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Organic light-emitting diodes featuring layers with a spontaneously formed buckled geometry are demonstrated to offer at least a twofold improvement in light extraction efficiency across the entire visible spectrum.

We fabricated a hybrid structure composed of a dye-doped low-molecular-weight cholesteric liquid crystal (low CLC) sandwiched between polymer cholesteric liquid crystal (PCLC) films with the same handedness as the low CLC, and studied its lasing characteristics. Defect-mode lasing was observed with a threshold reduced by a factor of 3 compared with that in a simple dye-doped low CLC cell. Experimental and simulated results for the transmittance, emission, and photonic density-of-states spectra are also discussed.

A liquid crystal (LC) photonic device with an anisotropic optical heterojunction structure has been fabricated. The device has a phase-retarding nematic LC (NLC) layer sandwiched between two polymer cholesteric LC films with right-handed helices of different pitches. Electrotunable non-reciprocal light transmittance and unidirectional circularly polarized (CP) lasing emission have been successfully demonstrated for this device structure. Two left CP (LCP) lasing emission peaks are observed at the edges of the overlapping region between the two photonic bands in the structure and are shifted upon the application of a voltage. In contrast, a non-reciprocal right CP (RCP) lasing emission peak emerges at one of the band edges and diminishes upon the application of a voltage. These phenomena are interpreted based on the selective reflection of RCP light and the reorientation of the NLC molecules by the application of a voltage.

We have experimentally demonstrated the optical diode performance in a two-layered device consisting of a cholesteric liquid crystal (CLC) film with a right-handed helical structure and a nematic liquid crystal (NLC) layer as a phase retarder of a half wave. Right-circularly polarized (RCP) light of the wavelength the same as the optical pitch of the helix is totally reflected by the CLC film when the light is incident from the CLC film side. On the other hand, if the incidence is made from the NLC side, RCP is transformed to left-circularly polarized (LCP) light and is then passed through the CLC film. Not only such an optical diode performance, i.e., unidirectional propagation (non-reciprocal transmission), but also its electro-tunability was also shown. The transmittance can be essentially tuned between 0% and 100%.

Manipulation of light is in strong demand in information technologies. Among the wide range of linear and nonlinear optical devices that have been used, growing attention has been paid to photonic crystals that possess a periodic modulation of dielectric function. Among many photonic bandgap (PBG) structures, liquid crystals with periodic structures are very attractive as self-assembled photonic crystals, leading to optical devices such as dye lasers. Here we report a new hetero-PBG structure consisting of an anisotropic nematic layer sandwiched between two cholesteric liquid-crystal layers with different helical pitches. We optically visualized the dispersion relation of this structure, displaying the optical diode performance: that is, the non-reciprocal transmission of circular polarized light at the photonic-bandgap regions. Transmittance spectra with circularly polarized light also reveal the diode performance, which is well simulated in calculations that include an electro-tunable diode effect. Lasing action was also confirmed to show the diode effect with a particular directionality.

The effect of the introduction of polymer cholesteric liquid crystal (PCLC) films on the threshold of dye-doped cholesteric liquid crystal (CLC) distributed feedback (DFB) cavity lasing has been investigated. A PCLC film used to reflect a pump beam brings about the efficient use of incident energy, whereas a PCLC film used to reflect the emission contributes to amplifying the stimulated emission. As a result, the cell, in which both PCLC films are introduced, gains about a 60% reduction in the lasing threshold. It is also found that a lasing threshold exists not only for the excitation energy but also for the emission intensity. Namely, the lasing starts to occur at a certain emission level irrespective of the cell structures.

We have studied the lasing characteristics of a dye-doped nematic layer sandwiched by two polymeric cholesteric liquid crystal (CLC) films as photonic band gap (PBG) materials. The nematic layer acts as a defect layer, the anisotropy of which brings about the following remarkable optical characteristics: (1) reflectance in the PBG region exceeds 50% due to the retardation effect, being unpredictable from a single CLC film; (2) efficient lasing occurs either at the defect mode wavelength or at the photonic band edge; and (3) the lasing emission due to both the defect mode and the photonic band edge mode contains both right- and left-circular polarizations, while the lasing emission from a dye-doped single CLC layer with a left-handed helix is left-circularly polarized.

The research on birefringence and polarization has a long history and began with the discovery of light polarization by the Dutch scientist Christiaan Huygens in 1690 when he was experimenting with two calcite plates. Then, Etienne L. Malus accidentally discovered that the light reflected at an angle from the windows of Luxembourg Palace was polarized, which he reported in 1809, and in 1812 David Brewster announced the law of light polarization by reflection and refraction, which now takes his name. Furthermore, William Herapath discovered in 1852 that a synthetic crystalline compound, iodoquinine sulfate (also called herapathite), can polarize the light of all wavelengths in the visible region, a phenomenon that is now the underlying principle of current absorption-type polarizers.

