Twin Stripe Research Articles

Atomic-level mechanism of spallation microvoid nucleation in medium entropy alloys under shock loading

Spallation, rupture under impulsive tensile loading, is a dynamic failure process involving the collective evolution and accumulation of enormous microdamage in solids. In contrast to traditional alloys, the spallation mechanism in medium entropy alloys, the recently emerged multiprinciple and chemically disordered alloys, is poorly understood. Here we conduct molecular dynamics simulations and first principle calculations to investigate the effects of impact velocities and the local chemical order on spallation microvoid nucleation in a CrCoNi medium entropy alloy under shock wave loading. As the impact velocity increases, the microvoid nucleation site exhibits a transition from the grain boundaries to the grains to release redundant imposed energy. During the intragranular nucleation process, microvoids nucleate in the poor-Cr region with a large local nonaffine deformation, which is attributed to the weak metallic bonds in this position with sparse free electrons. For intergranular nucleation, a Franke-like dislocation source forms through the dislocation reaction, leading to enormous dislocations piling up in a narrow twin stripe, which markedly increases the local stored energy and promotes microvoid nucleation. These results shed light on the mechanism of spallation in chemically complexed medium entropy alloys.

Mixture domain states in PbTiO3 film with potentials for functional application

We investigated the microstructure of PbTiO3 films epitaxially grown on DyScO3 (110) substrates using synchrotron-based 3D reciprocal space mapping and X-ray reflection interface microscopy. The results show that an in-plane anisotropic mixture domain state (a* + a/c) exists in the PbTiO3 films, where a* domains reside between a/c twin stripe domains. Furthermore, when compared with traditional a domains in a/c twins, the a* domain is found to possess a similar in-plane lattice parameter but a much smaller out-of-plane lattice (∼0.5%). We also discovered a temperature-driven transition between a* and a/c pointing to potential applications in functional devices due to the huge mechanical response (4.85%) and polarization rotation between the a* and c domains.

Lump-stripe interaction solutions to the potential Yu–Toda–Sasa–Fukuyama equation

By means of Hirota bilinear method and symbolic computation, this paper studied two types of interaction solutions for the potential Yu–Toda–Sasa–Fukuyama equation. The first type of interaction between lump soliton and one stripe soliton generate the fusion and fission phenomenon, while the second type of interaction solution between lump soliton and twin stripe solitons generate the rogue wave. The corresponding dynamic plots of the above phenomena are graphically displayed respectively.

The expression of Flrt3 during chick limb development

The Flrt3 (Fibronectin-Leucine-Rich Transmembrane protein) gene encodes a fibronectin and leucine-rich repeat transmembrane protein whose expression is controlled by fibroblast growth factors (FGFs). FLRT3 has been implicated in neurite outgrowth after nerve damage, as a positive regulator of FGF signalling and in homotypic cell adhesion. Here we describe Flrt3 expression during chick embryonic limb development using whole-mount in situ hybridization. We found very dynamic expression during apical ridge formation and limb bud outgrowth. Initially Flrt3 is expressed in the apical ectodermal ridge and underlying mesenchyme, but then becomes restricted to the dorsal and ventral sides of the apical ridge as a twin stripe. At later stages, abundant expression is seen in the hindlimb and in both the pectoral and pelvic girdle-forming regions. FLRT3 may have a crucial role in regulating cellular adhesion between the epithelial apical ridge and the underlying mesenchyme and in establishing the dorso-ventral position of the ridge.

Fast modulation scheme for a two laterally coupled laser diode array

The present letter reports a modulation scheme that takes advantage of the unique characteristics of a two laterally coupled laser diode (also known as twin stripe array) to overcome the limit on the modulation imposed by the laser’s relaxation oscillation frequency. Through the use of the rate equation description of the device we uncover the device dynamics behind the modulation scheme generating 35 ps (full width at half maximum) laser pulses at 8 Gb/s modulation rate. Our scheme relies on the fast dynamics of the phase difference, controlled by means of the current injection on each stripe.

Channelled substrate window twin stripe GaAs/GaAIAs visible lasers: fabrication and steady-state analysis

GaAs/GaAIAs high-power window stripe lasers have been developed with a uniform active layer in the region adjacent to the device facets and with a curved active layer in the central region. A single-step liquid-phase epitaxy growth is used in the fabrication process to form two internal lateral current paths, so allowing for a very simple fabrication process. The optical coupling between the two stimulation emission regions reduces the beam divergence. The steady-state analysis of such a laser structure, including heating effects, agrees well with experimental results.

