digital holographic 3d display seminar

DIGITAL HOLOGRAPHIC THREE DIMENSIONAL DISPLAYS 1

CHAPTER 1

INTRODUCTION

Three-dimensional video displays that can generate ghost like optical duplicates of 3-

D objects and scenes have been depicted in science-fiction movies as futuristic means of visual

media tools; such display devices always attracted public interest .

One immediate question is whether such a display is possible; and a quick answer is

“Yes, it is”.Noting that “seeing” is a purely optical interaction, and what we (or any other observer,

including living organisms and machines) see is only due to the light that enters through our pupils,

the design target for such a display is simple to state: if we can record the volume filling time-

varying light field in a 3-D scene, with all its needed physical properties, and then regenerate the

same light field somehow at another place, maybe at another time, the observer will not be able to

distinguish the original scene from its duplicate since the received light will be the same, and

therefore, any visual perception will also be the same.

Then the natural question is whether we can record the light with all its relevant

physical properties, and then regenerate it. The classical video camera is also a light recorder.

However, not all necessary physical properties of light for the purpose outlined above can be

recorded by a video camera; indeed, what is recorded by a video camera is just the focused intensity

patterns (one for each basic color) over a planar sensing device. What is needed to be recorded

instead is indeed much more complicated: we also need the directional decomposition of incoming

light as well. Briefly, and in an idealized sense, we can say that we need to record the light field

distribution. The term light field distribution is usually associated with ray optics concepts, and

therefore, can be a valid optics model only in limited cases. If it can be recorded, we then need

physical devices that can also regenerate (replay) the recorded light field. Prototypes for light field

recording and rendering devices are reported in the literature . Integral imaging gets close to a light

field imaging device in the limit under some mathematical idealizations; however such limiting

cases are not physically possible. A better optical model than the ray optics is the wave optics. The

propagation of light in a volume is modeled as a scalar wave field; the optical information due to a

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3-D scene is carried by this wave field. Therefore, if such a wave field can be recorded and

replayed, we achieve visual duplication of 3-D scenes; this is holography . Scalar wave model is

usually satisfactory, and more accurate models of light are rarely needed, if any, for 3-D imaging

and display purposes.

Therefore, the term holography refers to recording and replaying optical wave fields.

In a more restrictive usage, holography refers only to a specific form of such recording where

interference of the desired wave field with a reference wave (sometimes self-referencing is

employed, as in in-line holography) is formed and recorded; we prefer the broader usage as stated

above. Indeed, the usage of the term may even be further broadened to include all kinds of physical

duplication of light, and therefore, may also cover integral imaging, in a sense .

Here in this paper, our focus is on the display of holograms. We focus only on

dynamic displays for video. Still holographic display technology has been well developed since

1960s, whereas dynamic display technology is still in its infancy, and therefore, a current research

topic. We further restrict our focus to pixelated display devices that can be driven digitally. Such

displays are usually called digital electroholographic displays since they are driven electronically.

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CHAPTER 2

THREE DIMENSIONAL DISPLAYS

A 3D display is any display device capable of conveying a stereoscopic perception of

3-D depth to the viewer. The basic requirement is to present offset images that are displayed

separately to the left and right eye. Both of these 2-D offset images are then combined in the brain

to give the perception of 3-D depth. Although the term "3D" is ubiquitously used, it is important to

note that the presentation of dual 2-D images is distinctly different from displaying an image in

three full dimensions. The most notable difference is that the observer is lacking any freedom of

head movement to increase information about the 3-dimensional objects being displayed.

Holographic displays do not have this limitation, so the term "3D display" fits accurately for such

technology.

Similar to how in sound reproduction it is not possible to recreate a full 3-

dimensional sound field merely with two stereophonic speakers, it is likewise an overstatement of

capability to refer to dual 2-D images as being "3D". The accurate term "stereoscopic" is more

cumbersome than the common misnomer "3D", which has been entrenched after many decades of

unquestioned misuse.

The optical principles of multiview auto-stereoscopy have been known for over 60

years.Practical displays with a high resolution have recently become available commercially.

2.1 TYPES OF THREE-DIMENSIONAL DISPLAYS

2.1.1 STERIOSCOPIC

Stereoscopy (also called stereoscopic For 3-D imaging) refers to a technique for

creating or enhancing the illusion of depth in an image by presenting two offset images separately

to the left and right eye of the viewer. Both of these 2-D offset images are then combined in the

brain to give the perception of 3-Ddepth. Three strategies have been used to accomplish this: have

the viewer wear eyeglasses to combine separate images from two offset sources, have the viewer

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wear eyeglasses to filter offset images from a single source separated to each eye, or have the

lightsource split the images directionally into the viewer's eyes (no glasses required).

