Search

Aiming at the problem of limited transmission energy of liquid crystal tunable filter (LCTF), a dual-wavelength transmission system with high signal-to-noise ratio (SNR) is proposed in this paper. The proposed transmission factor Qp is the main influence on the number and location of transmission wavelengths as well as the bandwidth of each transmission wavelength for dual-wavelength systems. Dual-wavelength LCTF can improve the effective transmission energy of the system by increasing the number of filtering channels, and the transmission energy can be increased by about 1.8 times and 70% at short and long wavelengths, respectively, which improves the signal-to-noise ratio (SNR) of the system. Moreover, the dual-wavelength LCTF system is even possible to increase the transmission energy by about 7% at a 33% increase in spectral resolution. Therefore, the dual-wavelength LCTF transmission method not only can improve the SNR of target detection with dual-wavelength response features, but also can effectively solve the problem of contradiction between spectral resolution and spectral transmission energy. [ABSTRACT FROM AUTHOR]

There is a significant gap in cost-effective quantitative phase microscopy (QPM) systems for studying dynamic cellular processes while maintaining accuracy for long-term cellular monitoring. Current QPM systems often rely on complex and expensive voltage-controllable components like Spatial Light Modulators or two-beam interferometry. To address this, we introduce a QPM system optimized for time-varying phase samples using azobenzene liquid crystal as a Zernike filter with a polarization-sensing camera. This system operates without input voltage or moving components, reducing complexity and cost. Optimized for gentle illumination to minimize phototoxicity, it achieves a 1 Hz frame rate for prolonged monitoring. The system demonstrated accuracy with a maximum standard deviation of ±42 nm and low noise fluctuations of ±2.5 nm. Designed for simplicity and single-shot operations, our QPM system is efficient, robust, and precisely calibrated for reliable measurements. Using inexpensive optical components, it offers an economical solution for long-term, noninvasive biological monitoring and research applications. Current quantitative phase microscopy (QPM) systems to study dynamic cellular processes are often expensive and complex. The authors develop a cost-effective QPM system using azobenzene liquid crystals, which operate without input voltage or moving parts. This system achieves accurate, low-noise measurements and is ideal for dynamic and non-invasive biological monitoring. [ABSTRACT FROM AUTHOR]

Tunable filters are vital not only for dynamic display but also in the miniaturized spectral imaging system. Yet, the present tunable devices possess low optical throughput, bulky volume, slow response, or complex configuration. In this paper, the study proposed and experimentally demonstrated a compact tunable filter module based on metagratings combined with liquid crystals (LC). By the synergetic effect between the birefringent LC and the dichroic metagratings, the module possesses distinct transmissive features by electrically tuning the LC material, resulting from the polarization interference effect. A simple nanoimprinting method, which is suitable for the mass production of nanostructures is adopted for low‐cost fabrication. These unique features endow the present tunable filter module with low cost, high optical throughput, and compact volume. As a proof of concept, a multispectral imager is built with this filter based on a commercial microscope. Experimental results show the system response is five times higher in optical throughput across the whole visible region than the traditional liquid crystal tunable filter and the signal‐to‐noise ratio can be improved by 7 dB. Considering the feasibility of nanoimprinting, this module paves the way for spectral imaging in low‐light conditions and on‐site scenarios such as tongue diagnosis and food quality inspection. [ABSTRACT FROM AUTHOR]

A liquid crystal is used as an electro-optical device with the advantages of low voltage driving, low power consumption, and thin flatness by utilizing its refractive index anisotropy (birefringence). In this research, a liquid crystal tunable filter (LCTF) with control of a main peak wavelength λ0 and a full-width Δλ at half maximum is developed. The device contains two stacking liquid crystal layers with different wavelength dependences of birefringence Δn with their optical axes perpendicular to each other and controlling the light wavenumbers in a complementary manner (S-ECB). [ABSTRACT FROM AUTHOR]

