Effects of polymer concentration and localization on the electro-optical performance of cholesteric flexoelectro-optical devices
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We discussed the effect of polymer concentration and localization on flexoelectro-optical device using short pitch cholesterics oriented in uniform lying helix texture. By using a small concentration of photoreactive liquid crystal monomer with various concentrations and selecting the illumination conditions, we have been able to create a localized polymeric network at both substrate surfaces. We can stabilized the two switching modes and eliminating at the same time the effect of the residual birefringence of the polymeric network in the field-unwound state of the sample. The device has two operating modes: amplitude and phase modulation mode, respectively. The amplitude modulation mode is a fast in-plane switching of the device optic axis that enables to achieve a 100 % modulation of the transmitted light intensity whereas the phase mode gives a continuous change of the refractive index and thus of the phase shift of the transmitted light.Keywords:
Modulation (music)
Contrast ratio
A twisted nematic liquid crystal is shown by theory and experiment to rotate incident plane-polarised light by π/2 only at specified wavelengths. At other wavelengths, elliptically polarised light is produced. This action determines the contrast ratio of some twisted nematic devices.
Contrast ratio
Biaxial nematic
Ray
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Abstract Nematic liquid crystal modulators with fast response time, high contrast ratio and low operation voltage are demonstrated. The transient nematic effect, together with reflective mode operation, is responsible for the observed fast response times. The use of a tunable liquid crystal phase compensator results in excellent contrast at a reasonably low operation voltage.
Contrast ratio
Biaxial nematic
Transient (computer programming)
Response time
High contrast
Fast switching
Switching time
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Optical switches using two electro-optical effects in liquid crystals are proposed and investigated for incorporation in a switch matrix for optical networks. These two devices employ selective reflection in cholesteric layers and total reflection at the border between glass and nematic liquid crystal. Prototypes of these switches have been designed and their parameters have been investigated. Initial results show the switching contrast ratio of 38,5 and 42 dB, respectively, with insertion loss about 2.3.2.9 dB for polarized light.
Contrast ratio
Reflection
Switching time
Optical cross-connect
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Birefringence patterns of nematic liquid crystalline droplets are investigated both theoretically and experimentally. Gridding method is developed to calculate optical birefringence patterns of nematic droplets with different director configurations. Series of birefringence patterns of the four typical nematic droplets (radial, bipolar, axial and equatorial) with different orientations of droplets' axes are obtained. By comparing experimental polarizing photographs with theoretical birefringence patterns, the authors find out that only bipolar configuration represents the self-organized structure of nematic droplets in our epoxy-based polymer dispersed liquid crystal (PDLC). It is also pointed out that the very gridding method can be easily extended to deal with other complicated anisotropic entities.
Biaxial nematic
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A 2×2 high contrast ratio optical switch composed of holographic optical switching elements is presented. This switch consists of two electro-optic halfwave plates, four layers of holographic gratings, two dielectric substrates, and one spacer. The contrast ratio can be higher than 54 dB. The contrast ratio improvement of this device is the same as a dilated optical switch.
Contrast ratio
High contrast
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Principles for selecting or synthesizing liquid crystal mixtures with desired birefringence are analyzed. Based on these principles a liquid crystal mixture exhibiting large birefringence and low visco-elastic coefficient at room temperature was formulated. Optical and electro-optic properties of this liquid crystal were characterized at elevated temperature. Results are compared with those of some commercially available liquid crystals.
Crystal (programming language)
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Optical switches using two electro-optical effects in liquid crystals are proposed and investigated for incorporation in a switch matrix for optical networks. These two devices employ selective reflection in cholesteric layers and total reflection at the border between glass and nematic liquid crystal. Prototypes of these switches have been designed and their parameters have been investigated. Initial results suggest the switching contrast ratio of 38.5 and 42 dB, respectively, with insertion loss about 2.3…2.9 dB for polarized light.
Contrast ratio
Reflection
Cholesteric liquid crystal
Switching time
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Abstract Optical switches using two electro-optical effects in liquid crystals are proposed and investigated for incorporation in a switch matrix for optical networks. These two devices employ selective reflection in cholesteric layers and total reflection at the border between glass and nematic liquid crystal. Prototypes of these switches have been designed and their parameters have been investigated. Initial results suggest the switching contrast ratio of 38.5 and 42 dB, respectively, with insertion loss about 2.3…2.9 dB for polarized light. Keywords: all-optical switchcholesteric mirrorliquid crystaltotal reflection
Reflection
Contrast ratio
Cholesteric liquid crystal
Light reflection
Switching time
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In this study, we have chemically modified multi-walled carbon nanotubes (MWNTs) with different side chains for better dispersion in liquid crystal solutions, and fabricated twisted nematic liquid crystal cells doped with such MWNT derivatives. The introduction of MWNT derivatives affects the alignment of LC molecules with or without external electric fields. Electro-optical property tests showed that the contrast ratio changed slightly with the sharp decrease in drive voltage, improving the drive ability of the twisted nematic liquid crystal display (TN-LCD) mode.
Contrast ratio
Biaxial nematic
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Switchable nematic emulsions are micron‐sized droplets of nematic liquid crystal, floating in isotropic fluid matrices. Such droplets can be switched from an opaque (off) to a transparent (on) state by application of very low electric fields. It is known that the electro‐optical properties of liquid crystal dispersions are affected by several parameters, including the liquid crystal loading. The electro‐optical response of nematic emulsions has been investigated as a function of liquid crystal weight percentage. Almost transparent films with a reduced contrast ratio are obtained with lower liquid crystal contents. A macroscopic phase separation is observed when liquid crystal content exceeds 45 wt %. On the contrary, large contrast ratios and very low switching fields can be obtained if liquid crystal ranges from 25 to 35 wt %. Consequently, nematic emulsions prepared in this liquid crystal range can be used as promising systems for electro‐optical applications. In addition to technological developments, these results can help computational and basic studies of phase separation in novel multiphase liquid crystalline materials.
Contrast ratio
Opacity
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