Stereoscopy creates the illusion of three-dimensional depth from images on a two-

dimensional plane. Human vision uses several cues to determine relative depths in a perceived

scene.Some of these cues are:

• Stereopsis

• Accommodation of the eyeball (eyeball focus)

• Occlusion of one object by another

• Subtended visual angle of an object of known size

• Linear perspective (convergence of parallel edges)

• Vertical position (objects higher in the scene generally tend to be perceived as further away)

• Haze, desaturation, and a shift to bluishness

• Change in size of textured pattern detail

All the above cues, with the exception of the first two, are present in traditional two-dimensional

images such as paintings, photographs, and television. Stereoscopy is the enhancement of the

illusion of depth in a photograph, movie, or other two-dimensional image by presenting a slightly

different image to each eye, and thereby adding the first of these cues (stereopsis) as well. It is

important to note that the second cue is still not satisfied and therefore the illusion of depth is

incomplete.

Many 3D displays use this method to convey images. It was first invented by Sir Charles

Wheatstone in 1838.Stereoscopy is used in photogrammetry and also for entertainment through the

production of stereograms. Stereoscopy is useful in viewing images rendered from large multi-

dimensional data sets such as are produced by experimental data. An early patent for 3D imaging in

cinema and television was granted to physicist Theodor V. Ionescu in 1936. Modern industrial three

dimensional photography may use 3D scanners to detect and record 3 dimensional information.The

three-dimensional depth information can be reconstructed from two images using a computer by

corresponding the pixels in the left and right images . Solving the Correspondence problemin the

field of Computer Vision aims to create meaningful depth information from two images.

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2.1.2 AUTOSTERIOSCOPIC

Autostereoscopy is any method of displaying stereoscopic images (adding perception

of 3D depth) without the use of special headgear or glasses on the part of the viewer. Because

headgear is not required, it is also called "glasses-free 3D" or "glasses-less 3D". The technology

also includes two broad approaches used in some of them to accommodate motion parallax and

wider viewing angles: those that use eye-tracking, and those that display multiple views so that the

display does not need to sense where the viewers' eyes are located.Examples of autostereoscopic

displays include parallax barrier, lenticular, volumetric, electro-holographic, and light field displays.

Many organizations have developed autostereoscopic 3D displays, ranging from

experimental displays in university departments to commercial products, and using a range of

different technologies.The method of creating auto-stereoscopic 3D using lenses was mainly

developed by Reinhard Boerner at the Heinrich Hertz Institute (HHI) in Berlin from 1985.The HHI

was already presenting prototypes of Single-Viewer displays in the nineties. Nowadays, this

technology has been developed further mainly by European companies. One of the most known 3D

display developed by HHI was the Free2C, a display with very high-resolution and very good

comfort achieved by an Eye tracking system and a seamless mechanical adjustment of the lenses.

Eye tracking has been used in a variety of systems in order to limit the number of displayed views

to just two, or to enlarge the stereoscopic sweet spot. However, as this limits the display to a single

viewer, it is not favored for consumer products.

Currently, most flat-panel solutions employ lenticular lenses or parallax barriers that

redirect incoming imagery to several viewing regions at a lower resolution. When the viewer's head

is in a certain position, a different image is seen with each eye, giving a convincing illusion of 3D.

Such displays can have multiple viewing zones allowing multiple users to view the image at the

same time, though they may also exhibit dead zones where only a monoscopic, crosseyed, or no

image at all can be seen.

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2.1.3 COMPUTER GENERATED HOLOGRAPHIC AND VOLUMRTEIC

Computer Generated Holography (CGH) is the method of digitally generating

holographic interference patterns. A holographic image can be generated e.g. by digitally computing

a holographic interference pattern and printing it onto a mask or film for subsequent illumination by

suitable coherent light source.Alternatively, the holographic image can be brought to life by a

holographic 3D display (a display which operates on the basis of interference of coherent light),

bypassing the need of having to fabricate a "hardcopy" of the holographic interference pattern each

time. Consequently, in recent times the term "computer generated holography" is increasingly being

used to denote the whole process chain of synthetically preparing holographic light wavefronts

suitable for observation.

Computer generated holograms have the advantage that the objects which one wants to show do not

have to possess any physical reality at all (completely synthetic hologram generation). On the other

hand, if holographic data of existing objects is generated optically, but digitally recorded and

processed, and brought to display subsequently, this is termed CGH as well. Ultimately, computer

generated holography might serve all the roles of current computer generated imagery: holographic

computer displays for a wide range of applications from CAD to gaming, holographic video and TV

programs, automotive and communication applications (cell phone displays) and many more.

