Narrow Results

Single layer (SLAR: TiO₂ and ZnO), and DLAR: TiO₂/ZnO bi-layer were deposited on glass substrates by sol–gel dip and spray pyrolysis for TiO₂ and ZnO thin films respectively. The structural and optical properties have been studied by different characterization techniques: Raman spectroscopy, UV–Visible spectrophotometer and m-lines spectroscopy. The SLAR of TiO₂ and ZnO thin films crystallizes in the Anatase and the wurtzite phase, respectively. The fabrication of the DLAR bi-layer increased the optical gap energies. Also, the DLAR film experienced a decrease in the visible transmittance. However, the present work is principally focused on the influence of the DLAR on the performance of the waveguide characterized by the m-lines measurements. The SLAR samples exhibit a single mode in the TE and TM polarizations. The DLAR sample had two modes in each polarization, one mode in the TE polarization was due to light traveling in the TiO₂ film and the rest three were assigned to ZnO. The results shed light on the effect of the deposition method and the role of refractive index difference in bi-layer waveguide design.

This study presents a tunable phononic crystal (PnC) composed of liquid–solid components, demonstrating adjustable waveguiding and directional transmission capabilities through the rotation of embedded scatterers. A two-dimensional model featuring grooved steel rods in water is analyzed using finite element simulations to evaluate band structures and transmission spectra. To achieve the widest full band gap, a genetic algorithm is integrated to optimize the structural parameters. By examining a supercell with a central defect, wave localization is achieved, facilitating tunable waveguide formation. Analysis of equifrequency contours reveals that, at a scatterer rotation angle of $0^{\circ }$, the structure enables directional transmission, with wave propagation preferentially aligned with specific crystal axes. This work pioneers a new strategy for designing tunable acoustic metamaterials with applications in advanced waveguiding and directed acoustic manipulation technologies.

A model for the analytic description of vortices in a system consisting of a long Josephson junction and a waveguide is formulated. For this system all types of elementary vortices and its chains are listed. The allowed range of velocities of an elementary vortex is found. It is established that a free vortex can be a fast one which moves with velocity much greater than the Swihart velocity of Josephson junction. The effect of the waveguide on the induced vortices motion is studied. It is shown that fast vortex can be generated by relatively small values of bias current density. The effect of vortex Cherenkov losses on the bias current is described.

The entanglement of two distant quantum dots coupled to metallic waveguide has been investigated theoretically in the presence of the flip-flop interaction with the analytic solutions of eigenvalue equations of the system. High entanglement of two quantum dots could be achieved by adjusting the direct-coupling strength of two quantum dots, the coupling strength of quantum dots with surface plasmon along metallic waveguide, the group velocity of surface plasmon and detuning. The discussed system with the flip-flop interaction provides us with a rich way to realize the quantum device for quantum information processing, such as quantum communication and quantum computation.

We have theoretically studied the designable quantum beamsplitter of single photons interacting with the two-level quantum dot placed in the node of a Y-type waveguide on the basis of the real-space approach. We showed that splitting of incoming single photons from one quantum channel to the others could be achieved by controlling the coupling strength of two-level quantum dot with waveguide, detuning between the quantum dot and the incoming single photon, and so on. Such quantum devices based on the controllable single photon transport behave as quantum beamsplitter at the single photon level, which provides us rich ways of configuration of important elements for the practical realization of the quantum information network.

To explore the directional transmission channel that can efficiently transport acoustic energy, we analyzed the local state characteristics of a mirror symmetric interface (MSI) in an artificial periodic structure. It was found that in a one-dimensional (1D) waveguide structure with alternating high- and low-resonant units, the acoustic energy can be localized at the symmetric interface. The result can be extended to a 2D waveguide array, implying that the acoustic energy can be transported efficiently along the interface. In addition, to improve the robustness of the acoustic system, we designed a graphene-like periodic structure based on a hexagonal lattice. By breaking the six-fold rotation symmetry of the structure, the topological interface was constructed, and the backscattering of the acoustic wave was effectively suppressed, enabling the acoustic wave energy to be transported with low reflection even in the curved waveguide. These results may provide a new direction for the realization of high-tech applications such as micromotor and 2D integrated communication.

