Subwavelength deep gratings are an excellent platform that exhibits several types of resonances depending on the wavelength-to-period ratio, the refractive index, and the depth, such as guided mode resonance (GMR), surface electromagnetic waves, bound in the continuum (BIC) states, Fano resonances, and more. When the period is much less than the wavelength, the gratings can be homogenized into a uniform negative uniaxial waveplate. In this work, we have shown that nematic LC material can be filled in between the grating lines to provide electro-optic and thermal tunability of resonances of tens of nanometers. The confinement in a resonant sub-micron region of 560nmX700nm sheds new light on the behavior of LC molecules in nanocavities and the possibilities for future improved design and manufacture of tunable metamaterial devices with improved performance.

This study examines the tuning capabilities in Yagi-Uda antenna arrays for terahertz frequencies through electro-optic modulation using nematic liquid crystals. The investigated structure consists of a periodic 2D array of Yagi-Uda antennas on a dielectric substrate. The substrate is covered below with a metallic ground plane, and further beneath is a vacuum layer. The space above the antenna array is filled with a nematic liquid crystal, which is bounded above by a glass substrate. Strong anchoring boundary conditions for the liquid crystal ensure an initial pi/2 twist configuration. The plane wave is normally incident on the Yagi-Uda antenna arrays while following the Mauguin regime. The application of an external electric field perpendicularly to the substrates reorients the liquid crystal director from its initial twisted state to a homeotropic state, resulting in the change of polarization of the light when it reaches the antenna array. The numeric simulations of the mentioned structure were conducted in COMSOL Multiphysics, and have shown that varying the applied voltage in the mentioned structure enables the tunability of the plasmonic resonances in the antenna array. The tunability frequency interval was found to span approximately 7 to 12THz, with the absorbance tuning range reaching 95% of the incident intensity. By leveraging the electro-optic properties of nematic liquid crystals, the research highlights a controlled method for tuning THz antenna arrays, presenting a solution for the advanced control of antenna properties in THz applications.

Smart window devices have garnered significant attention recently. Traditional thermochromic windows can control infrared (IR) radiation but not visible light, while liquid crystals (LCs) control visibility through voltage-controlled scattering, neglecting IR control due to forward scattering. Our recent research demonstrates that nematic LCs with a minor concentration of nanoporous microparticles (NMPs) can rapidly modulate transparency in thin devices called NMP-LCs. To concurrently control both visible and IR spectra, we propose combining a layer of ultrashort pulsed laser-patterned vanadium dioxide (VO₂) with a 2% NMP composite in the LC. The patterned VO₂ film serves two key functions: (i) inducing LC alignment along the nanograting lines formed by pulsed laser patterning, and (ii) enabling IR radiation control with enhanced thermochromic properties compared to closed structures. The LC component facilitates visibility control via voltage or temperature modulation. The combined system thus presents a superior smart window solution, capable of efficiently managing heat and visibility with high-speed response, low voltage requirements, and minimal LC and NMP concentrations.

Liquid crystal network has been in scope to obtain responsive material. Inspired by biomimicry, a large scale of applications based on tunability of surface properties are developed. Different stimuli such as temperature, light, electric field, and chemical environment have been used. The response and modulation are featured by the director field of the material which is kept by the photopolymerization process. The spatial distribution of the director n represents the long axes of our nematic liquid crystal, and it can be controlled using different techniques. Our method generates topological defects before photopolymerization as a template to induce tunable surface topographic patterns. The richness of the different structures allows us to create a library of surface morphology. Here we present the modulation of different pseudo objects, as torons, twistions, cholesteric fingers of different natures and looped onto themselves. Those structures exhibit exotic modulation upon thermal deformation with an amplitude reaching up to 40% of the initial thickness.