We demonstrate the use of a low-cost liquid-crystal-based wavelength-tunable filter and CMOS video camera to add hyperspectral imaging capabilities to a probe station equipped with a simple optical microscope. The resultant setup is used to rapidly resolve the spectral and spatial variations in electroluminescence typically observed for InxGa1−xN/GaN light-emitting diodes. Applying standard statistical analyses of variation within the multivariate datasets, such as moments and principal components, we observe inhomogeneities on a spectral scale significantly smaller than the bandwidth of the tunable filter. The resultant tool offers an alternative to scanning beam luminescence techniques for high-throughput hyperspectral analysis of optoelectronic devices. [ABSTRACT FROM AUTHOR]

Liquid crystal tunable filters (LCTFs) are extensively used in hyperspectral imaging systems to obtain spectral information of target scenes. However, a typical LCTF can only filter linearly polarized light, greatly reducing the transmittance of the system and limiting its application in spectral and polarization imaging. In this paper, a spectropolarimeter using Mach–Zehnder structured LCTFs (MZ-LCTFs) combined with liquid crystal variable retarders (LCVRs) is proposed. The polarized beam splitter (PBS) can make full use of the two polarization components of the incident light to improve the transmittance of the system. Specifically, the results show that the mean pixel intensity (MPI) of spectral images is improved by 93.48% compared to a typical LCTF. Subsequently, the average signal to noise ratio (SNR) of filtered and unfiltered images when simultaneously using polarization S and P channels is increased by 2.59 dB compared to a single channel. In addition, the average Standard Deviations (STDs) of DoLP and DoCP are 0.016 and 0.018, respectively. The proposed method has the potential to be applied to obtain polarization information with high optical efficiency and a full spectrum in a wide band. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

An optical filter is one of the indispensable devices in massive and high-speed communication, optical signal processing, and display. Twist-structure liquid crystals, cholesteric liquid crystals, blue-phase liquid crystals, and sphere-phase liquid crystals show potential application in optical filters originating from the periodic nanostructures. Wavelength and bandwidth tuning can be controlled via temperature, electric fields, light, angle, spatial control, and templating technology. In this review, we discuss the recent developments of twist-structure liquid crystal filters. [ABSTRACT FROM AUTHOR]

Fouling control coatings (FCCs) are used to prevent the accumulation of marine biofouling on, e.g., ship hulls, which causes increased fuel consumption and the global spread of non-indigenous species. The standards for performance evaluations of FCCs rely on visual inspections, which induce a degree of subjectivity. The use of RGB images for objective evaluations has already received interest from several authors, but the limited acquired information restricts detailed analyses class-wise. This study demonstrates that hyperspectral imaging (HSI) expands the specificity of biofouling assessments of FCCs by capturing distinguishing spectral features. We developed a staring-type hyperspectral imager using a liquid crystal tunable filter as the wavelength selective element. A novel light-emitting diode illumination system with high and uniform irradiance was designed to compensate for the low-filter transmittance. A spectral library was created from reflectance-calibrated optical signatures of representative biofouling species and coated panels. We trained a neural network on the annotated library to assign a class to each pixel. The model was evaluated on an artificially generated target, and global accuracy of 95% was estimated. The classifier was tested on coated panels (exposed at the CoaST Maritime Test Centre) with visible intergrown biofouling. The segmentation results were used to determine the coverage percentage per class. Although a detailed taxonomic description might be complex due to spectral similarities among groups, these results demonstrate the feasibility of HSI for repeatable and quantifiable biofouling detection on coated surfaces. [ABSTRACT FROM AUTHOR]

In this paper, a systematic design method for polarization-insensitive tunable liquid crystal (LC)-based metamaterial filter with the passband of flat-top and sharp roll-off is proposed. A compact LC-based bandpass metamaterial filter unit cell with a dimension of 0.09 λ × 0.09 λ is designed. The metamaterial filter element consists of a pair of planar pinwheel-shaped metallic structures with four symmetrically distributed isosceles triangular patches. LC is sandwiched in this pair of metallic structures. The metal pattern on each layer is 90° rotationally symmetrical leading that the LC-based metamaterial filter is insensitive to the polarization of incident waves. In order to obtain the transmission characteristics of flat top and sharp roll-off, a double-layer LC-based metamaterial filter structure is proposed. Full-wave simulations show that the central frequency of the metamaterial filter is tuned from 10.88 GHz to 11.78 GHz, and the tuning range reaches up to 7.9%. Meanwhile, under TE and TM polarizations, the double-layer LC-based metamaterial filter structure achieves filtering characteristics with a flat-top passband of not less than 997 MHz and sharp roll-off for arbitrary LC states. Moreover a prototype sample is designed, fabricated, and measured to verify the proposed design method. [ABSTRACT FROM AUTHOR]

