Liquid Crystal Filter Research Articles

FERROELECTRIC LIQUID CRYSTAL GLASSES FOR AMBLYOPIA RESEARCH

ABSTRACT Ferroelectric Liquid Crystal (FLC) filters offer the speed of electronic light shutters and the vibration free operation. These characteristics make them ideal for applications requiring short exposure times and minimal blur, offering switching times of 0.0002 of a second. FLC filters can be used as the optical shutters for machine vision purposes, also in vision research. On the basis of FLC filters we have developed ferroelectric glasses, allowing temporal separation of optical information for both eyes. In the case of amblyopia (“lazy eye”) the only way to oblige the “lazy” eye to work is to close the other better-seeing eye. We advice an appliance for dynamic visual system training to promote the functionality of the worse-seeing eye. For fast switching the filters are powered by a bipolar minus to plus control voltage power supply separate for two left and right channels, with optical isolation for higher safety reasons. The duration of the shutters open-close state are controlled through the PC parallel port. The main application of the system is use for amblyopia research and training.

Verification of switched liquid crystal eye protection filters

Protective eye-wear which utilizes switched liquid crystal can provide protection for operators using intense pulsed light sources (IPLs). Such eye protection devices combine the properties of useful visual transmittance in the nonactivated state and low light transmission in the active blocking state. The performance of a specific LightSpeed device has been determined using a series of bandpass optical filters coupled to photodiode detectors with signals being captured using a USB interface. Such measurements have allowed key switching parameters of these devices to be determined as part of the process of assessing their effectiveness. Measurements of optical density of transmitting state and blocking state were also determined using a double grating spectroradiometer. A simple model of active filter function was developed and applied to specific IPL pulse profiles.

Estimation of the lunar reflectance by ground-based observation using a tunable liquid-crystal filter telescope

Abstract Lunar reflectance data are useful not only for lithological identification of the lunar surface but also for radiometric calibration and determination of exposure time for optical sensors of lunar probes. To gain data on lunar reflectance, we acquired multi-band images (five bands: 650, 750, 900, 950, and 1000 nm) of the lunar surface and those of some standard stars using a liquid-crystal tunable filter (LCTF) telescope located on the peak of Mt. Haleakala (Hawaii, USA). The data obtained indicate that the reflectance data of Clementine UV/VIS is too high and that the correction factor is 0.59±0.06 at 950 nm. Our new reflectance data are available to the public at the web site of one of authors (K.S.). We report here our method of deriving the lunar reflectance images from the ground-based observation with a hyperspectral telescope for the users of our reflectance data. The results suggest that ground-based observation is more suitable for the radiometric calibration of the sensor of a lunar probe than laboratory data.

Intraoperative bile duct visualization using near-infrared hyperspectral video imaging

Background Current methodologies for imaging the biliary system during cholecystectomy are cumbersome and do not eliminate the risk of bile duct injury. We describe an approach to intraoperative biliary imaging that will enable surgeons to see through the hepatoduodenal ligament and visualize the anteriorly placed biliary system. Methods A laparoscopic-capable, near-infrared, hyperspectral imaging system was built. Reflected light passes through a liquid crystal filter that is continuously tunable in the near-infrared spectrum (650–1,100 nm). Spectroscopic image data are collected from laparoscopic surgery images onto array detectors formatted into a 3-dimensional hyperspectral data cube having spatially resolved images in the x-y plane and wavelength data in the z plane. Deconvoluting and color-coding the spatial and spectral information provides an image representative of inherent chemical properties to the imaged tissue. Results Images of porcine biliary structures were obtained. The common duct–reflected spectra displayed a characteristic lipid shoulder at 930 nm and a strong water peak at 970 nm. Venous structures had absorption peaks at 760 nm (deoxyhemoglobin), 800 nm (oxyhemoglobin), and 970 nm (water). Arterial vessels had absorption peaks at 800 nm and 970 nm that would be expected for oxyhemoglobin and water. Conclusions We have designed and constructed a device to significantly enhance intraoperative biliary imaging. This system should enable surgeons to see through the hepatoduodenal ligament and image the anteriorly placed biliary system without the need for dissection of the cystic duct, as is needed with intraoperative cholangiography. Because the biliary system can be seen before any dissection is performed, this dimensional imaging technology has the potential for eradicating bile duct injury.

