Nonlinear Dielectric Material Research Articles

Optical bistability in gap-plasmon metasurfaces in consideration of classical nonlocal effects.

Optical bistability of linear reflectance and third-harmonic generation is investigated in a metasurface consisting of metallic grating coupled with metallic film spaced with nonlinear dielectric material. Linear optical reflectance and electric field enhancement are achieved for gaps <20 nm in the presence of classical nonlocality in metallic nanostructures. Enlarged thresholds from the higher to lower reflectance states are observed from 140 kW/cm2 for the local model to 300 kW/cm2 for the nonlocal model for 0.5-nm gaps. Though the linear reflectance almost overlaps for local and nonlocal models for 20-nm gaps, the optical bistability hysteresis loops retain large differences because local field differences are amplified owing to the relation of nonlinear refraction with square of local field and historical evolution of the optical bistability.

Measurements of Nonlinear Polarization Dynamics in the Tens of Gigahertz.

Frequency-dependent linear-permittivity measurements are commonplace in the literature, providing key insights into the structure of dielectric materials. These measurements describe a material's dynamic response to a small applied electric field. However, nonlinear dielectric materials are widely used for their responses to large applied fields, including switching in ferroelectric materials, and field tuning of the permittivity in paraelectric materials. These behaviors are described by nonlinear permittivity. Nonlinear-permittivity measurements are fraught with technical challenges because of the complex electrical coupling between a sample and its environment. Here, we describe a technique for measuring the complex nonlinear permittivity that circumvents many of the difficulties associated with other approaches. We validate this technique by measuring the nonlinear permittivity of a tunable thin film up to 40 GHz and comparing our results with a phenomenological model. These measurements provide insight into the dynamics of nonlinear dielectric materials down to picosecond timescales.

Raman scattering and self-steepening in nonlinear plasmonic waveguide pulse equation

In this paper, we use Maxwell equations and the first order perturbation theory to obtain pulse propagation equation in a plasmonic waveguide made of nonlinear dielectric material. In this study, the effects of nonlinear self-steepening and Raman scattering are considered. Nonlinear coefficients of phase modulation, Raman and self-steepening are calculated numerically in terms of frequency and compared with a standard silica fiber. Obtained values of the nonlinear coefficients are about up to 300 times larger than that of standard silica optical fibers. So they can be used as part of all optical integrated circuit such as continuum generation, optical switching and frequency conversion.

Guided TE-waves in a slab structure with lossless cubic nonlinear dielectric and magnetic material: parameter dependence and power flow with focus on metamaterials

The parameter dependence and power flow of guided TE-waves in a lossless cubic nonlinear, dielectric, magnetic planar three-layer structure is studied as follows.Using a travelling wave ansatz with stationary amplitude, Maxwell’s equations are transformed to a system of ordinary nonlinear differential equations.The solutions of the system are presented compactly (in terms of hyperbolic and elliptic functions).The nonnegative and bounded (“physical”) solutions are determined by using a phase diagram condition (PDC) that is applied to express the continuity (transmission) conditions at the interfaces leading to the dispersion relation (DR).Based on the PDC, the parameter dependence and stability of the solutions to the DR and corresponding power flow are studied numerically for permittivities and permeabilities that may be appropriate to describe metamaterial.

Solvability of wave propagation with Debye polarization in nonlinear dielectric materials and its finite element methods approximation

In this paper, we consider the wave propagation with Debye polarization in nonlinear dielectric materials. The Rothe's method is employed to derive the well-posedness of the electric fields and the polarized fields by monotonicity theorem as well as the boundedness of the two fields are established. Then, the decoupled full-discrete scheme is established with the first order approximation in time and Raviart-Thomas-Nédélec element k≥2 in spatial. Based on the truncated error, we present the convergent analysis with the order O(Δt+hs) under an a-prior L∞ assumption of numerical solutions. For k=1, we employ the superconvergence technique to ensure the a-prior L∞ assumption. In the end, we give some numerical examples to demonstrate our theories.