The Hyperspectral Imaging System can obtain the spectral response value of each pixel in a fabric sample image while being applied to fabric color measurement. Compared with the common grating Hyperspectral Imaging System, the Hyperspectral Imaging System based on Liquid Crystal Tunable Filter (LCTF) has the advantages of small size, high spatial resolution, and easy integration, which has potential application prospects in textile industry. In this article, the performance of the LCTF Hyperspectral Imaging System for fabric color measurement was evaluated, and an improved model for calibrating the consistency between it and Datacolor 650 was proposed. First, the 210 Pantone cotton color cards were used as samples to study the color repeatability and reproducibility of the LCTF Hyperspectral Imaging System. For evaluation its color measurement ability, the measured reflectance values were converted to the CIELAB color space and compared with those of Datacolor 650. Then, a Radial Basis Function neural network model was proposed to calibrate the color consistency between LCTF Hyperspectral Imaging System and Datacolor 650 which can fully use the reflectance information of the whole band instead of only adjacent wavelengths. Experimental results show that the LCTF Hyperspectral Imaging System can accurately measure the fabric color with good repeatability and reproducibility, and the consistency between the two instruments was significantly improved based on the Radial Basis Function neural network model compared with the R model. [ABSTRACT FROM AUTHOR]

A portable 4D snapshot hyperspectral imager (P4DS imager) with compact size, fast imaging time, low cost, and simple design is proposed and demonstrated. The key components of the system are a projector, a liquid crystal tunable filter (LCTF), and a camera. It has two operating modes depending on the set state of the LCTF: a 3D light measurement mode that produces a 3D point cloud reconstruction of an object and a hyperspectral imaging mode yielding spectral data. The camera imaging plane is the same for both operating modes allowing the collected spatial and spectral data to be directly fused into a 4D data set without post-processing. The P4DS imager has excellent performance with a spectral resolution of 10 nm, a spatial depth accuracy of 55.7 µm, and a total 4D imaging time of 0.8 s. 4D imaging experiments of three different samples, namely, a colored figurine, green broccoli, and a human face, are presented to demonstrate the efficiency and applicability of the system. Due to being cost-effective, portable, and good imaging performance, the proposed system is suitable for commercialization and mass production. [ABSTRACT FROM AUTHOR]

In recent years, as a hot inorganic luminescent materials, Quantum dots have been widely used in display devices because of their high photoluminescence efficiency and excellent color gamut. In order to further improve the performance of LCD display devices, we consider introducing quantum dot color film into the structure of LCD. In this report, we pixelate the QDs to replace the traditional color film, this is different from the QD was widely used method which QDs was made into thin film as part of the back light unit. Compared with the general LCD, QDCF can achieve higher efficiency, higher color gamut and wider viewing angle, in order to solve the polarization of the liquid crystal cell, we use WGP In liquid crystal cell to achieve high contrast ratio. [ABSTRACT FROM AUTHOR]

