Total Refractive Index Research Articles

Magneto‐optical specifications of Rosen‐Morse quantum dot with screw dislocation

AbstractThis is the first study to consider a quantum dot with screw dislocation that has Rosen‐Morse (RM) confinement potential, generated by a GaAs/GaAlAs heterostructure. An external magnetic field and Aharonov‐Bohm (AB) flux field were also applied on RM quantum dot (RMQD) in order to stave the effects of a screw dislocation defect. The combined effect of the screw dislocation defect, the external magnetic field, and AB flux field on the total refractive index changes (TRICs) and the total absorption coefficients (TACs) of RMQD are thus investigated. Cylindrical coordinates are used due to the direction of application of the torsion and the external fields, as well as due to the structure's symmetry. The effective mass approximation and tridiagonal matrix methods are used in order to obtain the subband energy spectra and electronic wave functions of RMQD. The nonlinear optical specifications of RMQD are checked using compact‐density‐matrix formalism within the framework of the iterative method. Reviews without screw dislocation are also carried out in order to be able to clarify the effects of a screw dislocation defect on the optical properties, and then, both cases are deliberated. This study is the first attempt to analyze the AB flux field for RMQD without screw dislocation. In the present study, the influences of a screw dislocation defect on RMQD's TRICs and TACs are probed by considering different values of the external magnetic field and AB flux field, and the ranges of corresponding parameters on the optimum of the structure are specified. Moreover, the study also elucidates how to rule out the effects of screw dislocation on optical specifications by means of the external fields. Despite a certain screw dislocation, the frequency range is determined where the structure behaves as if it is perfect (namely, without screw dislocation) for its optimum, which in turn is crucial for experimental applications.

An ultrafast all-optical half adder using nonlinear ring resonators in photonic crystal microstructure

Half adder and half subtractor are the basic building blocks of an arithmetic logic unit used in every optical central processing unit (CPU) to provide computational operators. In this paper, we aim to design an ultrafast all-optical half adder based on nonlinear ring resonators. The proposed structure consists of the concurrent designs of the AND and XOR logic gates inside a rod-based photonic crystal microstructure. The linear dielectric rods made of silicon and nonlinear dielectric rods composed of doped glass are used to design the nonlinear ring resonators as the fundamental blocks of a half adder. We demonstrate as the intensity of the incoming light increases, the nonlinear Kerr effect appears, and the total refractive index increases. It diverts the direction of light propagation to the desired nonlinear ring resonator depending on the signal wavelength, the radius of rods and lattice constant. Finally, after several resonances, the light is coupled to the output. Our numerical simulations using a two-dimensional finite-difference time-domain method reveal depending on the light intensity, the maximum and minimum transmissions of the half adder are 100% and 96%, respectively. The calculations also show the delay of the designed half adder is 3.6 ps. Due to the small area of 249.75 µm2, the proposed half adder is an appropriate candidate for photonic integrated circuits used in the next generation of all-optical CPUs.

Using Narrow Line-Width Laser to Measure the Thickness and Refractive Index of the Film

We demonstrate applications of a novel setup which is used for measuring the relative phase difference between S and P polarization at an oblique incidence point in optically denser medium by analyzing the relative frequency shift of adjacent axial modes of S and P resonances of a monolithic folded Fabry-Perot cavity (MFC). The relative phase difference at a reflection point A in an optically denser medium is inferred to be around -167.4° for a confocal cavity and -201.1° for a parallel cavity. Given the n1, n3, φ1, φ3, λ, and Δ, the elliptic formula tan(ψ)exp(iΔ) = Rp/Rs is used to find a solution for thickness d and refractive index n2 of the thin film coated on point A, where Rs and Rp are total refractive index of s and p component of light related to two unknown values. Since it is hard to deduce an analytical solution for thickness and refractive index of the film, we firstly used exhaustion method to find the set of solution about thickness and refractive index when assumed there is no light absorption by the film and then Particle Swarm Optimization (PSO) to find a set of solution of thickness and complex refractive index which accounts the light absorption by the film.