Subvacuum effects on light propagation

Subvacuum effects arise in quantum field theory when a classically positive quantity, such as the local energy density, acquires a negative renormalized expectation value. Here we investigate the case of states of the quantized electromagnetic field with negative mean-squared electric field, and their effects on the propagation of light pulses in a nonlinear dielectric material with a nonzero third-order susceptibility. We identify two distinct signatures of the subvacuum effect in this situation. The first is an increase in the speed of the pulse, which is analogous to the superluminal light propagation in gravity which can arise from negative energy density. This increase in speed leads to a phase shift which might be large enough to observe. The second effect is a change in the frequency and power spectra of the pulse. We identify a specific measure of the modified spectra which can signal the presence of a negative mean squared electric field. These ideas are implemented in the particular example of a wave guide filled with a nonlinear dielectric material.

Slow light in a hyperbolic metamaterial waveguide cladded with arbitrary nonlinear dielectric materials

We have demonstrated a hyperbolic metamaterial (HMM) waveguide cladded with arbitrary nonlinear dielectric materials to explore the properties of slow light. The HMM proposed in this paper is assumed as a metal–dielectric stack which can lead to slow light phenomena while being cladded by dielectric materials. Both the asymmetric (i.e., linear–HMM–linear case and nonlinear–HMM–linear case) and symmetric (i.e., linear–HMM–linear case and nonlinear–HMM–nonlinear case) dielectric structures are considered to examine the properties of slow light in the paper. The dispersion relations which are required to investigate the properties of slow light are derived and presented in detail. The results show that the metal filling factor, the dielectric permittivities, and the arbitrary nonlinearity have significantly changed the characteristics of slow light. Parameter dependence of the effects is calculated and discussed.

Pressure and Temperature Study on the Structural Stability of GdNbO4:Eu3+

Lanthanide niobate is an excellent nonlinear optical and high dielectric constant material. However, development and application of these novel properties depend on an understanding of its structural stability. In this work, Raman and luminescence spectra of GdNbO4 with different Eu3+ ions doping concentrations under high pressure and low temperature were obtained. The evolution of Raman spectra indicated that an irreversible structural phase transition of GdNbO4 from monoclinic phase to M′-fergusonite phase occurred at 6.2 GPa, and the phase transition was completed at about 13.1 GPa. An obvious discontinuity on Eu3+ ions luminescence intensity ratio between the 5D0 → 7F2 and the 5D0 → 7F1 transition lines was observed with increasing pressure. The results indicated that the site symmetry of Eu3+ ions in GdNbO4:Eu3+ was changed, which was in agreement with high-pressure Raman spectra data. Meanwhile, Raman and luminescence spectra showed that the crystal structure remained stable in the temperature range...

Nonlinear surface waves in photonic hypercrystals

Photonic crystals and hyperbolic metamaterials are merged to give the concept of photonic hypercrystals. It combines the properties of its two constituents to give rise to novel phenomena. Here the propagation of Transverse Magnetic waves at the interface between a nonlinear dielectric material and a photonic hypercrystal is studied and the corresponding dispersion relation is derived using the uniaxial parallel approximation. Both dielectric and metallic photonic hypercrystals are studied and it is found that nonlinearity limits the infinite divergence of wave vectors of the surface waves. These states exist in the frequency region where the linear surface waves do not exist. It is also shown that the nonlinearity can be used to engineer the group velocity of the resulting surface wave.

Study of band structure of one-dimensional photonic crystal composed of dispersive and nonlinear dielectric materials

The analysis of band structure of one-dimensional (1-D) photonic crystal containing dispersive and non-linear dispersive materials has been presented. The band spectra for the different combination of photonic crystals have been calculated by the well-known plane wave expansion method. The effect of the dispersive and non-linear materials on the band structures has been determined. The third-order nonlinearity has been considered in the non-linear material, and Lorentz–Drude model has been taken for dispersive material. The band gaps of considered photonic crystal are affected by the nonlinearity in the presence of dispersive material like gold. We have observed that the normalized frequency difference between photonic bands decreases on increasing intensity of input beam. This work may be useful in optical switching devices.

