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Abstract
Holography has been considered as the ultimate technology for three-dimensional visual experience. Compared to the well-established static holographic technology, holographic video display is still in the research and development stage, before commercial products. This paper reviews various kinds of researches and related systems from the beginning of holographic video display to recent improvements, compares each specification, and describes their features. We discuss the key requirements for holographic display to be commercialized and widely used in everyday life.
© 2021 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. INTRODUCTION
People want to visualize ideas, to turn their imaginations into reality. They also want to record what they have experienced and then share the information with others. Even in the Paleolithic period, people painted their daily lives on cave walls. As science and technology advance, the ways of visualizing ideas and experiences have changed from painting to photographs, and recently to display. Photography is very close to perfection in representing reality, except that the projection of the three-dimensional (3D) world is limited to two dimensions. Overcoming this limit was achieved only after we had a deeper understanding of light. Light has not only photographic properties such as brightness and color, but also the property of waves, described by phase. The information on the direction of light can be represented by the phase distribution of light. A method to record both the intensity and phase of light, holography, was invented by D. Gabor in 1948 [1]. It was 60 years after scientists realized that light is an electromagnetic field. Actual holograms have been demonstrated after the first laser was developed [2,3]. Using conventional holography, one is able to store and reproduce a complete snapshot of this 3D world onto a film. However, that was only an upgraded version of a photogram.
People are already getting interested in video, which is a series of two-dimensional (2D) pictures changed in a short time. A 2D image with time variation is more useful in many cases than the 3D image with no temporal information. A recent display technology provides high pixel density so that humans cannot distinguish a pixel, like a photograph, and the frame rate is fast enough so that our eyes feel a series of pictures as a video. The repetition rate of 240 Hz became commercially available, which is three times greater than the image processing frequency of a human brain. So far, the current 2D display already seems to replicate reality “almost” perfectly. However, human desire for an ideal visual experience keeps us pursuing the third spatial dimension. So in the past few decades, there have been many studies and prototypes for 3D displays.
3D displays can be classified into four major groups: stereoscopic display, auto-stereoscopic display, volumetric display, and holographic display [4]. The stereoscopic method typically requires the aid of a near eye display or a head mount display, while there is no need to wear devices for the auto-stereoscopic method, such as multi-view display and light field display. Both stereoscopic and auto-stereoscopic displays exploit binocular disparity to make people recognize the scene as 3D. However, using binocular disparity alone is not adequate for the ideal 3D display, since 3D images get blurrier as they move away from the screen. There are many reasons of blurring such as cross talk, aberrations, and ultimately the diffraction of light. Thus, the depth range of 3D space should be limited. Otherwise, one may experience eye fatigue due to accommodation–vergence conflict [5]. The volumetric display dynamically places emitting light sources at the actual location of virtual objects; thus, there is no such visual conflict. However, 3D space is limited by its container, and 3D images are usually not accessible for user interaction.
Holography has been known as the most appropriate way to display real-looking 3D images, because it can control important properties of light including the phase, which is not accessible by other means. Looking at holographic art work, it is hard to tell the difference from reality except the fact that time has frozen. Thus, the next step after the holographic photogram is creating holographic video. However, implementing video-enabled holography is another challenge, because it requires a lot of pixels and data. The highest currently available resolution is insufficient to reproduce holographic video. To create a dynamic hologram in a mobile phone, a resolution of over 200 k is required to provide the viewing angle of 30°. It immediately increases both the level of difficulty in manufacturing spatial light modulators (SLMs) and the cost of computing a hologram. Also, conventional backlight used in 2D display cannot be applied to reconstruct the hologram due to the lack of spatial coherency. So in the past 30 years, there have been various attempts to overcome the barriers on dynamic holographic display. In this review paper, we look back at some of the distinguished systems on holographic video display. We look into what more we need to hold a holographic display in our hands.
2. ISSUES
Before reviewing each system, it is good to mention several barriers on commercializing the holographic display so that one can understand the reason for each approach better. First, there is the limitation of the space–bandwidth product (SBP), which determines both the size of a holographic image and the viewing angle. The product of hologram size and viewing angle is proportional to the information capacity of the holographic medium. The pixel pitch and diffraction angle can be represented by the equation $\theta = {\rm arc} \sin\;(\lambda /p)$, where $\theta$ is the diffraction angle, $\lambda$ is the wavelength, and $p$ is the pixel pitch. They have a trade-off relation as shown in Fig. 1. The static hologram using an optically recordable medium such as a photopolymer or silver halide, typically has a huge information capacity, because the light is recorded at the molecular level. The size of a hologram can be scalable by using larger recording film, as long as enough laser power and optics are provided. On the other hand, the information capacity is mainly determined by the total number of pixels for SLM where the light is spatially controlled in a discrete manner. Thus, the holographic display using the SLM typically provides SBP by a few hundred times less than the SBP of static holographic media. It means that either hologram size or viewing angle has to be insufficient to generate a hologram using an SLM.
