NCHU, Taiwan

The structure of Blue Phase I LC

 (from Hiroyuki Yoshida)


    Liquid Crystal Materials Research Laboratory (LCMRL) was established at Department of Photonics, Feng Chia University in Taichung, Taiwan since 2007, and moved to Department of Physics, National Chung Hsing University. The main research topic is to study the electro-optic effects and physical properties of blue phase liquid crystal and cholesteric liquid crystal.


Our Research Highlight

Field-induced second-harmonic generation induced by distorted soft chiral crystal

Journal of Physics D: Applied Physics, 56, 125303 (2023)

The nonlinear optical response of soft chiral crystal system-blue-phase (BP) liquid crystals was studied experimentally using a second-harmonic-generation (SHG) microscope. With the aid of the SHG microscope (SHM), the internal coupling between the polarization and structural deformation was visualized in a short time. In this study, a fringing field, formed at the electrode edges, causes lattice deformation of the cubic BPs, which contributes to the flexoelectric-optic response and field-induced SHG at low frequencies. Using the SHM, we can observe the spatial distribution of the induced polarization in the BPs, and the mean SHG intensity of the cubic BP depends quadratically on the strength of the electric field at a lower value. As the applied electric field increases, the structure of the BPs transfers to the chiral nematic phase (N*), and then the SHG intensity remains constant. Compared to the mean intensities of the SHG signal in N* and the different BPs in the low electric field, the SHG signal caused by the lattice deformation in BPs is weaker in N* and depends on the cubic structure of the BPs. The experimental results demonstrate that through the SHM, the influence of the inhomogeneous electric field on the BPs can be exhibited clearly because the response of the SHG signal in BPs is sensitive to field-induced lattice deformation and phase transitions between the BPs and chiral nematic. This will help us elucidate the mechanism of the secondary electro-optical response in BPs and for further improvement and development of high-performance photonic devices using BPs.

A stable reflective state induced by a disturbed planar texture in surface- treatment-free chiral nematic liquid crystals

Optics Express, 29 (19), 30644-30654 (2021)

Chiral nematic liquid crystals possess a one-dimensional periodic helical structure and are one of the oldest known materials with the ability of selective reflection of light. Their helix orientation, determining their optical properties, can be changed by a variety of stimuli, and it is also dominated by the surface treatment, ratio of the elastic constants and cell thickness. Here, we present a simple method to realize an angular independence reflective state, induced by a stable disturbed planar texture, in a surface-treatment-free chiral nematic liquid crystal cell. The scattering state caused by the defect-rich focal-conic texture can be electrically tuned to the reflective state from the disturbed planar texture in a very short time, and vice versa. These two optical conditions are both stable states in the null field until the next trigger. We find that the disturbed planar texture in the chiral nematic can provide a 100viewing angle without reflected wavelength shift. The gray level of the reflected intensity can be tuned via application of the voltage pulses. Moreover, in this work, we discuss the effect of the chiral concentration on stabilizing the disturbed planar texture. When the chiral concentration is higher to induce the blue phases, the change in the texture of the ChNLCs after removing the strong electric field can stop at the disturbed planar texture with high reflectivity. In this work, the optical performance and the bistability based on the disturbed planar texture exhibits great potential for many applications, such as tunable filters, see-through/reflective displays and large-area smart windows.



Pockels Effect in a Tilted Field Switching BPIII Cell," Crystals 2019, 9(11), 598.

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