A volumetric display device is a graphical display device that forms a visual

representation of an object in three physical dimensions, as opposed to the planar image of

traditional screens that simulate depth through a number of different visual effects. One definition

offered by pioneers in the field is that volumetric displays create 3-D imagery via the emission,

scattering, or relaying of illumination from well-defined regions in (x,y,z) space. Though there is no

consensus among researchers in the field, it may be reasonable to admit holographic and highly

multiview displays to the volumetric display family if they do a reasonable job of projecting a three-

dimensional light field within a volume.

Most, if not all, volumetric 3-D displays are autostereoscopic; that is, they create 3-D imagery

visible to the unaided eye. Note that some display technologists reserve the term “autostereoscopic”

for flat-panel spatially-multiplexed parallax displays, such as lenticular-sheet displays. However,

nearly all 3-D displays other than those requiring headwear, e.g. stereo goggles and stereo head-

mounted displays, are autostereoscopic. Therefore, a very broad group of display architectures are

properly deemed autostereoscopic.

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Volumetric 3-D displays embody just one family of 3-D displays in general. Other types of 3-D

displays are: stereograms / stereoscopes, view-sequential displays, electro-holographic displays,

parallax "two view" displays and parallax panoramagrams (which are typically spatially-

multiplexed systems such as lenticular-sheet displays and parallax barrier displays), re-imaging

systems, and others.

Although first postulated in 1912, and a staple of science fiction, volumetric displays are still under

development, and have yet to reach the general population. With a variety of systems proposed and

in use in small quantities — mostly in academia and various research labs — volumetric displays

remain accessible only to academics, corporations, and the military.

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CHAPTER 3

HOLOGRAPHY

3.1 OVERVIEW OF HOLOGRAPHY

Even though we focus on dynamic holographic displays in this paper, we feel that it

is appropriate to start with a brief history of holography in general. Gabor (1900–1979) invented the

holography to reduce the aberrations in electron microscopy . However, due to low quality of

obtained images holography did not become popular until early 1960s. After the developments in

laser technologies, Leith and Upatnieks developed the off-axis holography. In the meantime,

Denisyuk invented the volume holography by bringing the work of Lippmann to holography . Still

holography has been significantly developed since then, and many excellent monochromatic and

color holograms have been made.

The first computer generated hologram was introduced by Lohmann and Paris in 1967 . In the same

year, Goodman and Lawrence brought forward the idea of the digital holography . Then, in 1980,

the fundamental theory of digital holography was introduced by Yaroslavskii and Merzlyakov . We

use the term digital holography in a broader sense to include all sorts of digital techniques to

compute wave propagation, diffraction, and interference, as well as, digital capture and digital

display of holograms.

Conventional thick holograms on photographic plates can provide high resolution

and full parallax. However, dynamic displays for holographic video are still far from providing

satisfactory results. In electroholography, the resolution is significantly lower compared to thick

holograms. Moreover, pixelated structures bring some additional problems. Pixel period determines

the maximum frequency that can be represented when digital-to-analog conversion is conducted in

the Shannon sense, and this in turn determines the maximum diffraction angle as outlined.

Unfortunately, the pixel periods are not currently small enough to support sufficiently large viewing

angles. Problems associated with pixelated electroholographic display are known .

Since liquid crystal spatial light modulators (SLMs) are currently the primary choice

for digital holographic displays, it is quite relevant to briefly mention current capabilities of such

devices. Bauchert et al. reported the desirable features of liquid crystal SLMs. These features can

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be summarized as higher number of pixels, smaller pixel period, better optical efficiency, and faster

operation. There are various SLMs such as liquid-crystal-based devices (liquid crystal devices and

liquid crystal on silicon devices), mirror based devices (digital micromirror devices) and solid

crystal devices (acousto–optical devices). The acousto–optical modulators (AOMs) are mostly used

in 1-D applications. The digital micromirror devices are usually for binary modulation and they

may result in additional noise due to vibration of micromirrors. The liquid crystal-based light

modulators are more commonly used in electroholographic applications. Michalkiewicz et al. Pre

sented the progress in liquid crystal on silicon (LCoS) SLMs and their applications ]. Ohmura et al.

proposed a method to increase the viewing angle using such SLMs ].In their proposed system, they

used a single SLM that wasdriven by a mirror module. As a consequence of this method the

resolution along the horizontal direction increases. Therefore, the horizontal diffraction angle also

increases; and thus the viewing angle is improved.