Analysis of the in-plane bandgap distribution in selectively grown InGaAs/InGaAsP multiple quantum well by low pressure metalorganic chemical vapor deposition

The in-plane distribution of growth rate enhancement and bandgap ( E g) of the selectively grown InGaAs/In GaAsP multiple quantum well (MQW) structure using a twin stripe mask is investigated. The dependence of the growth rate enhancement and E g transition profile on the mask widthand mask opening width is investigated experimentally, and discussed by the simulation based on the vapor phase diffusion model of the re-evaporated reactant from the mask to the open area. Growth profile in the direction perpendicular to the stripe is explained by one-dimensional vapor phase diffusion. Bandgap transition length along the mask opening stripe decreases with decreasing the mask width and the mask opening width. In-plane bandgap distribution is calculated by simple two-dimensional diffusion model, and the results are consistent with the experimental data.

Applications of Polarisation Switching In Twin Stripe Semiconductor Lasers

Polarisation switching in a twin stripe laser is exploited to produce logic operations with possible applications in optical data processing and computing. Experimental results are presented showing polarisation based logical inversion, and this operation is used to enable the configuration of the laser device as an optical “clock” and optical pseudo-random pulse generator. Phase locking of the optical clock is also demonstrated.

GaInAsP twin-stripe lasers with asymmetrical waveguide channels

Design and lasing characteristics of ?=1.3 ?m GaInAsP twin-stripe (TS) metal-clad ridge-waveguide lasers, with a varying degree of index guiding between the channels are reported. The TS devices operate stably in the TE polarised mode, even if under single-stripe injection TM polarisation is observed. Effective longitudinal mode selectivity has been obtained for the TS lasers with an effective index step in the range of 1×10?2 to 5×10?3 between the channels. This mode selectivity can be explained by assuming coupling of lateral modes of the twin waveguide structure via the common gain-medium.

Optically triggered polarisation bistability in GaInAsP twin stripe injection lasers using integrated devices

A bistable polarisation switching element and optical triggering source has been produced by etching a facet in a twin stripe semiconductor laser. The switching element is formed by a pair of stripe segments at one end of the device and triggered with short light pulses from the other two segments. Detector limited switching risetimes have been measured at 250 ps.

Optical bistability in semiconductor lasers

Absorptive, dispersive and modal bistabilities are considered in semiconductor injection lasers. Previous work is briefly reviewed and the discussion is concerned with experimental work with transverse modal bistability in twin stripe injection lasers. A simple circuit analogy indicates how modal bistability can arise and how it is possible to have stronger light output on the side where the current drive is weakest. Experimental results are reviewed for an optical flip-flop with the use of twin-stripe lasers with three such lasers coupled together in an optical logic circuit. Various mode patterns that have been observed by using different geometries of twin-stripe lasers are discussed. Use is foreseen for active bistable devices in front-end optical signal processing.

Optical bistability in semiconductor lasers

Absorptive, dispersive and modal bistabilities are considered in semiconductor injection lasers. Previous work is briefly reviewed and the discussion is concerned with experimental work with transverse modal bistability in twin stripe injection lasers. A simple circuit analogy indicates how modal bistability can arise and how it is possible to have stronger light output on the side where the current drive is weakest. Experimental results are reviewed for an optical flip-flop with the use of twin-stripe lasers with three such lasers coupled together in an optical logic circuit. Various mode patterns that have been observed by using different geometries of twin-stripe lasers are discussed. Use is foreseen for active bistable devices in front-end optical signal processing.

Interstripe coupling and current spreading in a subthreshold double heterostructure twin stripe laser

TWin stripe laser structures show great promise in integrated optics Systems. It has been proposed that optical interactions in such Structures should produce properties such as beam steering, optical pulse generation and bistability. However, fundamental properties of these devices, including the effect of the resistive p-type cladding layer on the current density distribution injected into the active region, the terminal behavior of the device, and the effect of the stripe width and spacing current density distributions have not yet been considered. This paper considers the current density distribution problem of a twin stripe laser, and examines the effect on the distribution of current injection into both stripes, interstripe coupling via the resistance of the p-type cladding layer and the geometric factors of cladding layer thickness, electrode width and spacing. A diode model is assumed for the heterostructure, and finite difference techniques are used to calculate the 2 D potential distribution in the p-type cladding layer and the current density distribution in the active layer. Numerical and experimental results highlight the effect of the nonlinear diode boundary on the current density distribution and show the changes in the current distribution which occur for relatively small fluctuations in current injected into the stripes and equally small changes in the geometry.

Effect of current rise time on beam stability in twin stripe lasers

The transient behaviour of the output of a twin stripe laser is found to be dependent upon the rise time and levels of the injection currents. Under certain biasing conditions the transient output has a high initial value which relaxes to a much lower value if the pulse rise time is fast but not if it is slower. This effect is found to be associated with beam steering.

New mechanism for bistable operation of closely coupled twin stripe lasers

Evidence for a novel mechanism causing bistable operation of closely coupled twin stripe lasers is reported. Current switched bistable operation has been demonstrated stably at room temperature, through the light beam being switched from a central mode to one where the optical filament crosses diagonally from under one laser stripe to the other.