Near-IR- and UV-femtosecond laser waveguide inscription in silica glasses

The influence of laser parameters on silica based waveguide inscription is investigated by using femtosecond laser pulses at 1030 nm (near-IR) and at 343 nm (UV). Negative phase contrast microscopy technique is used to measure the refractive index contrast for different photo-inscribed waveguides and shows the effects of both laser wavelength and scanning speed. In particular, UV photons have a higher efficiency in the waveguide production process as also confirmed by the lower optical losses at 1550 nm in these waveguides. These measurements are combined with micro-Raman and photoluminescence techniques, highlighting that laser exposure induces both structural modification of the silica and point defects generation. The contribution of induced defects to the total refractive index change is singled out by applying two different thermal treatments on the waveguide. The first, up to 500 °C, is able to remove the most of the induced non-bridging-oxygen-hole-centers (NBOHCs) while the second up to 750 °C erases almost all absorbing induced defects, highlighting the strong contribution of additional defects, not yet identified.

Tailoring the optical properties of quantum ring irradiated by THz laser

ABSTRACTThis study set out to introduce the optical nonlinearities of a intense laser-driven two-dimensional quantum ring subjected to external uniform magnetic field. Inclusion of the effect of non-resonant, high-frequency THz laser radiation is realised by the laser-dressed potential, whereas the total optical absorption coefficients, total relative refractive index changes and third-harmonic generation (THG) coefficient are inferred from the scheme of compact density-matrix formalism and iterative method. Our results reveal that the laser field smoothens the antidot region of the ring that consequences with remarkable modifications in the electronic structure and correspondingly the optical response of the system. We have found that the height and location of the resonant peaks of total optical absorption coefficient, total relative refractive index changes and THG coefficient can be controlled by the externally applied fields and system parameters. The tunability of the intersubband transitions could be beneficial for practical device application relying on the electronic optical transitions.

Excitonic nonlinear optical properties in AlN/GaN spherical core/shell quantum dots under pressure

Abstract

The functionality of the external electric and magnetic field on optical specifications of Rosen–Morse quantum well

In this study, for the first time, we probe the influences of the external electric and magnetic field (EF and MF) on the total refractive index changes (TRICs) and the total absorption coefficients (TACs) of quantum well (QW) with the Rosen–Morse (RM) potential confinement constituting by GaAs/GaAlAs heterostructure. To do this, the bound state energies and the wave functions of the Rosen–Morse quantum well (RMQW) under the influence of the external EF and MF are determined by solving the corresponding wave equation using the diagonalization method within the framework of the effective mass approach and the parabolic band approximation. As the purpose of the present work is to find out the functionality of the external EF and MF on TRICs and TACs of RMQW, same RMQW with V1 = 250 meV, V2 = 228 meV, η = 0.01 cm−1 is taken into consideration throughout the work. The TRICs and TACs of RMQW in the weak and strong regimes of the external fields are discussed in detail. The present work introduces to researches that how to and in what regimes apply the EF and MFs to be considered in devices designs and applications including RMQW.

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.

The optimal ranges for the optical properties of two-electron quantum dot immersed in plasmas

In this study, for the first time, the total refractive index changes (TRICs) and the total absorption coefficients (TACs) of the spherically confined two-electron parabolic quantum dot (TEPQD) embedded in the Debye and quantum plasmas generated by GaAs/GaAlAs heterostructure and modeled through the more general exponential cosine screened Coulomb (MGECSC) potential are analyzed by solving the corresponding wave equation using the tridiagonal matrix method. Two different types of MGECSC potential are used in the calculations. One of them is the most basic form of it obtained by adjusting the potential parameters for modeling the Debye plasma case, and other is the most common form of it in order to model the quantum plasma case. In addition to plasma environment is an important experimental argument in the synthesis and modification of quantum dots (QDs), the results of the screening effects on these and the fact that screening effect can be adjusted are the main motivation of considering the plasma environments in this study. In this context, the effects of external and structural parameters as well as plasma shielding parameters on TRICs and TACs of TEPQD are investigated in detail. The behavior of the external, structure and plasma shielding parameters on TEPQD's optical properties are compared and their alternativeness to each other are studied. The role of the Debye and quantum plasma environments on the behavior of external and structural parameters in consideration of the nonlinear optical properties is also researched. For the nonlinear optical properties of TEPQD, optimal ranges of all parameters, especially plasma shielding parameters, are determined. It is clear that these detailed determinations will also be very important in further theoretical investigations as well as the necessity for experimental applications.