The second barrier is the volume of the display system. To produce a hologram properly, maintaining spatial coherency of a reference light is crucial. The simplest way to generate such coherent light, is placing a point light source at the focal distance away from a collimating lens. The least method costs the most space. Instead of using a refractive lens, one can save some volume of the backlight by using a reflective curved mirror and folding mirrors. However, it will not become as flat as the backlight of current 2D displays. Since no one would buy a cathode ray tube television set these days, the holographic display should find a way to make the coherent backlight slim. Diffusing light along the thin planar light-guide will work only for a conventional display since it spoils the spatial coherency of the light. Thus, sophisticated diffractive optical components are inevitable for the manipulation of light in a small volume, using diffractive optics limits in applying the light source. Since diffraction is more sensitive to the wavelength of light compared to refraction, it induces severe chromatic aberration, and efficiency drops even with a small change in wavelength. Thus, the light with a narrow bandwidth such as the laser diode (LD) is typically used instead of broadband light. Depending on the optical system, light from the LD can cause speckle noise on holograms due to its high temporal coherency.
Last, the computational cost for calculating holograms becomes a bigger burden as the holographic display improves its SBP. If there is a 10-inch (254 mm) holographic display having 1 µm pixel pitch for a 30° viewing angle, about 3 zettaflops (${{1}}{{{0}}^{21}}$) is required to calculate the hologram for generating 4 k voxels by using the Rayleigh–Sommerfeld equation. There have been a lot of efforts to make an efficient hologram calculation, and a clustered computer or a GPU is required to calculate a high-resolution color hologram at video frame rate.
Fig. 2. (left) Picture of Mark-V, (top right) target image, and (bottom right) measured color image. Reprinted with permission from [18], Copyright © The Optical Society.
Fig. 3. (left) Next version prototype and (right) photograph of test holographic 3D scene using a bulk-optic backlight. Reprinted with permission from [25], Copyright © The Optical Society.
3. HOLOGRAPHIC VIDEO DISPLAYS
A. Massachusetts Institute of Technology
The first practical dynamic holographic display, Holovideo, was developed at MIT Media Lab in 1989. They developed a series of holographic display prototypes named as Mark-I, Mark-II, Mark-III, Mark-IV, and Mark-V [6–18]. The latest version was developed by Smalley and co-researchers at Brigham Young University with significantly minimized costs. While the liquid crystal (LC) based matrix is commonly used as an SLM, they applied acousto-optic modulators (AOMs) to produce holographic videos. The key idea is trading temporal bandwidth of sound to the spatial bandwidth of light. The AOM is usually not suitable for generating large diffraction angles, so the telescope was placed after the AOM to extend the diffraction angle by the ratio of magnification.
Mark-I is a monochromatic holographic display, which can be convertible to full-color by dividing resolution into three-color channels. It can produce horizontal parallax-only holograms with the size of ${{25}}\;{\rm{mm}}\;\times\;{{25}}\;{\rm{mm}}\;\times\;{{25}}\;{\rm{mm}}$ (${\rm{width}}\;\times\;{\rm{height}}\;\times\;{\rm{depth}}$), viewing angle of 15°, and frame rate of 20 frames per second (fps). Three-channel tellurium-dioxide (${\rm{Te}}{{\rm{O}}_2}$) AOMs were used to convert the radio frequency (RF) signal into a holographic fringe. The hologram patterns are combined using a polygonal spinner with 18 facets. The resulting horizontal resolution is 32 k pixels so that it can cover a wide viewing angle. The vertical resolution is determined by a galvo-scanner, so that 64 lines are made. A vertical diffuser is used to ensure the vertical angle of viewing.
Second generation holographic display Mark-II used an 18-channel AOM to scale up the hologram size and viewing angle. The scanning mirror replaced the rotating polygon mirror due to the parallel modulators. Mark-II was designed to be readily scaled by adding multiple AOMs and scanning mirrors. It enabled the hologram size of ${{150}}\;{\rm{mm}}\;\times\;{{75}}\;{\rm{mm}}\;\times\;{{150}}\;{\rm{mm}}$ with a viewing angle of 30°. Mark-II was driven by the supercomputer Cheops so that the frame rate was 2.5 fps for the holographic video of ${{256}}\;{\rm{k}}\;\times{{144}}$ resolution.
Mark-III focused more on commercialization by increasing the bandwidth of the modulator and keeping cost down. The major difference from the former prototype is the type of AOM. ${\rm{Te}}{{\rm{O}}_2}$ AOM used in Mark-II was replaced by the guided-wave optical scanner (GWS), which uses a surface acoustic wave (SAW). The GWS consists of a ${\rm{LiNb}}{{\rm{O}}_3}$ based waveguide. Since lithium niobate has less acoustic attenuation than ${\rm{Te}}{{\rm{O}}_2}$, the acoustic frequency can be used up to the GHz range. Thus Mark-III obtained the holographic video size of ${{80}}\;{\rm{mm}}\;\times\;{{60}}\;{\rm{mm}}\;\times\;{{80}}\;{\rm{mm}}$ with a viewing angle of 24°. In addition, by replacing the scanning mirror with a holographic optical element (HOE), the system was stabilized without a mechanical driving device. Mark-IV and Mark-V aimed to reduce the cost of display and to increase robustness of the optical system while both the hologram size and viewing angle are reduced. Mark-V and the resulting image are shown in Fig. 2. Since the AOM modulates a light in one dimension, Holovideo will remain a single-parallax holographic display until a proper 2D AOM is developed.
