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Through soliton excitation in a fiber integrated nematic liquid crystals cell, we demonstrated an all-optical response and electrical tunable structure for light coupling and mode conversion in few mode fibers. The light is guided and controlled from the transmitting to the receiving end, making use of the soliton induced waveguide channel, the so called self-guided effect. Both a near-infrared laser, i.e., signal light, and a visible laser, i.e., the probe light, are introduced to demonstrate the self-guided effect and mode conversion, which results match well theoretically and experimentally. Our results show that, the transmitting light can be guided and selectively coupled into lower or higher order modes of the receiving fiber by steering its ‘walk-off’ through voltage control. Besides, the proposed mode converting operation can work in both the polarization-mixed and polarization-separated regimes, and is realizable in a remarkably wide wavelength band.

Employing a low-frequency external electric field bias in nematic liquid crystals with negative dielectric anisotropy, we demonstrate that the trajectory fluctuations of reorientational spatial solitons can be substantially reduced, improving confinement and polarization purity of the output beams.

We report on novel features of random lasers assisted by near-infrared spatial solitons in nematic liquid crystals. Specifically, we study the role of light-induced reorientational waveguides (nematicons) on the spatial and spectral distributions of the laser modes. We show that the spatially spiky character of the laser emission propagating backwards with respect to the pump tends to disappear in the forward direction, due to the soliton confinement of the generated light. Moreover, the spectral features associated with various random laser resonances appear to merge upon guided-wave propagation along the nematicon, making the nematicon-aided random laser a bidirectional device with distinct emission properties at the two opposite outputs.

While curved waveguides are fundamental elements in photonics, those induced all-optically in nonlinear uniform dielectrics tend to be straight. In uniaxial soft matter with a reorientational response, such as nematic liquid crystals, light beams in the extraordinary polarization undergo self-focusing via an increase in refractive index and eventually form spatial solitons, i.e., self-induced waveguides. Hereby we investigate the bending of such waveguides by analyzing the trajectory of solitons in nematic liquid crystals— nematicons— in the presence of a linearly varying transverse orientation of the optic axis. Tothis extent we use and compare two approaches: i) a slowly varying (adiabatic) approximation based on momentum conservation of the nematicon in a Hamiltonian sense; ii) the Frank-Oseen elastic theory coupled with a fully vectorial and nonlinear beam propagation method. The models provide comparable results in such a non-homogeneously oriented uniaxial medium and predict bent soliton paths with either monotonic or non-monotonic curvatures, enabling the design of curved channel waveguides induced by light beams.

We investigate light self-confinement in nematic liquid crystals with homogeneous planar distribution of the molecular director. Using comb-patterned electrodes we are able to vary the initial orientation, exploiting different degrees of nonlinearity by the electro-optic effect. We experimentally demonstrate tuning of the nonlinearity by studying both single nematicon propagation and planar interactions between two nematicons.

We report on nematicon self-steering in two settings: pure nematic liquid crystals, where the steering stems directly from optical reorientation, and dye-doped liquid crystals, where strong confinement owing to a guest-host interaction allows the appearance of a transverse force acting on the beam.

We investigate the propagation of nematicons in various nematic liquid crystals. Following some general considerations on the role of material parameters in light self-trapping via a reorientational nonlinear response, we discuss numerical results on light self-action and transverse localization. Finally, we validate our findings with experimental measurements in three liquid crystalline mixtures featuring different amounts of birefringence.

Light filaments or optical spatial solitons are self-confined (non-spreading) beams that originate from the balance between diffraction and self-focusing in nonlinear optical media (those with a response dependent on the level of excitation)(1-3). Owing to their ability to self-trap as well as to guide weaker signals (even if differing in colour or modulation format) within the waveguides or 'light-pipes' they induce, optical spatial solitons could form the basis of future all-optical processing networks(4,5). One of the most interesting challenges in soliton propagation and engineering concerns light. laments incident on linear/nonlinear or nonlinear/nonlinear interfaces. Here we report the robust propagation, refraction and reflection of optical spatial solitons at the interface between two regions of a nematic liquid crystal. The ability to independently tune the optical properties of each region enables us to steer the beams by refraction and total internal reflection by as much as - 18 and +22 degrees, respectively. Moreover, the extended (nonlocal) and anisotropic response of our system supports polarization healing of the solitons across the interface as well as non-specular filament reflection. Finally, exploiting the inherent and all-optically tunable birefringence, we demonstrate unprecedented nonlinear Goos-Hanchen lateral shifts in excess of 0.5 mm.

