ABSTRACT
Pancharatnam-Berry phase optical elements (PBOEs) have received much attention due to their ability to generate complex structured light or to manipulate the shape of a light beam. This work demonstrates a tunable liquid crystal (LC) Pancharatnam-Berry (LCPB) lens using a simple and cost-effective PB phase hologram optical setup and thermal polymerization to form an irreversible photo-patterning alignment layer. The LCPB lens with high photo-stability supports ultra-broadband operation and provides a diffraction efficiency of â¼90% throughout the visible spectral range, achieved by applying the appropriate voltages. The LCPB lens functions as a convex or a concave lens, depending on the handedness of the circularly polarized incident light, so its image reduction and magnification functions are demonstrated, and its photo-stability is characterized. The fabrication of the proposed LC PBOEs is simpler and more cost-effective than previous methods, and the irreversible photo-patterning alignment layer that is formed by thermal polymerization allows larger operational bandwidths, supporting new applications.
ABSTRACT
We propose here a novel multi-layered waveguide liquid crystal (LC) smart window with full color rendering based on a polymer-network liquid crystal system. The inserted position of three-primary-color LED light bars is specially designed, which is parallel to the LC alignment to obtain a higher difference between transparent and scattering states. The optimal matching of polymer-network LC system is experimentally achieved by comparing several groups of LC and reactive mesogen materials. The prepared smart window is measured and analyzed in detail including optical/chromatic test, morphology characterization, and actual application effect. The proposed architecture opens up new prospects of flexible color switchable ability and synchronized full-color display for smart windows without limitations of slow LC response time and complicated field sequential driving scheme.
ABSTRACT
Bistable electrical switching of high-efficiency grating diffractions is realized by adding a front π-bistable twisted nematic (π-BTN) cell to a passive liquid crystal polarization grating (LCPG). The π-BTN cell can be switched between stable non- and 180°-twisted states, acting as a polarization converter that switches the polarization of a laser beam and thus changes the diffraction behavior of the LCPG. Both states of the π-BTN cell are stable and can be reversibly switched to each other by applying a voltage pulse of different frequencies. We experimentally demonstrate two bistable-switching operations: (i) the BTN-LCPG can either split or deflect the laser beam; and (ii) the BTN-LCPG can selectively diffract the laser beam to the +1st and -1st orders, while maintaining a high diffraction efficiency of â¼90%. With electrical switchability, a simple optical design, and low power consumption, the proposed BTN-LCPG concept is favorable in various applications.
ABSTRACT
A front polarizer-free optically rewritable (ORW) liquid crystal display (LCD) has been made via a hybrid alignment configuration with dye-doped LCs. The hybrid structure consists of one optically active planar and one optically passive homeotropic alignment layer. The rewritability of the device is achieved by photo-reorienting the azo dye molecules in the active planar alignment layer. The dye is doped in LCs to function as a polarizer by following the LCs' direction via a guest-host effect so that the front polarizer can be eliminated. This makes the device more compact and easier to operate for image erasing and rewriting. The image rewriting time only requires â¼9.0 s, which is determined by the exposure energy and LC parameters. The hybrid-mode dye-doped ORW LCD devices could find applications in E-paper, transparent display, and various photonics devices.
ABSTRACT
As one of the diffractive optical elements, circular Dammann grating has shown its excellent versatility in practical applications. The electrically switchable Dammann grating has been extensively investigated; however, the research on the optically tunable circular Dammann grating has received less attention and reports on this subject have been insufficient in the past decade. In this paper, three-order and eight-order binary-phase liquid crystal circular Dammann gratings with two mutually orthogonal photo-induced alignments in every two adjacent alignment domains, fabricated by a micro-patterned liquid crystal polymer phase mask, are proposed to generate annular uniform-intensity patterns in the far field. A simple maskless optical tuning of an eight-order liquid crystal circular Dammann grating is demonstrated by controlling the polarization of an ultraviolet light as well as the energy dose. The proposed liquid crystal circular Dammann gratings with high efficiencies and desirable uniformities exhibit outstanding optical as well as electrical tunabilities, enabling the widespread prospective applications in adaptive photonic chips stimulated flexibly by only light or by the combination of light and electric field.
