Light energy accumulation by cholesteric liquid crystal layer at oblique incidence

Oblique propagation of light through a planar layer of a cholesteric liquid crystal (CLC) is solved by Ambartsumian’s modified layer addition method. Two cases are considered, namely, the case when dielectric boundaries have a minimum influence on light transmission and the case when the CLC layer is in a vacuum. It is shown that in the first case a total internal reflection can happen for the fast eigen-mode at large incidence angles. New important features of light reflection (transmission) spectra, photonic density of states and accumulated energy density in the CLC layer are studied. The light localisation peculiarities in the CLC layer at oblique incidence is investigated too. It is shown that the light localisation for both the long-wavelength edge mode and the short-wavelength edge mode changes differently when the incidence angle changes. The obtained results can be used in the design of low-threshold lasers, in solar cell systems, in chiral photonics, in systems strongly absorbing light at certain wavelengths and when designing systems with absorption suppression created on the base of absorbing media, etc.     

Double telecom band thermo-optic switch based on dual-line filled photonic liquid crystal fibres

We demonstrate a thermo-optic switch based on photonic liquid crystal fibres (PLCFs) in which two lines of air hole are selective filled with liquid crystal (LC), with a high extinction ratio of more than 20 dB around 1310 nm and 1550 nm. Only in the range of 2.0°C it can perform a turn off and on operation of transmitted light in the second telecom band around 1550 nm while the first telecom bands around 1310 nm is still on. Due to the splitting of the bandgap, the switching function is achieved in this kind of PLCFs. Before the cleaning point (CP) of LC, a broad bandgap from about 1120 nm to 1320 nm splits into two ones, which are continuing inducing huge bandgap extension to shorter wavelength and longer wavelength after the CP of LC, respectively. Moreover, the temperature responses around the CP of LC is also investigated. Its sensitivity is about ?92.32 nm/°C around the CP of LC. Therefore, such kind of selective-filled PLCFs could find potential applications as thermo-optic switch and temperature sensor in the telecom band.     

Temperature-controllable beam splitter and optical filter based on filling liquid crystal into both ends of photonic crystal fibres

We first presented an optical device of integrated beam splitter and filter based on the photonic crystal fibres (PCFs) with both ends of the air-holes filled with liquid crystal (LCs). All of the air-holes of one end of PCFs were filled with LCs and for the other end two air-holes near the solid core were selectively filled with LCs. As a beam splitter, when the two-filled-holes end was heated, the light power partly transmitted steadily from the central solid core into the two holes filled with LCs after the clearing point. As a filter, when the two-filled-holes end was heated, a peak near 760 nm of transmission spectrum got weak and another peak near 608 nm was maintained. While heating the full-filled end, the peak near 760 nm got strong and the peak near 608 nm got extremely weak. So this optical device could be applied to beam splitter and filter.     

Tuning of Photonic band gap via combined effect of electric and optical fields in a blue phase liquid crystal composite

ABSTRACT

Blue phase liquid crystals are soft 3D photonic crystals in which the liquid crystal molecules self-assemble to form a cubic structure with lattice spacing of a few hundred nanometers resulting in selective reflection of colours in the visible spectrum. The corresponding wavelength or the ‘photonic band gap’ can be tuned using various external stimuli such as thermal, electric, magnetic and optical fields. Here, we report efficient tuning of photonic band gap by utilising the combination of electric and optical fields in a blue phase liquid crystalline system. The studies indicate that the chirality of the medium has a direct bearing on the direction of the wavelength shift and the extent of the photonic band gap tunability. More importantly, the synergistic effect of the two fields helps in reversible tuning of the band gap.