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Accurate optical modeling for design and optimization of liquid crystal on silicon spatial light modulators (LCoS SLMs) is important for phase-related applications. Traditional matrix method cannot accurately predict the optical performance when the LC distribution is complex, therefore the rigorous finite element method (FEM) is preferred. However, the optical modeling of LCoS is a multidimensional problem, which is difficult to simulate with FEM. Here, we present the development of an improved FEM by combining the scattering matrix method with the domain decomposition method to reduce the computational burden for optical simulation of LCoS. Furthermore, a 2D simulation example with phase grating displayed on LCoS is presented and compared with experiment.

Sıvı kristaller uzun çubuksu yapıdaki moleküller olup, doğada katı ve sıvı fazlar arasında bir ara faz olarak gözlemlenebilen kimyasal maddelerdir. Moleküllerinin belirli yöndeki dizilişleri sayesinde, dışarıdan bir elektrik akımı ile uyarıldığında üzerinden geçen ışığın özelliğini değiştirme özelliğine sahiptirler. Bu özelliklerinden yararlanılarak, günümüzde ışık geçirgenliği ayarlanabilir pencerelerin yanı sıra televizyon, telefon, tablet bilgisayarlar, yazılabilir elektronik tablet ve elektronik kitap gibi dokunmatik ekranlı cihazlarda kullanılabilirler. Uygulamalarda LCD ekran ismiyle önemli bir yer işgal eden sıvı kristaller kendi içerisinde temelde termotropik ve liyotropik olmak üzere iki ana faz içerirler. Faz değişimi liyotropik sıvı kristallerde konsantrasyon ve sıcaklığa bağlı olarak gerçekleşirken termotopik sıvı kristallerde sadece sıcaklığa bağlıdır. Sıcaklık değişimine karşı hassas olan ve artan sıcaklıkla sıvının, azalan sıcaklıkla da katının özelliklerine benzer özellikler gösteren termotropik sıvı kristal molekülleri de kendi içerisinde smektik, nematik ve kiral nematik (kolesterik) fazlar olmak üzere de değişik fazlar içerir. Bununla birlikte, termotropik sıvı kristal fazı içerisinde, artan sıcaklıkla birlikte, smektik veya kolesterik faz ile izotropik faz arasında çok küçük bir sıcaklık aralığında görülen ve sıvı kristal moleküllerinin kendiliğinden çifte sarmal yapı oluşturmasıyla meydana gelen diğer bir ara faz olan mavi faz sıvı kristaller, nematik sıvı kristallerle karşılaştırıldığında, elektrik akımına karşı tepki süresinin çok daha az olması, görünür bölgede seçici yansıma vermesi, optikçe izotropik olması gibi mükemmel elektro-optik özelliklere sahip olmasından dolayı lazerden, objektif lenslerine kadar pek çok uygulamada kullanılmaktadır. Bu avantajının yansıra, bu fazın çok dar bir sıcaklık aralığında görülmesi, uygulamalarında bir sınırlamaya neden olmaktadır. Sıcaklık aralığını genişletmek amacıyla, günümüzde polimer stabilizasyonu [1], ve nano parçacık eklenmesi [3] gibi değişik yöntemler kullanılmaktadır. Bu çalışmada, hazırlanan mavifaz-sıvı kristalleri içerisine değişik konsantrasyonlarda tek (SWCNT) ve çok duvarlı (MWCNT) karbon nanotüpleri eklenerek, söz konusu karbon naotüplerin mavi faz sıvı kristalinin termal stabilizasyonu üzerine etkisi incelenmiştir. Mavi-faz sıvı kristal numunesine içerisine %0.001 ile %0.05 aralığındaki konsantrasyonlarında eklenen karbon nanotüplerin, mavi fazın gözlenebilme sıcaklık aralığını 30oC’den 42oC’ye çıkardığı gözlemlenmiştir. Ayrıca yapılan çalışmada karbon nanotüp varlığında polimer stabilizasyonu da yapılarak numunenin dalga boyu stabil hale getirilmiştir.