In certain materials, the spontaneous spreading of a laser beam (owing to diffraction) can be compensated for by the interplay of optical intensity and material nonlinearity. The resulting non-diffracting beams are called ‘spatial solitons’ (refs 1–3), and they have been observed in various bulk media4,5,6. In nematic liquid crystals7,8,9, solitons can be produced at milliwatt power levels10,11,12 and have been investigated for both practical applications13 and as a means of exploring fundamental aspects of light interactions with soft matter14,15. Spatial solitons effectively operate as waveguides, and so can be considered as a means of channelling optical information along the self-sustaining filament. But actual steering of these solitons within the medium has proved more problematic, being limited to tilts of just a fraction of a degree16,17,18,19,20. Here we report the results of an experimental and theoretical investigation of voltage-controlled ‘walk-off’ and steering of self-localized light in nematic liquid crystals. We find not only that the propagation direction of individual spatial solitons can be tuned by several degrees, but also that an array of direction-tunable solitons can be generated by modulation instability21,22,23,24,25. Such control capabilities might find application in reconfigurable optical interconnects, optical tweezers and optical surgical techniques.

We investigate the role of competing nonlinear responses in the formation and propagation of bright spatial solitons. We use nematic liquid crystals (NLCs) exhibiting both thermo-optic and reorientational nonlinearities with continuous-wave beams. In a suitably prepared dye-doped sample and dual beam collinear geometry, thermal heating in the visible affects reorientational self-focusing in the near infrared, altering light propagation and self-trapping.

Optical waveguides are usually fabricated by top-down methods. Hereby, this study demonstrates a bottom-up approach based on nonlinear optics in reorientational nematic liquid crystals with polymerizable materials. Near-infrared optical spatial solitons—nematicons—in conjunction with UV exposure are employed in order to achieve (i) real-time signal waveguiding for point-to-point beam-induced interconnects by effectively quenching the fluctuations of nematicon trajectories through polymer stabilization; (ii) the molding of permanent channel waveguides in a crosslinked polymer network, so that they persist after turning off the soliton beam and confine signals of various wavelengths and intensities. These findings introduce a novel, highly versatile platform and a wealth of possibilities for guided-wave photonics, signal addressing, and processing in liquid crystalline soft matter.

It has been possible to excite a spatial soliton in a dye doped liquid crystal confined in a capillary tube. The phenomenon is explained by a pure thermal nonlinear effect due to dye absorption.

We demonstrate some basic all-optical (electrically unbiased) logic gates in azobenzene liquid crystalline cells, exploiting their large nonlinearity for light localization and the trans-cis photoisomerization for all-optical external control. Spatial solitons were excited at microwatt power levels at 632.8 nm, whereas gating and switching were achieved with milliwatt beams at 409 nm

We investigate light self-trapping and nematicon generation in reorientional nematic liquid crystals, addressing the role of phase-front curvature and size of the TEM00 input beam excitation. The experimental results in planar cells are in excellent agreement with a semi-analytical model and numerical simulations. These findings can substantially aid characterization and generation of spatial solitons in liquid crystals and be readily generalized to other nonlocal nonlinear media and soft matter systems.

We investigate the excitation and propagation of self-confined beams and the electric steering of soliton-based optical waveguides in nematic liquid crystalline planar cells. Controlled addressing of a signal is achieved in space by exploiting the electro-optic response of the uniaxial material, employing either uniform or patterned electrodes to alter either the Poynting vector or the wavevector, respectively.

