Polarization-independent liquid crystal lens based on axially symmetric photoalignment

Low-voltage driving high-resistance liquid crystal micro-lens with electrically tunable depth of field for the light field imaging system

Light field imaging (LFI) based on Liquid crystal microlens array (LC MLAs) are emerging as a significant area for 3D imaging technology in the field of upcoming Internet of things and artificial intelligence era. However, in scenes of LFI through conventional MLAs, such as biological imaging and medicine imaging, the quality of imaging reconstruction will be severely reduced due to the limited depth of field. Here, we are proposed a low-voltage driving LC MLAs with electrically tunable depth of field (DOF) for the LFI system. An aluminum-doped zinc oxide (AZO) film was deposited on the top of the hole-patterned driven-electrode arrays and used as a high resistance (Hi-R) layer, a uniform gradient electric field was obtained across the sandwiched LC cell. Experimental results confirm that the proposed LC MLAs possess high-quality interference rings and tunable focal length at a lower working voltage. In addition, the focal lengths are tunable from 3.93 to 2.62 mm and the DOF are adjustable from 15.60 to 1.23 mm. The experiments demonstrated that the LFI system based on the proposed structure can clearly capture 3D information of the insets with enlarged depths by changing the working voltage and driving frequency, which indicates that the tunable DOF LC MLAs have a potential application prospects for the biological and medical imaging.

Dual-polarized light-field imaging micro-system via a liquid-crystal microlens array for direct three-dimensional observation

Light-field imaging is a crucial and straightforward way of measuring and analyzing surrounding light worlds. In this paper, a dual-polarized light-field imaging micro-system based on a twisted nematic liquid-crystal microlens array (TN-LCMLA) for direct three-dimensional (3D) observation is fabricated and demonstrated. The prototyped camera has been constructed by integrating a TN-LCMLA with a common CMOS sensor array. By switching the working state of the TN-LCMLA, two orthogonally polarized light-field images can be remapped through the functioned imaging sensors. The imaging micro-system in conjunction with the electric-optical microstructure can be used to perform polarization and light-field imaging, simultaneously. Compared with conventional plenoptic cameras using liquid-crystal microlens array, the polarization-independent light-field images with a high image quality can be obtained in the arbitrary polarization state selected. We experimentally demonstrate characters including a relatively wide operation range in the manipulation of incident beams and the multiple imaging modes, such as conventional two-dimensional imaging, light-field imaging, and polarization imaging. Considering the obvious features of the TN-LCMLA, such as very low power consumption, providing multiple imaging modes mentioned, simple and low-cost manufacturing, the imaging micro-system integrated with this kind of liquid-crystal microstructure driven electrically presents the potential capability of directly observing a 3D object in typical scattering media.

Three-dimensional imaging based on electronically adaptive liquid crystal lens

In this paper, we present a relatively simple method to acquire a 3D image based on an electrically controlled liquid crystal (LC) lens. Its advantage is that this proposed method does not need any mechanical movements to acquire a 3D image. The tunable-focus LC lens combined with a high-resistance layer (PEDOT) is applied by an overdrive method to become a key optical component for use in a 3D imaging system. Multiple 2D images of slightly different perspectives are recorded, respectively, and 3D images, according to a proposed mapping and projection method, can be reconstructed. This is the first report, to the best of our knowledge, on using an LC lens to reconstruct 3D images. The proposed 3D imaging system is novel for its compact and smart features, so it is attractive for some compact 3D imaging systems.

Polarization-insensitive liquid crystal microlens array with dual focal modes

We demonstrate a liquid crystal (LC) microlens array (MLA) fabricated by LCs possessing negative dielectric anisotropy, in conjunction with a cell with a three-electrode structure. The presented LC MLA is polarization-insensitive and can be operated in both concave and convex modes. The shortest focal length of the LC MLA is -2.54 and 2.22 mm in concave and convex mode, respectively. Disclination lines that are usually observed in conventional hole-patterned LC lens can also be avoided because of the vertical alignment treatment of LCs.

Topography from topology: photoinduced surface features generated in liquid crystal polymer networks

Films subsumed with topological defects are transformed into complex, topographical surface features with light irradiation of azobenzene-functionalized liquid crystal polymer networks (azo-LCNs). Using a specially designed optical setup and photoalignment materials, azo-LCN films containing either singular or multiple defects with strengths ranging from |½| to as much as |10| are examined. The local order of an azo-LCN material for a given defect strength dictates a complex, mechanical response observed as topographical surface features.

Polarization rotators fabricated by thermally-switched liquid crystal alignments based on rubbed poly(N-vinyl carbazole) films

This paper demonstrates the thermally-switched liquid crystal (LC) alignments based on a rubbed poly(N-vinyl carbazole) (PVK) film, and their application for polarization rotators. The mechanically rubbed PVK layer can induce a planar alignment of LCs with their director axis perpendicular to the direction of rubbing. This direction can be switched toward the rubbing direction by thermal treatment. Experimentally, the angle of re-orientation of the director axis increases with the temperature in a specific range of temperatures. In this study, the optical properties of linear and concentric polarization rotators, fabricated using a rubbed PVK film with thermal treatment, are examined.