Extension of distance measurement range in a sinusoidal wavelength-scanning interferometer using a liquid-crystal wavelength filter with double feedback control

The optical path difference (OPD) and amplitude of a sinusoidal wavelength scanning (SWS) are controlled with a double feedback control system in an interferometer, so that a ruler marking every wavelength and a ruler with scales smaller than a wavelength are generated. These two rulers enable us to measure an OPD longer than a wavelength. A liquid-crystal Fabry-Perot interferometer (LC-FPI) is adopted as a wavelength-scanning device, and double sinusoidal phase modulation is incorporated in the SWS interferometer. Because of a high resolution of the LC-FPI, the upper limit of the measurement range can be extended to 280 microm by the use of the phase lock where the amplitude of the SWS is doubled in the feedback control. The ruler marking every wavelength is generated between 80 microm and 280 microm, and distances are measured with a high accuracy of the order of a nanometer in real time.

Automatic correction of the effects of the light source on spherical objects. An application to the analysis of hyperspectral images of citrus fruits

This study proposes a method for correcting the adverse effects produced by the curvature of spherical objects in acquiring images with a computer vision system. Its suitability has been illustrated in a specific case of citrus fruits. The images of this kind of fruit are darker in areas nearer the edge than in the centre, and this makes them more difficult to analyse. This methodology considers the fruit as being a Lambertian ellipsoidal surface and produces a 3D model of the fruit. By doing it becomes possible to calculate the part of the radiation that should really reach the camera and to make the intensity of the radiation uniform over the whole of the fruit surface captured by the camera, no matter what region is being sampled. Some tests have been carried out in order to prove that using the proposed correction methodology the reflectance in all the surface of the fruit is similar, minimising the differences from the central area to the peripheral areas. The methodology presented here has been tested using a hyperspectral computer vision system based on tunable liquid crystal filters and it has proved to be effective for minimising the adverse side effects produced by the curvature of the fruit on the intensity of the radiation captured by the camera. The experiments show that applying our method homogenises the grey level of the pixels belonging to the same class, regardless of the region of the fruit surface they are from; standard deviation is also reduced, which facilitates subsequent classification tasks.

Semiautomated Multiplexed Quantum Dot-Based in Situ Hybridization and Spectral Deconvolution

Gene expression profiling has identified several potentially useful gene signatures for predicting outcome or for selecting targeted therapy. However, these signatures have been developed in fresh or frozen tissue, and there is a need to apply them to routinely processed samples. Here, we demonstrate the feasibility of a potentially high-throughput methodology combining automated in situ hybridization with quantum dot-labeled oligonucleotide probes followed by spectral imaging for the detection and subsequent deconvolution of multiple signals. This method is semiautomated and quantitative and can be applied to formalin-fixed, paraffin-embedded tissues. We have combined dual in situ hybridization with immunohistochemistry, enabling simultaneous measurement of gene expression and cell lineage determination. The technique achieves levels of sensitivity and specificity sufficient for the potential application of known expression signatures to biopsy specimens in a semiquantitative way, and the semiautomated nature of the method enables application to high-throughput studies.

