WO2003096104A1

WO2003096104A1 - Multiview stereoscopic 3d display device using volume holographic optical element

Info

Publication number: WO2003096104A1
Application number: PCT/KR2002/000523
Authority: WO
Inventors: Eun-Soo Kim; Byung-Chul Cho
Original assignee: Maxsoft Co., Ltd
Priority date: 2002-03-26
Filing date: 2002-03-26
Publication date: 2003-11-20
Also published as: AU2002243053A1

Abstract

The present invention relates to a multiview stereoscopic 3D image displaying device using a volume holographic optical element (“VHOE”). According to the present invention, a device for displaying a multiview stereo 3D image using the VHOE is comprises the following: an image source; an interference beam generator for generating first and second interference beams; a first interference beam controller for controlling an incidence angle of the first interference beam; a second interference beam controller for controlling an incidence angle of the second interference beam; a synchronization signal controller for controlling the first the interference beam controller and the second interference beam controller to synchronize the time-divisional multiview image with the first interference beam and the second interference beam; and a display for diffracting the multiview stereo image that is synchronized with the first interference beam and the second interference beam, whose incidence angles are controlled, toward each multiview direction in order to display images.

Description

MULTIVIEW STEREOSCOPIC 3D DISPLAY DEVICE USING VOLUME

HOLOGRAPHIC OPTICAL ELEMENT

Technical field of the invention

The present invention relates to a multiview stereoscopic 3D image displaying

device using a volume holographic optical element(hereinafter 'VHOE'). In particular,

the multiview stereoscopic 3D image displaying device reproduces a stereo 3D image

by diffracting the multiview images in a predetermined direction time-divisionally.

Background of the invention

The "Information Super Highway" being discussed in the developed countries

including Korea is the basis for a broadband digital network that will be constructed in

the future. It is expected that the services through the Information Super Highway will

be developed from a "Just See and Listen" multimedia service on the conventional

digital device to a "More Naturally and Actually See and Listen" real 3D multimedia

service on a 3D information device. Especially, the 3D image display technology

having various application fields, for example, broadcasting, communication, game,

education, military, aviation, medical service, etc., is the core of next generation

information communication, which is under a very competitive development race.

According to the recommendation of the CCIR working group in 1958, the predecessor of the ITU, the 3D display technology must comply with several

requirements as follows: (1) an auto-stereoscopic type that does not cause eye fatigue,

(2) higher resolution than the conventional flat panel display, and (3) compatibility with

the conventional 2D display and multiple seeing and hearing. The articles about CCIR

recommendation have become the core of 3D image display technology, and various

solutions for satisfying them have been developed.

To the present, conventional technologies for implementing a 3D display device

exist as follows: a lenticular method, a parallax barrier method and an optical element

method that all use the binocular parallax, along with an IP(integral photography)

method, and a volume type displaying method, providing full parallax. Since the

lenticular method and the parallax barrier method are types of the auto-stereoscopic

method, many studies have been conducted on them. However because the lenticular

method and the parallax method are types of spatial-sequential methods, it is difficult to

implement a 3D device for displaying non-artificial images due to the limitation of a

visual point, a giddiness, and the limitation of peripheral element. Also, studies

regarding an IP method as a method for supporting a 3D image and full color are being

conducted by NHK in Japan. Regardless, because of the precise arrangement between

pickup and display and the aberration of micro-lens array, the IP method cannot

reproduce the perfect 3D image. Also, there are many problems due to the super

multiview caused by the physical limits of the elements. To the contrary, the Rainbow Group of Cambridge University, England, has

developed a time-divisional multiview stereo 3D image display method as opposed to

the conventional space-divisional method. Still the device developed by the Rainbow

Group requires a high frame rate CRT, and complicated control and synchronization for

forming a visual region at each visual point in the display.

Recently, to overcome the aforementioned problems of the conventional 3D

display methods, a time-divisional multiview stereo image display method using VHOE

has been proposed. This method, after manufacturing the NHOE by multiplexing

recording on the multiview diffraction grating of the optical recording medium having

Bragg's angle selectivity, diffracts the multiview images of the flat display at high

speed toward the predetermined directions time-divisionally to display the images.

These NHOE methods require an optical recording medium having high

diffraction efficiency and angle selectivity. Recently, many studies have been conducted

regarding a photopolymer to serve as a new optical recording medium in various fields

such as 3D image display, holographic memory, HOE(holographic optical element), etc.

