Antonio d’Alessandro

Liquid Crystal Channel Waveguides: A Monte Carlo Investigation of the Ordering

We present detailed Monte Carlo (MC) simulations of a nematic cell with homeotropic boundary conditions at the four confining surfaces. The simulations are based on the Lebwohl-Lasher lattice spin model with boundary conditions chosen to mimic the cell anchoring. We have investigated the model using a standard Metropolis Monte Carlo method to study the optical transmission and the ordering through the cell.

Design of Optical Directional Couplers Made of Polydimethysiloxane Liquid Crystal Channel Waveguides

We present numerical simulations of a directional coupler based on three-dimensional waveguides made of a nematic liquid crystal, acting as the waveguide core, infiltrated in polydimethysiloxane channels. Modeling is based on the combination of minimization of Oseen-Frank energy of the liquid crystal molecules with a beam propagation algorithm. Design of the coupler waveguides is optimized to minimize coupling lengths and maximise efficiencies. Such components can be made at low cost on flexible plastic substrates and can be also integrated with optofluidic devices for biomedical applications.

An electro-optically tunable Bragg reflector based on liquid crystals

In this paper we report the analysis of a distributed feedback guided-wave reflector in liquid crystals and we describe the main properties of the device. The device is based on a comb-shaped interdigitated electrodes and a liquid crystal slab. The device shows a wide tuning range exceeding 100 nm covering C and L bands for wavelength division multiplexing.

Low power photonic devices based on electrically controlled nematic liquid crystals embedded in poly(dimethylsiloxane)

ABSTRACT We present a new class of photonic devices in which light is confined in channel waveguides, named LC:PDMS, made of a nematic liquid crystal (LC) core in a poly(dimethylsiloxane) flexible substrates. Monte Carlo techniques have been used to study LC orientation. Homeotropic alignment of LC molecules has been observed without any applied electric field. A theoretical study of LC orientation under an electric field between coplanar gold electrodes deposited by electroplating has been carried. We report the design of two photonic devices based on LC:PDMS waveguide technology: a 2 × 2 optical switch made of a zero-gap electro-optical-controlled directional coupler and a multimodal interferometer (MMI) acting as an optical multi/demultiplexer. The electro-optical-controlled directional coupler is able to switch light from one waveguide to a second one with an extinction ratio of 16 dB with an applied voltage of just 1.62 V. Light remains in the same waveguide with an extinction ratio of about 18 dB with a voltage of 1.76 V. An MMI based on LC:PDMS technology has been designed to demultiplex wavelengths at 980 and 1550 nm in two output waveguides with an extinction ratio better than 11 dB by applying about 7 V. Graphical Abstract

Addressing techniques of liquid crystal displays, by Temkar N. Ruckmongathan, Chichester, UK, Wiley SID Display Technology Series, 2015, 352 pp., £82.50 (

molecules. Rod–coil block molecules are introduced in chapter 9 by Myongsoo Lee and Wen Li. They show copolymers based on different rod-like systems and discuss structural models, as well as morphological images. Rod–coil block systems with multiblocks are further discussed. Takishi Kato and Yuko Kamikawa contributed a chapter on hydrogen-bonded systems. Phase diagrams and polymorphism of rod-like systems formed by end-on hydrogen bonds are discussed, so are disc-like molecules. Hydrogenbonded side-groups of polymers, as well as main-chain polymers are introduced. The chapter continues with more complex structures, all based on hydrogen bonding. These include some biomolecular complexes. The last chapter 11 of the volume is written by Junji Sakuda, Takuma Yasuda and Takishi Kato, and relates to liquid-crystalline catenanes and rotaxanes, and thus ringshaped and dumbbell-shaped supramolecules, respectively. Again, molecular structures are provided with their polymorphism and structural models. The present volume of the Handbook of Liquid Crystals contains some interesting chapters on rather complex, supramolecular liquid crystals, always relating molecular structure to phase properties and polymorphism. The volume is possibly more of interest to chemists than to physicists, except for the aspects of characterisation, but nonetheless, due to the fact that all chapters are very well referenced, it serves as an excellent introduction for someone who would like to learn more about the field of liquidcrystalline supramolecular structures.

126, 111 Euro) (hardcover), ISBN: 978-1-119-94045-6

We present several approaches to make integrated optic filters, which include either liquid crystals or composite structures including polymers. The presence of liquid crystals allows tunability of the filters controlled by means of low power electric signals. All-optical tuneable filters are also presented in which optical nonlinear properties of liquid crystals are deployed to drive the device.