The applicability of photo-alignment technique to bent-core nematics (BCN) is demonstrated in this paper. In order to cope with the inherent problems of BCN such as high working temperature and large working current, a photo-alignment technique, based on two superimposed photosensitive layers of azo and reactive mesogen, is used to produce symmetric and asymmetric planar alignments. With various surface conditions, defect lines arrays are self-assembled and ac-driven electro-convection (EC) rolls are modulated. Further inspections indicate that the defect lines arrays and EC rolls are in a competitive state, which reveal that the EC rolls in BCN belong to nonstandard EC scenarios. By producing defect lines and modulating EC rolls via photo-alignment technique, we could customize patterns in liquid crystals towards new photonic devices.

A new photoresponsive bent-core nematic (BCN) material, which exhibits flexoelectric domains (FDs) driven by electric field, is reported. Unexpectedly, it is found that the morphologies of FDs can be controlled by irradiation with light fields. This light tunability is ascribed to the photoisomerization effect of the azo moiety within the BCN molecules, where the ratio of trans and cis isomers changes according to the parameters of the light field, resulting in adjustable electric threshold and periodicity of FDs. Based on this principle, a prototype of controllable optical grating is assembeled, whose operation can be manipulated by the wavelength or intensity of light. Due to the easy, instant, and remote operation by light, this optical, contactless tunability has a great advantage over traditional electric control in tunable photonic devices.

The influence of UV light-induced pitch contraction and dilation on the electroconvection patterns (ECPs) of a chiral nematic liquid crystal containing a photoresponsive chiral dopant is investigated in planar-aligned cells. It is observed that the helical twisting power of the dopant changes (even undergoes handedness inversion) under UV irradiation; consequently, the pitch and the direction of the convection rolls in ECPs (being either parallel with or perpendicular to the surface alignment) could be controlled by the UV intensity and the ac voltage. In contrast to traditional methods, where the pitch is modulated by electric or thermal fields, our method of applying a light field allows a remote and contactless manipulation of the pitch, which is easily detectable via the morphological changes of ECPs. The ability to control the orientation of ECPs by tuning the light intensity can conveniently be utilized as an optical grating, allowing switchable, dual-mode operation.

In this paper we present a method that can balance a robotic bicycle at zero velocity. Based on our earlier work of nonlinear bicycle dynamic model, we developed a novel linearized dynamic equation near large steer angle. The newly developed linear equation is analyzed for its stability and a LQR controller is designed for balancing the robotic bicycle at zero velocity. We also built a prototype robotic bicycle to verify our design. Both theoretical work and experiment shows the robotic bicycle can achieve its balance at zero velocity with our LQR controller without using either fly-wheel or any other devices that provides roll torque.

In order to solve the positioning problem of indoor robots, we present visual positioning system for indoor robots based on ground features. The system firstly collects the ground image through the fisheye camera, then uses the Canny operator to perform edge detection on the captured images, then performs the distortion correction of the fisheye camera on the contour points obtained by the edge detection. It restores the contour points to the undistorted plane. Using RANSAC algorithm and least squares method to compute the relative position of the camera to the ground line segment feature contained in the contour, then using the IPM algorithm to transform the feature into the real world space. We finally obtain the distance and orientation angle from the camera to the ground feature segment. Since we measured and stored all the feature features into a map beforehand, this method can locate robot position when a feature segment is observed. Experimental results show that the positioning method has high positioning accuracy, good real-time performance even with embedded CPU and low cost, so it can solve the positioning problem of indoor robots well.

The influence of UV light-induced pitch contraction and dilation on the electroconvection patterns (ECPs) of a chiral nematic liquid crystal containing a photoresponsive chiral dopant is investigated in planar-aligned cells. It is observed that the helical twisting power of the dopant changes (even undergoes handedness inversion) under UV irradiation; consequently, the pitch and the direction of the convection rolls in ECPs (being either parallel with or perpendicular to the surface alignment) could be controlled by the UV intensity and the ac voltage. In contrast to traditional methods, where the pitch is modulated by electric or thermal fields, our method of applying a light field allows a remote and contactless manipulation of the pitch, which is easily detectable via the morphological changes of ECPs. The ability to control the orientation of ECPs by tuning the light intensity can conveniently be utilized as an optical grating, allowing switchable, dual-mode operation.