In particular when the photopolymer can be used to produce a hologram only through a

dry process, unlike a dry photographic plate that needs a wet process, and

self-development and fixation is accomplished by exposure, it is very easy to process

and the hologram has a high diffraction rate. Summary of the invention

The primary object of the present invention is to provide a device for displaying

a multiview stereo 3D image using NHOE in order to overcome the aforementioned

problems: (1) the limitation of visual point, a giddiness, and the limitation of peripheral

element of the lenticular method and the parallax method, (2) the precise arrangement

between pickup and display and the aberration of a micro-lens array of the IP method,

and a high frame rate CRT, and (3) complicated control and synchronization for

forming a visual region at each visual point in the display of Rainbow's device.

Another object of the present invention is to provide a device for displaying a

multiview stereo 3D image, which can display a 3D image spatially by time-divisionally

reading the multiview images of a flat display at high speed and diffracting the read

images toward a predetermined direction through a NHOE where eight diffraction

gratings that correspond to eight multiviews are multiplexing recorded.

To achieve aforementioned objects, according to the present invention, there is

provided a device for displaying a multiview stereo 3D image using NHOE(Nolume

Holographic Optical Element), the device comprising: an image source for providing a

time-divisional multiview image; an interference beam generator for generating a first

interference beam and a second interference beam; a first interference beam controller

for controlling an incidence angle of the first interference beam; a second interference

beam controller for controlling an incidence angle of the second interference beam; a synchronization signal controller for controlling the first interference beam controller

and the second interference beam to synchronize the time-divisional multiview image

with the first interference beam and the second interference beam; and a display for

diffracting the multiview stereo image that is synchronized with the first interference

beam and the second interference beam, whose incidence angles are controlled, toward

each multiview direction in order to display images.

The interference beam generator comprises: a laser source; a first shutter, being

located at the output of the laser source, for shutting the output of the laser source; a

spatial filter for diffusing the laser source's output that passed through the first shutter;

and a beam splitter for dividing the laser source's output, which is inputted from the

spatial filter, into the first interference beam and the second interference beam.

The first interference beam controller comprises: a focusing lens pair, being

located at the output of a first interference beam outputting means of the interference

beam generator, for focusing the first interference beam; a rotatable mirror for reflecting

the focused first interference beam so that the focused first interference beam and the

focused second interference beam are inputted to the display while being maintained at

a predetermined angle; and an incidence angle controlling lens for changing the

incidence angle of the reflected first interference beam.

The second interference beam controller comprises: a focusing lens pair, being

located at the output of a second interference beam outputting means of the interference beam generator, for focusing the second interference beam; a rotatable mirror for

reflecting the focused second interference beam so that the focused first interference

beam and the focused second interference beam are inputted to the display while being

maintained at 30° ; and an incidence angle controlling lens for changing the incidence

angle of the reflected second interference beam.

The display comprises: a NHOE upon which diffraction gratings corresponding

with the number of multiviews are recorded for the first interference beam and the

second interference beam to be diffracted toward each multiview direction; an LCD

SLM(spatial light modulator) for time-divisionally displaying the multiview images that

are synchronized with the first interference beam and the second interference beam,

both incident upon the NHOE; and a holographic diffuser for preventing cross talk of

the multiview images that are reproduced by the NHOE and the LCD SLM.

The device records the diffraction gratings corresponding to the number of

multiviews on the NHOE by using the first interference beam and the second

interference beam as a reference beam and an object beam, respectively.

The number of the multiviews is 8.

Brief description of drawings

FIG. la shows the principle of multiple diffraction grating recording.

FIG. lb shows the wave vectors of interaction corresponding to the reference beam and the object beam.

FIG. 2 is a concept of the multiview 3D display device using NHOE.

FIG. 3a shows the process of recording diffraction gratings having multiview

images.

FIG. 3b shows the process of reproducing the multiview images.

FIG 4 is a schematic of device of displaying multiview stereo 3D image

according to the present invention.

Embodiments

Hereinafter, the preferred embodiment of the present invention will be

described with the accompanying drawings. Before elaborating with the detailed

description, the multiview NHOE will be described here.

FIG. la shows the principle of multiple diffraction grating recording. Generally,

the multiview NHOE is produced through multiplexing recording the multiview

diffraction gratings on a volume optical recording medium having Bragg's angle

selectivity. When a reference beam is projected onto the NHOE while being

synchronized with the multiview images on the flat display at high speed, each

multiview image is diffracted toward the time-divisionally determined directions and

displayed.