In this paper, we propose an active photonic-crystal microcavity waveguide with two-level atom-doped-dielectric slab as background material, and derive the model for signal gain calculation and analyze its gain characteristics. The analytical results show that the structure can generate high gain in a short length because of the efficient utilization of pump power in the microcavity. The proposed waveguide will be promising for the development of an active integrated photonic system.

This paper designs a thermal waveguide using thermal phonon insulators, to manipulate the loss of thermal radiation. Two-dimensional (2D) photonic crystals with dielectric background and air holes have been used in the waveguide clad to suppress thermal radiation so that thermal radiation cannot escape out from the waveguide clad. The photonic crystals may reduce the loss of thermal radiation through waveguide clad which surges the thermal energy confinement in the waveguide core and propagation along the longitudinal axis. The photonic crystals have been designed with the bandgap covering the thermal phonon frequency range and thus can be used to construct thermal phonon insulators to suppress or trap thermal emission generated through phonon wave propagation. The finite-difference-time-domain simulation results demonstrate that electromagnetic bandgap in photonic crystals has enough width in the thermal phonon frequency range to confine the thermal energy within the core of the waveguide and effective transmission of thermal radiation can be conquered within the waveguide core.

We propose a simple optical model, which consists of two Kerr nonlinear parallel planar waveguides sandwiching a one-dimensional photonic crystal for demonstrating the phenomenon of spontaneous symmetry breaking in optics. We study the shape and stability of soliton pairs propagating in two planar waveguides and the spontaneous symmetry breaking of the power distribution of solitons in the two waveguides. The results of numerical simulation show that there is supercritical type of spontaneous symmetry breaking in this system. More optical power P and smaller refractive index of photonic crystals $C_0$ make soliton solutions more prone to spontaneous symmetry breaking bifurcation. Asymmetric soliton solutions and symmetric soliton solutions correspond to different dispersion relations. Under the given total power P, for the symmetric soliton solutions, the propagation constant k increases linearly with $C_0$, and for asymmetric soliton solutions, the propagation constant k decreases nonlinearly with $C_0$. The minimum point of $k(C_0)$ is just the demarkation between the symmetric soliton solutions and the asymmetric soliton solutions. If $C_0$ is fixed, the minimum point of the Hamiltonian of the system, $E(P)$, is also the critical point of the two different kinds of soliton solutions. We also study stable and unstable distributions of two kinds of soliton solutions.

A planar waveguide is demonstrated in the Yb³⁺-doped tellurite glass, using (5+6) MeV O³⁺ ion implantation with doses of (4+8)×10¹⁴ ions/cm². The implantation process of O³⁺ ions into the Yb³⁺-doped tellurite glass is simulated by the stopping and range of ions in matter (SRIM) 2010 code. The dark-mode spectra are measured by the prism-coupling system at λ = 632.8 nm. The reflectivity calculation method and the finite-difference beam propagation method are used to calculate the refractive index profile and the modal profile of transverse electric (TE) mode of the fabricated waveguide, respectively. The absorption spectra show that the transmission properties are not affected by the waveguide fabrication process.

