Optically switchable twist nematic grating based on a dye-doped liquid crystal film

Huang, San-Yi; Wu, Shu‐Chen; Fuh, Andy Ying–Guey

doi:10.1063/1.2167393

Cited by 43 publications

(36 citation statements)

References 22 publications

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“…The combination of bulk-mediated hybrid photoalignment and homeotropic alignment in a single pixel supports the fabrication of LCDs with a controllable viewing-angle, [52] on which simultaneously displays two images that can be seen from different viewing angles. Other applications in photonic devices, such as optical gratings [53][54][55] and Fresnel lenses have also been investigated [56][57][58][59][60]. Photoalignment is a unique tool for achieving LC alignment in mechanically inaccessible volumes.…”

Section: Bulk-mediated Photo-isomerization and Adsorption Effectsmentioning

confidence: 99%

Photo-Alignment Technology

Lin

2014

Topics in Applied Physics

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LCDs are used in many everyday devices, including mobile phones, notebook computers and wide screen televisions. A typical LCD is composed of two glass substrates between which is a gap that is filled with LC. The arrangement of the LC is controlled by the boundary condition of an alignment film. A long-range orientational interaction causes the preferable alignment of a LC by the surface boundary to extend into the LC bulk. The alignment layer is typically rubbed with a special cloth to induce a unidirectional alignment of the LC. In the first devices based on twisted LCs, these LCs were aligned only by rubbing transparent electrodes. The rubbing technique became much more reliable when the glass substrate was covered with a rubbed polymer layer. The rubbing of polymers is a very simple technique and it is now extensively utilized in both small scientific laboratories and large LCD factories.Despite the extensive use of rubbing in LCD manufacturing, it has some serious shortcomings that arise from the contact involved in rubbing. These critically affect the production of the most recent generation of LCDs and miniature LC photonic devices. First, rotational rubbing for the polymer surface causes the accumulation of static charges and the formation of fine dust particles. The accumulation of static electricity may destroy the transistors or diodes in the LCD. The second shortcoming is the effect of decreasing in manufacturing yield. Rubbing for large and high-resolution active matrix LCDs (AMLCDs) involve additional difficulties that are associated with the precise control of the rubbing characteristics. Other problems are the difficulty of producing local structures with the required LC director alignment in the selected areas of the device. Finally, this method cannot be used to align LCs in closed volumes.For all of the above reasons, new alignment solutions and approaches are sought. There are some alternative methods of rubbing include laser writing, micro-rubbing, ion beam irradiation and photoalignment. Of these methods, the

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Section: Bulk-mediated Photo-isomerization and Adsorption Effectsmentioning

confidence: 99%

Photo-Alignment Technology

Lin

2014

Topics in Applied Physics

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“…Another approach, based on a polydimethylsiloxane periodic microstructure on a glass substrate, separated by a thin LC film, with a DE of 35% and switching time of 145 s at the irradiance of 600 mW∕cm 2 , has been reported [18]. Other than LC, a metamaterial [19] fabricated by encapsulating photochromic solution in nano-holes of polycarbonate has also been proposed for fabricating optically tunable gratings [4]. The interference pattern by the green laser was used to write the grating profile, whereas it can be erases by UV irradiation [20,21].…”

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confidence: 99%

“…A tunable liquid crystal (LC) grating is one of the most important tools for many of the applications that have been well explored recently [1][2][3][4]. The most common approach deals with arrays of parallel electrodes for generating a longitudinal [5,6] or lateral [7,8] periodic electrical field distribution and locally controlling the directors of the LCs and thus the diffraction.…”

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confidence: 99%

Optically tunable and rewritable diffraction grating with photoaligned liquid crystals

et al. 2013

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An optically tunable and rewritable liquid crystal (LC) diffraction grating cell has been revealed that consists of an optically active and an optically passive alignment layer. The grating profile is created by confining the LC director distribution in alternate planar and twisted alignment domains by means of photoalignment of the LCs. The proposed grating is optically tunable for diffractive and nondiffractive states with a small response time that depends on the exposure energy and LC parameters. In addition, the grating can be erased and rewritten for different diffracting characteristics. Another approach is to utilize the natural diffracting ability of the chiral LCs [12]. Such gratings are electrically tunable but cannot be tuned optically [12,13]. In recent years some reports dealing with optical tunability of dye-doped organic materials have been written [14]. Confined complex structures such as polymer-LC-polymer-slide (PLCPS) gratings containing azo compounds show optical switching times of 0.5 s at the irradiance of 245 mW∕cm 2 and diffraction efficiencies (DEs) up to 85% [15]. In another report, a 90% DE and switching time of 0.2 s (at the irradiance of 54 mW∕ cm 2 ) were reported for PLCPS with photosensitive LC [16]. Most of these reports include dye-doped LC for a photopolymerizable mixture for recording the grating. However, azo dyes, because of their chemical instability, are not stable in the LC mixture, and therefore the efficiency of these devices is highly limited and they manifest a rather complex fabrication procedure [17]. Another approach, based on a polydimethylsiloxane periodic microstructure on a glass substrate, separated by a thin LC film, with a DE of 35% and switching time of 145 s at the irradiance of 600 mW∕cm 2 , has been reported [18]. Other than LC, a metamaterial [19] fabricated by encapsulating photochromic solution in nano-holes of polycarbonate has also been proposed for fabricating optically tunable gratings [4]. The interference pattern by the green laser was used to write the grating profile, whereas it can be erases by UV irradiation [20,21]. However, the technology is restricted by the large switching time of ∼30 s (at an irradiance of 300 mW∕cm 2 ). Recently, we have disclosed a relatively easier and more reliable method to fabricate electrically tunable gratings, by defining the LC director in alternate alignment domains of alternate planar (PA) and twisted (TN) alignments by means of photoalignment [22]. Moreover, among all of these strategies, patterned photoalignment has been demonstrated to be efficient [11][12][13].In this article, we present an optically tunable LC grating based on PA and TN alignment domains. The blue light (λ 450 nm) can be used to tune the diffractive and nondiffractive states. Such gratings can also be erased and rewritten for different grating vectors. Thus, they could find several applications.The optically tunable and rewritable (OTRW) LC cell consists of two substrates with different aligning materials, one of which is optically pas...

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“…The process is accompanied by liquid crystal (LC) reorientation, and accordingly a polarization hologram is generated. 4 The experimental setup for generating a polarization hologram in dye-doped liquid crystal films is shown in Fig. 1(b).…”

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confidence: 99%

“…Photorefractive crystals 1,2 and azo-dye-doped liquid crystals [3][4][5] are currently attractive rewritable materials for holographic memory. However, the reversibility of these materials also leads to volatile readout, i.e., the recorded hologram would be gradually erased during the readout process.…”

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confidence: 99%