Active Optical Media Research Articles

Electrically reconfigurable non-volatile metasurface using low-loss optical phase-change material.

Active metasurfaces promise reconfigurable optics with drastically improved compactness, ruggedness, manufacturability and functionality compared to their traditional bulk counterparts. Optical phase-change materials (PCMs) offer an appealing material solution for active metasurface devices with their large index contrast and non-volatile switching characteristics. Here we report a large-scale, electrically reconfigurable non-volatile metasurface platform based on optical PCMs. The optical PCM alloy used in the devices, Ge2Sb2Se4Te (GSST), uniquely combines giant non-volatile index modulation capability, broadband low optical loss and a large reversible switching volume, enabling notably enhanced light-matter interactions within the active optical PCM medium. Capitalizing on these favourable attributes, we demonstrated quasi-continuously tuneable active metasurfaces with record half-octave spectral tuning range and large optical contrast of over 400%. We further prototyped a polarization-insensitive phase-gradient metasurface to realize dynamic optical beam steering.

Intense red emissive organic crystals with elastic bending ability and optical waveguiding behaviour

Orange (Cry-1O) and red (Cry-1R) emissive crystals were obtained based on a green emissive molecule 1. The light transducing capability of Cry-1R in both the straight and bent states can be applied as an active optical waveguiding medium.

Two-beam accelerator based on a Cherenkov wake amplified by an optical active medium

We develop the basic scaling laws for the design of a proof of principle two-beam accelerator based on a solid-state active medium (TBA-AM). The essence of the paradigm is to rely on a low-charge trigger bunch which will generate a weak intensity Cherenkov wake in a dielectric extraction structure. The wake consists of a discrete spectrum of eigenfrequencies, one of which is amplified by the active dielectric material. The exponential growth of the wake, behind the trigger bunch, continues as long as virtually all the energy from the medium is depleted. At this point, the electromagnetic field reaches saturation and thus its maximum value. Beyond this peak gradient, a trailing bunch may be placed and thus accelerated. Evidently, the major difference between the proposed paradigm and the existing ones is the energy source: in existing schemes the energy is stored in the driving bunch, whereas in ours, the required energy is stored in the active medium. Special attention is paid to three quantities which characterize the interacting mode: its initial amplitude generated by the trigger bunch, its exponential growth, and its saturation level. The latter indicates that accelerating gradients in excess of $1\text{ }\text{ }\mathrm{GV}/\mathrm{m}$ are feasible in a less than 10 cm long structure.

Simulation of the light propagation in structured matrices with liquid crystal for optical sensor active medium designing

Simulation of the light propagation in structured matrices with liquid crystal for optical sensor active medium designing

Reversible laser-assisted structural modification of the surface of As-rich nanolayers for active photonics media

Reversible structural changes of As-rich As–Se nanolayers occurring during in situ thermal annealing and above-bandgap laser illumination were studied by synchrotron radiation photoelectron spectroscopy. It was found that the first thermal annealing of As56Se44 nanolayers led to a decrease of the concentration of As that can be connected with evaporation of more volatile As-rich fractions from the surface. This process is accompanied by structural rearrangements in the nanolayers. In situ green laser illumination of annealed samples causes an increase in the concentration of homopolar As–As bonds associated with As-Se2As s.u., while the opposite effect was detected during further thermal treatment. These processes appeared to be reversible for three sequences of annealing and illumination. The observed effect of the reversible photoinduced structural modification is discussed in detail, and possible applications as an active optical medium for photonics are proposed.

Liquid crystal material with gold nanoparticles as optical sensors active medium for the amino acids detection

In the article, the possibility of using the cholesteric liquid crystal mixture doped by the gold nanoparticles as an active medium of optical amino acid sensors is shown. The BLO-62 and the 5CB were used as a cholesteric liquid crystal and a nematic liquid crystal correspondingly. This mixture was doped by the gold nanoparticles. The method of gold nanoparticles synthesis is considered and their parameters are determined. Studies on the spectral characteristics of the investigated materials have shown that the addition of gold nanoparticles to the system leads to a significant decreasing in the spectral characteristic steepness and give the possibility of expanding the measurement range of amino acid concentration.