A planar waveguide in the Nd${}^{3+}$-doped fluorophosphate glass is fabricated by a 6.0 MeV C${}^{3+}$ ion implantation at a low-fluence of $1.0\times 10^{14}$ ions/cm². The fluence is close to that in semiconductor industry. The dark mode spectra are recorded by a model 2010 prism coupler. The energy losses during the implantation process and the refractive index profile of the waveguide are simulated by the SRIM 2010 code and the reflectivity calculation method (RCM), respectively. The near-field light intensity profile and the propagation loss of the waveguide are measured by an end-face coupling system. The two-dimensional (2D) modal profile of transverse electric (TE) mode for the fabricated waveguide is calculated by the finite difference beam propagation method (FD-BPM). The results of microluminescence and optical absorption reveal that the spectroscopic characteristics of the Nd${}^{3+}$-doped fluorophosphate glass are nearly unaffected by the carbon ion implantation process. This work suggests that the carbon-implanted Nd${}^{3+}$-doped fluorophosphate glass waveguide is a promising candidate for integrated active devices.

The design and characterization of perfect metamaterial absorbers (MAs) based on simple configurations including square- and triangle-shapes, which operate in X-band frequency region are numerically and experimentally investigated. The proposed MAs provide perfect absorption with the polarization angle independency. In X-band waveguide, the absorption rates are 99.69% and 99.97% at the resonance frequencies of 10.57 GHz and 10.93 GHz for the square- and triangle-shaped MAs, respectively. In addition, the same configurations are numerically tested under free space boundary conditions to compare and discuss the obtained results. The suggested MAs enable myriad potential application areas for security and stealth technologies in X-band including wireless communication.

Neodymium-doped calcium niobium gallium garnet (Nd:CNGG) waveguide operated at 632.8 nm is demonstrated by the 3.0-MeV oxygen-ion implantation with a fluence of $6.0\times 10^{14}$ ions/cm². The annealing treatment at 300${}^{\circ }$C for 45 min is carried out to optimize the waveguide quality. The dark-mode spectra are measured by the $m$-line technique. The refractive index profiles are calculated from the effective refractive indices of the waveguide modes. The near-field intensity distributions are simulated based on the reconstructed refractive index profiles. The annealing treatment process could effectively remove unwanted defects and optimize the waveguide quality. The optical properties of the annealed waveguide are better than that of the as-implanted waveguide.

An arsenic tri-selenide-based strip/slot hybrid waveguide with a single horizontal silica slot is proposed to achieve an extremely low and flat dispersion with three zero dispersion wavelengths. By adjusting the geometrical structural parameters of the hybrid waveguide, dispersion tailoring is fully obtained. The flat group velocity dispersion varying between ±0.08 ps²/(m) is obtained over a 1253 nm bandwidth. The parameters of effective area, nonlinear coefficient, and third-order dispersion are all investigated. Moreover, a compact on-chip all-optical wavelength converter is designed based on degenerate four-wave mixing in this waveguide. The dependencies of conversion efficiency and conversion bandwidth on the pump wavelength are discussed. The impact of pump power and signal power on the conversion efficiency is also investigated. The results show that a maximal conversion efficiency of −0.46 dB, and a 3-dB conversion bandwidth of 830 nm in the mid-infrared is achieved.

We analyze guided waves in the linear media separated nonlinear interface. The mathematical formulation of the model is a one-dimensional boundary value problem for the nonlinear Schrödinger equation. The Kerr type nonlinearity in the equation is taken into account only inside the waveguide. We show that the existence of nonlinear stationary waves of three types is possible in defined frequency ranges. We derive the frequency of obtained stationary states in explicit form and find the conditions of its existence. We show that it is possible to obtain the total wave transition through a plane defect. We determine the condition for realizing of such a resonance. We obtain the reflection and transition coefficients in the vicinity of the resonance. We establish that complete wave propagation with nonzero defect parameters can occur only when the nonlinear properties of the defect are taken into account.

The influences of second-order dispersion (SOD) and third-order dispersion (TOD) on spectral properties of wavelength conversion based on FWM at mid-infrared region (mid-IR) are theoretically investigated in a silicon nitride waveguide. It is found that the SOD and TOD can affect the frequency shift and temporal profiles of idler pulses. Moreover, the temporal and frequency spectrum of output signal are also discussed with different SODs and TODs. Meanwhile, the numerical simulation results imply that the efficiency of FWM process will be reduced and the wavelength range of phase-match will be shifted due to the change of SOD or TOD.

