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In this work we analyze the behavior of pressure sensors based on membranes of chemically very inert materials and robust to atmospheric agents with non-neutral pH. The selected material for cheapness and chemical stability for the manufacture of low-cost pressure sensors is Silicon Carbide, even if a special section is dedicated to diamond membranes pressure sensors because of its unique chemical inertness. Considering also the electromagnetic noise as an aggressive element of the measurement environment, the low-cost reproduction via sensor - optical fiber coupling of a low-finesse Fabry-Perot interferometer was chosen as the reading setup. SiC membranes are realized by nanosecond LASER processing while those in diamond are made by CVD deposition and microelectronic etching techniques.

This erratum amends some errors in Opt. Lett.43, 2296 (2018)OPLEDP0146-959210.1364/OL.43.002296.

Thin polycrystalline diamond films chemically vapor deposited on thinned silicon substrates were used as membranes for pressure sensor fabrication by means of selective chemical etching of silicon. The sensing element is based on a simple low-finesse Fabry&ndash, P&eacute, rot (FP) interferometer. The FP cavity is defined by the end-face of a single mode fiber and the diamond diaphragm surface. Hence, pressure is evaluated by measuring the cavity length by an optoelectronic system coupled to the single mode fiber. Exploiting the excellent properties of Chemical Vapor Deposition (CVD) diamond, in terms of high hardness, low thermal expansion, and ultra-high thermal conductivity, the realized sensors have been characterized up to 16.5 MPa at room temperature. Preliminary characterizations demonstrate the feasibility of such diamond-on-Si membrane structure for pressure transduction. The proposed sensing system represents a valid alternative to conventional solutions, overcoming the drawback related to electromagnetic interference on the acquired weak signals generated by standard piezoelectric sensors.

Combining a reorientational spatial optical soliton with optical gain and scattering in dye-doped liquid crystals, we demonstrate that a random laser can emit a smooth laser beam in a well-defined direction.

We demonstrate the electro-optic control of self-confined beams via frequency modulation in dual-frequency nematic liquid crystals. Proper design of comb electrodes in a planar cell allows the maximization of the overall steering angle when only walk-off variations are used. A span angle as large as two times the maximum walk-off angle is achieved.

Spatial solitons can affect and enhance random lasing in optically-pumped dye-doped nematic liquid crystals. Upon launching two collinear beams in the sample, the first to pump the fluorescent guest molecules and the second to induce a reorientational soliton, strikingly the second beam not only guides the emitted photons in the soliton waveguide, but also enhances the lasing efficiency and modulates its spectral width. By altering the scattering paths of the emitted photons, the soliton also contributes to the selection of the lasing modes, as further confirmed by the observed kinks in the input/output characteristics. These experimental results demonstrate that random lasing can be efficiently controlled by a light beam which does not interact with the gain molecules, opening a route towards light-controlled random lasers. publishedVersion

Light-controlling-light is one of the most advanced paradigms in optical signal processing, including light-induced waveguides as well as all-optical switching and routing. Other fundamental aspects of all-optical processing are optical memories and sequential elements, which require responses depending on the evolution history of the system, such as the hysteresis stemming from optical multistability. Hereby, we report on optical bistability and hysteresis in cavityless geometries and in the presence of self-localized beams, i.e., spatial optical solitons, exploiting the nonlocal reorientational nonlinearity of nematic liquid crystals (NLC). When the optic axis of NLC is initially orthogonal to the applied electric field, the molecular dipoles start to rotate above a threshold named after the Fréedericksz transition, the latter being usually of the second order. Here, we show that such transition become of the first order via the intrinsic feedback provided by self-focusing, in turn leading to the appearance of a hysteresis loop between diffracting and self-confined beams. We report on hysteresis of the beam size versus input power, as well as hysteresis versus applied voltage at a fixed beam power. Our findings introduce a novel kind of cavity-less optical bistability with propagating light beams and disclose a novel approach to information storage based on light self-localization.

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.

