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We propose a thermal modulation structure made of two identical SiO2 slabs coated by Dirac semimetal (DSM) films and separated by a nanoscale vacuum gap. The energy transmission probability reveals that the coupled surface plasmon polaritons (SPPs) between the two DSM films, and the surface phonon polaritons (SPhPs) supported by the SiO2 substrate can vary sensitively with the Fermi level, the degenerate factor of 3D Dirac points and the thickness of the DSM film, thus providing the possibilities for modulating the radiative heat transfer by tuning these parameters. Based on Maxwell's equations incorporating fluctuational electrodynamics, the effects of these parameters on the heat transfer coefficient and the thermal modulation contrast are numerically analyzed. Under proper parameters, higher modulation contrasts are obtained by continuously tuning the Fermi level from 0.05 eV to 0.3 eV. The obtained results might be helpful in designing a DSM-based thermal modulator with higher modulation contrasts. [ABSTRACT FROM AUTHOR]

This study proposes a simple method of designing a high-speed liquid crystal variable retarder (LCVR) with reflection mode. First, a series of simple formulas is provided for analysing the effects of tilt incidence and birefringence of the liquid crystal on the phase retardation and response time of the LCVR. Then, a reflective LCVR is fabricated to validate the theoretical analysis. Measured results show that the response speed can reach 2.7 kHz with a phase retardation of 1 λ. Furthermore, the theoretical curve is close to the measured curve while the incident angle is less than 10°. However, the theoretical and measured values show a considerable difference under a large incident angle. This problem is discussed, and a modified method is given. This work is helpful for the design and fabrication of high-speed LCVR. [ABSTRACT FROM AUTHOR]

We propose a voltage-tunable hyperbolic dispersion metamaterial (HDM) consisting of silver nanowires and nematic liquid crystals (NLCs). The metamaterial shows a novel electro-optic effect, in which the dispersion relation switches between elliptic and hyperbolic dispersions at the visible waveband with an external electric field. HDM functionality is analysed in detail based on the effective medium theory. 5CB NLC is chosen for the simulation, and tunability is achieved between 454 and 475 nm. The effects of filling ratio on tunability are also analysed. Tunable bandwidth widens from 21 to 45 nm with decreased filling ratio from 0.27 to 0.09. Finally, the effects of birefringence (Δn) are considered. Tunable bandwidth widens from 21 to 63 nm as Δnchanges from 0.2 to 0.6. These novel tunable performances of the HDM can be applied to optical devices and optical systems. [ABSTRACT FROM PUBLISHER]

A series of 4ʹ-(4-alkyl-phenyl)-2ʹ,6ʹ-difluorotolane isothiocyanate liquid crystal (LC) compounds were synthesised, and their phase transitions and electrooptical properties were investigated. These compounds exhibit high birefringence, about 0.47–0.52. As the number of carbon atoms in the alkyl chains increases, these LC compounds can exhibit smectic phases. When these LCs were mixed into the commercial LCs, the birefringence values of LC mixtures become higher than pure commercial LCs, and the visco-elastic coefficients of five LC mixtures are very close to each other at every test temperature. The results of response properties indicate that the compounds with a tri-fluorine substitution andn-propyl end group possess better response performance than the others. These LC compounds are particularly attractive for achieving fast response times in LC optic devices. [ABSTRACT FROM AUTHOR]

It has been a crucial technique to improve the dynamic response characteristics of a liquid crystal wavefront corrector (LCWFC) with optimal cell gap since the LCWFC needs at least 2π(orπ) phase modulation in adaptive optics systems (AOSs). We have given a complete process for obtaining the optimal cell gap accurately from a single photoelectric measurement, which can be conducted with a liquid crystal (LC) cell of any known thickness. This method has been analysed theoretically and confirmed experimentally by using a wedge-shaped cell; the experimental results match very well with the theoretical analysis. The response time of an optimal gap cell can be a novel evaluation method of response performance of LC materials. [ABSTRACT FROM PUBLISHER]

Self-aligned liquid crystals containing randomly dispersed nanoparticles are proposed to realise hyperbolic metamaterials at visible spectrum. Opposite signs for anisotropic permittivity tensors originated from the scattering of metallic nanoparticles in liquid crystals are achieved. Tunable effective wavelength properties are also demonstrated by choosing dielectric-metal core-shell nanoparticles. [ABSTRACT FROM AUTHOR]

Ultrafast switchable wide angle negative refraction in a novel dual-frequency liquid crystal mixture is demonstrated experimentally. Laterally fluorinated isothiocyanato phenyl-tolane liquid crystal compound is doped into Merck MLC-2048 to acquire the high birefringence dual-frequency liquid crystal. The maximum negative refraction angle achieved is about 12° and the switching time is only 25 ms for a 40-μm cell which is two orders faster than switchable negative refraction achieved before in nematic liquid crystals. Such properties provide a feasible approach to design negative refraction devices based on liquid crystals. [ABSTRACT FROM AUTHOR]

Negative refraction (NR) is a promising technique that provides an opportunity to manipulate beam behaviour. We have demonstrated experimentally the controllable NR with large refraction angle at visible wavelength in the novel high birefringence (Δn) liquid crystals. When the Δnof liquid crystal reaches 0.42, the NR angle and critical incident angle reach –14° and 23.2°, respectively, which are much larger than those achieved before by other liquid crystals. By applying the electric field, we control the switch from NR to positive. [ABSTRACT FROM AUTHOR]

In this study, three kinds of low-viscosity difluorooxymethylene-bridged (CF2O) liquid crystals (LCs) were synthesised. These materials exhibit low melting point and low viscosity at room temperature. The viscosity of the final LC mixture significantly decreased when LC compounds were mixed with high-birefringence (Δn) isothiocyanato LCs. The tested curves with varied temperatures of LC mixtures showed that some CF2O LC compounds could enhance the response performance of high-ΔnLCs in a specific temperature range. Therefore, LC compounds with low viscosity could become a component of LC mixtures with fast response performance. [ABSTRACT FROM AUTHOR]