Jiatong Sun

Polarization independent liquid crystal gratings based on orthogonal photoalignments

The polarization independence of liquid crystal gratings with alternate orthogonal aligned regions is theoritically studied and demonstrated by means of photoalignment technique. The different alignments in adjecent regions are achieved by two-step photo exposure to guide orientations of sulfonic azo dye layers and further align the liquid crystal molecules. Both one-dimensional and two-dimensional switchable phase gratings have been demonstrated. Such polarizer-free gratings show very high transmittance (∼92%), diffraction efficiency (over 31%), and optical contrast (over 150) including low power consumption.

Liquid crystal gratings based on alternate TN and PA photoalignment

A diffraction grating is proposed by periodically defining the liquid-crystal director distribution to form alternate parallel aligned and twist nematic regions in a cell placed between two crossed polarizers. Based on the combined phase and amplitude modulation, both 1D and 2D tunable gratings are demonstrated. Low voltage ON/OFF switching of 1st order diffracted light with extinction ratio over 80 is achieved within a small voltage interval of 0.15 Vrms. Unique four-state feature of the cell is obtained and their applications in optical logic devices are discussed.

Optically tunable and rewritable diffraction grating with photoaligned liquid crystals

An optically tunable and rewritable liquid crystal (LC) diffraction grating cell has been revealed that consists of an optically active and an optically passive alignment layer. The grating profile is created by confining the LC director distribution in alternate planar and twisted alignment domains by means of photoalignment of the LCs. The proposed grating is optically tunable for diffractive and nondiffractive states with a small response time that depends on the exposure energy and LC parameters. In addition, the grating can be erased and rewritten for different diffracting characteristics. These optically tunable diffractive elements could find application in various photonic devices.

Optically rewritable ferroelectric liquid-crystal grating

This paper describes the fabrication procedure and optical characterization of ferroelectric liquid-crystal (FLC) gratings based on photo-alignment. The fabrication procedure includes only one side photo-alignment substrate, while the other substrate does not have any alignment layer. Both 1D and 2D gratings have been fabricated. The proposed diffraction element shows high diffraction efficiency ~ 65% and fast response time of 50 μs, which is much faster than the existing technologies. Such gratings can be operated with high frequency of around 2 kHz at the electric field of 6.67 V/μm. Moreover, the proposed grating can be erased and rewritten optically for different grating vector in simple steps. Therefore, with these advance features, such gratings have high potential to be applied in verity of devices and for the improvement of some important existing devices.

Optically rewritable 3D liquid crystal displays

Optically rewritable liquid crystal display (ORWLCD) is a concept based on the optically addressed bi-stable display that does not need any power to hold the image after being uploaded. Recently, the demand for the 3D image display has increased enormously. Several attempts have been made to achieve 3D image on the ORWLCD, but all of them involve high complexity for image processing on both hardware and software levels. In this Letter, we disclose a concept for the 3D-ORWLCD by dividing the given image in three parts with different optic axis. A quarter-wave plate is placed on the top of the ORWLCD to modify the emerging light from different domains of the image in different manner. Thereafter, Polaroid glasses can be used to visualize the 3D image. The 3D image can be refreshed, on the 3D-ORWLCD, in one-step with proper ORWLCD printer and image processing, and therefore, with easy image refreshing and good image quality, such displays can be applied for many applications viz. 3D bi-stable display, security elements, etc.

Complex Nanoscale‐Ordered Liquid Crystal Polymer Film for High Transmittance Holographic Polarizer

A special design of a complex-ordered liquid crystal polymer film is developed into a holographic polarizer. The holographic polarizer shows over 90% transmittance, which provides a simple solution to make LEDs polarized. Furthermore, the holographic polarizer exhibits intensity and polarization maintenance properties, which could be further developed for photonics applications.

Effect of Azo Dye Layer on Rewriting Speed of Optical Rewritable E-paper

A new method to increatse the operation speed for optical rewritable (ORW) liquid crystal alignment technology has been proposed. Conventionally, we prepared the azo dye layer by spin-coating solution of SD1 with different concentrations. The new method is to form a super thin azo-dye molecular alignment layer for LC display cell without spin-coating and rubbing processes. Compared to the conventional one, the new method provides much smaller azimuthal anchoring energy, and increases the rewriting speed a lot. Providing the advantages of conventional photoalignment methods, the use of super thin layer can obviously improve the operation speed of ORW technology for e-paper application.

Photoalignment in Rheology of Liquid Crystals

The application of photoalignment technique for rheological study of liquid crystals is considered. Such technique can be used for the initial preparation and rotation of mono domain samples of liquid crystals. It provides new possibilities in measurements of anisotropic viscosities of liquid crystals. Three shear and the rotational viscosities of nematic liquid crystals can be determined at additional usage of the electric field.

A flexible optically re-writable color liquid crystal display

It is very difficult to make a liquid crystal display (LCD) that is flexible. However, for an optically re-writable LCD (ORWLCD), only the spacers and the substrates need to be flexible because the driving unit and the display unit are separate and there are no electronics in the display part of ORWLCD. In this paper, three flexible-spacer methods are proposed to achieve this goal. A cholesteric liquid crystal colored mirror with a polarizer behind it is used as the colored reflective backboard of an ORWLCD. Polyethersulfone substrates and flexible spacers are used to make the optically re-writable cell insensitive to mechanical force.

Increasing rewriting speed of optically driving liquid crystal display by process optimisation

ABSTRACT Process optimisation for increasing the response speed of optical driving liquid crystal cell was investigated in this paper. It is demonstrated that by filling LC in atmosphere condition rewriting time could be decreased to 6 s with good repeatability. Increasing the spin coating speed, the rewriting time could also decrease the azimuthal anchoring energy, but it will cause non-continuous film form of alignment layer, which causes large speed dispersion that is not good for practical use. Serial experiments show that with smaller azimuthal anchoring energy the rewriting time could be smaller. The results demonstrate that with proper fabrication process of alignment layer for liquid crystal optical rewritable e-paper, azimuthal anchoring energy could be adjusted to an optimal value, which is beneficial for achieving fastest rewriting speed and at the same time strong enough to well align LC. GRAPHICAL ABSTRACT