Search Results (38)

Electromagnetic phase reconfigurability is a critical functionality for many emerging applications in electronics, defence, and other disruptive technologies. This work addresses a significant challenge in developing nematic liquid crystal (NLC)-based phase shifters: inaccurate and ambiguous calculations of differential phase shift, which can jeopardise on-time, on-budget device development. We investigate and correct two vulnerable cases of these calculation errors, demonstrated using a 60 GHz strip line and a 300 GHz coaxial line. For completeness, we also present a third case—a 1 mm long 60 GHz strip line—that correctly calculates phase shift, illustrating a “false positive” scenario. A unique contribution of this paper is the statistical analysis of how often these different phase shift processing errors occur during NLC delay line parameterisation. This statistical insight provides practical guidance for research and development. By numerically testing common assumptions, we establish traceable know-how to support smarter design decisions for radiofrequency (RF) engineers and academics. This work aims to advance NLC devices beyond classical display applications towards commercial viability. It also serves as a valuable reference and educational resource for students, physicists, and designers working on the precise phase characterisation of NLC-based reconfigurable devices. Full article

This work is devoted to the study of the effect of the oscillating Poiseuille flow on the diffraction of light passing through a nematic layer bounded by a submicron relief at one of the inner surfaces of the plane capillary. In experimental nematic liquid crystal (NLC) cells with a hybrid planar–homeotropic orientation, a photo-profiled PAZO polymer layer with a sinusoidal relief with a depth of 180 and 360 nm and a period of 2 μm was used as a diffraction grating. The experimentally obtained dependencies of the flow-induced changes in the intensity of polarized light at the main and the first diffraction maxima on the amplitude of the low-frequency oscillating pressure gradient applied to the NLC layer are presented. Processing of the obtained results indicates the possibility of modulating the intensity of diffracted polarized light transmitted through the NLC layer by up to 10% when applying an oscillating pressure difference of up to 700 Pa to the layer of corresponding experimental cells in the absence of an analyzer in the optical scheme. Possible mechanisms responsible for the modulation of optical radiation in the main and first diffraction maxima are discussed. The discussed principles of controlling diffracted electromagnetic radiation can be used to create optofluidic modulators operating in both the visible and THz ranges. Full article

The present reported work deals with the preparation of an energy-efficient smart window based on liquid crystal (LC) using a polymer-dispersed liquid crystal (PDLC) technique. The smart window was prepared using an LC–polymer composite by mixing photopolymer NOA-71 into nematic liquid crystal (NLC) 4-cyano-4’-pentylbiphenyl (5CB). The liquid crystal cell was prepared, the LC–polymer composite was filled inside the cell, and voltage was applied after the exposure of ultraviolet (UV) light. Textural analysis was carried out, and microscope images were taken out with the variation in voltage. Optical measurements were also performed for the smart window based on the PDLC system. Threshold voltage and saturation voltages were measured to carry out the operating voltage analysis. Transmittance was measured as a function of wavelength at different voltages. An absorbance study was also performed, varying the voltage and wavelength. The change in the power of the laser beam passing through the prepared smart window as a function of voltage was also investigated. The working of a prepared smart window using liquid crystal and a photopolymer composite is also demonstrated in opaque and transparent states in the absence and presence of voltage. The output of the present investigation into a PDLC-based smart window can be useful in the applications of adaptive or light shutter devices and in aerospace technology, as it shows the dual nature of opaque and transparent states in the absence and presence of electric field. Full article

Chiral inorganic nanomaterial-based circularly polarized luminescence (CPL) materials have shown substantial promise in multiple research areas. However, the luminescence dissymmetry factor (g_lum), a key parameter for CPL, is far from satisfactory, especially for inorganic molecules with high luminescent quantum efficiency and diverse shapes and sizes. Obtaining large g_lum values is an urgent and crucial task in the field of CPL research. Among different approaches, the combination of inorganic nanomaterials and chiral nematic liquid crystals (N*-LCs) offers distinct advantages in achieving high g_lum values due to their distinctive optical characteristics and remarkable versatility. This concise review systematically investigates the recent advancements in CPL-active materials consisting of perovskites and N*-LCs. It elaborates on their preparation techniques, optical characteristics, and potential applications. Additionally, a brief outlook on their future development is offered. It is expected that this combination will assume an increasingly significant role in the CPL research field and attract more researchers to explore this area. Full article

