Imaging of nanoscale birefringence using polarization-resolved chromatic confocal microscopy

We demonstrate a homebuilt confocal microscope with ∼60 nm axial resolution to visualize the optical path length (OPL) of liquid crystals (LCs) inside a 2-domain alignment LC cell. Since the microscope is sensitive to light polarization, it is capable of determining LC orientation by accounting for the OPL variation, ΔOPL. The resolution of birefringence depends on the measured ΔOPL from two cross-polarized channel detections, of which the concept is different from other polarization-resolved optical imaging techniques, but is relatively simple in optical layout and analysis. The different orientations of LCs and the voltage-dependent LC rotation properties in the 2-domain LC cell are monitored and analyzed. Additionally, the complicated LC orientation distribution at the junction of the two domains with different alignments can be clearly observed. It shows great possibilities of examining tissue birefringence related to disease progression and tiny birefringence variation of electro-optical materials under an external field, which are hardly resolved by conventional optical imaging techniques.

Multiple-Color Reflectors Using Bichiral Liquid Crystal Polymer Films and Their Applications in Liquid Crystal Displays

Multiple-color reflectors using bichiral liquid crystal polymer films (BLCPFs) are investigated. The BLCPFs consist of alternate layers of two different single-pitch cholesteric liquid crystal (CLC) layers, named CLC#A and CLC#B. The thickness of each CLC layer equals its single pitch length. The optical properties in terms of reflections, reflection-wavelength ranges, and distributions of reflection spectra of the BLCPFs that result from the fixed pitch length of CLC#A along with the decrease of the pitch length of CLC#B are qualitatively simulated and investigated. The results indicate that the above optical properties of the BLCPFs depend on the LC birefringence and pitch lengths of CLC#A and CLC#B layers. The concept of fabrication method of the BLCPFs by using polymerizable CLCs and thin films of poly(vinylalcohol) or photoalignment materials is discussed. They have potential practical applications in functional color filters, asymmetrical transmission systems, etc., owing to the multiple reflection bands of BLCPFs. Moreover, the BLCPFs, which can enhance the color gamut and light-utilization efficiency of light sources/LC displays, are reported herein.

Characterization of Second-Order Reflection Bands from a Cholesteric Liquid Crystal Cell Based on a Wavelength-Swept Laser

We report the results of an experimental study of the characterization of second-order reflection bands from a cholesteric liquid crystal (CLC) cell that depends on the applied electric field, using a wide bandwidth wavelength-swept laser. The second-order reflection bands around 1300 nm and 1500 nm were observed using an optical spectrum analyzer when an electric field was applied to a horizontally oriented electrode cell with a pitch of 1.77 μm. A second-order reflection spectrum began to appear when the intensity of the electric field was 1.03 V_rms/μm with the angle of incidence to the CLC cell fixed at 36°. The reflectance increased as the intensity of the electric field increased at an angle of incidence of 20°, whereas at an incident angle of 36°, when an electric field of a predetermined value or more was applied to the CLC cell, it was confirmed that deformation was completely formed in the liquid crystal and the reflectance was saturated to a constant level. As the intensity of the electric field increased further, the reflection band shifted to a longer wavelength and discontinuous wavelength shift due to the pitch jump was observed rather than a continuous wavelength increase. In addition, the reflection band changed when the angle of incidence on the CLC cell was changed. As the angle of incidence gradually increased, the center wavelength of the reflection band moved towards shorter wavelengths. In the future, we intend to develop a device for optical wavelength filters based on side-polished optical fibers. This is expected to have a potential application as a wavelength notch filter or a bandpass filter.

High-Contrast and Scattering-Type Transflective Liquid Crystal Displays Based on Polymer-Network Liquid Crystals

The methods to enhance contrast ratios (CRs) in scattering-type transflective liquid crystal displays (ST-TRLCDs) based on polymer-network liquid crystal (PNLC) cells are investigated. Two configurations of ST-TRLCDs are studied and are compared with the common ST-TRLCDs. According to the comparisons, CRs are effectively enhanced by assembling a linear polarizer at the suitable position to achieve better dark states in the transmissive and reflective modes of the reported ST-TRLCDs with the optimized configuration, and its main trade-off is the loss of brightness in the reflective modes. The PNLC cell, which works as an electrically switchable polarizer herein, can be a PN-90° twisted nematic LC (PN-90° TNLC) cell or a homogeneous PNLC (H-PNLC) cell. The optoelectric properties of PN-90° TNLC and those of H-PNLC cells are compared in detail, and the results determine that the ST-TRLCD with the optimized configuration using an H-PNLC cell can achieve the highest CR. Moreover, no quarter-wave plate is used in the ST-TRLCD with the optimized configuration, so a parallax problem caused by QWPs can be solved. Other methods for enhancing the CRs of the ST-TRLCDs are also discussed.

