Kyung-Il Joo

We propose an active‐switching light‐field (LF) camera system that significantly extends the measurable depth range over conventional passive‐optics‐based LF systems by integrating a stacked geometric phase lens (GPL) module in a compact design. During elemental image acquisition and LF rendering, chromatic aberration in the focus‐tunable GPL is compensated by adjusting the reconstruction depth and magnification for each color channel. Additionally, the optimal GPL operation sets are selected based on color‐dependent depth‐of‐focus conditions. These optimizations enable the proposed GPL‐based LF system to achieve full‐color, depth‐enhanced LF imaging while mitigating the typical trade‐off between spatial resolution and depth of field limitations.

We proposed a DHM system with improved spatial resolution compared with that of the polarized camera-based DHM system by employing a liquid crystal phase modulator (LCPM). The LCPM-based holographic interferometry optical system can reliably construct a four-step phase shifting scheme by changing the applied voltage, thus eliminating the need for mechanical moving parts. The spatial resolution characteristics of the proposed DHM system were analyzed using the 1951 USAF resolution target. These characteristics showed a fourfold improvement over the polarized camera-based DHM system. Additionally, the 3D information capturing capability of the proposed DHM system was experimentally confirmed using a via-hole array sample produced through the semiconductor fabrication process.

We developed a light-field (LF) camera which can switch between 2D and 3D capturing mode. LF camera was developed with switchable micro-lens array (MLA) according to the polarization state of incident light.

In this study, a printing‐based scalable method is proposed for the higher density of a liquid crystal (LC) nanodroplet structure suitable for the optically isotropic LC mode where the LC nanodomains are accurately templated by a nanoporous breath figure (BF) membrane. The highly porous BF polymeric template structure is reliably obtained by utilizing self‐structured packing effects of the silica nanospheres achieved by doctor blade coating. A nanocomposite film with densely packed silica nanospheres encapsulated by the UV‐crosslinked polymer matrix is made by controlling the blade coating velocity and blade gap conditions. This provides a higher LC fill‐factor condition of the optically isotropic nanodroplet LC (OI‐NDLC) mode with filling the LCs into the nanopores obtained after selective silica etching. The OI‐NDLC structure templated by the nanoporous BF membrane made with the silica nanospheres of 300 nm can effectively resolve the scattering‐induced optical loss and depolarization issues observable in the OI‐NDLC mode prepared by conventional phase separation approaches due to the sufficiently reduced LC droplet size. The structure exhibits a much‐improved light leakage level in the field‐off optically isotropic state, a higher transmittance level as the field‐induced Kerr operation, and resultant improved contrast ratio properties.

We improved the three-dimensional (3D) crosstalk level of multi-view 3D displays using a lens array with small f-number, thereby facilitating a wide 3D viewing window. In particular, we designed a polarization-dependent-switching liquid crystal (LC)-based gradient refractive index (GRIN) lens array that could be switched between 2D and 3D viewing modes. For the GRIN lens with a small f-number (1.08), we studied the effect of the interfacial curvature between the plano-concave isotropic polymer layer and the plano-convex birefringent LC layer on the aberration properties. We examined the conventional spherical, quadratic polynomial aspherical, and a high-order (fourth-order) polynomial aspherical curvature. For the high-order polynomial aspherical curvature, the achievable transverse spherical aberration (TSA = 10.2 µm) was considerably lower than that with the spherical (TSA = 100.3 µm) and quadratic polynomial aspherical (TSA = 30.4 µm) curvatures. Consequently, the angular luminance distributions for each view were sharper for the high-order polynomial interfacial curvature. We designed multi-view (43-view) 3D displays using the arrays of switchable LC lenses with different curvatures, and the average adjacent crosstalk levels within the entire viewing window (50°) were 68.5%, 73.3%, and 60.0% for the spherical, quadratic polynomial aspherical, and high-order polynomial aspherical curvatures, respectively.

We propose a time-sequential switching light-field (LF) camera for alternative image capture of high-resolution two-dimensional (2D) images and three-dimensional (3D) LF elemental images as additional functionalities. For image data acquisitions of both the 2D and 3D LF imaging of moving objects at a video-frame rate (or even higher frame rate up to approximately 1000 fps), a polarization-dependent-switching micro-lens array (PMLA) is implemented in the LF camera system instead of a conventional passive-type MLA. By controlling the incident polarization conditions using an electrically fast-switching liquid crystal layer, the imaging mode can be time-sequentially switched quite rapidly (switching times of approximately 220 μs and 290 μs for the mode conversions from the 3D LF to the 2D mode, and the reversal mode change, respectively). Using the elemental image sets sampled from the alternating time-sequential imaging results, either directional-view images or depth-refocused images can be reconstructed and provided at a moving picture frame-rate. The depth-refocused images are possible for a wide depth range from 25 cm to 350 cm. Directional views of 22 x 22 and 9 x 9 in portions can be reconstructed for the single shot image capture and the time-sequential video-rate image capture, respectively.

An augmented-reality (AR) device which presents virtual volumetric images to switchable integrated spaces is proposed and demonstrated. A bi-focal geometric phase (GP) lens can project the integrated volumetric images to switchable integrated spaces by switching the polarization of them. For that purpose, a combination of GP lens and an active polarization switching device (APSD) has been adopted. A demonstration of an AR display with switchable integrations is also provided to verify the proposed concept.