Liquid Crystal Filter Research Articles

Compact broadband high-resolution real-time four-dimensional imaging spectrometer

A broadband high-resolution real-time four-dimensional imaging spectrometer (HRRFDIS) is presented, which can acquire both broadband fine spectra and high-resolution three-dimensional (3D) spatial images of a 3D object in real time. The HRRFDIS consists of a first microlens array arranged in a plane to achieve orthographic view spatial imaging, a second microlens array arranged on a conical surface to measure the depth and to achieve 360-degree side-view spatial imaging, multiple optical fibers, a collimating microlens array arranged in a straight line, a parallel planar transmission grating pair to obtain high spectral resolution over a broadband spectral range, and an area-array detector. Compared with the scanning four-dimensional imaging spectrometer (FDIS), the HRRFDIS can obtain a broadband high-resolution four-dimensional dataset using only one frame of data, and it is more stable, compact, small-sized, and lightweight. Compared to the staring FDIS using a liquid crystal filter and requiring at least one modulation period of liquid crystal to acquire a complete hyperspectral image, the HRRFDIS can acquire a complete broadband hyperspectral image in real time. Compared to existing snapshot FDIS, the HRRFDIS can achieve much higher spectral resolution, especially over a broadband spectral range. The HRRFDIS is a unique concept that is the first to obtain both high-resolution broadband spectral information and high-resolution 3D spatial information in real time, to the best of our knowledge. The HRRFDIS will be suitable for real-time measurement of 3D objects in the ultraviolet to infrared spectral range.

Optical Filters Based on Cholesteric, Blue and Sphere Mesophases.

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.

СОВРЕМЕННЫЕ ДОСТУПНЫЕ БАЗЫ ДАННЫХ ОТПЕЧАТКОВ ЛАДОНИ: ОБЗОР

The palm print is a unique and very useful biometric. A lot of research has been done on thistopic over the past few decades. Various algorithms and systems have been developed and successfullyimplemented. Since this method does not provide more advanced information for personalityrecognition, multispectral or hyperspectral imaging and handprint recognition could be apotential answer to these systems. Biometric technologies have been widely used in the securityindustry for authentication and identification over the past few years. An improved recognitionsystem is required to improve accuracy and speed. This article reviews some modern handprintdatabases and describes the methods used and their accuracy. Face, fingerprint, iris, palm print,hands are physiological biometric data. Of all biometrics, physiological biometrics offers the mostbenefits. The PolyU-IITD non-contact palm image database compiled with a handheld cameraincludes residents of India and China. The database of IIT Touchless Palmprints is sourced fromDelhi India students and teachers and consists of complete hand images. The database ofhyperspectral fingerprints created by the Hong Kong Polytechnic University was collected in the Biometric Research Laboratory Department using Meadowlark liquid crystal filters. The MultispectralFingerprint Database, Hyperspectral Database was compiled by Chinese research teamsof scientists. The polyU fingerprint database was collected from 193 people and contains386 palms. The Chinese Academy of Sciences has developed the CASIA handprint database withits own handprint recognition device. The XJTU fingerprint database is collected using iPhone 6S,HUAWEI mate8, LG G4, Samsung Galaxy Note5 and MI8 gadgets. A literature review of currentresearch in this area is also presented. The advantages of hyperspectral images compared to multispectralimages are noted, hyperspectral images of palm prints are very difficult to fake.

Novel Hybrid Electric/Magnetic Bias Concept for Tunable Liquid Crystal Based Filter

This paper presents a novel hybrid bias concept for liquid crystal (LC) filter by using simultaneously electric and magnetic bias fields. It enables continuous tuning with a simplified electrode design, decreased number of electrodes and reduced bias voltage. Furthermore, the tuning efficiency is increased, since the homogeneous bias fields enable a full exploitation of the LC's anisotropy. To demonstrate this concept, a novel reconfigurable gap waveguide two-pole bandpass filter with tunable center frequency and coupling elements is designed at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$30 \,\mathrm{GHz}$</tex-math></inline-formula> . Liquid crystal technology is applied as tunable material, whereby tunability of the center frequency and coupling elements is obtained by controlling the LC's effective permittivity. The presented filter's center frequency can be tuned from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$28.88 \,\mathrm{GHz}\,\mathrm{to}\, 29.88 \,\mathrm{GHz}$</tex-math></inline-formula> with a maximum bias voltage of 100 V, with a return loss of 20 dB and low insertion loss of only 1.65 to 1.95 dB.