Simple model for estimating band edge wavelengths of selective reflection from cholesteric liquid crystals for oblique incidence

A simple model for estimating band edge wavelengths of selective reflection from cholesteric liquid crystals (CLCs) for oblique incidence is proposed. The proposed model and calculation method are based on a geometrical optics model and Bragg's law. Average refractive indices and Bragg angles in a CLC for the short- and long-wavelength edges of a reflection band are calculated using the model. The band edge wavelengths are determined by substituting the average refractive indices and Bragg angles into Bragg's law. The angular dependences of the band edge wavelengths show good agreement with those calculated by Berreman and Scheffer's [Phys. Rev. Lett. 25, 577 (1970)10.1103/PhysRevLett.25.577] 4×4 matrix method. Although the derived equations are not exact solutions of Maxwell's equations, the proposed method can approximately predict the angular dependences of the center wavelength, bandwidth, and band edge wavelengths of the selective reflection in CLCs.

Microfluidic-based flexible reflective multicolor display

This paper describes a microfluidic-based flexible reflective display constructed using dyed water droplets and air gaps as pixel elements. Our display is composed of a flexible polydimethylsiloxane sheet with a connected pixel-patterned microchannel. Several types of dyed water droplets and air gaps are sequentially introduced to the microchannel through a suction process to display a multicolor image. The displayed image is stable and can be retained without an energy supply. To ensure that images are displayed correctly, the geometric parameters of the dot pixel design and minimum differential pressure necessary to drive the water droplets are evaluated. As a demonstration, we successfully display three-color dot-matrix reflective images and bitmap characters in the microchannel. Our proposed method can be applied to energy-less and color-changeable displays for use in future daily-life accessories, such as bags, shoes, and clothes, and can change the surface color and pattern of these accessories.

Orthogonal Liquid Crystal Alignment Layer: Templating Speed-Dependent Orientation of Chromonic Liquid Crystals

Lyotropic chromonic liquid crystals (LCLCs) have been extensively studied because of the interesting structural characteristics of the linear aggregation of their plank-shaped molecules in aqueous solvents. We report a simple method to control the orientation of LCLCs such as Sunset Yellow (SSY), disodium cromoglycate (DSCG), and DNA by varying pulling speed of the top substrate and temperatures during shear flow induced experiment. Crystallized columns of LCLCs are aligned parallel and perpendicular to the shear direction, at fast and slow pulling speeds of the top substrate, respectively. On the basis of this result, we fabricated an orthogonally patterned film that can be used as an alignment layer for guiding rodlike liquid crystals (LCs) to generate both twisted and planar alignments simultaneously. Our resulting platform can provide a facile method to form multidirectional orientation of soft materials and biomaterials in a process of simple shearing and evaporation, which gives rise to potential patterning applications using LCLCs due to their unique structural characteristics.

Optical simulation of single-cell-gap transflective liquid crystal displays based on surface anchoring energy of periodical nano-grooved structures

The single-cell-gap transflective liquid crystal display (TR-LCD) based on periodic distribution of surface anchoring energy (SAE) of periodical nano-grooved structures is reported in this study. Different SAEs of planar-aligned nematic LC cells are associated with the threshold and operation voltages of the adopted LCs. Thus, according to the transmittance versus applied voltage curves, the regions with strong and weak SAEs in LC cells can be the transmission and reflection regions of a TR-LCD, respectively. According to the simulation results using 1D-DIMOS software, the phase retardation of a strong SAE region is approximately twice as large as that of a weak SAE region when a specific voltage is applied, and a suitable difference in SAE exists between these two regions. Moreover, various SAEs based on periodical nano-grooved structures can be fabricated to demonstrate the TR-LCD.

