Tunneling Effects on Fine-Structure Splitting in Quantum Dot Molecules

We theoretically study the effects of bias-controlled interdot tunneling in vertically coupled quantum dots on the emission properties of spin excitons in various bias-controlled tunneling regimes. As a main result, for strongly coupled dots we predict substantial reduction of optical fine structure splitting without any drop in the optical oscillator strength. This special reduction diminishes the distinguibility of polarized decay paths in cascade emission processes suggesting the use of stacked quantum dot molecules as entangled photon-pair sources.Comment: 12 pages, 4 figures, submitted to a APS journa

Effects of Shear Coupling on Shear Properties of Wood

Under pure shear loading, an off-axis element of orthotropic material such as pure wood undergoes both shear and normal deformations. The ratio of the shear strain to a normal strain is defined as the shear coupling coefficient associated with the direction of the normal strain. The effects of shear coupling on shear properties of wood as predicted by the orthotropic elasticity theory were validated using our recently developed shear test fixture. The validation also serves to demonstrate that the shear test fixture possesses the capability to introduce a state of pure shear to the critical section of a specimen as required and that orthotropic elasticity theory should be used to describe the mechanical properties of pure wood

Analysis Of Off-Axis Tension Test Of Wood Specimens

This paper presents a stress analysis of the off-axis tension test of clear wood specimens based on orthotropic elasticity theory. The effects of Poisson's ratio and shear coupling coefficient on stress distribution are analyzed in detail. The analysis also provides a theoretical foundation for the selection of a 10° grain angle in wood specimens for the characterization of shear properties. The Tsai-Hill failure theory is then applied to derive a formula for predicting shear strength. Existing strength data for Sitka spruce (Picea sitchensis Carr.) were used in a numerical analysis. Because of the large discrepancies in published test data from different sources, the accuracy of the formula is limited to the data used to derive it. However, the procedures are believed to be accurate. The off-axis tension test is attractive mainly because of its economy and ease of application. This research promises to pave the way for the adoption of the off-axis tension test for characterizing the shear properties of clear wood by the practicing engineer once representative input data become available

Influence of the miniband on emission mechanism in Zn1−xCdxSe/ZnSe quantum wells

[[abstract]]The stimulated emission has been investigated in Zn1-xCdxSe/ZnSe quantum wells with a constant sample width of 60 Å and barrier widths from 47 Å to 500 Å. A redshift of the stimulated emission peak with increasing excitation intensity was observed in samples with barrier widths narrower than 350 Å, and the stimulated emission mechanism in these samples is found to be dominated by exciton-exciton scattering. In contrast, no redshifts were observed for the sample with a barrier width of 500 Å, and the stimulated emission in this sample appears to be dominated by biexcitons. Time-resolved spectroscopy measurements were also performed on samples with barrier width of 47 and 500 Å below the threshold of stimulated emission, and it was found that the exciton lifetime decreases with increasing exciton energy for both of the samples. With a ten times smaller barrier width in the 47 Å sample, the lifetime of high energy exciton is significantly shorter than that of the other sample, while the low energy lifetime becomes longer. This implies that with a narrower barrier width of the quantum wells the excitons move faster to lower energy regions. The narrower the barrier, the easier it is for excitons to move through the miniband. This freedom of movement increases the exciton concentration at low energies in localized areas in the wells. High exciton concentration made exciton-exciton scattering more probable and reduce the stimulated emission threshold value.[[notice]]補正完畢[[booktype]]紙

Replica-molded electro-optic polymer Mach–Zehnder modulator

A Mach-Zehnder electro-optic polymer amplitude modulator is fabricated by a simple and high-throughput soft-stamp replica-molding technique. The modulator structure incorporates the highly nonlinear and stable chromophore, AJL8, doped in amorphous polycarbonate. Single-arm phase-retardation results in a halfwave voltage (V-pi) of 8.4 V at 1600 nm. The on/off extinction ratio is better than 19 dB, resulting from precise Y-branch power splitters and good waveguide uniformity. These results indicate that the simple fabrication process allows for good optical performance from high-fidelity replicas of the original master devices