Liquid Crystal Gratings and Their Photonic Applications
Yan-qing Lu,* Wei Hu and Vladimir Grigorievich Chigrinov
College of Engineering and Applied Sciences and National Laboratory of Solid State
Microstructures, Nanjing University, Nanjing 210093, P. R. China
SUMMARY
Liquid crystal (LC) technologies play important roles in various tunable photonic devices with the advantages of low
cost, no moving parts, low power consumption and high reliability. Switchable grating is a widely used key component
that has been studied extensively. In this talk, we will report some of our recent progresses on LC gratings, from nematic
to blue phase. The related applications in optical communication, optical interconnect and optical logic gates are also
discussed.
The first kind of grating is fabricated by periodically adjusting the LC’s director distribution to form alternate micro
parallel aligned regions and twist nematic regions in a cell placed between crossed polarizers. Depending on their
different voltage-dependency of phase retardation and transmittance, both 1D and 2D gratings are demonstrated. The
intensity of 1st order could be suppressed by ~2 orders of magnitude within the voltage interval of 0.15 V at driving
voltage below 1 Vrms. In addition, based on the unique four-state feature, the presented cell exhibits potential applications
in optical logic devices.
The second type of LC grating is demonstrated also by means of photoalignment technique exhibits polarization
independent characteristics thanks to the alternate orthogonal aligned domains. Such polarizer-free gratings show very
high transmittance (ca. 92%) and diffraction efficiency (over 31%). Based on a similar strategy, ferroelectric LC gratings
are also demonstrated. These gratings show 7000:1 high contrast, < 10 s response with modulation frequency up to 5
kHz at the field of 7V/m, which should have great potential in high speed telecom and display applications.
Finally, a blue phase LC (BPLC) grating is demonstrated by applying a vertical electric field with lateral periodic
distribution. It also shows high transmittance (ca. 85%), polarization independent high efficiency (38.7%) and
submillisecond switching on/off time. Discussions on further suppressing the driving voltage is given, which is very
important for future practical application of BPLC.
Reference:
1. W. Hu, et. al., “Liquid crystal gratings based on alternate TN and PA photoalignment” Opt. Express, 20,
5384–5391 (2012)
2. W. Hu, et. al., “Polarization independent liquid crystal gratings based on orthogonal photoalignments ”
Appl. Phys. Lett., to be published
3. G. Zhu, et. al., “Polarization-independent blue phase liquid crystal gratings driven by vertical electric
field”, J. Soc. Info. Display, Accepted for publication
4. X. W. Lin, et. al., “Self-polarizing terahertz liquid crystal phase shifter”, AIP Advances, 1, 032133 (2011)
* yqlu@nju.edu.cn; phone 86 25 8362-1205; fax 86 25 8259-5535; http://light.nju.edu.cn