Nonlinear light propagation in photonic crystal fibers filled with nematic liquid crystals

Orzechowski²,

Sierakowski³

2016

Photon. Lett. Poland

Abstract-In this letter we present a wedge-cell method and then compare it with other techniques that can be used to determinate refractive indices of liquid crystalline materials. This simple goniometric technique is of particular significance when used for liquid crystalline materials characterized by high refractive indices, for which refractometric methods are approaching their upper limits. Importantly, the measurement technique proposed here requires a relatively small amount of liquid crystalline material and gives appropriate results for different light sources from the wide spectral range, allowing thus for chromatic dispersion curves (in different temperatures) to be obtained.Liquid crystals (LCs) are unique anisotropic materials with special optical properties. In particular, their refractive indices strongly depend on temperature and molecular orientation, which plays an important role in practical applications of LCs in photonics. Most of LCs are uniaxial and their optical birefringence, defined as a difference between an extraordinary and ordinary refractive index (Δn=n e −n o ), together with their chromatic dispersion, are the most important parameters to be determined in order to ensure proper design, fabrication and functionality of LC-based photonic elements and devices. It is critical thus to deliver and elaborate a convenient and accurate method for refractive index measurements, specifically in a broad spectral range and as a function of temperature [1][2][3][4][5][6][7]. Typically, optical characterization of liquid crystalline materials in terms of chromatic dispersion is performed at room temperature, while the thermal dependence of refractive indices is usually given for one wavelength only (e.g. 589nm which is characteristic for D-sodium-line). Such information is insufficient when needed for proper design and operation of LC-based photonic devices.The experimental setup proposed here, schematically shown in Fig. 1, allows for various monochromatic lasers sources, as well as tunable light source as a monochromator to be applied in order to determine the refractive indices of liquid crystalline materials under tests. A critical issue in the method described here is to place a liquid crystalline material between two glass plates forming a wedge-cell of relatively small angle (of a single degree) and to introduce planar alignment of liquid crystalline molecules on glass substrates. For experimental procedure, the wedge angle has to be known and it can be determined by illuminating an empty cell with a beam perpendicular to one of the glass plates, measuring the distance between the spots coming from the reflection (d 1 on screen A).When a liquid crystal is placed inside the wedge-cell two spots are observed on screen B due to the anisotropy of the LC material. These spots correspond to ordinary and extraodinary rays and are distanced by d 2o and d 2e , respectively, with respect to the initial spot given by the beam passing through the wedge-cell when it was empty. Relatively long distanc...

Section: Wedge-cell Technique As a Simple And Effective Methods For Chmentioning

confidence: 48%

Wedge-cell technique as a simple and effective method for chromatic dispersion determination of liquid crystals

Orzechowski²,

Sierakowski³

2016

Photon. Lett. Poland

“…It causes that digital representation of the periodic matrix does not consists of identical elements anymore. This problem can be partially solved by implementation of the triangular grid mesh [21] or the radial coordinates [22]. Digitalization of the refractive index distribution in the fiber cross-section can be also improved when the index-averaging technique is implemented [23].…”

Section: Results Of Numerical Simulationsmentioning

confidence: 99%

Discrete light propagation in microstructured fibers infiltrated with liquid crystals

Orzechowski

2012

SPIE Proceedings

Self Cite

In this report, the results of theoretical analyses on the light guidance in the microstructured fibers infiltrated with liquid crystalline materials are presented. More precisely, the analyzed photonic structure is considered as 2D optical lattice (i.e., matrix of the mutually parallel waveguide channels) allowing thus the light to be switched (tunneled) between adjacent channels, as predicted by the series of the numerical simulations performed. The latter are based on the finite difference beam propagation method with the Crank-Nicholson scheme applied. It has been demonstrated that different scenarios for discrete light propagation can be obtained, depending on the internal and external factors governing geometrical and optical properties of both the light beam and the fiber. Our findings pave the way for all-optical switching to be successfully developed in the future practical photonic devices.

“…due to the existence of the photonic bandgap), as well as in the region of infiltrated holes, and moreover, the mechanism of light propagation can be switched by modification of NLC refractive indices [7]. The latter may be achieved thermally, by applying external (electric or magnetic) fields, or by increasing optical power [8][9]. In particular, when the refractive index of an infiltrating material is higher than the one of the silica surround, the analyzed PLCFs with a spatial periodicity of refractive index distribution may be considered as a matrix of waveguide channels.…”

mentioning

confidence: 99%

“…In particular, when the refractive index of an infiltrating material is higher than the one of the silica surround, the analyzed PLCFs with a spatial periodicity of refractive index distribution may be considered as a matrix of waveguide channels. This architecture, analogical to a multi-core optical fiber, allows for discrete light propagation [8][9][10].…”

mentioning

confidence: 99%

Modeling of light propagation in photonic liquid crystal fibers

Woliński

2010

Photon. Lett. Poland

Self Cite