"NISSEKI LC Film" is a liquid crystalline polymer film, which has unique optical properties as well as excellent reliability and thermal stability. There are two types of film, one has a twisted nematic structure and another has a hybrid nematic structure. They are suitably used as color compensator of STN-LCD and viewing angle compensator of TFT-LCD, respectively.

Lasing from a dye-doped cholesteric liquid crystal (CLC) has been studied in cells with a single-output window. One of the glass substrates of the cells was coated with a polymeric CLC film having a high reflectance for laser emission or an aluminum layer for reflection of both pump and lasing beams. Laser emission toward one direction was observed with enhanced intensity.

We have demonstrated a new type of lasing mode in a dye-doped 100-µm-thick nematic liquid crystal layer sandwiched between two polymeric cholesteric liquid crystal films functioning as a photonic crystal. The fabricated cell exhibits several characteristic dips in the transmittance spectrum in addition to fine fringes originating from a Fabry–Perot cavity mode. These dips are due to the phase retardation between optical eigenmodes in the birefringent medium, which is not realized in an isotropic layer. The cell shows multimode lasing at wavelengths corresponding to transmittance maxima within the stopband region when the nematic layer is doped with dyes.

We demonstrate that the devices with buckling as a grating can effectively extract the substrate mode as well as the indium tin oxide/organic mode even without any hemisphere lens or microlens array. This is achieved by multiple reflections of the substrate mode with the randomly buckled cathode layer through appropriate device dimensions.

We fabricate a buckling structure by thermally depositing aluminum on a polymer surface and cooling it to room temperature, and utilize the structure as a microlens aggregate for organic light emitting diodes. The aspect ratio of the lens is increased by a multiple deposition process. We demonstrate that the characteristics of the outcoupled emission of this device are improved from various perspectives such as efficiency, emission angle, and reduced spectral change. These improved characteristics originate from randomized double-curvatured lens structure with full surface coverage.

We compared the viewing angle performance of NW-TN-LCDs compensated with hybrid-aligned discotic (DH) and hybrid-aligned nematic (NH) films. We find that the DH films give superior contrast over wider viewing angles than the NH films, but that the NH films show less color shift at wider angles with better gray scale stability. We conclude that DH films are most suitable for data viewing in notebook computer displays and desktop monitors, whereas NH films are more suitable for viewing natural images in television and multimedia applications.

Photoinduced circular anisotropy has been demonstrated in thin films of a main-chain polymeric liquid crystal (PLC) system doped with photochromic $\mathsf{W}$-shaped molecules containing two azobenzene groups by irradiating with circularly polarized light (CPL). Reversible photoinduced circular dichroism (CD) was observed with sign relevant to the handedness of the CPL. The experimentally observed CD spectra were analyzed using the DeVoe polarizability model associated with the coupled oscillator method. We also propose a mechanism for the photoinduced circular anisotropy in our system; nucleating the $\mathsf{W}$-shaped molecules with preferential twisted conformation by CPL irradiation, and triggering the local formation of a chiral structure in the $\mathsf{W}$-shaped-molecule-doped main-chain PLC medium.

We have studied the lasing characteristics from a dye-doped nematic layer sandwiched by two polymeric cholesteric liquid crystal (PCLC) films as photonic band gap materials. The nematic layer possessing birefringence brings about the following remarkable optical characteristics; (1) reflectance in the photonic band gap (PBG) region exceeds 50% due to the retardation effect, being unpredictable from a single CLC film, (2) efficient lasing occurs either at the notch of PBG or at the photonic band edge, (3) the lasing emisions contain both right- and left-circular polarizations, and (4) tunable lasing can be achieved by the reorientation of nematic liquid crystal molecule under the application of an electric field.

We have succeeded in fabricating monodomain polymer cholesteric liquid crystal (PCLC) films by spin coating a polymer solution onto glass substrates with polyimide coated and rubbed unidirectionally. The thickness and helical pitch were well characterized by controlling the rotational speed of the spin coater and the chiral unit content of the polymer solution, respectively. Lasing from dye-doped PCLC films utilizing the photonic structure was confirmed.

