Wenjiang Ye

Reverse-mode polymer-stabilized liquid crystal (RPSLC) smart windows exhibit voltage off transparency and voltage on scattering, which are well aligned with the requirements of daylighting and solar heat insulation in buildings. These characteristics make RPSLC smart windows promising energy-saving light-modulating devices for building applications. Existing RPSLC devices suffer from uneven interfacial alignment, the mutual restriction between electro-optical properties, and poor cyclic stability. To address these problems, this work carries out an integrated collaborative optimization from three dimensions of interface, polymer components, and microstructure. A self-assembled monolayer (SAM) is constructed using a mixed system of octadecyl phosphate and bis(2-(methacryloyloxy)ethyl) phosphate. The resulting SAM enables uniform vertical alignment of the liquid crystals and strengthens interfacial coupling stability through chemical bonding. Flexible polyurethane acrylate is then introduced to optimize the internal polymer network structure and alleviate the trade-off in the electro-optical performance of the devices. In addition, a two-step exposure method is used to construct periodic polymer-wall microstructures and enhance the electro-optical properties and cyclic stability of the devices. The experimental results show that the saturation voltage of the prepared reverse-mode polymer-wall stabilized liquid crystal smart windows is only 7.2 V, the contrast ratio can reach 178, and they simultaneously possess excellent long-term cyclic stability. This strategy provides useful guidance for the design of RPSLC smart windows with improved electro-optical performance and cyclic stability for building-related applications.

To meet the demand for highly sensitive temperature sensing in low-temperature environments, a surface plasmon resonance photonic crystal fiber (SPR-PCF) sensor with a central air hole and a dual-layer air-hole arrangement is designed and optimized. In this work, these air-hole features are used for mode-field regulation in a low-temperature sensing structure based on surface plasmon resonance (SPR), together with a polished gold film and an ethanol/chloroform (1:1) temperature-sensitive medium. The finite element method (FEM) was employed to analyze the resonance behavior and thermal response, and key structural parameters, including gold-film thickness, air-hole sizes, and radial positions, were optimized through cumulative parametric scanning. The optimized sensor shows good temperature response from −25 °C to 40 °C, with a maximum sensitivity of 36 nm/°C, a full width at half-maximum (FWHM) of 18.57 nm, and a figure of merit (FOM) of 1.2923. It is promising for cold-chain monitoring, low-temperature storage and transportation, and low-temperature sensing.

A field-induced multimode liquid crystal (LC) switchable grating is proposed, fabricated via a patterned alignment process combined with a LC cell integrated with in-plane switching (IPS) electrodes. By applying voltages of different amplitudes, the grating enables flexible multimode switching: in the absence of an external voltage, it functions as a one-dimensional (1D) grating based on the patterned alignment; under a low driving voltage, it switches to a two-dimensional (2D) grating; and under a high driving voltage, it rapidly switches to another 1D grating (1D*) dominated by the IPS electrodes. Essentially, this grating is an alignment layer-electrode synergistically regulated phase grating, formed by the coupling of two independent gratings. The period sizes and fringe directions of the two constituent gratings can be flexibly tailored by virtue of photomask design, electrode arrangement, and exposure process parameters. In addition, it possesses advantages such as a simple fabrication process and flexible switching, exhibiting broad application prospects in fields including optical communication and 3D displays.

A 1D/2D switchable grating based on polymer-stabilized liquid crystal (PSLC) is proposed using a two-step exposure method. The first exposure anchors the tilt angle of liquid crystal (LC) molecules via the polymer network, forming a 1D grating in the absence of an electric field. The second exposure modulates the threshold voltage of LCs through the polymer, and a phase difference is generated between the exposed region and the unexposed region under an external field, thus forming a 2D grating. The device features low driving voltage (1 V), fast response, high diffraction efficiency, no scattering, and low cost. Moreover, the gratings corresponding to the two exposures are independent and non-interfering, and diverse diffraction patterns can be flexibly constructed by adjusting the period and stripe orientation of the two gratings, showing great potential in photonic applications.