Liquid-crystal-based SLMs are classified into various types such as complex

amplitude, amplitude-only, phase only, transmissive- and reflective-type SLMs, and so on. The

discussions corresponding to the bandwidth restriction and the pixel period given in Section III are

valid for all such types of pixelated SLMs. Among them, the fully complex amplitude-type SLM

may be the ultimate solution for the accurate reproduction from the hologram corresponding to a 3-

D object. Ability to support complex functions at the display is highly desirable since diffraction

fields are represented as complex valued fields where both the amplitude and the phase are needed.

An ideal SLM pixel should modulate both the amplitude and the phase of the incident light.

However, it is difficult to manufacture the complex amplitude-type SLMs based on current

technology. Phase-only SLMs may be the next best solutions for electroholography because they

have several advantages over amplitude-only SLMs such as suppressed zeroth-order and high-

diffraction efficiency, which can theoretically reach 100%. Amplitude-only SLMs can also be used

for electroholography. However, problems associated with strong undesired diffraction orders are

more severe compared to the phase-only case. A research group from Barcelona University,

Barcelona, Spain, combined two SLMs to display full complex Fresnel holograms They used one

SLM for the amplitude and the other one for the phase. They also investigated the quality of the

reconstructions using real-only, imaginary-only, amplitude-only, and phase-only holograms .

Schwerdtner et al. reported a novel hologram technology, which they called tracked

viewing window (TVW) . By this approach they only calculate a small portion of a hologram,

which then reconstructs a narrow angle light that falls onto the tracked pupils of the observer. They

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demonstrated that thin film transistor (TFT) monitors can then be used as SLMs to build

holographic displays. Another electroholographic display technique was presented by Hahn et al. [2.

In their research, they used curved array of SLMs to increase the field of view. Spatial Imaging

Group at the Massachusetts Institute of Technology (MIT, Cambridge, MA) developed a series of

holographic display systems named Mark-I, Mark-II, and Mark-III . Mark-I and Mark-II use

acoustooptical modulators, whereas Mark-III uses guided-wave optical scanners. All three can

render 3-D objects at video rates. A company developed another holographic display system . The

system uses active tiling where an electrically addressed SLM (EASLM) projects tiles of a big

hologram onto an optically addressed SLM (OASLM). With the help of the setup, more than 100

megapixels holograms can be displayed. Another system, so-called Horn (HOlographic

ReconstructioN), was presented by a group in Chiba University, Chiba, Japan Field programmable

gate arrays (FPGAs) were used in the developed holographic display system to achieve video frame

rates. Another group from Japan also demonstrated a holographic display system ; the system at the

National Institute of Information and Communications Technologies (NICT, Tokyo, Japan) captures

the 3-D scene by an integral imaging camera. The digital holograms of the captured scene is

calculated and displayed in real time. For further details, the reader is referred to a broad survey on

dynamic holographic displays, which was recently published .

3.2 HOLOGRAPHIC TECHNIQUE

Holography (from the Greek hólos, "whole" + grafē, "writing, drawing") is a

technique that allows the light scattered from an object to be recorded and later reconstructed so that

when an imaging system (a camera or an eye) is placed in the reconstructed beam, an image of the

object will be seen even when the object is no longer present. The image changes as the position

and orientation of the viewing system changes in exactly the same way as if the object were still

present, thus making the image appear three-dimensional. The holographic recording itself is not an

image – it consists of an apparently random structure of either varying intensity, density or profile –

an example can be seen below.

The technique of holography can also be used to store, retrieve, and process

information optically. While it has been possible to create a 3-D holographic picture of a static

object since the 1960s, it is only in the last few years that arbitrary scenes or videos can be shown

on a holographicvolumetric display.

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3.2.1 HOW HOLOGRAPHY WORKS

Holography is a technique which enables a light field to be recorded, and

reconstructed later when the original light field is no longer present. It is analogous to sound

recording where the sound field is encoded in such a way that it can later be reproduced.

Though holography is often referred to as 3D photography, this is a misconception. A

photograph represents a single fixedimage of a scene, whereas a hologram, when illuminated

appropriately, re-creates the light which came from the original scene; this can be viewed from

different distances and at different orientations just as if the original scene were present. The

hologram itself consists of a very fine random pattern, which appears to bear no relationship to the

scene which it has recorded.

To record a hologram, some of the light scattered from an object or a set of objects

falls on the recording medium. A second light beam, known as the reference beam, also illuminates

the recording medium, so that interference occurs between the two beams. The resulting light field

generates a seemingly random pattern of varying intensity, which is recorded in the hologram. The

figure below is a photograph of part of a hologram – the object was a toy van. The photograph was

taken by backlighting the hologram with diffuse light, and focusing on the surface of the plate.