Recently discovered ferroelectric nematic liquid crystals (FNLCs) offer the opportunity to make liquid crystalbased, high-speed electro-optic devices. The lack of a center of symmetry combined with having the polar axis oriented parallel to the long, polarizable molecular axis allows for large second-order nonlinear optical susceptibility and therefore a large Pockels effect. The electro-optic response at high frequencies is purely electronic, making possible high-speed modulators with bandwidths limited only by device architecture. Facile and thermodynamically stable alignment of the polar axis over large areas makes FNLCs an attractive alternative to organic crystals and poled polymers, which have been pursued for decades as Pockels materials. A novel methodology for characterizing the electro-optic coefficient (r33) of this new class of Pockels material was developed. Using this methodology, FNLCs engineered to have large nonlinearities were demonstrated to have r33 values approaching that of lithium niobate.

We investigated gastric tissue biopsies using a liquid crystal-based Mueller microscope and a machine-learning approach to examine the degree of inflammation. Machine learning and statistical analysis were performed with the multidimensional dataset including the polarimetric properties (linear retardance and dichroism, and circular depolarization) and total transmitted intensity images of the unstained thin sections of gastric tissue to identify and quantify the microstructural differences between healthy control, chronic gastritis, and gastric cancer.

Application of liquid crystal (LC) photoalignment for spatial modulation of geometrical phase is a unique tool for fabrication of arbitrary shape flat optical elements. The liquid crystal devices (LCD) technologies are currently one of the most perspective and cost effective solutions for fabrication of switchable flat optical elements. Laser based photoalignment enables linear polarization orientation pattern recording into photoalignment layer by phase interference exposure for initializing surface orientation (alignment) of LC. Exposure of photoalignment layer to light patterns of two circular-polarized interfering laser beams, known as holographic recording, allows formation of LC geometrical phase distributions. This technology allows constructing low-voltage electrically controlled flat LC lenses with ON-OFF switchable distribution of geometrical phase. However, it is the switching between ‘lens’ and ‘no lens’ states only, while electrical switching between two different focuses is not common known. Since the focus of a LC polarization hologram lens is subject to geometry phase distribution, predetermined by the pattern of LC cell alignment, electrical change of the shape of geometrical phase surface is highly desired. In the present work we consider this question and suggest a possible solution. Classical LCDs use voltage to control the liquid crystal reorientation. We applied model of electrically changing liquid crystal distribution to observe geometrical phase modification and made calculations of this process. We were able to derive conditions when specially designed LC polarization hologram lens system has two different focuses F1 and F2 at two different voltage levels V1 and V2, correspondingly. Both states have different LC director and geometrical phase distributions, but same LC alignment patterns. The F1 and F2 are dependent, and we obtained the next formula: 𝐹₂ = (5𝐹₂ ± 3√𝐹₂² + 𝑅²)/4, where R is the lens radius. The sign ‘+’ or ‘–’ depends on the choice of states notation for F1 and F2. The designed flat lens has low complexity of LC cell with single uniform electrode and can be electrically switched between 3 different states: ON1 (F1, V1), ON2 (F2, V2) and OFF (F3 = ∞, V3). The lightweight electrically switchable flat lens is perspective for various applications in photonics, lighting and information display devices.

In this work we discuss liquid-crystal (LC) anisotropic axicons for the dynamic control of the Bessel beam polarization variation along propagation. We first present a technique that employs a LC spatial light modulator (LC-SLM) to display two diffractive axicons, each one affecting one of the two orthogonal linear polarization components. If the two axicons have a slightly different period, a periodic variation in the polarization state of the Bessel beam occurs over propagation. Second, we present a more compact alternative consisting in a combination of a refractive axicon and a LC element of linear phase profile along the radial coordinate. This combination creates a compound compact and tunable anisotropic axicon that produces Bessel beams with tunable polarization modulation. The capability of changing the polarization state of the Bessel beam along its propagation opens new venues in axial polarimetry, optical trapping in multiple planes or axial-dependent laser microfabrication.