Light confining effect in a zero-index waveguide with unenclosed sidewalls and a design scheme of a reflectionless polarization converter.

In our work, we have demonstrated an interesting effect: the light confining effect in an epsilon-mu-near-zero (EMNZ) waveguide with unenclosed sidewalls. The EMNZ waveguide can have perfect transmittance even though the sidewalls are unenclosed. All of the light propagating in the EMNZ waveguide is confined to the EMNZ when the connection of each sidewall is not broken. We also demonstrate that even though most of the surfaces of EMNZ are exposed to air rather than covered by perfect electric conductor or perfect magnetic conductor side walls, it is still possible for the EMNZ waveguide to exhibit the light confining effect, which is quite different from a conventional waveguide. The light confining effect of the EMNZ waveguide has rarely been discussed in previous works. Based on the light confining effect, we propose a new design scheme of a reflectionless polarization converter without using an optical active medium or structures. Our proposal provides the possibility of the application of zero-index metamaterials in the field of modulation of optical polarization.

Application of Core-Shell Metallic Nanoparticles in Hybridized Perovskite Solar Cell-Various Channels of Plasmon Photovoltaic Effect.

We analyze the microscopic mechanism of the improvement of solar cell efficiency by plasmons in metallic components embedded in active optical medium of a cell. We focus on the explanation of the observed new channel of plasmon photovoltaic effect related to the influence of plasmons onto the internal cell electricity beyond the previously known plasmon mediated absorption of photons. The model situation we analyze is the hybrid chemical perovskite solar cell CHNHPbICl with inclusion of core–shell Au/Si0 nanoparticles filling pores in the AlO or TiO porous bases at the bottom of perovskite layer, application of which improved the cell efficiency from 10.7 to 11.4% and from 8.4 to 9.5%, respectively, as demonstrated experimentally, mostly due to the reduction by plasmons of the exciton binding energy.

Inverse scattering transform for two-level systems with nonzero background

We formulate the inverse scattering transform for the scalar Maxwell-Bloch system of equations describing the resonant interaction of light and active optical media in the case when the light intensity does not vanish at infinity. We show that pure background states in general do not exist with a nonzero background field. We then use the formalism to compute explicitly the soliton solutions of this system. We discuss the initial population of atoms and show that the pure soliton solutions do not correspond to a pure state initially. We obtain a representation for the soliton solutions in determinant form and explicitly write down the one-soliton solutions. We next derive periodic solutions and rational solutions from the one-soliton solutions. We then analyze the properties of these solutions, including discussion of the sharp-line and small-amplitude limits, and thereafter show that the two limits do not commute. Finally, we investigate the behavior of general solutions, showing that solutions are stable (i.e., the radiative parts of solutions decay) only when initially atoms in the ground state dominate, i.e., initial population inversion is negative.

Asymmetric and Single-Side Splitting of Dissipative Solitons in Complex Ginzburg–Landau Equations with an Asymmetric Wedge-Shaped Potential**Supported by the National Natural Science Foundation of China under Grant No 61665007, and the Natural Science Foundation of Jiangxi Province under Grant No 20161BAB202039.

We report some novel dynamical phenomena of dissipative solitons supported by introducing an asymmetric wedge-shaped potential (just as a sharp ‘razor’) into the complex Ginzburg–Landau equation with the cubic-quintic nonlinearity. The potentials corresponding to a local refractive index modulation with breaking symmetry can be realized in an active optical medium with respective expanding antiwaveguiding structures. Using the razor potential acting on a central dissipative soliton, possible outcomes of asymmetric and single-side splitting of dissipative solitons are achieved with setting different strengths and steepness of the potentials. The results can potentially be used to design a multi-route splitter for light beams.