The electron-related optical responses for the square tangent quantum well: Role of applied external fields

In the present work, a detailed investigation of the influence of external perturbations, in particular intense terahertz radiation, static electric and magnetic fields on the electron-related optical responses such as total optical absorption coefficients and relative refractive index changes for a quantum well with the square tangent potential is presented. The subband energy levels and their corresponding wave functions are obtained by solving the one-electron Hamiltonian of the system under the framework of the effective-mass and parabolic band approximations. Optical coefficients are reported for varying incident photon energies. The numerical results show that the optical response is shifted towards the blue with the increase in the magnitude of the applied external fields. These results can provide an input for use in optoelectronic device applications.

Computation of the nonlinear optical properties of n-type asymmetric triple δ-doped GaAs quantum well

Abstract In the present study, we present numerical results for the influence of non-resonant intense THz laser radiation as well as the structure parameters, such as well width and central doping concentrations, on the total optical absorption coefficients (TOACs) and relative refractive index changes (RRICs) in n-type asymmetric triple δ-doped G a A s quantum well (QW) by using the compact-density-matrix formalism via iterative method. In order to obtain these numerical results, we have first obtained the subband energy spectrum and the electronic wave functions of the structure by using the effective-mass and parabolic band approximation. We have then calculated the nonlinear optical (NLO) properties of the system, by employing these energy eigenvalues and eigenfunctions. The numerical results for these calculations show that; (i) the magnitude of the resonant peak of TOACs decreases and the peak position shifts towards the lower energies when the central doping concentration and the well width are increased; (ii) due to the intense laser field effect, the magnitude of the TOACs resonant peak initially increases and its position shifts towards higher energies and then it decreases, shifting towards lower energies; (iii) by increasing the central doping concentration (well width), the magnitude of the resonant peak of RRICs increases (decreases), and the resonant peak position shifts towards the lower energies; and finally (iv) because of the increase in the intensity of the laser field applied to the structure, the magnitude of the resonant peak of RRICs increases, and the resonant peak position initially shifts towards the higher energies and then shifting towards the lower energies.

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.

Optical specifications of laser-induced Rosen-Morse quantum well

In this study, for the first time, the influences of a monochromatic linearly polarized laser field on the total refractive index changes (TRICs) and the total absorption coefficients (TACs) of quantum well (QW) with the Rosen-Morse potential confinement by constituting GaAs/GaAlAs heterostructure are considered. Time-dependent in the Schrödinger equation is modified through the Kramers-Henneberger (KH) transformation and the dipole approximation, and then the laser-dressed counterpart of well potential is generated by using the Ehlotzky approximation. The bound state energy values and the wave functions of the Rosen-Morse quantum well (RMQW) under the influence of the intense laser field (ILF) are obtained by using the diagonalization method in the framework of the effective mass approach and the parabolic band approximation. The effects of structure parameters on TRICs and TACs of RMQW are also explained in detail, as well as the ILF's ones. In addition to these, the alternativeness to each other of the structure parameters and the ILF on the optical specifications is also discussed. The results of the present work are necessary and crucial in optimization of the optical specifications of RMQW to be fabricated for devices applications.

Comparison of plasma-enhanced atomic layer deposition AlN films prepared with different plasma sources

A comparative study of thin aluminum nitride (AlN) films deposited by plasma-enhanced atomic layer deposition in the SENTECH SI ALD LL system applying either a direct inductively coupled plasma (ICP) or an indirect capacitively coupled plasma (CCP) source is presented. The films prepared with the ICP source (based on a planar triple spiral antenna) exhibit improved properties concerning the growth rate per cycle, total cycle duration, homogeneity, refractive index, fixed and mobile electrical charges, and residual oxygen content compared to the CCP source, where the comparison is based on the applied plasma power of 200 W. The increase of the plasma power to 600 W in the ICP process significantly reduces the residual oxygen content and enhances the electrical breakdown field. The AlN layers grown under these conditions, with a growth rate per cycle of 1.54 Å/cycle, contain residual oxygen and carbon concentrations of about 10% and 4%, respectively, and possess a refractive index of 2.07 (at 632.8 nm).

