Dimitris Alexandropoulos

A new family of nonanuclear lanthanide clusters displaying magnetic and optical properties.

The initial employment of 2-(hydroxymethyl)pyridine in 4f metal chemistry has afforded a new family of Ln(III)(9) clusters with a sandglass-like topology and dual physical properties; the Dy(III) member shows single-molecule magnetism behavior, while the Eu(III) analogue exhibits intense red photoluminescence.

Survey and Evaluation of Space Division Multiplexing: From Technologies to Optical Networks

Single-mode fibers physical capacity boundaries will soon be reached; hence, alternative solutions are much needed to overcome the multiplying and remarkably large bandwidth requests. Space division multiplexing (SDM) using multicore fibers (MCFs), multielement fibers, multimode fibers, and their combination; few-mode MCFs; or fibers based on orbital angular momentum are considered to be the propitious stepping-stones to overcome the capacity crunch of conventional single-core fibers. We critically review research progress on SDM fibers and network components, and we introduce two figures of merit aiming for quantitative evaluation of technologies such as amplifiers, fan-in/fan-out multiplexers, transmitters, switches, and SDM nodes. Results show that SDM fibers achieve a 1185-fold (18-fold) spectral-spatial efficiency increase compared with the 276-SMF bundle (single-core fiber) currently installed on the ground. In addition, an analysis of crosstalk in MCFs shows how SDM concepts can be further exploited to fit in various optical networks such as core, metro, and especially future intra-data center optical interconnects. Finally, research challenges and future directions are discussed.

Slow magnetization relaxation in unprecedented Mn(III)4Dy(III)3 and Mn(III)4Dy(III)5 clusters from the use of N-salicylidene-o-aminophenol.

The first use of N-salicylidene-o-aminophenol in 3d/4f chemistry has led to Mn(III)(4)Dy(III)(5) and Mn(III)(4)Dy(III)(3) clusters with unprecedented metal topologies and stoichiometries; both compounds exhibit out-of-phase signals indicative of the slow magnetization relaxation of a single-molecule magnet.

Tetranuclear Lanthanide(III) Complexes with a Zigzag Topology from the Use of Pyridine-2,6-dimethanol: Synthetic, Structural, Spectroscopic, Magnetic and Photoluminescence Studies

Reaction between Ln(NO3)3·xH2O (x = 5 or 6) and the potentially tridentate (N,O,O) chelating/bridging ligand pyridine-2,6-dimethanol (pdmH2), in the presence of base NEt3, affords a family of isostructural tetranuclear [Ln(III)4(NO3)2(pdmH)6(pdmH2)2](NO3)4 (Ln(III) = Eu(III), Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Yb(III)) complexes with a rare zigzag topology. All complexes contain a [Ln4(μ-OR)6](6+) core with bridging ligation provided by the alkoxido arms of six η(1):η(1):η(2):μ pdmH(-) groups. The Ln(III) ions are eight coordinate with distorted geometries. Direct current magnetic susceptibility studies revealed predominant weak antiferromagnetic exchange interactions between the metal centers, which were quantified in the case of isotropic Gd(III)4 to give J = -0.09(1) cm(-1) and g = 2.00(1). The observation of out-of-phase (χ″M) ac susceptibility signals suggested that the Dy(III)4 analogue might be a molecular nanomagnet. Solid-state photoluminescence studies showed that the Eu(III)4 and Tb(III)4 compounds exhibit intense, sharp, and narrow emission bands in the red and green visible regions, respectively, which arise from the characteristic (5)D0 → (7)FJ and (5)D4 → (7)FJ transitions. The combined results demonstrate the ability of pdmH2 ligand to yield homometallic 4f clusters with interesting magnetic and optical properties.

The highest-nuclearity manganese/oximate complex: An unusual MnII/III15 cluster with an S = 6 ground state

The synthesis, structure, and magnetochemical characterization of the largest manganese oxime cluster are reported. The Mn(15)/2-pyridinealdoxime compound is mixed-valence (II/III) and possesses an irregular structural motif with a novel Mn/O core. The oximato-bridged cluster exhibits an S = 6 ground state and a negative magnetoanisotropy.