Color Enrichment Solids of Spectrally Pure Colloidal Quantum Wells for Wide Color Span in Displays

AbstractColloidal quantum wells (CQWs) are excellent candidates for lighting and display applications owing to their narrow emission linewidths (&lt;30 nm). However, realizing their efficient and stable light‐emitting solids remains a challenge. To address this problem, stable, efficient solids of CQWs incorporated into crystal matrices are shown. Green‐emitting CdSe/CdS core/crown and red‐emitting CdSe/CdS core/shell CQWs wrapped into these crystal solids are employed as proof‐of‐concept demonstrations of light‐emitting diode (LED) integration targeting a wide color span in display backlighting. The quantum yield of the green‐ and red‐emitting CQW‐containing solids of sucrose reach ≈20% and ≈55%, respectively, while emission linewidths and peak wavelengths remain almost unaltered. Furthermore, sucrose matrix preserves ≈70% and ≈45% of the initial emission intensity of the green‐ and red‐emitting CQWs after &gt;60 h, respectively, which is ≈4× and ≈2× better than the drop‐casted CQW films and reference (KCl) host. Color‐converting LEDs of these green‐ and red‐emitting CQWs in sucrose possess luminous efficiencies 122 and 189 lm W−1elect, respectively. With the liquid crystal display filters, this becomes 39 and 86 lm W−1elect, respectively, providing with a color gamut 25% broader than the National Television Standards Committee standard. These results prove that CQW solids enable efficient and stable color converters for display and lighting applications.

P‐105: Cholesteric Liquid Crystal Filters with Single Layer template

The template effects on bandwidth tunable and reflectivity improvement of cholesteric liquid crystal (CLC) filters were investigated. A single layer bandwidth tunable CLC filter was fabricated by multiple templating process. In addition, high reflectivity CLC filters with single layer templating process was proposed which may reflect both right‐ and left‐ circularly polarized light. High‐reflectivity of 65%, 69%, and 72% in the red, green, and blue color regions was achieved. The templated CLC filters show great potential applications in optical community, display, smart windows, and lasing.

Genetic Optimization of Liquid Crystal Matrix Based Interference Suppression for VLC MIMO Transmissions

Optical channel decorrelation is a key aspect in designing a multi-user visible light communication system. As light-emitting diodes (LEDs) are commonly used for illumination and data transmission in such a system simultaneously, the interference between them is a major problem for suitable modulation schemes. We have proposed to position liquid-crystal (LC) matrix elements in front of the receivers in order to block unwanted light – so effectively acting as filter and reducing the interference. To do so, the appropriate pixels of the LC filter are switched either to a transmissive state or to an opaque state. The selection of the correct pixel patterns is a high-order optimization problem, which makes it challenging for classic algorithms. In this paper, we suggest applying a genetic optimization to find suitable pixel patterns. We combine this kind of receiver-side optimization with conventional convex precoding at the transmitter side in an iterative manner. The overall optimization goal is to maximize the sum rate over all users. To prove the effectiveness, we use a numeric ray-tracing simulation with different settings. Also we analyze the impact of the main parameters for the genetic algorithm.

High-Reflective Templated Cholesteric Liquid Crystal Filters

Cholesteric liquid crystals (CLCs) have been widely applied in optical filters due to Bragg reflection caused by their helical structure. However, the reflectivity of CLC filters is relatively low, commonly less than 50%, as the filters can only reflect light polarized circularly either left- or right-handedly. Therefore, a high-reflective CLC filter with a single-layer template was proposed which may reflect both right- and left-handed polarized light. The CLC filters of the red, green, blue color were fabricated by the templating technology, which show good wavelength consistency. Additionally, a multi-phase liquid crystal filter with high reflectance was demonstrated by the single-layer templating technology. The templated CLC or multi-phase liquid crystal filters show great potential applications in the optical community, reflective display, and lasing.

Multi-Pitch Liquid Crystal Filters with Single Layer Polymer Template.

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.

Multi-wavelength and bandwidth tunable liquid crystal filter

Multi-wavelength and bandwidth tunable liquid crystal filter

Liquid crystal filter based tunable transmitter for 25Gps wavelength division multiplexing-passive optical network fronthaul.

A novel tunable transmitter structure based on liquid crystal filter, to the best of our knowledge, is presented. The structure is designed for application to 5G fronthaul and supports 25 Gbps dense wavelength division multiplexing (WDM) transmission and tunable range of 35 nm. The design takes into account easy change of operation band over coarse WDM grid. Prototype samples are developed to test feasibility of the design.

