Image magnified lensless holographic projection by
convergent spherical beam illumination
Chenliang Chang (常琛亮)
1,2,
*, Yijun Qi (祁怡君)
2
, Jun Wu (吴 俊)
2
,JunXia(夏 军)
2
,
and Shouping Nie (聂守平)
1
1
Jiangsu Key Laboratory for Opto-Electronic Technology, School of Physics and Technology, Nanjing Normal
University, Nanjing 210023, China
2
Joint International Research Laboratory of Information Display and Visualization, School of Electronic Science and
Engineering, Southeast University, Nanjing 210096, China
*Corresponding author: changchenliang@hotmail.com
Received July 11, 2018; accepted August 27, 2018; posted online September 21, 2018
In liquid crystal spatial light modulator (SLM)-based holographic projection, the image is usually displayed at a
distant projection screen through free space diffraction from a computer-generated hologram (CGH). Therefore,
it allows for removing of the projection lens for the sake of system simplification and being aberration free, known
as the “lensless holographic projection”. However, the maximum size of the optical projected image is limited by
the diffraction angle of the SLM. In this Letter, we present a method for the implementation of image magni-
fication in a lensless holographic projection system by using convergent spherical wave illumination to the SLM.
The complete complex amplitude of the image wavefront is reconstructed in a lensless optical filtering system
from a phase-only CGH that is encoded by the off-axis double-phase method. The dimensions of the magnified
image can break the limitation by the maximum diffraction angle of the SLM at a given projection distance.
Optical experiment results with successful image magnification in the lensless holographic projection system are
presented.
OCIS codes: 090.2870, 090.1760.
doi: 10.3788/COL201816.100901.
Attention to holographic projection has increased in the
past decade. In a traditional holographic projector, the
size of the projected images can be easily magnified
through the imaging system, which involves zoom lenses.
For example, the optical projected image could be magni-
fied by using either the 4f system
[1]
or one lens with a di-
vergent spherical illumination
[2,3]
. However, the existing
projection lenses would increase the complexity of the pro-
jection system and introduce lens aberration.
Since in holographic projection the projected image is
reconstructed via diffraction from the computer-generated
hologram (CGH), the reconstructed distance and size
of the image can be controlled digitally in the numerical
calculation of Fresnel diffraction from the image to the
CGH. Therefore, it allows abandoning bulks of imaging
and zoom lenses, also referred as lensless holographic pro-
jection
[4,5]
, and shows great potential in a variety of appli-
cations towards portable and miniature projection systems.
Generally, while the holographic projection is optically
achieved by loading the CGH into a dynamic spatial
light modulator (SLM), the concept of “lensless” in a
holographic projection system could be classified into
two categories according to the previously reported works.
(1) There are absolutely no lenses in the whole optical
setup
[4–6]
, as shown in Fig. 1(a). In this type, the direct
point light source with high divergence, such as an optical
fiber, is usually used as the illumination source, allow-
ing the realization of miniaturized holographic pico-
projectors. (2) There are no lenses existing between the
SLM and the projection screen, but a lens (or lenses)
responsible for beam collimation could be permitted before
illumination to the SLM
[7–9]
, such as in the case shown in
Fig.
1(b). Although the beam collimation lens is used, it
can still be called a “lensless” holographic projection since
the expression of “lensless” mainly refers to the substan-
tive holographic projection process that happens between
the SLM (CGH) and the screen via Fresnel diffraction. In
this Letter, our work of lensless holographic projection is
mainly focused on the second case.
In lensless holographic projection, the CGH that needs
to be loaded into the SLM is calculated from the projected
image at a given distance by using the Fresnel diffracti on
algorithms. The fast Fourier transforms (FFTs) used in
the Fresnel diffraction calculation map the CGH in the
SLM plane onto a target image in the image plane, and
then, the image size is restricted by the diffraction angle
of the used SLM. Due to the fact that the maximum
diffraction angle depends on the pixel pitch of the SLM,
the maximum reachable dimension of the projected image
is determined by the so-called Nyquist criterion of
Fig. 1. Two cases for lensless holographic projection.
COL 16(10), 100901(2018) CHINESE OPTICS LETTERS October 10, 2018
1671-7694/2018/100901(6) 100901-1 © 2018 Chinese Optics Letters