Diffractive optical elements (DOEs) are increasingly used as miniaturized and lightweight components in photonic devices. Efficient steering of light can be obtained with the help of photoaligned liquid crystal (LC) devices that modulate the geometric phase of light. We study a multitude of diffractive LC structures, ranging from simple one-dimensional gratings with a periodically rotating surface alignment, to highly dispersive gratings, multi-stable gratings and different types of lenses. All these components are enabled by photoalignment technology, that allows to control the geometric phase of the transmitted or reflected light by locally varying the azimuthal anchoring direction of the LC. Next to the standard nematic LCs, we also investigate the use of chiral nematic LCs (with different chiral pitches) and dual-frequency nematic LCs. The use of short pitch chiral LC gives rise to highly efficient diffraction in reflective devices, as we have demonstrated in linear gratings and on- and off-axis lenses. Dual-frequency LC on the other hand allows to substantially enhance the diffraction efficiency over large angles in transmissive devices. Imposing well-designed anchoring patterns at the substrates also allows to obtain highly dispersive configurations or structures with hysteresis switching as a function of the applied electric field. In all case, the working principles of the component can be understood with the help of finite element Q-tensor simulations for the LC director.

Optical coherent detection in non-spatially uniform beams propagating through highly scattering media is achieved by performing wave mixing in an optically addressed spatial light modulator (OASLM) with a contin- uous reference and a speckled signal beam. Thanks to its intrinsic nonlinear dynamics, the OASLM adjusts its properties with sub-ms response time following the phase and intensity changes of the interacting beams. It, therefore, filters out low frequency modulations and noise effects. A phase modulation on the speckled signal is directly transformed into intensity modulation and recorded on the plane reference wave at the exit of the OASLM. Applications include dynamic holography and imaging in biomedical tissues and turbid media.

Spin-orbit photonic technologies are a powerful resource to structure light in different degrees of freedom, allowing for simultaneous control of the polarization and spatial component of the beam. A key example is the q-plate, a liquid-crystal device enabling fast and accurate polarization-conditioned beam shaping. Here, we report on recent advances in the field, specifically, the observation of spin-orbit coupling in crystallized ascorbic acid, the generalization of q-plates to dual-q-plates, and a new class of liquid-crystal devices working as photonic quantum simulators.

Optical Vector Matrix Multipliers (OVMMs) offer a promising avenue for accelerating computations due to their inherent parallelism. However, their integration with quantum algorithms remains unexplored. Here, we present the implementation of a quantum algorithm, the Deutsch-Josza algorithm, on an OVMM.

The early detection of precancerous cervical lesions is essential to improve patient treatment and prognosis. Hyperspectral (HS) imaging (HSI) has demonstrated a high potential to become a new non-invasive and label-free imaging technique in the medical field for performing quick diagnosis of different diseases. This study presents the research and development process to integrate and characterize a KURIOS-XE2 filter (Thorlabs, Inc., NJ, USA), based in a liquid crystal tunable filter (LCTF) technology, into an existing colposcope (C5, OPTOMIC, Spain). The main goal was to capture spectral information in the near infrared range (650 to 1100nm) by using a monochrome camera and acquiring 90 spectral wavelengths with a spectral resolution of 5nm. Two different integration strategies were studied: i) filtering the emitted light by the sensor and ii) filtering the received light by the sensor, evaluating their respective benefits and limitations. Furthermore, a custom software was developed for HS image acquisition, integrating a variable acquisition time per wavelength, which allows improving the signal-to-noise ratio at wavelengths where the system presents lower quantum efficiency. The proposed system simplifies the adaptation of existing optical systems to HSI technology, improving the signal-to-noise ratio in the studied spectral range respect to other approaches. The results were compared against a previous custom implementation based on a Snapscan camera (IMEC, Belgium), covering the visual and near infrared and highlighting the advantages and limitations of both technologies for the development of a HS colposcope system targeting early detection of precancerous cervical lesions during routine clinical practice.

