High-resolution pseudo-inverse ghost imaging
Wenlin Gong
Key Laboratory for Quantum Optics and Center for Cold Atom Physics of CAS, Shanghai Institute of Optics and
Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China (gongwl@siom.ac.cn)
Received June 19, 2015; revised July 21, 2015; accepted July 21, 2015;
posted July 23, 2015 (Doc. ID 243400); published August 21, 2015
We present a pseudo-inverse ghost imaging (PGI) technique which can dramatically enhance the spatial transverse
resolution of pseudo-thermal ghost imaging (GI). In comparison with conventional GI, PGI can break the limitation
on the imaging resolution imposed by the speckle’s transverse size on the object plane and also enables the
reconstruction of an N-pixel image from much less than N measurements. This feature also allows high-resolution
imaging of gray-scale objects. Experimental and numerical data assessing the performance of the technique are
presented. © 2015 Chinese Laser Press
OCIS codes: (270.0270) Quantum optics; (110.2990) Image formation theory; (100.3010) Image
reconstruction techniques; (030.6140) Speckle.
http://dx.doi.org/10.1364/PRJ.3.000234
1. INTRODUCTION
Ghost imaging (GI), which is based on the quantum or
classical correlation of fluctuating light fields, has been
demonstrated theoretically and experimentally to show that
an unknown object can be nonlocally imaged without being
scanned by using a single-pixel detector at the object path
[1–10]. Because all the photons reflected (or transmitted)
from the object illuminate the same single-pixel detector, this
technique has the capability of being highly sensitive in detec-
tion and offers great potentialities with respect to standard
conventional imaging [11–15]. For example, the dosage of
fluorescence protein used for GI can be dramatically reduced
compared with modern fluorescence-imaging methods in bio-
medical imaging, and the imaging in the wavebands without
cameras can be achieved with a single pixel detector.
Other potentialities are in the direction of high efficiency in
information extraction, where an N-pixel image can be recon-
structed from less than N measurements because the mea-
surement mechanism of GI is random and global [8,16,17].
Due to these remarkable features, GI has been gradually ap-
plied to biomedical imaging [12,13], remote sensing [14,15],
optical encryption [18], secure key distribution [19], and so
on. However, the spatial resolution of GI is limited by the
speckle’s transverse size on the object plane, and improving
its spatial transverse resolution becomes a key issue
[5,9,20,21]. When the object’s sparsity has been taken as
a priori, ghost imaging via sparsity constraint (GISC) has
been experimentally demonstrated to show that the spatial
transverse resolution of GI can be enhanced for simple binary
objects (transmission 0 or 1), but the reconstruction time is
much longer than the conventional GI method and the
high-resolution capability for a low-contrast object or gray-
scale object has not been reported [20,21]. Even if GISC
can improve the imaging resolution of low-contrast or gray-
scale objects, the improvement degree of imaging resolution
may be limited because these objects are not sparse. In real
sensing and imaging applications, the object is usually gray-
scale. Therefore, in order to promote and expand the practical
applications of GI, it is imperative to develop a universal and
real-time high-resolution GI method for gray-scale objects.
Recently, the object’s ghost image has been reconstructed
by a pseudo-inverse method, and the measurement number
required for reconstructing GI with a good signal-to-noise ra-
tio is on the same order of magnitude as GISC [22]. However,
the object’s sparsity is not utilized. Based on the property of
the pseudo-inverse matrix, it is possible to enhance the spatial
resolution of GI. In this article, we present a pseudo-inverse
ghost imaging (PGI) method that dramatically improves the
spatial transverse resolution of GI and reconstructs an
N-pixel
image from much less than N measurements even for gray-
scale objects. Based on previous GI research achievements,
PGI further paves the way for real applications of the GI pro-
tocol, with the possibility of exploiting all the advantages of GI
against standard conventional imaging.
2. EXPERIMENTAL SETUP AND IMAGE
RECONSTRUCTION
To demonstrate high-resolution PGI, we constructed the setup
illustrated in Fig. 1. The pseudo-thermal light source, which is
obtained by passing a collimated laser beam (with wavelength
λ 650 nm and the source’s transverse size D 4.0 mm)
through a slowly rotating ground glass disk [7,17], goes suc-
cessively through a hole with diameter D
0
8.0 mm and a
lens f , and then is divided by a beam splitter into object
and reference paths. In the object path, the light goes through
a transmission object O and its transmitted image is imaged
onto a bucket detector D
t
by a standard conventional imaging
setup. In the reference path, the light propagates directly to a
CCD camera D
r
. Both the camera D
r
and the object are placed
on the conjugate plane of the hole.
In the framework of conventional GI, the object’s image
O
GI
x; y can be reconstructed by computing the intensity cor-
relation between the speckle’s intensity distributions I
s
r
x; y
recorded by the CCD camera D
r
and the total intensities B
s
recorded by the bucket detector D
t
[8,9],
234 Photon. Res. / Vol. 3, No. 5 / October 2015 W. Gong
2327-9125/15/050234-04 © 2015 Chinese Laser Press