The principle of recording and reproducing the diffraction grating by multiview on NHOE will be described briefly. Firstly, assume the electric fields of an object beam

and a reference beam for recording the angle multiplexed 8-view diffraction grating are

indicated below as nos. (1) and (2):

E_t = 4 exp[j(wt - k_t ^■ r)] (i=l,2~ 8) (1)

E_R = A_R exp[/(wt - k_R ^• r)] (R=l,2~ 8) (2)

where, Aj and A_R are the amplitude of electric fields of the object beam and the

reference beam respectively, w is an angular frequency, and kj and kβ represent wave

vectors of the object beam and the reference beam respectively. Also, the interference

pattern when the time-divisionally interference of two different beams Ej and E_R occurs,

in which both correspond to 8 views, can be represented below as no. (3).

/ =\E_t + E_R |² =|4 |² + | A_R |² +A A_R cx_P(-]K-r) ₊ A_iA_R ^* exp(-jK -r) (3)

where, K is a wave vector of diffraction grating, which is formed by incidence

of the reference beam and the object beam, and can be represented below as no. (4).

K = k₂ -k_x (4)

As indicated in no. (4) above, \K \= 2πl A and A represent the period of the

interference pattern. Due to the change of a diffraction ratio, the pattern recorded on the

recording medium works as a diffraction grating. Thus, if the reference beam is

projected onto the diffraction grating, the parallel surfaces of the grating diffract the

reproduction beam when Bragg's condition sin Φ = λ /2 Λ is satisfied. Accordingly,

Φ represents the angle between the grating and the projected reference beam. Thus, if the reference beam is projected with θ' different from that of diffraction grating

recording, then Bragg's condition sin #' = /2Λ is not satisfied and there is no

reproduction beam. For this result, the object beam is reproduced only when the

incidence angle of light in the reproduction is the same as the incidence angle of light in

the recording.

FIG. lb shows the wave vectors of interaction corresponding to the reference

beam and the object beam. Referring to FIG. lb, though the reference beam is projected

into the same region when being projected on the recording medium, each wave vector

of the reference beam has different directional characteristics. That is, as shown in FIG.

lb, the interferences with the object beam and the different reference beam, both having

the same vector, form grating vectors that are different from each other. Thus, when the

object beam is intercepted and the reference beam is projected on the recording medium,

object beams having different directional information corresponding to each reference

beam are reproduced. Thus, in the present invention, an 8-view VHOE is produced by

use of a holographic high-density angle multiplexing technique, and a device for

displaying an 8-view stereo 3D image is implemented.

FIG. 2 shows a concept of the multiview 3D display device using NHOE.

VHOE of the multiview 3D display device is implemented by angle multiplexing

recording the diffraction gratings corresponding with the number of views using multiplexing recording characteristics. Also, the multiview 3D display device displays

multiview images spatially by time-divisionally projecting the multiview images, which

are inputted to the flat display at high speed, while being synchronized with the

reference beam of the multiplexed diffraction gratings. Furthermore, a holographic

multiplexing memory technique that effectively records and reproduces diffraction

gratings as many times as required to correspond with the number of view images is

needed to time-divisionally display the multiview stereo images.

Referring to FIG. 2, if the view direction data to be recorded on the VHOE is

defined by the angle of the reference beam, each of the view direction data can be

reproduced as fast as the change of the beam's angle. Thus, when using an electric beam

scanner like an AOD(Acousto-Optic Deflector) 10, 20, then high-speed random access

is possible without mechanical error. Namely, if two laser beams(reference beam and

object beam), which are electrically controlled by the AOD 10, 20, interfere with each

other in the photopolymer, then diffraction grating patterns are formed in the

photopolymer. The view direction data recorded in the form of a diffraction gratings

pattern can be reproduced by projecting a reference beam with the same angle(or wave

length, phase code) that was used when the view direction data was recorded. When

passing through the diffraction grating formed in the photopolymer, the reference beam

is diffracted in a direction corresponding to a projecting direction of the object beam,

and synchronization of the AOD 10, 20 for controlling LCD and the reference beam is required. Thus, the multiview stereo images reproduced by high-speed LCD are

diffracted to the predetermined direction whenever the synchronized reference beam is

projected on the VHOE.

FIGS. 3a and 3b show the process of recording diffraction gratings having

multiview and reproducing the multiview, respectively. After producing the VHOE by

multiplexing recording the diffraction gratings corresponding with the number of

multiviews on the photopolymer(See FIG. 3a), multiview stereo 3D images can be

reproduced by time-divisionally projecting images of any view on the VHOE (See FIG

3b).

