Material gain of InGaAs/GaAs quantum well-dots
We study material gain of a novel type of quantum heterostructures of mixed (0D/2D)
dimensionality referred to as quantum well-dots (QWDs). To evaluate the material gain in a
broad range of injection currents (30–1200 A cm−2 per-layer) we studied edge-emitting lasers
with various numbers of InGaAs/GaAs QWD layers in the active region and different
waveguide designs. The dependence of the material gain on the current is well fitted by an
empirical exponential equation similar to the one used for quantum dots (QDs) in the whole
range of injection current densities. The estimated QWD transparency current-density-per-layer
of 31 A cm−2 ranks between the values reported for quantum wells and QDs. The maximal
QWD material gain as high as 1.1·104 cm−1 has been measured. The results obtained confirm
specific gain properties of InGaAs QWDs making them promising active media for lasers,
superluminescence diodes and optical amplifiers.
We present a study of diode lasers with two identical optically coupled ridges. Two coupled ridges were made gradually divergent to a distance of 50 μm which allowed creating three electrically isolated sections within a single laser. We carried out numerical simulations of the electromagnetic modes in the coupled ridge waveguide and calculated far-field patterns for each mode. The results are in good agreement with the experimental data. We have found that current spreading provided unwanted optical gain in the active region in between ridges and dramatically changed the structure of the lasing modes. The obtained numerical and experimental results can be used to design twin-ridge diode lasers able to operate in mode-locking regimes.
We report on broad-area lasers, mode-locked lasers (MLLs), and superluminescent light-emitting diodes (SLDs) based on a recently developed novel type of nanostructures that we refer to as quantum well-dots (QWDs). The QWDs are intermediate in properties between quantum wells and quantum dots and combine some useful properties of both. 1.08 μm InGaAs/GaAs QWDs broad area edge-emitting lasers based on coupled large optical cavity waveguides show high internal quantum efficiency of 92%, low internal loss of 0.9 cm-1 and material gain of ~1.1∙104 cm-1 per one QWD layer. CW output power of 14.2 W is demonstrated at room temperature. Superluminescent light-emitting diodes with one QWD layer in the active region exhibit stimulated emission spectra centered at 1050 nm with the maximal full width at half maximum of 36 nm and the output power of 17 mW. First results on mode-locked operation in QWD lasers are also presented. 2 mm long two-section devices demonstrate the pulse repetition rate of 19.3 GHz and the pulse duration of 3.5 ps. The width of the radio frequency spectrum is 0.2 MHz.
We analyzed the localized charge dynamics in the system of interacting single-level quantum dots (QDs) coupled to the continuous spectrum states in the presence of Coulomb interaction between electrons within the dots. Different dots geometry and initial charge configurations were considered. The analysis was performed by means of Heisenberg equations for localized electrons pair correlators. We revealed that charge trapping takes place for a wide range of system parameters and we suggested the QDs geometry for experimental observations of this phenomenon. We demonstrated significant suppression of Coulomb correlations with the increasing of QDs number. We found the appearance of several time scales with the strongly different relaxation rates for a wide range of the Coulomb interaction values.
We demonstrated that electron-phonon interaction leads to the increasing of localized charge relaxation rate. We also found that several time scales with different relaxation rates appear in the system in the case of non-resonant tunneling between the dots. We revealed the formation of oscillations in the filling numbers time evolution caused by the emission and adsorption processes of phonons.
Two laser heterostructures with active region based on seven InGaAs quantum wells and on InGaAs/InGaAlAs superlattice were grown on InP substrates by molecular beam epitaxy. Both active regions were designed for vertical-cavity surface-emitting lasers of 1535- 1565 nm spectral range and had total thickness about 80-90 nm. Characteristics of edgeemitting laser diodes fabricated from grown laser heterostructures were studied and compared.
The problems of creation of a low intensity optical radiation signal standard sources based on the nanosized apertures and semiconductor quantum dots are considered. The use of technology of the focused ionic beam technology for isolation of a single quantum dot is offered suggested.
The dynamics of a two-component Davydov-Scott (DS) soliton with a small mismatch of the initial location or velocity of the high-frequency (HF) component was investigated within the framework of the Zakharov-type system of two coupled equations for the HF and low-frequency (LF) fields. In this system, the HF field is described by the linear Schrödinger equation with the potential generated by the LF component varying in time and space. The LF component in this system is described by the Korteweg-de Vries equation with a term of quadratic influence of the HF field on the LF field. The frequency of the DS soliton`s component oscillation was found analytically using the balance equation. The perturbed DS soliton was shown to be stable. The analytical results were confirmed by numerical simulations.
Radiation conditions are described for various space regions, radiation-induced effects in spacecraft materials and equipment components are considered and information on theoretical, computational, and experimental methods for studying radiation effects are presented. The peculiarities of radiation effects on nanostructures and some problems related to modeling and radiation testing of such structures are considered.
The paper provides a number of proposed draft operational guidelines for technology measurement and includes a number of tentative technology definitions to be used for statistical purposes, principles for identification and classification of potentially growing technology areas, suggestions on the survey strategies and indicators. These are the key components of an internationally harmonized framework for collecting and interpreting technology data that would need to be further developed through a broader consultation process. A summary of definitions of technology already available in OECD manuals and the stocktaking results are provided in the Annex section.