Photonic films prepared by self-assembly from sustainable resources are promising functional materials for applications in optics, sensing and coloring. Up to now, such films have mainly been fabricated from aqueous cellulose nanocrystal suspensions which require hydrolysis in concentrated sulfuric acid and highly controlled drying conditions. We present here for the first time that analog photonic films can be prepared from aqueous xanthan solutions which do not require any chemical treatment and only little control over the drying process. We achieve uniform structural color with different wavelengths of selective reflection by simply drying xanthan solutions of different starting mass fractions in closed containers. Surprisingly, the helical pitch in the dried xanthan films is significantly shorter than suggested by the helical twisting power which was determined from the cholesteric liquid crystal phase. This hints at distinct differences in the drying process of lyotropic liquid crystals containing stiff cellulose nanocrystals and semiflexible xanthan polymer chains.

We demonstrate fibre-forming behaviour in a proper 3D ferroelectric fluid (ferroelectric nematic). Those materials stand out for their high spontaneous polarisation and strong optical nonlinearity. In this presentation, we discuss the role of electrostatics on the mechanical properties of ferroelectric nematics, fibre stability and thinning dynamics.

We demonstrate that Direct Laser Writing (DLW) can be used to print low loss planar polymer waveguides on glass, thus promising a novel soft matter platform for polymer all-optic micro-photonics. We printed straight waveguides with various cross sections and lengths up to 900μm on a 500nm thin layer of low refractive index CYTOP on glass. We also printed two rectangular micro-prisms at each end of the waveguide, which provides coupling of light in and out of the waveguides. The printed structures were imaged and characterized by SEM and we measured the attenuation of light, propagating along the waveguides. While the high refractive index photosensitive resin IP-n162 shows moderate attenuation of ∼14dB/cm at 580nm, the IP-S photosensitive resin shows lower attenuation of ∼5-9dB/cm in a rather broad window around 580nm.

Coating water-soluble photoalignment material AbA-2522 on top of the patterned polymerizable liquid crystal (PLC) retarder obtain liquid crystal photoalignment direction at the angle to the direction of the bottom retarder. Combination of single patterned exposure of the bottom photoalignment layer with linear polarized light for orientation of the bottom retarder and non-patterned exposure of the top photoalignment layer with circular polarized light allows fabricating of the patterned top PLC layer that is at every point at 45° degree to the orientation pattern of the bottom PLC retarder. We optimized the PLC layers design in optical simulations with respect to PLC dispersion and obtained a solution that can be equivalently represented as a broadband half-wave retarder (420 to 620nm). The measured polarized transmission spectra are in good agreement with the derived analytical model.

Two-photon Direct Laser Writing enables the fabrication of shape-changing microstructures that can be exploited in stimuli responsive microrobotics and photonics. The use of Liquid Crystalline Networks allows to realise 3D micron-sized objects that can contract anisotropically, along a specific direction in response to stimuli, such as temperature or light. In this paper, we demonstrate the fabrication of free-standing LCN microstructures as graphical units of a couvert tag for simple physical and optical encryption. Using an array of identical Liquid Crystalline pixels, information can be hidden to the observer and revealed only upon application for a specific stimulus. The reading mechanism is based on a specific shape-change of each pixel so that once the stimulus is removed and the pixels recover their original shape the message remains completely hidden. We have therefore realised an opto-mechanical equivalent of an “invisible ink”. This new concept paves the way for introducing enhanced functionalities in micro-optomechanical systems within a single lithography step, spanning from storage devices with physical encryption to complex motion actuators.

Optical solitary wave beams in nematic liquid crystals -Nematicons- when propagating in orientation-modulated planar cells with a non-symmetric layout evolve along different paths when launched from opposite sides, thereby exhibiting nonreciprocal behavior with non-overlapping trajectories. We model such solitary-waveguides in cells with non-homogeneously oriented molecular director, with anchoring linearly changing along the sample length or across its width. We report on numerical experiments about generation and propagation of nematicons injected from the opposite two ends of the cell and investigate the trajectories of forward and backward propagating self-confined beams. The obtained non-specular transmission suggests a diode-like response as a backward propagating beam does not reach the forward propagating input port.