Model for lightcone fluctuations due to stress tensor fluctuations

We study a model for quantum lightcone fluctuations in which vacuum fluctuations of the electric field and of the squared electric field in a nonlinear dielectric material produce variations in the flight times of probe pulses. When this material has a non-zero third order polarizability, the flight time variations arise from squared electric field fluctuations, and are analogous to effects expected when the stress tensor of a quantized field drives passive spacetime geometry fluctuations. We also discuss the dependence of the squared electric field fluctuations upon the geometry of the material, which in turn determines a sampling function for averaging the squared electric field along the path of the pulse. This allows us to estimate the probability of especially large fluctuations, which is a measure of the probability distribution for quantum stress tensor fluctuations.

Measuring vacuum polarization with high-power lasers

When exposed to intense electromagnetic fields, the quantum vacuum is expected to exhibit properties of a polarizable medium akin to a weakly nonlinear dielectric material. Various schemes have been proposed to measure such vacuum polarization effects using a combination of high- power lasers. Motivated by several planned experiments, we provide an overview of experimental signatures that have been suggested to confirm this prediction of quantum electrodynamics of real photon–photon scattering.

Metal–organic frameworks for electronics: emerging second order nonlinear optical and dielectric materials

Metal–organic frameworks (MOFs) have been intensively studied over the past decade because they represent a new category of hybrid inorganic–organic materials with extensive surface areas, ultrahigh porosity, along with the extraordinary tailorability of structure, shape and dimensions. In this highlight, we summarize the current state of MOF research and report on structure–property relationships for nonlinear optical (NLO) and dielectric applications. We focus on the design principles and structural elements needed to develop potential NLO and low dielectric (low-κ) MOFs with an emphasis on enhancing material performance. In addition, we highlight experimental evidence for the design of devices for low-dielectric applications. These results motivate us to develop better low-dielectric and NLO materials and to perform in-depth studies related to deposition techniques, patterning and the mechanical performance of these materials in the future.

Discrete gap solitons in nonlinear binary plasmonic waveguide arrays

We investigate plasmonic mode propagation in nonlinear binary plasmonic waveguide arrays composed of two kinds of metal slabs alternately embedded in nonlinear dielectric materials, and numerically obtain soliton solutions with different symmetries. In particular, we find discrete gap solitons with strong transverse confinements reaching the scale of 10 nm. The equations to describe the mode propagations indicate that the system also provides a plasmonic platform to simulate aspects of quantum dynamics.

Global transmission diagrams for evanescent waves in a nonlinear hyperbolic metamaterial

A theoretical model of a nonlinear hyperbolic metamaterial is presented in the form of a stack of subwavelength layers of linear plasmonic and nonlinear dielectric materials. A broad picture of the properties of evanescent waves (high-k modes) in this stack is investigated by plotting global transmission diagrams. The presence of nonlinearity strongly modifies these diagrams. The emergence and modification of nonlinear evanescent waves is observed. Some signatures of nonlinear phenomenon such as formation of orbits and trajectories around fixed points are also seen in our work.

Nonlinear tuning techniques of plasmonic nano-filters

In this paper, a fitting model to the propagation constant and the losses of Metal–Insulator–Metal (MIM) plasmonic waveguide is proposed. Using this model, the modal characteristics of MIM plasmonic waveguide can be solved directly without solving Maxwell's equations from scratch. As a consequence, the simulation time and the computational cost that are needed to predict the response of different plasmonic structures can be reduced significantly. This fitting model is used to develop a closed form model that describes the behavior of a plasmonic nano-filter. Easy and accurate mechanisms to tune the filter are investigated and analyzed. The filter tunability is based on using a nonlinear dielectric material with Pockels or Kerr effect. The tunability is achieved by applying an external voltage or through controlling the input light intensity. The proposed nano-filter supports both red and blue shift in the resonance response depending on the type of the used non-linear material. A new approach to control the input light intensity by applying an external voltage to a previous stage is investigated. Therefore, the filter tunability to a stage that has Kerr material can be achieved by applying voltage to a previous stage that has Pockels material. Using this method, the Kerr effect can be achieved electrically instead of varying the intensity of the input source. This technique enhances the ability of the device integration for on-chip applications. Tuning the resonance wavelength with high accuracy, minimum insertion loss and high quality factor is obtained using these approaches.

