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The behaviour of nanoscale optical devices in a variety of burgeoning research areas, such as photonic crystals1,2,3,4, near-field microscopy5,6,7, surface plasmonics8,9,10,11 and negative index of refraction materials12,13,14,15,16, is governed by strongly localized electromagnetic waves. Although such light waves are analogous to the localized electronic wavefunctions that determine the properties of solid-state quantum devices, unlike matter waves, these optical fields are vectorial in nature, and their orientation and magnitude vary on a subwavelength scale. In order to obtain a complete description of light in nanoscale devices, it is therefore crucial to be able to map the field vectors with subwavelength resolution. Thus far, local field vectors have mostly been studied by theoretical means. Here, we describe and demonstrate the first experimental mapping of vector fields of light on the nanoscale. By directly accessing the local field in its entirety, new capabilities and applications in nanophotonics may emerge.

We have carried out a double-crystal X-ray diffraction (DCXRD) study on ternary In 1− x Ga x As/InP and quaternary In 1− x Ga x As y P 1− y /InP strained multi-quantum well (MQW) structures on (001) InP substrates grown by chemical beam epitaxy. The presence of well-defined higher-order harmonics in the DCXRD results and also the presence of intense and sharp peaks in the low- and room-temperature photoluminescence measurements confirm the high quality of strained MQW structures. This is further supported by the observation of defect-free interfaces in transmission electron microscope photographs. By comparing the DCXRD measurements with X-ray simulation results, we could obtain layer thicknesses and profiles of perpendicular strains relative to the InP barrier.

We report optical properties of AlxGa1−xP (0⩽x⩽0.52) alloys grown by gas source molecular-beam epitaxy on S-doped GaP(001) substrates. Room-temperature pseudodielectric function spectra from 1.5 to 6.0 eV were obtained by spectroscopic ellipsometry. By applying the parabolic-band critical point model to numerically calculated second energy derivatives of these spectra, we obtained accurate room-temperature values of the E1, E0′, E2, and E2′ critical point energies and their dependence on composition x.

We present optical studies of a series of GaAs/AlAs short period superlattices grown by molecular beam epitaxy. The structural properties were examined by X-ray diffraction measurements. The quantum confinement of the electronic and the vibronic states were observed in the low temperature photoluminescence and Raman scattering experiments, respectively. Spectroscopic ellipsometric (SE) measurements were also performed. We found a new structure at the lower E 2 peak, which is the best resolution of the E 2 structure in these SLs so far obtained by SE.

Femtosecond four-wave mixing experiments on GaAs/AlGaAs quantum wells are performed with two independently tunable lasers. Many new results are found, including the heavy-hole-light-hole beating with these two mutually incoherent lasers.

We study by photoluminescence excitation the heretofore unsolved puzzle of a significant charge transfer over a thick ~100 to 1500 A ! AlxGa12xAs barrier in GaAs/AlxGa12xAs asymmetric double quantum wells, which the normally considered tunneling cannot account for. This phenomenon is completely general, observed in all the samples grown under standard growth conditions ~;600 °C!, that originated from many different sources. The existence of such leakage is also confirmed by time-resolved photoluminescence experiments. However, when the alloy barrier is replaced by an equivalent GaAs/AlAs digital alloy, or by AlAs, the leak largely disappears. In addition, a GaAs barrier separating two shallow In xGa12xAs quantum wells permits only relatively small transfer. The leak has a weak dependence on the barrier thickness at x50.3, but is a very strong function of x around x50.3. We argue that there is no way to explain all of the observed phenomena simultaneously other than by the existence of intrinsic structural inhomogeneities in the alloy. Essentially, there may exist low potential channels in the alloy barrier created by microscopic clustering of like molecules, through which percolationlike transport occurs. This picture is supported by a three-dimensional quantummechanical model calculation. Our work pins down the dynamical implications of the partial ordering and clustering in AlxGa12xAs and related semiconductor ternary alloys. The scope of this paper is exclusively for the transport over thick AlxGa12xAs barriers ( x,0.35) and does not include the relatively small but still non-negligible transport over thick homogeneous barriers such as GaAs, AlAs, and AlAs/GaAs digital alloys, and AlxGa12xAs (x.0.35). We contend that transport over these thick, homogeneous barriers may be owing to other mechanisms such as dipole-dipole transfer, photon reabsorption, nonequilibrium distribution of carriers, and polariton transport that are also unrelated to conventional tunneling. @S0163-1829~96!02144-3#