We study the interaction of a spatial soliton waveguide with a voltage defined and electrically tuned interface in nematic liquid crystals, whereby the optic axis is reoriented through the use of patterned electrodes. We investigate refraction and total internal reflection of nematicon wavepackets, disclosing the role of anisotropy and obtaining a remarkable in-plane steering as large as 55°.

Using mW light beams to generate spatial solitons in nematic liquid crystals, all-optical switching/logic can be performed on a signal launched in the soliton-induced waveguides. Through the collisional behavior of solitons in a nonlocal medium, the signal can be steered in angle and output position. A power-dependent X junction, AND, and NOR gates are demonstrated.

We report on the first (to our knowledge) experimental observation of higher-order modes guided by soliton-induced waveguides in nematic liquid crystals. We find that the nematicon waveguides operate in a bounded power region specific to each guided mode. Below this region, the guided beams diffract; above this region, the mode mixing and coupling give rise to an unstable output.

We demonstrate power-dependent steering of self-confined light beams propagating in the nonparaxial regime in a guest-host nonlinear medium. Exploiting the Janossy enhancement in dye-doped liquid crystals with reorientational response, we observe sub-mW spatial soliton self-steering as large as 39 degrees, accompanied by trapping of the light spontaneously emitted by the excited dye. The self-turning is modeled in terms of an effective transverse force stemming from the longitudinal electric field in the tightly confined beams, with good agreement between data and simulations.

We experimentally investigate the interaction of two counter-propagating spatial optical solitons (nematicons) in bias-free nematic liquid crystals. We demonstrate the existence of vector solitons composed of two nematicons propagating in opposite directions and analyze their stability versus relative distance and input power.We observe the dynamic instability of two counterpropagating nematicons in the form of time-dependent splitting and spatial entanglement.

Using external beams on the photoconductive layer of a liquid crystal light valve we demonstrate all-optical control of soliton induced waveguides in nematics. Using this approach we implement a half-adder and a 3-bit demultiplexer.

The propagation of solitary waves in nematic liquid crystals in the presence of localized nonuniformities is studied. These nonuniformities can be caused by external electric fields, other light beams, or any other mechanism which results in a modified director orientation in a localized region of the liquid-crystal cell. The net effect is that the solitary wave undergoes refraction and trajectory bending. A general modulation theory for this refraction is developed, and particular cases of circular, elliptical, and rectangular perturbations are considered. The results are found to be in excellent agreement with numerical solutions.

We excite spatial solitons by reorientational nonlinearity of the nematic liquid crystals, using a photoconductive light valve to implement an external light-driven control of their trajectories. Control spots provide deviations of the solitons and allow implementing various routing operations. We demonstrate 2-bit (4-output) and 3-bit (8-output) spatial demultiplexers and a continuously adjustable X/Y power-dependent junction.

The steering of a self-guided beam in a dye-doped nematic liquid crystal caused by an external illumination (control beam) that induces changes in the refractive index of the medium is theoretically analyzed. The interaction between the control beam and the dye molecules modifies the anchoring of the nematic molecules, so changing the director orientation in the bulk of the medium. Beam evolution is investigated by use of a modulation theory approach. It is found that the beam trajectory is independent of the beam profile, as long as this profile is self-similar. Solutions obtained from the modulation theory approach are in excellent agreement with numerical solutions.

We demonstrate, both experimentally and theoretically, excitation-dependent self-bending of spatial solitons in nematic liquid crystals. The observed deflection is explained by nonlinear changes in walk-off, as induced by the rotation of the optic axis via power-driven reorientation.

In the paper the steering possibility of nonlinear light beam in chiral nematics film are presented. We measured the propagation of light beam at the distance of few millimeters and the nonlinear self-focusing was observed for a light power of order of few tenths of milliwatts. Additional, in a waveguide induced by the nematicon, other low-power light beam (signal beam) with different wavelength was trapped. The experimental results are in a good agreement with theoretical predictions and numerical simulation.

Optical anisotropy plays a fundamental role on light propagation in nematic liquid crystals. With specific reference to nematicons, we investigate the transverse dynamics due to the interplay of nonlinear self-confinement, birefringent walk-off and a bias-dependent transverse index profile.

