Experimental realization to efficiently sort vector
beams by polarization topological charge via
Pancharatnam–Berry phase modulation
SHUIQIN ZHENG,
1,2,†
YING LI,
2,†
QINGGANG LIN,
1
XUANKE ZENG,
1
GUOLIANG ZHENG,
1
YI CAI,
1
ZHENKUAN CHEN,
1
SHIXIANG XU,
1,
* AND DIANYUAN FAN
2
1
Shenzhen Key Laboratory of Micro-Nano Photonic Information Technology, College of Electronic Science and Technology, Shenzhen University,
Shenzhen 518060, China
2
SZU-NUS Collaborative Innovation Center for Optoelectronic Science & Technology, Key Laboratory of Optoelectronic Devices and
Systems of Ministry of Education and Guangdong Province, Shenzhen University, Shenzhen 518060, China
*Corresponding author: shxxu@szu.edu.cn
Received 17 November 2017; revised 4 February 2018; accepted 11 February 2018; posted 13 February 2018 (Doc. ID 312504);
published 18 April 2018
This paper reports the experimental realization of efficiently sorting vector beams by polarization topological
charge (PTC). The PTC of a vector beam can be defined as the repetition number of polarization state change
along the azimuthal axis, while its sign stands for the rotating direction of the polarization. Here, a couple of
liquid crystal Pancharatnam–Berry optical elements (PBOEs) have been used to introduce conjugated spatial
phase modulations for two orthogonal circular polarization states. Applying these PBOEs in a 4-f optical system,
our experiments show the setup can work for PTC sorting with a separation efficiency of more than 58%. This
work provides an effective way to decode information from different PTCs, which may be interesting in many
fields, especially in optical communication.
© 2018 Chinese Laser Press
OCIS codes: (260.5430) Polarization; (350.1370) Berry's phase; (260.1960) Diffraction theory; (060.4230) Multiplexing.
https://doi.org/10.1364/PRJ.6.000385
1. INTRODUCTION
In the recent decades, orbital angular momentum (OAM) of
optical vortex beams has drawn much attention. As one of
the promising applications of OAM, some research has shown
that OAM-based multiplexing and demultiplexing technolo-
gies can drastically enhance the capacity of optical communi-
cations systems due to the orthogonality of OAM eigenstates
[1,2]. So detecting optical vortex (OV) beams becomes critical
in spite of challenges. Since the first demonstration of the abil-
ity to sort OAM for a single photon by using a cascading series
of Mach–Zehnder interferometers [3], many efforts have been
devoted to decoding OAM information for developing vortex
optical communication [4–8]. A highly efficient design for
OAM sorting is noticeable. It can be implemented by optical
geometric conversion and optical phase correction to convert a
helical phase into a linear phase gradient [9,10 ]. Based on this
idea, Walsh [11] has theoretically improved the OAM sorting
system with Pancharatnam–Berry phase optical elements
(PBOEs) to simultaneously sort the OAM and spin angular
momentum (SAM) compositions of optical beams.
A vector beam is a beam with a space-dependent polariza-
tion distribution or a pure laser mode with an additional spatial
polarization modulation characterized by polarization topologi-
cal charge (PTC) [12–16]. Recently, vector beams have also
been deemed to be available for improving the capacity of op-
tical communication systems because the vector beam modes
with different PTCs are also orthogonal to each other [17–19].
In addition, the vector modes are the eigenmodes in an
optical fiber, which have the robustness of propagation in fiber
[20–22]. Nevertheless, so far, we have not found any reports on
experimental realization to efficiently sort vector light by PTC,
like the efficient OAM sorting system.
As we know, a vector beam with a PTC value of m can be
decomposed into two vortex components with two opposite
topological charge values m, corresponding to two orthogo-
nal polarization states [17]. Apparently, if a vector beam passes
into an OAM sorting system, the beam will be split into two
spots due to their opposite topological charges, which means
the OAM sorting system [10,23 ] fails to sort vector beams
by PTC. Here we experimentally demonstrate an efficient sys-
tem to sort vector beams by PTC. In the setup, we use a pair of
PBOEs in a 4-f optical imaging system for optical geometric
transformation and optical phase correction. The PBOEs are
created from liquid crystals (LCs). Our setup can convert
Research Article
Vol. 6, No. 5 / May 2018 / Photonics Research 385
2327-9125/18/050385-05 Journal © 2018 Chinese Laser Press