Dye-doped nematic liquid crystals support random lasing under optical pumping, as well as reorientational optical spatial solitons acting as all-optical waveguides. By synergistically combining these two responses in a collinear pump-soliton geometry, the resulting soliton-enhanced random laser exhibits higher conversion efficiency and better directional properties. After a short account on random lasers and solitons in nematic liquid crystals–nematicons–we describe our experimental results on nematicon-molded random lasers.

We demonstrate thermo-optic control on the propagation of optical spatial solitons in nematic liquid crystals. By varying the sample temperature, both linear and nonlinear optical properties of the reorientational material are modulated by acting on the refractive indices, the birefringence, and the elastic response. As a result, both the trajectory and transverse confinement of spatial solitons can be adjusted, demonstrating an effective means to tune and readdress self-induced optical waveguides.

We demonstrate a guided-wave random laser configuration by exploiting the coexistence of optical gain and light self-localization in a reorientational nonlinear medium. A spatial soliton launched by a near-infrared beam in dye-doped nematic liquid crystals enhances and confines stimulated emission of visible light in the optically-pumped gain-medium, yielding random lasing with enhanced features.See also erratum at:Appl. Phys. Lett. 110, 019902 (2017); https://doi.org/10.1063/1.4973864

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.

We demonstrate that light refraction at a straight interface between an isotropic dielectric and a nematic liquid crystal can change from positive to negative depending on power. The phenomenon relies on the reorientational response and the all-optical rotation of the optic axis, causing in turn variations in walk-off and beam self-steering.

Refraction at a dielectric interface can take an anomalous character in anisotropic crystals, when light is negatively refracted with incident and refracted beams emerging on the same side of the interface normal. In soft matter subject to reorientation, such as nematic liquid crystals, the nonlinear interaction with light allows tuning of the optical properties. We demonstrate that in such material a beam of light can experience either positive or negative refraction depending on input power, as it can alter the spatial distribution of the optic axis and, in turn, the direction of the energy flow when traveling across an interface. Moreover, the nonlinear optical response yields beam self-focusing and spatial localization into a self-confined solitary wave through the formation of a graded-index waveguide, linking the refractive transition to power-driven readdressing of copolarized guided-wave signals, with a number of output ports not limited by diffraction.

We investigate optical bistability with light beams propagating in reorientational nematic liquid crystals. In a given interval of input powers, light beams can propagate in either diffracting or soliton states, depending on the “history” of the system. We use biased planar samples exhibiting an abrupt self-focusing response with threshold.

We theoretically investigate light self-trapping in nonlinear dielectrics with a reorientational response subject to threshold, specifically nematic liquid crystals. Beyond a finite excitation, two solitary waves exist for any given power, with an hysteretic dynamics due to feedback between beam size, self-focusing and the nonlinear threshold. Soliton stability is discussed on the basis of the system free energy.

We investigated bistability with light beams in reorientational nematic liquid crystals. For a range of input powers, beams can propagate as either diffracting or self-trapped, the latter corresponding to spatial solitons. The first-order transition in samples exhibiting abrupt self-focusing with a threshold is in agreement with a simple model.

Liquid crystals in the nematic phase exhibit substantial reorientation when the molecules are driven by electric fields of any frequencies. Exploiting such a response at optical frequencies, self-focusing supports transverse localization of light and the propagation of self-confined beams and waveguides, namely “nematicons”. Nematicons can guide other light signals and interact with inhomogeneities and other beams. Moreover, they can be effectively deviated by using the electro-optic response of the medium, leading to several strategies for voltage-controlled reconfiguration of light-induced guided-wave circuits and signal readdressing. Hereby, we outline the main features of nematicons and review the outstanding progress achieved in the last twelve years on beam self-trapping and electro-optic readdressing.