B. SeeReal Technologies
SeeReal Technologies proposed a new approach to holographic displays [19–25]. The primary concept of this approach is to calculate and project holograms only to the area of interest, which is called a “viewing window.” The window is typically at the Fourier plane of the hologram where the observer is located. The solid angle of the viewing window can be much smaller than the actual viewing angle of the holographic display. The most optimized size of the viewing window is the size of an eye pupil as long as one has the proper means to dynamically adjust the position of the viewing window to the center of the pupils, measured by an eye-tracker. Both the pixel pitch and the focal length of the field lens determines the size of the viewing window. The smaller pixel pitch and the longer focal length provide a larger area of the viewing window. To calculate a hologram, the concept of a sub-hologram plays a role to minimize the computational cost. The voxels closer to the SLM require fewer holographic fringes depending on the diffraction angle.
A 20-inch (508 mm) holographic monitor called “VISIO-20” was built and demonstrated in 2007. The pixel pitch of SLM is about ${{70}}\;\unicode{x00B5}{\rm m}\;\times\;{{210}}\;\unicode{x00B5}{\rm m}$, and thus, the diffraction angle is relatively small, which is proportional to the size of the viewing window. To ensure enough size of the viewing window, the viewing distance was about 4 m. The method of switching light sources with a lens array was used to steer the backlight so that the hologram was projected with respect to the location of the observer. Two CCD cameras were used to track eyes illuminated by infrared light. Since the amount of calculation is reduced by eye-tracking and sub-holograms, it operated at 30 Hz. SeeReal is building the next version holographic display using a volume grating based backlight unit that supports a ${{300}}\;{\rm{mm}} \times {{200}}\;{\rm{mm}}$ active area. The outlook of the prototype and the corresponding test hologram are shown in Fig. 3.
Fig. 4. (left) Four channel Active Tiling unit and (right) image of full parallax color hologram using ${{3}} \times {{8}}\;{\rm{billion}}$ pixels for testing fixed CGH. Reprinted by permission from [29] SPIE, Copyright © 2004.
Fig. 5. (left) Overall view of optical systems including image-readout optical system and (right) experimental result. Reprinted by permission from [36] Springer Nature, Copyright © 2014.
C. QinetiQ
An electronic holographic display system called Active Tiling (AT) was developed by QinetiQ [26–31]. The system takes advantage of the non-pixelated structure of an optically addressed SLM (OASLM), along with a fast electronically addressed SLM (EASLM). As a result, the system is able to reproduce a 3D color image of the full parallax by providing a much larger number of pixels than had previously been reached.
The key idea is using the temporal bandwidth of EASLM to update OASLM, which has a large spatial bandwidth. Since an OASLM has a great number of continuous “pixels,” it also requires a large number of data to record a hologram. By spatiotemporal multiplexing the fast EASLM, it is possible to update the entire holographic fringe in the OASLM in every frame. To do this, the AT system consists of a replication optics and a readout optics in addition to the SLMs. The ferroelectric LC (FLC) on silicon (FLCoS) writes the hologram pattern multiple times in a single frame, while the replication optics enables spatial multiplexing of OASLM by switching on and off the target segment. FLCoS has ${{1024}} \times {{1024}}$ binary pixels and 2.5 kHz driving frame rate. To replicate the light from FLCoS into ${{5}} \times {{5}}$ segments, a binary-phase diffractive optical element was used.
The OASLM consists of three layers: a photoconductor layer for incoherent detection, a blocking layer for selecting the segment, and an FLC layer for the hologram readout. The AT scheme system of QinetiQ has a high pixel area density of ${2.2} \times {{1}}{{{0}}^6}\;{\rm{pixels\cdot c}}{{\rm{m}}^{- 2}}$. The total number of pixels exceeds ${{1}}{{{0}}^9}\;{\rm{pixels}}$. Figure 4 shows the four-channel AT module and the 3D image photograph by using ${{3}} \times {{8}}$ billion spatially multiplexed pixels. However, QinetiQ’s AT approach has limitations to be solved, such as the thickness and weight of the system itself, and the difficulty of running real-time video.
D. National Institute of Information and Communications Technology
NICT developed an electronic holographic display system that can be scaled by tiling many SLMs. Since the physical gap between adjacent SLMs is unavoidable, they designed optical filter and lens arrays for reducing seam patterns on the tiled hologram. In addition to enlarging the size of the hologram by tiling, the holographic image acquisition from real objects was implemented. The acquisition system used an integral photography (IP) camera with high definition. The computing system generates a digital hologram from an IP image taken by the acquisition system in real time [32–36].
