Analysis of output coupling efficiencies for directional emission triangle and square microlasers

Output coupling efficiencies are analyzed for triangular and square microlasers connected with an output waveguide by FDTD simulation. The results show that square resonator with an output waveguide connected to the midpoint of one side can have high output coupling efficiency and a good mode selection.

Design and optimization of photonic crystal coupling layer for bi-color quantum well infrared photodetectors

Finite difference time domain (FDTD) method is used for the simulation and analysis of electromagnetic field in the top coupling layer of GaAs/AlGaAs quantum well infrared photodetector (QWIP). Simulation results demonstrated the coupling efficiencies and distributions of electromagnetic (EM) field in a variety of 2D photonic crystal coupling layer structures. A photonic crystal structure for bi-color-QWIP is demonstrated with high coupling efficiency for two wavelengths.

Generation of a high-quality partially coherent dark hollow beam with a multimode fiber

We report the experimental generation of a high-quality partially coherent dark hollow beam (DHB) by coupling a partially coherent beam into a multimode fiber (MMF) with a suitable incidence angle. The interference experiment of the generated partially coherent DHB passing through double slits is demonstrated. It is found that the coupling efficiency of the MMF, the quality, and the coherence of the generated partially coherent DHB are closely controlled by the coherence of the input beam. (c) 2008 Optical Society of America.

Cost-effective 10 Gb/s polymer-based chip-to-chip optical interconnect

Board-level optical links are an attractive alternative to their electrical counterparts as they provide higher bandwidth and lower power consumption at high data rates. However, on-board optical technology has to be cost-effective to be commercially deployed. This study presents a chip-to-chip optical interconnect formed on an optoelectronic printed circuit board that uses a simple optical coupling scheme, cost-effective materials and is compatible with well-established manufacturing processes common to the electronics industry. Details of the link architecture, modelling studies of the link's frequency response, characterisation of optical coupling efficiencies and dynamic performance studies of this proof-of-concept chip-to-chip optical interconnect are reported. The fully assembled link exhibits a -3 dBe bandwidth of 9 GHz and -3 dBo tolerances to transverse component misalignments of ±25 and ±37 μm at the input and output waveguide interfaces, respectively. The link has a total insertion loss of 6 dBo and achieves error-free transmission at a 10 Gb/s data rate with a power margin of 11.6 dBo for a bit-error-rate of 10 -12. The proposed architecture demonstrates an integration approach for high-speed board-level chip-to-chip optical links that emphasises component simplicity and manufacturability crucial to the migration of such technology into real-world commercial systems. © 2012 The Institution of Engineering and Technology.

Low-cost PCB-integrated 10-Gb/s optical transceiver built with a novel integration method

A novel integration method for the production of cost-effective optoelectronic printed circuit boards (OE PCBs) is presented. The proposed integration method allows fabrication of OE PCBs with manufacturing processes common to the electronics industry while enabling direct attachment of electronic components onto the board with solder reflow processes as well as board assembly with automated pick-and-place tools. The OE PCB design is based on the use of polymer multimode waveguides, end-fired optical coupling schemes, and simple electro-optic connectors, eliminating the need for additional optical components in the optical layer, such as micro-mirrors and micro-lenses. A proof-of-concept low-cost optical transceiver produced with the proposed integration method is presented. This transceiver is fabricated on a low-cost FR4 substrate, comprises a polymer Y-splitter together with the electronic circuitry of the transmitter and receiver modules and achieves error-free 10-Gb/s bidirectional data transmission. Theoretical studies on the optical coupling efficiencies and alignment tolerances achieved with the employed end-fired coupling schemes are presented while experimental results on the optical transmission characteristics, frequency response, and data transmission performance of the integrated optical links are reported. The demonstrated optoelectronic unit can be used as a front-end optical network unit in short-reach datacommunication links. © 2011-2012 IEEE.

