Relationship between liquid crystal layer thickness and variable-focusing characteristics of an ultrasound liquid crystal lens

The effect of the liquid crystal (LC) layer thickness on the optical characteristics of an ultrasound LC lens was explored. Three LC lenses with differing LC layer thicknesses (100, 200, and 300 µm) were fabricated, and the optical focal lengths were measured by an optical microscope with a varying driving voltage. For the lens with a 200-µm-thick LC layer, a larger change in the focal length was observed for a smaller driving voltage compared with that of the other two lenses, indicating that the LC layer thickness is appropriate for a variable-focus lens.

High Precision Optical Wavefront Generation Using Liquid Crystal Spatial Light Modulator (LC-SLM)

LC-SLM provides a flexible way to modulate the phase of light with the help of a grayscale pattern loaded on it. Nevertheless, the modulated phase profile is of relatively low accuracy due to the nonlinear and nonuniform response of the liquid crystal layer in the SLM. To improve the performance of LC-SLM on the wavefront generation, the nonlinear and nonuniform phase response needs to be calibrated and compensated effectively. In this chapter, we present some state-of-art methods to measure the phase modulation curve of the LC-SLM. Some methods to measure the static aberration caused by the backplane of the LC-SLM are then presented. Last but not the least, the future development of the LC-SLM in phase modulation is also presented.

Optofluidic Platform Based on Liquid Crystals in X-Cut Lithium Niobate: Thresholdless All-Optical Response

In this study, we present a new configuration of the recently reported optofluidic platform exploiting liquid crystals reorientation in lithium niobate channels. In order to avoid the threshold behaviour observed in the optical control of the device, we propose microchannels realized in a x-cut crystal closed by a z-cut crystal on the top. In this way, the light-induced photovoltaic field is not uniform inside the liquid crystal layer and therefore the conditions for a thresholdless reorientation are realized. We performed simulations of the photovoltaic effect based on the well assessed model for Lithium Niobate, showing that not uniform orientation and value of the field should be expected inside the microchannel. In agreement with the re-orientational properties of nematic liquid crystals, experimental data confirm the expected thresholdless behaviour. The observed liquid crystal response exhibits two different regimes and the response time shows an unusual dependence on light intensity, both features indicating the presence of additional photo-induced fields appearing above a light intensity of 107 W/m2.

Magnetically Induced Transparency in Media with Helical Dichroic Structure

In our paper, the magneto-optical properties of a dichroic cholesteric liquid crystal layer with large values of magneto-optical parameter g and low values of dielectric permittivity were investigated. The solutions of the dispersion equation and their peculiarities were investigated in detail. The specific properties of reflection, transmission, absorption, rotation, ellipticity spectra and also the spectra of ellipticity and azimuth of eigen polarization were investigated. The existence of a tunable linear and nonreciprocal transmission band was shown.

Response Improvement of Liquid Crystal-Loaded NRD Waveguide Type Terahertz Variable Phase Shifter

Liquid crystals, which have high dielectric anisotropy even in the terahertz region and are easily controllable for dielectric permittivity by applying an electric field, have become increasingly attractive in recent years. The non-radiative dielectric (NRD) waveguide has a structure in which a dielectric line is sandwiched between two metal plates and by replacing the dielectric part with liquid crystal, a low loss liquid crystal-loaded NRD waveguide type terahertz phase shifter can be obtained. However, since the thickness of the liquid crystal layer is several hundred micrometers, it has a response time of as long as several hundred seconds when the driving voltage is removed. It is necessary to devise improvements for practical application. By inserting two polyethylene terephthalate (PET) films and reducing the thickness of the liquid crystal layer, the decay time was improved well, but the phase change was significantly reduced. In this study, we report improving both decay time and phase change with aligned nanofiber/liquid crystal complex. In addition, we demonstrate liquid crystal-load phase shifter, which has 360° phase change and the response time below one second.

Limits of applicability of the direct ray approximation in modeling optical properties of liquid-crystal diffraction gratings

Using computer modeling, we estimate limits of applicability of the direct ray approximation in modeling the optical properties of liquid-crystal diffraction gratings with continuous spatial modulation of the local optic axis orientation in a liquid crystal layer. The data presented concerning the influence of the spatial frequency and character of modulation of the local optic axis, as well as the magnitude of birefringence of the medium, on the accuracy of the results obtained in this approximation are also useful in considering birefringent layers with an aperiodic variation of the local optic axis.