Deformed Helix Ferroelectric Liquid Crystal Research Articles

The Birefringence and Extinction Coefficient of Ferroelectric Liquid Crystals in the Terahertz Range

In this paper, the refractive index and extinction coefficient of ferroelectric liquid crystals have been examined by the terahertz time-domain spectroscopy system. Two modes of ferroelectric liquid crystal materials, deformed helix ferroelectric liquid crystal (DHFLC), and electric suppressed helix ferroelectric liquid crystal (ESHFLC) are tested as experimental samples. Nematic liquid crystal (NLC) was also investigated for comparison. The birefringence of DHFLC 587 slowly increases with the growth of frequency, and it averages at 0.115. Its extinction coefficients gradually incline to their stable states at 0.06 for o-wave and 0.04 for e-wave. The birefringence of ESHFLC FD4004N remains between around 0.165 and 0.175, and both of its e-wave and o-wave extinction coefficients are under 0.1, ranging from 0.05 to 0.09. These results of FLC will facilitate the examination and improve the response performance of THz devices using fast liquid crystal materials.

Short helix pitch ferroelectric liquid crystals induced in nematic matrix by chiral non-mesogenic dopants

We report the development of chiral smectic C (SmC*) ferroelectric liquid crystals (FLCs) obtained by mixing of a nematic liquid crystal (NLC) as a host and chiral non-mesogenic dopants. The NLC is a binary eutectic mixture of phenyl- and biphenyl-pyrimidines, while chiral dopants belong to homologous series of secondary dilactates with terphenyldicarboxylate core. The induction in the mixtures not only the cholesteric phase, but also the wide temperature range ferroelectric SmC* phase with the helix pitch p0≈100 nm and the spontaneous polarization Ps about 70 nC/cm2 has been confirmed by dielectric, optical, and electro-optical measurements. The developed FLC mixtures are highly efficient for the deformed helix ferroelectric liquid crystal electro-optical mode because the mixtures combine mechanical stability (or mechanical shock resistance) of NLCs and kilohertz switching frequency (due to short helix pitch) of FLCs. These FLCs can be used to create various photonic devices, such as generators of vortex light fields and field-sequential color displays.

Reconfigurable Geometrical Phase Spatial Light Modulator Using Short‐Pitch Ferroelectric Liquid Crystals

AbstractThis article presents an approach to achieve a fast and analog geometrical phase modulation based on the optical axis rotation of the defect‐free Deformed Helix Ferroelectric Liquid Crystal (DHFLC) with a short pitch. This study demonstrates a Spatial Light Modulator (SLM) prototype with a feature size of 3 µm without Fringe Field Effect (FFE), having a phase depth of 1.9π, fast switching time (<250 µs) at a low operating voltage (<7 V), and high diffraction efficiency (>77%). The high phase modulation depth is achieved by developing DHFLC with a cone angle of up to 85˚, which is inherently immune to FFE. The ellipticity is minimized by using a compensation film that can suppress the changes in birefringence under the applied electric field. The proposed SLM is promising in applications such as a real‐time hologram and dynamic beam steering in Light Ranging and Detector (LiDAR).

27‐3: Deformed Helix Ferroelectric Liquid Crystal Based Threshold‐Less Passive Vibration Sensing System

In this article, we proposed a passive vibration sensing system using a threshold‐less deformed helix ferroelectric liquid crystal (DHFLC) cell. Combining the DHFLC cell, piezoelectric film, and optical detector, the system can transform the slight vibration into light intensity signal without a power supply. The system can reach the sensitivity of 165 V/(m/s) and the linearity <1% full range output. The proposed system will be combined with optical fibers to play an essential role in various vibration‐sensing array applications.