The great interest arisen in the past decades in optical spatial solitons, i.e. self-confined waves supported by the balance between diffraction and nonlinear self-focusing, stems from their character of light-induced waveguides, thus allowing versatile and reconfigurable schemes for optical signal handling and processing [1]. Nematic Liquid Crystals (NLC) are excellent materials for the generation, propagation and the control of spatial solitons, also known as Nematicons [2]: NLC exhibit large birefringence and transparency, coupled with a high reorientational nonlinearity owing to (mean) molecular rotation induced by quasi-static and/or optical frequency electric fields. In addition, the high nonlocal character of their response stabilizes two-dimensional selfconfinement of beams into solitons [3,4]. Hereby we illustrate planar NLC cell configurations whereby nematicons can be electrically routed by propagating in a non-uniform dielectric with transverse and longitudinal variations of the refractive index and/or the orientation of the optic axis, i.e. by undergoing voltage-driven modulation of linear and nonlinear properties. The numerical models and numerical results are in excellent agreement with the experimental data.

We investigate, both theoretically and experimentally, spatial soliton interaction with dielectric interfaces in a strongly anisotropic medium with non-locality, such as nematic liquid crystals. We throw light on the role of refractive index gradients as well as optic axis variations in both voltage- and self-driven angular steering of non-local solitons. We specifically address and then employ in experiments a suitably designed electrode geometry in a liquid crystalline cell in order to define and tune a graded dielectric interface by exploiting the electro-optic response of the material through the in-plane reorientation of the optic axis in two distinct regions. We study both refraction and total internal reflection as well as voltage controlled steering of spatial solitons.

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°.

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.

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.

Using a photoconductive light valve with nematic liquid crystals, we introduce a versatile platform for the excitation and routing of spatial optical solitons, with external beams controlling the whereabouts of the underlying all-optically induced waveguides and their spatial dynamics. Using this all-optical control of soliton trajectory, we demonstrate a NOR gate, an XNOR, and a Boolean half-adder.

We demonstrate that photoconductive light valves with nematic liquid crystals support the propagation of spatial solitons and provide a convenient and effective environment for their all-optical routing and switching by means of external illumination.

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.

Blue light self-confinement in active dye-doped nematic liquid crystals is reported, demonstrating trapping of the emitted red light in dissipative spatial solitons formed by all-optical reorientation.

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.

Conspicuous efforts have been devoted to exploit spatial solitons for signal processing. In nematic liquid crystals steering of spatial solitons or nematicons has been reported in planar cells. In this Communication, we demonstrate excitation and tunable propagation of spatial solitons in photoconductive Light Valves filled with nematic Liquid Crystals (LCLV). We show that nematicons can be effectively launched and deviated in LCLV, combining self-guidance with parallel nonlinear optical processing.

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]

Spatial soliton interactions, such as crossing, merging and spiraling, have been widely studied in the past years as means to exploit non-locality and ways to implement all-optical signal addressing or processing. With reference to spiraling, if attraction provided by the non-linear potential is exactly balanced by the system momentum, the initial soliton distance remains unchanged over the propagation. This phenomenon has been studied in different materials with Kerr, photorefractive or thermal non-linearities, both theoretically and experimentally. However, all such studies have been conducted acting on the initial conditions or comparing distinct longitudinal sections. Here we present an experimental study on soliton spiraling in nematic liquid crystal with another approach: we gain non-linear control over the two-soliton cluster by simply varying the total power excitation of the system.

We demonstrate an original approach, to the best of our knowledge, to acquire nonlinear control over the angular momentum of a cluster of solitary waves. We show that the angular momentum can be adjusted by acting on the global excitation of the system. The effect is verified in liquid crystals by observing power-dependent rotation of a two-soliton cluster.

We investigate, both theoretically and experimentally, self-trapping of light beams in nematic liquid crystals arranged so as to exhibit the optical Fréedericksz transition in planar cells. The resulting threshold in the nonlinear reorientational response supports a bistable behavior between diffracting and self-localized beam states, leading to the appearance of a hysteretic loop versus input excitation. Our results confirm the role of nematic liquid crystals in the study of non-perturbative nonlinear photonics.

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 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.

Liquid crystals in the nematic phase support light self-confinement via reorientational nonlinearity and nonlocality, yielding robust spatial solitons which can trap, switch and route optical signals. We review the major achievements in the field.

We demonstrate random lasing control exploiting optical gain and light self-localization in a reorientational medium. A spatial soliton in dye-doped nematic liquid crystals modulates stimulated emission of visible light, yielding random lasing with enhanced features.