Nonlinear Refractive Index Changes Research Articles

Intense laser field-induced nonlinear optical properties of Morse quantum well

Abstractauthoren This paper investigates the effects of an intense laser field and electric field on the optical properties of quantum well represented by Morse potential. The non-resonant, high-frequency intense laser effects upon the system are treated within the framework of non-perturbative approach, modifying the confinement potential associated to the heterostructure. The analytical expressions of the linear and third-order nonlinear optical absorption coefficients and refractive index changes are obtained by using the compact-density matrix formalism. The results for a typical GaAs quantum well correspond to several configurations of the structural parameter, the strengths of the intense laser radiation, and the static electric field. Numerical results reveal the striking influence of the external fields on the magnitude and resonant peak energy positions of the optical absorption coefficients and refractive index changes. Besides, the control of intersubband optical transitions by the structure parameter seems feasible.

Linear and nonlinear optical absorption coefficients and refractive index changes in Morse quantum wells under electric field

In this paper, we investigate theoretically the effects of electric field on the linear and nonlinear optical properties of Morse quantum wells considering a two-level system. The effective mass approximation and the envelope function approach are used to calculate the energy levels and wave functions. The analytical expressions of the optical properties are obtained by using the compact density-matrix approach. The linear and third-order nonlinear optical absorption coefficients and the refractive index changes are investigated as a function of the incident photon energy for several configurations of the structural parameter and the applied electric field. Numerical results, presented for a typical GaAs/AlGaAs quantum well, reveal that the electric field has a significant effect on the optical characteristics of these structures and intersubband transitions can be modified by tuning the structural range parameter of the potential.

Effects of applied electric fields on optical responses in elliptical quantum nanosystems

The optical absorption response of an elliptical quantum-dot-type nanostructure is investigated by numerically determining the electron states within the effective mass and parabolic approximations via the finite element method, taking into account the effect of an externally applied electric field. Validation of the numerical procedure is discussed through the comparison with analytical results of previous works for zero external field conditions. For finite field, the comparison is made with the outcome of degenerate perturbation theory. The calculated electron energies and wavefunctions are used to evaluate the linear and nonlinear light absorption and refractive index change coefficients in the system. Their corresponding expressions are those typically derived within a perturbative approach for solving the density matrix equation of motion. It is shown how the electric field and the change in the elliptical geometry affect the optical response of the considered structures. The extension of the treatment to consider the properties of elliptic nanoparticles under external field influences is briefly discussed.

Donor-impurity-related optical absorption and refractive index changes in GaAs/AlGaAs core/shell spherical quantum dots

In this study, the linear and nonlinear intersubband optical absorption coefficients (OACs) and refractive index changes (RICs) in GaAs/AlGaAs core/shell spherical quantum dots (QDs) are theoretically investigated within the framework of the compact-density-matrix approach and iterative method for both cases with and without on-center impurity. The energy eigenvalues and their corresponding eigenfunctions of the system are calculated by using the differential method. Our results show that the position and the magnitude of the resonant peaks of the nonlinear OACs and RICs depend strongly on the hydrogenic impurity and QDs radius. It was found that the total OACs indicates saturation at sufficiently high incident intensities. Also we found that the binding energy of the ground and excited states of the impurity depend on the QDs radius.

Linear and nonlinear optical properties in spherical quantum dots: Manning-Rosen potential

In this work, we studied the optical properties of spherical quantum dots confined in Manning-Rosen potential with the appropriate centrifugal term included. The approximate solution of the bound state and wave functions were obtained from the Schrodinger wave equation by applying the standard methods. Also, we have used the density matrix formalism to investigate the linear and third-order nonlinear absorption coefficient and refractive index changes.