Liquid-crystal display technology is ubiquitous, but these materials can also be used to make electrically tunable components for optics and photonics. The authors demonstrate voltage control of the wavelength of flexoelectric domains in a transmissive diffraction grating, which enables dynamic light steering. They prove that the mechanism of pattern onset differs from that of switching between flexodomain states, and they explain the surprising finding that the response to increasing voltage is much slower than that to decreasing voltage.

Optically-induced grating in ZnTPP doped chiral nematic liquid crystals (CLC) is demonstrated by dual-mode operations, where the dynamic or storage functionality is selected by the amplitude of dc voltage. While the storage can be erased and rewritten by a high dc pulse, it can persist without an electric field, which is the result when the CLC undergoes a switching between a planar and a focal conic state. This tunable dual-functionality grating combines the advantages of bistable storage of CLC and high photosensitivity of dopant, and thus can be potentially exploited in photonic devices to implement different optical information processing in situ. (C) 2017 Optical Society of America

We examined the flexodomains (FDs) in chiral bent-core nematics (BCNs), and demonstrated the morphology changed from parallel stripes in pure BCN to oblique ones in chiral BCNs. While the magnitude of obliqueness angle strongly depended on the concentration of chiral dopant, its sign was determined by the polarity of the driving voltage, thus FDs appeared alternately as symmetrical oblique stripes in the positive and negative half a.c. voltage cycles, respectively. Also the HTP value of chiral dopant in BCNs can be determined based on this phenomenon. The polarity-dependent behavior of FDs can be potentially exploited in photonic devices with a bistable function. (C) 2016 Optical Society of America

Two kinds of electroconvection patterns in an ether-bridged bent-core nematic liquid crystal material (BCN), which appear in different frequency ranges, are examined and compared. One is a longitudinal pattern with the stripes parallel to the orientation of the BCN and with a periodicity of approximately the cell thickness, occurring in the high-frequency range of several hundreds Hz; the other one is oblique stripes, which results in a zigzag pattern, and appears in the low-frequency range of several tens Hz. In addition, within an intermediate-frequency range, transformations from oblique to longitudinal and then to normal stripes occur at increased ac voltages. In particular, we investigated the temperature behavior of longitudinal and oblique stripes: When the temperature T increases and approaches the clearing temperature T-c, the contrast of the domains is enhanced and the frequency range of existence becomes wider, while the onset voltages increase only moderately instead of diverging, thus suggesting an isotropic mechanism of pattern formation.

We observed a fast light-induced grating in bent-core nematic liquid crystal (LC) using an in-plane switching cell. Combining weak writing beams and a dc field, this grating can be easily built up and decay within 10 ms, which is two orders of magnitude faster than that in conventional device composed of doped rodlike LC and planar cell. Besides, this grating is produced by the periodic twist deformation of LC, whereas the conventional grating is produced by the periodic bend deformation, therefore, this grating can be used to explore the twist elastic properties of LC systems. (C) 2013 AIP Publishing LLC.

We present a new observation of photorefractive (PR) effects in bent-core nematic (BCN) liquid crystal (LC) materials, where two kinds of optical-induced gratings are demonstrated and compared in pure and surface-doped BCN systems. The experimental results showed that these two kinds of gratings exhibit distinctive different polarization-dependent and angular-dependent behaviors, respectively. Furthermore, we supplied the pure and surface-doped rodlike LC systems for comparison, which revealed that V shape molecular structure of BCN can produce charge carrier more efficiently than rodlike molecular structure does. Thus BCN materials can offer an exciting potential for optical information processing.

We demonstrated the geometrical effect of nano zinc-oxide (ZnO) on the electro-optical response of a nematic liquid crystal (LC). The experimental results indicated that anisotropic geometrical (nano-rod) ZnO will markedly enhance the photo-refractive effects of host LC, whereas isotropic geometrical (nano-particle) ZnO possess no such effects at all. With the help of photoluminescence spectra and photo-current measurement, we further prove that the geometries of dopants play decisive roles in determining the yield of photo-electron. These results are useful to the nano-technology application of nano-ZnO.