Hubert Seiberle

Photo-generation of linearly polymerized liquid crystal aligning layers comprising novel, integrated optically patterned retarders and color filters

For the first time photo cross-linking of linearly polymerizable polymers (LPPs) is shown to induce uniaxial planar alignment in adjacent liquid crystal polymer (LCP)-layers on single substrates. Ways and novel materials allowing integration of LPP-aligning layers with optical retarders in patterned, hybrid LPP-LCP-configurations with freely adjustable optical axes are presented. The novel multifunctional, anisotropic photopolymer configurations are shown to render in-situ optical retarders and polarization interference filters for black-white and color liquid crystal displays (LCDs) feasible. The molecular mechanisms inducing the anisotropic film properties and their thermal and optical stabilities are outlined. The photo-patternable, high resolution hybrid configurations are shown to exhibit excellent thermal and light stability.

Photo-Induced Alignment and Patterning of Hybrid Liquid Crystalline Polymer Films on Single Substrates.

By means of photo alignment and simultaneous cross-linking of linearly photopolymerizable (LPP)-polymers we have succeeded in generating uniaxial planar alignment in adjacent liquid crystal polymer (LCP)-films deposited on single LPP-substrates. It became thus possible to design optically anisotropic and photopatternable hybrid layers of LPP- and LCP-films on single substrates. Hybrid photopolymer configurations were made and are shown to render high resolution optical phase retarder images feasible. The new technology opens-up the possibility to generate and photopattern polarization interference color filters and color compensators integrated directly on liquid crystal display substrates. Moreover, the technology is the basis for new copy proof optical devices.

Determination of Director Distributions in Liquid Crystal Polymer-Films by Means of Generalized Anisotropic Ellipsometry

We report on how to achieve and measure director tilt angle distributions θ(z) in cross-linked nematic liquid crystal polymer (LCP) films by means of generalized anisotropic ellipsometry. LCP-alignment is made by linearly photopolymerized (LPP)-photo-alignment of LCP films on single substrates. For the first time arbitrary tilt angle distributions are achieved and experimentally verified. It is shown that not only the birefringence Δn of novel LCP-materials, which exhibit values up to Δn=0.4, but also the tilt distribution θ(z) of the LC director can be varied. θ(z) is shown to be tunable between substrate surface and LCP/air interface over the entire range 90°≥θ≥0°. The control of the tilt distribution in thin LCP-films on single substrates is essential for many applications, for instance in LPP/LCP wide-view films designed to increase the field of view of liquid crystal displays (LCDs).

Photo-aligned anisotropic optical thin films

Photo-alignment of an isotropic optical thin films enables realization of novel optical elements, which were not feasible up until now. Photo-aligned anisotropic thin films can be applied to rigid or flexible substrates, which may be flat or curved. The optical performance of such films can be tailored to application-specific requirements by introducing tilt profiles of the optical axis and/or generate patterned retarders with continuous or periodical in-plane variation of the optical axis.

38.1: Invited Paper: Photo‐Aligned Anisotropic Optical Thin Films

Photo-alignment of anisotropic optical thin films enables realization of novel optical elements, which were not feasible so far. Photo-aligned anisotropic thin films can be applied to rigid or flexible substrates, which may be flat or curved. The optical performance of such films can be tailored to application specific requirements by introducing tilt profiles of the optical axis and/or generate patterned retarders with continuous or periodical in-plane variation of the optical axis.

Volume photo-aligned retarder

Coated retarders based on liquid crystal materials are typically aligned by brushing or photo-alignment. Recently, we have managed to combine the aligning and retarder function into a single material. Alignment of the new volume photo-alignable retarder (VPR-) material is induced in the bulk upon exposure to linearly polarized light. The new alignment mechanism opens up a new dimension for the design of optical retarders, especially when combined with conventional surface alignment, which allows to induce complex tilt and twist profiles. key words: LPP, LCP, photo-alignment, volume photo-alignment, optical retarder

Photoalignment and photo‐patterning of planar and homeotropic liquid‐crystal‐display configurations

Optical alignment and micro-patterning of the alignment of liquid-crystal displays (LCDs) by linear photopolymerization (LPP) technology renders high-quality multi-domain twisted-nematic (TN) and supertwisted-nematic (STN) displays with broad fields of view over wide temperature ranges feasible. The prerequisites are the generation of photo-induced high-resolution azimuthal alignment patterns with defined bias-tilt angles 0° ≤ 0 ≤ 90°. For the first time, LPP-aligned single- and dual-domain vertically aligned nematic LCDs (VAN-LCDs) are presented. Dual-domain VAN-LCDs are shown to exhibit broad fields of view which are further broadened by combining the displays with LPP-aligned optical compensators made of liquid-crystal polymers.

Four-unit linking groups V. Optically active dopants

Abstract A number of diesters incorporating a four-unit linking group in the acid part (3-propyloxy, (E)-3-propenyloxy, and 4-butyl units) and an optically active centre in the diol part have been prepared. Structurally related three and four ring dioxolanes derived from the corresponding aldehyde precursors to the acids (i.e., also containing 3-propyloxy, (E)-3-propenyloxy, and 4-butyl groups) and the optically active tartaric acids have also been synthesized. The physical properties of these potential chiral dopants pertinent to electrooptic display device and thermochromic applications have been determined. These new chiral dopants are characterized by short pitches, good solubility in nematic hosts, excellent chemical, photochemical and thermal stability, etc. Most of these new optically active substances are well suited for at least one potential application for a chiral nematic mesophase with exactly denned properties made from a standard nematic mesophase and an optically active dopant. A small num...

Photoalignment of LCoS LCDs

Because the pixel area of liquid-crystal-on-silicon (LCoS) microdisplays is about 100 times smaller than that of direct-view liquid-crystal displays (LCDs), the limitations of the conventional alignment by brushing are obvious: Scratches and particle contamination caused by brushing become visible due to the strong optical magnification required for LCoS LCDs both in front or rear projection. As an alternative, photoalignment with the linear photo-polymerization (LPP) technology avoids the generation of defects, thus increasing production yields considerably. For application in LCoS LCDs, alignment layer materials must match the high-voltage holding ratio (VHR) specifications of TFT-LCDs. The VHR performance of the newly developed second-generation LPP materials is shown to be similar to standard TFT polyimides used for conventional brushed alignment. We report investigations of pretilt-angle generation by photoalignment on reflective CMOS substrates. UV light reflected from the CMOS surface during LPP exposure affects the resulting pretilt angle. Compared to pretilt angles on transmissive substrates, the reflected UV light can induce lower, higher, or identical pretilt angles, depending on LPP material properties. In any case, the pretilt angles are well defined, which results in perfect LCD alignment.

Video-compatible subtractive color projection with cholesteric liquid-crystal band-modulation filters

— A highly compact single-beam cholesteric liquid-crystal video projection optics is presented. Cholesteric filters in series with liquid-crystal light modulators are switched pixel by pixel in a subtracting color-modulation scheme. No absorbing polarizers or dye filters are used. The projector exhibits an excellent efficiency of 20% for white light, high contrast, and full-color saturation.