40.3: Fast Fringe‐field‐effect Free Continuous 2.25π Phase Modulation Based on Non‐linear Kerr Effect of Vertical Aligned Deformed Helix Ferroelectric Liquid Crystal

40.3: Fast Fringe‐field‐effect Free Continuous 2.25π Phase Modulation Based on Non‐linear Kerr Effect of Vertical Aligned Deformed Helix Ferroelectric Liquid Crystal

43.3: Metal‐Oxide Thin‐Film Transistors for Driving High‐Resolution Active‐Matrix Ferroelectric Liquid‐Crystal Displays

43.3: Metal‐Oxide Thin‐Film Transistors for Driving High‐Resolution Active‐Matrix Ferroelectric Liquid‐Crystal Displays

63‐1: Distinguished Student Paper: Microsecond High‐contrast Continuous 2.25π Phase Modulation Based on Non‐linear Kerr Effect of VADHFLC

Here we disclose a fast (ON time ~50μs and OFF time‐25μs at 55°C), high‐contrast, continuous phase modulator without fringe field effect (FFE). The phase modulator using the Kerr effect of vertical aligned deformed helix ferroelectric liquid crystal (VADHFLC). Specifically, FFE is a long‐term problem for nematic liquid crystal (NLC). In this article, we are disclosing, for the 1st‐time found, that no FFE exists for VADHFLC, even for phase modulator with 1μm pixel pitch, which is an attractive feature for ultra‐high‐resolution display and photonic applications. Moreover, the Kerr constant is 88 nm/V2, and the contrast ratio is larger than 1000:1. It is a promising candidate for high‐PPI AR/VR displays, wavelength selective switch (WSS), hologram, adaptive optics, and LiDARs.

Cover Image, Volume 30, Issue 5

The cover image is based on the Special Section Paper Microsecond high-contrast continuous 2.25π phase modulation based on non-linear Kerr effect of vertically aligned deformed helix ferroelectric liquid crystal by Zheng-Nan Yuan et al., https://doi.org/10.1002/jsid.1123.

Microsecond high‐contrast continuous 2.25π phase modulation based on non‐linear Kerr effect of vertically aligned deformed helix ferroelectric liquid crystal

AbstractHere we disclose a fast (ON time ∼50 μs and OFF time ∼25 μs at 55 ), high‐contrast, continuous phase modulator without fringe field effect (FFE). The phase modulator uses the Kerr effect of vertically aligned deformed helix ferroelectric liquid crystals (VADHFLCs). Specifically, FFE is a long‐term problem for nematic liquid crystals (NLCs). In this article, we are disclosing, for the first‐time found, that no FFE exists for VADHFLCs, even for phase modulator with 1‐μm pixel pitch. It is an attractive feature for ultra‐high‐resolution display and photonic applications. Moreover, the Kerr constant is 88 , and the contrast ratio is larger than 1000:1. It is a promising candidate for high‐PPI augmented reality (AR)/virtual reality (VR) displays, wavelength selective switch (WSS), hologram, adaptive optics, and LiDARs.

P-Terphenyl-containing symmetric tetraesters for nano-scale pitch ferroelectric liquid crystal materials

Design and studying of derivatives of fluorinated and non-fluorinated p-terphenyl-containing symmetric tetraesters as chiral components (CCs) of ferroelectric liquid crystal (FLC) materials working in deformed helix FLC (DHFLC) mode are described. The tetraesters combine a lactate and alcoholic residues in chiral tails. The new CCs induce short helix pitch (as short as 78 nm) and large spontaneous polarization (PS > 100 nC/cm2) at moderate concentrations (as low as 12 mol. %) in a non-chiral biphenylpyrimidine host. We have studied the effects of the (S)-lactate linker, terminal alkyl chains and fluorine atoms on helix pitch and other useful properties of the chiral tilted smectic (SmC*) phase induced by these CCs in the biphenylpyrimidine host. Depending on positions of the fluorine atoms, the fluorination of the p-terphenyl core shows little effect or even reduces the helical twisting power (HTP) of the CCs. At the same time, modifications in the chiral tails can essentially enhance the HTP and other CC performance characteristics. Thus, the combination of the (S)-lactate linker with a (S)-alkan-2-olic residue results in high HTP (up to 85 μm−1) even without fluorine atoms in the chiral tails. Substitution of the (S)-alkan-2-olic residue with a fluorinated analogue, viz. (R)-1,1,1-trifluoroalkan-2-ol derivative, provides further increase of the HTP in the induced SmC* phase up to the highest known to date value of 101 μm−1.

