Activity clusters in dynamical model of the working memory system

A mathematical model of working memory is proposed in the form of a network of neuron-like units interacting via global inhibitory feedback. This network is capable of storing information items in the form of clusters of periodical spiking activity. Several sequentially excited clusters can coexist simultaneously, corresponding to several items stored in the memory. The capacity of the memory is studied as the function of the system parameters.     

Experimental determination of the optimum number of quantum wells in multiwell heterolasers with radiation leakage into a substrate

The dependence of the mode structure and threshold characteristics of laser diodes with significant (～94%) radiation leakage into a substrate on the number of quantum wells (QWs) in a laser-diode heterostructure has been studied. It is established that laser diodes with a small number of QWs generate on the fundamental waveguide mode. As the number of QWs increases, the first waveguide mode begins to dominate and the threshold current increases, which is probably related to a weak filling of central QWs with nonequilibrium carriers and increased losses of the fundamental mode.     

GaAs-Based Laser Diode with InGaAs Waveguide Quantum Wells

Semiconductors - The results of studying a GaAs-based laser with InGaAs waveguide quantum wells, which operates at room temperature in the electric-pumping mode, are presented. The minimal...     

Efficient generation of the first waveguide mode in the InGaAs/GaAs/InGaP heterolaser

Generation of the first excited transverse mode (TE₁) in a new InGaAs/GaAs/InGaP diode heterolaser with a thin InGaP layer at the waveguide center was studied. This laser design decreases the competition of the first and fundamental modes and provides TE₁ mode lasing at a threshold current comparable to that of an ordinary laser oscillating at the fundamental TE₀ mode.     

Controlling the wavelength of InGaAs/GaAs/InGaP lasers by ion implantation

The possibility of controlling the wavelength of emission from an InGaAs/GaAs/InGaP laser heterostructure with strained quantum wells (QWs) using medium-energy proton implantation followed by thermal annealing has been studied. It is established that the optimum proton energy is related to the arrangement of QWs in the structure (e.g., 150 keV for QWs at a depth of ≈1.3 μm). Proton irradiation to a total dose of 6 × 10¹⁴ cm⁻² followed by annealing at 700°C allows the wavelength of emission from the modified region to be decreased by 8–10 nm at minimum losses in the output intensity. The observed effect can be used to obtain two-band emission from the same chip and has good prospects for use in the development of new optoelectronic schemes.     

Simultaneous TE<Subscript>1</Subscript> and TE<Subscript>2</Subscript> mode lasing yielding dual-wavelength oscillation in a semiconductor laser with a tunnel junction

Dual-frequency oscillation is obtained and investigated in a new type of injection heterolaser, an interband two-stage cascade laser with a tunneling p-n junction separating two active regions with quantum wells located in a common waveguide. The laser design provides for simultaneous oscillation at the first-order TE mode of wavelength λ = 1.086 μm and the second-order TE mode of wavelength λ = 0.96 μm in the continuous-wave regime at room temperature.     

Blue-green radiation in GaAs-based quantum-well lasers

Second-harmonic generation in InGaAs/GaAs/InGaP quantum-well lasers is studied. It is shown that second-order lattice nonlinearity of permittivity leads to the generation of the fundamental TM mode of the dielectric waveguide at a doubled lasing frequency. Additional lasing lines near the second-harmonic peak are observed.     

The mode competition,instability, and second harmonic generation in dual-frequency InGaAs/GaAs/InGaP lasers

InGaAs/GaAs/InGaP-based heterolasers with asymmetrically grown quantum wells of two types are developed. For the first time, dual-wavelength operation and second-harmonic generation are realized in these lasers over a wide range of injection currents: from 0.2 A in CW mode up to 10 A in injection with 200-ns-long pulses. Previously unknown special features of such a generation are experimentally revealed and interpreted in terms of the competition and coexistence of various short-and long-wavelength modes, including the “whispering-gallery” modes.     

The emergence of form by replication

It is shown with a simple mathematical model that if a system exhibits a given form (a spatial structure) and is put in contact with another system of the same type but in a state of spatial disorder, then under certain conditions their mutual interaction as they evolve in time allows replication of form in the disordered system with a controllable degree of faithfulness.