electrical and Computer Engineering has developed a holographic augmented reality (AR) display that significantly enhances realism through the incorporation of optical occlusion effects.

By combining a holographic display with an occlusion optics system, the researchers succeeded in improving the visual realism of AR environments. Furthermore, they demonstrated opaque 3D virtual images and optically generated virtual shadows, reproducing the visual effect of virtual objects interacting naturally with real-world environments.

Recognizing that visual information in AR environments tends to concentrate around virtual objects rather than being distributed across the entire space, the team also introduced an AI-based hologram generation algorithm optimized for sparse holographic imagery*.

* Sparse holographic image: A hologram in which visual information is concentrated only in certain regions of the spatial field rather than uniformly distributed.

The study, titled “Enhancing Realism in Holographic Augmented Reality Displays Through Occlusion Handling,” was published on October 7 as an inside cover article in Laser & Photonics Reviews (Impact Factor: 10.0), a leading international journal in optics published by Wiley-VCH (Germany).

AR glasses, often regarded as the next-generation smart device following smartphones, have advanced rapidly due to major global investments. However, most commercial or prototype AR glasses still lack the occlusion effect, in which virtual imagery can block or obscure real-world objects. Without this effect—a key visual cue for human depth perception—virtual images appear semi-transparent and overlaid on real objects, significantly reducing the realism and immersion of AR experiences.

Additionally, current AR glasses typically reconstruct 3D imagery using only binocular disparity (the difference between the two eyes’ views) while keeping monocular depth cues fixed, leading to the vergence–accommodation conflict (VAC)—a mismatch between the eyes’ focus and convergence cues. This mismatch often causes eye strain and visual discomfort, hindering the widespread adoption of near-eye displays such as AR headsets.

To address these issues, prior research has attempted to incorporate occlusion optics that selectively block real-world light in front of the display to create opaque virtual images, or to reproduce monocular depth using holography, light-field, or varifocal technologies. However, no previous study had successfully combined both occlusion and true 3D holographic rendering, leaving room for more advanced solutions to achieve realistic AR visuals.

Professor Jae-Hyeung Park's research team has developed a holographic AR display that achieves the most realistic AR environment by combining a holographic AR display capable of reproducing ideal three-dimensional images with an optical occlusion system that optically masks the actual background.

The researchers first observed that the Fourier filter structure in a 4f optical system—commonly used to remove noise in holographic displays—shares the same architecture as an occlusion optics system. Leveraging this insight, they implemented a single Digital Micromirror Device (DMD) within a single 4f optical system to function both as a Fourier filter and an occlusion mask, using time multiplexing to perform occlusion control and noise filtering simultaneously.

* Fourier filter structure: An optical setup that analyzes image frequency components to selectively remove or correct noise.

* DMD (Digital Micromirror Device): A reflective optical element composed of thousands of tiny mirrors that rapidly adjust brightness and pattern of holographic images.

Furthermore, unlike conventional static Fourier filters, the team incorporated the dynamic modulation capability of the DMD into their AI-based hologram generation algorithm. This drastically reduced the optimizer’s search space, improving the Peak Signal-to-Noise Ratio (PSNR) of sparse holographic images by an average of 11 decibels (dB) compared to existing methods. In addition, by employing time multiplexing, they successfully suppressed speckle noise*—a granular interference pattern that degrades holographic image quality—and doubled the field of view (FOV) of the holographic display.

* Speckle noise: A granular pattern of noise caused by optical interference in coherent light systems.

* PSNR: A standard metric for measuring image quality; higher PSNR indicates better reconstruction fidelity.

Based on the proposed system, the team fabricated a benchtop prototype to experimentally reproduce opaque 3D AR images in which virtual objects visibly block real backgrounds. They further demonstrated AR scenes where virtual objects cast shadows onto real environments through optical occlusion, achieving unprecedented realism. Experimental results showed significant improvements in contrast and clarity compared to conventional AR setups without occlusion, successfully realizing the world’s first high-contrast, interference-free 3D AR scenes.

* Benchtop prototype: A small-scale experimental device built to verify the performance and working principles of a system prior to commercialization.

This research marks an important milestone by realizing a truly interactive AR system in which virtual imagery optically interacts with real-world light. The proposed technology enables natural AR environments where virtual objects can selectively block or cast shadows on real scenes, representing a key advancement toward next-generation immersive display technologies.

Moreover, the study offers a new research direction by integrating dynamic Fourier filtering directly into the hologram generation algorithm, shifting away from purely software-based optimization. This hardware–algorithm co-design approach demonstrates how physical devices can enhance computational performance, paving the way for advanced co-optimized architectures in future immersive display systems.

Professor Jae-Hyeung Park, who led the research, stated, “Our study demonstrates a new paradigm for augmented reality—one where virtual imagery can physically interact with light from the real world. We will continue to pursue research that merges optics and artificial intelligence to create next-generation display technologies that deliver more natural and immersive visual experiences.”

The first author, Woongseob Han, is currently pursuing his Ph.D. in the Department of Electrical and Computer Engineering at Seoul National University, focusing on AR/VR near-eye displays and next-generation 3D display technologies. After graduation, he plans to work as an optical design engineer specializing in immersive display systems at research institutes or global technology companies.

□ Introduction to the SNU College of Engineering

Seoul National University (SNU) founded in 1946 is the first national university in South Korea. The College of Engineering at SNU has worked tirelessly to achieve its goal of ‘fostering leaders for global industry and society.’ In 12 departments, 323 internationally recognized full-time professors lead the development of cutting-edge technology in South Korea and serving as a driving force for international development.