This work demystifies the role that packaging boundary conditions (both physically and electromagnetically) can play in a nematic liquid crystal (NLC)-based inverted microstrip (IMS) phase shifter device operating at the 60 GHz band (from 54 GHz to 66 GHz). Most notably, the air box radiating boundary and perfect electric conductor (PEC) enclosing boundary are numerically examined and compared statistically for convergence, scattering parameters, and phase-shift-to-insertion-loss ratio, i.e., figure-of-merit (FoM). Notably, the simulated phase tunability of the radiating air box boundary structure is 8.26°/cm higher than that of the encased (enclosed) PEC boundary structure at 60 GHz. However, the maximum insertion loss of the encased PEC structure is 0.47 dB smaller compared to that of the radiant air box boundary structure. This results in an FoM increase of 29.26°/dB at the enclosed PEC limit (relative to the less-than-optimal airbox radiation limit). Arguably, the NLC-filled IMS phase shifter device packaging with metals fully enclosed (in addition to the default ground plane) enhances the symmetry of the structure, both in the geometry and the materials system. In electromagnetic parlance, it contributes to a more homogenously distributed electric field and a more stable monomodal transmission environment with mitigated radiation and noise. Practically, the addition of the enclosure to the well-established NLC-IMS planar fabrication techniques provides a feasible manufacturing (assembling) solution to acquire the reasonably comparable performance advantage exhibited by non-planar structures, e.g., a fully enclosed strip line and rectangular coaxial line, which are technically demanding to manufacture with NLC. Full article

This paper presents a novel pentagonal structure dual-core photonic crystal fiber polarizing beam splitter (PS-DC-PCF PBS) filled with a nematic liquid crystal (NLC) in the central hole. Unlike previous designs with symmetric arrangements, the upper and lower halves of the structure have different air hole arrangements. The upper half consists of air holes arranged in a regular quadrilateral pattern, while the lower half features a regular hexagonal arrangement of air holes. By filling the central hole with birefringent liquid crystal, the birefringence of the structure is enhanced, reducing the coupling lengths along the x polarization and y polarization directions. The polarization properties, coupling characteristics, and the influence of different structural parameters on the extinction ratio of the polarizing beam splitter are analyzed using the full-vector finite element method. Simulation results demonstrate that the designed PS-DC-PCF PBS achieves a maximum extinction ratio (ER) of 72.94 dB with a splitting length of only 61.9 μm and a wide operating bandwidth of 423 nm (1.324–1.747 μm), covering most of the O, E, S, C, L, and U communication bands. It exhibits not only ultra-short splitting lengths and ultra-wide splitting bandwidth but also good manufacturing tolerances and anti-interference capabilities. The designed PS-DC-PCF PBS could provide crucial device support for future all-optical communication systems and has potential applications in fiber optic communication or fiber laser systems. Full article

This paper develops an optical power limiter (OPL) utilizing dye-doped nematic liquid crystals (NLCs) in a twisted nematic configuration designed to protect charged-coupled devices from intense light damage. The device harnesses the intrinsic optical properties of NLCs, enhanced by dye doping, to control light transmission without external electric fields. Placed between two crossed polarizers, the NLC cell exploits both reorientational and thermal nonlinearities to reduce the activation thresholds and enhance responsiveness to fluctuating light intensities. The experiments employ a continuous-wave green laser, chosen for its peak interference in the visual field and alignment with CCD camera sensitivities, emphasizing the practical relevance of the OPL in the military and aviation sectors. The results indicate that integrating plastic polarizers and strategically adjusting thermal nonlinearity significantly lowers the operational threshold of the limiter, effectively counteracting high-intensity light exposure while allowing safe light levels. This approach offers effective CCD protection and demonstrates the potential for broad wavelength applications. The developed NLC-based OPL represents a significant advancement in dynamic light management technologies, promising extensive industrial applications. Full article

Optical spatial solitons are self-guided wave packets that maintain their transverse profile due to the self-focusing effect of light. In nematic liquid crystals (NLC), such light beams, called nematicons, can be induced by two principal mechanisms: light-induced reorientation of the elongated molecules and thermal changes in the refractive index caused by partial light absorption. This paper presents a detailed investigation of the propagation dynamics of light beams in nematic liquid crystals (NLCs) doped with Sudan Blue dye. Building on the foundational understanding of reorientational and thermal solitons in NLCs and the effective breaking of the action–reaction principle in spatial solitons, this study examines the interaction of infrared (IR) and visible beams in a [-4-(trans-4′-exylcyclohexyl)isothiocyanatobenzene] (6CHBT) NLC. Our experimental results highlight the intricate interplay of beam polarizations, power levels, and the nonlinear properties of NLCs, offering new insights into photonics and nonlinear optics in liquid crystals. Full article

We theoretically study the generic mechanisms that could establish critical behavior in nematic liquid crystals (NLCs). The corresponding free energy density terms should exhibit linear coupling with the nematic order parameter and, via this coupling, enhance the nematic order. We consider both temperature- and pressure-driven, order–disorder phase transitions. We derive a scaled effective free energy expression that describes how qualitatively different mechanisms enforce critical behavior. Our main focus is on the impact of nanoparticles (NPs) in homogeneous NP-NLC mixtures. We illustrate that in the case of pressure-driven phase changes, lower concentrations are needed to impose critical point conditions in comparison with pure temperature variations. Full article

In this paper, the refractive index and extinction coefficient of ferroelectric liquid crystals have been examined by the terahertz time-domain spectroscopy system. Two modes of ferroelectric liquid crystal materials, deformed helix ferroelectric liquid crystal (DHFLC), and electric suppressed helix ferroelectric liquid crystal (ESHFLC) are tested as experimental samples. Nematic liquid crystal (NLC) was also investigated for comparison. The birefringence of DHFLC 587 slowly increases with the growth of frequency, and it averages at 0.115. Its extinction coefficients gradually incline to their stable states at 0.06 for o-wave and 0.04 for e-wave. The birefringence of ESHFLC FD4004N remains between around 0.165 and 0.175, and both of its e-wave and o-wave extinction coefficients are under 0.1, ranging from 0.05 to 0.09. These results of FLC will facilitate the examination and improve the response performance of THz devices using fast liquid crystal materials. Full article