A nonlinear extension of geometric optics is used to derive a modulation theory solution for the trajectory of an optical solitary wave in a nematic liquid crystal-i.e., a nematicon-in which a wide waveguide has been defined by an externally applied static electric field. This solution is used to find the power threshold for the solitary wave to escape the trapping waveguide. This threshold is found to be in excellent agreement with experimental results.

We review the impressive progress on light self-localisation into spatial optical solitons in nematic liquid crystals. We summarise the basic physics and models, outlining the main properties of nematicons and providing an overview of the most significant experimental achievements in undoped, planar, twisted and chiral nematic liquid crystals.

Soliton induced waveguides can be all-optically readdressed in planar cells by modifying the molecular anchoring with an external light source. Using an elliptically shaped control beam we demonstrate refraction and total internal reflection of spatial solitons in dye-doped nematic liquid crystals. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3009658]

Fully three-dimensional spatial solitons in bulk nematic liquid crystals form self-consistent waveguides that are able to confine a weak, collinear copolarized signal at different wavelengths and with large trapping angles. We use a milliwatt cw source to generate a soliton and, by angular steering of the soliton, spatially readdress the guided signal.

We investigate total internal reflection of nonlocal spatial optical solitons at the interface between two differently oriented regions of a highly birefringent nematic liquid crystal. The solitons survive the interaction with an induced index mismatch and undergo nonspecular reflection, with an emerging angle differing appreciably from the incidence angle.

In this work we present the observation of spatial optical solitons in liquid crystal cells by recording the diffraction pattern of the out-coupled beam on a distant screen. Simultaneously, the light propagation is observed via scattering measurements. The most important observation is displacement of the beam on the screen due to the transverse undulation inside the cell. This undulation is caused by the anisotropic walk-off of the beam. The displacement is in good agreement with the values of the undulation earlier reported., SCOPUS: cp.j, info:eu-repo/semantics/published

The reorientational nonlinearity of nematic liquid crystals enables a self-localized spatial soliton and its waveguide to be deflected or destroyed by a control beam propagating across the cell. We demonstrate a simple all-optical readdressing scheme by exploiting the lens-like perturbation induced by an external beam on both a nematicon and a co-polarized guided signal of different wavelength. Angular steering as large as 2.2 degrees was obtained for control powers as low as 32mW in the near infrared.

Spatial nonlocality has a crucial role in the optical response of bulk liquid crystals. With specific reference to one-dimensional modulation instability, we demonstrate the tuning of transverse nonlocality in the nonlinear response of nematics.

We report on what is, to our knowledge, the first experimental observation of spatial soliton interaction with charged conductive microelectrodes in nematic liquid crystals. We show that solitons can undergo voltage-controlled deflection and reflection with a nematicon steering larger than 100° over distances of a few micrometers. Using bias-defined perturbations, we observe reconfigurable soliton geometries with several reflections.

Nematic liquid crystals exhibit a saturable, non-instantaneous nonlinear response through light-induced reorientation. In such a material, we demonstrate that (2+1)-dimensional spatial solitary waves can be generated at milliwatt power levels not only with a coherent optical beam, but also with incoherent excitations. Self-trapping also allows the efficient guidance of a weak co-polarized probe.

We investigate the attractive interaction between spatial solitons in nematic liquid crystals with a tunable nonlinearity and a constant nonlocality. The experimental study, carried out by controlling the orientation of the optic axis via the electro-optic response, shows how the interactions depend on reorientation, in excellent agreement with a model accounting for the anisotropic nature of the dielectric.

We present an experimental study of strong self-focusing in nematic liquid crystals. In a planar geometry, a linear dependence of the focal power on the input intensity for 100-\ensuremath{\mu}m-thick samples turns into an exponential one when thicker samples are used. A transverse visualization of the beam structure is performed in a cylindrical geometry. We observe an undulation and a filamentary structure of the laser beam for large intensities. Also, multiple focal points appear along the beam axis in this configuration. Undulation and filamentation of the beam are also observed in a spherical geometry.