Optical design for single-mode and single-cell gap transflective liquid crystal displays

Generally, for transflective liquid crystal displays with different modes and different cell gaps between the refractive and transmissive parts, precise process control to pattern the electrode and match the cell gaps may reduce the yield and thus, require high cost. This paper proposes a simple transflective liquid crystal display with a single-mode and single-cell thickness without a patterned electrode to achieve better productivity. The proposed transflective liquid crystal display consists of three half-wave retardation films, two quarter-wave retardation films, and an LC layer, whose optical performance was confirmed by both simulation and experiment. The optimal optical configuration to obtain an excellent dark state in the visible range was determined by the Mueller matrices calculus, which was applied to each optical component. The calculated and experimental results showed that the proposed transflective LC structure has excellent electro-optical properties and is expected to have many liquid crystal display applications.

Single-cell gap polymer-stabilized fringe-field switching transflective liquid crystal display

Transflective liquid crystal displays are highly desired for mobile devices because they can be operated either in transmissive mode, illuminated by backlight in dark ambient light conditions, or reflective mode, illuminated by ambient light in bright ambient light conditions. We developed a single-cell gap transflective display based on fringe-field switching. The display consists of transmissive and reflective subpixels whose operations are synchronized through polymer stabilization. This display has a high contrast ratio because the transmittance-voltage dependences of the two subpixels are similar (they are both in dark state at 0 V and in bright state at an applied voltage) and do not interfere with each other. It has the advantages of single-cell gap and no in-cell retarder and its manufacturing process is simple.

Reflective-emissive photoluminescent cholesteric liquid crystal display

We fabricated a photoluminescent cholesteric liquid crystal (PL-CLC) cell for a display application that can be used to display high-quality moving pictures under all ambient conditions including dark and sunlit conditions. The PL-CLC cell is switchable between the reflective mode under bright conditions and the emissive mode in the dark. The effective reflectance of the PL-CLC is higher than that of a conventional CLC device by more than 30%, and the contrast ratios were approximately 10 and 7 in the reflective and emissive modes, respectively. We directly compared the proposed PL-CLC cell with conventional LCD and CLC cells under sunlit, office, and dark environments and confirmed that the PL-CLC cell exhibited superior visibility under all ambient conditions.

Optically controllable bistable reflective liquid crystal display

This Letter demonstrates a photo-addressable, bistable reflective liquid crystal display that is based on a dye-doped liquid crystal (DDLC). Bistable bright and dark states can be attained using the 45 deg twisted nematic (TN) and photo-induced isotropic states (PHI) of the DDLC, respectively. Both the 45 deg TN and PHI states can exist stably for tens of hours, and each can be rapidly switched to the other by the isomerization effect using UV and green light. A bistable reflective liquid crystal display is simply fabricated, easily operated, and rapidly switched. It therefore has the potential to be used in portable information systems.

Transflective digital holographic microscopy and its use for probing plasmonic light beaming

We present a novel digital holographic microscopy technique termed transflective digital holographic microscopy in order to probe plasmonic beaming fields and to view their platform structures. Here, we borrow the term, 'transflective', a portmanteau meaning a blend of transmission and reflection according to the light-collecting condition, which is conventionally used in liquid crystal display systems. Incorporating the transmission type holographic microscopy with the reflection type, achieved by the utilization of polarization property of coherent light waves, we propose an application of the system to probing the beam path and its corresponding structure in plasmonic beaming phenomena.

Transflective display using a polymer-stabilized blue-phase liquid crystal

A wide view, submillisecond response, and single-cell-gap transflective display using a blue-phase liquid crystal (BPLC) is proposed. To balance the optical phase retardation between transmissive (T) and reflective (R) regions, in-plane protrusion electrodes are formed with different gaps in the two regions. This display exhibits reasonably high optical efficiency and well matched voltage dependent transmittance and reflectance curves. Using biaxial films and broadband wide-view circular polarizers, the viewing angle with 100:1 contrast ratio is obtained over the entire viewing cone in the T region, and 10:1 over 50 degrees in the R region. The potential application is emphasized.

Wide-view and sunlight readable transflective liquid-crystal display for mobile applications

A wide-view single cell gap transflective liquid-crystal display (TR-LCD) using the fringe field switching effect is proposed by incorporating a quarter-wave in-cell-retarder below the liquid-crystal (LC) cell in the reflective part. By optimizing the angle between the electrode stripes and the LC rubbing direction in the transmissive and the reflective regions, this TR-LCD exhibits a high optical efficiency and good match between the voltage-dependent transmittance and reflectance curves. Without using any phase compensation films, this TR-LCD exhibits a wide view with 10:1 contrast ratio over a 60 degrees viewing cone in the transmissive mode and over a 40 degrees cone in the reflective mode, which is adequate for mobile displays.