We report long-period waveguide grating (LPWG) based tunable wavelength de-multiplexer and tunable coupler/filter in liquid crystal (LC) clad rib waveguides on silicon nitride on insulator platform. High birefringence and electrically tunable refractive index of the MLC-9200-000 LC have been used to achieve a tuning range covering most of the S, C and L bands of the optical communication system. The structure consists of two parallel rib waveguides with an elevated slab. We have considered a new concept of injecting power into a higher-order slab mode. The power from the slab mode is coupled to the rib modes using LPWGs inscribed on the sidewalls of the ribs. The structure works as a tunable wavelength de-multiplexer when the grating periods in both ribs are different. The wavelength tunability of the de-multiplexer is achieved by an external voltage applied across the liquid crystal cell. Our numerical results show wavelength tuning of the de-multiplexer in the range 1.437 - 1.627 μm. The structure works as an electrically tunable coupler/filter when the grating period of both the gratings are the same. We numerically demonstrate the tuning of the coupler in the wavelength range 1.487 - 1.572 μm and that of the filter in the range 1.484 - 1.577 μm with 20-dB rejection. • Long-period waveguide grating based tunable wavelength de-multiplexer and tunable coupler/filter. • The wavelength tunability of the de-multiplexer is achieved by an external voltage applied across the liquid crystal cell. • Wavelength tuning of the de-multiplexer in the range 1.437–1.627 µm. • Wavelength tuning of the coupler in the wavelength range 1.487–1.572 µm. • Wavelength tuning of the filter in the range 1.484–1.577 µm. [ABSTRACT FROM AUTHOR]

This letter introduces two continuously tunable bandpass filters with substrate integrated coaxial line (SICL) and liquid crystal (LC) technologies. The tunability of the filters is a kind of electric tuning, achieved by the permittivity changing of the LC material filled in the SICL cavities. The SICL resonator and the electric and magnetic coupling between the resonators are investigated. Then, fourth‐order direct‐coupled and cross‐coupled tunable filters (Filter I and II) with center frequency of 6.5 GHz are designed, fabricated, and measured. The experimental results show that the continuous tuning ranges are 220 and 280 MHz for Filter I and II, respectively. Furthermore, the insertion losses of the Filter I and II are 3.93–4.78 dB and 3.65–4.3 dB over the whole tuning range. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A distinctive method is used to achieve transverse-mode control by building and integrating a tunable liquid crystal (LC) mode filter on top of traditional vertical-cavity surface-emitting lasers (VCSELs). An LC cell is fabricated by injecting a type of nematic LC material (E7) in an annular groove patterned by SiO2. By electrically tuning the refractive index of the LC, a spatially dependent reflectivity profile can be achieved and optimized, which directly influences the threshold modal gain of each transverse mode provided by oxide-confined VCSELs. The flexible and accurate control performance of the LC mode filter structure have been demonstrated by the simulation results and our analysis. This design is a completely novel method to realize VCSELs with an accurate and real-time controllable transverse-mode, and it will probably play a significant role in the future. [ABSTRACT FROM AUTHOR]

There are two kinds of operation mode of plant protect multi-rotor UAV, hover and fixed-speed flight, so corresponding working modes of spectral remote are needed. However, general-purpose remote sensing equipment couldn’t satisfy the needs. A set of liquid crystal spectral imaging device was designed to meet the requirements of low-altitude spectral remote of multi-rotor UAV based on the principle of two-dimensional optical splitting. Firstly, the hardware and the software of the device were developed to realize the synchronization of three modules: the acquisition module, the control module and the communication module. The acquisition module consists of a16-bit CCD grayscale camera, a color aberration lens, a liquid crystal tunable filters (LCTFs), and a UV filter. The control module consists of a microcomputer controller and a USB connector. The communication module consists of a data transmission device, BEIDOU positioning systems, and the ground workstations. The software was developed to control hardware for working synchronously and analyze data. The functions of software were not only for parameter adjustment before formal capturing, but also for spectral images analysis alone and achieving spectral abstraction. Secondly, the data acquisition method based on the principle of device was studied. The relationship between the flight speed, altitude and capturing parameters of the device was established, which guaranteed the quality of spectral images, the possibility of image mosaics, spectral continuity and stability of the captured spectral images. Thirdly, indoor and outdoor experiments were carried out to test the device performance and data acquisition method. The indoor experiment was performed in the wind tunnel laboratory of South China Agricultural University by a stepper motor equipped. Compared with the millimeter-defocus blur spectral images, and the micro motion blur spectral images, the original images taken indoors were 10 and 15 times clearer respectively. Furthermore, image mosaics could be achieved based on feature point algorithm. The outdoor experiment was carried out in Xinxiang, Henan Province, China, with a Quadrotor UAV equipped. The results showed that the original images taken outdoors had high-quality, and the spatial resolution was up to 1 392×1 040 pixels. The spectra abstracted from original images were stable and reliable. The spectral range was 400-720 nm, and the spectral step was up to 2 nm. Both the comprehensive indoor simulation tests and the outdoor tests showed that the liquid crystal spectral imaging device developed in the paper could obtain qualified spectral images, and showed that the device could match two operating modes of multi-rotor UAV, hover and fixed speed motion. Based on the design of direct coupling optical path, the whole set of device is compact structure, vibrate resistance, high reliability and stability, and suitable for plant protection working. The new method and the device were provided for low-altitude remote sensing of multi-rotor UAV in the paper, which is expected to be applied to precision spraying, crop prescription map generation and other related fields. [ABSTRACT FROM AUTHOR]