The first system was demonstrated using ${{3}} \times {{3}}$ tiled SLMs of 4 k resolution, which forms 12 k in total. Overall image size was 63 mm and the viewing angle was 5.6°. A full parallax color holographic video was played at 20 fps. The second version was further scaled so that ${{4}} \times {{4}}$ SLMs were tiled. The diagonal size of a hologram was increased to 85 mm with the same viewing angle. The optical system and the holographic video are shown in Fig. 5.
E. Korea Advanced Institute of Science and Technology
The study at KAIST is on the extension of the hologram’s viewing angle using a diffuser [37]. At that time, imaging through turbid media was getting attention. It was experimentally confirmed that even if the image was spoiled after the scattering medium, one can restore the image as long as the transfer matrix of the medium is known. In this study, this idea was applied reversely in the holographic display. The viewing angle was widened as much as the diffusing angle. The problem is that the diffuser breaks the hologram reconstruction. However, when a SLM sends a waveform that compensates for the action of the diffuser in reverse, one can create a desired hologram after passing through the diffuser. This process can also be understood as controlling the volume speckle field induced by diffusers. Both the optical system and the resulting hologram are shown in Fig. 6. A viewing angle of 36° was achieved. There is a trade-off between the number of voxels and image contrast.
Fig. 6. (left) Optical layout for the holographic display using volume speckle field and (right) hologram for number “3” using 15 voxels with 30° viewing angle. Reprinted by permission [37] from Springer Nature, Copyright © 2017.
Fig. 7. (left) Holographic display using 16 K SLMoG with driver board and (right) experimental result of a monochromatic cube hologram. Reprinted by permission from [38] John Wiley and Sons, Copyright © 2019.
F. Electronics and Telecommunications Research Institute
While many ideas and devices were introduced to increase the viewing angle of holograms, there is still a straightforward way—reducing pixel pitch of a SLM. ETRI has achieved fabrication of an LC based SLM with 1 µm pixel pitch for electronic holography, which is called SLM on glass (SLMoG) as shown in Fig. 7 [38–40].
High pixel density is commonly implemented in LCoS devices due to their advantage of hiding thin-film transistors (TFTs) behind the panel. Since the SLMoG is transmissive, there is not much room for hiding TFTs. By depositing the TFT vertically, the pitch can be reduced to 1 µm in addition to the help of the aspect ratio of a pixel. The size of the pixel is 1 µm in the horizontal direction and 9 µm in the vertical direction. The SLMoG with 16 k resolution generated a hologram that can cover a 30° viewing angle for green wavelength.
G. Samsung Advanced Institute of Technology
Recently, SAIT demonstrated an interactive slim-panel holographic video display using the steering-backlight unit (S-BLU) and the holographic video processor as shown in Fig. 8. They tried to solve major issues on holographic displays: narrow viewing angle, bulky optics, and heavy computing power. The S-BLU enables to expand the viewing angle by 30 times, and its diffractive waveguide architecture makes a slim display form factor [41]. The holographic video processor computes high-quality holograms in real-time on a single chip [42].
Fig. 8. (left) Slim-panel holographic video display and (right) snapshot of full color real-time holographic movie. Reprinted under Creative Commons CC BY license [41].
Table 1. Holographic Display Systems Compared with Various Parametersa
SBP was expanded effectively without directly increasing the number of pixels of the SLM. To overcome the small SBP, the S-BLU was introduced, which is able to tilt the angle of the backlight for reconstructing holograms. Since the S-BLU steers the backlight and can deliver the holographic image to a desired direction, the viewing angle can be effectively expanded for an observer up to the maximum steering angle of S-BLU.
The beam deflector (BD), one of the key elements of S-BLU, plays the role of steering a beam [43]. The BD consists of multiple transmission phase arrays, which can provide the linear phase profile for tilting the transmission angle. By using the BD, the SBP is enhanced by the factor of (${{1}}\;{ + }\;{{{p}}_{{\rm SLM}}}/{{{p}}_{{\rm BD}}}$) where ${{{p}}_{{\rm SLM}}}$ and ${{{p}}_{{\rm BD}}}$ are the pixel pitches of the SLM and BD. The pixel pitch of the BD was designed as 2 µm, while the pixel pitch of the SLM is 58 µm. Then, the effective SBP is increased about 30 times without increasing the number of pixels in the SLM itself. The ${{{p}}_{{\rm BD}}}$ can be reduced further, since the structure of 1D electrodes in the BD is much simpler than a 2D matrix in the SLM. The holographic video processor calculates ultra high definition (UHD), computer generated hologram (CGH) resolution at 30 fps. The overall system thickness is $\lt 10\,\,\rm cm$. The thickness of the flat panel display parts is 1 cm. The slim holographic video display is achieved by using a 10.1-inch (256.54 mm) conventional LCD.
