Dual-wavelength digital holographic phase
reconstruction based on a polarization-
multiplexing configuration
Zhe Wang (王 喆)
1,2
, Yifei Chen (陈依菲)
1,2
, and Zhuqing Jiang (江竹青)
1,2,
*
1
College of Applied Sciences, Beijing University of Technology, Beijing 100124, China
2
Institute of Information Photonics Technology, Beijing University of Technology, Beijing 100124, China
*Corresponding author: zhqjiang@bjut.edu.cn
Received August 31, 2015; accepted November 26, 2015; posted online January 6, 2016
We present a polarization-multiplexing off-axis Mach–Zehnder configuration for dual-wavelength digital holog-
raphy to achieve phase imaging in one shot. In this configuration, two orthogonal linear-polarized waves with
respect to different wavelengths are employed to record respective holograms synchronously, where two record-
ing waves transmit independently through the same optical paths of the interferometer, and by installing two
analyzer polarizers each to filter off either of two wavelengths, and filtering through the other, the holograms are
acquired, respectively, by a pair of CCDs at the same time. The unwrapped phase image of a grating with groove
depth 7.1 μm is retrieved via spatial frequency filtering.
OCIS codes: 090.1995, 090.5694.
doi: 10.3788/COL201614.010008.
Digital holography is a technique that can reconstruct
the phase images of an object by the acquisition of the
object’s holograms with a CCD camera and numerical
reconstruction imaging via simulation of the hologram’s
diffraction imaging process
[1–7]
. The phase reconstruction
imaging of digital holography using a single wavelength
is just suitable to handle smooth profiles and step heights
less than the wavelength. While a target object is of larger
optical thickness than the recording wavelength in digital
holography, its phase image typically contains 2π discon-
tinuities, referred to as phase wrapping. Thus, the actual
phase image of the object has to be retrieved from its
wrapping phase image by using numerical phase unwrap-
ping algorithms
[8]
. The numerical phase unwrapping in
single-wavelength digital holography may induce some
error if the target structure has a high aspect ratio. How-
ever, dual-wavelength digital holography may complete
the phase imaging for a target object of larger or abrupt
height variance via careful choice of two wavelengths. It
can retrieve the phase image just by yielding a synthetic
phase map free of 2π discontinuities from two holograms
recorded with different wavelengths, without the need of
numerical phase unwrapping in phase reconstruction
[9,10]
.
Since dual-wavelength digital holography has the advan-
tage of imaging a height step object without unwrapping,
various recording configurations and phase reconstruction
based on dual-wavelength digital holography have been
actively researched in recent years
[11–15]
.
In this Letter, a polarization -multiplexing off-axis
Mach–Zehnder configuration of dual-wavelength digital
holography is proposed for the reconstruction of quantita-
tive phase images in which two orthogonal linear-polarized
waves with respect to different wavelengths pass through
the same off-axis interferometer to record the holograms.
According to the independent propagation of two linear-
polarized waves orthogonal to one another, two different
wavelength lasers, respectively, to a p-polarization and a
s-polarization can transmit together in the same optical
path of the interferometer without any optical interference
between them. The two holograms from the different wave-
lengths can be synchronously acquired with a pair of CCDs
by installing one polarizer with its polarization state
parallel to the s-polarization and the other polarizer paral-
lel to the p-polarization, each in front of the CCDs. Both
polarizers act as a filter through one pair of interference
beams among the two wavelengths to form one interfero-
gram and filtering off the other. Thus, the holograms of
dual-wavelength digital holography can be captured in
one shot based on this polarization-multiplexing configu-
ration. The presented configuration provides the capabil-
ities of polarization-multiplexing transmission for two
separate wavelengths and of automatic spatial-frequency
filtering in dual-wavelength digital holography. Further-
more, it is more compact because one interferometer
path is simultaneously provided as two polarization chan-
nels. The phase image of a phase-only grooved grating
is retrieved with relevant spatial frequency filtering and
dual-wavelength numerical reconstruction in the pre-
sented polarization-multiplexing optical configuration.
For dual-wavelength digital holographic imaging, two
interferograms formed with two pairs of the interference
beams of different wavelengths are required to be recorded
by image sensors, such as CCD cameras, which are
referred to as the digital holograms corresponding to
the separate wavelengths. After obtaining two indepen-
dent phase images from respective digital holograms, a
synthetic phase image can be yielded with the subtraction
of the two single-wavelength phase images. Thus, the
COL 14(1), 010008(2016) CHINESE OPTICS LETTERS January 10, 2016
1671-7694/2016/010008(5) 010008-1 © 2016 Chinese Optics Letters