Active tuning of photonic device characteristics during operation by ferroelectric domain switching

Ferroelectrics have many unusual properties. Two properties that are often exploited are first, their complex, nonlinear optical response and second, their strong nonlinear coupling between electromagnetic and mechanical fields through the domain patterns or microstructure. The former has led to the use of ferroelectrics in optical devices and the latter is used in ferroelectric sensors and actuators. We show the feasibility of using these properties together in nanoscale photonic devices. The electromechanical coupling allows us to change the domain patterns or microstructure. This in turn changes the optical characteristics. Together, these could provide photonic devices with tunable properties. We present calculations for two model devices. First, in a photonic crystal consisting of a triangular lattice of air holes in barium titanate, we find the change in the band structure when the domains are switched. The change is significant compared to the frequency spread of currently available high-quality light sources and may provide a strategy for optical switching. Second, we show that periodically poled 90° domain patterns, despite their complex geometry, do not cause dispersion or have band gaps. Hence, they may provide an alternative to the antiparallel domains that are usually used in quasiphase matching and allow for tunable higher-harmonic generation

Frequency tunability of solid-core photonic crystal fibers filled with nanoparticle-doped liquid crystals

We infiltrate liquid crystals doped with BaTiO3 nanoparticles in a photonic crystal fiber and compare the measured transmission spectrum with the one achieved without dopant. New interesting features, such as frequency modulation response of the device and a transmission spectrum with tunable attenuation on the short wavelength side of the widest bandgap, suggest a potential application of this device as a tunable all-in-fiber gain equalization filter with an adjustable slope. The tunability of the device is achieved by varying the amplitude and the frequency of the applied external electric field. The threshold voltage for doped and undoped liquid crystals in a silica capillary and in a glass cell are also measured as a function of the frequency of the external electric field and the achieved results are compared

Ferroelectric Based Photonic Crystal Cavity by Liquid Crystal Infiltration

Cataloged from PDF version of article.A novel type of two-dimensional photonic crystal is investigated for it optical properties as a core-shell-type ferroelectric nanorod infiltrated with nematic liquid crystals. Using the plane wave expansion method and finite-difference time-domain method, the photonic crystal structure, which is composed of a photonic crystal in a core-shell-type ferroelectric nanorod, is designed for the square lattice and the hexagonal lattice. It has been used 5CB as a photonic crystal core, and LiNbO3 as a ferroelectric material. The photonic crystal with a core-shell-type LiNbO3 nanorod infiltrated with nematic liquid crystals is compared with the photonic crystal with solid LiNbO3 rods and the photonic crystal with hollow LiNbO3 rods

Liquid Crystals on Ferroelectric Thin Films

Barium titanate (BTO) and lead zirconate titanate (PZT) are two of the most common ferroelectric materials used in applications. These two materials offer excellent dielectric, piezo-electric, electro-optic and pyro-electric properties. The excellent electro-optic properties of our PZT and BTO deposited thin films may lead to cheap and versatile ultra-fast electro-optic modulators on existing photonic platforms [1], such as the Si or the SiN nanophotonic platform. In this work however, we exploit the extremely high dielectric permittivity of PZT (in the order of 500 to 1000). The permittivity is quasi independent of the underlying substrate material (glass, glass + ITO, glass + Pt, Si, etc.). Liquid crystals exhibit electro-optic effects that are an order of magnitude larger compared to PZT, which makes them ideal materials for use in beam steering applications of focus tunable lenses. In these applications the liquid crystal imposes a spatially varying optical path length to light passing through the liquid crystal layer. By working with a number of separately addressable electrodes the optical path length variation can be accurately controlled. Using multi-electrode designs for example, tunable lenses with high optical quality have been demonstrated. One major problem of multi-electrode designs is the appearance of fringe fields which leads to unwanted behavior of the liquid crystal and may eventually lead to the formation of disclination lines which reduces the optical performance drastically. Using a PZT thin film, we demonstrate that the fringe fields are eliminated and that designs with fewer separately addressable electrodes are necessary. Tunable lenses with a liquid crystal layer integrated on top of a PZT layer are demonstrated [2]. Next to the experimental demonstration we provide numerical simulations of the effect of the high permittivity layer on the liquid crystal. [1] J.P. George, et al. Lanthanide-Assisted Deposition of Strongly Electro-optic PZT Thin Films on Silicon: Toward Integrated Active Nanophotonic Devices. ACS Appl. Mater. Inter. 7 13350-9 (2015) [2] O. Willekens, et al., Ferroelectric thin films with liquid crystal for gradient index applications, Optics Express (submitted