H. Other Types of Holographic Displays
There are various approaches other than the conventional flat-panel geometry to maximize the certain features of holographic video display. Yaras et al., at Bilkent University, demonstrated a circularly tiled SLM to increase the field of view [44]. Nine phase-only SLMs are cross-arranged with respect to the beam splitter to tile the holograms seamlessly. Kujawinska et al., at Warsaw University of Technology, constructed a holographic television pipeline that includes hologram acquisition and data processing [45]. Using six CCD sensors with individual interferometers, real-world objects are captured. Six SLMs are horizontally arranged, and holograms from each SLM are combined at an asymmetric diffuser. Thus, a monochromatic horizontal parallax-only hologram is generated with a wide field of view. Lim et al., at ETRI, demonstrated a 360° tabletop holographic display using a mechanically rotating platform with a pair of parabolic mirrors [46]. Four synchronized high-speed digital micromirror devices (DMDs) are used to create 628 views around 360° horizontally at 20 fps. Recently, Li et al., at the University of Cambridge, proposed a scalable tiling approach called coarse integral holography [47]. They demonstrated seamlessly tiling two SLMs using a hybrid resonant scanner that consists of a vertical galvo scanner and a horizontal resonant scanner.
Fig. 9. Display size versus viewing angle diagram for various holographic video displays (blue diamond: full parallax; red triangle: single parallax only). Three slanted lines indicate the size and angle limits from SBP given by the resolution of 2 K, 16 K, 128 K for each.
4. COMPARISON
So far, we have reviewed distinguished studies on a holographic video displays. The approaches and devices were different, but they all have the common purpose of creating a video hologram that can be used in everyday life. Each holographic display system is compared as shown in Table 1, based on the requirements for everyday usage from the user’s point of view. It is divided into five categories: screen size, viewing angle, form factor, frame rate, and parallax. In Fig. 9, the SBP of each system is compared in terms of hologram size versus viewing angle. The SBP has now reached the level of 128 k SLM, which is capable of providing a 5-inch (127 mm) holographic display with a 30° viewing angle.
5. TOWARDS COMMERCIALLY AVAILABLE HOLOGRAPHIC VIDEO DISPLAY
Although many studies on holographic display devices have been conducted and significant progress has been made, there is still work to be done for the growth of the holographic display industry. To do so, not only display devices but also their eco-systems must be well established.
A. Acquisition
Methods for acquiring holographic information have been studied in various ways; however, most of them mainly use coherent light. Nevertheless, to obtain hologram data as easily as we take pictures with a digital camera in our daily lives, it is desirable to acquire holograms using an incoherent light sources as follows. The first method is to calculate a hologram inversely from color images and depth information (RGB-D), the other is to create a holographic fringe by interfering with an incoherent light source. Researches using incoherent light such as Fresnel incoherent correlation holography [48] and self-interference incoherent digital holography [49] have been actively studied recently. Since this method can also extract depth information using the measured hologram, it can be used not only as a holographic display but also as a substitute for light detection and ranging (LIDAR).
B. Data Format and Transformation
Data formats and their compression methods for 2D images and videos have already been standardized. A common agreement on how to handle content as well as development of devices is essential to enhance the popularization of holograms. The format for sharing the hologram falls into two broad categories: one is to store the model information of the scene itself, and the other is to store the complex field of light generated in the scene. In the former case, data obtained by RGB-D or integral imaging are examples. Since they do not have wavefront information, CGH has to be recalculated at the point to display the data. This post-processing method has flexibility to match the hologram for various display devices. When the latter complex field data are implemented, there is an advantage that it can be displayed directly on a suitable display without calculating holograms, while the scene may not be rendered properly when the type or size of the display device is different.
C. Light Source
One of the factors that affects the quality of holographic displays is the coherency of the light source. In particular, a light source with high spatial coherence such as a diode-pumped solid-state (DPSS) laser or LD is required to improve the sharpness of holograms. However, an LD light source also has high temporal coherence, and it causes speckle noise, which decreases the uniformity of the hologram. To provide a high-quality hologram, a light source with high sharpness and that is speckle-free is required. Related light sources are the vertical-cavity surface-emitting laser (VCSEL), light-emitting diode (LED), super luminescent LED (sLED), micro LED (mLED), and so on. However, since the speckle contrast and image sharpness of light sources are proportional to each other, it is important to apply them according to the required specifications of the holographic display.
D. Complex–Amplitude SLM
Due to the complex nature of the light, the holographic video can be properly reconstructed when the complex–amplitude SLM is used, which can control both amplitude and phase at the same time. So far, the amplitude-only or phase-only SLM has been commonly used generate a dynamic hologram, but it causes extra noise such as the direct current and conjugate, and degrades the contrast of the hologram. By using an off-axis hologram, one can avoid those noises in different angles. However, the presence of noise is not proper for a commercialized display in many cases, so the complex–amplitude SLM is necessary for holographic display at last. There are several methods of complex modulating: cascading amplitude and phase, combining two phases, and combining three amplitudes with different phases. There are also other methods without using independent phase and amplitude pixels. Some LC modes or materials such as germanium-antimony-tellurium (GST) exhibit phase and amplitude modulation at the same time, which can be used in complex–amplitude SLMs, while they are well controllable and cover a full phase range of ${{2}}\pi$. Even in the complex–amplitude SLM, the quantization of CGH can cause noise at a reconstructed hologram; thus, a CGH has to be optimized to suppress the quantization noise [50].
