Polarisation sensitive liquid crystal filter for polarization difference imaging

2010

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mentioning

confidence: 96%

Electromagnetic wave beam self - guidance in liquid crystal - semiconductor cell

2010

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“…(16). The resulting director field distribution allows for refraction index determination [15]. (16 Figure 2 illustrates the results obtained with the method described in the article.…”

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confidence: 99%

Analysis and model of the photorefractive-like effect in non-conductive asymmetric liquid crystal hybrid cell

Moszczyński

2015

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Abstract-In this paper we describe a non-conductive liquid crystal hybrid cell with the photoconductive polymer (PP) layer. The orientation of the liquid crystal (LC) molecules in the described optical device is controlled by an external electric field and proper illumination. A method to calculate photoinduced refractive index distribution in the liquid crystal layer has been presented. We propose the model of a space charge formation in the photoconductive polymer layer in the presence of light. We assumed that the carriers generated by the light in the PP diffuse into an unlighted area and drift in an external field and local field of the generated charge. In determining the distribution of the space charge field, we take into account the field-induced charges on the borders of individual layers. After calculation of the final distribution of the space charge and proper field distribution, we determine the director field distribution and refractive index distribution in an LC layer.The liquid crystal cell with a photoconductive polymer layer for controlling the liquid crystal layer is a structure that potentially allows laser beam steering and optical switching. In the cell, the light of small power can locally change the refractive index of the LC layer. This phenomenon is called a photorefractive-like effect and allows the formation of self-organizing LC fiber and its coupling [1,2]. Photoconductive layer presence is crucial for light control. In literature, two influence mechanisms of a photoconductive polymer layer on a liquid crystal layer [3][4][5][6][7] are described. The first effect is the reduction of resistance of a PP layer and increase of the voltage drop across the LC layer. The second effect is the formation of a space charge due to localized illumination, which causes LC molecules movement.In this paper, we present a three-step method to calculate refractive index distribution in a liquid crystal layer. In the first step the LC permittivity and field distribution inside the PP layer are calculated for a hybrid cell, which is only driven by external voltage (absence of a laser beam). In the second step, the space-charge distribution formed in a photoconductive polymer layer is calculated after the appearance of laser beam illumination. In this step, the transport and generation of carriers in the photoconductive polymer are described. In the third step, electric field distribution is determined with all previously determined components, and the refractive index distribution of the liquid crystal layer n eff is * E-mail: pawel.moszczynski@wat.edu.pl calculated as well. This method takes into account the external driving voltage U, laser beam properties, LC and PP properties, and the configuration of a hybrid cell. All enumerated values have their own, particular impact on the final results. Mathematical models and results were obtained for asymmetric hybrid cells in which the laser beam propagates along the liquid crystal layer. The analyzed cell is composed as in Fig. 1 and we assumed that the ...

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“…Such a change of the LC layer orientation can create an optical waveguide along the way of an external beam propagated along the layer [1,2]. In this letter we present how to calculate an additional control field that is derived from a photoinduced space-charge inside the photoconductive command surfaces.…”

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confidence: 99%

Model for simulation of photo-induced charges inside the hybrid LC cells.

Marciniak

Moszczyński

2013

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