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.

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.

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.

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.

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.

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).

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.

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.

Efficient calculation scheme for high pixel resolution non-hogel-based computer generated hologram from light field.

We propose a method that reduces the computation time and memory requirement in non-hogel-based hologram synthesis from light field data. The non-hogel-based technique synthesizes coherent complex field for a three-dimensional scene from its light field. Unlike conventional holographic stereogram, the non-hogel-based technique reconstructs continuous parabolic wavefront for individual three-dimensional object point by globally processing the light field. However, the global processing increases the computational load significantly, making it hard to synthesize holograms with high pixel resolution. The proposed technique reduces the computational burden by processing each two-dimensional angular frequency slice of the four-dimensional light field independently. Hologram tiling technique is also proposed to make the hologram synthesis process scalable. Using the hologram tiling and the angular-frequency-slice-based processing, 25K×25 K pixel resolution hologram was synthesized successfully.

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.

Pre-compensation of an image blur in holographic projection display using light emitting diode light source.

Holographic projection displays suffer from image blur when reconstructed from an incoherent light source like a light emitting diode. In this paper, we propose a method that enhances the reconstruction sharpness by pre-compensating the target image. The image blur caused by the incoherent nature of the light emitting diode is analyzed and the corresponding spatially varying point spread function is obtained. The pre-compensation is then performed using an iterative optimization algorithm. Finally, the hologram of the pre-compensated target image is loaded onto a spatial light modulator to obtain optically reconstructed image with reduced blur. The numerically simulated results and optically reconstructed results are in good agreement, showing feasibility of the proposed method.

Hologram conversion for speckle free reconstruction using light field extraction and deep learning.

A novel hologram conversion technique for speckle-less reconstruction is proposed. Many speckle-less reconstruction methods require holograms specially created for those techniques, limiting their applications to general pre-existing holograms. The proposed technique transforms an existing hologram with random phase distribution to new holograms for the application of the speckle-less reconstruction methods. The proposed technique first extracts a set of orthographic views from the existing hologram, then the extracted orthographic views are processed for the speckle noise removal using convolutional neural network. The processed orthographic views are finally used to synthesize new holograms with desired carrier waves by using non-hogel based computer generated hologram technique. The selection of the carrier wave is determined by the desired speckle-less reconstruction method. In this paper, we demonstrate the proposed technique with two speckle-less reconstruction methods; i.e. temporal speckle averaging of different random phase distributions and time-multiplexing of interleaved angular spectrums.

Holographic near-eye display with continuously expanded eyebox using two-dimensional replication and angular spectrum wrapping.

Holographic near-eye displays present true three-dimensional images with full monocular depth cues. In this paper, we propose a technique to expand the eyebox of the holographic near-eye displays. The base eyebox of the holographic near-eye displays is determined by the space bandwidth product of a spatial light modulator. The proposed technique replicates and stitches the base eyebox by the combined use of a holographic optical element and high order diffractions of the spatial light modulator, achieving horizontally and vertically expanded eyebox. An angular spectrum wrapping technique is also applied to alleviate image distortions observed at the boundaries between the replicated base eyeboxes.

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.

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.

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.