E. Computing Holograms
Depending on the method of handling 3D objects, there are several categories of generating CGHs such as point clouds, polygons, RGB-D, and ray-based methods. Although there are certain conditions for each method to work effectively, computing high-resolution holograms is still a common challenge for all methods since the amount of computation increases in proportion to the order of ${{{N}}^2}$ or ${{N}}\;{{\cdot}}\;{\rm{Log}}({{N}})$ as the resolution ${{N}}$ of the hologram increases. To compensate for this problem, hardware solutions such as GPUs, clustered computers, and field-programmable gate arrays (FPGAs) have been proposed. However, more efficient computational algorithms are essential for holographic displays to be more common. A wavefront recording plane (WRP), wavelet, and more recently, network-based CGH using deep learning have been proposed as methods to accelerate the calculation of holograms.
6. CONCLUSION
Holography is one of the advanced technologies for 3D display. This review paper presents past and current research activities on holographic video display. Since there are huge technical barriers to directly tackle the problems of commercialized holographic display, various unique ideas and methods are proposed and demonstrated. MIT showed AOM using SAW can produce holograms without a pixelated SLM. SeeReal proposed that a viewing window incorporated with eye-tracking can dramatically reduce the number of pixels and data for producing holograms. QinetiQ proposed an AT system using OASLM so that the size of a holographic display can be scalable. NICT demonstrated the tiling holographic display with real-time 3D acquisition. KAIST expanded the viewing angle of a hologram in the volume speckle field by exploiting the scattering from diffusers. ETRI pushed the limit of pixel pitch on an LC-based SLM down to 1 µm, so that the viewing angle of a 16 K resolution hologram can be 30° wide. SAIT demonstrated a slim-panel holographic display by using steering-BLU so that the viewing angle is increased by 30 times more than the viewing angle provided by SLM itself. The single-chip holographic video processor can provide 4 k resolution holograms in real time.
In addition to the recent advances in holographic display devices, the ecosystem and related technology should be well developed for the holographic display industry. They include hologram acquisition technology, hologram data format and transformation, light sources, complex SLMs, and efficient computing algorithms.
Disclosures
The authors declare no conflicts of interest.
Data availability
No data were generated or analyzed in the presented research.
REFERENCES
1. D. Gabor, “A new microscopic principle,” Nature 161, 777–778 (1948). [CrossRef]
2. E. N. Leith and J. Upatnieks, “Reconstructed wavefronts and communication theory,” J. Opt. Soc. Am. 52, 1123–1130 (1962). [CrossRef]
3. Y. N. Denisyuk, “Photographic reconstruction of the optical properties of an object in its own scattered field,” Sov. Phys. Dokl. 7, 543 (1962).
4. J. Geng, “Three-dimensional display technologies,” Adv. Opt. Photon. 5, 456–535 (2013). [CrossRef]
5. D. M. Hoffman, A. R. Girshick, K. Akeley, and M. S. Banks, “Vergence–accommodation conflicts hinder visual performance and cause visual fatigue,” J. Vis. 8(3), 33 (2008). [CrossRef]
6. J. S. Kollin, S. A. Benton, and M. L. Jepsen, “Real-time display of 3-D computed holograms by scanning the image of an acousto-optic modulator,” Proc. SPIE 1136, 178–185 (1989). [CrossRef]
7. P. St. Hilaire, “Scalable optical architectures for electronic holography,” Ph.D. dissertation (Massachusetts Institute of Technology, 1994).
8. P. St-Hilaire, M. E. Lucente, J. D. Sutter, R. Pappu, C. J. Sparrell, and S. A. Benton, “Scaling up the MIT holographic video system,” Proc. SPIE 2333, 374–380 (1995). [CrossRef]
9. D. E. Smalley, “Integrated optics for holographic video,” M.S. thesis (Massachusetts Institute of Technology, 2006).
10. D. E. Smalley, Q. Y. J. Smithwick, and V. M. Bove, “Holographic video display based on guided-wave acousto-optic devices,” Proc. SPIE 6488, 64880L (2007). [CrossRef]
11. D. E. Smalley, Q. Y. J. Smithwick, V. M. Bove, J. Barabas, and S. Jolly, “Anisotropic leaky-mode modulator for holographic video displays Holovideo for everyone: a low-cost Holovideo monitor,” Nature 498, 313–317 (2013). [CrossRef]
12. P. St-Hilaire, S. A. Benton, and M. E. Lucente, “Synthetic aperture holography: a novel approach to three-dimensional displays,” J. Opt. Soc. Am. A 9, 1969–1977 (1992). [CrossRef]
13. P. St-Hilaire, S. A. Benton, M. E. Lucente, J. D. Sutter, and W. J. Plesniak, “Advances in holographic video,” Proc. SPIE 1914, 188–196 (1993). [CrossRef]
14. Q. Y. J. Smithwick, D. E. Smalley, V. M. Bove, and J. Barabas, “Progress in holographic video displays based on guided-wave acoustooptic devices,” Proc. SPIE 6912, 69120H (2008). [CrossRef]
15. V. M. Bove, D. E. Smalley, and Q. Y. J. Smithwick, “Making holographic television a consumer product,” in Digital Holography and Three-Dimensional Imaging (Optical Society of America, 2007), paper DWA4.
