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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.

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.

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.

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.