| Liquid crystal (LC) has been widely used in information display and non-display areas due to its unique electro-optic characteristics. Its optical birefringence covers very wide spectral range, and the related researches have extended to infrared and even THz ranges. Designed LC director distribution could be obtained by external field control or alignment technologies, thus effective local control on the incident light’s intensity, polarization, phase and wavefront would be realized. In this paper, two optical-field control applications are introduced, which realize effective control on intensity and phase respectively, and can be find important applications in bistable display and beam shaping.The ion-doped Smectic-A (SmA) materials have two stable states via applying specified electric signals:homeotropic alignment transparent state and random focal-conic arranged state. This bistable liquid crystal display (BLCD) requires power only in updating images, while electrical field is unneeded in maintaining two states. Therefore, it is quite suitable for displays that would not be frequently updated, such as electronic signage cards, e-books and so on. Traditional SmA LCs exhibit reliable performances and good stability. However, they still suffer from several disadvantages such as low optical contrast and relative high operating voltages, thus limiting both the display quality and device life-time. Here, we developed two kinds of bistable SmA LCs. The isothiocyanato group is used to substitute cyano fluoro groups, the fluoro groups are added on 3 and 5 positions of the isothiocyanato substituent terminal phenyl ring, and derivatives of (4-isothiocyanatophenyl) pyridine are also introduced. By this molecular design, the dielectric and optical anisotropy are increased, the viscosity is decreased, and the smectic range is also widen. And the electro-optical measurements demonstrate that the devices based on the two new materials exhibit highly improved properties:lower operation voltages, faster response time and higher optical contrast.Optical vortex (OV) is a particular type of optical beams which has spiral wavefront and carries orbital angular momentum (OAM). It has broad applications in optical communication, quantum informatics and optical tweezers. There are many ways to generate OV, however, there still some challenges remain, such as how to generate high quality, high efficient beams and make the generation tunable and more convenient, q-plate (QP), a birefringent half-wave plate with inhomogeneous patterned distribution of the local optical axis in the transverse plane, has all the above merits. When a circularly polarized Gaussian beam incidents a QP, a vortex beam with topological charge 2q is generated with polarization reversed, which enables the spin-to-optical angular momentum conversion. However, traditional QP can only generate OV with single integer topological charge. Here, we propose a new concept of meta-q-plate, which is featured by arbitrarily space-variant LC director with variant q or initial angle along radius and azimuthal angle, and the capability of beam shaping is greatly enhanced. Several meta-q-plates are demonstrated via a dynamic maskless micro-lithography system and photoalignment technology based on a polarization-sensitive alignment agent. Accordingly, complex beams with elliptical, asymmetrical, multi-ringed and hurricane OVs are generated, making the manipulation of optical vortex up to a point-to-point manner. What’s more, the evolution of the hurricane one is theoretically analysed and experimentally verified. This design drastically enhances the capability of beam shaping. |
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