Speckle reduction for single sideband-encoded computer-generated holograms by using an optimized carrier wave.

Computer-generated hologram (CGH) is an evolving field that facilitates three-dimensional displays, with speckle noise reduction being a pivotal challenge. In hologram synthesis, complex data with random phase distributions are typically employed as carrier waves for wide viewing angles and a shallow depth of focus (DOF). However, these carrier waves are a source of speckle noise, which can significantly degrade image quality. In this paper, we propose a novel technique for speckle reduction for single sideband (SSB)-encoded holograms, applicable to any arbitrary 3D object. The proposed method focuses on optimizing the random carrier wave used in the hologram synthesis to achieve a uniform amplitude distribution at the object's location. This optimization results in a carrier wave that consistently exhibits uniform amplitude at specific depth planes, leading to a significant reduction of the speckle occurring from the carrier wave. The proposed method has been validated through simulations and optical experiments.

Effect of shrinkage in photopolymer film on the information transmitted through the holographic waveguide for near eye displays.

Due to shrinkage in photopolymer materials, the angle of the reconstruction beam in holographic optical elements (HOEs) does not match with the Bragg condition, resulting in a decreased amount of light in the desired direction or loss of transmitted information to rematch the Bragg condition. Thus, to ensure final display features it is imperative to precompensate the shrinkage effect. We derived simplified expressions for precompensation in recording geometries of required HOEs in holographic waveguide-based Maxwellian near eye displays. An acceptable range of detuning from the Bragg angle is also analyzed. The experimentally measured 4.95% shrinkage in photopolymer film for 0° and 45° recording angles of beams was precompensated using -0.86∘ and 43.7° recording angles. Theoretical results are validated through simulation and experiments.

Sustainable Strategies for Synthesizing Lignin-Incorporated Bio-Based Waterborne Polyurethane with Tunable Characteristics.

In this study, we introduce a novel approach for synthesizing lignin-incorporated castor-oil-based cationic waterborne polyurethane (CWPU-LX), diverging significantly from conventional waterborne polyurethane dispersion synthesis methods. Our innovative method efficiently reduces the required solvent quantity for CWPU-LX synthesis to approximately 50% of that employed in traditional WBPU experimental procedures. By incorporating lignin into the polyurethane matrix using this efficient and reduced-solvent method, CWPU-LX demonstrates enhanced properties, rendering it a promising material for diverse applications. Dynamic interactions between lignin and polyurethane molecules contribute to improved mechanical properties, enhanced thermal stability, and increased solvent resistance. Dynamic interactions between lignin and polyurethane molecules contribute to improved tensile strength, up to 250% compared to CWPU samples. Furthermore, the inclusion of lignin enhanced thermal stability, showcasing a 4.6% increase in thermal decomposition temperature compared to conventional samples and increased solvent resistance to ethanol. Moreover, CWPU-LX exhibits desirable characteristics such as protection against ultraviolet light and antibacterial properties. These unique properties can be attributed to the presence of the polyphenolic group and the three-dimensional structure of lignin, further highlighting the versatility and potential of this material in various application domains. The integration of lignin, a renewable and abundant resource, into CWPU-LX exemplifies the commitment to environmentally conscious practices and underscores the significance of greener materials in achieving a more sustainable future.

Digital Holography and 3D Imaging: introduction to the joint feature issue in Applied Optics and Journal of the Optical Society of America A.

This feature issue is a continuation of a tradition to follow the conclusion of the Optica Topical Meeting on Digital Holography and 3D Imaging (DH+3D). It addresses current research topics in digital holography and 3D imaging that are also in line with the topics of Applied Optics and Journal of the Optical Society of America A.

Digital Holography and 3D Imaging: introduction to the joint feature issue in Applied Optics and Journal of the Optical Society of America A.

This feature issue is a continuation of a tradition to follow the conclusion of the Optica Topical Meeting on Digital Holography and 3D Imaging (DH+3D). It addresses current research topics in digital holography and 3D imaging that are also in line with the topics of Applied Optics and Journal of the Optical Society of America A.