Vibrational spectroscopy and X-ray study of three stilbene dyes combined with DFT calculations

Stilbene and its derivatives have a wide application in materials science and biomedical investigations where they are used as the active optical medium or bioactive agents. To provide these researches with new knowledge about stilbenes properties we have performed the structural and spectroscopic analysis of three amino derivatives of trans-stilbene. The DFT calculations in hybrid B3LYP version employing 6-31G (d,p) basis set were used to support the experimental results. The calculated optimized geometries together with the crystal structure obtained from X-ray analysis indicate that all three molecular structures include practically planar stilbene moiety with almost coplanar amino group. The inversion center was revealed in the structure of 4,4′-diaminostilbene. The Raman and IR spectra were registered for solid state in the range of 150–3500 and 500-3500 cm−1, respectively. On the basis of good agreement between the computed frequencies and experimental ones, the thorough vibrational assignment was made. The vibrations of phenyl rings, ethylenic bridge and amino (dimethylamino) group are discussed in detail. The main features of vibrational spectra are revealed for the considered stilbene dyes.

Spectral method for numerical solution of the electric field envelope propagation equation

We report new method for solving propagation equation for the electric field envelope, obtained from the Maxwell equations under the slowly varying envelope approximation and the paraxial approximation. This propagation equation usually represents part of Maxwell–Bloch system of equations. Method is semi-analytical and semi-numerical. We use analytical solution of the Fourier transform of the envelope equation, for a given initial condition, to find numerical solutions on grid nodes in 3+1 dimensions. We have tested our numerical results by comparing them with exact particular solutions of the envelope equation. We show that results of our method are in good agreement with the exact solutions for sufficient density of grid nodes. Solving the propagation equations by using this method is important for modelling many phenomena in areas of quantum and nonlinear optics dealing with the propagation of light through an active optical medium.

Resonant optical pulses on a continuous-wave background in two-level active media

We present exact N-soliton optical pulses riding on a continuous-wave (c.w.) beam that propagate through and interact with a two-level active optical medium. Their representation is derived via an appropriate generalization of the inverse scattering transform for the corresponding Maxwell-Bloch equations. We describe the single-soliton solutions in detail and classify them into several distinct families. In addition to the analogues of traveling-wave soliton pulses that arise in the absence of a c.w. beam, we obtain breather-like structures, periodic pulse-trains and rogue-wave–type (i.e., rational) pulses, whose existence is directly due to the presence of the c.w. beam. These soliton solutions are the analogues for Maxwell-Bloch systems of the four classical solution types of the focusing nonlinear Schrödinger equation with non-zero background, although the physical behavior of the corresponding solutions is quite different.

Thresholds for Existence of Dispersion Management Solitons for General Nonlinearities

We prove a threshold phenomenon for the existence of solitary solutions of the dispersion management equation for positive and zero average dispersion for a large class of nonlinearities. These solutions are found as minimizers of nonlinear and nonlocal variational problems which are invariant under a large noncompact group. There exists a threshold such that minimizers exist when the power of the solitons is bigger than the threshold. Our proof of existence of minimizers is rather direct and avoids the use of Lions' concentration compactness argument. The existence of dispersion-managed solitons is shown under very mild conditions on the dispersion profile and the nonlinear polarization of an optical active medium, which cover all physically relevant cases for the dispersion profile and a large class of nonlinear polarizations; for example, they are allowed to change sign.

Polarization-dependent optics using gauge-field metamaterials

We show that effective gauge field for photons with polarization-split dispersion surfaces, being realized using uniaxial metamaterials, can be used for polarization control with unique opportunities. The metamaterials with the proposed gauge field correspond to a special choice of eigenpolarizations on the Poincaré sphere as pseudo-spins, in contrary to those from either conventional birefringent crystals or optical active media. It gives rise to all-angle polarization control and a generic route to manipulate photon trajectories or polarizations in the pseudo-spin domain. As demonstrations, we show beam splitting (birefringent polarizer), all-angle polarization control, unidirectional polarization filter, and interferometer as various polarization control devices in the pseudo-spin domain. We expect that more polarization-dependent devices can be designed under the same framework.