FIG. 4 is a schematic view of the device for displaying a multiview stereo 3D

image according to the present invention. The laser source 100 is an Nd-YAG argon

laser having a 532 nm wavelength, and generates two interference beams to be

projected to the VHOE.

The first shutter 110 is located at the output of the laser source 100, and shuts

the first interference beam(or the reference beam) and the second interference beam(or

the object beam) simultaneously.

The spatial filter 120 diffuses the laser beam that passed through the first

shutter 110, removes the high frequency noises, and prevents distortion of the laser beam.

The beam splitter 200 is located at the output of the spatial filter 120, and splits

the laser beam that passed through the spatial filter into the first interference beam and

the second interference beam. The beam splitter 200 can split the laser beam by 130° in

order to maintain an optimal angle of 2Θ = 30 for the first interference beam and the

second interference beam.

The first focusing lens pair 210, 215 is located at the first interference beam

output of the beam splitter 200, and focuses the first interference beam.

The first rotatable mirror 300 controls the first interference beam, which is

focused by the first focusing lens pair, to maintain the projecting angle of the first

interference beam and the projecting angle of the second interference beam to be

2Θ = 30° . The radius of the first rotatable mirror is 3 inches, and the rotatable mirror is

rotated by a step motor having 0.02° angle resolution. When recording diffraction

grating on the VHOE 410, the first rotatable mirror 310 causes the first interference

beam to interfere with the second interference beam through an angle multiplexing by

1.2° based on Bragg's angle of the first interference beam and the second interference

beam.

The first incidence angle controlling lens pair 302, 304 changes the incidence

angle of the first interference beam that is reflected by the first rotatable mirror 300.

Total focal distance of the controlled path of the first interference beam is 2fι + 2f₂, where fi is the focal distance of the first incidence angle controlling lens 302, and f₂ is

the focal distance of the first incidence angle controlling lens 304. The direction of the

diffraction beam, which is diffracted by the VHOE 410, is determined by the incidence

angle of the object beam; also the direction must be assigned to eight diffraction

gratings respectively. Thus, the first rotatable mirror 300 (a convex lens having 3 inches

radius), must be appropriately controlled for angle multiplexing after arraying the

second lens pair horizontally. At this time, the control angle θ of the first rotatable

mirror 300 for recording eight diffraction gratings by angle multiplexing must be

controlled identically with the incidence angle θ of recording medium.

The first interference beam controller is composed of the first focusing lens pair

210, 215, the first rotatable lens 300, and the first incidence angle pair 302, 304. The

second shutter 115 is located at the second interference beam output of the beam splitter

200, and shuts the second interference beam. The second focusing lens pair 220, 225 are

located at the second interference beam output of the beam splitter 200, and focus the

second interference beam.

The second rotatable mirror 350 controls the second interference beam, which

is focused by the second focusing lens pair, to maintain the projecting angle of the first

interference beam and the second interference beam to be 2Θ = 30° . The radius of the

second rotatable mirror 350 is three inches, and the second rotatable mirror 350 is

rotated by a step motor having 0.02° angle resolution. When recording diffraction grating on the VHOE 410, the second rotatable mirror 350 causes the first interference

beam.

The second incidence angle controlling lens pair 352, 354 change the incidence

angle of the second interference beam that is reflected by the second rotatable mirror

350. Total focal distance of the controlled path of the first interference beam is 2fχ + 2f₂,

where fi is the focal distance of the first incidence angle controlling lens 352, and f₂ is

the focal distance of the first incidence angle controlling lens 354.

The second interference beam controller is composed of the second focusing

lens pair 220, 225, the second rotatable lens 350, and the second incidence angle pair

352, 354.

The display 400 comprises the VHOE 410, LCD SLM 420, and a holographic

diffuser 430, and displays 8-view 3D images through 8-direction diffraction beams that

the VHOE 410 produces by diffracting the reference beam. Namely, when projecting

the reference beam, which is synchronized with the multiview images of the high-speed

LCD SLM 420, on the VHOE 410, then images of each view are time-divisionally

diffracted to the predetermined directions to be displayed. A permeable photopolymer is

preferable for the VHOE 410 because of high angle selectivity and diffraction ratio. The

holographic diffuser 430 has 30° of a diffusion angle to preventing cross talk with the multiview diffraction beams. The present invention uses DUPONT's HRF-150-100 as

the VHOE, and SONY'S 1024X768 XGA LCD SLM as the LCD SLM for displaying

multiview stereo 3D images.