The investigation on the terbium gallium garnet (TGG) crystal waveguides in the visible and near-infrared bands is significant for potential applications in science and technology. In this work, we report on a TGG planar waveguide based on the proton irradiation with an energy of 400 keV and a dose of $8\times 10^{16}$ ions/cm². The annealing treatments are adopted to improve optical performances of the waveguide on the conditions of 260${}^{\circ }$C and 410${}^{\circ }$C severally for 1 h. The dark-mode spectra and the refractive index distributions of the TGG waveguide are obtained before and after the thermal treatments. There is a strange phenomenon that nine modes are observed on the m-line curve after the annealing treatment at 410${}^{\circ }$C. The theoretical and experimental results demonstrate that the fabricated waveguide annealed at the temperature of 410${}^{\circ }$C can propagate more guided modes and have better capacity to confine light.

A proper lattice structure consisting of homogeneous material is designed in this paper to investigate the maximum bandwidth of perfect lattice structures and tunable property of waveguide with linear geometric defect by means of selecting optimal geometric lattice cell. A simulation model based on finite element method is used to calculate dispersion curves and transmission spectrums of lattice structures with different geometric parameters. Meanwhile, a simplified theoretical model of unit cell, which considers the mass of grid bar and stiffness of node area, is applied to validate the accuracy of simulation result and may provide an effective approach for prediction of band gap lower boundary. Then, the validated numerical results show different orders of widest band gap that can be realized by different optimal geometric structures. Moreover, waveguide property can be effectively controlled and manipulated by changing defect parameters. The present study may establish theoretical and simulation foundation to control and manipulate band structures and other acoustic propagation characteristics of waveguide devices.

Elastic wave metamaterials, such as phononic crystals (PnCs) always composed of several materials in terms of periodical structures, possess unique acoustic characteristic which can exhibit outstanding performance in forbidding wave propagation with some specific frequencies. In this paper, due to the thermal sensitivity of the thermally induced shape memory polymers (SMP) and period thermal fields, a tunable planar acoustic metamaterial which is constituent homogeneous is proposed and designed to realize the function of waveguides. A thin plate model composed of homogenous thermally induced SMP and adhered with a series of metallic films at the top boundary which plays the role of local heating sources is established. The homogenous plate can be transferred into acoustic metamaterial once the non-uniform period thermal fields are imported. Based on the Fourier law of heat conduction and finite element method (FEM), a two-dimensional numerical model via COMSOL Multiphysics is carried out to perform the in-plane mode band structures and transmission spectra. The results show that the bandgap will be effectively opened and change obviously as the injected heat flux increases. Furthermore, band structures of $7\times 1$ supercell with thermal defect are performed to reveal the design guideline of waveguides which is supposed to be the basis of line-type and L-type waveguides. The tunable characteristics of waveguides based on thermal fields with thermal defects are also discussed. These results may pave a new avenue for the design of tunable acoustic metamaterial composed of thermal sensitive material which own a prospect to be applied in area of acoustic waveguides.

Modes and wavenumbers are the principal ingredients that characterize the pressure field in an oceanic waveguide. However, wavenumber and mode inversions are well-known to be a difficult task in underwater acoustics. Moreover, this double inversion has never been performed simultaneously from the same configuration of emitters and receivers. We present a new approach to this problem in a shallow water environment between two vertical arrays of sources and receivers. Starting from a classical modal decomposition of the pressure field, our algorithm focuses on a specific treatment of phase and amplitude variables. The key idea is to run a three-stage optimization by working separately on the phase and amplitude of the acoustic field. The high number of variables of the problem is turned into an advantage by using an adjoint code generated by an Automatic Differentiation software. Numerical results in the presence of noise show that modes and wavenumbers are estimated with a high accuracy.