16. D. E. Smalley, Q. Y. J. Smithwick, J. Barabas, V. M. Bove, S. Jolly, and C. DellaSilva, “Holovideo for everyone: a low-cost Holovideo monitor,” J. Phys. Conf. Ser. 415, 012055 (2013). [CrossRef]
17. D. Henrie, B. Haymore, M. Zhang, D. Alrabidi, D. Smalley, S. Jolly, and V. M. Bove, “Progress on a low-cost holographic video monitor,” in Imaging and Applied Optics, OSA Technical Digest (2014), paper DW2B.3.
18. A. Henrie, J. R. Codling, S. Gneiting, J. B. Christensen, P. Awerkamp, M. J. Burdette, and D. E. Smalley, “Hardware and software improvements to a low-cost horizontal parallax holographic video monitor,” Appl. Opt. 57, A122–A133 (2018). [CrossRef]
19. A. Schwerdtner, N. Leister, and R. Häussler, “A new approach to electroholography for TV and projection displays,” in Proc. SID Symp. Dig. Tech. Papers (2007) 1224–1227.
20. S. Reichelt, R. Häussler, N. Leister, G. Futterer, and A. Schwerdtner, “Large holographic 3D displays for tomorrow’s TV and monitors—solutions, challenges, and prospects,” in Proc. IEEE 21st Annu. Meeting Lasers Electro-Opt. Soc. (LEOS’08) (2008), pp. 194–195.
21. R. Häussler, S. Reichelt, N. Leister, E. Zschau, R. Missbach, and A. Schwerdtner, “Large real-time holographic displays: from prototypes to a consumer product,” Proc. SPIE 7237, 72370S (2009). [CrossRef]
22. E. Zschau, R. Missbach, A. Schwerdtner, and H. Stolle, “Generation, encoding, and presentation of content on holographic displays in real time,” Proc. SPIE 7690, 76900E (2010). [CrossRef]
23. R. Häussler, A. Schwerdtner, and N. Leister, “Large holographic displays as an alternative to stereoscopic displays,” Proc. SPIE 6803, 68030M (2008). [CrossRef]
24. N. Leister, A. Schwerdtner, S. Furhapter, S. Buschbeck, J.-C. Olaya, and S. Flon, “Full-color interactive holographic projection system for large 3D scene reconstruction,” Proc. SPIE 6911, 69110V (2008). [CrossRef]
25. R. Häussler, Y. Gritsai, E. Zschau, R. Missbach, H. Sahm, M. Stock, and H. Stolle, “Large real-time holographic 3D displays: enabling components and results,” Appl. Opt. 56, F45–F52 (2017). [CrossRef]
26. M. Stanley, R. W. Bannister, C. D. Cameron, S. D. Coomber, I. G. Cresswell, J. R. Hughes, V. Hui, P. O. Jackson, K. A. Milham, R. J. Miller, D. A. Payne, J. Quarrel, D. C. Scattergood, A. P. Smith, M. A. G. Smith, D. L. Tipton, P. J. Watson, P. J. Webber, and C. W. Slinger, “100-megapixel computer-generated holographic images from Active Tiling: a dynamic and scalable electro-optic modulator system,” Proc. SPIE 5005, 247–258 (2003). [CrossRef]
27. S. D. Coomber, C. D. Cameron, J. R. Hughes, D. T. Sheerin, C. W. Slinger, M. A. G. Smith, and M. Stanley, “Optically addressed spatial light modulators for replaying computer-generated holograms,” Proc. SPIE 4457, 9–19 (2001). [CrossRef]
28. C. W. Slinger, R. W. Bannister, C. D. Cameron, S. D. Coomber, I. Cresswell, P. M. Hallett, J. R. Hughes, V. Hui, J. C. Jones, R. Miller, V. Minter, D. A. Payne, D. C. Scattergood, D. T. Sheerin, M. A. G. Smith, and M. Stanley, “Progress and prospects for practical electroholographic display systems,” Proc. SPIE 4296, 18–32 (2001). [CrossRef]
29. C. W. Slinger, C. D. Cameron, S. D. Coomber, R. J. Miller, D. A. Payne, A. P. Smith, M. G. Smith, M. Stanley, and P. J. Watson, “Recent developments in computer-generated holography: toward a practical electroholography system for interactive 3D visualization,” Proc. SPIE 5290, 27–41 (2004). [CrossRef]
30. M. Stanley, M. A. G. Smith, A. P. Smith, P. J. Watson, S. D. Coomber, C. D. Cameron, C. W. Slinger, and A. Wood, “3D electronic holography display system using a 100-megapixel spatial light modulator,” Proc. SPIE 5249, 297–308 (2004). [CrossRef]
31. C. Slinger, C. Cameron, and M. Stanley, “Computer-generated holography as a generic display technology,” Computer 38, 46–53 (2005). [CrossRef]
