Electrically tunable holographic waveguide display based
on holographic polymer dispersed liquid crystal grating
Zhihui Diao (刁志辉)
1
, Lingsheng Kong (孔令胜)
1
, Junliang Yan (闫俊良)
1
,
Junda Guo (郭俊达)
1
, Xiaofeng Liu (刘小沣)
1
, Li Xuan (宣 丽)
1
, and Lei Yu (于 磊)
2,
*
1
Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China
2
Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China
*Corresponding author: yulei@aiofm.ac.cn
Received August 14, 2018; accepted November 12, 2018; posted online December 25, 2018
In this Letter, we present an electrically tunable holographic waveguide display (HWD) based on two slanted
holographic polymer dispersed liquid crystal (HPDLC) gratings. Experimental results show that a see-through
effect is obtained in the HWD that both the display light from HWD and the ambient light can be clearly seen
simultaneously. By applying an external electric field, the output intensity of the display light can be modulated,
which is attributed to the field-induced rotation of the liquid crystal molecules in the two HPDLC gratings.
We also show that this electrically tunable performance enables the HWD to adapt to different ambient
light conditions. This study provides some ideas towards the development of HWD and its application in
augmented reality.
OCIS codes: 230.3720, 160.3710, 050.1950, 090.2890.
doi: 10.3788/COL201917.012301.
Recently, augmented reality (AR) has become a hot re-
search topic, as it can build a bridge b etween the virtual
world and real world, which enables people to ob ta in
virtual information while being immersed in the real
environment
[1,2]
. As the key display element in AR, holo-
graphic waveguide display (HWD) based on volume
holographic gratings has attracted a great deal of inter-
est, since it shows some advantages of high see-through
transmittance, small size, light weight, and low cost,
which is suitable f or near-eye display
[3,4]
. Many research-
ers have done excellent work on HWD to improve its
display characteristics, such as full-color display
[5,6]
,
color uniformity optimization
[7,8]
, field of view enlarge-
ment
[9]
, exit pupil expansion
[10,11]
, and efficiency improve-
ment
[12,13]
. Among these reports, however, no report has
been devoted to solving the problem that is the intensity
mismatch between the display light of virtual informa-
tion and the ambient light of the real environment. It
is well known that the display light generated by a
micro-display source always has a more stable intensity
compared to the variable ambient light
[3,4]
. When the am-
bient light darkens (e.g., driving a car into a tun nel from
open-air), the display light would become relatively
stronger for the hu man eyes. The excessive intensity con-
trast ratio between display light and ambient light would
not only reduce the m erging effect between virtual infor-
mation and real environment, but also lead to viewing
fatigue or even serious visual discomfort, such as head-
aches
[14]
. Similarly, when the ambient light brightens,
the display light would become relatively weaker so that
the people can hardly recognize the virtual information.
Therefore, the intensity mismatch between display light
and ambient light will b e a serious problem that limits
the application of HWD in AR.
In this Letter, to solve that problem, we present an elec-
trically tunable HWD based on two slanted holographic
polymer dispersed liquid crystal (HPDLC) gratings, which
are utilized to couple in and couple out the display light,
respectively. The HPDLC grating, formed by photopoly-
merization-induced phase separation
[15–17]
, has the merits
of ease of fabrication, rapid and large-area prototyping,
low cost, and electrically tunable capability
[18]
.Thediffrac-
tion efficiency of the HPDLC grating can be tuned under
the electric field
[15]
, because the liquid crystal (LC) mole-
cules in the grating are electro-optical birefringent materi-
als, and their refractive indices can be changed due to the
field-induced rotation
[19]
. In the HWD, the output intensity
of the display light is highly dependent on the diffraction
efficiency of the grating
[3,12]
, so the tunable HPDLC grating
provides a method to modulate the display light. Experi-
mental results show that when the input intensity of the
display light is fixed at 374 μW, the output intensity can
be modulated from 199 to 9 μW by increasing the
external electric field. During the modulation process, no
optical apparatuses are moved or altered, but only the elec-
tric field is changed. Therefore, the output intensity of the
display light from the HWD can be modulated actively and
simply according to the variance of the ambient light, and
then the intensity mismatch problem can be solved. It
should be noted that the HPDLC grating has been used
to fabricate the HWD previously
[20]
, but the electrically tun-
able performance of HWD and its tuning mechanism have
not been investigated. Therefore, this Letter is the first
time, to the best of our knowledge, that an electrically tun-
able HWD is presented, showing its potential to improve
the environmental adaptability of HWD.
Figure
1 shows the fabrication process of the proposed
HWD. Two indium tin oxide (ITO)-coated glasses were
COL 17(1), 012301(2019) CHINESE OPTICS LETTERS January 10, 2019
1671-7694/2019/012301(5) 012301-1 © 2019 Chinese Optics Letters