Фотоориентация и фотопаттернинг: Новая жидкокристаллическая технология для дисплеев и фотоники

Objectives. Since the end of the 20th century, liquid crystals have taken a leading position as a working material for the display industry. In particular, this is due to the advances in the control of surface orientation in thin layers of liquid crystals, which is necessary for setting the initial orientation of the layer structure in the absence of an electric field. The operation of most liquid crystal displays is based on electro-optical effects, arising from the changes in the initial orientation of the layers when the electric field is turned on, and the relaxation of the orientation structure under the action of surfaces after the electric field is turned off. In this regard, the high quality of surface orientation directly affects the technical characteristics of liquid crystal displays. The traditional technology of rubbing substrates, currently used in the display industry, has several disadvantages associated with the formation of a static charge on the substrates and surface contamination with microparticles. This review discusses an alternative photoalignment technology for liquid crystals on the surface, using materials sensitive to polarization of electromagnetic irradiation. Also, this review describes various applications of photosensitive azo dyes as photo-oriented materials. Results. The alternative photoalignment technology, which employs materials sensitive to electromagnetic polarization, allows to create the orientation of liquid crystals on the surface without mechanical impact and to control the surface anchoring force of a liquid crystal. This provides the benefits of using the photoalignment technology in the display industry and photonics—where the use of the rubbing technology is extremely difficult. The optical image rewriting mechanism is discussed, using electronic paper with photo-inert and photoaligned surfaces as an example. Further, different ways of using the photoalignment technology in liquid crystal photonics devices that control light beams are described. In particular, we consider switches, controllers and polarization rotators, optical attenuators, switchable diffraction gratings, polarization image analyzers, liquid crystal lenses, and ferroelectric liquid crystal displays with increased operation speed. Conclusions. The liquid crystal photoalignment and photopatterning technology is a promising tool for new display and photonics applications. It can be used for light polarization rotation; voltage controllable diffraction; fast switching of the liquid crystal refractive index; alignment of liquid crystals in super-thin photonic holes, curved and 3D surfaces; and many more applications.Цели. С конца XX века жидкие кристаллы занимают лидирующее положение среди рабочих материалов для дисплейной индустрии. В частности, это стало возможным благодаря достижениям в области управления поверхностной ориентацией в тонких слоях жидких кристаллов, необходимой для задания исходной ориентационной структуры слоя в отсутствие электрического поля. Работа большинства жидкокристаллических дисплеев основана на электрооптических эффектах, возникающих за счет изменения исходной ориентации слоев при включении электрического поля и обратной релаксации ориентационной структуры под действием поверхностей после выключения электрического поля. По этой причине высокое качество поверхностной ориентации напрямую влияет на технические характеристики жидкокристаллических дисплеев. Используемая в настоящее время в дисплейной индустрии традиционная технологии натирания подложек имеет ряд недостатков, связанных с образованием на подложках статического заряда и загрязнением поверхности микрочастицами. В данном обзоре рассмотрена альтернативная технология фотоориентации жидких кристаллов на поверхности с использованием материалов, чувствительных к поляризации электромагнитного излучения. Также описаны различные приложения с использованием фоточувствительных азокрасителей в качестве фотоориентируемых материалов. Результаты. Альтернативная технология фотоориентации позволяет создавать ориентацию жидких кристаллов на поверхности без механического воздействия, а также контролировать силу сцепления жидкого кристалла с поверхностью подложек. Это обеспечивает преимущество использования технологии фотоориентации в дисплейной индустрии и в фотонике, где применение технологии натирания крайне затруднительно. На примере электронной бумаги с фотоинертной и фоточувствительной поверхностями рассмотрен механизм оптической перезаписи изображения. Описаны различные варианты использования технологии фотоориентации в жидкокристаллических устройствах фотоники, обеспечивающих управление световыми пучками. В частности, рассмотрены переключатели, контроллеры и вращатели поляризации, оптические аттенюаторы, переключаемые дифракционные решетки, поляризационные анализаторы изображения, жидкокристаллические линзы, а также ферроэлектрические жидкокристаллические дисплеи с повышенным быстродействием. Выводы. Технология фотоориентации и фотопаттернинга жидких кристаллов является многообещающей для новых приложений в области дисплеев и фотоники. Технология может быть использована для вращения поляризации света; дифракции, управляемой напряжением; быстрого переключения показателя преломления жидкого кристалла; ориентации жидких кристаллов в супертонких фотонных дырах, на искривленных и 3D поверхностях; и многого другого.