We present the investigation of a monoclinic compound SeCuO 3 using x-ray powder diffraction, magnetization, torque, and electron-spin-resonance. Structurally based analysis suggests that SeCuO 3 can be considered as a three-dimensional network of tetramers. The values of intratetramer exchange interactions are extracted from the temperature dependence of the susceptibility and amount to ∼ 200 K. The intertetramer coupling leads to the development of long-range antiferromagnetic order at T N = 8 K. An unusual temperature dependence of the effective g tensors is observed, accompanied with a rotation of macroscopic magnetic axes. We explain this unique observation as due to site-selective quantum correlations.

We report a novel synthesis route of homogeneously manganese-doped TiO2 nanotubes in a broad concentration range. The scroll-type trititanate (H2Ti3O7) nanotubes prepared by hydrothermal synthesis were used as precursors. Mn 2+ ions were introduced by an ion exchange method resulting MnxH2−xTi3O7. In a subsequent heat-treatment they were transformed into MnyTi1−yO2 where y = x/(3 + x). The state and the local environment of the Mn 2+ ions in the precursor and final products were studied by Electron Spin Resonance (ESR) technique. It was found that the Mn 2+ ions occupy two positions: the first having an almost perfect cubic symmetry while the other is in a strongly distorted octahedral site. The ratio of the two Mn 2+ sites is independent of the doping level and amounts to 15:85 in MnxH2−xTi3O7 and to 5:95 in MnyTi1−yO2. SQUID magnetometry does not show long-range magnetic order in the homogeneously Mn 2+ -doped nanotubes.

Digital chemical etching is used to trim the output mirror thickness of wafer-fused VCSELs emitting at a wavelength near 1.5µm. The fine control of the photon cavity lifetime thus achieved is employed to extract important device parameters and optimize the combination of the threshold current, output power, and direct current modulation characteristics. The fabrication process is compatible with industrial production and should help in improving device yield and in reducing manufacturing costs.

We investigate experimentally the impact of photon cavity lifetime variations on the static and dynamic performance of high-speed 1.3-μm wavelength wafer-fused vertical-cavity surface-emitting lasers (VCSELs). The photon lifetime is modified by decreasing the top mirror reflectivity either by shallow-surface etching or by Bragg-reflector layer-pair removal. Significant improvements in both static and dynamic VCSEL performance as well as the extraction of internal VCSEL device parameters are achieved.

Wafer fusion vertical cavity surface emitting laser (VCSEL) technology has produced devices that successfully passed all mechanical and electrical Telcordia qualification tests. Accelerated lifetime tests result in times to 1% failure at 70 °C of 18 years and 30 years at VCSEL driving currents of 9 and 8 mA, respectively. These lifetimes meet the telecom industry reliability requirements for applications in fiber-optic communications networks.