Mitsuru Sugawara

This paper reports the effect of homogeneous broadening of the optical gain on lasing spectra in self-assembled ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ quantum dot lasers. We measured the current-output power characteristics and light-emission spectra for columnar-shaped self-assembled ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ quantum-dot lasers that show lasing from the ground state. While lasing occur

We report here on the cloning and functional characterization of the protein responsible for the system A amino acid transport activity that is known to be expressed in most mammalian tissues. This transporter, designated ATA2 for amino acid transporter A2, was cloned from rat skeletal muscle. It is distinct from the neuron-specific glutamine transporter (GlnT/ATA1). Rat ATA2 consists of 504 amino acids and bears significant homology to GlnT/ATA1 and system N (SN1). ATA2-specific mRNA is ubiquit

This work presents a theory of optical signal amplification and processing by quantum-dot semiconductor optical amplifiers (SOA's) based on the density matrix equations to treat electron-light interaction and the optical pulse propagation equations. The theory includes the linear optical response as well as the incoherent and coherent nonlinear response of the new devices with arbitrary spectral and spatial distribution of quantum dots in the active region under the multimode light. The incohere

This paper presents recent progress in the field of semiconductor lasers and optical amplifiers with InAs-based self-assembled quantum dots in the active region for optical telecommunication. Based on our design in terms of the maximum bandwidth for high-speed modulation and p-type doping in quantum dots for high temperature stability, we realized temperature-insensitive 10 Gb s−1 laser diodes on a GaAs substrate at 1.3 µm. The output waveform at 10 Gb s−1 maintained a clear eye opening, average

A theoretical study of the spontaneous-emission lifetime of Wannier excitons in mesoscopic quantum disks is presented. We begin by introducing our experiments on the spontaneous emission of free and bound excitons in the ${\mathrm{In}}_{0.53}$${\mathrm{Ga}}_{0.47}$As/InP quantum wells. Using magneto-optical measurements, we show that excitons are localized at a certain potential minima below 20 K and that the bound excitons have a lifetime that is about 30 times longer than free excitons. To ana

M. Sugawara, Theoretical Bases of the Optical Properties of Semiconductor Quantum Nano-Structures. Y. Nakata, Y. Sugiyama and M. Sugawara, Molecular Beam Epitaxial Growth of Self-Assembled InAs/GaAs Quantum Dots. K. Mukai, M. Sugawara, M. Egawa, N. Ohtsuka, Metalorganic Vapor Phase Epitaxial Growth of Self-Assembled InGaAs/GaAs Quantum Dots Emitting at 1.3 um. K. Mukai and M. Sugawara, Optical Characterization of Quantum Dots. K. Mukai, M. Sugawara, Phonon Bottleneck Effect in Quantum Dots. H. S

This paper presents a theory and simulation of quantum-dot semiconductor optical amplifiers (SOAs) for high-bit-rate optical signal processing. The theory includes spatial isolation of quantum dots, carrier relaxation and excitation among the discrete energy states and the wetting layer, grouping of dots by their optical resonant frequency under the inhomogeneous broadening, and the homogeneous broadening of the single-dot gain, which are all essential to the amplifier performance. We show that

The effect of phonon bottleneck on quantum-dot laser performance is examined by solving the carrier-photon rate equations including the carrier relaxation process into the quantum-dot ground state. We show that the retarded carrier relaxation due to phonon bottleneck degrades the threshold current and the external quantum efficiency. We also show that quantum-dot lasers are quite sensitive to the crystal quality outside as well as inside quantum dots. Our results clarified that the relaxation li

Abstract The focus of this book is the remarkable advances in understanding of low pressure RF (radio frequency) glow discharges. A basic analytical theory and plasma physics are explained. Plasma diagnostics are also covered before the practicalities of etcher use are explored.

We studied the injection current dependence of room-temperature lasing spectra of a 1.3-μm self-assembled InAs∕GaAs quantum-dot laser both experimentally and theoretically. Starting from the ground-state lasing with a few longitudinal modes, the spectra showed splitting, broadening, excited-state lasing, and quenching of the ground-state lasing as the current increased. We could explain this unique current dependence by numerical simulation based on our quantum-dot laser theory, taking into acco

This paper provides a theory and simulation of traveling-type semiconductor optical amplifiers (SOAs) with self-assembled quantum dots in their active region. We calculated their continuous-wave and 40-Gbit/s dynamic performance, and compared them with 1.55-µm SOAs with bulk InGaAsP active layers. The results demonstrate that quantum-dot SOAs can process multiple-wavelength high bit-rate optical pulse trains over 40 Gbit/s under gain saturation. This promises diverse functions like regeneration,

We examined the current–output power characteristics and light emission spectra for columnar-shaped self-assembled InGaAs quantum-dot lasers with a room temperature lasing threshold of 6 mA. Lasing threshold currents became obscure as temperature decreased below 180 K. While lasing occurred with one line including a series of longitudinal modes at room temperature, spectra at 80 K showed broad lasing emission over a range of 50–60 meV. We conclude that dots with different energies start lasing i