An innovative hyperspectral LIDAR instrument has been developed for applications in marine environment monitoring research activities, remotely detecting the fluorescence spectra produced in the spectral interval between 400 nm and 720 nm. The detection system is composed by a custom made photomultiplier charge integrating and measuring (CIM) unit, which makes automatic background signal subtraction, and a liquid crystal tunable filter (LCTF). The new instrument therefore has hyperspectral resolution and allows automatic background subtraction; it is compact and automated by custom software that permit to adapt the instrument properties depending on the environmental conditions. Laboratory tests to characterize the instrument performance have been carried out, concluding that this sensor can be employed in remote sites for Chl-a detection. [ABSTRACT FROM AUTHOR]

In this work, switchable liquid crystal infrared filter is presented. The tailored superfluorinated liquid crystal material exhibiting low parasitic absorption at the operating range has been used for the construction of the filter. The switching range as high as 300 nm is achieved by applying 18 V. The filter can operate continuously from 3.45 up to 3.75 μm. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Stand‐off Raman spectroscopy offers a highly selective technique to probe unknown substances from a safe distance. Often, it is necessary to scan large areas of interest. This can be done by pointwise imaging (PI), that is, spectra are sequentially acquired from an array of points over the region of interest (point‐by‐point mapping). Alternatively, in this paper a direct hyperspectral Raman imager is presented, where a defocused laser beam illuminates a wide area of the sample and the Raman scattered light is collected from the whole field of view (FOV) at once as a spectral snapshot filtered by a liquid crystal tunable filter to select a specific Raman shift. Both techniques are compared in terms of achievable FOV, spectral resolution, signal‐to‐noise performance, and time consumption during a measurement at stand‐off distance of 15 m. The HSRI showed superior spectral resolution and signal‐to‐noise ratio, while more than doubling the FOV of the PI at laser power densities reduced by a factor of 277 at the target. Further, the output hyperspectral image data cube can be processed with state of the art chemometric algorithms like vertex component analysis in order to get a simple deterministic false color image showing the chemical composition of the target. This is shown for an artificial polymer sample, measured at a distance of 15 m. [ABSTRACT FROM AUTHOR]

• Enables four-dimensional imaging in the polarization, spectral and spatial domains. • LCTF plays both a high-resolution hyperspectral filter and a joint linear polarizer. • QWP joins LP to measure full-Stokes parameters of hyperspectral images compressively. • It uses precise solving instead of fuzzy reconstructing the first Stokes parameter. • Improving measurement approach can further separate the last three Stokes parameters. Polarization hyperspectral compressive imaging has wide application prospects due to reflecting rich information of the target from the spatial, spectral and polarization dimensions. However, compressive imaging methods are limited in system complexity and reconstruction efficiency. In this paper, the combination of a quarter-wave plate, a linear polarizer and a liquid crystal tunable filter enables compressive full-Stokes polarization and flexible hyperspectral imaging. Then, the four Stokes parameters can be quickly reconstructed with high precision through numerical operations and compressive sensing. Both simulations and experiments verify the effectiveness of this method. Compared with the feature scaling method, this work shortens the reconstruction time by 83.73%, and greatly improves the reconstruction result of the first Stokes parameter from limited reconstruction to accurate solution. This work not only gives insights from efficient reconstruction to system design, but also creates conditions for the application of polarization hyperspectral imaging in specific fields. [ABSTRACT FROM AUTHOR]