High efficiency and broad bandwidth grating coupler between nanophotonic waveguide and fibre

A high efficiency and broad bandwidth grating coupler between a silicon-on-insulator (SOI) nanophotonic waveguide and fibre is designed and fabricated. Coupling efficiencies of 46% and 25% at a wavelength of 1.55 mu m are achieved by simulation and experiment, respectively. An optical 3 dB bandwidth of 45 nm from 1530 nm to 1575 nm is also obtained in experiment. Numerical calculation shows that a tolerance to fabrication error of 10 nm in etch depth is achievable. The measurement results indicate that the alignment error of +/-2 mu m results in less than 1 dB additional coupling loss.

Output Characteristics of an InP/InGaAsP Triangle Microcavity Laser

Mode competitions between modes with different output coupling efficiencies can result in optical bistability under certain asymmetric nonlinear gain. For a GaInAsP/InP equilateral triangle microlaser with the side length of 10 mu m, the drop of the output power with the increase of the injection current is observed corresponding to transverse mode transitions. Furthermore, the measured laser spectra up to 270 K show that lasing modes coexist with the wavelength interval of 39 nm at 240 K. The emission at 5.2 THz can be expected by the mode frequency beating with the 39 nm interval.

An Improvement on 2× 2 Silicon-on-Insulator Mach-Zehnder Thermo-Optical Switch

An improved 2 ×2 silicon-on-insulator Mach-Zehnder thermo-optical switch is designed and fabricated, which is based on strongly guided multimode interference couplers and single- mode phase-shifting arms. The multimode interference couplers and input/output waveguides are deeply etched to improve coupler performances and coupler-waveguide coupling efficiencies. However, shallow etching is used in the phase-shifting arms to guarantee single-mode property. The strongly guided coupler presents an attractive uniformity about 0. 03 dB and a low propagation loss of -0.6 dB. The 2× 2 switch shows an insertion loss as low as -6.8 dB, where the fiber-waveguide coupling loss of -4.3 dB is included, and the response-time is measured as short as 6.8 μs, which are much better than our previous results.

AN INJECTOR AMPLIFIER DOUBLE TARGET CONFIGURATION FOR THE NE-LIKE GE X-RAY LASER SCHEME

The XUV lasing output from one germanium slab target has been efficiently coupled into, and further amplified in, a second plasma produced by irradiation of a similar target from the opposite direction. The operation of such a double target was shown to be strongly dependent on the distance by which the two target surfaces were displaced. The line brightness peaked for a surface displacement of approximately 200-mu-m and it was observed that the pointing direction of one output beam could be controlled by the surface separation in an asymmetric geometry. Gain length products of approximately 16 with estimated output powers close to the megawatt level were achieved on both the 23.2 and 23.6 nm J=2-1 transitions for an optimised target configuration. Maximum effective coupling efficiencies of the individual outputs from double targets, comprising 2.2 and 1.4 cm length components, approached 100% for beams propagating from the shorter to the longer target.

Molecular mechanisms of protein kinase-mediated desensitization and internalization of the $\beta$-adrenergic receptor