Soliton solutions of coupled Maxwell–Bloch equations

In this paper we study the soliton solutions of the coupled Maxwell–Bloch equations which describe pulse propagation in an active optical medium with coherent three-level atomic transitions and inhomogeneous broadening. The soliton solutions and polarization shifts due to soliton interactions are investigated. An infinite set of conservation laws as well as the soliton trace formulae are derived.

New method for determining the optical rotatory dispersion of hydroxypropyl cellulose polymer solutions in water

The proposed method employs the recorded channeled spectrum of an optical active medium (crystal or liquid solution) placed between two crossed polarizers. The method of channeled spectrum, previously validated for quartz samples, is used to determine the optical rotatory dispersion of hydroxypropyl cellulose solutions (HPC) in water. Both the specific rotation and dispersion parameter depend on the wavelengths of the maxima and minima from the channeled spectrum and on the thickness of the optical active sample. The circular birefringence and its dispersion determined for HPC solutions in water of concentrations 30% and 45% were estimated with a precision of about 0.5%. The rotatory birefringence of HPC in water at 45% is (119.75–57.60)10−6 and the specific rotation determined in the visible range for these solutions has values between 4782 and 1402 degrees/dm, in agreement with the literature. The specific rotation (angle) of HPC solutions is independent of the polymer concentration and represents a dispersive parameter which decreases with the light wavelength. POLYM. ENG. SCI., 55:1077–1081, 2015. © 2014 Society of Plastics Engineers

Tailoring Optical Fields Emitted by Subwavelength Nanometric Sources

In this work, we study a simple way of controlling the emitted fields of subwavelength nanometric sources. The system studied consists of arrays of nanoparticles (NPs) embedded in optical active media. The key concept is the careful tuning of NP’s damping factors, which changes the eigenmode’s decay rates of the whole array. This inevitably leads, at long time, to a locking of relative phases and frequencies of individual localized-surfaces-plasmons (LSPs) and, thus, controls the emitted field. The amplitude of the LSP’s oscillations can be kept constant by embedding the system in optical active media. In the case of full loss compensation, this implies that not only the relative phases, but also the amplitudes of the LSPs remain fixed, leading us, additionally, to interpret the process as a new example of synchronization. The proposed approach can be used as a general way of controlling and designing the electromagnetic fields emitted by nanometric sources, which can find applications in optoelectronic, nanoscale lithography, and probing microscopy.

Random polarization dynamics in a resonant optical medium

Random optical-pulse polarization switching along an active optical medium in the Λ configuration with spatially disordered occupation numbers of its lower energy sublevel pair is described using the idealized integrable Maxwell-Bloch model. Analytical results describing the light polarization-switching statistics for the single self-induced transparency pulse are compared with statistics obtained from direct Monte Carlo numerical simulations.

Continuous emission of fundamental solitons from vortices in dissipative media by a radial-azimuthal potential

We report novel dynamical regimes of dissipative vortices supported by a radial-azimuthal potential (RAP) in the 2D complex Ginzburg-Landau (CGL) equation with the cubic-quintic nonlinearity. First, the stable solutions of vortices with intrinsic vorticity S = 1 and 2 are obtained in the CGL equation without potential. The RAP is a model of an active optical medium with respective expanding anti-waveguiding structures with m (integer) annularly periodic modulation. If the potential is strong enough, m jets fundamental of solitons are continuously emitted from the vortices. The influence of m, diffusivity term (viscosity) β, and cubic-gain coefficient ε on the dynamic region is studied. For a weak potential, the shape of vortices are stretched into the polygon, such as square for m = 4. But for a stronger potential, the vortices will be broke into m fundamental solitons.