Nonlinear Refractive Index Changes Research Articles

Diffraction patterns and nonlinear optical properties of Nanocomposite (Gold nanoparticles / Epoxy resin polymer)

We observed and analyzed diffraction rings produced by CW Nd: YAG visible laser beam in a nanocomposite of gold nanoparticles doped by epoxy resin polymer. Change of refractive index, Δn, and nonlinear refractive index, n2 were calculated based on the number of rings observed. A thermal effect is due to this major nonlinearity. With rising input power and sample thickness the number of rings increases. Spot diameter of rings was calculated and noted it increase wih input power increasing and decreasing thickness of sample.

Theoretical modeling of inter-sublevel optical properties of a ZnSe/ZnSxSe1-x and ZnSe/ZnSxSe1-x/ZnS core/shell and core/shell/shell quantum dot

In this work, we have modelling a ZnSe/ZnSxSe1-x and ZnSe/ZnSxSe1-x/ZnS core/shell and core/shell /shell quantum dot (QDs) respectively in the intent to study the effect of the second shell ZnS on the electronic and optical properties. To solve the three dimensional Schrödinger equation, we have used a theoretical method which is combined the coordinate transformation and the finite difference method (FDM). We have evaluated the influence of ZnS shell material, first on the energy eigenvalues and on the transition lifetime, then on the linear, non-linear and total absorption coefficient and refractive index changes. The first linear and third order nonlinear susceptibilities are also investigated.

Nonlinear Optical Investigation of Microbial Chromoproteins.

Membrane-bound or cytosolic light-sensitive proteins, playing a crucial role in energy- and signal-transduction processes of various photosynthetic microorganisms, have been optimized for sensing or harvesting light by myriads of years of evolution. Upon absorption of a photon, they undergo a usually cyclic reaction series of conformations, and the accompanying spectro-kinetic events assign robust nonlinear optical (NLO) properties for these chromoproteins. During recent years, they have attracted a considerable interest among researchers of the applied optics community as well, where finding the appropriate NLO material for a particular application is a pivotal task. Potential applications have emerged in various branches of photonics, including optical information storage and processing, higher-harmonic and white-light continuum generation, or biosensorics. In our earlier work, we also raised the possibility of using chromoproteins, such as bacteriorhodopsin (bR), as building blocks for the active elements of integrated optical (IO) circuits, where several organic and inorganic photonic materials have been considered as active components, but so far none of them has been deemed ideal for the purpose. In the current study, we investigate the linear and NLO properties of biofilms made of photoactive yellow protein (PYP) and bR. The kinetics of the photoreactions are monitored by time-resolved absorption experiments, while the refractive index of the films and its light-induced changes are measured using the Optical Waveguide Lightmode Spectroscopy (OWLS) and Z-scan techniques, respectively. The nonlinear refractive index and the refractive index change of both protein films were determined in the green spectral range in a wide range of intensities and at various laser repetition rates. The nonlinear refractive index and refractive index change of PYP were compared to those of bR, with respect to photonics applications. Our results imply that the NLO properties of these proteins make them promising candidates for utilization in applied photonics, and they should be considered as valid alternatives for active components of IO circuits.

Effects of external electric and magnetic fields on the linear and nonlinear optical properties of InAs cylindrical quantum dot with modified Pöschl-Teller and Morse confinement potentials

The theoretical investigation of linear and third-order nonlinear absorption coefficients and refractive index changes in the cylindrical quantum dot with two models of confinement potentials in axial direction, namely, modified Pöschl-Teller and Morse potentials, and parabolic potential in radial direction, have been considered in the presence of external electric and magnetic fields. The selection rules for intraband transitions have been obtained for both potentials in the presence and absence of external fields. The behavior of linear, nonlinear and total absorption spectra have been observed for different values of temperatures for both potentials taking into account electron population on energy levels. The effect of change in the direction of electric field on the absorption spectra have been investigated, and the asymmetric and symmetric characters of these potentials manifest themselves differently: the peak positions of absorption lines for Morse potential undergo blue and red shifts compared to the case when the external electric field is absent, while for the case of modified Pöschl-Teller potential the absorption lines have only red shift. The same dependencies have been obtained for refractive index changes for both potentials. The second and third harmonic generation coefficients as a function of the photon energy have been plotted both in the absence and presence of external fields.