Using the principle of photo-alignment it has become possible to pattern the orientation of liquid crystal on a substrate. With this approach liquid crystal gratings and lenses with high optical quality have been realized. Recently we have demonstrated that the period of the photo-alignment can be reduced below one micrometer. Chiral liquid crystal that is deposited on this photo-alignment layer will tilt its helical axis and circularly polarized light is diffracted over a certain angle with high yield. The resulting device behaves as a volume hologram with interesting properties: high reflectivity in a certain wavelength range, tunable diffraction angle and low scattering.

The challenges associated with developing a flexible defect-mode liquid crystal (LC) laser are addressed in this paper. To begin with, we discuss the process for creating a well-aligned photopolymerized film of chiral nematic LC using various surface alignment layers such as polyvinyl alcohol, sulphonic azo-dye and rubbed polyimide. A single mode flexible defect-mode laser is demonstrated with an excitation threshold fluence of 60μJ/cm2/pulse. In accordance with previous studies, results from simulations based on the 4×4 Berreman model show that the wavelength and the number of laser modes are determined by the thickness of the defect layer. The proposed flexible laser can be used to form lasers that can be integrated into conformable platforms and that can be used to control the beam direction without the need for additional optical components.

Liquid crystal (LC) phase transition dynamics can be used as a powerful tool to control the assembly of dispersed nanoparticles. Tailored mesogenic ligands can both enhance and tune particle dispersion in the liquid crystal phase to create liquid crystal nano-composites - a novel type of material. Soft nanocomposites have recently risen to prominence for their potential usage in a variety of industrial applications such as photovoltaics, photonic materials, and the liquid crystal laser. Our group has developed a novel phase-transition-templating process for the generation of micron-scale, vesicle-like nanoparticle shells stabilized by mesogenic ligand-ligand interactions. The mesogenic ligand’s flexible arm structure enhances ligand alignment with the local LC director, providing control over the dispersion and stabilization of nanoparticles in liquid crystal phases. In this paper we explore the capsule formation process in detail, generating QD-based capsules over a surprisingly wide range of radii. We demonstrate that the initial nanoparticle concentration and cooling rate are important parameters influencing capsule size. By increasing particle concentration of nanoparticles and reducing the cooling rate we developed large shells up to 96±19 μm in diameter whereas decreasing concentration and increasing the cooling rate produces shells as small as 4±1 μm.

Most liquid crystal devices use transparent conductive electrodes such as indium tin oxide (ITO) to apply a potential difference in order to achieve electro-optic switching. As an alternative, we study a device with narrow metallic electrodes in combination with dielectric layers with large dielectric permittivity. In this approach the applied voltage can be a continuous function of the lateral distance from the electrode line. Simulations for a one-dimensional beam-steering device show that the switching of the liquid crystal (LC) director depends indeed on the distance from the addressing electrodes and on the value of the relative permittivity. We show that in a device with electrodes spaced 60 pm apart, the LC director halfway between the electrodes shows a considerable reorientation, when a dielectric layer with permittivity of epsilon(r) = 550 is used, whereas no reorientation is observed for the uncoated reference sample at the same voltage. An added advantage is that the proposed configuration only contains dielectric materials, without resistive losses, which means that almost no heat is dissipated. This indicates that this technology could be used in low-power LC devices. The results show that using dielectric thin films with high relative permittivity in liquid crystal devices could form a cost-efficient and low-power alternative to many LC technologies where a gradient electric field is desirable.

We present a method to fabricate a thin film color filter based on a mixture of photo-polymerizable liquid crystal and chiral dopant. A chiral nematic liquid crystal layer reflects light for a certain wavelength interval ∆λ (= ∆n.P) with the period and ∆n the birefringence of the liquid crystal. The reflection band is determined by the chiral dopant concentration. The bandwidth is limited to 80nm and the reflectance is at most 50% for unpolarized incident light. The thin color filter is interesting for innovative applications like polarizer-free reflective displays, polarization-independent devices, stealth technologies, or smart switchable reflective windows to control solar light and heat. The reflected light has strong color saturation without absorption because of the sharp band edges. A thin film polarizer is developed by using a mixture of photo-polymerizable liquid crystal and color-neutral dye. The fabricated thin film absorbs light that is polarized parallel to the c axis of the LC. The obtained polarization ratio is 80 % for a film of only 12 µm. The thin film polarizer and the color filter feature excellent film characteristics without domains and can be detached from the substrate which is useful for e.g. flexible substrates.