The $\beta$-adrenergic receptor ($\beta$AR), which couples to G$\sb{\rm s}$ and activates adenylylcyclase, has been a prototype for studying the activation and desensitization of G-protein-coupled receptors. The main objective of the present study is to elucidate the molecular mechanisms of protein kinase-mediated desensitization and internalization of the $\beta$AR.^ Activation of cAPK or PKC causes a rapid desensitization of $\beta$AR stimulation of adenylylcyclase in L cells, which previous studies suggest involves the cAPK/PKC consensus phosphorylation site in the third intracellular loop of the $\beta$AR, RRSSK$\sp{263}$. To determine the role of the individual serines in the cAPK- and PKC-meditated desensitizations, wild type (WT) and mutant $\beta$ARs containing the substitutions, Ser$\sp{261} \to$ A, Ser$\sp{262} \to$ A, Ser$\sp{262} \to$ D, and Ser$\sp{261/262} \to$ A, were constructed and stably transfected into L cells. The cAPK-mediated desensitization was decreased 70-80% by the Ser$\sp{262} \to$ A, Ser$\sp{262} \to$ D, and the Ser$\sp{261/262} \to$ A mutations, but was not altered by the Ser$\sp{261} \to$ A substitution, demonstrating that Ser$\sp{262}$ was the primary site of the cAPK-induced desensitization. The PMA/PKC-induced desensitization was unaffected by either of the single serine to alanine substitutions, but was reduced 80% by the double serine to alanine substitution, suggesting that either serine was sufficient to confer the PKC-mediated desensitization. Coincident stimulation of cAPK and PKC caused an additive desensitization which was significantly reduced (80%) only by the double substitution mutation. Quantitative evaluation of the coupling efficiencies and the GTP-shift of the WT and mutant receptors demonstrated that only one of the mutants, Ser$\sp{262} \to$ A, was partially uncoupled. The Ser$\sp{262} \to$ D mutation did not significantly uncouple, demonstrating that introducing a negative charge did not appear to mimic the desensitized state of the receptor.^ To accomplish the in vivo phosphorylation of the $\beta$AR, we used two epitope-modified $\beta$ARs, hemagglutinin-tagged $\beta$AR (HA-$\beta$AR) and 6 histidine-tagged $\beta$AR (6His-$\beta$AR), for a high efficiency purification of the $\beta$AR. Neither HA-$\beta$AR nor 6His-$\beta$AR altered activation and desensitization of the $\beta$AR significantly as compared to unmodified wild type $\beta$AR. 61% recovery of ICYP-labeled $\beta$AR was obtained with Ni-NTA column chromatography.^ The truncation 354 mutant $\beta$AR(T354), lacking putative $\beta$ARK site(s), displayed a normal epinephrine stimulation of adenylylcyclase. Although 1.0 $\mu$M epinephrine induced 60% less desensitization in T354 as compared to wild type $\beta$AR, 1.0 $\mu$M epinephrine-mediated desensitization in T354 was 35% greater than PGE$\sb1$-mediated desensitization, which is essentially identical in both WT and T354. These results suggested that sequences downstream of residue 354 may play a role in homologous desensitization and that internalization may be attributed to the additional desensitization besides the cAMP mechanism in T354 $\beta$AR. (Abstract shortened by UMI.) ^

$\beta\sb2$-adrenergic receptor desensitization, internalization and phosphorylation in response to full and partial agonists

The objective of this study is to test the hypothesis that partial agonists produce less desensitization because they generate less of the active conformation of the $\beta\sb2$-adrenergic receptor ($\beta$AR) (R*) and in turn cause less $\beta$AR phosphorylation by beta adrenergic receptor kinase ($\beta$ARK) and less $\beta$AR internalization. In the present work, rates of desensitization, internalization, and phosphorylation caused by a series of $\beta$AR agonists were correlated with a quantitative measure, defined as coupling efficiency, of agonist-dependent $\beta$AR activation of adenylyl cyclase. These studies were preformed in HEK-293 cells overexpressing the $\beta$AR with hemagglutinin (HA) and 6-histidine (6HIS) epitopes introduced into the N- and C-termini respectively. Agonists chosen provided a 95-fold range of coupling efficiencies, and, relative to epinephrine, the best agonist, (100%) were fenoterol (42%), albuterol (4.9%), dobutamine (2.5%) and ephedrine (1.1%). At concentrations of these agonists yielding $>$90% receptor occupancy, the rate and extent of the rapid phase (0-30 min) of agonist induced desensitization of adenylyl cyclase followed the same order as coupling efficiency, that is, epinephrine $\ge$ fitnoterol $>$ albuterol $>$ dobutamine $>$ ephedrine. The rate of internalization, measured by a loss of surface receptors during desensitization, with respect to these agonists also followed the same order as the desensitization and exhibited a slight lag. Like desensitization and internalization, $\beta$AR phosphorylation exhibited a dependency on agonist strength. The two strongest agonists epinephrine and fenoterol provoked 11 to 13 fold increases in the level of $\beta$AR phosphorylation after just 1 min, whereas the weakest agonists dobutamine and ephedrine caused only 3 to 4 fold increases in phosphorylation. With longer treatment times, the level of $\beta$AR phosphorylation declined with the strong agonists, but progressively increased with the weaker partial agonists. The major conclusion drawn from this study is that the occupancy-dependent rate of receptor phosphorylation increases with agonist coupling efficiencies and that this is sufficient to explain the desensitization, internalization, and phosphorylation data obtained.^ The mechanism of activation and desensitization by the partial $\beta$AR agonist salmeterol was also examined in this study. This drug is extremely hydrophobic and its study presents possibly unique problems. To determine whether salmeterol induces desensitization of the $\beta$AR its action has been studied using our system. Employing the use of reversible antagonists it was found that salmeterol, which has an estimated coupling efficiency near that of albuterol caused $\beta$AR desensitization. This desensitization was much reduced relative to epinephrine. Consistent with its coupling efficiency, it was found to be similar to albuterol in its ability to induce internalization and phosphorylation of the $\beta$AR. (Abstract shortened by UMI.) ^