• Enables simultaneous compression in the polarization, spectral and spatial domains. • Change the fast axis angle of QWP 2 or 3 times to reconstruct full-Stokes parameters. • LCTF with dense modulation function encodes and reconstructs high-resolution spectra. • Combine DMD encoding and detector multiplexing to achieve spatial super-resolution. • It's beneficial to reduce the compression rate, so shorten the data acquisition time. Polarized hyperspectral images contain rich information representing both surface texture and spectral signature of target scene. However, it is difficult to obtain the full-Stokes parameters of hyperspectral images directly. A compressive imaging system is proposed in this paper to recover the four-dimensional polarized hyperspectral images with full-Stokes parameters using quarter-wave plate (QWP) and liquid crystal tunable filter (LCTF). Changing the fast axis angle of QWP provides the degrees of freedom to modulate the polarization states. The LCTF serves as the broad-band spectral filter to modulate the spectral signatures. The output of LCTF is modulated by a coded aperture in spatial domain, and then the modulated polarized hyperspectral images are projected and multiplexed on a two-dimensional detector. Based on the compressive sensing theory, the full-Stokes polarized hyperspectral images can be reconstructed from several compressive measurements by solving the convex optimization problems with sparsity prior. The feasibility of proposed system is verified by simulations and experiments. Compared to the traditional compressive spectropolarimetric imaging methods, the proposed method is beneficial to reduce the compression rate, and thus shorten the data acquisition time. This work also paves a new way for the full-Stokes polarized hyperspectral imaging system with simple and compact structure. [ABSTRACT FROM AUTHOR]

This paper presents tunable liquid crystal filter consists of three interference filters (LC - cells) with different cell thicknesses. These filters use nematic liquid crystal (with high birefringence). Such design allows to select precisely (using the electric field) the wavelength of outgoing light. [ABSTRACT FROM AUTHOR]

Abstract: We analyze the tunability of full band gap in two-dimensional photonic crystals created by square and triangular lattices of anisotropic tellurium rods in air background, considering that the rods are infiltrated with liquid crystal. Using the plane-wave expansion method, we study the variation of full band gap by changing the optical axis orientation of liquid crystal. [Copyright &y& Elsevier]

In the past decade, underwater spectral imaging (USI) has shown great potential in underwater exploration for its high spectral and spatial resolution. This proposal presents a stare-type USI system combined with the liquid crystal tunable filter (LCTF) spectral splitting device. Considering the working features of LCTF and the theoretical model of USI, the core structure containing "imaging lens-LCTF-imaging sensor" is designed and developed. The system is compact, and the optical geometry is constructed minimally. The spectral calibration test analysis proved that the spectral response range of the system covers a full band of 400 nm to 700 nm with the highest spectral resolution between 6.7 nm and 18.5 nm. The experiments show that the system can quickly collect high-quality spectral image data by switching between different spectral bands arbitrarily. The designed prototype provides a feasible and reliable spectral imaging solution for in situ underwater targets observation with high spectrum collecting efficiency. [ABSTRACT FROM AUTHOR]

• The LCTF-based spectral imaging system can be used for color reproduction. • A correction method is proposed to reduce the spectral shift caused by LCTF. • Adaptive band selection provides more accurate results than the conventional method. Spectral imaging systems using liquid crystal tunable filters (LCTFs) can be applied to color reproduction. However, the spatially-varying spectral shift caused by inherent LCTF characteristics affects the results' accuracy. This paper proposes a spectral shift correction method employing high-chroma color patches as calibration targets, which reduces the color difference from 3.67 to 1.98 (CIEDE2000). Additionally, a method is developed for adaptively selecting wavebands for image acquisition according to the target's pre-estimated spectral reflectance, whereby color differences are reduced by 21.2% over the conventional method with a limitation of 15 spectral images acquired. These methods avoid LCTF's drawbacks and exploit its tunability, making it more suitable for color-relevant applications. [ABSTRACT FROM AUTHOR]