Exciton effect on the linear and nonlinear optical absorption coefficients and refractive index changes in Morse quantum wells with an external electric field

Previously, much work on nonlinear optical effects in Morse quantum wells (MQWs) was based on electronic state transitions. However, exciton effect in MQWs is neglected and needs to be considered due to its great significance in determining nonlinear optical effects. Here, the variational method and the diagonalization method are utilized to acquire excitonic states in AlxGa1−xAs/GaAs MQWs. The exciton effect in MQWs induces an obvious enhancement of the linear and nonlinear optical absorption coefficients (OACs) and refractive index changes (RICs). The linear and nonlinear OACs and RICs are dynamically manipulated through tuning the electric field, and even are suppressed under a strong electric field. In addition, the linear and nonlinear OACs and RICs in MQWs are strongly affected by the hole mass, the width parameter and the aluminum concentration, which provides direction for obtaining desired nonlinear optical effects.

Consequences of dielectric mismatch on linear and third order nonlinear optical properties for CdS/ZnSe core/shell QD-matrix

In this work, we have performed a detailed investigation on optical properties for CdS/ZnSe spherical core/shell quantum dots surrounded by various dielectric matrices such as PVA, PMMA and SiO2. The wave functions and eigenenergies of confined electrons have been theoretically computed using the effective-mass formalism and the density matrix approach. The linear and third-order nonlinear optical properties have been evaluated for different matrices. Our results demonstrated that the linear, third order nonlinear optical absorption coefficients and refractive index changes are considerably sensitive to the geometrical parameters, the incident optical intensity and the dielectric environment.

Nonlinear optical absorption coefficient and refractive index change in symmetric semiconductor nanostructures: Comparison between different methods

Abstract We present a systematic study of the optical absorption coefficient (OAC) and refractive index change (RIC) for a symmetric semiconductor nanostructure. We derived the OAC and RIC following two approaches, one without approximations, besides the usual ones (rotating-wave approximation and application of a two-level model), and the other using an approximation keeping only the contribution of the linear and third-order nonlinear terms. In the derivation we consider properly the contribution of the population decay time and the dephasing time, which may be different to each other, in general, in semiconductor nanostructures, extending previous works. We also apply the derived formulae for the calculation of the OAC and RIC in a specific semiconductor quantum well with position-dependent mass and compared the results obtained from the derived formulae. We find that while for low light intensities the different formulae for OAC and RIC give similar results for higher light intensities only the formulae obtained without approximations can lead to correct physical results. We also present a critical intensity below which the different formulae for OAC and RIC give practically the same results. This critical intensity can be used for obtaining correct behavior for the OAC and RIC in any symmetric semiconductor nanostructure.

Electrodynamics of conductive oxides: Intensity-dependent anisotropy, reconstruction of the effective dielectric constant, and harmonic generation

We study electromagnetic pulse propagation in an indium tin oxide nanolayer in the linear and nonlinear regimes. We use the constitutive relations to reconstruct the effective dielectric constant of the medium, and show that nonlocal effects induce additional absorption resonances and anisotropic dielectric response: longitudinal and transverse effective dielectric functions are modulated differently along the propagation direction, and display different epsilon-near-zero crossing points with a discrepancy that increases with increasing intensity. We predict that hot carriers induce a dynamic redshift of the plasma frequency and a corresponding translation of the effective nonlinear dispersion curves that can be used to predict and quantify nonlinear refractive index changes as a function of incident laser peak power density. Our results suggest that large, nonlinear refractive index changes can occur without the need for epsilon-near-zero modes to couple with plasmonic resonators. At sufficiently large laser pulse intensities, we predict the onset of optical bistability, while the presence of additional pump absorption resonances that arise from longitudinal oscillations of the free electron gas give way to corresponding resonances in the second and third harmonic spectra. A realistic propagation model is key to unraveling the basic physical mechanisms that play a fundamental role in the dynamics.