Synthesis of Novel Shape Memory Thermoplastic Polyurethanes (SMTPUs) from Bio-Based Materials for Application in 3D/4D Printing Filaments.

Bio-based thermoplastic polyurethanes have attracted increasing attention as advanced shape memory materials. Using the prepolymer method, novel fast-responding shape memory thermoplastic polyurethanes (SMTPUs) were prepared from 100% bio-based polyester polyol, poly-propylene succinate derived from corn oil, diphenyl methane diisocyanate, and bio-based 1,3-propanediol as a chain extender. The morphologies of the SMTPUs were investigated by Fourier transform infrared spectroscopy, atomic force microscopy, and X-ray diffraction, which revealed the interdomain spacing between the hard and soft phases, the degree of phase separation, and the intermixing level between the hard and soft phases. The thermal and mechanical properties of the SMTPUs were also investigated, wherein a high hard segment content imparted unique properties that rendered the SMTPUs suitable for shape memory applications at varying temperatures. More specifically, the SMTPUs exhibited a high level of elastic elongation and good mechanical strength. Following compositional optimization, a tensile strength of 24-27 MPa was achieved, in addition to an elongation at break of 358-552% and a hardness of 84-92 Shore A. Moreover, the bio-based SMTPU exhibited a shape recovery of 100%, thereby indicating its potential for use as an advanced temperature-dependent shape memory material with an excellent shape recoverability.

Super multi-view near-eye display with a lightguide combiner.

We propose a lightguide-type super multi-view near-eye display that uses a digital micromirror device and a LED array. The proposed method presents three-dimensional images with a natural monocular depth cue using a compact combiner optics which consists of a thin lightguide and holographic optical elements (HOEs). Feasibility of the proposed method is verified by optical experiments which demonstrate monocular three-dimensional image presentation over a wide depth range. We also analyze the degradation of the image quality stemming from the spectral spread of the HOEs and show its reduction by a pre-compensation exploiting an adaptive moment estimation (Adam) optimizer.

One-Shot Synthesis of Thermoplastic Polyurethane Based on Bio-Polyol (Polytrimethylene Ether Glycol) and Characterization of Micro-Phase Separation.

In this study, a series of bio-based thermoplastic polyurethane (TPU) was synthesized via the solvent-free one-shot method using 100% bio-based polyether polyol, prepared from fermented corn, and 1,4-butanediol (BDO) as a chain extender. The average molecular weight, degree of phase separation, thermal and mechanical properties of the TPU-based aromatic (4,4-methylene diphenyl diisocyanate: MDI), and aliphatic (bis(4-isocyanatocyclohexyl) methane: H12MDI) isocyanates were investigated by gel permeation chromatography, Fourier transform infrared spectroscopy, atomic force microscopy, X-ray Diffraction, differential scanning calorimetry, dynamic mechanical thermal analysis, and thermogravimetric analysis. Four types of micro-phase separation forms of a hard segment (HS) and soft segment (SS) were suggested according to the [NCO]/[OH] molar ratio and isocyanate type. The results showed (a) phase-mixed disassociated structure between HS and SS, (b) hydrogen-bonded structure of phase-separated between HS and SS forming one-sided hard domains, (c) hydrogen-bonded structure of phase-mixed between HS, and SS and (d) hydrogen-bonded structure of phase-separated between HS and SS forming dispersed hard domains. These phase micro-structure models could be matched with each bio-based TPU sample. Accordingly, H-BDO-2.0, M-BDO-2.0, H-BDO-2.5, and M-BDO-3.0 could be related to the (a)-form, (b)-form, (c)-form, and (d)-form, respectively.

Learning-based complex field recovery from digital hologram with various depth objects.

