Chi Yen Huang

Bistable transflective cholesteric light shutters

We have presented a bistable transflective cholesteric light shutter. The shutter contains dual-frequency cholesteric liquid crystals that incorporate a photocurable monomer. The electro-optical properties and optical microscope images of the shutter were examined. Good correlations between the cholesteric textures and optical properties of the shutters were obtained. The shutter was switched into a wide-band homogeneous transmission mode by a low frequency voltage pulse, and into a selective reflection mode using a high-frequency voltage pulse. The concentration of the monomer apparently affected the electro-optical characteristics of the shutter.

Fast switching of polymer-stabilized liquid crystal pi cells

This work demonstrates a dual-frequency polymer-stabilized liquid crystal pi cell with zero bias and a short response time. The high curing voltage and low curing intensity give the cell a low dark state and a high bright state, such that the transmittance against the applied voltage curve is steep. The response time is under 1ms and is independent of monomer concentration because a strong electric torque is exerted on the liquid crystals. The cell is useful in field-sequential color systems, and the low operating voltage of ∼5V makes the cell compatible with conventional thin film transistor driving voltages.

Switching of polymer-stabilized vertical alignment liquid crystal cell

This work investigates the switching characteristics of the polymer-stabilized vertical alignment (VA) liquid crystal (LC) cell. The experimental results reveal that the fall time of the cell declines as the monomer concentration increases because the vertically-aligned polymer networks accelerate the relaxation of the LC molecules. Furthermore, the formed polymer networks impede the growth and annihilation of LC defects, suppressing the optical bounce in the time dependent transmittance curve of the cell when the voltage is applied to the cell, substantially reducing the rise time of the cell. A step-voltage driving scheme is demonstrated to eliminate completely the optical bounce and hence improve further the rise time of the VA LC cell. The rise times of the pristine and the polymer-stabilized VA LC cells under the step-voltage driving scheme are less than 50% of those under the conventional driving scheme.

Silica-nanoparticle-doped nematic display with multistable and dynamic modes

We demonstrate a silica-nanoparticle-doped hybrid-aligned nematic device, which can be operated in the dynamic mode and the multistable mode. Under ac voltage excitation, the interfacial polarization effect between the homogeneously dispersed nanoparticles and the liquid crystal (LC) host reduces the dielectric relaxation time of the LC-silica dispersion, giving the LC cell a fast response time for the dynamic mode. Under dc voltage excitation, the silica nanoparticles accumulated on the planar side of the cell, creating agglomerates to stabilize the homeotropically aligned LCs, which is retained after switching off the voltage, giving the cell bistable/multistable switching characteristics.

Irreversible redshift of transmission spectrum of gold nanoparticles doped in liquid crystals

The absorption peak of gold (Au) nanoparticles doped in liquid crystal (ANDLC) is controllable by applying an external applied voltage before aggregation occurs. Au nanoparticles aggregate when the dielectrophoresis force, which is induced by the gradient of the square of the electric filed close to the sides of the host liquid crystal cell, overcomes the viscosity between Au nanoparticles and the LCs. This result leads to the irreversible redshift. A controllable filter with unpolarized light enables an ANDLC cell under the threshold voltage to prevent the aggregation effect.

Dual-operation-mode liquid crystal lens

We demonstrate a dual-operation-mode liquid crystal (LC) lens, which is fabricated with the silica nanoparticle-doped (SND) hybrid-aligned nematic (HAN) LC cell. With AC voltage, the cell behaves as a conventional LC lens. The response time of the SND HAN LC lens is faster than that of the conventional LC lens, which is fabricated using the pristine HAN LC cell. This is because that the doped silica nanoparticles may decrease the dielectric relaxation time constant of the cell. The addition of the silica nanoparticles also increases the viscosity of the LC host, suppresses the backflow motion of the LCs and then decreases the response time of the SND LC lens. With DC voltage, the electrophoretic motion of the doped silica nanoparticles and the agglomerate silica networks on the substrate surface cause the SND HAN LC cell to function as a bistable LC lens.

Twisted Nematic Dual-View Liquid Crystal Display Based on Patterned Electrodes

This paper presents a dual-view (DV) liquid crystal display (LCD) fabricated with a twisted nematic (TN) cell that has patterned electrodes on its substrates. The TN DV LCD effectively inhibits the bright state light leakage in the un-intended viewing direction, improving the contrast ratio of the DV LCD when the right and the left subpixels of the DV LCD are addressed simultaneously. In the preferred viewing direction, the TN DV LCD has a high contrast ratio of ~ 140:1.

Electro-optical response of the in-plane switching liquid crystal device fabricated using two-easy-axes substrate.

We investigate the electro-optical response of an in-plane switching (IPS) liquid crystal (LC) device, which is fabricated using the two-easy-axes substrate. The two-easy-axes substrate is fabricated by slightly rubbing the substrate in two different directions. Experimental results indicate that the IPS LC device fabricated using the two-easy-axes substrate has a lower threshold voltage and a faster response time than the traditional IPS LC device, which is fabricated using the unidirectionally rubbed substrate. The weak anchoring condition and the anchoring strengths in two different rubbing directions on the substrate contribute to the fast electro-optical response of the IPS LC device.

In-plane switching dual-frequency liquid crystal cell

The electro-optical responses of the in-plane switching (IPS) dual-frequency liquid crystal (LC) cell operated with the amplitude-modulation method and the frequency-modulation method were investigated. The obtained results reveal that the electric torque exerted to the LCs and the strong anchoring energy produced from the rubbed polyimide dominate the reorientation of the LCs. With the frequency-modulation method, the generated electric torque combined with the strong surface anchoring energy give the cell a very short fall time, which is independent of the applied frequency. A new waveform composed of the amplitude modulation and the frequency modulation of the supplied voltage-pulse to achieve a fast responding IPS LC cell is proposed. The obtained response time is much less than that of the conventional amplitude-modulation method.

Dual-View Blue Phase Liquid Crystal Display

In this paper, we propose a dual-view (DV) liquid crystal display (LCD) using blue phase (BP) liquid crystal (LC) in conjunction with the patterned electrode cell. Given the optically isotropic state of the BP LC material, the DV BP LCD is equipped with a low dark state and, therefore, a high contrast ratio that exceeds 1000 in the intended viewing direction. The patterned electrode structure provides inclined electric field parallel to the unintended viewing direction and creates approximately zero phase retardation, thus suppressing light leakage in the unintended viewing direction.