Study of molecular aggregation effects on the nonlinear refractive index and absorption of Oxazin 720 laser dye

In this experimental work, nonlinear optical properties of Oxazine 720 laser dye in acetone, dimethyl sulfoxide, ethanol, and water were studied using the z-scan method. It is found that the nonlinear behavior of Oxazine 720 dye in water is different from other organic solvents. The magnitude of the nonlinear refractive index was obtained in the order of 10−8 and 10−7 cm2/W for the 0.2 mmol/L solutions of this dye in water and other solvents, respectively. Also, it was observed that, in the aqueous solution, reverse saturation absorption occurs while, in other organic solvents, saturation absorption occurs and, near the focal point of the lens, it is converted to reverse saturation absorption. These differences in the nonlinear refractive index and nonlinear absorption changes of aqueous solution and other solutions may be due to strong aggregative behavior of dye molecules in water.

Effect of the shape of quantum dots on the refractive index changes

We have intensively studied the influence of the shape of quantum dots on the refractive index changes. Within the framework of the effective-mass approximation, numerical results are performed by means of calculation methods of the compact-density-matrix and the matrix diagonalization. We analyze the properties of the linear, third-order nonlinear and total refractive index changes (RICs) as a function of the incident photon energy in circular, elliptic, and triangular shaped quantum dots. The results show that the shape of quantum dots has a significant impact on the refractive index changes.

Linear and Nonlinear Optical Properties in Spherical Quantum Dots: Generalized Hulthén Potential

In this work, we studied the optical properties of spherical quantum dots confined in Hulthen potential with the appropriate centrifugal term included. The approximate solution of the bound state and wave functions were obtained from the Schrodinger wave equation by applying the factorization method. Also, we have used the density matrix formalism to investigate the linear and third-order nonlinear absorption coefficient and refractive index changes.

Rashba spin–orbit interaction effect on the optical properties of a disk-like quantum dot

Using the density matrix approach and iterative method, we have theoretically investigated the optical properties of a disk-like quantum dot (QD) with hard-wall confining potential subjected to an external static magnetic field in the presence of a Rashba spin–orbit interaction. The results of numerical calculations for the typical InAs QD show that the linear, nonlinear and total absorption coefficients (ACs) and refractive index (RI) changes are sensitive to the parameters of the magnetic field and dot size. Moreover, the resonance peaks of ACs and RI changes redshift when increasing the Rashba spin–orbit interaction strength. The role of this interaction as a control parameter on the ACs and RI changes has been demonstrated in detail.

Rashba spin-orbit coupling effects on the optical properties of double quantum wire under magnetic field

We investigate the effects of Rashba spin-orbit interaction on the optical absorption coefficients and refractive index changes associated with transitions between the first two lower-lying electronic levels in double quantum wire. The wire system represented by a symmetric, double quartic-well confinement potential is subjected to a perpendicular magnetic field. The analytical expressions of the linear and third-order nonlinear optical absorption coefficients and refractive index changes are obtained by using the compact-density matrix formalism and iterative scheme. Optical properties are investigated as a function of structural parameter, magnetic field, Rashba spin-orbit interaction and photon energies. Numerical results reveal that competing effects between spin-orbit interaction and magnetic field modify strongly the optical properties and can be altered by these parameters.

Optical properties of double quantum wires under the combined effect of spin-orbit interaction and in-plane magnetic field

In this work, we investigate the intersubband optical absorption coefficients and refractive index changes for transitions between the lower-lying electronic levels of double quantum wires formed by a symmetric, double quartic-well potential. The system is subjected to an external in-plane magnetic field and Rashba and Dresselhaus spin-orbit couplings are taken into account. The analytical expressions of the linear and nonlinear absorption coefficients and refractive index changes are obtained by using the compact density-matrix approach and iterative method. The dependence of the optical characteristics on the magnetic field, spin-orbit interactions, quantum wire radius, structural parameter and photon energies has been examined. Numerical results exhibit that the optical properties are considerably sensitive to the strength and orientation of magnetic field as well as to the spin-orbit couplings and thus can be controlled by these parameters.