In this paper, we investigate a learning-based complex field recovery technique of an object from its digital hologram. Most of the previous learning-based approaches first propagate the captured hologram to the object plane and then suppress the DC and conjugate noise in the reconstruction. To the contrary, the proposed technique utilizes a deep learning network to extract the object complex field in the hologram plane directly, making it robust to the object depth variations and well suited for three-dimensional objects. Unlike the previous approaches which concentrate on transparent biological samples having near-uniform amplitude, the proposed technique is applied to more general objects which have large amplitude variations. The proposed technique is verified by numerical simulations and optical experiments, demonstrating its feasibility.

Non-hogel-based computer generated hologram with occlusion processing between the foreground light field and background hologram.

A novel technique is proposed to process the occlusion of a background hologram when synthesizing a front scene hologram from its light field. Unlike conventional techniques which process the occlusion in the light field domain after converting the background hologram to its light field, the proposed technique directly processes the occlusion between different domains, i.e., the background hologram and foreground light field. The key idea is to consider the background hologram as a carrier wave illuminating the front scene when synthesizing the front scene hologram from its light field. The proposed technique is not only computationally efficient as it does not require conversion between the light field and hologram domains but also accurate because all angular information of the background hologram and foreground light field is naturally considered in the occlusion processing. The proposed technique was verified by numerical synthesis and reconstruction.

Digital Holography and 3D Imaging: introduction to the joint feature issue in Applied Optics and Journal of the Optical Society of America A.

This feature issue is a continuation of a tradition, since 2007, to follow the conclusion of the OSA Topical Meeting on Digital Holography and 3D Imaging (DH+3D). It addresses current research topics in digital holography (DH) and 3D imaging that are also in line with the topics of Applied Optics (AO) and the Journal of the Optical Society of America A (JOSA A).

Digital Holography and 3D Imaging: introduction to the joint feature issue in Applied Optics and Journal of the Optical Society of America A.

This feature issue is a continuation of a tradition, since 2007, to follow the conclusion of the OSA Topical Meeting on Digital Holography and 3D Imaging (DH+3D). It addresses current research topics in digital holography (DH) and 3D imaging that are also in line with the topics of Applied Optics (AO) and the Journal of the Optical Society of America A (JOSA A).

Waveguide-type Maxwellian near-eye display using a pin-mirror holographic optical element array.

We propose a novel, to the best of our knowledge, waveguide-type optical see-through Maxwellian near-eye display for augmented reality. A pin-mirror holographic optical element (HOE) array enables the Maxwellian view and eye-box replication. Virtual images with deep depth of field are presented by each pin-mirror HOE, alleviating the discrepancy between vergence and accommodation distance. The compact form factor is achieved by the thin waveguide and HOE couplers.

Waveguide-type see-through dual focus near-eye display with a polarization grating.

Waveguide-type near-eye displays have useful properties such as compact form factor, lightweight and see-through capability. Conventional systems, however, support only a single image plane fixed at a certain distance, which may induce eye fatigue due to the vergence-accommodation conflict. In this paper, we propose a waveguide-type near-eye display with two image planes using a polarization grating. Two images with orthogonal polarizations propagate within the waveguide with different total internal reflection angles and form virtual images at different distances. The use of the polarization grating and two pairs of holographic optical elements enables dual image plane formation by a single waveguide with high transparency for the real scene. Optical experiments confirm the principle of the proposed optical system.

Compact in-line floating display system using a dihedral corner reflector array.

We propose a compact type floating display system using a dihedral corner reflector array. Conventional floating displays using the dihedral corner reflector array usually have a folded configuration which makes the system bulky. The proposed technique achieves the compact in-line configuration using a pair of decentered lenses. The decentered lenses make the effective incident angle to the dihedral corner reflector array be tilted while maintaining the display panel and the dihedral corner reflector array in parallel. The ghost images are also refracted largely by the decentered lenses, being separated from the desired floating images. The proposed technique is verified by optical experiments.

Quality enhancement of binary-encoded amplitude holograms by using error diffusion.