It is important to note that the holographic recording is contained in the random

intensity structure (which is a speckle pattern), and not in the more regular structure, which is due to

interference arising from multiple reflections in the glass plate on which the photographic emulsion

is mounted. It is no more possible to discern the subject of the hologram from this random pattern

than it is to identify what music has been recorded by looking at the hills and valleys on a

gramophone record surface or the pits on a CD.

When the original reference beam illuminates the hologram, it is diffracted by the

recorded hologram to produce a light field which is identical to the light field which was originally

scattered by the object or objects onto the hologram. When the object is removed, an observer who

looks into the hologram "sees" the same image on his retina as he would have seen when looking at

the original scene. This image is avirtual image as the rays forming the image are all divergent. The

figure shown at the top of this article is an image produced by a camera which is located in front of

the developed hologram which is being illuminated with the original reference beam. The camera is

focused as if on the original scene, not on the hologram itself.

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Fig 3.1Holographic recording

fig 3.2 Holographic reconstruction

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3.3 DIGITAL HOLOGRAPHY

Digital holography is the technology of acquiring and processing holographic

measurement data, typically via a CCD camera or a similar device. In particular, this includes the

numerical reconstruction of object data from the recorded measurement data, in distinction to an

optical reconstruction which reproduces an aspect of the object. Digital holography typically

delivers three-dimensional surface or optical thickness data. There are different techniques available

in practice, depending on the intended purpose.

3.3.1 DIGITAL ANALYSIS OF HOLOGRAMS

Phase-shifting holograms

The phase-shifting digital holography process entails capturing multiple

interferograms that each indicate the optical phase relationships between light returned from all

sampled points on the illuminated surface and a controlled reference beam of light that is collinear

to the object beam (in-line geometry). From a set of these interferograms, holograms are computed

that contain information defining the shape of the surface. Multiple holograms gathered at multiple

laser light wavelengths are then combined to compile the full shape of the illuminated object over

its full dimensional extent.

Off-axis configuration

At the off-axis configuration where a small angle between the reference and the

object beams is used. In this configuration, a single recorded digital hologram is sufficient to

reconstruct the information defining the shape of the surface, allowing real-time imaging.

Multiplexing of holograms

Digital holograms can be numerically multiplexed and demultiplexed for efficient

storage and transmission. Amplitude and phase can be correctly recovered.The numerical access to

the optical wave characteristics (amplitude, phase, polarization) made digital holography a very

powerful method. Numerical optics can be applied to increase the depth of focus (numerical

focalization) and compensate for aberration.

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Wavelength multiplexing of holograms is also possible in digital holography as in

classical holography. It is possible to record on the same digital hologram interferograms obtained

for different wavelengths.) or different polarizations

Super-resolution in Digital Holography

Superresolution is possible by means of a dynamic phase diffraction grating for

increasing synthetically the aperture of the CCD array

Optical Sectioning in Digital Holography

Optical sectioning, also known as sectional image reconstruction, is the process of

recovering a planar image at a particular axial depth from a three-dimensional digital hologram.

Various mathematical techniques have been used to solve this problem, with inverse imaging among

the most versatile.

Extending Depth-of-Focus by Digital Holography in Microscopy

By using the 3D imaging capability of Digital Holography in Amplitude an Phase it

is possible to extend the depth of focus in Microscopy.

Combining of holograms and interferometric microscopy

The digital analysis of a set of holograms recorded from different directions or with

different direction of the reference wave allows the numerical emulation of an objective with large

numerical aperture, leading to corresponding enhancement of the resolution.This technique is called

interferometric microscopy.

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CHAPTER 4

RECENT DEVELOPMENTS TO HOLOGRAPHIC DISPLAYS

Holographic displays have been investigated at Bilkent University, Ankara,

Turkey .Recently, they used SLMs for such purposes and demonstrated single and multiple SLM

holographic displays. They mostly use phase-only SLMs. For example, in a study involving only

one phase-only SLM , in-line phase holograms, which were calculated by Gerchberg–Saxton

algorithm , were used to show that reconstructions that are larger than the SLM size are feasible. In

another system, three SLMs were used to generate color holographic reconstructions . Again the

Gerchberg–Saxton algorithm was used to generate the in-line phase holograms that were written on

the SLMs. Three phase holograms were calculated separately (for red, green, and blue channel) and

loaded to the SLMs. Color light-emitting diodes (LEDs) were used as light sources; all three

reconstructions were combined to obtain a color reconstruction. Yet another system generates and

displays holograms in real time . The phase-only holograms for the display were computed using a

fast, approximation-based algorithm called accurate compensated phase-added stereogram

(ACPAS) , which was implemented on graphics processing units (GPUs) to render the holograms at

video rates. LEDs were used as light sources for reconstructions that can be observed by naked eye.

