Tetsuomi Sogawa

Photon-spin controlled lasing oscillation in surface-emitting lasers

We report on photon-spin controlled lasing oscillation in GaAs surface-emitting lasers at room temperature. We demonstrate experimentally that the partial electron-spin alignment, created by optically pumping the GaAs laser active media with circularly polarized pulses, drastically changes the polarization state of the lasing output, causing circularly polarized lasing emission. We discuss the laser polarization characteristics in relation to the measured electron-spin relaxation time.

Theory of optical transitions in graphene nanoribbons

Matrix elements of electron-light interactions for armchair and zigzag graphene nanoribbons are constructed analytically using a tight-binding model. The changes in wavenumber (

Phase-noise characteristics of a 25-GHz-spaced optical frequency comb based on a phase- and intensity-modulated laser

\Delta n

VLS Growth of Alternating InAsP/InP Heterostructure Nanowires for Multiple-Quantum-Dot Structures

) and pseudospin are the necessary elements if we are to understand the optical selection rule. It is shown that an incident light with a specific polarization and energy, induces an indirect transition (

Generation of 120-fs laser pulses at 1-GHz repetition rate derived from continuous wave laser diode

\Delta n=\pm1

Vertically Aligned GaP/GaAs Core-Multishell Nanowires Epitaxially Grown on Si Substrate

), which results in a characteristic peak in absorption spectra. Such a peak provides evidence that the electron standing wave is formed by multiple reflections at both edges of a ribbon. It is also suggested that the absorption of low-energy light is sensitive to the position of the Fermi energy, direction of light polarization, and irregularities in the edge. The effect of depolarization on the absorption peak is briefly discussed.

Structural, Compositional, and Optical Characterizations of Vertically Aligned AlAs/GaAs/GaP Heterostructure Nanowires Epitaxially Grown on Si Substrate

We investigated phase-noise characteristics of both a phase/intensity-modulated laser with 25-GHz mode spacing and a mode-locked fiber laser with carrier-envelope-offset (CEO) locking. As the separation from the frequency of the continuous wave (CW) laser diode (LD) for a seed light source increases, the integrated phase noise of each comb mode of both the phase/intensity-modulated laser and supercontinuum light originating from it increases with the same slope as a function of mode number. The dependence of the integrated phase noise on mode number with the phase/intensity-modulated laser is much larger than with the mode-locked fiber laser of the CEO locking. However, the phase noise of the phase/intensity-modulated laser is extremely lower than that of the mode-locked fiber laser with CEO locking in the frequency region around the CW LD. The phase noise of the phase/intensity-modulated laser with 25-GHz mode spacing and that of the mode-locked fiber laser with the CEO locking could be estimated and were found to be almost the same at the wavelengths required in an f-to-2f self-referencing interferometer. Our experimental results indicate the possibility of achieving an offset-frequency-locked frequency comb with the phase/intensity-modulated laser.

Growth and characterization of GaP nanowires on Si substrate

We investigated the Au-assisted growth of alternating InAsP/InP heterostructures in wurtzite InP nanowires on InP(111)B substrates for constructing multiple-quantum-dot structures. Vertical InP nanowires without stacking faults were obtained at a high PH(3)/TMIn mole flow ratio of 300-1000. We found that the growth rate changed largely when approximately 40 min passed. Ten InAsP layers were inserted in the InP nanowire, and it was found that both the InP growth rate and the background As level increased after the As supply. We also grew the same structure using TBAs/TBP and could reduce the As level in the InP segments. A simulation using a finite-difference time-domain method suggests that the nanowire growth was dominated by the diffusion of the reaction species with long residence time on the surface. For TBAs/TBP, when the source gases were changed, the formed surface species showed a short diffusion length so as to reduce the As background after the InAsP growth.

Au-free InAs nanowires grown in In-particle-assisted vapor-liquid-solid mode: growth, structure, and electrical property

We report the first demonstration of continuous-wave laser diode based 100-fs-class pulse lasers operating at a gigahertz repetition rate without a mode-locking technique. We describe the performance of a 1-W, 120-fs optical pulse train at 1 GHz and a 1-W, 80-fs optical pulse train at 250 MHz by using a simple configuration. Sub-100-fs pulse durations are achieved by using a progressive expansion of the spectrum in the self-phase modulation process in an erbium-doped fibre amplifier. Our scheme can achieve continuously tunable repetition rate in the range of ± 20%, and develop powerful tools for use in nanomechanical systems and nanobiotechnology.

GAAS/ALAS TRENCH-BURIED QUANTUM WIRES WITH NEARLY RECTANGULAR CROSS SECTIONS GROWN BY METALORGANIC CHEMICAL VAPOR DEPOSITION ON V-GROOVED SUBSTRATES

We report the core-multishell GaP/GaAs/GaP nanowires grown in a metalorganic vapor phase epitaxy system by a combination of the vapor–liquid–solid growth mode and conventional vapor phase epitaxy method. By growing GaAs sacrificial segments on the core GaP nanowires followed by selective chemical etching, Au particles were removed and top faceted core-shell nanowires were formed after the shell growth. Analysis by transmission electron microscopy indicated that the shell layers were epitaxially grown on the sides of core GaP nanowires.