Alignment Technology and Applications of Liquid Crystal Devices

Takatoh, Kohki; Sakamoto, Masanori; Hasegawa, Ray; Koden, Mitsushiro; Itoh, Nobuyuki

doi:10.1201/9781420023015

Cited by 176 publications

(43 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The LC is aligned to produce a bend structure in the middle of this typical cell. 58 Compared with traditional LC devices, the pi-cell has the same direction of alignment on the two substrates rather than having opposite directions as in the traditional ECB cells. In OCB, the pre-tilt angle must be larger (.8 6 ), and it only operates between the bend deformation and homeotropic state.…”

Section: Ocbmentioning

confidence: 99%

Fundamentals of phase-only liquid crystal on silicon (LCOS) devices

2014

View full text Add to dashboard Cite

This paper describes the fundamentals of phase-only liquid crystal on silicon (LCOS) technology, which have not been previously discussed in detail. This technology is widely utilized in high efficiency applications for real-time holography and diffractive optics. The paper begins with a brief introduction on the developmental trajectory of phase-only LCOS technology, followed by the correct selection of liquid crystal (LC) materials and corresponding electro-optic effects in such devices. Attention is focused on the essential requirements of the physical aspects of the LC layer as well as the indispensable parameters for the response time of the device. Furthermore, the basic functionalities embedded in the complementary metal oxide semiconductor (CMOS) silicon backplane for phase-only LCOS devices are illustrated, including two typical addressing schemes. Finally, the application of phase-only LCOS devices in real-time holography will be introduced in association with the use of cutting-edge computer-generated holograms. The architecture of LCOS devices is similar to conventional LC devices except that a silicon backplane constitutes one of the substrates (Figure 1). The silicon CMOS backplane consists of the electronic circuitry that is buried underneath pixel arrays to provide a high 'fill factor'. The pixels are aluminum mirrors deposited on the surface of the silicon backplane. The incident light is transmitted through the LC layer with almost zero absorption. The integration of high-performance driving circuitry allows the applied voltage to be changed on each pixel, thereby controlling the phase retardation of the incident wavefront across the device. Currently, there are two types of light modulation using LCOS devices, amplitude modulation and phase modulation. In the former case, the amplitude of the light signal is modulated 6,7 by varying the linear polarzation direction of the incident light passing through a linear polarizer, the same principle used in a standard LC television. In the latter case, the phase delay is accomplished by electrically adjusting the optical refractive index along the light path, which is possible because of the non-zero birefringence of the LC materials in use but should be carefully characterized. [8][9][10][11][12][13] In a phase-only LCOS SLM modulator, no light absorption by polarizers or other light-absorbing components will occur, such that the maximum light efficiency can be expected.Currently, most of the conventional LC devices are not able to efficiently modulate the phase of an incident wavefront. For instance, the LC device structure using thin film transistors is not suitable for phase modulation because an appropriate electro-optic effect has not been used (see the section on 'Twisted nematic (TN) configuration' and the section on 'VAN configuration' for details). Moreover, the pixels of this type of device are too large to provide acceptably large diffraction angles. In addition, the pixel circuitry and connection tracks are in the light path such that the ...

show abstract

Section: Ocbmentioning

confidence: 99%

Fundamentals of phase-only liquid crystal on silicon (LCOS) devices

2014

View full text Add to dashboard Cite

show abstract

“…This is a consequence of the fact that the resolution, aspect ratio and damage of ITO layers are directly related to the respective optical properties of the devices, uniformity of LC alignment and electrical conductivities. 14,15 Uniform alignment of LCs by the ITO pattern Nematic LC, 5CB, was introduced into cells having a 2-mm gap in the isotropic phase. The cells were inspected by using a POM (LV-100POL, Nikon Korea, Seoul, Korea) equipped with a rotational stage in the plane perpendicular to the direction of light propagation.…”