Multi-reflective peak and bandwidth scalable liquid crystal (LC) filters were investigated. By refilling a cholesteric LC (CLC) whose chiral pitch is different to the target template into a blue phase LC (BPLC) template, a multi-reflective peak single layer LC filter can be fabricated. With multiple templating and refilling processes, the number of reflective peaks can be further increased. Moreover, by refilling the CLCs of designed chiral pitch into a CLC template sequentially, a bandwidth scalable single layer CLC filter can be fabricated. The LC filters show great potential applications in optical communication, display, and LC lasing. [ABSTRACT FROM AUTHOR]

Abstract: The effect of temperature on the spectrum characteristic of the liquid crystal filter in the region of visible light was investigated theoretically and experimentally in detail. The conclusion shows that with the increasing temperature, the center wavelength of the filter will shift toward the short wavelength, and the center wavelength of the filter will shift toward long wavelength as the temperature decreases. The result of numerical simulation is in excellent agreement with the experiment result. In addition, the experiment results indicate that with the increasing temperature and reducing wavelength the transmittance of liquid crystal filter will reduce. According to the above conclusion we propose a new structure for maintaining a stable central wavelength output of the liquid crystal filter with the changing temperature, and it does not require temperature control equipment, is easy to operate, and has no need to look for special temperature coefficient birefringence, etc. This structure may find a certain application for liquid crystal filter as we believe, particularly, in the condition of different environment temperature. [Copyright &y& Elsevier]

Detecting a variety of biological samples accurately and swiftly in an integrated way is of great practical significance. Currently, biofluorescent spectrum detection still largely relies on microscopic spectrometers. In this study, we propose an integrable method to detect biofluorescent spectrums with designed liquid crystal tunable filter (LCTF), in order to identify typical biological samples such as cells and bacteria. Hela cells labeled with red and green fluorescent proteins and Pseudomonas with fluorescence wavelengths of 610 nm, 509 nm and 450 nm, respectively, are inspected. High-resolution (6 μm) biofluorescent results have been achieved, together with clear images of the Hela cell clusters and the Pseudomonas bacteria colonies. Biofluorescence signals can be detected at a high transmittance (above 80%), and the response time of the device can reach 20 ms or below. The proposed method has the potential to be integrated into a microfluidic system to detect and identify the biofluorescent signals as a high throughput, low-cost option, for both high resolution and large field observation applications. [ABSTRACT FROM AUTHOR]

Polarized hyperspectral images can reflect the rich physicochemical characteristics of targets. Meanwhile, the contained plentiful information also brings great challenges to signal processing. Although compressive sensing theory provides a good idea for image processing, the simplified compression imaging system has difficulty in reconstructing full polarization information. Focused on this problem, we propose a two-step reconstruction method to handle polarization characteristics of different scales progressively. This paper uses a quarter-wave plate and a liquid crystal tunable filter to achieve full polarization compression and hyperspectral imaging. According to their numerical features, the Stokes parameters and their modulation coefficients are simultaneously scaled. The first Stokes parameter is reconstructed in the first step based on compressive sensing. Then, the last three Stokes parameters with similar order of magnitude are reconstructed in the second step based on previous results. The simulation results show that the two-step reconstruction method improves the reconstruction accuracy by 7.6 dB for the parameters that failed to be reconstructed by the non-optimized method, and reduces the reconstruction time by 8.25 h without losing the high accuracy obtained by the current optimization method. This feature scaling method provides a reference for the fast and high-quality reconstruction of physical quantities with obvious numerical differences. [ABSTRACT FROM AUTHOR]

A guided-mode resonant filter incorporating an electro-optically tunable liquid crystal refractive index is demonstrated at a wavelength of 655 nm and a tuning range of 4 nm. Rigorous coupled wave analysis and finite difference time domain analysis are used to simulate the characteristics of the filter during liquid crystal reorientation. Tuning performance is demonstrated that is consistent with the device simulations. Tunable filters in the visible wavelength range that are inexpensively fabricated over large surface areas are expected to find applications in optical limiting and video display. [ABSTRACT FROM AUTHOR]