Fig.4.1 shows the overall setup for the real-time color holographic display system and Fig. 4.2(a)–

(c) shows the original color 3-D model, the computer reconstruction from the phase-only hologram,

and the optical reconstruction from the same hologram written on the SLM, respectively. They also

compared the quality of optical reconstructions obtained by using a laser and a LED as the light

source . Even though LEDs have broader spectra than lasers, they conclude that reconstructions

using LEDs can be still satisfactory in quality. In a recent prototype, a curved array of six phase-

only SLMs was used to increase the field of view. As a consequence of the achieved large field of

view, the observer can look at the optical reconstruction binocularly and see a real 3-D image

floating in the space. Reconstructions can also be observed from different angles without any

discontinuity and with a larger horizontal parallax. shows the optical reconstructions of a pyramid

recorded from different angles. The ghost-like 3-D image (a real optical image) was positioned next

to a similar physical object located at the same depth, and the recording camera was focused to that

plane; such a setup shows the depth location of the reconstruction, as well as its quality of parallax

and sharpness by providing a similar physical object for comparison. The actual size of the base of

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the pyramid is about 1 cm Â 1 cm, and its height is about 2 cm. The reconstruction (real image) is

about 50 cm in front of the SLMs. This brief overview of current state of the art indicates that

dynamic holographic displays do have the potential for highly satisfactory futuristic 3DTV displays;

however, they do not yet provide such satisfactory results to the consumer who expects the

counterpart of crisp clear conventional 2DTV displays. Further research is certainly needed.

fig 4.1 Overall setup: BEVbeam expander; BSVnonpolarized beam splitter.

fig 4.2 Color holographic reconstruction using SLMs. (a) A rigid color 3-D object. (b) Computer

reconstruction from the hologram of the 3-D object. (The hologram was calculated by using the

ACPAS algorithm.) (c) Optical reconstruction (a single frame of the holographic video)

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CHAPTER 5

WORKING SETUP OF DIGITAL HOLOGRAPHIC 3D DISPLAY SYSTEM

5.1 INTRODUCTION TO SETUP

Electro-holography is one of the common method for holographic display

researches . There are several pixelated devices which are suitable for digital holographic display

systems. Liquid crystal (LC) displays, liquid crystal on silicon (LcoS) displays, digital micro-mirror

devices are only some of them. Since all those pixelated devices modulate the incoming light in the

spatial domain, either transmissively or reflectively, they are called spatial light modulators (SLMs).

Full complex modulators would be the ultimate solution; however, most of the spatial light

modulators usually modulate only the amplitude or the phase of the incident light. In our

holographic display prototypes we use phase-only LCoS SLMs.

Although those SLMs are easy to use, have high diffraction efficiency and are rich in

term of pixel count, they are quite small in size. Typical phase-only SLM size is approximately 1cm

× 2cm. As a result of it, reconstructions are also quite small. It is almost impossible to see the

reconstructions binocularly and rotate around them when only one such SLM is used. Therefore

researchers are trying to come up with ideas to overcome this bottleneck. Maeno et al. proposed a

method to increase the size of the holographic display system and also the field of view . In their

system they use five transmissive type SLMs and place them side by side. They increase the field of

view in horizontal direction, but they discard the vertical parallax by using a lenticular sheet. Yet

another holographic display system is reported by Hahn et al. and they use mirror modules and

other optical components to increase the size of the display system . Their horizontal parallax only

(HPO) curved holographic display system provides approximately 23◦ viewing angle. A company

from Germany, called SeeReal Technologies, developed a novel technique . With the help of the

technique, only a part of the wavefront that enters to the eye pupil of the observer is reconstructed.

Different from the above systems, we propose to build a fullparallax circularly

configured multi-SLM holographic display system. We use six phase-only reflective type spatial

light modulators to increase the horizontal size of the holographic display. With the help of the

proposed system, observers can see ghost-like 3D images floating in the space binocularly with

naked eye. Methods and configurations for enlargement of the viewing angle will be presented in

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the following section. Next Section presents the optical setup and hologram generation algorithm.

Experimental results will be also presented .

5.2 ENLARGEMENT OF THE VIEWING ANGLE

For the pixelated devices, local maximum diffraction angle for Shannon recovery case can be

calculated as:

θmax = sin−1 (λfmax ), (1)

where;

(2)

Here ∆p denotes the pixel period of the device, λ is the wavelength of the incident light. Within the

limit of the local maximum frequency, we can reconstruct 3D objects larger than the SLM size .