Potential of InGaAs/GaAs Quantum Dots for Applications in Vertical Cavity Semiconductor Optical Amplifiers

The use of InGaAs/GaAs quantum dots (QDs) in vertical cavity semiconductor optical amplifiers (VCSOAs) is proposed and analyzed. The results underline the distinctive differences between practical designs for QD vertical cavity semiconductor lasers and QD-VCSOAs. By means of a QD rate-equation scheme that accounts for both homogeneous and inhomogeneous broadening and the VCSOA cavity characteristics, the effects of material properties are identified. The design routes outlined here ensure the suitability of QD-VCSOAs for high-speed applications (>100 Gb/s) that rely on the fast carrier dynamics.

Gain, differential gain and linewidth enhancement factor of GaInNAs/GaAs strained quantum well lasers

We present calculations of the material gain, differential gain and linewidth enhancement factor (alpha) for GaInNAs/GaAs quantum wells based on the free-carrier theory. We explore the effect of N composition on peak differential gain and transparency concentration. The nitrogen-induced conduction band non-parabolicity is accounted for through the band anti-crossing model, and valence band mixing effects and strain are treated exactly. The alpha factor is found to have similar values to those of the conventional material InGaAsP/InP, which is encouraging for the use of GaInNAs as the active material for a high speed emitter.

Proposed scheme for polarization insensitive GaInNAs-based semiconductor optical amplifiers

A novel scheme for polarization insensitive GaInNAs-based semiconductor optical amplifiers is proposed in which TE and TM polarization gain is almost equal for GaInNAs quantum wells with GaInAs barriers. The proposed scheme involves the growth of GaInAs metamorphic layers on GaAs. Based on a k /spl middot/ p Hamiltonian that accounts for the N-induced modifications of the bandstructure, we calculate the optical properties of GaInNAs-GaInAs quantum wells and explore the effect of GaInAs barriers on the valence band mixing effects. The TE and TM amplifier gain of GaInNAs-based semiconductor optical amplifiers with GaInAs barriers is then analyzed.

Dynamic Analysis of Crosstalk Performance in Microring-Based Add/Drop Filters

In this paper, the impact of the simultaneous presence of input and add signals in add/drop filters realized with microring resonators is numerically investigated. It is shown that the notch spectral response of output ports is responsible for the intraband crosstalk appearing on the dropped signals in add/drop operation. The investigation of the filter performance is performed with modulated signals at both the input and the add port. The analysis highlights the strong competition between the levels of induced intraband crosstalk and the wavelength selectivity at high bit rate add/drop operation, even in higher order filters. Multistage add/drop topologies that address the inefficiencies of the single-stage add/drop filters are proposed, and successful operation at 40 Gbps nonreturn to zero and return to zero signals is numerically demonstrated.

Increased skeletal muscle glucose uptake by rosemary extract through AMPK activation

Stimulation of the energy sensor AMP-activated kinase (AMPK) has been viewed as a targeted approach to increase glucose uptake by skeletal muscle and control blood glucose homeostasis. Rosemary extract (RE) has been reported to activate AMPK in hepatocytes and reduce blood glucose levels in vivo but its effects on skeletal muscle are not known. In the present study, we examined the effects of RE and the mechanism of regulation of glucose uptake in muscle cells. RE stimulated glucose uptake in L6 myotubes in a dose- and time-dependent manner. Maximum stimulation was seen with 5 μg/mL of RE for 4 h (184% ± 5.07% of control, p < 0.001), a response comparable to maximum insulin (207% ± 5.26%, p < 0.001) and metformin (216% ± 8.77%, p < 0.001) stimulation. RE did not affect insulin receptor substrate 1 and Akt phosphorylation but significantly increased AMPK and acetyl-CoA carboxylase phosphorylation. Furthermore, the RE-stimulated glucose uptake was significantly reduced by the AMPK inhibitor compound C, but remained unchanged by the PI3K inhibitor, wortmannin. RE did not affect GLUT4 or GLUT1 glucose transporter translocation in contrast with a significant translocation of both transporters seen with insulin or metformin treatment. Our study is the first to show a direct effect of RE on muscle cell glucose uptake by a mechanism that involves AMPK activation.