Modifications of protoporphyrin IX fluorescence during ALA-based photodynamic therapy of endometriosis

Modifications of the porphyrin fluorescence during photodynamic treatment of ovarian cells, endometrial adenocarcinoma cells and rat uterus after administration of the porphyrin precursor δ-aminolevulinic acid and exposure with 630 nm laser radiation have been studied. The intracellular and intratissue fluorescence was excited with 407 nm radiation of a krypton ion laser and detected by spectral microscopic imaging using a modified microscope equipped with a slow-scan cooled camera and a liquid crystal filter. In particular, singlet oxygen induced effects due to photobleaching as well as formation of chlorin-type fluorescent photoproducts were detected at around 500, 630 and 670 nm. The photodynamically induced fluorescence modifications were found to vary between cell types. The major fluorescence peak of PP IX was photobleached 63% by a phototoxic fluence of about 20-40 J/cm2 in cells and within rat endometrium. Higher fluences were required to bleach the fluorescence at around 670 nm due to the formation of fluorescent photoproducts. No significant photoinduced modifications of autofluorescence occurred around 500 nm. © 2006 Elsevier GmbH. All rights reserved.

透過型液晶フィルタリング方式によるカメラの広ダイナミックレンジ化

To generate a wide dynamic range image (WDRI), a system which consists of a camera and a liquid crystal filter has been proposed. The system can adaptively control scene radiance using the liquid crystal filter placed in front of the camera. Although the masking effect of the filter blurs, the blurring function was not strictly analyzed. In this paper, the blurring function is estimated using an experimental system. We have confirmed that WDRIs are clearly generated using the blurring function.

Liquid-crystal bandpass filter based on the optical rotatory dispersion effect.

A bandpass spectral filter and the test measurement results are presented and described. The filter is developed and constructed by use of a ferroelectric liquid-crystal polarization rotator in combination with dispersive quartz optical rotators, and its wavelength selection is mechanically tunable and electrically switchable.

Low-Voltage Continuous Tunable Hybrid Filter for Tailored Optical-Bandwidth Operation

We describe the performance characteristics of a continuously tunable hybrid liquid-crystal filter over extended spectral ranges for implementation of multiwavelengths systems. This device is based on the linear electrooptic (Pockels) effect where tuning is achieved via externally applied voltage. A folded ten-stage S/spl caron/olc configuration is adopted which demonstrates a tuning range of 34 nm around 1550 nm. This opens the way to the achievement of various wavelength-division-multiplexing functions based on filtering [(de)multiplexers, add and drop devices, tunable emitters, etc.].

Novel transmissive color filter using cholesteric liquid crystal with wide viewing angle

Abstract— A new design for a cholesteric liquid‐crystal (CLC) color filter has been devised. Since this system absorbs no light, it uses backlight energy very efficiently. When CLCs of this type with an expanded selective reflection band are combined with light sources with sharp RGB emission peaks, such as LEDs, it is possible to reduce the dependence of color shift on viewing angle and make more efficient use of light.

An electrically addressed liquid crystal filter for tunable lasers

A ferroelectric liquid crystal device has been used as an electrically addressable birefringent tuning element in a linear dye laser. The device operates within the laser cavity and replaces the manually adjusted birefringent filter that previously provided the wavelength selection mechanism. The device demonstrates switching between two selected wavelengths at rates of 10 kHz with potential to increase this to around 1 MHz. The lasing wavelengths allowed by the device are determined by the retardance, the ferroelectric tilt angle and the relative orientation of the device symmetry axis and the laser polarisation axis. Lasing was demonstrated for two device orientations, switching between wavelengths of 583.2 and 587.5 nm and from 569 to 591 nm.

Calibration and exploitation of a narrow-band imaging polarimeter

The integration and calibration of a narrow-band imaging po- larimeter is described. The system is designed to exploit subtle spectral details in visible and near-IR polarimetric images. All of the system components were commercial off the shelf. This device uses a tunable liquid crystal filter and a 16-bit cooled CCD camera. The challenges of calibrating a narrow-band imaging polarimeter are discussed. We describe examples of image data collected in the laboratory, which show that spectral polarimetric data is superior to unpolarized intensity data in facilitating the extraction of detail in shadowed regions below a vegetative canopy. In particular, we introduce a polarization-based normalized difference vegetation index (NDVI) algorithm that demonstrates significant contrast enhancement between a man-made object and a foilage background.

