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.

A regular domain structure consisting of parallel stripes – flexodomains – have been induced by low frequency (subHz) electric voltage in a bent core nematic liquid crystal. The wavelength of the pattern is in the range of 1–10 micrometers and thus can conveniently be observed in a polarizing microscope. It also serves as an optical grating and produces a regular system of laser diffraction spots. The pattern was found to emerge and disappear consecutively in each half period of the driving, with the wavelength of the flexodomains changing periodically as the ac voltage oscillates. Analyzing the polarization characteristics of the diffracted light, the polarization of the first order spot was found perpendicular to that of the incident light, in accordance with a recent theoretical calculation.

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.

The optically induced grating enhanced by dc electric field in nematic liquid crystal (LC) doped with copper porphyrin is studied. The reorientational effect of the LC was not observed for the writing beams with the intensity up to $500\text{mW}/{\text{mm}}^2$ , but the threshold of the reorientation was reduced to $1\text{mW}/{\text{mm}}^2$ with the assistance of an electric pulse applied to the LC. The low threshold for the induced grating can be retained even after switching off the dc pulse, indicating that an induced field inside the LC is present to sustain the low threshold operation for the induced grating. The low threshold operation does not persist by short circuiting of LC electrodes. The underlying mechanism is explained by an optical surface-charge mediated effect.

We numerically propose a scheme for realizing an all-optical femtosecond soliton diode based on a tailored heterojunction Bragg grating, which is designed by two spatially asymmetric chirped cholesteric liquid crystals. Our simulations demonstrate that with the consideration of optical nonlinearity, not only the femtosecond diode effect with nonreciprocal transmission ratio up to 120 can be achieved but also the optical pulse evolving into soliton which maintains its shape during propagation through the sample is observed. Further, the influence of pulse width and the carrier wavelength to the femtosecond diode effect is also discussed in detail. Our demonstrations might suggest a direction for experimentally realizing the femtosecond soliton diode based on the cholesteric liquid crystals.