We investigate soliton self-steering owing to the power-dependent walk-off in undoped nematic liquid crystals. The theoretical analysis, carried out in three dimensions and then reduced to an effective two-dimensional model retaining the nonlocal features, clarifies the trade-off between self-focusing and self-steering, as mediated by the initial orientation of the optic axis. Experimental results obtained in planar cells are in excellent agreement with the predictions, even when employing the two-dimensional model and in the presence of linear losses.

We discuss the interactions between self-guided light beams and light-induced perturbations in a liquid crystal light valve. The model and data are in perfect agreement. (C) 2010 Optical Society of America

Liquid-crystal light valves can control the orientation of a nematic layer under the independent or combined action of applied voltage and impinging light intensity; hence, they offer a unique environment for the propagation of spatial optical solitons or nematicons. We demonstrate nematicon excitation, propagation, and steering in photoconductive light valves.

Using an external voltage and interdigitated electrodes in a liquid crystalline cell, we demonstrate tunable steering of light beams and spatial solitons without the detrimental walk-off out of the plane of propagation. The results agree well with a simple model describing birefringence and reorientation in uniaxial nematic liquid crystals.

We investigate, both experimentally and theoretically, the interaction of (2D + 1) spatial solitons with the boundaries of a nonlinear medium in the presence of nonlocality. We demonstrate power-dependent nonlinear repulsion at the boundaries, in quantitative agreement with the model predictions. (c) 2007 Optical S ociety of America.

As a result of development of optics during many centuries the concept was formed that a medium can strongly influence on the light propagation, but the light itself cannot have backward influence on the medium. That concept was refuted only with appearing of coherent and high power radiation of lasers, see, e.g., Nobel Lecture by N. Bloembergen in 1981. A new field in physics–nonlinear optics—formed as a result. The main part of laser investigations concerns with nonlinear optical phenomena, nowadays. First of all these phenomena are of extraordinary interest and beauty and provide for new methods of physical investigations. Secondly, the knowledge of laws governing the interaction of a powerful light with a medium is necessary for the correct utilization of laser beams. Finally, a great number of devices of up-to-date laser optics is totally based on utilization of nonlinear optical effects; generation of higher harmonics of light, stimulated scattering of light, optical phase conjugation, self...

We report on spatial soliton formation and self/cross waveguiding in planar cells containing a nematic liquid crystal in the presence of an externally applied voltage. Self-confinement and cross-induced guidance are demonstrated with an Argon ion laser (514 nm) and a helium–neon probe (633 nm), respectively, over millimeter lengths and with milliwatt pump powers.

The interaction between spatial optical solitons in undoped nematic liquid crystals is governed by reorientational nonlinearity with a significant nonlocality. We demonstrate several cases of interactions, including crossing, interlacing, and merging of spatial solitons in voltage-biased liquid-crystal cells. A scalar model accounts for the main features that were experimentally observed.

We discuss and report refraction and total internal reflection of optical spatial solitons in nematic liquid crystals at the interface between two differently-biased regions, with angular steering as large as -18 and +22 degrees, respectively.

Spatial soliton are self-trapped light beams where diffraction is counterbalanced by optical nonlinearity. Since spatial optical soliton induce waveguides into the nonlinear medium they can be used for all optical switching and signal processing. Moreover, they can form reconfigurable guiding channels which can guide other optical beams [1]. An important characteristic of many nonlinear media, which is known to strongly affect the propagation of beams through the medium. It tends to improve the stability of soliton and also allows to observe nematicon interaction. In this work, we present the soliton interaction and crossing in geometries where two solitons propagate perpendicular to each other. As an experimental platform we utilize chiral nematic liquid crystals (NLCs) which belong to one of the most prominent representatives of the soft matter demonstrate a rich variety of strong nonlinear phenomena [2-4]. Since NLCs allow soliton propagation at the moderate power level and offer high tunability and strong nonlocality they can be employed for an active control of optical properties [5].