Optical response of a two dimensional quantum ring in presence of Rashba spin orbit coupling

The influence of Rashba spin orbit interaction on the optical properties of two dimensional mesoscopic ring has been investigated in the presence of uniform perpendicular magnetic field. The Schrodinger equation for the Rashba coupled system is solved by effective mass approximation and diagonalization technique. Using the calculated energies and eigenfunctions, the laser field induced change in refractive index and optical absorption have been studied under the density matrix formalism. It has been found that Rashba spin orbit interaction removes the intersection of energy levels; however, avoided crossings are observed at finite magnetic field. At sufficient high values of Rashba coupling or laser intensity, the optical response of quantum ring is found to be dominated by third order nonlinear term. Also, Rashba interaction shifts the value of magnetic field that is needed to suppress the absorption drastically and to pass the incident light unattenuated. The results reveal that the geometry of the ring plays an important role in determining the magnitude of nonlinear absorption coefficient and change in refractive index which enable us to design the device with optimum efficiency.

Effect of Si δ-Doping on the Linear and Nonlinear Optical Absorptions and Refractive Index Changes in InAlN/GaN Single Quantum Wells**Supported by the Deanship of Scientific Research of University of Dammam under Grant No 2015134.

In the framework of effective mass approximation, we theoretically investigate the electronic structure of the Si δ-doped InAlN/GaN single quantum well by solving numerically the coupled equations Schrödinger–Poisson self-consistently. The linear, nonlinear optical absorption coefficients and relative refractive index changes are calculated as functions of the doping concentration and its thickness. The obtained results show that the position and the amplitude of the linear and total optical absorption coefficients and the refractive index changes can be modified by varying the doping concentration and its thickness. In addition, it is found that the maximum of the optical absorption can be red-shifted or blue-shifted by varying the doping concentration. The obtained results are important for the design of various electronic components such as high-power FETs and infrared photonic devices.

Plasmon-soliton waves in planar slot waveguides. I. Modeling

We present two complementary models to study stationary nonlinear solutions in one-dimensional plasmonic slot waveguides made of a finite-thickness nonlinear dielectric core surrounded by metal regions. The considered nonlinearity is of focusing Kerr type. In the first model, it is assumed that the nonlinear term depends only on the transverse component of the electric field and that the nonlinear refractive index change is small compared to the linear part of the refractive index. This first model allows us to describe analytically the field profiles in the whole waveguide using Jacobi elliptic special functions. It also provides a closed analytical formula for the nonlinear dispersion relation. In the second model, the full dependency of the Kerr nonlinearity on the electric-field components is taken into account and no assumption is required on the amplitude of the nonlinear term. The disadvantage of this approach is that the field profiles must be computed numerically. Nevertheless, analytical constraints are obtained to reduce the parameter space where the solutions of the nonlinear dispersion relations are sought.

The effect of hydrostatic pressure, temperature and magnetic field on the nonlinear optical properties of asymmetrical Gaussian potential quantum wells

In this study, simultaneous effects of hydrostatic pressure, temperature and magnetic field on the linear and nonlinear intersubband optical absorption coefficients (OACs) and refractive index changes (RICs) in asymmetrical Gaussian potential quantum wells (QWs) are theoretically investigated within the framework of the compact-density-matrix approach and iterative method. The energy eigenvalues and their corresponding eigenfunctions of the system are calculated with the differential method. Our results show that the position and the magnitude of the resonant peaks of the nonlinear OACs and RICs depend strongly on the hydrostatic pressure, temperature and external magnetic field. This gives a new degree of freedom in various device applications based on the intersubband transitions of electrons.

Enhanced nonlinear interaction in a microcavity under coherent excitation.