The applications of liquid crystals in the field of renewable, clean and sustainable technologies of energy storage are of utmost importance at present. This paper delves into dielectric spectroscopic studies of a weakly polar nematic liquid crystal (NLC) enriched with an anthraquinone dye. The primary objective is to assess the impact of increasing dye concentrations on various properties. Anthraquinone dye has been found to increase the dielectric permittivity of weakly polar NLC, leading to a 4.7-fold increase in dielectric anisotropy. Simultaneously, a reduction of around 11% in threshold and operating voltages of the NLC has also been recorded after using dye as the guest material. The added dipolar contributions provided by dye molecules have been attributed to this surplus permittivity. The NLC has been found to have an approximately 54% faster response to the applied field. The intrinsic polarization field of dye molecules accelerates nearby LC molecule reorientation, leading to a 56.5% faster fall time and a 29.8% faster rise time in a 3.0 wt% dye-doped LC cell. These experimental results have been validated via computational studies as well. The simulation results about dipole moment and polarizability provide robust support for our experimental results. Such composites evince their potential for energy storage and 5G communication technologies with adjustable impedance and permittivity. Full article

In this article, we employed the saturation voltage method (SVM) to investigate the interaction between a nematic liquid crystal (NLC) and a graphene oxide (GO) substrate. The SVM approach involved applying a potential difference (ΔV) to the cell containing the NLC (specifically, 5CB) to reorient the nematic director (n) from a parallel to a perpendicular configuration with respect to the cell’s surface. By utilizing sandwich cells with indium–tin oxide semi-transparent electrodes covered by GO, we measured the anchoring energy between the NLC and the thin GO film. To evaluate the strength of this anchoring energy, we compared the results with two other cells: one exhibiting strong anchoring energy (polyimide cell) and the other demonstrating weak anchoring energy (formvar cell). The influence of GO thin films on the alignment of nematic 5CB was distinctly observed. Full article

This work addresses the achievement of efficient control of laser light transmission through stationary microperiodic parallel stripe textures formed in films of nematic liquid crystals (NLCs) in planar-oriented cells upon a direct-current (DC) electric field. By varying the field intensity and, thereby, the field-induced periodic modulation of the nematic director and hence the complex transmittance function corresponding to the longitudinal domain texture induced in NLC films with initial planar alignment, the intensity of a linearly polarized laser beam passed through the films can be well controlled. In 25 µm-thick films of room-temperature NLCs pentylcyanobiphenyl (5CB), this results in a low-voltage (~4 V) sharp and deep V-shaped behavior of their electro-optically controlled transmittance. Such a reversible electro-optical effect is interesting for active control of laser beam intensity and other applications. The relevant physical mechanism is analyzed and explained. Full article

We study numerically the reconfiguration process of colliding $\left|m\right|=1/2$ strength disclinations in an achiral nematic liquid crystal (NLC). A Landau–de Gennes approach in terms of tensor nematic-order parameters is used. Initially, different pairs $\left\{m_1,m_2\right\}$ of parallel wedge disclination lines connecting opposite substrates confining the NLC in a plane-parallel cell of a thickness h are imposed: {1/2,1/2}, {−1/2,−1/2} and {−1/2,1/2}. The collisions are imposed by the relative rotation of the azimuthal angle $\theta$ of the substrates that strongly pin the defect end points. Pairs {1/2,1/2} and {−1/2,−1/2} “rewire” at the critical angle ${\theta }_c^{\left(1\right)}=\frac{3\pi }{4}$ in all cases studied. On the other hand, two qualitatively different scenarios are observed for {−1/2,1/2}. In the thinner film regime $h<h_c$, the disclinations rewire at ${\theta }_c^{\left(2\right)}=\frac{5\pi }{4}$. The rewiring process is mediated by an additional chargeless loop nucleated in the middle of the cell. In the regime $h>h_c$, the colliding disclinations at ${\theta }_c^{\left(2\right)}$ reconfigure into boojum-like twist disclinations. Full article

The tunable properties of nematic liquid crystals (NLC) are here exploited in a peculiar leaky waveguide with artificial magnetic conductors as the lateral walls, a bottom metal ground plane, and a homogenized metasurface on top to obtain dynamic beamsteering at a fixed terahertz frequency. The waveguide consists of an NLC cell sandwiched between two dielectric layers. The proposed antenna system works on its transverse-magnetic leaky mode and is capable of radiating a beam that scans either by frequency or by changing the bias voltage applied across the NLC cell. The design parameters are optimized through a rigorous modal analysis of the structure, and the radiation performance is validated through full-wave simulations. The results are promising for the realization of next-generation tunable terahertz leaky-wave antennas. Full article