Occlusion-capable Head-mounted Display
Kwangsoo Kim
a
, Daerak Heo
b
and Joonku Hahn
c
School of Electronics Engineering, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu, 41566, South Korea
Keywords: 3D Displays, Head-mounted Display, Augmented Reality.
Abstract: Head-mounted display (HMD) is regarded as one of the most popular device for providing three-dimensional
(3D) contents in virtual reality (VR) or augmented reality (AR). Technologies on HMD have been deeply
studied because it has a potential to make the people enjoy 3D contents. In this paper, we propose the
application for digital micro-mirror device (DMD) as both the filter and the combiner. DMD has a benefit
that it generates many images in short time. The real background image and the image generated by the
organic light-emitting diode (OLED) are watched through the DMD, and these two images are combined as
one image to generate AR.
1 INTRODUCTION
Head-mounted display (HMD) is one of the most
prospective systems to display 3D contents (Inoguchi
et al., 1995, Ando et al., 1998, Cakmakci et al., 2004,
Rolland et al., 2005, Hong et al., 2011, and Arens-
Arad et al., 2016). Since HMD is the best device for
representing VR and AR, many research groups have
developed these technologies (Earnshaw, 1993,
Drascic et al., 1996, Ando et al., 1999, Zhou et al.,
2008). Occlusion capability and accommodation
effect are very important factors in enhancing the
reality of 3D contents in HMD. In consideration of
accommodation effect, the holographic technique is
ideal to provide 3D contents within diffraction limit
(Moon et al., 2014 and Gao et al., 2017). However,
the narrow viewing window owing to the space-
bandwidth of the spatial light modulator (SLM) is a
practical problem (Lohmann et al., 1996). In addition,
it brings about the sacrifice of the quality of 3D
contents resulting from annoying speckle noise. The
occlusion capability is necessary to block the
appearance of some background part where the 3D
contents appear (Kiyokawa et al., 2004 and Wilson et
al., 2017). In occlusion-capable HMDs, two
components are required, one is an SLM for selective
pass of the environmental scene and the other is a
combiner to overlay the selectively filtered
a
https://orcid.org/0000-0002-9786-6921
b
https://orcid.org/0000-0002-0446-4991
c
https://orcid.org/0000-0002-5038-7253
environmental scene and the virtual contents. Some
multi-layered displays meet the purpose of occlusion
capability (Lim et al., 2017). Triple-layered LC can
function as displaying near and far contents and
selectively filtering one of them (Kim et al., 2017).
In this paper, we designed a novel HMD using a
DMD as both filter and combiner. In IMID 2018, we
already presented its concept (Kim et al., 2018). The
DMD has a benefit that it can generate many images
in a short time (Cossairt et al., 2004, Kim et al., 2016,
and Lim et al., 2017). In addition, the DMD combines
the background image and 3D contents reproduced on
the OLED, allowing observers to watch the image
with low distortion.
2 OPTICAL DESIGN OF
OCCLUSION-CAPABLE HEAD
MOUNTED DISPLAY
This system consists of two parts, OLED part and
background part. Figure 1 shows the optical design of
the system. In Fig. 1(a), the optical path of the whole
system is shown. The real scene is seen through the
HMD as a background and the 3D images is displayed
by the OLED. These two images are combined by the
DMD selectively by choosing the state of the DMD
Kim, K., Heo, D. and Hahn, J.
Occlusion-capable Head-mounted Display.
DOI: 10.5220/0007612702990302
In Proceedings of the 7th International Conference on Photonics, Optics and Laser Technology (PHOTOPTICS 2019), pages 299-302
ISBN: 978-989-758-364-3
Copyright
c
2019 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
299
between on sate and off state. Therefore, the observer
watches the combined image through the DMD.
Figure 1(b) shows 4f system including the DMD. The
images from the outside and the image from the
OLED are projected on the DMD through the first 4f
system, and each image are combined and relayed to
the observer by the second 4f system.
When we design the system, we use small size
optical elements in order to build a compact HMD.
The OLED is useful since backlight is not required
for displaying 3D contents.
(a)
(b)
Figure 1: Occlusion-capable head-mounted display; (a)
system layout, (b) 4f system including the DMD.
Figure 2: Optical layout using Zemax.
Figure 2 shows the optical layout. This was
designed with a Zemax. The distance from the lens to
the observer that is the size of the main optical system
of the HMD is about
100 100mm mm
. Since the
optical system is designed in a limited space, we use
an aspheric lens with large F/#. In addition, it is
difficult to design a small lens with a large refraction
angle at a short distance, so that two aspheric lenses
are placed in serial to shorten the focal length.
3 EXPERIMENT
This system uses both the OLED and the DMD. Table
1 and 2 show the specification of them respectively.
The OLED has an active area with 38.1
mm
30.5
mm
and its resolution is 1,280
1,024 with the pixel
pitch 29.7
m
. 3D contents generated by the OLED
are projected on the DMD. As the DMD, V7001
model made by Vialux corporation is used. It has an
active area with 14.0
mm
10.5
mm
and the
resolution is 1,024
768 with the pitch 13.7
m
. In 6-
bit gray level mode, the switching rate of the
micromirror is 1,091 Hz. We made a program code
by Matlab to control the DMD.
This setup is constructed to prove the feasibility
of our idea. So, we set up our system on the optical
breadboard and it is not proper for the observer to
wearing this system. For the purpose that our compact
system is made compact as a wearable system, there
remains several issues such as minimizing the control
board of the DMD and the OLED.
Table 1: The specification of OLED.
OLED
Video input type
OLED resolution
Refresh rate
Active area
mm
mm
Table 2: The specification of DMD.
DMD
Vialux V7001
DLP chipset
Discovery 4100
DMD resolution
XGA (1024
768)
Micro-mirror pitch
13.7
m
Active mirror array
area
14.0
mm
10.5
mm
Array switching rate
1bit B/W
22,727 Hz
Array switching rate
6bit Gray
1, 091 Hz
Array switching rate
8bit Gray
290 Hz
PHOTOPTICS 2019 - 7th International Conference on Photonics, Optics and Laser Technology
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Figure 3: System setup of occlusion-capable head-mounted
display.
4 CONCLUSIONS
In this paper, we proposed a novel HMD with a DMD
and an OLED where the DMD functions as both filter
and combiner. With this system, the observer watches
both the environmental scene and the virtual contents.
The virtual contents are displayed by the OLED and
they are combined with the environmental scene at
the DMD. With our setup, we succeed in proving the
feasibility of our idea. For the next step, we have a
plan to make the system compact suitable for the user
to wear it.
ACKNOWLEDGEMENTS
This research was supported by Basic Science
Research Program through the National Research
Foundation of Korea (NRF) funded by the Ministry
of Education (NRF- 2017R1D1A3B03035831).
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