Liquid crystals (LCs) are a versatile class of materials capable of modulating their effective refractive index for specific light polarization when subjected to an external electric field. This unique feature positions LCs as valuable components in the creation of electronically reconfigurable optical elements by eliminating the need for mechanical components. This study presents LC-based Fresnel diffractive elements, with spiral shaped phase profiles, that convert planar light beams into vortex beams. The devices feature directly addressable electrodes, facilitating dynamic adjustment of the vortex beam generation. Consequently, a single device may be configured to introduce an arbitrary orbital angular momentum (OAM) into a passing planar light beam. The devices may be calibrated to any desired wavelength within the visible and NIR light spectrum. The developed devices are characterized by high fill factor, low operating voltages, and are suitable for various applications, including optical trapping or OAM multiplexing, due to their lack of moving parts, reconfigurability, and ease of integration. The control of these optical devices is accomplished by an in house developed electronic driver that generates pulse width modulation (PWM) signals to independently address each element electrode. In this way, the element phase profile can be precisely controlled. The devices are fabricated through Direct Laser Writing (DLW) ablation on glass substrates coated with Indium-Tin Oxide (ITO), utilizing nematic LCs for phase modulation of incident light beams.

Differential interference contrast (DIC) technique is an advanced tool of polarization microscopy applied for visualization of transparent refractive profiles and heights of complex objects. Based on utilization of special anisotropic prisms it is widely used in studies of biology, microelectronics and etc. Classical DIC prism comprises sub-prisms’ cuts of two quartz crystals with orthogonal optical axes. The cut angle is fixed to match to the single objective lens only, while prism operation requires precise mechanical translation. Thus traditional DIC microscopy is complex in implementation and rather expensive. We developed tunable liquid crystal (LC) prism suitable for direct replacement of DIC prism in existing optical designs. The unique tunability of LC allows omitting mechanical displacement and replacing it with electrical control. The elegant solution of LC DIC prism comprises two wedge LC cells and two pairs of electrodes for V1 and V2 voltage levels control. The cells have orthogonal azimuthal LC alignment to have a compensated birefringence zone in the middle of the wedge. Application of the base voltage level V to prism electrodes changes the DIC prism angle to match the selected objective lens. The tunable LC DIC prism is universal and capable to operate with different microscope objective lenses. Introduction of the small voltage difference allows to shift the position of compensated birefringent zone. Thus control of voltage levels at the DIC prism electrodes releases the need of precise mechanical translation. So mechanical translation can be omitted and replaced with digital-to-analog converter (DAC) outputs of low voltage microcontroller. Tunable liquid crystal DIC prism was fabricated and successfully tested in differential interference contrast mode of industrial polarizing microscope. Tunable LC prisms make DIC microscopy cost affordable, suitable for automation and integration into optical measurement systems.

The research has unveiled the remarkable potential of the vertically aligned negative dielectric anisotropy LC cell doped with 10% cochleate particles as a tunable scattering device. The device exhibits an initial haze of 20%, which increases to approximately 80% upon the application of voltage, consequently yielding a good contrast ratio. This intriguing behavior stems from the distinct molecular arrangement of the liquid crystal within the cochleate particles and on their surface. Our findings suggest that the cochleate particles adopt an inclined orientation relative to the surface, effectively balancing the dielectric forces with the elastic forces exerted by the surrounding LC environment. The interplay between this NMP-LC configuration and the EHDI effect contributes to the device's ability to function at lower operating frequencies and with reduced voltage requirements. In practical terms, this translates to enhanced energy efficiency.

