COL 12(6), 060004(2014) CHINESE OPTICS LETTERS June 10, 2014
Real-time pupil tracking backlight system for
holographic 3D display
(Invited Paper)
Hyon-Gon Choo
1
, Minsik Park
1
, Hyun-Eui Kim
1
, Chanyeol Bae
2
,
Byung Gyu Chae
1
, Hwi Kim
2
, Kyungae Moon
1
, Jinwoong Kim
1
,
and Joonku Hahn
3∗
1
Electronics and Telecommunications Research Institute, Taejon 305-700, Korea
2
Korea University, Sejong Campus, Sejong 339-700, Korea
3
Kyungpook National University, Daegu 702-701, Korea
∗
Corresponding author: jhahn@knu.ac.kr
Received February 27, 2014; accepted April 4, 2014; posted online May 28, 2014
We propose an automatic three-dimensional (3D) pupil tracking backlight system for holographic 3D
display system with large image size and full-parallax accommodation effect. The proposed tracking
module is applied to a holographic 3D display system with two sets of directional holographic imaging
module composed of 2×2 large scale lens array and 22-inch high-resolution liquid cry stal display 3D panel.
System architecture is described and experimental results are presented.
OCIS codes: 090.2870, 090.1705, 090.1760.
doi: 10.3788/COL201412.060004.
Holographic three-dimensional (3D) displays have been
actively researched for generating realistic 3D images in
free space for last decades. The spatial light modulator
(SLM) technology for control and manipulation of wave
front of light wave in free space is a core technology for
the holographic 3D imaging. In practice, however, com-
mercially available SLMs have technological limitation
in pixel size, screen size, and dynamic range for realistic
holographic 3D display.
The information capacity of an SLM in holographic
3D display is theoretically represented by the space-
bandwidth product
[1]
. The space-bandwidth product is
interpreted as the product of the holographic image size
and viewing angle and its invariance means that there is
a robust trade-off relationship between image size and
viewing angle in any type of holographic 3D displays
using SLM.
With respect to engineering viewpoint, there can be
indirect methods for widening viewing angle by time-
domain technique such as fast sequential scanning of
holographic images or spatial domain technique such as
optical spatial multiplexing of independent holographic
display modules
[2−6]
.
We can take a strategy that large size image is, firstly,
secured and then the viewing angle widening issue is
resolved. The SeeReal have shown a holographic dis-
play system with the tracked viewing window (VW)
technique
[7−11]
. The directional backlight system syn-
chronized with an eye-tracking module enables observer
to see holographic image comfortably in a specified range
of a VW plane. It is known that in the system of SeeReal,
the observer’s VW should be in a specified plane distant
from the display system since the directional backlight
system can control the focal point position only hor-
izontally, thus does not provide an adaptive focusing
functionality along the axial direction. In addition, since
vertical–only hologram patterns are used, their system
cannot show full parallax accommodation effect.
In this letter, we propose an automatic 3D pupil track-
ing backlight system for holographic 3D display system
with large image size and full-parallax accommodation
effect. The pupil tracking system is composed of hy-
brid camera setup using Kinect and stereo camera and
motorized XY Z stage for 3D pupil tracking. The pro-
posed tracking module is applied to a holographic 3D
display system. The display system provides large size
stereoscopic holographic 3D images to a freely movable
observer in a real-time manner through two sets of di-
rectional holographic imaging module composed of 2×2
large scale lens array and 22-inch high-resolution liquid
crystal display (LCD) panel
[12]
.
In Fig. 1(a), the layout of one lens in the display sys-
tem is illustrated. A diverging light emitted from a point
light source is transformed to a spherical convergent wave
toward a VW created in the focal plane of the field lens.
The computer generated hologram (CGH) displayed in
the SLM generates a holographic 3D scene to the ob-
server through the narrow VW. The VW position can
be changed according to the position of the point source.
As shown in Figs. 1(b) and (c), if we can control the 3D
position of the point source, the VW tracking range can
be also a 3D volume.
The relation between the position of the VW and that
of the light source can be derived from a simple geomet-
ric optics of the field lens. If the lens is assumed to be
the first-order optical lens with an effective focal length
f
eff
, and (x
S
, y
S
, z
S
) represents the relative position of a
light source at the distance d
o
from the front principal
plane of the lens, the relative position of the VW, (x
VW
,
1671-7694/2014/060004(4) 060004-1
c
2014 Chinese Optics Letters