High-Speed Plasmonic-Silicon Modulator Driven by Epsilon-Near-zero Conductive Oxide

Transparent conductive oxides (TCOs) such as indium-tin oxide (ITO) have attracted increasing interests in integrated photonics and silicon photonics, owing to their large plasma dispersion and epsilon-near-zero (ENZ) effect. The nonlinear change of refractive index induced by free carrier modulation leads to a large electro-optic modulation with ultra-compact device footprint and unprecedented energy efficiency. However, high-speed modulation result is rare, mainly due to the lack of high-speed device design and fabrication quality. In this article, we characterize the fundamental electro-optic modulation structure consisting of Au/ITO/oxide/p-Si capacitor, showing that the property of ITO is greatly affected by the process condition. We also report an 8-μm-long hybrid plasmonic-silicon modulator driven by an ENZ ITO capacitor, achieving 100fJ/bit energy efficiency, 3.5 GHz modulation bandwidth, and 4.5 Gb/s data rate. The electro-absorption modulator covers a broad optical bandwidth from 1515 to 1580 nm wavelength. For future development of such modulators, we point out that by replacing ITO with higher mobility TCO materials, we can achieve 40 GHz modulation bandwidth and 0.4 fJ/bit energy efficiency using a 3-μm-long device.

Nonlinear optical properties of semiconductor double quantum wires coupled to a quantum-sized metal nanoparticle

We theoretically investigate linear and nonlinear optical absorption coefficients (OACs) and refractive index changes (RICs) of two quantum wires (QWs) separated by a quantum-sized metal nanoparticle (MNP) using a density matrix method and dielectric quantum theory. The exciton-plasmon coupling and the dipole-dipole interaction (DDI) between the two QWs are taken into account. We find that the magnitudes of the linear and nonlinear OACs (RICs) from the QWs are enhanced by one order of magnitude, in contrast to the case without a MNP, due to the exciton-plasmon coupling and the DDI between the two QWs. The quantum size effect in a MNP induces a pronounced enhancement in the magnitudes of the linear and nonlinear OACs (RICs) with the increase of the MNP radius. Furthermore, the optical responses can be further strengthened via increasing the MNP radius or decreasing the radius and gap of the QWs, owing to the enhanced exciton-plasmon coupling and the DDI between the two QWs. Moreover, the magnitudes of the total OACs (RICs) are reduced by increasing the optical intensity, along with a splitting effect of the OACs under strong optical intensity. Our results provide the possibility of designing the hybrid nanostructures with large nonlinearity for applications in nano-devices such as optical switches and amplifiers.

Modulational instability in oppositely doubled-doped directed couplers with a non-kerr-like nonlinear refractive-index change

We theoretically investigate modulation instability (MI) in a two-core nonlinear oppositely directed coupler with a negative-index material channel in the presence of a non-kerr-like nonlinear refractive-index change. Using linear stability analysis, we obtain an expression for the instability gain. It is found that the MI in the nonlinear two-core oppositely directed coupler is significantly influenced by the ratio of the forward- to backward-propagating wave power, nonlinearity, power and saturation. In the normal dispersion regime, the septic nonlinearity is found to suppress the MI by reducing both the gain and width of the instability nonlinearity. But in anomalous dispersion regime, the situation is different because septic nonlinearity enhances the MI by increasing both the gain and width of MI. The increase of septic nonlinearity both in normal and anomalous dispersion regimes increases the gain of the instability nonlinearity. Thus, we report new ways to generate and manipulate the MI and solitons in two-core oppositely directed couplers with a particular emphasis on a negative-index material (NIM) channel in presence of septic nonlinearity.

Impurity related optical properties in tuned quantum dot/ring systems

ABSTRACTIn this paper, we explore the linear, third-order nonlinear, and total optical absorption coefficient (OAC) and refractive index change coefficient (RICC) of a GaAs doped quantum dot/quantum ring (QD/QR) with parabolic-inverse squared potential in conjunction with modified Gaussian confinement and taking into account the presence of on-centre shallow donor and or acceptor impurity. Calculations are done via the compact density matrix formalism and the iterative method. The two-dimensional parabolic QD/QR is subjected to uniform magnetic field oriented perpendicularly to the plane of the structure. The energy levels and wave function are derived within the framework of effective-mass and parabolic band approximation. The results exhibit that the OACs and RICC are clearly affected by different parameters of the applied confinement, strength of magnetic field, and the presence of impurity. The variation of confinement potential, nature of impurity, dot radius, cyclotron frequency of the parabolic confinement potential, and geometric parameter of the on-centre repulsive potential lead to either a red-shift or a blue-shift of the resonant peaks of the OACs and of the maximum and minimum of the RICC together with significant variations of the magnitudes of these resonant structures.

