COL 11(Suppl.), S21102(2013) CHINESE OPTICS LETTERS September 30, 2013
Single 3D laser projector with speckle suppression
Lei Dong (
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), Anting Wang (
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∗
, Fugui Yang (
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), Shulu Wang (
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Lixin Xu (
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), Chun Gu (
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), and Hai Ming (
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Department of Optics and Optical Engineering, Anhui Key Laboratory of Optoelectronic
Science and Technology, University of Science and Technology of China, Hefei 230026, China
∗
Corresponding author: atwang@ustc.edu.cn
Received July 2, 2013; accepted August 20, 2013; posted online August 25, 2013
In this letter, a new single three-dimensional (3D) laser projector is proposed. As liqu id crystal (LC) can
produce two image patterns with orthogonal polarization states at 120 Hz, only one projector is required
in this approach for reconstruction of a 3D object. The light source is made up of RGB (red, green, and
blue) lasers because laser has lots of advantages such as longer life, higher brightness, and larger color
gamut. A novel diffusive media with good polarization-maintaining quality is u sed as rear p rojection
screen for its high transmission efficiency (∼90%) and low reflection efficiency. When laser incidents into
the diffusive media, which contains lots of spherical particles with sizes between 2 and 15 µm, laser is
scattered randomly and th e laser speckle is reduced. A spatial p hase mask is also inserted into the optical
path to reduce speckle. With these techniques, the speckle c ontrast is reduced t o 0.1 and the quality of
image patterns has been greatly improved.
OCIS codes: 110.0110, 140.0140, 230.0230, 290.0290, 330.0330.
doi: 10.3788/COL201311.S21102.
Nowadays, three-dimensional (3D) display technology
has been used widely in aerospace, military, medical, de-
sign, and entertainment due to its possibility of providing
comprehensive information of object in the 3D sense of
depth
[1,2]
. Most of the 3D display products based on
binocular dispar ity in the market are polarization-based
style and shutter-based style. In cinemas, polarization-
based style 3D display equipment with two projectors
are used very popularly but there are many disadva n-
tages. For example, two projectors are expensive, it’s
very cockamamie to synchronize the two electrical signa ls
and overlap the two optical paths, a nd the silver screen
with good polarization-maintaining quality is very ex-
pens ive. So it’s not appro priate for home use. To meet
this challenge, shutter glasses have been used to replace
polarization glasses. With a receptor in the g lasses, the
liquid crystal (LC) shutter glasses can alternately accept
the corresponding images in different eyes. But there
also have some disadvantages: the glasses before two
eyes alternately sw itch on/ off state and it make eyes
feel tired soon
[3]
, and the shutter glasses are much more
exp ensive and bulky than polarization glasses. To avoid
all these unfavorable factors mentioned above, we use
high-speed (120 Hz) LC polarization rotator before pro-
jection system to change images’ polarization states, and
the stereo images can be seen from general polarization
glasses.
Besides, Xe lamps are used as light sources of projec-
tors very p opularly, whose lives are no more than 1 000
hours. Relatively, laser diodes (LD) ca n be used for more
than 100 000 hours, and it has lots of advantages such as
high brightness, large color gamut, and good polariza-
tion. However, the speckle limits the display application
of the laser. Speckle are random spots with grainy struc-
tures arise in space when rough s urface is illuminated
with la ser. The formation of speckle is due to coherent
supe rimposition of all the wavelets emanating from the
“random” rough surface
[4]
, and it is regarded as noise
that always re duces the images’ quality. Several tech-
niques have been proposed to remove speckle noise, such
as a rotating diffuser
[5,6]
, moving diffuser
[7,8]
, moving
screen
[9,10]
and some o ther approaches
[11,12]
. The use of
rotating diffuser is well known a s one speckle reduction
method. A rota ting diffuser produces variable r andom
phase patterns s e quentially at the diffusion point, so the
objective speckle is averaged out on a screen. Although
this method is effective in reducing objective speckle,
it barely dec reases subjective speckle that generates on
the screen
[13]
. The reason for the r e maining subjective
sp e ckle is that the speed of the phase modulation by
using a rotating diffuser is not enough to eliminate the
phase difference of surface height fluctuation. And me-
chanical principle has a major disadvantage that large
area is needed
[14]
. Thus another speckle suppression
method with small space and high efficiency is needed.
Based on LC polarization rotation characteristics, a
novel single 3D laser projector is proposed, and laser is
used as light source. By the use of re ar projection scre e n
and a vibrant diffuser, laser s peckle limited to 0.1 can be
achieved. Therefo re, the movie-going expe rience can be
hugely impr oved by using the proposed system.
As shown in Fig. 1, the 3D projection system is con-
sisted of three parts: light s ource, projection system, and
3D control sy stem.
The light source is comprised of three kinds of lasers.
The red LD arr ay is made up of four LDs (ML520G71,
Mitsubishi, Japan) with wavelength of 632 nm w hich
have an output of 300 mW each. The blue LD array
is made up of two LDs (NDB7112E, Nichia, Japan)
with wavelength of 450 nm which have an output
of 50 0 mw each. Green las er is the combination of
LD pumped Nd:YAG laser with wavelength of 1 064
nm and periodically poled lithium niobate (PPLN)
for quasi-phase-matched second har monic generation.
It has an output of 1 000 mW with wavelength of
532 nm. Different mirrors reflect laser to the same
1671-7694/2013/S21102(5) S21102-1
c
2013 Chinese Optics Letters