Nonlinear effects in photonic crystal fibers filled with nematic liquid crystals

Abstract

Abstract:We have investigated the nonlinear propagation of light in photonic crystal fibers filled with nematic liquid crystals. We analyzed a configuration with a periodic modulation of the refractive index corresponding to a matrix of waveguides. Matrices of coupled waveguides allow observing a variety of new phenomena both for low power light beam propagation and with an existence of nonlinear effects. The opportunity for the creation of solitary waves caused by the interplay between diffraction and nonlinear effects in these kinds of fibers is investigated. At low power the propagating light beam spreads as it couples to more and more waveguides. When the intensity is increased the light modifies the refractive index distribution, inducing a defect in the periodic structure. The creation of such a defect can lead to a situation in which the light becomes self-localized and its diffractive broadening is eliminated. Eventually, in the case of positive Kerr-type nonlinearity, a discrete soliton can be created. In the case of negative nonlinearity the refractive index decreases with the optical power and can lead to bandgap shifting. The incident beam, with a frequency initially within the bandgap, is then turned outside the bandgap resulting in the changing of the propagation effect for the discrete diffraction effect. As a consequence the delocalization of the light can be observed. PACS

Tunability of discrete diffraction in photonic liquid crystal fibres

“…The second one, a photonic bandgap (PBG) mechanism, allows for the light (from the particular spectral range) to be guided in the region of lower refractive index (e.g., in the air−core). On the other hand, PCF can also be considered as a two−dimensional photonic lattice (with pe− riodic modulation of refractive index in two dimensions), thus allowing (in specific cases) for a discrete light propagation (typical for waveguide arrays/photonic lattices as described below) [10][11][12].…”

“…Propagation properties of PCFs can be dynamically changed (including switching between different guiding mechanisms) by introducing gaseous, liquid or solid media into the air−channels [1,[11][12][13][14][15][16][17]. This simple idea has been found to be very useful while broadening the applicability of PCFs.…”

“…Specifically, the concept of using liquid crystals (LCs), resulting thus in a new type of optical fibres, has gained significant amount of the scientific attention. These particular photonic structures are often referred to as pho− tonic liquid crystal fibres (PLCFs) [12][13], liquid crys− tal−photonic crystal fibres (LC−PCFs) [14], or liquid crys− tal−photonic bandgap fibres [15]. LCs are anisotropic, and, in most cases, their (averaged) refractive indices are higher than that of silica (glass).…”

“…Furthermore, the refractive indices of LCs can also be engineered and/or dynamically adjusted [18]. High tunability of optical properties of PLCFs [mani− fested, e.g., by (i) tuning and/or switching of the guiding mechanisms or (ii) changes in discrete propagation], achie− ved by applying external factors like temperature, strain, pressure, electric or/and magnetic fields, as well as by the light−beam itself (e.g., when nonlinear effects in LCs are considered), brings various potential applications to the field of fibre optics [12][13][14][15][16][17].…”

“…It can be shown that in such photonic struc− tures, output intensity profile strongly depends on optical and geometrical parameters of the system (including wave− length, beam−size, lattice arrangement and index contrast). Discrete photonic systems (of different dimensionality) have been practically achieved in various materials, includ− ing (fused) silica [19][20][21], semiconductors [22][23], photo− refractives [24][25], polymers [26], ferroelectrics [27], and liquid crystals [12,28], thus giving a rise to many new phe− nomena which are not accessible in homogeneous bulk media. An overview of theoretical and experimental devel− opments in the area of discrete light propagation in linear and nonlinear photonics lattices can be found in Refs.…”