Electro-optic routing in a nematic liquid-crystal waveguide

Electrical Control of Optical Liquid-Crystal-Guided Microstructures

This work investigates nematic liquid crystal (NLC) optical guiding structures designed in typical sandwich-like NLC cells. With the support of an electrically controlled spatial topology of director orientation, we manage a linear and nonlinear light propagation with the realization of optical beam switching.

Light Propagation in Confined Nematic Liquid Crystals and Device Applications

Liquid crystals are interesting linear and nonlinear optical materials used to make a wide variety of devices beyond flat panel displays. Liquid crystalline materials can be used either as core or as cladding of switchable/reconfigurable waveguides with either an electrical or an optical control or both. In this paper, materials and main device structures of liquid crystals confined in different waveguide geometries are presented using different substrate materials, such as silicon, soda lime or borosilicate glass and polydimethylsiloxane. Modelling of the behaviour of liquid crystal nanometric molecular reorientation and related refractive index distribution under both low-frequency electric and intense optical fields is reported considering optical anisotropy of liquid crystals. A few examples of integrated optic devices based on waveguides using liquid crystalline materials as core for optical switching and filtering are reviewed. Reported results indicate that low-power control signals represent a significant feature of photonic devices based on light propagation in liquid crystals, with performance, which are competitive with analogous integrated optic devices based on other materials for optical communications and optical sensing systems.

Theoretical Study of Tunable Optical Resonators in Periodic and Quasiperiodic One-Dimensional Photonic Structures Incorporating a Nematic Liquid Crystal

In this work, the transfer matrix method (TMM) is employed to investigate the optical properties of one-dimensional periodic and quasiperiodic photonic crystals containing nematic liquid crystal (NLC) layers. This structure is expressed as (ABC)J(CBA)J and made of alternated layers of isotropic dielectrics SiO2 (A), BGO (B) and nematic liquid crystal (C). The simulation study shows that the proposed ternary configuration exhibits tunable defect mode within the photonic band gap (PBG) that can be manipulated by adjusting the thicknesses of NLC layers in order of the periodic lattice. In addition, the optimized structure permits for strong confinement light giving rise to an optical microcavity. The application of an applied voltage into NLC layers enables improving the sensitivity by guiding the local defect mode. It has been also shown that by applying quasiperiodic inflation according to Rudin Shapiro Sequence (RSS) scheme to main periodic structure, several tunable resonant modes appear within the PBG. The presence of such sharp resonant peaks reflects that the quasiperiodic NLC-based structure behaves like multiple microcavites with strong light-matter coupling.

Electrically Controlled Self-Focusing and Self-Localization in the Guided Channels

In this paper, we demonstrate the potential of liquid crystals (LCs) on the applications of small, simple, and tunable optical guided channels. Experimental results show that three operation modes of beam coupling can be achieved, depending on the feature of the electrically controllable refractive index, the incident position, and the specific design of electrodes. The dependence of the beam polarization on self-focusing and coupling effect are also discussed. The electrically controllable self-focusing and beam coupling are highly potential on integrated photonic circuits.

Guided-wave liquid-crystal photonics

In this paper we review the state of the art in the field of liquid-crystal tunable guided-wave photonic devices, a unique type of fill-once, molecular-level actuated, optofluidic systems. These have recently attracted significant research interest as potential candidates for low-cost, highly functional photonic elements. We cover a full range of structures, which span from micromachined liquid-crystal on silicon devices to periodic structures and liquid-crystal infiltrated photonic crystal fibers, with focus on key-applications for photonics. Various approaches on the control of the LC molecular orientation are assessed, including electro-, thermo- and all-optical switching. Special attention is paid to practical issues regarding liquid-crystal infiltration, molecular alignment and actuation, low-power operation, as well as their integrability in chip-scale or fiber-based devices.

Distributed feedback grating in liquid crystal waveguide: a novel approach

We design a distributed feedback guided-wave device in liquid crystals, utilizing a simple geometry based on electro-optic molecular reorientation in uniaxial nematics. We numerically test the structure and demonstrate an effective Bragg reflector with voltage-tunable resonance.

Tunable integrated optical filter made of a glass ion-exchanged waveguide and an electro-optic composite holographic grating

We report the fabrication and the optical characterization of a hybrid tunable integrated optical filter. It consists of a diffused ion-exchanged channel waveguide on a borosilicate glass substrate with a cover of the same glass to form a gap filled with a holographic grating. The grating morphology, called POLICRYPS (POlymer LIquid CRYstal Polymer Slices), is made of alternating stripes of polymer and liquid crystal acting as overlayer for the underneath waveguide. The filter structure includes aluminum coplanar electrodes to electrically control the grating properties, allowing the tunability of the filter. The electric driving power required to tune the filter obtained was in the range of submilliwatts due to the efficient liquid crystal electro-optic effect.

Integrated liquid-crystal switch for both TE and TM modes: proposal and design

An integrated optical switch is proposed and designed based on a weak-anchoring liquid-crystal (LC) cell with a substrate integrating planar lightwave circuits. It consists of a polarization splitter, two switchable polarization converters and a polarization combiner. The polarization splitter/combiner is a directional coupler with an etched slot and filled-in LC covering layer. The switchable polarization converters are straight waveguides with a designed length and covering LC. The proposed configuration is superior to the existing integrated LC switches, as it works for both the TE and TM modes.

Demonstration of 100 GHz electrically tunable liquid-crystal Bragg gratings for application in dynamic optical networks

We demonstrate liquid-crystal-based integrated optical devices with >140 GHz electrical tuning for potential applications in dynamic optical networks. Bragg wavelength tuning covering five 25 GHz wavelength-division multiplexing channel spacing has been achieved with 170 V (peak-to-peak) sinusoidal voltages applied across electropatterned indium tin oxide-covered glass electrodes placed 60 microm apart. This tunability range was limited only by the initial grating strength and supply voltage level. We also observed two distinct threshold behaviors that manifest during increase of supply voltage, resulting in a hysteresis in the tuning curve for both TE and TM input light.