Liquid-crystal on silicon spatial light modulators (LCOS-SLM) with pixel size as small as few microns enable the implementation of programmable diffraction gratings with large deflection angles (small period). We study triplicator phase gratings at the limit of the LCOS spatial resolution, where the binary phase profile is the only alternative. First, we show the effect of the sinc envelope that unavoidably arises from the LCOS pixelation. Then, we use the Fourier transform theory to analyze the binary phase grating in a pixelated device in terms of the pixel size, fill factor and phase difference between the two levels in the grating. The experimental diffraction pattern of a binary triplicator grating displayed on the SLM with a period of 2 pixels reveals that pixel crosstalk becomes relevant. Its effect on the conditions to render a triplicator and on the diffraction efficiency is analyzed.

Photovoltaic spatial light modulators (PSLMs) form a new type of optically addressed liquid crystal (LC) devices, capable of adapting its optical properties to incident light in less than a second, without external power supply. Since the photo-induced voltage generated by a PSLM is continuous, the presence of residual ions in the LC may interfere with the device operation and compromise the performances. Here, we investigate the influence of the alignment layers (AL) in a PSLM on ion accumulation/neutralization at the LC/AL interfaces by probing the optical and dielectric response under DC bias of LC light valves based on Poly(3-hexylthiophene-2,5-diyl) (P3HT) and/or poly(vinyl-alcohol) (PVA) as ALs. We find that charge injection into the P3HT layer allows neutralization of ions accumulated at LC/ALs interfaces thereby avoiding the screening of the electric field in the LC.

The most common configuration of liquid crystal devices incorporated within spectral imaging systems is using LCTFs. Usually, these filters suffer from low light throughput or slow response times which may not meet the growing demands of industry and research. However, in most applications multispectral imaging is adequate, and no need for hyperspectral imaging. In this work, we implemented a discrete tunable Lyot-based filter in such systems to obtain spectral images more efficiently. The filter consists of 3 LC cells combined with 9 narrow bands of passive filter covering the VIS and NIR, which makes it a potential candidate for various applications. A system with a smaller number of bands designed for oximetry imaging is even faster and shows higher light throughput. Experimental results show that our system holds a relatively faster response time with high light throughput while providing reliable spectral information.

Ferromagnetic liquid crystalline suspensions of scandium-doped barium hexaferrite (Sc-BaHF) nanoplatelets exhibit intricate magnetic dynamics and robust magnetic response, making them promising for use in novel magnetooptical devices. We explore magnetic dynamics, optical properties and self-assembly of these liquid magnets employing optical imaging and magnetic susceptometry in oscillating (AC) fields. The dynamics of the optical response and the formation of magnetohydrodynamic patterns in AC magnetic fields were studied using optical microscopy. The observations are discussed in the light of magnetic dynamics and orientational order.

The possibility of controlling laser generation in a layered structure using a nematic liquid crystal (NLC) is theoretically studied. This structure consists of a thin layer of silver (Ag), a layer of NLC doped with a light-absorbing dye, and a distributed Bragg reflector (DBR). The spectral dependencies of the reflection, transmission, and absorption coefficients of light by such a structure, as well as the enhancement coefficient of the light field in the NLC layer in the DBR's band gap, are calculated. The narrow dips in the reflection coefficient and the peaks in the transmission coefficient are caused by the excitation of Tamm plasmon-polaritons (TPPs) at the Ag-NLC interface. The excitation of TPPs is accompanied by a significant increase in the intensity of the light field in the NLC volume compared to the intensity of the incident light. With an increase in the thickness of the NLC, the density of Tamm-plasmon peaks increases. It is shown that in the case of an optical anisotropy 𝛥𝑛=𝑛𝑒−𝑛𝑜=0.3, the control range for the position of the plasmon peaks reaches up to 100nm. Temporal luminescence pulses for pump pulses of different power settings are also presented. Above threshold, luminescence in the system manifests itself in the form of a series of short pulses with their amplitude and duration monotonically decreasing over time. Increases in the peak power of the pump cause the duration of the individual luminescence pulses to decrease.