Real-Time Interferometric Refractive Index Change Measurement for the Direct Detection of Enzymatic Reactions and the Determination of Enzyme Kinetics.

Back scatter interferometry (BSI) is a sensitive method for detecting changes in the bulk refractive index of a solution in a microfluidic system. Here we demonstrate that BSI can be used to directly detect enzymatic reactions and, for the first time, derive kinetic parameters. While many methods in biomedical assays rely on detectable biproducts to produce a signal, direct detection is possible if the substrate or the product exert distinct differences in their specific refractive index so that the total refractive index changes during the enzymatic reaction. In this study, both the conversion of glucose to glucose-6-phosphate, catalyzed by hexokinase, and the conversion of adenosine-triphosphate to adenosine di-phosphate and mono-phosphate, catalyzed by apyrase, were monitored by BSI. When adding hexokinase to glucose solutions containing adenosine-triphosphate, the conversion can be directly followed by BSI, which shows the increasing refractive index and a final plateau corresponding to the particular concentration. From the initial reaction velocities, KM was found to be 0.33 mM using Michaelis–Menten kinetics. The experiments with apyrase indicate that the refractive index also depends on the presence of various ions that must be taken into account when using this technique. This study clearly demonstrates that measuring changes in the refractive index can be used for the direct determination of substrate concentrations and enzyme kinetics.

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.

Linear and Nonlinear Intersubband Optical Properties of Direct Band Gap GeSn Quantum Dots.

Intersubband optical transitions, refractive index changes, and absorption coefficients are numerically driven for direct bandgap strained GeSn/Ge quantum dots. The linear, third-order nonlinear and total, absorption coefficients and refractive index changes are evaluated over useful dot sizes’ range ensuring p-like Γ-electron energy state to be lower than s-like L-electron energy state. The results show strong dependence of the total absorption coefficient and refractive index changes on the quantum dot sizes. The third order nonlinear contribution is found to be sensitive to the incident light intensity affecting both total absorption coefficient and refractive index changes, especially for larger dot sizes.

Effect of applied electric field on the nonlinear optical properties of modulation-doped GaAs/AlxGa1-xAs double quantum well

In the present study, the effects of varying doping concentration and applied electric field on the intersubband-related optical absorption and relative refractive index change coefficients in modulation-doped GaAs/AlxGa1-xAs double quantum wells are theoretically investigated. The allowed energy levels and the corresponding wave-functions are calculated by solving the Schrödinger and Poisson equations self-consistently within the framework of the effective-mass and parabolic band approximations. The optical coefficients are evaluated using the compact density matrix formalism within an iterative procedure. The numerical results are presented for two different doping concentration and several values of the electric field. They show that both the peak position and the magnitude of the calculated total optical absorption coefficients and refractive index changes are significantly affected by the applied electric field and the doping concentration. The treatment is suitable to consider the general problem with different wells and barrier sizes, although the barrier width should preferably be small enough as to allow for an effective inter-well coupling.

Study of non-linear optical properties of center and edge delta-doped multiple quantum wells

In the present paper, the linear and non-linear optical properties of GaAs/AlGaAs multiple quantum well with on-center and on-edge delta doping are studied within the effective mass approximation. The delta potential is analytically modeled within each quantum well potential to obtain the energy levels and the corresponding wave functions using the robust finite difference method. The linear and non-linear optical absorption coefficients and changes in the refractive index are studied in the presence of a static magnetic and a periodic laser field using the density matrix approach. The obtained results show that the position of resonances and the amplitude of the optical absorption coefficients and the refractive index changes can be modified by varying the magnetic field and strength and position of doping potential. Lastly, an increase of the optical intensity appreciably changes the total absorption coefficient, as well as the total refractive index changes. Obtained results are important for the design of various electronic components such as high-power FETs and infrared photonic devices based on the intersubband transition of electrons in δ-doped multiple quantum wells.