Bent-core nematic (BCN) liquid crystals (LCs) can form a variety of grating structures under different orientations and exhibit exceptional optical tunability due to their unique flexoelectric effect. Here, we develop a flexoelectric nematic LC (NLC) mixture with broad temperature range (0--65 \ifmmode^\circ\else\textdegree\fi{}C). Based on this material system, we investigate the grating structure formed by the flexoelectric NLCs under different orientations (planar, vertical, and annular photoalignment) and analyze their responses to voltage and temperature. As a result, we achieve one-dimensional, two-dimensional, and annular diffraction patterns with tunable periodicity. Notably, under an external field, we observed the microdomain multidomain phenomenon of NLC gratings in the vertical cell: numerous micrometer-scale segmented gratings spontaneously align in different directions while maintaining a uniform periodicity. This isotropic grating array exhibits an anomalous annular diffraction pattern under laser irradiation: whereas an individual segmented grating produces directional diffraction, the statistically uniform distribution of segmented gratings results in the superposition of diffracted intensities in multiple directions, ultimately forming concentric annular patterns with tunable radius. This tunable diffraction angle grating, applied to spectral scanning, is simple to prepare, low-cost, and can complete a visible light scan in 1.25 s, providing new possibilities for the development of miniaturized spectrometers.

This letter proposes a 1D/2D switchable grating that is fabricated by injecting a mixture of polymer and liquid crystal (LC) into a LC cell with in-plane switching (IPS) electrodes and using a photomask for polymer-induced phase separation. The switching between 1D and 2D gratings is achieved through an external electric field. In the absence of an external electric field, a 1D polymer dispersed LC (PDLC) grating is presented; under the presence of an external electric field, the PDLC grating couples with the IPS electrode to form a 2D grating. It features a low driving voltage, low saturation voltage, and fast response. It is worth noting that since the 1D/2D switchable grating is composed of two independent gratings coupled together, it is not limited by the period and angle of conventional 2D gratings. The period size and fringe direction of the two gratings can be adjusted by replacing the IPS electrode or PDLC grating, thereby forming diverse diffraction patterns, which has great potential in photonics applications.

Traditional opto-ultrasonic grating instruments exhibit several limitations. Firstly, piezoelectric ceramics are prone to electrochemical corrosion, which shortens the instrument’s lifespan. Secondly, the sound velocity in liquids is highly sensitive to temperature variations, leading to measurement discrepancies under different thermal conditions. Additionally, the instrument’s large size not only complicates its operation and handling but also indirectly affects measurement accuracy. These issues collectively result in high maintenance costs and low portability of the equipment. To address these challenges, this instrument improved the traditional instrument by modifying the ultrasonic cavity structure, adding a temperature control system, and using a cage-like structure. The enhanced experimental instrument features a clear structure, complete functionality, and a prolonged lifespan. It meets experimental requirements, serving as a bridging experimental instrument from undergraduate to graduate studies, allowing students to better understand and master the use of related scientific research tools while also holding the potential to integrate Science, Technology, Engineering, and Mathematics education into experimental physics.

Most properties of liquid crystal (LC) materials will change with the change of temperature, which makes the performance of liquid crystal display (LCD) and other devices change. However, at low temperature, the properties of LC will mutate with the decrease of temperature, which directly leads to the defects of LC devices. This paper makes use of the developed homemade temperature control device to realize the construction of high temperature to low temperature environment, using precision LCR meter (Agilent E4980A) and self-built optical path, combined with LC cell capacitance model and dual-cell model, the dynamic response properties of LC materials with temperature change law was explored. The results show that the decay time τ_d of the LC with positive dielectric anisotropy increases from 12.04 ms to 159.7 ms, and the rotational viscosity coefficient γ₁ increases exponentially from 12.04 mPa·s to 1582.45 mPa·s. While τ_d of the LC with negative dielectric anisotropy increases from 13.10 ms to 408.1 ms, γ₁ also increases exponentially from 162.73 mPa·s to 7903.69 mPa·s. The conclusions presented in this paper provide some guidance for the improvement of low temperature properties of LC.

Temperature measurement and control has an extremely important role in both scientific research and manufacturing. Capacitive liquid crystal (LC) temperature sensors can monitor the temperature using the linear variation of the capacitance of LC cell with temperature, but the sensitivity and other properties need to be improved. In order to improve the performance of capacitive LC temperature sensor, we propose to mix twisted nematic LC (1M10600-100) with ferromagnetic nanoparticles γ-Fe₂O₃ to prepare LC temperature sensor in this paper. The relationship between the capacitance change rate of different concentrations of nano-doped LC materials at 0.1–20 V and different temperatures was tested, the sensitivity of the sensor was calculated, and the mechanism of the effect of doped nanoparticles on the performance of the device was analyzed. The experimental results show that the sensitivity of the capacitive temperature sensor made of nano-doped LC with the concentration of 0.03 wt% is as high as 9.5 pF/°C at 12 V, which is about 14.87% higher than the undoped device, and its recovery and stability remain almost unchanged. The Pearson correlation coefficient only changes by 0.02%. The results of this paper provide some guidance for the improvement of the performance of capacitive LC temperature sensors, and the development of high-sensitivity temperature sensors based on LC materials.