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Now showing 1 - 6 of 6

Color tuning in thermo-sensitive chiral photonic liquid crystals based on the pseudo-dielectric heating effect
(2019-12-15)
Yeh, Min-Chih
;
Yang, Sheng-Hsiung
;
Lee, Wei
;
照明與能源光電研究所
;
影像與生醫光電研究所
The ability of electro-thermal tuning in center wavelength (X,) of the Bragg reflection band is promoted in cholesteric liquid crystal (CLC) containing a positive-dielectric-anisotropy liquid crystal host (E7) and a binary chiral dopant (R-811 and R-5011). In the CLC mixtures with a fixed R-811 content of 30 wt%, the transition temperature of the smectic-A phase to CLC phase decreases when the R-5011 loading increases. The CLC systems are temperature-sensitive, each exhibiting a temperature range of about 9-12 degrees C in the CLC phase. Optimization of the content of R-5011 at 1.5 wt% allows for the remarkably effective thermal tuning in lambda(c )from 780 nm to 380 nm in response to a temperature increase of merely 3 degrees C from the room temperature. Under the mechanism of pseudo-dielectric heating, the tunable lambda(c) can shift in the entire visible spectrum by an applied voltage as low as 7 V-rms at a frequency of 2 MHz across the cell gap of a 4.8-mu m-thick cell. Furthermore, a multifunctional and operation-reversible device is demonstrated by the control of the applied AC voltage, yielding an optical device in which the reflection band can be tuned and the mode can be switched among the reflection, scattering, and transparent states. (C) 2019 Elsevier B.V. All rights reserved.
Pseudo-dielectric relaxation-enabled electrothermal tuning of reflective color in a soft chiral photonic crystal
(2019-01-01)
Wu, Po-Chang
;
Wu, Guan-Wei
;
Lee, Wei
;
照明與能源光電研究所
;
影像與生醫光電研究所
Many published papers bear flaw information caused by misinterpreting the pseudo-dielectric relaxation in liquid crystal (LC) confined in thin cells. The pseudo-dielectric relaxation stems from the cell geometries or parameters, which should not be misrecognized as an inherent material property of the LC. In this work, we explored the pseudo-dielectric relaxation and demonstrated an unconventional tuning means to electrically manipulate the reflective color of a typical cholesteric LC cell based on the heating due to the pseudo-dielectric relaxation. A tuning range in the full-color spectrum can be easily achieved by a limited temperature change of merely a few degrees Celsius.
Chiral liquid crystals as biosensing platforms
(2016-01-01)
Lee, Mon-Juan
;
Sung, Yu-Chien
;
Hsiao, Yu-Cheng
;
Lee, Wei
;
影像與生醫光電研究所
The texture observation has long been the core technique in liquid crystal (LC)-based bioassays. Its working principle stems from the dark-to-bright texture change induced by the interruption of the initially homeotropic alignment in nematic bulks or from the radial-to-bipolar configuration transition in LC droplets in the presence of biomolecules. One of the drawbacks of this observational scheme, which requires a polarizing optical microscope, is the difficulty in quantitative analysis. In this invited paper, we report on our recent development of alternative optical biosensing techniques based on cholesteric LCs (CLCs) without the use of a polarizer. The increase in structural order in a vertically anchored CLC cell in the quasi-planar state provides a means to allow detection and quantification of the concentration of biomolecules immobilized on the interface between the mesophase and the surfactant DMOAP for LC vertical alignment.
Conditions for the formation of a uniformly lying helix structure induced by the electrohydrodynamic effect
(2017-01-01)
Nian, Yu-Lin
;
Wu, Po-Cheng
;
Lee, Wei
;
影像與生醫光電研究所
;
Institute of Imaging and Biomedical Photonics
The uniform lying helix (ULH) structure in a cholesteric liquid crystal (CLC) cell has been widely discussed in the literature. Based on the electrohydrodynamic (EHD) effect, we have suggested that the voltage-induction of a well-aligned ULH state can be fine-tuned in a CLC cell by optimizing both the amplitude and the frequency of the applied voltage. However, since the EHD effect is correlated with the migration of mobile ions within the bulk of the cell, the ionic conditions for such an EHD-induced ULH state have not been clarified. In this research, we focus on studying the influence of ion density and the diffusivity on the formation of the EHD-induced ULH structure in a CLC cell, followed by finding out some key conditions for the generation of well-aligned ULH states.
Advanced color-reflective dual-frequency cholesteric liquid crystal displays and the driving matrix
(2017-01-01)
Hsiao, Yu-Cheng
;
Yeh, En-Rong
;
Lee, Wei
;
影像與生醫光電研究所
;
Institute of Imaging and Biomedical Photonics
We propose a novel color-reflective, dual-frequency cholesteric liquid crystal display (DFCLCD) by employing hybrid alignment treatment. The switching voltage is significantly lowered to favor the thin-film transistors used in the current display market and the response time is drastically reduced to the millisecond level while the bistability remains. Test cells with three distinct helical pitches were fabricated to demonstrate the concept of color pixels. The DFCLCD can be directly switched from the bright planar state to the light-scattering state by a low-frequency voltage pulse, and reversibly by a high-frequency pulse. A drive scheme is presented for the advanced color DFCLCD.
A thermally tunable narrowband selector based on a chiral nematic containing a binary thermosensitive chiral dopant mixture
(2017-01-01)
Yang, Zong-Han
;
Hsiao, Yu-Cheng
;
Shen, Dong
;
Lee, Wei
;
光電系統研究所
We employed a thermosensitive chiral dopant (CD), characterized by its thermoinduced change in helical twisting power (HTP) in terms of the handedness and strength, to shift the Bragg reflection band of a CLC. A thermally tunable photonic bandgap (PBG) device was demonstrated using a one-dimensional asymmetric photonic crystal (PC) infiltrated with the CLC as a defect layer. With a temperature controller to shift the PBG of the CLC, two narrow transmission bands can be tuned in the spectrum dominated by the asymmetric PC structure. This optical device can find applications as a tunable narrowband wavelength selector or an intensity controller.

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