scholarly journals Photochemical On–Off Switching of One-Dimensional Photonic Crystals Consisting of Azo-Functionalized Liquid Crystal Polymer and Polyvinyl Alcohol

Crystals ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 610 ◽  
Author(s):  
Sunnam Kim ◽  
Seiji Kurihara
Keyword(s):  
Phase Transition ◽  
Refractive Index ◽  
Liquid Crystal ◽  
Photonic Crystals ◽  
Polyvinyl Alcohol ◽  
Refractive Index Change ◽  
Liquid Crystal Polymer ◽  
Index Change ◽  
One Dimensional ◽  
Crystal Polymer

One-dimensional (1D) photonic crystals (PCs) are prepared from multi-bilayered films stacked with alternating azo-functionalized liquid crystal polymer (PAz) films and polyvinyl alcohol (PVA) films. Reflection with a wavelength that depends on the thickness of the films is observed, and the reflection can be turned on and off by switching between the two states, based on whether there is a difference in the refractive index between the two films. The refractive index change of PAz can be photochemically caused by a phase transition, based on the alignment states of the liquid crystal (LC). In this review, we focused on an effective photo-induced on–off switching approach in 1D PCs using LC properties and described the basic optical and chemical principles, the experimental results, and further optimizations.

Polarization Measurements of Molded Liquid Crystal Polymer/Titania Composites

2010 ◽  
Author(s):  
B. R. Dantal ◽  
A. Saigal ◽  
M. A. Zimmerman
Keyword(s):  
Refractive Index ◽  
Liquid Crystal ◽  
Dielectric Properties ◽  
Millimeter Wave ◽  
Hybrid Materials ◽  
Broad Band ◽  
High Refractive Index ◽  
Liquid Crystal Polymer ◽  
Frequency Range ◽  
Crystal Polymer

During the past decade, the preparation of inorganic/organic hybrid materials with high refractive index has attracted considerable attention. In particular, TiO2 (Titanium dioxide or Titania), as inorganic domains, have been incorporated into a polymer matrix to produce high refractive index hybrid materials [1–3]. Polarization of injection molded liquid crystal polymer/Titania composite parts have been investigated in the broad band millimeter wave frequency range. The measurements have been performed by using two different spectroscopy techniques. First, free space quasi optical millimeter wave spectrometer, equipped with a high power source coherent radiation tunable in the 40–90 GHz frequency range is used. Second, low power dispersive Fourier transform spectrometer has been used for higher frequencies in the range of 100–600 GHz. Dielectric properties of liquid crystal polymer/Titania composites have been determined in the broad band millimeter wave frequency range. A correlation between dielectric properties and dispersed Titania weight percent has been observed using the two spectroscopy techniques. It is found that the absorption coefficient and loss tangent is a strong function of the output power of the sources of the incident radiation. On the other hand, refractive index and real permittivity values measured from both spectroscopy techniques are similar. In addition, it has been found that transmittance level and absorption losses depend on the orientation of the samples with respect to the orientation of electric and magnetic fields in the incident electro-magnetic wave. Finally, the polarization of the parts varies with the direction of flow of the molten plastic into the cavity.

scholarly journals Gradient polymer network liquid crystal with a large refractive index change

2012 ◽  
Vol 20 (24) ◽  
pp. 26464 ◽  
Author(s):  
Hongwen Ren ◽  
Su Xu ◽  
Shin-Tson Wu
Keyword(s):  
Refractive Index ◽  
Liquid Crystal ◽  
Polymer Network ◽  
Refractive Index Change ◽  
Index Change

DETAILED CHARACTERISTICS OF PHOTOTHERMAL INDEX CHANGE IN GUEST-HOST LIQUID CRYSTALS

2002 ◽  
Vol 11 (03) ◽  
pp. 219-237 ◽  
Author(s):  
HIROSHI ONO
Keyword(s):  
Refractive Index ◽  
Liquid Crystal ◽  
Liquid Crystals ◽  
Phase Modulation ◽  
Refractive Index Change ◽  
Index Change ◽  
Self Phase Modulation ◽  
Cell Parameters ◽  
Analytical Technique ◽  
Crystal Cells

Detailed characteristics have been performed for optical nonlinearity originating in photothermal effects in guest-host liquid crystals. The effects of liquid crystal cell parameters and irradiation conditions on photothermal self-phase modulation and the resulting self-diffracted beam characteristics were quantitatively investigated by heat-conduction analysis and Kirchhoff's diffraction theory. We successfully explained all optical phenomena and our experimental and theoretical technique described here was useful for characterizing the photothermal self-phase modulation. This means that the photothermal mechanism was dominant in the laser-induced refractive index change in our guest-host liquid crystal cells and it is expected that our analytical technique described here will be useful for characterizing the extent to which the photothermal refractive-index change affects the laser-induced refractive index change in other kinds of guest-host liquid crystal cells in the future.

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