Plasmonic bistability in the nonlinear cylindrical metal-dielectric multilayers

We study the nonlinear cylindrical plasmonic waveguide arrays composed of the metal-dielectric multilayers with the Kerr-type nonlinear dielectric materials. The theory of the nonlinear propagation mode is presented and finally expressed as two coupled nonlinear equations with the help of the Lorentz reciprocity theorem. Numerical results demonstrate there exists plasmonic bistability of the propagation modes for a given intensity. This kind of bistability corresponds to the totally different energy distributions in the system, which can be used to develop the applications in the optical switches and optical detectors.

Optimization design of optical waveguide control by nanoslit-enhanced THz field

We discuss design issues of devices which were proposed recently [Opt. Lett. 37 (2012) 3903] for terahertz (THz) control of the propagation of an optical waveguide mode. The mode propagates through a nonlinear dielectric material placed in a metallic nanoslit illuminated by THz radiation. The THz field in the slit is strongly localized and thus significantly enhanced, facilitating nonlinear interactions with the dielectric waveguide material. This enhancement can lead to notable changes in the refractive index of the waveguide. The closer the waveguide is to the slit walls, the higher the nonlinear effects are, but with the cost of increasing propagation losses due to parasitic coupling to surface plasmon polaritons at the metal interfaces. We analyze several optical waveguide configurations and define a figure of merit that allows us to design the optimal configuration. We find that designs with less overlap of the THz and optical fields but also with lower losses are better than designs where both these parameters are higher. The estimated terahertz field incident onto the metallic nanoslit required to manipulate the waveguide mode has reasonable values which can be achieved in practice.

Orders of magnitude enhancement of optical nonlinearity in subwavelength metal-nonlinear dielectric gratings

We show that the optical properties of a metal-nonlinear dielectric grating can be precisely described by a uniform nonlinear dielectric slab. Based upon such a metamaterial mapping, we show that the effective optical nonlinearity in a metal-dielectric grating can be enhanced by orders of magnitude higher than that of the underlying nonlinear dielectric material, is broadband, and can be operated at a low quality-factor regime so as to have an extremely short intrinsic temporal response of a few picoseconds. Furthermore, we demonstrate extraordinary harmonic generation efficiency enhancement and large threshold-power reduction in bistability.

Nonlinear dielectric thin films for high-power electric storage with energy density comparable with electrochemical supercapacitors

Although batteries possess high energy storage density, their output power is limited by the slow movement of charge carriers, and thus capacitors are often required to deliver high power output. Dielectric capacitors have high power density with fast discharge rate, but their energy density is typically much lower than electrochemical supercapacitors. Increasing the energy density of dielectric materials is highly desired to extend their applications in many emerging power system applications. In this paper, we review the mechanisms and major characteristics of electric energy storage with electrochemical supercapacitors and dielectric capacitors. Three types of in-house-produced ferroic nonlinear dielectric thin film materials with high energy density are described, including (Pb(0.97)La(0.02))(Zr(0.90)Sn(0.05)Ti(0.05))O(3) (PLZST) antiferroelectric ceramic thin films, Pb(Zn(1/3)Nb(2/3))O(3-)Pb(Mg(1/3)Nb(2/3))O(3-)PbTiO(3) (PZN-PMN-PT) relaxor ferroelectric ceramic thin films, and poly(vinylidene fluoride) (PVDF)-based polymer blend thin films. The results showed that these thin film materials are promising for electric storage with outstandingly high power density and fairly high energy density, comparable with electrochemical supercapacitors.