Electronic System of Counteraction to Laser Means of Location and Destruction

The work is devoted to the development of a device for counteracting laser means of location and destruction. The analysis of data from open literature on similar systems and technologies have been performed. Theoretical calculations of the effectiveness of protecting the human eye or optical device from laser damage with various types of protection have been carried out.Laser technology has been used by the military since the mid-1950s. The military uses lasers in systems of direct thermal destruction of the object, pointers, detection systems of snipers, systems of interference with snipers, rangefinders, etc. In the late 1970s and early 1980s, military-experimental blinding self-propelled complexes were created in the USSR. The development of laser and computer technology has significantly reduced the dimensions of the devices, as well as their cost. Now such systems are widely used in combat operations.On the other hand, there is a challenge to counteract such complexes. Systems are needed that can hide optical systems from detection, as well as prevent them from being destroyed by blinding complexes.The purpose of the work is to develop a system to counteract the laser complexes of location and damage. Its task is to hide the optical device from laser scanning systems and prevent the damage of the optical device or the human eye by blinding laser radiation.The relevance of this article is due to the need to create new and improve existing electronic systems to counteract the laser means of location and destruction. Despite the fact that studies in this area are conducted for more than one year, the choice of such systems is very small.To minimize the probability of detecting an optical device, mechanical means of narrowing the beam glare angle are commonly used. One example is cellular blinds. The length of one cell must be much higher than its diameter. The surface of the cell tubes should be blackened to reduce the reflection of light rays. For more accurate narrowing of the flare angle, it possible to set several cellular blends in a row - the number depends on their optical qualities.Optical means include optical filters that absorb, block, or scatter the infrared spectrum, because laser detectors of optical devices are in it. Such a filter should be placed on the optical sight between the lens and the lens hood. After all, it reflects the infrared rays, working as a mirror. Therefore, this angle of reflection should be reduced by all means, in particular tubular blinds, as described above.However, these methods cannot fully protect the operator of the optical observation device from the powerful laser radiation directed to the device. To solve this problem, you can use technology that completely blocks the optical channel when you receive high-power laser radiation on an optical device. The radiation sensors respond to the high-power laser radiation of the destruction and transmit the signal to an electronic circuit, which turn on a liquid crystal filter that covers the optical channel. Under the influence of electric current, liquid crystals become a special structure in such a way that infrared radiation does not pass through the filter. When the radiation is lost, the electronic system returns the liquid crystal filter to a transparent state.The power impulse of laser means of location and destruction can significantly damage a person's vision, and at large lens diameters or at short distances between a these means and an observer, a person may lose it completely. The same applies to light-sensitive arrays of optoelectronic devices. As shown in the calculations, the maximum permissible level of radiation energy density in unprotected optics is much lower than the radiation energy density provided by laser means of location and destruction.The opto-electronic protection system reduces the time of laser radiation to the human eye or the light-sensitive matrix of the optoelectronic device to safe limits. As shown by the calculations, this increased the maximum allowable level of radiation energy density above the level provided by power lasers for their entire range of use and lenses with diameters from 24 mm to 100 mm, which will protect them from the blinding effect of laser means of location and destruction.

Multi-Wavelength Filters of Templated Blue Phase Liquid Crystal

The multi-wavelength filters in the visible light band using the blue phase liquid crystal (BPLC) template was investigated. A multi-layer templated BPLC (T-BPLC) filter without intermediate dielectric layers was fabricated, which may reflect multi-wavelength in one filter. Compared with the cholesteric liquid crystal (CLC) filter, the T-BPLC filter may get a much narrower reflection bandwidth (&lt;15 nm), show better angular stability of incident light, and have a more stable wavelength and bandwidth with a temperature shift. Furthermore, the central wavelength and bandwidth can be easily controlled by the fabrication process and the optimization of the material concentration. When the incident angle varies, the shift of the center wavelength of the T-BPLC filter is much smaller than that of the CLC filter. The multi-wavelength filter shows a potential application in color filters and high-density wavelength division multiplexed networks.

Tunable-liquid-crystal-filter-based low-light-level color night vision system and its image processing method.

We introduce and verify a single-channel time-division filtering low-light-level (LLL) color night vision system (3LCNV). The imaging scheme, comprising a tunable liquid crystal filter, three-generation GaAsP image intensifier, and CMOS camera, achieves LLL color imaging and ensures sensitivity. The image enhancement and color reconstruction algorithm flow suitable for LLL night vision combines overexposure-against white balance, color correction matrix (CCM) color correction, and color image denoising to improve color visibility and reduce color difference and image noise. The proposed night vision system extends the minimum working illuminance to 10-4 lx and achieves natural and clear color LLL imaging, improving night-time observations.

Effect of Sectional Polymerization Process on Tunable Twist Structure Liquid Crystal Filters

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.