This paper, for the first time, presents a wavelength-scanning surface plasmon resonance microscope (WS-SPRM) as a label-free biosensor capable of measuring cell-substrate interaction. The approach utilized a liquid crystal tunable filter (LCTF) as a fast and flexible wavelength-scanning device that can implement a wavelength-scanning and SPR imaging cycle within 1 s. The system was verified by monitoring the dynamics of cellular processes including cell detachment and electroporation of individual cells. It was found that the WS-SPRM presented better performance than the intensity-based SPRM (I-SPRM) in the imaging of cell adhesion. The results also indicated that the WS-SPRM exhibited a larger dynamic range in monitoring cell electroporation than that of I-SPRM. In summary, the developed WS-SPRM in this study provides a promising technique for real-time monitoring of cell-substrate interaction. • For the first time, a wavelength-scanning SPRM is developed as a label-free biosensor to measure cell-substrate interaction. • The WS-SPRM has been exploited to monitor the dynamics of cellular processes including detachment and electroporation. • The WS-SPRM exhibits larger dynamic range compared to the intensity SPRM, which is beneficial for the cell adhesion imaging. [ABSTRACT FROM AUTHOR]

In order to improve the performance properties of electro-optical devices based on mesogenic materials, a cholesteric liquid crystal (cholesteryl tridecylate, X-20) was doped with nanoscale fragments of multilayer fluorinated graphene (GrF). A stable dispersion of X-20 with GrF was obtained. It was shown that the addition of 0.02 wt% of the nanosized GrF slightly affects phase transition temperatures of the mesogen, insignificantly reducing the mesophase temperature range due to increasing of Cr–SmA and decreasing N*–Iso transition temperatures. The dielectric properties of the pure X-20 and X-20/GrF composition were investigated in the frequency range from 20 Hz to 5 MHz and within the temperature range from 303 to 373 K. It was established that the introduction of the dopant is accompanied by an increase of the absolute value of the dielectric permittivity of the composition. At the same time, for the X-20/GrF composition a significant increase of the specific ionic conductivity was observed in the range of all studied phases due to an increase of free charge carriers. At the low frequencies of the electric field, the main contribution to the loss of dielectric permittivity makes the ionic conductivity. For the pure X-20, with the frequency increase, the contribution of the ionic conductivity decreases rapidly. This leads to a serious decrease of the imaginary part of the dielectric permittivity values and at the frequency of around 20 kHz it becomes negligible. For the X-20/GrF composition, this effect can be observed at the frequency of approximately 500 kHz and the imaginary part of the dielectric permittivity increases almost 10 times. The obtained results show the real possibility to modify conductive and dielectric properties of cholesteric liquid crystal by doping it with carbon nanomaterials. This approach opens up new opportunities in creating and improving of microantennas, frequency filters and photonic crystals based on liquid crystals. Unlabelled Image • System of cholesteric liquid crystal (LC) with fluorinated graphene was obtained. • Effect of nanographene on conductive and dielectric properties of LC was studied. • Increase of specific ionic conductivity at Cr–SmA–N*–Iso transitions was observed. • Proposed approach opens new opportunities in non-display applications of LC. [ABSTRACT FROM AUTHOR]

The effect of sectional polymerization process on tunable filters with cholesteric liquid crystal (CLC) and blue phase liquid crystal (BPLC) is demonstrated. The bandwidths of the polymer-stabilized cholesteric liquid crystal (PSCLC) and polymer-stabilized blue phase liquid crystal (PSBPLC) filters can be broadened by the holding treatment without distortion. The reflection bandwidth of the CLC filter can be broadened from 120 nm to 220 nm, and that of the BPLC filter can be broadened from 45 nm to 140 nm. Meanwhile, the intensity of reflection can be retained very well. The central wavelength of polymer-stabilized CLC filter can be thermally tuned from 1614 nm to 1460 nm with a stable wide bandwidth. The tunable C-band CLC filter and BPLC filter show great potential application in multi- and hyper-spectral systems and wide-band color filters. [ABSTRACT FROM AUTHOR]