This study demonstrates all optical switches between the four diffractive light levels of a body-centered tetragonal
photonic crystal. The sample is based on holographic polymer-dispersed liquid crystals that are fabricated using a twobeam interference with multiple exposures. The switching mechanism bases on the effective index modulation of the PC that contains a liquid crystal/azo-dye mixture could be controlled by two pumping laser beams. The switching time between the blue-laser-pumped and the blue-and-green-laser-pumped levels is fast.
This investigation reports for the first time a novel phenomenon, called band-tunable color cone lasing emission (CCLE),
based on a single-pitched one-dimensional photonic crystal-like dye-doped cholesteric liquid crystal (DDCLC) cell. The
lasing wavelength in the CCLE pattern is distributed continuously at 676.7-595.6 nm as the oblique angle increases
continuously from 0° to 50° relative to the helical axis. The variation of the lasing wavelength in the CCLE with the
oblique angle is consistent with that of the wavelength at the long-wavelength edge (LWE) of the CLC reflection band
(CLCRB) with the oblique angle. Simulation results obtained utilizing Berreman's 4×4 matrix method show that, at each
oblique angle, the associated group velocity and density of photonic state (DOS) are near zero and large at the shortwavelength
edge (SWE) and LWE of the CLCRB, respectively, and are in good agreement with experimental results.
The particularly strong lasing ring emission at a cone angle of ~35° can be explained to be likely due to a special effect
that, under the condition of overlap between the LWE of the CLCRB measured at 35° and the SWE of the CLCRB
measured at 0°, the LWE and SWE fluorescence propagating along 35° and 0°, respectively, may indirectly enhance
each other due to individual enhanced rate of spontaneous emission. Furthermore, the lasing band of the CCLE can be
tuned from long-wavelength (deep red~orange) to short-wavelength (orange~green) regions by changing the
concentration of the chiral or by the photo-irradiation on a DDCLC cell with a photoisoemerizable chiral dopant.
This work studies the biphotonic effect in samples that are cholesteric liquid crystals (CLCs) doped with azo-C5. The
experimental results show that the photo-isomerization of azo-C5 not only changes the clearing point of the sample, but
also shifts the reflection band that is associated with the planar texture. Additionally, azo dye-doped CLCs (DDCLCs)
have bi-stable or tri-stable states, as determined by the ambient temperature. Photo-switching between these bi-stable/tristable
states is systematically studied. The result indicates that photo-addressing one of these states (planar, focal conic,
and isotropic states) using a low- or high-intensity Ar+ laser beam is feasible. The results thus obtained are used to
fabricate a photo-rewritable DDCLC display.
To investigate the effect of cholesteryl pendant groups on the phase behaviors of
related copolymers, a new cholesteryl-containing liquid crystalline monomer was
synthesized and copolymerized with an achiral comonomer in various molar ratios. The
phase diagram and optical properties of the synthesized copolymers containing the
cholesteryl pendant group were studied and compared with those of the monomer
mixtures. The layer-like arrangement of the smectic mesophase with different monomeric
compositions of copolymers was investigated using an X-ray diffraction analyzer. The
dependence of the reciprocal central reflection wavelength on the mole fraction of the
chiral monomer for monomer mixtures and copolymers was investigated.
A series of novel side chain liquid crystalline polyacrylates with pendent chiral
groups was synthesized. Copolymerization of the monomers was carried out and the
physical properties of the copolymers were investigated. Two miscible chiral compounds
were also synthesized and used as chiral dopants to induce cholesteric liquid crystalline
phases of polymers. The optical properties of the induced cholesteric liquid crystalline
polymers were investigated by using UV-vis spectrometer. The appearance and the color
variation of the polymer films before and after UV irradiation were also investigated.
This letter examines a planar cholesteric cell (CLC) doped with a collocation of two laser dyes as a one-dimensional photonic crystal. Adding the photo-tunable chiral material-AzoB allows the CLC photonic crystal can be lased at the band edges of the photonic band gap with a tuning range of over 100nm. Tuning is performed by irradiating the chiral AzoB material with UV light so that it undergoes trans-cis isomerization in the CLC film. The tuning range is the visible region from 563nm to 667nm. Moreover, the tuning is reversible.