Dukho Lee

Holographic display for see-through augmented reality using mirror-lens holographic optical element

A holographic display system for realizing a three-dimensional optical see-through augmented reality (AR) is proposed. A multi-functional holographic optical element (HOE), which simultaneously performs the optical functions of a mirror and a lens, is adopted in the system. In the proposed method, a mirror that is used to guide the light source into a reflection type spatial light modulator (SLM) and a lens that functions as Fourier transforming optics are recorded on a single holographic recording material by utilizing an angular multiplexing technique of volume hologram. The HOE is transparent and performs the optical functions just for Bragg matched condition. Therefore, the real-world scenes that are usually distorted by a Fourier lens or an SLM in the conventional holographic display can be observed without visual disturbance by using the proposed mirror-lens HOE (MLHOE). Furthermore, to achieve an optimized optical recording condition of the MLHOE, the optical characteristics of the holographic material are measured. The proposed holographic AR display system is verified experimentally.

Study of spin-ordering and spin-reorientation transitions in hexagonal manganites through Raman spectroscopy.

Spin-wave (magnon) scattering, when clearly observed by Raman spectroscopy, can be simple and powerful for studying magnetic phase transitions. In this paper, we present how to observe magnon scattering clearly by Raman spectroscopy, then apply the Raman method to study spin-ordering and spin-reorientation transitions of hexagonal manganite single crystal and thin films and compare directly with the results of magnetization measurements. Our results show that by choosing strong resonance condition and appropriate polarization configuration, magnon scattering can be clearly observed, and the temperature dependence of magnon scattering can be simple and powerful quantity for investigating spin-ordering as well as spin-reorientation transitions. Especially, the Raman method would be very helpful for investigating the weak spin-reorientation transitions by selectively probing the magnons in the Mn3+ sublattices, while leaving out the strong effects of paramagnetic moments of the rare earth ions.

Space bandwidth product enhancement of holographic display using high-order diffraction guided by holographic optical element

A space bandwidth product (SBP) enhancement method for holographic display using high-order diffraction of a spatial light modulator (SLM) is proposed. Among numerous high order diffraction terms, the plus-minus first and the zeroth are adopted and guided by holographic optical elements (HOEs) to an identical direction with the same intensity. By using a set of electro-shutters synchronized with corresponding order component, the system acts as if three SLMs are tiled in the horizontal direction. To confirm the feasibility of using HOE as the guiding optics for the system, several optical characteristics of the recording material are measured before using them. Furthermore, a computer generated hologram algorithm is proposed for compensating the wavefront distortion caused by use of the HOE. The demonstrated system achieves a three-fold increase in SBP of a single SLM. The results are verified experimentally.

Layered Display with Accommodation Cue Using Scattering Polarizers

A projection-type layered display inducing the accommodation cue is proposed. To support the accommodation cue, the concept of multiplane displays, especially the principle of additive type compressive light field display, is adopted. To achieve the additive type light field display, two layered scattering polarizers and a single projector which is synchronized with polarization rotator are used. Scattering polarizer diffuses light rays with specific linear polarization state while transmits the other rays with the orthogonal polarization state. Utilizing this characteristic, two layer images can be displayed at different depths presenting multiplane display. By adopting an additional computational process, several viewpoints can be provided to a single eye and support the accommodation cue. We expect that the proposed method can be adopted to virtual reality system. Detailed principle of the proposed system and its feasibility are explained with simulations and experiments.

Fourier holographic display for augmented reality using holographic optical element

A method for realizing a three-dimensional see-through augmented reality in Fourier holographic display is proposed. A holographic optical element (HOE) with the function of Fourier lens is adopted in the system. The Fourier hologram configuration causes the real scene located behind the lens to be distorted. In the proposed method, since the HOE is transparent and it functions as the lens just for Bragg matched condition, there is not any distortion when people observe the real scene through the lens HOE (LHOE). Furthermore, two optical characteristics of the recording material are measured for confirming the feasibility of using LHOE in the proposed see-through augmented reality holographic display. The results are verified experimentally.

Simplified Multi-wavelength Laser Speckle Contrast Imaging System by Using Single Holographic Optical Element

A simplified multi-wavelength laser speckle contrast imaging system by using a single holographic optical element which is recorded by wavelength precompensation method is proposed. The feasibility of proposed method is verified by experimental results.

Comparison between LED and LD as a light source for near-eye holographic display

In this paper, we analyze the image quality reconstructed by holographic display depending on spatial coherency and temporal coherency of the light source in holographic display system. The simulation was conducted by changing both spatial coherency and temporal coherency independently using proper modeling of coherency. A holographic display setup was composed to verify simulation results. LED and LD were respectively used as a light source for holographic display, and the quality of reconstructed images reproduced by using LED or LD was compared. The scheme of near-eye holographic display adopting LED as a light source which generates low speckle noise but narrow depth range was proposed. The proposed scheme of near-eye holographic display system was verified experimentally.

Shape scanning displays: tomographic decomposition of 3D scenes

Although there have been a desire to implement ideal three-dimensional (3D) displays, it is still challenging to satisfy commercial demands in resolution, depth of field, form factor, eye-box, field of view, and frame rate. Here, we propose shape scanning displays that may have extremely large depth of field (10cm-infinity) without loss of frame rate or resolution, and enough eye-box (7.5mm) with moderate field of view (30°). Furthermore, our prototype provides quasi-continuous focus cues as well as motion parallax by reconstruction of 120 tomographic layers. Shape scanning displays consist of a tunable lens, a display panel, and a spatially adjustable backlight. The synchronization of the tunable lens and spatially adjustable backlight could provide additional dimension of depth information. In summary, we introduce a novel 3D display technology called shape scanning displays that present superior performance in resolution, depth of field, and focus cue reproduction. This approach has a lot of potential to be applied for various field in 3D displays including head-up displays, tabletop displays, as well as head-mounted displays. It could be efficient solution for vergence-accommodation conflict as providing accurate focus cues.

Generation of wide viewing angle depth map hologram and its realization by complex wavefront printing

We proposed a method to generate wide viewing angle and high angular resolution hologram based on depth map hologram generation method. The generated hologram is realized by a complex wavefront holographic printer.

Viewing zone enlargement of holographic display using high order terms guided by holographic optical element

​A method for enlarging viewing zone of holographic display by time-multiplexing of high order terms of a spatial light modulator (SLM), which is previously wasted, is proposed.