Resolution enhancement of optical scanning holography
with a spiral modulated point spread function
Ni Chen,
1
Zhenbo Ren,
1
Haiyan Ou,
2
and Edmund Y. Lam
1,
*
1
Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam, Hong Kong, China
2
Institute of Applied Physics, University of Electronic Science and Technology of China, 610054 Chengdu, China
*Corresponding author: elam@eee.hku.hk
Received August 26, 2015; revised November 2, 2015; accepted November 4, 2015;
posted November 10, 2015 (Doc. ID 248509); published December 15, 2015
In optical scanning holography, one pupil produces a spherical wave and another produces a plane wave. They
interfere with each other and result in a fringe pattern for scanning a three-dimensional object. The resolution of
the hologram reconstruction is affected by the point spread function (PSF) of the optical system. In this paper, we
modulate the PSF by a spiral phase plate, which significantly enhances the lateral and depth resolution. We
explain the theory for such resolution enhancement and show simulation results to verify the efficacy of the
approach. © 2015 Chinese Laser Press
OCIS codes: (090.1995) Digital holography; (110.1758) Computational imaging; (110.4850) Optical transfer
functions.
http://dx.doi.org/10.1364/PRJ.4.000001
1. INTRODUCTION
Optical scanning holography (OSH) is a digital holographic
technique that records the volumetric information of a
three-dimensional (3D) scene by two-dimensional (2D) scan-
ning [1]. Compared with other forms of digital holography,
OSH has distinct advantages, such as fluorescence imaging
[1,2] and partially coherent illumination [3]. In addition to de-
veloping OSH applications, such as microscopy and remote
sensing, compressive sensing [4], sectional reconstructions
[5], and others [6], much attention has been focused on im-
proving the resolution of the OSH system [7]. Several different
techniques have been developed for this purpose. It has been
shown that image resolution can be enhanced by obtaining
more information about the object, such as the multiple detec-
tion techniques with synthetic apertures [8], dual wavelengths
(DW-OSH) [9], double detection [10], and using configurable
pupils (CP-OSH) [11]. Meanwhile, another approach is to
manipulate the point spread function (PSF) of the OSH system
by designing the pupils [12–14]. In this way, the system does
not need extra time to record more information about the
object, thus making it more suitable in applications where
the capture time is more constrained.
In this paper, we propose a new way to enhance the reso-
lution of the OSH reconstruction by designing the PSF with a
spiral phase plate (SPP), an approach we call SPP-OSH. The
SPP has been applied to other applications due to its capabil-
ity in edge enhancement [15–17]. Recently, it also has been
applied to the OSH [18,19], where the SPP is used to modulate
one of the two beams to achieve edge enhancement or reso-
lution enhancement. For the former, the open aperture in the
conventional OSH is replaced by an SPP, such that the scan-
ning pattern is the interference of a plane wave beam and
a vortex beam. In this work, however, the SPP is used as a
modulation to the spherical wave arising from one of the
pupils, such that the interference at the scanning plane is
from a spherical wave beam and a vortex. This produces a
denser PSF, improving both the lateral and depth resolu-
tions while enhancing the edges. The theory is explained in
Section 2 and verified by simulation in Sections 3 and 4.
2. PRINCIPLE OF THE SPP-OSH SYSTEM
The proposed SPP-OSH system is shown in Fig. 1. Similar to the
conventional OSH system, the laser light source with a fre-
quency ω is divided into two paths with a beam splitter. One
path goes through a pupil p
1
and a thin lens L
1
to form a spheri-
cal beam. For the other path, which passes through an acousto-
optic frequency shifter (AOFS), a 4f system is placed instead of
a single pinhole pupil p
0
in the conventional OSH, as the part in
the blue-dashed rectangle enclosed in Fig. 1 shows. Thin lens
L
2
and L
3
with focal length f form the 4f system. An SPP and
the pupil p
0
are placed at the front focal plane of L
2
, while the
pupil p
2
is located at its back focal plane of L
2
. Thus, the output
from this path is a time-varying vortex beam. Unlike in the con-
ventional OSH, where the scanning pattern is the interference
between a spherical beam and a plane wave, in SPP-OSH, the
plane wave is replaced by a vortex beam. The pattern is re-
flected by a scanning mirror into a 3D object located at a dis-
tance z. The transmitted optical wave passing through the 3D
object becomes an electrical signal on the photodetector,
which is turned into a digital hologram. Because the pattern
used to scan the object is the interference of the two beams,
the optimum location of the object is the position where the
two beams have the same size. Because the size of the two
beams is limited by the pupils of the objective lens, the aper-
tures are chosen to match the later. Therefore, the same aper-
ture size for p
0
, p
1
, and p
2
with radius of R is chosen. In this
system, the SPP can be a digital holographic element or spatial
light modulator. Furthermore, the SPP used in our system has a
topological charge of 1, leading to a uniform edge enhance-
ment for the whole object [20], with a transmittance function:
Chen et al. Vol. 4, No. 1 / February 2016 / Photon. Res. 1
2327-9125/16/010001-06 © 2016 Chinese Laser Press
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