Large Kerr effects in transparent encapsulated liquid crystals

The ability to realise frequency agile filters has always been a major goal of materials and device scientists. Polymer dispersed liquid crystal materials (PDLCs), in which the droplets are deliberately produced with dimensions smaller than the Rayleigh limit for optical scatter, provide a means of realising this goal. At visible wavelengths the material has the appearance of a phase-homogeneous medium both with and without applied electric field. Refractive indices are an average of those of the liquid crystal and those of its host and can be described on the basis of effective medium approximations using orientationally averaged values for the randomly aligned LC material for the ambient state. On application of electric field, the individual liquid crystal molecules align with a resulting reduction in the effective index of the medium. Extensive studies of the variation of process parameters and their effect on the morphology of the composite have enabled field induced changes in refractive index in excess of 0.05 to be achieved without recourse to the use of polarisers and with little or no hysteresis effects. At wavelengths associated with WDM devices for telecommunication applications, the degree of scatter loss is negligible. Design trade-offs have been assessed for candidate tunable WDM filters based on resonant cavity devices.

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“…This is quite different to the behaviour highlighted by Sansome et al [10] in a study of Kerr constants in similar systems.…”

Section: Resultscontrasting

confidence: 68%

Frequency Agile Optical Filters using Nanoscopic Polymer Dispersed Liquid Crystals

et al. 2001

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“…Of course the polymer is necessary for obtaining such a state, because the LC-B without polymer shows strong light scattering and large birefringence in a liquid crystal phase. So far a similar state, that is, an apparent isotropic state of liquid crystals has been found for PDLCs including high fraction of polymer, more than 65 wt% [8]. When the size of nematic droplets dispersed by the polymer matrix is much smaller than the wavelength of visible light, the PDLC is optically transparent and isotropic even the liquid crystals in the droplets are in a nematic state.…”

Section: Resultsmentioning

confidence: 94%

39.1: Invited Paper: Optically Isotropic Nano‐Structured Liquid Crystal Composites for Display Applications

Kikuchi

Haseba

Yamamoto

et al. 2009

Symp Digest of Tech Papers

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In this paper, we present the phase behavior and electro-optical Kerr effect of the optically isotropic liquid crystal composites, which require no surface treatment for device fabrication. Anomalously large Kerr constant, more than 10 -8 mV -2 and fast response, less than sub-milli-second were observed at a room temperature. IntroductionThe Kerr effect is a kind of quadratic electro-optic effect which is caused by an electric field induced-ordering of polar molecules and/or the second dipole hyperpolarizability of molecules in optically transparent and isotropic materials. It is well known that nematic liquid crystals exhibit an anomalously large electro-optic Kerr effect in an isotoropic phase just above the nematic-isotropic phase transition temperature, T NI . This is due to that the isotropic phase has the nematic-like short range ordering on a distance scale defined by a coherence length, ξ in that temperature region.Since such an anomalously large Kerr effect is associated with pretransitional fluctuation of the isotropic phase, the phenomenon inevitably disappears in a temperature range below T NI . The response time of the Kerr effect for nematic liquid crystals in an isotropic phase is much shorter (~1 μs) than that of realignment of directors in a nematic phase (10~100 ms). Considering practical applications in electro-optics, the Kerr effect in an isotropic phase of a nematic liquid crystal is attractive because of the short response time, but the problem of the steep temperature dependence of the Kerr constant should be overcome.It is an important challenge in electro-optic applications to develop a material which shows the anomalously large Kerr effect over a broad temperature range. In the case of usual nematics, ξ increases rapidly with decreasing temperature in the isotropic phase near T NI and diverges infinitely at T * as shown in Figure 1(a). If the rapid increase of ξ is suppressed within a finite size less than optical wavelength but larger than molecular dimension below T NI , an optically-isotropic state showing an anomalously large Kerr effect is expected to appear over a broad temperature range below T NI with low temperature dependence as shown in Figure 1(b).As the matter of course, the thermodynamic behavior of the optically-isotropic state in the nematic phase is intrinsically different from that of a genuine isotropic phase in the vicinity of T NI . One could draw, however, a phenomenological analogy between them if one focuses on only the orientational behavior of the local directors upon an application of an electric field. We have investigated the phase behavior and electro-optical properties of nano-structured liquid crystal composites including the polymer-stabilized blue phases [1][2][3][4][5][6][7]. This paper presents an anomalously large Kerr effect over a broad temperature range below T * with low temperature dependence for the polymer-network / chiral liquid crystals composites due to suppressing ξ below T* and their electrooptical properties.

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“…Reduction of the size of the LC droplet relative to the wavelength of visible light. Use of polymer-dispersed (PD)-LCDs, [224][225][226][227][228][229] fine particle dispersion, and micro-emulsion. 230 In the case of PD-LCDs, a twostep response has been observed.…”

Section: Fast Response By Alignment Controlmentioning

confidence: 99%

Alignment control technology of liquid crystal molecules

Ishihara

Mizusaki

2019

J Soc Info Display

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Liquid crystal displays are now indispensable in everyday life. The display characteristics considerably depend on the configuration of liquid crystal (LC) molecules and interactions between the LC molecules and an alignment film surface. In this paper, we introduce various methods to control parameters that dominate the LC alignment. These parameters include order parameters, the pretilt angle, the director direction, and surface anchoring strength. We also introduce their evaluation methods. In particular, recent alignment film‐free technology is explained in detail. In addition, details of how these parameters are related to the display characteristics, particularly wide viewing angles and fast response characteristics, are described primarily with reference to recent technologies.

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Large Kerr effects in transparent encapsulated liquid crystals

Cited by 51 publications

References 9 publications

Frequency Agile Optical Filters using Nanoscopic Polymer Dispersed Liquid Crystals

Frequency Agile Optical Filters using Nanoscopic Polymer Dispersed Liquid Crystals

39.1: Invited Paper: Optically Isotropic Nano‐Structured Liquid Crystal Composites for Display Applications

Alignment control technology of liquid crystal molecules

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