49.5: True Glass‐based Micro‐display with 3µm pixel size using Deformed Helix Ferroelectric Liquid Crystal for VR/AR Displays

A glass‐based micro‐display with pixel size (<3µm) has been fabricated and verified in this work using deformed helix ferroelectric liquid crystal. High contrast (over 600:1), fast response time (< 400μs) and continuous gray scale within 5 V driving voltage are achieved in the prototype.

33‐3: Student Paper: True Microdisplay with 3µm Pixel Size Using Deformed‐Helix Ferroelectric Liquid Crystal for VR/AR Displays

A glass‐based micro‐display with pixel size (<3µm) has been fabricated and verified in this work using deformed helix ferroelectric liquid crystal. High contrast (over 600:1), fast response time (< 400µs) and continuous gray scale within 5V driving voltage are achieved in the prototype.

Phase-only modulation of light.

We disclose the method to obtain polarization insensitive phase-only modulation that preserves both the state and the degree of polarization of light modulated using a medium with controlled birefringence. We find that, in the double-pass configuration involving reflection from the Faraday rotator mirror, such a medium acts as the phase-only modulator. The experimental data measured in the Michelson-interferometer-based setup for deformed-helix ferroelectric liquid crystal cells are found to be in good agreement with the theoretical results. For such cells, we experimentally demonstrate high-frequency (4 kHz modulation rate) 2π phase-only light modulation governed by the average phase shift and solve the problem of optical axes switching.

Ferroelectric liquid crystal with sub-wavelength helix pitch as an electro-optical medium for high-speed phase spatial light modulators

Deformed-helix ferroelectric liquid crystals (DHFLCs) with sub-wavelength helix pitch usually demonstrate sub-millisecond electro-optical response time, but they cannot provide pure phase modulation. However, here, it is shown experimentally that the planar aligned 50 μm thick layer of ferroelectric liquid crystal (FLC) mixture can be used as an electro-optical medium for the phase spatial light modulators (SLMs) if the mixture exhibits smectic C* phase (SmC*) with the helix pitch around 100 nm or less and operates in DHFLCs electro-optical mode. The electrically controlled spiral phase plate (SPP) was constructed on the base of non-chiral biphenylpyrimidines as liquid crystal smectic C matrix and trifluoromethylalkyl diester of p-terphenyldicarboxylic acid as a non-mesogenic chiral dopant. This SPP is able to form and reconfigure the vortex light fields at the frequency up to 3 kHz that was not yet achieved using known liquid crystal spatial light modulators.

Compact actively Q-switched laser for sensing applications

Current active Q-switching is mainly generated by acousto-optical modulators (AOMs) or electro-optical modulators (EOMs). However, EOMs make the setup bulky, while AOMs require the radiofrequency (RF) signal and water-cooling. We present a novel approach to active Q-switching of an integrated waveguide chip laser by utilizing a deformed helix ferroelectric liquid crystal cell (6mm×6mm) with a thickness of 2 mm. This device can be directly integrated onto the Ytterbium-doped waveguide chip and controlled by the electrical signal. In experiments, with an electrical signal with a pulse duration of 2 μs and a magnitude from 10 V to 84 V, the Q-switched lasers can be observed at a repetition rate ranging from 0.1 kHz to 20 kHz. The shortest pulse duration and the maximum slope efficiency is 38 ns and 22% respectively. This novel integrated and low-cost laser source is a promising tool for a broad range of applications such as gas sensing and LIDAR.

Fringe field effect free high-resolution display and photonic devices using deformed helix ferroelectric liquid crystal

ABSTRACT The fringe field effect (FFE) is one of the biggest bottlenecks for the display, and the photonic industry limiting the pixel per inch (PPI) to ~450. The modern applications such as AR/VR headsets and photonic elements such as wavelength selective switches required significantly higher PPI panel. Despite the rigorous research efforts, conventional LCs still show serious FFE, and therefore, hinder the progress of high PPI display and photonic elements. In this article, we studied FFE in the deformed helix ferroelectric liquid crystals (DHFLCs) and found that the subwavelength pitch of the DHFLCs is critically important to suppress the FFE. These DHFLCs show no FFE, for the electric field parallel to the FLC helix, however, we have observed some FFE for the electric field perpendicular to the FLC helix. Additionally, we have found that the high-frequency driving further suppresses the FFE. Later, we deployed DHFLCs to diffraction grating and display to confirm our findings. The proposed DHFLCs with subwavelength pitch can support pixel density up to 4233 PPI for displays, and up to 12,700 PPI for monochromatic photonic devices. Thus, the fast switchable DHFLCs with subwavelength pitch pave the way for the high-pixel density display and photonic devices.