A digital micro-mirror device is one of the most frequently used spatial light modulators for holographic three-dimensional displays due to its fast refresh rate. The modulation by the digital micro-mirror device is, however, limited to the binary amplitude modulation, and it degrades the reconstruction image quality. In this paper, we propose a novel binary hologram encoding technique which applies the error diffusion algorithm considering the carrier wave of the hologram. The error diffusion weights designed for the hologram carrier wave suppress the binarization noise around the carrier wave where the most signal energy is concentrated, which enhances the reconstruction quality. The combination with the time-multiplexing enables speckless enhanced-quality three-dimensional reconstruction with shallow depth of focus. The proposed technique is verified by simulations and optical experiments.

Gigapixel and 1440-perspective extended-angle display by megapixel MEMS-SLM.

Orders-of-magnitude increases are desired in the pixel count and density of spatial light modulators (SLMs) for next-gen displays. We present in-plane and simultaneous angular-spatial light modulation by a micro electro mechanical system (MEMS)-based SLM, a digital micromirror device (DMD), to generate gigapixel output by time and angular multiplexing. Pulsed illumination synchronized to the micromirror actuation achieves pixel-implemented and diffraction-based angular modulation, and source multiplexing increases angular selectivity. We demonstrate 1440-perspective image output across a 43.9∘×1.8∘ FOV, 8-bit multi-perspective videos at 30 FPS, and multi-focal-plane image generation. We discuss scalability to terapixels and implications for near-to-eye displays.

Styrene-Based Elastomer Composites with Functionalized Graphene Oxide and Silica Nanofiber Fillers: Mechanical and Thermal Conductivity Properties.

The mechanical and thermal conductivity properties of two composite elastomers were studied. Styrene-butadiene rubber (SBR) filled with functionalized graphene oxide (GO) and silica nanofibers, and styrene-butadiene-styrene (SBS) block copolymers filled with graphene oxide. For the SBR composites, GO fillers with two different surface functionalities were synthesized (cysteamine and dodecylamine) and dispersed in the SBR using mechanical and liquid mixing techniques. The hydrophilic cysteamine-based GO fillers were dispersed in the SBR by mechanical mixing, whereas the hydrophobic dodecylamine-based GO fillers were dispersed in the SBR by liquid mixing. Silica nanofibers (SnFs) were fabricated by electrospinning a sol-gel precursor solution. The surface chemistry of the functionalized fillers was studied in detail. The properties of the composites and the synergistic improvements between the GO and SnFs are presented. For the SBS composites, GO fillers were dispersed in the SBS elastomer at several weight percent loadings using liquid mixing. Characterization of the filler material and the composite elastomers was performed using x-ray photoelectron spectroscopy, x-ray diffraction, transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, dynamic mechanical analysis, tensile testing, nanoindentation, thermal conductivity and abrasion testing.

Single-chip holographic beam steering for lidar by a digital micromirror device with angular and spatial hybrid multiplexing.

A digital micromirror device (DMD) based holographic beam steering technique is reported that multiplexes fine-steering binary amplitude gratings with a coarse-steering programmable blazed grating. The angular spatial light modulation (ASLM) technique encodes the spatial pattern of the binary amplitude grating at the same plane as the angular modulation set by a phase map of the DMD-based beam steering technique. The beam steering technique is demonstrated at 532 nm and implemented into a 905 nm lidar system. The results of the lidar system tests are presented, achieving a 44° field-of-view, 0.9°×0.4° (H×V) angular resolution, 1 m max distance, 1.5 kHz sampling, and 7.8 FPS video. Scalability techniques are proposed, including max distance increases to over 100 m.

Occlusion-capable optical-see-through near-eye display using a single digital micromirror device.

Occlusion of a real scene by displayed virtual images mitigates incorrect depth cues and enhances image visibility in augmented reality applications. In this Letter, we propose a novel optical scheme for the occlusion-capable optical-see-through near-eye display. The proposed scheme uses only a single spatial light modulator, as the real-scene mask and virtual image display simultaneously. A polarization-based double-pass configuration is also combined, enabling a compact implementation. The proposed scheme is verified by optical experiments which demonstrate a 60 Hz red-green-blue video display with a 4-bit depth for each color channel and per-pixel dynamic occlusion of a 90.6% maximum occlusion ratio.