32. K. Yamamoto, T. Mishina, R. Oi, T. Senoh, and T. Kurita, “Real-time color holography system for live scene using 4K2K video system,” Proc. SPIE 7619, 761906 (2010). [CrossRef]
33. T. Senoh, T. Mishina, K. Yamamoto, R. Oi, and T. Kurita, “Viewing zone-angle-expanded color electronic holography system using ultrahigh-definition liquid crystal displays with undesirable light elimination,” J. Disp. Technol. 7, 382–390 (2011). [CrossRef]
34. Y. Ichihashi, R. Oi, T. Senoh, K. Yamamoto, and T. Kurita, “Real-time capture and reconstruction system with multiple GPUs for a 3D live scene by a generation from 4K IP images to 8K holograms,” Opt. Express 20, 21645–21655 (2012). [CrossRef]
35. H. Sasaki, K. Yamamoto, Y. Ichihashi, and T. Senoh, “Image size scalable full-parallax coloured three-dimensional video by electronic holography,” Sci. Rep. 4, 4000 (2014). [CrossRef]
36. H. Sasaki, K. Yamamoto, K. Wakunami, Y. Ichihashi, R. Oi, and T. Senoh, “Large size three-dimensional video by electronic holography using multiple spatial light modulators,” Sci. Rep. 4, 6177 (2014). [CrossRef]
37. H. Yu, K. Lee, J. Park, and Y. Park, “Ultrahigh-definition dynamic 3D holographic display by active control of volume speckle fields,” Nat. Photonics 11, 186–192 (2017). [CrossRef]
38. J. H. Choi, J. Pi, C. Hwang, J. Yang, Y. Kim, G. H. Kim, H. Kim, K. Choi, J. Kim, and C. Hwang, “Evolution of spatial light modulator for high-definition digital holography,” ETRI J. 41, 23–31 (2019). [CrossRef]
39. J. Yang, J. Choi, J. Pi, C. Hwang, G. H. Kim, W. Lee, H. Kim, K. Choi, Y. Kim, and C. Hwang, “High-resolution spatial light modulator on glass for digital holographic display,” Proc. SPIE 10943, 109430K (2019). [CrossRef]
40. Y. Kim, J. H. Choi, J. Pi, J. Yang, J. Y. Kim, W. Lee, H. Kim, G. H. Kim, S. M. Cho, K. Choi, S. Cheon, and C. Hwang, “Pathways to high definition holographic display,” Proc. SPIE 11708, 1170809 (2021). [CrossRef]
41. J. An, K. Won, Y. Kim, J. Hong, H. Kim, Y. Kim, H. Song, C. Choi, Y. Kim, J. Seo, A. Morozov, H. Park, S. Hong, S. Hwang, K. Kim, and H.-S. Lee, “Slim-panel holographic video display,” Nat. Commun. 11, 5568 (2020). [CrossRef]
42. H. Kim, Y. Kim, H. Ji, H. Park, J. An, H. Song, Y. T. Kim, H.-S. Lee, and K. Kim, “A single-chip FPGA holographic video processor,” IEEE Trans. Ind. Electron. 66, 2066–2073 (2019). [CrossRef]
43. Y. Kim, K. Won, J. An, J. Hong, Y. Kim, C. Choi, H. Song, B. Song, H. S. Kim, K. Bae, J. Burm, and H.-S. Lee, “Large-area liquid crystal beam deflector with wide steering angle,” Appl. Opt. 59, 7462–7468 (2020). [CrossRef]
44. F. Yaraş, H. Kang, and L. Onural, “Circular holographic video display system,” Opt. Express 19, 9147–9156 (2011). [CrossRef]
45. M. Kujawinska, T. Kozacki, C. Falldorf, T. Meeser, B. M. Hennelly, P. Garbat, W. Zaperty, M. Niemelä, G. Finke, M. Kowiel, and T. Naughton, “Multiwavefront digital holographic television,” Opt. Express 22, 2324–2336 (2014). [CrossRef]
46. Y. Lim, K. Hong, H. Kim, H. Kim, E. Chang, S. Lee, T. Kim, J. Nam, H. Choo, J. Kim, and J. Hahn, “360-degree tabletop electronic holographic display,” Opt. Express 24, 24999–25009 (2016). [CrossRef]
47. J. Li, Q. Smithwick, and D. Chu, “Scalable coarse integral holographic video display with integrated spatial image tiling,” Opt. Express 28, 9899–9912 (2020). [CrossRef]
48. B. Katz, J. Rosen, R. Kelner, and G. Brooker, “Enhanced resolution and throughput of Fresnel incoherent correlation holography (FINCH) using dual diffractive lenses on a spatial light modulator (SLM),” Opt. Express 20, 9109–9121 (2012). [CrossRef]
49. J. Rosen, A. Vijayakumar, M. Kumar, M. R. Rai, R. Kelner, Y. Kashter, A. Bulbul, and S. Mukherjee, “Recent advances in self-interference incoherent digital holography,” Adv. Opt. Photon. 11, 1–66 (2019). [CrossRef]
50. Z. He, X. Sui, G. Jin, D. Chu, and L. Cao, “Optimal quantization for amplitude and phase in computer-generated holography,” Opt. Express 29, 119–133 (2021). [CrossRef]
