Asymmetric cladding-ridge waveguide laser by selective-area MOCVD

Ridge waveguide lasers with a thin upper cladding layer are fabricated with a two-step selective-area MOCVD growth. The lower cladding, active region, and upper cladding are all grown in the initial MOCVD growth. A second growth over an oxide pattern is used to define the ridge with 0.15 μm of GaAs, which serves as both the contact and index increasing layer. Ridge lasers fabricated by this method (3×425 μm) have a cw threshold current of 12.6 mA, slope efficiency of 0.26 W/A, and operate in a fundamental transverse mode as well as stable fundamental lateral mode to 20 times threshold     

The design of the century

We construct a 2-chromatic Steiner system S(2, 4, 100) in which every block contains three points of one colour and one point of the other colour. The existence of such a design has been open for over 25 years.      

Monolithic serial InGaAs-GaAs-AlGaAs laser diode arrays

Top-contact monolithic serially-biased InGaAs-GaAs-AlGaAs (λ~0.93 μm) broad area strained-layer quantum well laser arrays have been fabricated on a semi-insulating GaAs substrate. The laser array consists of four individual laser diodes and operates up to 2.8 W at 3.6 A (supply limited) per uncoated facet under pulsed conditions (15 kHz, 2 μs). The threshold current is ~0.5 A, and the peak slope efficiency and the peak electrical-to-optical conversion efficiency of an individual laser element are ~0.53 W/A and 14%, respectively. The near-field intensity distribution is shown to be broad enough to fill the entire active region under the p-metal stripe (125 μm) of the individual laser diodes at high current levels     

A new buffer layer for MOCVD growth of GaN on sapphire

High quality GaN films have been grown on sapphire substrates (C face and A face) by atmospheric pressure metalorganic chemical vapor deposition (MOCVD) using a new buffer layer. With our reactor configuration and growth parameters, a GaN film grown on a single GaN buffer layer appears opaque with high density of hexagonal pits. Using a single A1N buffer layer results in extremely nonuniform morphology with mirror-like areas near the edge of the substrates and opaque areas in the center. The double buffer layer we report here, with GaN as the first layer and A1N as the second, each with an optimized thickness, leads to mirror-like films across the entire substrate. Scanning electron microscopy, photoluminescence, x-ray diffraction, and van der Pauw geometry Hall measurement data are presented to establish the quality of our films. The mechanism for this new buffer layer is also discussed.     

Strained-layer InGaAs-GaAs-AlGaAs lasers with monolithicallyintegrated photodiodes by selective-area MOCVD

Fabrication, design, and operation of strained layer, InGaAs-GaAs-AlGaAs lasers with monolithically integrated photodiodes fabricated by selective-area epitaxy are presented. Threshold currents as low as 8 mA (~300 A/cm²) were obtained for uncoated devices operating cw at room temperature. A responsivity of 71 μA/mW was obtained for a device with a photodiode etched facet angle of 3° and a photodiode bias of 0 V     

Polarisation-independent 20 Gbit/s soliton data transmission over12500 km using amplitude and phase modulation soliton transmissioncontrol

Polarisation-independent error-free 20 Gbit/s soliton data transmission over 12500 km with flat system Q dependence on distance, has been demonstrated using static filtering and a semiconductor polarisation-independent amplitude and phase modulator for soliton transmission control     

Die Bestimmung der Konzentration von Wasserstoff- oder Hydroxylionen mit 2,5-Dinitrohydrochinon

Ohne Zusammenfassung     

On 6-sparse Steiner triple systems

We give the first known examples of 6-sparse Steiner triple systems by constructing 29 such systems in the residue class 7 modulo 12, with orders ranging from 139 to 4447. We then present a recursive construction which establishes the existence of 6-sparse systems for an infinite set of orders. Observations are also made concerning existing construction methods for perfect Steiner triple systems, and we give a further example of such a system. This has order 135,859 and is only the fourteenth known. Finally, we present a uniform Steiner triple system of order 180,907.     

Ion beam mixing characteristics of MOCVD grown InGaAs/GaAs superlattices

The ion beam mixing behavior of InGaAs/GaAs strained layer superlattice structures grown by metalorganic chemical vapor deposition was studied using secondary ion mass spectroscopy and Rutherford backscattering channeling. The fluence dependence of intermixing by MeV Kr⁺ irradiation has been investigated. Significant intermixing occurs for fluences much lower than for similar intermixing in other superlattice systems (i.e. ALAs/GaAs). The intermixing exhibits no temperature dependence for fluences of 2 x 10¹⁵ to 5 x 10¹⁵ cm⁻² which sharply contrasts with the behavior of the AlAs/GaAs superlattice system which shows a strong temperature dependence, including a miscibility gap, in the temperature range 523 to 973K. Samples irradiated at 573K retain a high degree of crystallinity when compared to lower temperature irradiations indicating that the InGaAs/GaAs superlattice can be disordered and still retain crystallinity.     

Network Optimization Applied to Reclamation Works in Coal Mining

In this paper, a network transportation model is developed for determining the minimum cost recontouring of the surface of a spoil pile created in open cut coal mining operations to achieve a prespecified target surface. A fast algorithm for the resulting large-scale, highly dense transportation problem is presented. Computational experience on test data is presented and practical application to real data is illustrated.