Those reconstructions can be seen on a diffuser or a screen. However, in order to see the full

reconstruction by naked eye, 3D object should be in the viewable area (See Fig.5. 1). Otherwise

observer can only see a part of it. One way to solve this problem is to increase the hologram size

(See Fig. 5.2). Since viewable area is increased, observer can see large 3D reconstructions.

fig 5.1 Illustration of larger object reconstruction with single SLM

fig 5.2 llustration of larger object reconstruction with multiple SLM

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However, since SLMs have hard mount around it, when we place them side by side a

large gap occurs between two SLMs (See Fig.5. 3). There are methods to overcome this problem,

such as using mirror modules as in . In our system, we propose to use multiple beam splitters (half-

mirrors). As seen in Fig. 5.4, with the help of the beamsplitters, the gap between two SLMs are

filled by the image of the third SLM. The same configuration is applied to other three SLMs and

finally, these two sets are combined with a large beam-splitter (See Fig. 5.5). Therefore the resultant

hologram size increases six times in horizontal direction. This gives a freedom to the observer to

see the reconstructions binocularly and to rotate within the limit of the viewing angle.

fig 5.3 Gap between two SLM when they are aligned side by side

fig 5.4 Alignment of three SLMs to have continuous array without any gap

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fig 5.5 Schematic of the setup

5.3 OPTICAL SETUP AND HOLOGRAM GENERATION

Schematic of the setup can be seen in Fig. 5.5 The method to obtain larger hologram

size in horizontal direction described in the previous section. After aligning the six SLMs side by

side, we rotate the SLMs with the help of high precision stages to configure them cirlularly. Each

SLM is rotated by 1◦ with respect to the next SLM (This can be increased up to 3◦ ). Fine

adjustments are also needed after the rotations. Fig.5. 6 shows the front view of the holographic

display system. Continuous array of SLMs can be seen in the figure. In our experiments, we have

used computer generated 3D model of a cube. It is a wire-frame object. The model consists of a

point cloud. Each point in the point cloud has 3D coordinate and intensity information. Holograms

are calculated by using Fresnel light propagation algorithm . Each point of the 3D model propagated

to the hologram plane. Then, contributions of all the points in the point cloud are superposed to

obtain complex field at the hologram plane. Since our SLMs are phase-only, we discard the

amplitude and set to unity (plane wave illumination). Although discarding the amplitude lowers the

quality, degradations in reconstructions are acceptable. By applying the same procedure, six

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holograms are calculated one by one, by simply rotating the 3D object by the corresponding angle.

The rotation angles are −2.5◦ , −1.5◦ , −0.5◦ , +0.5◦ , +1.5◦ and +2.5◦ . Top view of the setup can be

seen in Fig. 5.7. There are two sets of Holoeye SLM modules . Each SLM module has three phase

only SLMs with 1920 × 1080 pixels each. SLMs in one module are aligned side by side by using

non-polarized cubic beam-splitters as described in the previous section. The resultant wide displays

(total of 5760 × 1080 pixels) are also combined with a plate beamsplitter (half-mirror) to obtain a

grand total of 11520 × 1080 pixels wide holographic display system. All alignments are done with

high precision stages.

Fig 5.6 Front view of the display

Fig 5.7 Top view of the display

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fig 5.8 Optical reconstruction of 3D wire-frame model of a cube. (a) Left, (b) center, and (c) right

views.

5.4 EXPERIMENTAL RESULTS

Fig. 5.8 shows the optical reconstruction of 3D wire-frame model of a cube. Pictures

are taken from different viewing angles (left, center and right). Reconstructions are captured when

laser is used as a light source. In order to avoid eye-hazard [20], LED illumination is also used and

such reconstructions are observed with naked eye. Reconstruction distance is approximately

400mm. We observed that the total field of view increased significantly. With the help of the same

configuration, we can increase the field of view and thus viewing angle by using larger number of

SLMs and larger beam-splitters.

5.5 CONCLUSION OF SET UP

The proposed system has six phase-only spatial light modulators that are aligned side

by side to obtain a 11520 × 1080 pixel wide circular holographic display system. All alignments are

accomplshed by using high precision stages. System works both with laser and LED illumination.

Optical reconstructions show that increase in the viewing angle is significant compared to single

SLM case. We conclude that circular configuration is superior than the previous planar

configurations. We also notice the parallax with the help of the optical reconstructions.

Experimental results are satisfactory and they show that circularly holographic display system

works successfully.