The large field enhancement that can be achieved in high quality factor and small mode volume photonic crystal microcavities leads to strengthened nonlinear interactions. However, the frequency shift dynamics of the cavity resonance under a pulsed excitation, which is driven by nonlinear refractive index change, tends to limit the coupling efficiency between the pulse and the cavity. As a consequence, the cavity enhancement effect cannot last for the entire pulse duration, limiting the interaction between the pulse and the intra-cavity material. In order to preserve the benefit of light localization throughout the pulsed excitation, we report the first experimental demonstration of coherent excitation of a nonlinear microcavity, leading to an enhanced intra-cavity nonlinear interaction. We investigate the nonlinear behavior of a Silicon-based microcavity subject to tailored positively chirped pulses, enabling to increase the free carrier density generated by two-photon absorption by up to a factor of 2.5 compared with a Fourier-transform limited pulse excitation of equal energy. It is accompanied by an extended frequency blue-shift of the cavity resonance reaching 19 times the linear cavity bandwidth. This experimental result highlights the interest in using coherent excitation to control intra-cavity light-matter interactions and nonlinear dynamics of microcavity-based optical devices.

Nonlinearity of Semiconductor Mach-Zehnder Modulator for Flat Optical Frequency Comb

Optical frequency combs (OFCs) generated by an InP-based semiconductor Mach-Zehnder modulator (MZM) are numerically investigated. Nonlinear phase modulation induced by drive voltages applied to the MZM prove to be useful in obtaining a flat OFC. The experimentally measured intensity deviations of OFCs reported previously are quantitatively reproduced using a numerical model considering nonlinear change of refractive index and optical absorption induced by the drive voltages applied to the MZM. It is found that such nonlinearities generate a flat nine-channel (9-ch) OFC with an intensity deviation of <1 dB when a moderate RF drive voltage of <5 V is used. This flat 9-ch OFC is sustained regardless of the ratio of RF drive voltages of two arms in the MZM. Conversion efficiency is reasonably high (27%), but it is decreased by optical absorption and extinction losses in the MZM.

Excitonic effects on linear and nonlinear optical absorption coefficients and refractive index changes in one-dimensional quantum dots with linear potential

Excitonic effects on linear and nonlinear optical absorption coefficients (OAC) and refractive index changes (RIC) in one-dimensional quantum dots with linear potential are theoretically investigated within the framework of the compact-density-matrix approach and iterative method. It is found that linear and nonlinear OAC and RIC with excitonic effects in one-dimensional quantum dots are larger than that without excitonic effects. Besides, when excitonic effects are considered, our results show a remarkable dependence of linear and nonlinear OAC and RIC on linear potential.

The effects of pressure and hydrogenic donor impurity on the linear and nonlinear optical properties of a GaAs/GaAlAs nanowire superlattice

The combined effects of hydrostatic pressure, presence and absence of hydrogenic donor impurity are investigated on the linear and nonlinear optical absorption coefficients and refractive index changes of a GaAs/Ga1−xAlxAs nanowire superlattice. The wave functions and corresponding eigenvalues are calculated using finite difference method in the framework of effective mass approximation. Analytical expressions for the linear and third order nonlinear optical absorption coefficients and refractive index changes are obtained by means of compact-density matrix formalism. The linear and third order nonlinear absorption coefficient and refractive index changes are presented as a function of photon energy for different values of hydrostatic pressure, incident photon intensity and relaxation time in the presence and absence of hydrogenic donor impurity. It is found that the linear and third order nonlinear absorption coefficients, refractive index changes and resonance energy are quite sensitive to the presence of impurity and applied hydrostatic pressure. Moreover, the saturation in optical spectrum and relaxation time can be adjusted by increasing pressure in presence of impurity whereas the effect of hydrostatic pressure is negligible in the case of absence of hydrogenic impurity.

Linear and nonlinear optical properties in asymmetric double semi-V-shaped quantum well

In this present work, the effects of the structure parameters such as the right-well width and the right-barrier height on the linear, third-order nonlinear and total absorption and refractive index changes of asymmetric double semi-V-shaped quantum well are theoretically studied by using the compact-density matrix approach and iterative method. The electronic structure of this system is obtained by solving Schrödinger equation within the framework of effective mass approximation. Numerical results are presented for a typical GaAs/AlxGa1-xAs asymmetric double semi-V-shaped quantum well. The obtained results show that the right-well width and the right-barrier height have great effects on the optical characteristics of these structures.