Hybrid organic-inorganic photorefractives

Cook, Gary; Wyres, Christopher A.; Deer, M. J.; Jones, David C.

doi:10.1117/12.507978

Cited by 26 publications

(16 citation statements)

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“…E hν = A 1 (z)e 1 exp (ik 1 r − iω t) + A 2 (z)e 2 exp(ik 2 r − iω t), (14) and satisfies the wave equation…”

Section: Beam Coupling and Gain Coefficientmentioning

confidence: 99%

“…In this case the coupled beams generate multiple order diffracted beams that leads to limited technological applicability of the effect. 13 However, in papers 10,14 it has been shown that inorganic photorefractive crystals can support efficient space-charge field generation in samples with thicknesses greater than the grating thickness. It allowed the Bragg regime to be reached, where only first order diffracted beams are generated.…”

Section: Introductionmentioning

confidence: 99%

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Two beam energy exchange in hybrid liquid crystal cells with photorefractive field controlled boundary conditions

et al. 2016

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We develop a theory describing energy gain when two light beams intersect in a hybrid nematic liquid crystal (LC) cell with photorefractive crystalline substrates. A periodic space-charge field induced by interfering light beams in the photorefractive substrates penetrates into the LC layer and reorients the director. We account for two main mechanisms of the LC director reorientation: the interaction of the photorefractive field with the LC flexopolarization and the director easy axis at the cell boundaries. It is shown that the resulting director grating is a sum of two in-phase gratings: the flexoelectric effect driven grating and the boundary-driven grating. Each light beam diffracts from the induced gratings leading to an energy exchange between beams. We evaluate the signal beam gain coefficient and analyze its dependence on the director anchoring energy and the magnitude of the director easy axis modulation.

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“…E hν = A 1 (z)e 1 exp (ik 1 r − iω t) + A 2 (z)e 2 exp(ik 2 r − iω t), (14) and satisfies the wave equation…”

Section: Beam Coupling and Gain Coefficientmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Two beam energy exchange in hybrid liquid crystal cells with photorefractive field controlled boundary conditions

et al. 2016

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“…Much work has been done to obtain comprehensive expressions for the thermotropic and elastic free energies. Details, including a full derivation of all possible SO(3) invariants up to powers ofQ 4 , can be found in [13,15,16].…”

Section: Free Energymentioning

confidence: 99%

“…A spatially periodic voltage is applied to one boundary, while the other is set to a uniform zero volts. This is a realistic model for a photorefractive liquid crystal cell [6,4], a device used for optical coupling and as an optically addressable spatial light modulator. This is an interesting device for testing this algorithm as it allows for three-dimensional orientation of the liquid crystal directors and has a simple geometry.…”

Section: Examplesmentioning

confidence: 99%

An Efficient $\mathcal{Q}$-Tensor-Based Algorithm for Liquid Crystal Alignment away from Defects

Daly¹,

D’Alessandro²,

Kaczmarek³

2010

SIAM J. Appl. Math.

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Abstract. We develop a fast and accurate approximation of the normally stiff equations which minimize the Landau-de Gennes free energy of a nematic liquid crystal. The resulting equations are suitable for all configurations in which defects are not present, making them ideal for device simulation. Specifically they offer an increase in computational efficiency by a factor of 100 while maintaining an error of order (10 −4 ) when compared to the full stiff equations. As this approximation is based on a Q-tensor formalism, the sign reversal symmetry of the liquid crystal is respected. In this paper we derive these equations for a simple two-dimensional case, where the director is restricted to a plane, and also for the full three-dimensional case. An approximation of the error in the perturbation scheme is derived in terms of the first order correction, and a comparison to the full stiff equations is given.

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“…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.…”

mentioning

confidence: 99%

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

Moszczyński

Walczak

2015

Photon. Lett. Poland

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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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Hybrid organic-inorganic photorefractives

Cited by 26 publications

References 0 publications

Two beam energy exchange in hybrid liquid crystal cells with photorefractive field controlled boundary conditions

Two beam energy exchange in hybrid liquid crystal cells with photorefractive field controlled boundary conditions

An Efficient $\mathcal{Q}$-Tensor-Based Algorithm for Liquid Crystal Alignment away from Defects

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

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