Electric field dependence of optical dispersion process in short pitch ferroelectric liquid crystal

The short pitch ferroelectric liquid crystal is also called as deformed helix ferroelectric liquid crystal (DHFLC) due to its property of deformation of helical structure by weak field. The DHFLC material has been studied for the analysis of optical diffraction process by varying the incidence and transmission angles. The applied direct current (DC) field has shown the blocking of dispersed light at various oblique angles of incidence due to the unwinding of helical structure. This confirms the fixed helical pitch unwinding model of DHFLC structure. On the other hand, the application of same DC field has also shown the enhancement in the direct transmission confirming the dispersed light at oblique angle which is realigned to the direct light direction. The application of alternating current (AC) field exhibited the tunability of dispersed transmission as a function of frequency of applied field due to the winding and unwinding process of helical structure. The phenomenon of dispersion in transmission mode due to Bragg diffraction phenomenon is significant for non display application of DHFLCs such as phase grating.

Low-frequency dielectric processes in deformed helix ferroelectric liquid crystals

A low-frequency dielectric relaxation mode in deformed helix ferroelectric liquid crystal (DHFLC) has been observed at the interface of strongly rubbed substrates and DHFLC material which may find applications in low power consumption FLC devices. The surface-induced dielectric relaxation process at the interface of DHFLC and substrate is called the partially unwound helical mode (p-UHM) due to the unwinding of the helical structure at this interface. After investigation of the material under various parameters such as temperature, variation of the amplitude of probing ac voltage and dc bias voltage, the relaxation frequency of p-UHM is found to be shifted towards Goldstone mode and merged with it. The relaxation frequency of Goldstone mode is found to decrease, whereas the relaxation frequency of p-UHM process increases with the increase in temperature of DHFLC. Finally, both the modes merge and the resultant relaxation frequency is found to be lower than Goldstone mode in SmC* phase. It seems that phason mode and partial helical unwinding mode are coupled together due to dipole moment that is resulting in a new relaxation frequency. p-UHM process is significant for low-power displays and non-displays applications like a part of sensor where weak electric signal is required to be realized without pre-amplification.

Modeling of electro-optic characteristics in vertically aligned deformed helix ferroelectric liquid crystals

New areas of application in the realms of fast phase modulators are stimulating fundamental studies in ferroelectric liquid crystalline materials. Investigation of temperature effect on light transmittance in vertically aligned deformed helix ferroelectric liquid crystal cell is the focus of our study. A fairly linear Kerr constant temperature dependence for two ferroelectric liquid crystal mixtures was analyzed by using linear regression analysis. The key result of this paper represents light transmittance dependencies as a function of squared electric field for a certain temperature range. We also report that strongly pronounced Kerr constant temperature dependence results in several temperatures with 2[Formula: see text] and higher phase modulation for the given electric field. The physics of change in light transmission plots has been analyzed.

Vertically aligned ferroelectric liquid crystals with high Kerr constant for field sequential color displays

In this article, we disclose a field sequential color display based on the vertically aligned deformed helix ferroelectric liquid crystals (VADHFLCs) with enhanced Kerr constant (KKerr). The KKerr for VADHFLCs strongly depends on the pitch (p0) and spontaneous polarization (Ps) of the ferroelectric liquid crystal (FLC) material. The longer pitch results in higher KKerr, but simultaneously provides a poor dark state and slower optical switching, therefore, a tradeoff exists here. A new FLC material has been developed to serve the device requirements. The KKerr of 104 nm/V2 has been achieved that provides response time ~300 μs at the electric field of 1 V/μm. Thereafter, the developed VADHFLC is deployed to a field sequential color display with a driving frame frequency~300 Hz.