Section: Conductive Alignment Layermentioning

confidence: 99%

Bifunctional ITO layer with a high resolution, surface nano-pattern for alignment and switching of LCs in device applications

et al. 2012

View full text Add to dashboard Cite

We describe a novel method for liquid crystal (LC) alignment using nano-patterns of electrically conductive indium-tin oxide (ITO) layers with high resolution (cao 20 nm) and high aspect ratio (ca 10), fabricated based on the secondary sputtering phenomenon. The ITO pattern developed in this manner not only provides high anchoring energy comparable to that of rubbed polyimides, but also maintains its low resistivity as an electrode. As a result, the patterned ITO can function as an electrode and alignment layer at the same time, which facilitates successful fabrication of bifunctional conductive alignment layer for LC devices. The LC cells fabricated using patterned ITO substrates show highly stable alignment of LCs over large area and good electro-optical responses. Moreover, systematic approach made by the precise control of pattern dimensions allows us to estimate a critical anchoring energy required for an effective LC alignment based on Berreman's theory.

show abstract

“…The continuous evolution of LCDs lies in the development of both current technologies and available materials. Literature surveys [5][6][7][8] on this subject show that many efforts have been made to control and/or improve the viewing angle, the contrast, the response time and the transparency of the alignment layer in the visible domain. The surface morphology of the rubbed alignment layer, the pretilt angle and surface energy of the alignment film are influenced by the conformation of the polymer molecular backbone [9].…”

Section: Introductionmentioning

confidence: 99%

The influence of polysilane chemical structure on optical properties, rubbed film morphology and LC alignment

Soroceanu¹,

Barzic²,

Stoica³

et al. 2015

Express Polym. Lett.

View full text Add to dashboard Cite

Abstract. Polysilane films were prepared by the drop casting method and their optical and morphological properties have been analyzed in order to investigate their suitability as alignment layers for nematic molecules. The samples do not absorb the radiations in the visible domain, particularly those containing methylhydrosilyl units, and present a transmittance of about 90% starting from 390 to 1100 nm. The optical band-gap is higher than 3.26 eV for all polysilanes indicating a low probability of optical absorption processes in the visible range. The morphology of the pristine samples shows isotropically distributed granular formations. The polymer surface was oriented by rubbing with two types of velvet: one with short fibers and the other with long fibers. The latter generates higher surface anisotropy, as shown by the reduction of the surface texture direction index values. The presence of methylhydrosilyl units allows a denser packing of the polymer structure and thus finer surface periodicities, leading to better orientation of the nematic molecules on the polysilane surface.Keywords : material testing, polysilane, rubbing, morphology, LC alignment eXPRESS Polymer Letters Vol.9, No.5 (2015) 456-468 Available online at www.expresspolymlett.com DOI: 10.3144/expresspolymlett.2015.43 * Corresponding author, e-mail: irina_cosutchi@yahoo.com © BME-PT layer in the visible domain. The surface morphology of the rubbed alignment layer, the pretilt angle and surface energy of the alignment film are influenced by the conformation of the polymer molecular backbone [9]. Many studies are focused on preparing alignment layers by rubbing polyimides [10][11][12][13], poly(vinylidene fluoride) [14] or polyamides [15]. Since the absorption characteristics of alignment layer determines unwanted light-transmission modulation of the liquid crystal leading to ghost images on the LCD panel [16,17], the investigations are focused on transparent polymers with good surface alignment ability. Another class of transparent polymers is represented by polysilanes. They consist of chains exclusively made up of silicon atoms with significant delocalization of the sigma electrons along the backbone. This aspect leads to interesting electrical and optical properties, such as high quantum efficiency of charge generation, high charge-carrier mobility, efficient luminescence, and optical non-linearity [18]. Their photophysical properties are strongly influenced by the chemical structure of the polymer side groups and/or dimensionality of the skeletal framework [19,20]. To our knowledge there are no investigations on polysilane-based alignment layers patterned by rubbing. Previous papers [21][22][23] showed that polysilanes exhibit good ability of aligning molecules. The morphological features of these polymers are affected by UV exposure due to the scission of the main chain and oxidation processes [21]. Since UV-irradiated polysilane generated different orientation of nematic molecules from that induced non-irradiated polymer, pattern...

show abstract

Alignment Technology and Applications of Liquid Crystal Devices

Cited by 176 publications

References 0 publications

Fundamentals of phase-only liquid crystal on silicon (LCOS) devices

Fundamentals of phase-only liquid crystal on silicon (LCOS) devices

Bifunctional ITO layer with a high resolution, surface nano-pattern for alignment and switching of LCs in device applications

The influence of polysilane chemical structure on optical properties, rubbed film morphology and LC alignment

Contact Info

Product

Resources

About