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CHAPTER 6

APPLICATIONS

➔ Geo-seismic and related 3D data visualization

Spatially manipulate complex data to extract key insights; communicate discoveries

across disciplines using an easily comprehensible visual representation.

➔ Medical training:

Analyze and manipulate complex physiological data sets from multiple

dimensions easily understood by experts as well as trainees. Navigate, enlarge and

manipulate the imagery to a degree limited only by data resolution.

➔ Military simulation and situational awareness:

Enable rapid understanding of regional landscapes and urbanscapes, quickly giving

viewers a feeling of familiarity that is essential for successful missions.

➔ 3D gaming:

Convey all aspects of the virtual 3D world during planning, production and post-

production; help facilitate the creation of 3D content with immediate access to all

perspectives. Your viewers can then escape into lifelike, three-dimensional entertainment

and games that explode with full-color, true-3D realism.

➔ In visual communication

Scientists are working to improve Video chat to become holography chat - or "3-

D Presence." The technique uses light beams scattered from objects and reconstructs a

picture of that object, a similar technique to the one human eyes use to visualize our

surroundings.

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➔ In holographic 3DTV applications

The holographic display technology will made revolutionary changes in the

television market.future televisions will show true 3d videos without the help of any 3d glasses

➔ In Cinema entertainment field

It will help in the true 3d projection of 3D films with a 360 ° viewing experience

➔ In cartography

It will help to create 360° viewable maps.

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CHAPTER 7

LIMITATIONS

➢ The display techniques are bit expensive

➢ The display panels for the system are not developed upto a full extent

➢ In order to create a faithful reproduction of the 3-D image of a physical object, the

holographic recording material is required to have a high sensitivity and a high resolution.

➢ The design and implementation of electronically controllable dynamic displays to support

holographic video are the key issues for the success of such true 3-D displays.

➢ Currently available devices have quite limited capabilities, and thus, do not yield

satisfactory performance, yet. We expect that such products will be significantly improved

in the future.

➢ The system will be bulky.

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CHAPTER 8

FUTURE SCOPES

This three dimensional holographic display technology will be a revolutionary

invension to many fields.In future you can chat with your friend in abroad by seeing his True 3D

video hologram in a 360° angle.We can able to see the live cricket or world cup football match at

your home as you where in the gallery with the 360° viewing angle .You will experince 3d video

call in your phone,can view the geographical features of an area through 3d hologram,can view

internal organs of our body in 3D.In future technologies like interactive skinputs will bring real time

communicatin through our gestures.

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CHAPTER 9

CONCLUSION

Digital holographic video displays are strong candidates for rendering ghost-

like “true 3-D” motion images. Interest in this technology is increasing among the research

community. Many laboratories have already reported different designs with promising results. Most

of these designs are based on SLMs; SLMs with different capabilities and specifications have been

used. Therefore, it is important to understand the limitations of such devices, and their effects on the

resultant 3-D images.

Reasonable sizes and resolutions seem to be sufficient for a stationary observer with

no lateral or rotational motion. However, the needed SLM size and pixel density quickly increase

beyond the capabilities of today’s electronic technology when such motion is allowed as in a natural

viewing environment. An alternative is to arrange planar SLMs on a curved mount to relieve the

requirement of small and high-density pixels.

Since the holograms are quite robust to quantization errors, and since frame refresh

rates are satisfactory for continuous perception, the focus of research is rather on designing digital

holographic display sets, which can effectively support more freedom in lateral and rotational

motion of the observer while providing satisfactory quality 3-D images.

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REFERENCE

1. Digital Holographic Three-Dimensional Video Displays

Onural, L.; Yaras , F.; Hoonjong Kang;Dept. of Electr. & Electron. Eng., Bilkent Univ.,̧

Ankara, Turkey, Proceedings of the IEEE April 2011

2. Reliability of 3D Imaging by Digital Holography atLong IR Wavelength

Anna Pelagotti, Massimiliano Locatelli, Andrea Giovanni Geltrude, Pasquale Poggi,

Riccardo Meucci,Melania Paturzo, Member, IEEE, Lisa Miccio, Student Member, IEEE,

and Pietro Ferraro, Senior Member, IEEE,oct 2010

3. Circularly configured multi-slm holographic display system

Fahri Yaras, Hoonjong Kang, Levent Onural ,Bilkent University Department of Electrical

and Electronics Engineering,TR-06800 Ankara, Turkey [email protected],

[email protected], [email protected]

4. Research Trends in Holographic 3DTV Displays

Levent Onural Dept. of Electrical and Electronics Eng. Bilkent University TR-06800

Ankara, [email protected]

5. www.ieee.org

6. www.digital holography.eu

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digital holographic 3d display seminar

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