Optical properties of an exciton trapped by an ionized donor in ellipsoidal quantum dots under electric field and hydrostatic pressure

The optical properties of an exciton trapped by an ionized donor in an ellipsoidal quantum dot (QD) with both oblate and prolate shapes under applied electric field and hydrostatic pressure have been studied. We have calculated the linear and third-order nonlinear absorption coefficients (ACs) and refractive index changes (RICs) by using a variational method within the perturbation theory. The results show that the QD shape and size have a significant influence on the positions and magnitudes of the peaks of the (ACs) and RICs, moreover, the influence of hydrostatic pressure and electric field under different QD shape is also different.

Non-linear optical properties of nanoscale elliptical ring-shaped at the presence of Rashba spin–orbit interaction and magnetic field

The significant information about the properties of matter can be described with the interaction between light and matter. On this subject, the effect of the applied magnetic field and structural variation on the optical properties of elliptical and circular GaAs quantum rings at the existence of Rashba spin–orbit interaction (RSOI) have been investigated. The effective mass equation for the system containing RSOI and magnetic flux has been solved in cylindrical coordinate with Matrix Diagonalization method for circular quantum ring and with finite difference method for elliptical quantum ring. Also, the linear and third-order nonlinear optical absorption coefficient (AC) and refractive index changes (RIC) are calculated by density matrix. According to the consequence, the geometry of quantum structure plays a significant role in specifying the AC and RIC which provide the methods for fabricating effective application.

Microcavity-enhanced Kerr nonlinearity in a vertical-external-cavity surface-emitting laser.

Self-mode-locking has become an emerging path to the generation of ultrashort pulses with vertical-external-cavity surface-emitting lasers. In our work, a strong Kerr nonlinearity that is so far assumed to give rise to mode-locked operation is evidenced and a strong nonlinearity enhancement by the microcavity is revealed. We present wavelength-dependent measurements of the nonlinear absorption and nonlinear refractive index change in a gain chip using the Z-scan technique. We report negative nonlinear refraction up to 5x10-12cm2/W in magnitude in the (InGa)As/Ga(AsP) material system close to the laser design wavelength, which can lead to Kerr lensing. We show that by changing the angle of incidence of the probe beam with respect to the gain chip, the Kerr nonlinearity can be wavelength-tuned, shifting with the microcavity resonance. Such findings may ultimately lead to novel concepts with regard to tailored self-mode-locking behavior achievable by peculiar Kerr-lens chip designs for cost-effective, robust and compact fs-pulsed semiconductor lasers.

Nonlinear absorption coefficient and refractive index changes of two-dimensional two-electron quantum dot in rigid confinement

The Hamiltonian and wavefunctions describing two-dimensional (2D) two-electron ZnO quantum dot in rigid confinement are developed. Then the Schrödinger equation is solved analytically and numerically for determining the ground and excited state energies. The ground state energy of 2D two-electron ZnO quantum dot (QD) in rigid confinement is studied using perturbation and variational methods. The obtained result show that our trial wavefunction is good enough to describe the 2D two-electron QD in rigid confinement. The wavefunction describing the ground state is the combination of symmetric spatial wavefunction and antisymmetric spin wavefunction which is a para-state. The ground state energy eigenvalue obtained by variational technique is a little above that of a perturbation technique. Based on this; the trial wavefunction for the excited state is developed. The excited state energy of 2D two-electron ZnO QD in rigid confinement is studied computationally using variational method. The wavefunction describing the excited state is the combination of symmetric spatial wavefunction with antisymmetric spin wavefunction (para-state) or vice versa (ortho-state). The para and ortho-state energies of the first excited state are calculated and their difference is twice of the exchange energy. Based on the obtained energy eigenvalues of the ground and the first excited state at the value of the coupling constant [Formula: see text] [Formula: see text] 1, the third-order nonlinear absorption coefficient and refractive index changes are investigated. The optical transition is only considered between the two lowest para states.