Підвищення достовірності даних в системі моніторингу з модифікованою архітектурою

У статті розглядається проблема підвищення адекватності даних дистанційного вимірювання за допомогою систем моніторингу на основі керованих рідкокристалічних фільтрів. Запропонована система моніторингу виконує спільні вимірювання в інфрачервоному та видимому діапазонах спектру, а також панхроматичні вимірювання, реалізує методику корекції їх даних, локальне управління кожним вимірювальним модулем, що підвищує надійність отриманих даних. Модифікована архітектура забезпечує можливість встановлення каналів альтернативної вимірювальної системи та підвищення ефективності прийняття рішень на основі результатів моніторингу. Корекція похибок каналів та даних вимірювань, локальний контроль кожного каналу вимірювальних модулів з регулюванням напівширини, передача рідкокристалічних фільтрів залежно від значень додаткових параметрів та гнучкої вимірювальної архітектури забезпечують корекцію внутрішніх та зовнішніх факторів системи. Запропонована багатофункціональна система з модифікованою архітектурою дозволяє отримувати достовірну інформацію про координати та ділянки нафтових плям на поверхні моря. За допомогою обмеженого обсягу даних, отриманих з трьох діапазонів за допомогою різних вимірювальних каналів, можна надійно оцінити стан досліджуваного об'єкта. Багаторівневі вимірювання для перевірки даних з урахуванням атмосферних впливів та використання WEB / GIS-комунікацій дозволяють здійснити облік та оцінку зовнішніх факторів для виправлення даних вимірювання системи.

Liquid crystal-based tunable photodetector operating in the telecom C-band

Liquid crystal (LC) microcells monolithically integrated on the surface of InGaAs based photodiodes (PDs) are demonstrated. These LC microcells acting as tunable Fabry-Perot filters exhibit a wavelength tunability of more than 100 nm around 1550 nm with less than 10V applied voltage. Using a tunable laser operating in the S and C bands, photocurrent measurements are performed. On a 70 nm tuning range covered with a driving voltage lower than 7V, the average sensitivity for the PD is 0.4 A/W and the spectral linewidth of the LC filter remains constant, showing a FWHM of 1.5 nm. Finally, the emission spectrum from an Er-doped fiber is acquired by using this tunable PD as a micro-spectrometer.

Switchable Plasmonic Holograms Utilizing the Electro-Optic Effect of a Liquid-Crystal Circular Polarizer

A concept for switchable holograms with high diffraction efficiency based on geometrical metasurfaces is proposed. The phase hologram studied is composed of plasmonic nanoantennae with varying orientations. Its diffraction pattern is known to depend on the state of polarization of the incident radiation. Maximum brightness of the reproduced holographic images is obtained by circularly polarized radiation, while the position of the respective image depends on the handedness of this circularly polarized radiation. For the purpose of switching, the hologram is illuminated through an electrically addressable liquid-crystal filter, which transforms linear polarization to either right circular or left circular polarization, depending on the applied voltage. First experimental results indicate reasonable switching when a twisted nematic active layer and a uniform nematic passive layer are combined in a compact polarization converter.

Analysing the impact of myopia on the Stiles-Crawford effect of the first kind using a digital micromirror device.

Photoreceptor light acceptance is closely tied to the Stiles-Crawford effect of the first kind (SCE-I). Whether the SCE-I plays a role in myopic development remains unclear although a reduction in directionality has been predicted for high myopia. The purpose of this study is to analyse the relationship between foveal SCE-I directionality, axial eye length, and defocus for emmetropic subjects wearing ophthalmic trial lenses during psychophysical measurements and for myopic subjects with their natural correction. A novel uniaxial flicker system has been implemented making use of a Digital Micromirror Device (DMD) to flicker between a 2.3 visual degrees circular reference and a set of circular test patterns in a monocular Maxwellian view at 0.5 Hz. The brightness of the test is adjusted by the duty cycle of the projected light to an upper limit of 22727Hz. The wavelength and bandwidth are set by a tuneable liquid-crystal filter centred at 550 nm. A total of four measurement series for 11 pupil entrance points have been realized for the right eye of 6 emmetropic and 10 myopic subjects whose pupils were dilated with tropicamide. Five of the emmetropic subjects wore ophthalmic trial lenses in the range of -3 to +9 dioptres to mimic hyperopic to highly myopic vision and resulting visibility plots have been fitted to a Gaussian SCE-I function. In turn, the myopic subjects wore their natural correction during the analysis of the SCE-I. All subjects had their axial eye length determined with an ultrasound device. A SCE-I directionality parameter in the range of 0.03 to 0.06/mm2 was found for the emmetropic subjects with corrected vision in fair agreement to values in the literature. The results also revealed a marked reduction in directionality in the range from 16% to 30% with every 3 dioptre increase of simulated myopia, as well as a 10% increased directionality in simulated hyperopic eyes. For both emmetropic and myopic subjects, a decrease in directionality with increase in axial length was found in agreement with theoretical expectations. The study confirms a clear link between SCE-I directionality, uncorrected defocus, and axial eye length. This may play a role for emmetropization and thus myopic progression as cone photoreceptors capture light from a wider pupil area in elongated eyes due to a geometrical scaling.

The effect of pretilt and twisted angle on twisted nematic liquid crystal filter

The effect of pretilt and twisted angle on twisted nematic liquid crystal filter