A proper pre-exposure is required for performing a stable recording on the

VHOE 410, and the present invention selects fifteen seconds as the optimal

pre-exposure time, where the radius and beam intensity of the object beam and the

reference beam are 1.25 cm and 65 / si.

The synchronization signal controller 500 synchronizes the LCS SLM 430 with

the first rotatable mirror 300 and the second rotatable mirror 350. The synchronization

signal controller 500 can display the multiview images spatially by time-divisionally

projecting multiview images on the LCD SLM 420 in synchronization with the

reference beam of the multiplexed diffraction grating. For this, the synchronization

signal controller 500 precisely controls the first rotatable mirror 300 and the second

rotatable mirror 350 to maintain the incidence angle of the first interference beam and

the second interference beam to be 2Θ = 30° and to synchronize the first interference

beam and the second interference beam with the multiview images.

The image source 600 is connected to the synchronization signal controller 500,

and inputs the multiview image to the LCD SLM 420 of the display.

An LCD driver 415 is connected between the synchronization signal controller

500 and the LCD SLM 420, and drives the LCD SLM 420 to time-divisionally display the multiview image spatially.

Although the present invention has been described with the preferred

embodiment, the spirit and the scope of the present invention will be determined only

by the following claims. Also, it will be apparent for those skilled in the art that

modifications or amendments to the aforementioned embodiment within the spirit and

the scope of the present invention are possible without departing from the boundary of

the claimed invention.

Industrial applicability

The present invention, as previously described, is a device for displaying a

multiview stereo 3D image. The device according to the present invention can display a

3D image spatially by time-divisionally reading the multiview images of a flat display

at high speed and diffracting the read images toward a predetermined direction through

a VHOE whereby 8 diffraction gratings corresponding to 8 multiviews are multiplexing

recorded.

Claims

1. A device for displaying a multiview stereo 3D image using VHOE( Volume

Holographic Optical Element), said device comprising:

an image source for providing a time-divisional multiview image;

an interference beam generator for generating a first interference beam and a

second interference beam;

a first interference beam controller for controlling an incidence angle of the first

interference beam;

a second interference beam controller for controlling an incidence angle of the

second interference beam;

a synchronization signal controller for controlling the first interference beam

controller and the second interference beam to synchronize the time-divisional

multiview image with the first interference beam and the second interference beam; and

a display for diffracting the multiview stereo image that is synchronized with

the first interference beam and the second interference beam, whose incidence angles

are controlled, toward each multiview direction in order to display images.

2. The device as stated in claim 1, wherein said interference beam generator comprises:

a laser source;

a first shutter, being located at the output of said laser source, for shutting the output of said laser source;

a spatial filter for diffusing said laser source's output that passed through said

first shutter; and

a beam splitter for dividing the laser source's output, which is inputted from

said spatial filter, into the first interference beam and the second interference beam.

3. The device as stated in claim 1, wherein said first interference beam controller

comprises:

a focusing lens pair, being located at the output of a first interference beam

outputting means of said interference beam generator, for focusing the first interference

beam;

a rotatable mirror for reflecting the focused first interference beam so that the

focused first interference beam and the focused second interference beam are inputted

to said display while being maintained at a predetermined angle; and

an incidence angle controlling lens for changing the incidence angle of the

reflected first interference beam.

4. The device as stated in claim 1, wherein said second interference beam controller

comprises:

a focusing lens pair, being located at the output of a second interference beam outputting means of said interference beam generator, for focusing the second

interference beam;

a rotatable mirror for reflecting the focused second interference beam so that

the focused first interference beam and the focused second interference beam are

inputted to said display while being maintained at a predetermined angle; and

an incidence angle controlling lens for changing the incidence angle of the

reflected second interference beam.

5. The device as stated in claim 1, wherein said predetermined angle is 30°

6. The device as stated in claim 1, wherein said display comprises:

a VHOE upon which diffraction gratings corresponding with the number of

multiviews are recorded for the first interference beam and the second interference

beam to be diffracted toward each multiview direction;

an LCD SLM(spatial light modulator) for time-divisionally displaying the

multiview images that are synchronized with the first interference beam and the second

interference beam, both incident upon said VHOE; and

a holographic diffuser for preventing cross talk of the multiview images that are

reproduced by said VHOE and said LCD SLM.

7. The device as stated in claim 1, wherein said device records the diffraction gratings

corresponding to the number of multiviews on said VHOE by using the first

interference beam and the second interference beam as a reference beam and an object

beam, respectively.

8. The device as stated in one of claims 1-7, wherein the number of said multiviews is 8.