The nonlinear optical properties of GaAs-based quantum wells with Kratzer–Fues confining potential: Role of applied static fields and non-resonant laser radiation

In the present paper, we report a theoretical investigations on the linear and nonlinear optical properties of a GaAs-based quantum well with the Kratzer-Fues confining potential, including the effects of external applied static electric, magnetic, and intense THz laser fields. The electronic structure of this system is obtained by using the effective-mass and envelope wave function approaches. Then, the coefficients of linear, third-order nonlinear, and total optical absorption (OACs) and relative refractive index changes (RICs) are calculated by using the iterative solutions of the compact-density matrix approach (CDMA). The obtained numerical results are reported as functions of the incident photon energy taking into account several values of static electric, static magnetic, and intense THz laser fields. These results show that the nonlinear optical properties of this structure are significantly affected by the magnitude of the external applied fields.

Nonlinear optical properties of a semi-exponential quantum wells: Effect of high-frequency intense laser field

In this present work, the effect of non-resonant, mono-chromatic intense laser field (ILF) on the linear and nonlinear optical properties of a semi-exponential quantum well (SEQW) is investigated theoretically within the effective-mass and envelope wave function approach. The bound subband energy levels and their envelope wave functions of the structure are calculated by using the diagonalization method. The optical properties of the system are obtained by using the compact-density matrix approach. The obtained numerical results show that the applied ILF and structure parameters have a significant impact on the optical properties of these structures, such as the linear, third-order nonlinear and total absorption coefficients and relative refractive index changes. Furthermore, from the findings of this study, it has been concluded that the linear and nonlinear optical properties in a SEQW under the ILF can be tuned by changing structure parameters, such as the effective range and depth of the system.

Characterization of nonlinear optical refractive index for graphene oxide–silicon oxide nanohybrid composite

In this work, Silicon oxide (SiO2) nanoparticles, graphene oxide nanosheet (GO) and GO–SiO2 nanohybrid composites have been synthesized. The role of GO concentration in the starting solution was investigated and correlated to the morphological, structural and optical properties of the studied samples. The structural studies for nanohybrid composites showed that by increasing GO:weight ratio from 0.5 to 2.0, not only does the SiO2 crystalline phase change from cubic to orthorhombic, but the structure of GO also transformed to RGO. The related FESEM images indicate that GO sheets are well-covered by SiO2 nanoparticles with very small grain size and that the accumulation of nanoparticles on each sheet has a high density. Linear Optical measurements showed two optical band gaps of [Formula: see text][Formula: see text]eV and 5.3[Formula: see text]eV for SiO2 nanoparticles, and band gap value of 4.15[Formula: see text]eV for GO nanosheets, which it reduces to 3.3[Formula: see text]eV after formation of the nanohybrid composite with GO: SiO2 weight ratio of 2.0. The nonlinear optical properties of GO–SiO2 with different weight ratio are measured using Z-scan technique. The results showed that the nonlinear refractive index of SiO2 and GO nanoparticles and nanohybrid composite (0.5:1,1:1,2:1) ([Formula: see text]–[Formula: see text]) changed and has a negative sign. It was observed that the nonlinear refractive index changes in different ratios of compounds. Experimental results show that after the formation of the composite, the nonlinear refractive index shows a significant increase in the presence and effectiveness of the GO.

Numerical modelling of electronic and optical properties of isolated and self-assembled InAs/InP quantum dots

In the present work, we are interested for an isolated and self-assembled InAs/InP quantum dots with a dome cross-section. We have tried to study the electronic and optical properties in the quantum dot by using an efficient and simple method. This numerical method is based on the coordinate transformation and the finite difference method (FDM). The influence of the parameters introduced in the mathematical function, is studied on the size, the shape and the number of the quantum dot. The electron, and heavy hole energy levels as well as their interband transition energies are also investigated. The linear, third-order nonlinear and total interband optical absorption coefficients and refractive index changes are investigated as a function of photon energy with varying height dot (H) and the incident optical intensity (I). The analytical expressions of these optical properties are obtained by using the compact-density matrix formalism.