Wide tunable laser based on electrically regulated
bandwidth broadening in polymer-stabilized
cholesteric liquid crystal
HONGBO LU,
1,2,7
CHENG WEI,
1
QIANG ZHANG,
1
MIAO XU,
1,2
YUNSHENG DING,
2
GUOBING ZHANG,
1,2
JUN ZHU,
1,2
KANG XIE,
3
XIAOJUAN ZHANG,
4
ZHIJIA HU,
3,4,5,6
AND LONGZHEN QIU
1,2
1
Key Laboratory of Special Display Technology, National Engineering Laboratory of Special Display Technology, State Key Laboratory of Advanced
Display Technology, Academy of Opto-Electronic Technology, Hefei University of Technology, Hefei 230009, China
2
Key Laboratory of Advanced Functional Materials and Devices, Anhui Province, School of Chemistry and Chemical Engineering,
Hefei University of Technology, Hefei 230009, China
3
School of Instrument Science and Opto-Electronics Engineering, Hefei University of Technology, Hefei 230009, China
4
Aston Institute of Photonic Technologies, Aston University, Birmingham B4 7ET, UK
5
State Key Laboratory of Environment-Friendly Energy Materials, Southwest University of Science and Technology, Mianyang 621000, China
6
e-mail: zhijiahu@hfut.edu.cn
7
e-mail: bozhilu@hfut.edu.cn
Received 15 October 2018; accepted 24 November 2018; posted 30 November 2018 (Doc. ID 348249); published 10 January 2019
Electrically responsive photonic crystals represent one of the most promising intelligent material candidates for
technological applications in optoelectronics. In this research, dye-doped polymer-stabilized cholesteric liquid
crystals (PSCLCs) with negative dielectric anisotropy were fabricated, and mirrorless lasing with an electrically
tunable wavelength was successfully achieved. Unlike conventional liquid-crystal lasers, the proposed laser aided
in tuning the emission wavelength through controlling the reflection bandwid th based on gradient pitch distri-
bution. The principal advantage of the electrically controlled dye-doped PSCLC laser is that the electric field
is applied parallel to the helical axis, which changes the pitch gradient instead of rotating the helix axis, thus
keeping the heliconical structure intact during lasing. The broad tuning range (∼110 nm) of PSCLC lasers,
coupled with their stable emission performance, continuous tunability, and easy fabrication, leads to its numerous
potential applications in intelligent optoelectronic devices, such as sensing, medicine, and display.
© 2019
Chinese Laser Press
https://doi.org/10.1364/PRJ.7.000137
1. INTRODUCTION
Liquid-crystal (LC) lasers have attracted significant attention in
the scientific community in recent years. The broad wavelength
tuning range, coupled with their microscopic size, narrow line-
width, large coherence area, and high optical efficiency, opens
up new application avenues such as miniature medical diagnos-
tic tools, sensing, informational displays, and lab-on-chip
devices [1,2]. LC materials are a class of soft matter that com-
bines crystalline-like ordering with fluid-like behavior. Due to
the strong interactions among the molecules, LCs can self-
assemble into different ordered mesophases, such as the
common nematic and smectic phases, without the aid of any
external stimulus. Introduction of the chiral center in the mol-
ecules and/or addition of some chiral dopants into nematic LCs
leads to the twisting and self-assembling of the molecules into a
periodic helical structure, forming cholesteric liquid crystal
(CLC) with a pitch (p) in the submicrometer and micrometer
range. The dielectric permittivity is periodic in space; therefore,
CLCs can be seen as one-dimensional photonic crystals, which
selectively reflect the specific band circularly polarized light
with the same handedness as the helix. The reflection band
edges are located at λ
o
p × n
o
and λ
e
p × n
e
, where n
o
and n
e
are the ordinary and extraordinary refractive indices
of the local uniaxial structure, respectively [3,4]. Once a laser
dye is doped into the CLCs, provided that the fluorescence
emission spectrum of the dye overlaps the edge of the photonic
bandgap, mirrorless lasing is observed at the edge under certain
pumping conditions, which is the so-called band-edge CLC
laser [5– 8].
One major attractive feature of CLC lasers is the tunability
of the emission wavelength over a wide range via controlling the
pitch. This can be obtained by changing the composition [9],
position [10,11], temperature [12], and mechanical strain
[13,14], and by using reversible photochemical reactions [15].
Research Article
Vol. 7, No. 2 / February 2019 / Photonics Research 137
2327-9125/19/020137-07 Journal © 2019 Chinese Laser Press
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