The direct measurement of the free-exciton binding energy ${\mathit{E}}_{\mathit{B}}$ in a GaAs-${\mathrm{Al}}_{0.25}$${\mathrm{Ga}}_{0.75}$As single quantum well is presented as a function of the well width ${\mathit{L}}_{\mathit{z}}$. In the 20-K photoluminescence excitation spectra, 1s and 2s states of both heavy- (HH) and light-hole (LH) coupled excitons were detected, and ${\mathit{E}}_{\mathit{B}}$ was obtained from the separation of the two states. The ${\mathit{E}}_{\mathit{B}}$ for both HH and LH coupled excitons have their maximum around ${\mathit{L}}_{\mathit{z}}$=10 monolayers (ML), and ${\mathit{E}}_{\mathit{B}}$ of LH excitons is smaller than that of HH excitons for ${\mathit{L}}_{\mathit{z}}$\ensuremath{\le}14 ML. The trend of ${\mathit{L}}_{\mathit{z}}$ dependence of ${\mathit{E}}_{\mathit{B}}$ agrees well with the theoretical prediction, which accounts for the finiteness of the barrier of a low-dimensionally confined electron and hole. However, the drastic increase of ${\mathit{E}}_{\mathit{B}}$ in the vicinity of the maximum, with the maximum value approximately four times the bulk value, is believed to be a transition to the two-dimensional exciton by the confinement of a quantum well.

By using gain nonlinearity characteristics of semiconductor optical amplifier, an all-optical binary half adder at 10 Gbps is demonstrated. No additional input beam such as clock signal or continuous wave light, which is required in many other all-optical logic gates, is used in this design concept. The half adder operates in single mechanism, which is XGM.

By using two input signals of A and B, an all-optical AND gate that utilize a XGM in semiconductor optical amplifiers is demonstrated at 10 Gbps. By achieving this experiment, it will be also explored the possibilities for the enhanced complex logic.

This study shows the optical properties of a vertical cavity laser (VCL) - depleted optical thyristor (DOT) fabricated using selective oxidation. The oxide confined PnpN VCL-DOT clearly shows the nonlinear s-shaped current-voltage and lasing characteristics.

Spatial and dynamical properties of optical phonons in AlxGa1−xAs alloys and GaAs/AlxGa1−xAs quantum wells are studied. An isotopically disordered harmonic crystal model is developed to study spatial properties of optical phonons in AlxGa1−xAs alloys. In the GaAs/AlxGa1−xAs system, transmission of the GaAs optical phonons through an AlxGa1−xAs barrier is studied using three-dimensional lattice dynamical model, fully accounting for the random arrangement of Ga and Al atoms in the alloy barrier. In the AlxGa1−xAs alloy, a localized-to-extended transition is found as a function of x. In GaAs/AlxGa1−xAs quantum wells, the transmission coefficient of the GaAs LO phonons through the alloy barrier remains significant below x < 0.3. These results are in good qualitative agreement with the experimentally deduced coherence length of LO phonons from nonequilibrium hot phonon populations.

We study coherent phonon oscillations in GaAs/AlxGa1−xAs MQW’s with varying x and fixed well and barrier widths of 100A. We have observed large plasmon-phonon coupling in x=0.2 MQW, although it is generally believed that the 2D nature of plasmon makes the plasmon-phonon coupling very difficult. One possible explanation for this phenomenon is the bulk-like, growth direction plasmon oscillations mediated by the anomalously large well-to-well coupling for small x (x

Numerous studies have reported various prognostic factors that affect graft and patient survival in living and cadaveric donor kidney transplantation (KT). The purpose of this study was to evaluate the clinical outcomes and prognostic factors affecting graft and patient survivals in living and cadaveric donor KT. Between February 1995 and December 2001, 421 patients who had undergone cadaveric donor KT (group I: 216 cases, 51.3%) or living donor KT (group II: 205 cases, 48.7%), were retrospectively analyzed. Five-year overall graft survival rates in living was significantly better than that in cadaveric donor KT, respectively (P = .0234). There was no difference in patient survival rates between the two groups. Such factors as absence of rejection, female donor, female recipient, adult KT according to recipient age (14 years), and donor serum creatinine level just before transplantation (2.5 mg/dL) were significantly associated with good graft survival among cadaveric donor KT, whereas two factors-absence of rejection and adult KT according to recipient age (14 years)-influenced graft survival in living donor KT. In multivariate analysis, the only significant prognostic factor related to graft survival was the presence of rejection. In conclusion, we suggest that the presence of rejection is the only factor that impairs graft survival in both cadaveric and living donor KT, while other factors affected graft survival differently in the two groups.

We discuss a few examples of cases in which the widely used mean-field approaches to alloys and alloy superlattices may not give complete solutions. These examples include the anomalously large Stokes and anti-Stokes real space-charge transfer over thick alloy barriers and the spatial extent of optical phonons in alloys and alloy superlattices, which have remained unsolved or controversial. We argue, both theoretically and experimentally, that approaches that fully account for inhomogeneities, partial ordering, and disorder effects in the alloys as well as the proper understanding of coupled quantum-mechanical systems do give answers to these important puzzles.