Dual Frequency Liquid Crystal Materials Research Articles

Multi-stable dye-doped dual-frequency twisted nematic liquid crystal smart window.

In this study, a novel, to the best of our knowledge, dye-doped dual-frequency liquid crystal multi-stable smart window is proposed. A chiral dopant with appropriate content was introduced into dye-doped dual-frequency liquid crystals to achieve an initial 180° twisted state. These liquid crystals can be switched to a nematic phase or a 360° twisted state by controlling the magnitude and frequency of the applied voltage. These nematic phase and 360° twisted states can exist stably for a long time because of the backflow effect and the anisotropic nature of the dual-frequency liquid crystal material. Due to the optical waveguide effect of dye-doped liquid crystals in the long-pitch state, the transmittance was different in nematic phase, 180°, and 360° twisted three zero-field stabilized absorption states. Finally, a multi-stable smart window is developed to switch between three zero-field stabilized absorption and scattering states.

Low aberration and fast response liquid crystal lens with optically compensated bend structures

A hole-patterned electrode (HPE) liquid crystal (LC) lens with positive (0 D – 0.7 D) and negative focal lengths (0 D - −1.1 D) is demonstrated. The lens uses an optically compensated bend (OCB) cell filled with dual-frequency LC materials and alignment films with an intermediate pretilt angle. Better reduction in tilt and coma aberration can be achieved using this simple one-layer structure with its symmetric LC orientation in an OCB cell than can be obtained with a complicated two-layer HPE LC lens. The use of dual-frequency switching together with the reduction of the backflow effect in the OCB cell also improves the response by about 7 times compared with the conventional HPE LC lens.

Low-aberration liquid crystal lens with positive and negative focal length.

A low-aberration hole-patterned-electrodes (HPE) liquid crystal (LC) lens with positive and negative focal lengths is demonstrated in this Letter by using four hybrid-aligned nematic LC layers filled with dual-frequency LC materials. The diopter can be controlled from the positive lens (0D∼1.1D) to the negative lens (0D∼-1.25D). The aberration is analyzed using the Zernike polynomial, and the wavefront optical path difference is improved from 2λ for the conventional one-layer HPE LC lens to less than 0.25λ for our proposed LC lens. The proposed LC lens does not require the use of a polarizer, increasing the optical efficiency two times compared with the conventional LC lens.

이중 주파수 액정을 적용한 액정 셔터의 고속 응답 특성

In this paper, by using a dual frequency liquid crystal material, we propose a liquid crystal device with a fast response characteristics. The dual frequency liquid crystal material has a positive dielectric anisotropy value at a low frequency. With a high frequency, the dielectric anisotropy becomes negative. Therefore, the relaxation process is governed by not only the elastic deformation, but also the dielectric interaction. The measured decay time and rise time were 0.88 ms and 0.33 ms, respectively.

Stereoscopic three-dimensional display based on polarization-switching device with low cross talk and high contrast ratio

We present a polarization-switching device with dual-frequency liquid crystal material for a stereoscopic three-dimensional (3D) display. This device shows good properties, such as low 3D cross talk and high brightness, due to a fast dynamic response time. Without optical compensation, however, this device has an asymmetric contrast ratio on the left- and right-hand sides of 3D glasses, because the viewing principles on both sides are different from each other. To solve this problem, we design an optical structure with two half-wave plate films using the Jones matrix method. As the results of simulation and experiment show, excellent dark states and high brightness are realized over the entire range of visible wavelengths on both sides.

폴리머 격벽에 의해 화소고립된 구조의 이중주파수 쌍안정 네마틱 액정셀의 전기광학 특성

We propose a novel bistable nematic liquid crystal cell, which has a dual-frequency liquid crystal material and pixel-isolating polymer wall formed by an anisotropic phase separation of a mixture of liquid crystals and UV-curable pre-polymers. The proposed cell has two stable states of left- and right-handed -twist. The switching between the two states is achieved by using a sequential waveform of low and high frequencies. A transmissive bistable liquid crystal display is designed, which achieves high contrast ratio by using the proposed cell and optical films.

Bistability of left- and right-handed π-twist states in a pixel-isolated dual-frequency nematic liquid crystal cell

The authors propose a bistable nematic liquid crystal cell which has two stable states of left- and right-handed π-twist. The switching between the two states is achieved by using a dual-frequency liquid crystal material and sequential waveform of low and high frequencies. Each state is stabilized by a multidimensional anchoring effect of a pixel-isolating polymer wall without any chiral additives. Therefore, the elastic free energies of left- and right-handed π-twist states are almost the same. As a result, the two states show superior retention time in spite of the topological equivalence.

Optical Phase Modulation Using Dual-Frequency Nematic Liquid Crystals

Phase modulation characteristics of dual-frequency liquid crystal materials possessing the dielectric anisotropy sign inversion have been studied in detail under the quasi-static and dynamic electric field control. It was found that the main obstacle in development of dual-frequency liquid crystal modulators having simultaneously short response time and large switchable values of phase retardation is related to an electrohydrodynamic instability, which disturbs the director reorientation. We are discussing general conditions at which a stable 2π phase modulation is possible at highest switching frequencies. In particular, for the developed dual-frequency liquid crystal material we have established conditions at which the stable phase retardation dynamic range of 2π at switching time ∼ 2 ms is realized at room temperature.

A dual frequency addressed polymer stabilized pi‐cell liquid crystal device

Dual frequency addressing of nematic pi‐cell devices produces submillisecond switching times since the liquid crystal can be driven both parallel and perpendicular to the applied field and there is no kick‐back of the director during switching. The nucleation of the V state in devices containing dual frequency liquid crystal materials is much slower than that in conventional pi‐cells, however. Polymer stabilization of the V state eliminates the need for nucleation each time the device is used. In this paper we present a polymer stabilized pi‐cell containing a dual frequency liquid crystal material, and show that the presence of the polymer network significantly influences the switching of the device. Some optimization of the addressing scheme is required when switching the polymer stabilized device in order to avoid transient formation of the twisted state. Using this optimization, the switching time is under 3 ms across a wide range of addressing voltages. 1Now at: School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, ML3 9PL.

Modeling of dual frequency liquid crystal materials and devices

We present a director-based model of the dual frequency nature of liquid crystals based on a Debye-type relaxation of the permittivity in the direction parallel to the director. This relaxation is governed by a first order differential equation in terms of the polarization and electric field along the long axis. We demonstrate that this equation can be used as an extension to the well-known Eriksen-Leslie-Parodi theory. Since solution is in the time domain, the frequency response of the applied waveform need not be calculated. Consequently, the device response to arbitrary applied waveforms can be modeled. As an example, we present the switching response of a dual frequency addressed hybrid-aligned nematic cell, and suggest some optimization of the addressing scheme.

Bistable chiral tilted-homeotropic nematic liquid crystal cells

A bistable chiral tilted-homeotropic nematic cell which uses dual-frequency liquid crystal is demonstrated. This cell can be switched between the tilted homeotropic state and the twisted state. The switching mechanisms are achieved by the backflow effect together with the anisotropic properties of the dual-frequency liquid crystal material. The experimental results of this bistable cell are described explicitly.