We have developed a novel transflective TFT-LCD with two hybrid aligned nematic compensators (NH film). Already we have presented the wide-viewing angle transflective TFT-LCD with one hybrid aligned nematic compensators. Based on the results of computer simulation, we introduced the second NH film, which located on the front of the LC cell, instead of the uniaxial film. We optimized the parameters of NH films, the retardation and the average tilted angle, by computer simulation. As the result, the newly developed TFT-LCD with two NH films (retardation Δnd = 100nm, average tilt angle = 20degree) is viewable at wider angles than that with one NH film in transmissive mode. Viewing angle range (CR >10) of this LCD, reached 145 degree (vertical direction) and over 160 degree (horizontal direction). This wide-viewing angle system can apply to not only transflective TFT-LCD, but also ordinary transmissive one.

We have developed a novel transflective TFT-LCD with a hybrid aligned nematic compensator (NH film). We discuss the effects of the optical parameters of NH film based on the results of computer simulations. When the parameters are optimized, a newly developed display made with NH film exhibits a high contrast ratio and good grayscale stability over a wide range of viewing angles in the transmissive mode. In particular, grayscale inversion in the vertical direction is well restrained.

The performance of a reflective color NB-STN-LCD with a single polarizer in combination with a twisted-nematic compensator is discussed. In contrast to combined uniaxial retarder sheets, it is possible to create a display with a high contrast ratio using only a single sheet, which is one of the advantages of the twisted-nematic compensator. For optimizing the performance of the display, the dispersion of the birefringence was found to be essential as well as the twist angle and the retardation of the compensator.

A novel single-polarizer reflective TN-LCD SPRTN-LCD with hybrid aligned nematic compensation films was developed. The newly developed SPRTN-LCD exhibits high contrast ratio and good achromaticity over a wide range of viewing angle. The SPRTN-LCD with hybrid aligned nematic compensation films is a promising candidate for the full color reflective LCD with a high quality of image.

The Frank elastic constant ratios, K 12 and K 32 in a homologous series of nCB (n = 5 − 8) were determined as a function of temperature by observing the angular dependence of Rayleigh light scattering intensity. The temperature dependence of K 12 exhibits an odd-even effect. Both K l2 and K 32 obtained are clearly smaller than the reported values by means of other methods, e.g., the Frederiks transition method. However, our K 31 indirectly deduced from K 32/K 12 shows good agreement with that by others. Characteristic temperature dependences due to the appearance of the pretransitional ordering were observed in 8CB which has the smeclic A phase below the nematic phase; K 12 significantly diverges and K 12 shows a sudden descent as a smectic A is approached. On the basis of these experimental results, we claim that the Rayleigh light scattering is the most adequate method of determining the Frank constant ratios.

In the current optical data storage, binary coding is used, in which mark and null states correspond to high and low levels of reflected light. In the binary coding, the capacity of recording information can be increased by minimizing the pit size and maximizing the track density. However, the minimization of pit size will reach a limit even if near-field optics are used. To overcome this limitation, we have proposed and demonstrated multilevel optical data storage by changing the pit depths of a birefringent film. In this method, the volume of stored information can be increased without increasing the pit density. Multilevel pits with the width of 1 µm and with various depths were formed on a liquid crystalline polymer film with the birefringence of 0.20, and the phase difference between orthogonal polarizations was confirmed to be proportional to the depth of the pits.

The twist elastic constant K 22 in 5CB was determined as a function of temperature by the following four independent methods; (1) electric field static light scattering, (2) electric field dynamic light scattering, (3) angular dependence of the scattered light intensity combined with a K 11 or K 33 measurement, and (4) Frederiks transition detected by forced Rayleigh scattering. The first one is a measurement of relative scattered light intensity as a function of the applied voltage in a proper optical geometry, and was used to determine K 22 for the first time. Each measurement gave a K 22 value within an accuracy of ±4%. The collected values that were determined by the four methods were located within ±7% from each other. It was also confirmed that they agree with other recent measurements.

A system based on photon correlation spectroscopy has been constructed using a microcomputer to measure the spectral width of Rayleigh light scattered from nematic liquid crystals. Maps in the (α, φ, θ=0° ) space have been devised to find the most suitable scatterinu geometries for the determination of K 1/ηsplay, K 2/ηtwist and K 3/ηbend, where α, φ and θ specify the scattering angle and the director direction. The ratios have been obtained as a function of T NI–T for 4'-alkyl-4-cyanobiphenyls (n=5∼8).

A novel method for determining the twist elastic constant K 22 is proposed. A critical magnetic field strength due to a Frederiks transition was detected by utilizing the anisotropy of diffusion constants of a dye by means of forced Rayleigh scattering technique. Measurements were made for 5CB and were compared with those made by other methods. It was found that the obtained values are comparable with those from other recent measurements.