Liquid-crystal micropolarizer array for polarization-difference imaging.

Fabrication and applications are discussed for a visible-wavelength micropolarizer array consisting of a linear polarizer and a micropatterned liquid-crystal (LC) cell. LC alignment direction is controlled by means of depositing an optically transparent gold film at an oblique angle and coating the surface with an alkanethiol self-assembled monolayer. Microdomains of two perpendicular LC alignment directions are created by photolithography and etching of the gold layer, rotating the substrate 90 deg, and depositing a second oblique gold layer in the etched areas. The resulting array is used for polarization-difference imaging (PDI), a technique that enhances image contrast in the presence of scattering. Images obtained with the array require more processing than do conventional PDI images, but this method eliminates the need for an electronically activated LC filter and is especially suited to systems whose filters are closely integrated with optical sensor arrays.

撮像用液晶フィルタのフレア抑制

We studied the flare appearing in video images when a liquid crystal filter is used in front of a video camera. To clarify the generating mechanism of the flare, the relationship between the concentration of spacer particles dispersed in the liquid crystal and the intensity of light scattered by the filer was examined in detail by using a schlieren optical system with a laser light beam. We found that the light scattering is mainly caused by the spacers and glass substrates, so we evaluated their contribution ratio. From microscopic observation, we determined that the light scattering originated by the spacers includes light scattered by the spacer particles and that resulting from by liquid crystal alignment deformation caused by the spacer surfaces. As the light scattering of the spacers was in proportion to the spacer concentration, it could be considerably reduced by decreasing the spacer density. The flare in video images was reduced by decreasing the light scattering. The liquid crystal filter fabricated by using the flare-reduction method described above was utilized in actual television program.

色温度を上げる液晶フィルタの設計と試作

色温度を上げる液晶フィルタの設計と試作

Color balancing filters using liquid crystal for image pickup

AbstractIn order to correct the color deviation due to variation of illumination in film shooting, a liquid‐crystal filter with dichroic dyes that can control the color temperature of the transmitted light in real time has been developed. By using Planck's radiation rule and the Lambert–Beer law, the absorption spectra of the dyes are designed. It is found that the color balance can be adjusted continuously between 4450 and 2530 K. The time needed for control is about 80 ms. When a liquid‐crystal filter is used for actual television film shooting, it is confirmed that the color balance of the image can be corrected naturally. The present device is useful in location film shooting for television when the color temperature of the image changes drastically under such conditions as the lighting changing from indoor light to solar light. © 2001 Scripta Technica, Electron Comm Jpn Pt 2, 84(10): 40–48, 2001

Automatic color-temperature compensator with guest–host liquid-crystal filter for video image sensing

A color-temperature compensating system with an electrically controllable liquid-crystal filter and a color sensor mounted on a video camera has been developed for color image sensing. The filter contains two guest-host liquid-crystal devices with dichroic dyes that have strong light absorption for shorter-wavelength light; two devices are necessary because of the spectral difference between the sun and an incandescent lamp as light sources. The filter's absorption is continuously controlled by the voltage applied to the filter. Because the filter is driven according to spectral information about the illumination detected by the color sensor, the color balance of the video image to be sensed can be compensated automatically and rapidly. This is especially useful for video image shooting in which a video camera experiences changes in illumination color temperatures.

Development of a multideveloping photoresist and its application to make liquid crystal display color filter

AbstractThis paper reports the fabrication of a single expose multideveloping positive Diazonaphthoquinone (DNQ) /Novolak photoresist capable of simplifying the fabrication process of color filter plates composed of red, green, blue pixels and black matrix. Film thickness retention was measured on multideveloping photoresist(MDPR) containing novolak resins made from various phenolic compounds including cresols, xylenols, trimethylphenol, resorcinol and their copolymers. It was found that there were suitable combinations of phenolic compounds to exhibit appropriate thermal stability, wide process window as well as compatibility to electrodeposition of color films.