Time-Resolved Studies of a Rolled-Up Semiconductor Microtube Laser

We report on lasing in rolled-up microtube resonators. Time-resolved studies on these semiconductor lasers containing GaAs quantum wells as optical gain material reveal particularly fast turn-on-times and short pulse emissions above the threshold. We observe a strong red-shift of the laser mode during the pulse emission which is compared to the time evolution of the charge-carrier density calculated by rate equations

Optical Properties of GaAs Quantum Dots Fabricated by Filling of Self-Assembled Nanoholes

Experimental results of the local droplet etching technique for the self-assembled formation of nanoholes and quantum rings on semiconductor surfaces are discussed. Dependent on the sample design and the process parameters, filling of nanoholes in AlGaAs generates strain-free GaAs quantum dots with either broadband optical emission or sharp photoluminescence (PL) lines. Broadband emission is found for samples with completely filled flat holes, which have a very broad depth distribution. On the other hand, partly filling of deep holes yield highly uniform quantum dots with very sharp PL lines

Three-Dimensionally Confined Optical Modes in Quantum Well Microtube Ring Resonators

We report on microtube ring resonators with quantum wells embedded as an optically active material. Optical modes are observed over a broad energy range. Their properties strongly depend on the exact geometry of the microtube along its axis. In particular we observe (i) preferential emission of light on the inside edge of the microtube and (ii) confinement of light also in direction of the tube axis by an axially varying geometry which is explained in an expanded waveguide model.Comment: 5 pages, 4 figure

Quantized Dispersion of Two-Dimensional Magnetoplasmons Detected by Photoconductivity Spectroscopy

We find that the long-wavelength magnetoplasmon, resistively detected by photoconductivity spectroscopy in high-mobility two-dimensional electron systems, deviates from its well-known semiclassical nature as uncovered in conventional absorption experiments. A clear filling-factor dependent plateau-type dispersion is observed that reveals a so far unknown relation between the magnetoplasmon and the quantum Hall effect.Comment: 5 pages, 3 figure

A 160Gb/s (4x40) WDM O-band Tx subassembly using a 4-ch array of silicon rings co-packaged with a SiGe BiCMOS IC driver

We present a 400 (8×50) Gb/s-capable RM-based Si-photonic WDM O-band TxRx with 1.17nm channel spacing for high-speed optical interconnects and demonstrate successful 50Gb/s-NRZ TxRx operation achieving a ~4.5dB Tx extinction ratio under 2.15Vpp drive

A bacteriorhodopsin analog reconstituted with a nonisomerizable 13-trans retinal derivative displays light insensitivity

With the aim of preparing a light-insensitive bacteriorhodopsin-like pigment, bacterio-opsin expressed in Escherichia coli was treated in phospholipid-detergent micelles with the retinal analog II, in which the C13-C14 trans-double bond cannot isomerize due to inclusion in a cyclopentene ring. The formation of a complex with a fine structure (λmax, 439 nm) was first observed. This partially converted over a period of 12 days to a bacteriorhodopsin-like chromophore (ebR-II) with λmax, 555 nm. An identical behavior has been observed previously upon reconstitution of bleached purple membrane with the analog II. Purification by gel filtration gave pure ebR-II with λmax, 558 nm, similar to that of light-adapted bacterio-opsin reconstituted with all-trans retinal (ebR-I). Spectrophotometric titration of ebR-II as a function of pH showed that the purple to blue transition of bacteriorhodopsin at acidic pH was altered, and the apparent pKa of Schiff base deprotonation at alkaline pH was lowered by 2.4 units, relative to that of ebR-I. ebR-II showed no light-dark adaptation, no proton pumping, and no intermediates characteristic of the bacteriorhodopsin photocycle. In addition, the rates of reaction with hydroxylamine in the dark and in the light were similar. These results show, as expected, that isomerization of the C13-C14 double bond is required for bacteriorhodopsin function and that prevention of this isomerization confers light insensitivity

Far-Infrared Excitations below the Kohn Mode: Internal Motion in a Quantum Dot

We have investigated the far-infrared response of quantum dots in modulation doped GaAs heterostructures. We observe novel modes at frequencies below the center-of-mass Kohn mode. Comparison with Hartree-RPA calculations show that these modes arise from the flattened potential in our field-effect confined quantum dots. They reflect pronounced relative motion of the charge density with respect to the center-of-mass.Comment: 8 pages, LaTeX with integrated 6 PostScript figure

CHRONO: a parallel multi-physics library for rigid-body, flexible-body, and fluid dynamics

Abstract. The last decade witnessed a manifest shift in the microprocessor industry towards chip designs that promote parallel computing. Until recently the privilege of a select group of large research centers, Teraflop computing is becoming a commodity owing to inexpensive GPU cards and multi to many-core x86 processors. This paradigm shift towards large scale parallel computing has been leveraged in CHRONO, a freely available C++ multi-physics simulation package. CHRONO is made up of a collection of loosely coupled components that facilitate different aspects of multi-physics modeling, simulation, and visualization. This contribution provides an overview of CHRONO::Engine, CHRONO::Flex, CHRONO::Fluid, and CHRONO::Render, which are modules that can capitalize on the processing power of hundreds of parallel processors. Problems that can be tackled in CHRONO include but are not limited to granular material dynamics, tangled large flexible structures with self contact, particulate flows, and tracked vehicle mobility. The paper presents an overview of each of these modules and illustrates through several examples the potential of this multi-physics library