An automated multiplex oligonucleotide synthesizer: development of high-throughput, low-cost DNA synthesis.

An automated oligonucleotide synthesizer has been developed that can simultaneously and rapidly synthesize up to 96 different oligonucleotides in a 96-well microtiter format using phosphoramidite synthesis chemistry. A modified 96-well plate is positioned under reagent valve banks, and appropriate reagents are delivered into individual wells containing the growing oligonucleotide chain, which is bound to a solid support. Each well has a filter bottom that enables the removal of spent reagents while retaining the solid support matrix. A seal design is employed to control synthesis environment and the entire instrument is automated via computer control. Synthesis cycle times for 96 couplings are < 11 min, allowing a plate of 96 20-mers to be synthesized in < 5 hr. Oligonucleotide synthesis quality is comparable to commercial machines, with average coupling efficiencies routinely > 98% across the entire 96-well plate. No significant well-to-well variations in synthesis quality have been observed in > 6000 oligonucleotides synthesized to date. The reduced reagent usage and increased capacity allow the overall synthesis cost to drop by at least a factor of 10. With the development of this instrument, it is now practical and cost-effective to synthesize thousands to tens of thousands of oligonucleotides.

Insights into the nature of the coupling interactions between uracil corrosion inhibitors and copper : a DFT and molecular dynamics study

In this study, the nature of the coupling interactions between copper and uracil as well as its several derivatives has been systematically investigated employing the atoms in molecules (AIM) theory and energy decomposition analyses. The whole interaction process has been investigated through the analyses of the radial distribution functions of the Cu⋯X (X = S and O) contact on the basis of the ab initio molecular dynamics. No direct relationship between the adsorption strengths and inhibition efficiencies of the inhibitors has been observed. Additionally, the possibility of the methyl-substituted dithiouracil species to act as copper corrosion inhibitors has been tested.

ITO-free top emitting organic light emitting diodes with enhanced light out-coupling

Bottom emitting organic light emitting diodes (OLEDs) can suffer from lower external quantum efficiencies (EQE) due to inefficient out-coupling of the generated light. Herein, it is demonstrated that the current efficiency and EQE of red, yellow, and blue fluorescent single layer polymer OLEDs is significantly enhanced when a MoOx(5 nm)/Ag(10 nm)/MoOx(40 nm) stack is used as the transparent anode in a top emitting OLED structure. A maximum current efficiency and EQE of 21.2 cd/A and 6.7%, respectively, was achieved for a yellow OLED, while a blue OLED achieved a maximum of 16.5 cd/A and 10.1%, respectively. The increase in light out-coupling from the top-emitting OLEDs led to increase in efficiency by a factor of up to 2.2 relative to the optimised bottom emitting devices, which is the best out-coupling reported using solution processed polymers in a simple architecture and a significant step forward for their use in large area lighting and displays.

Efficient photocatalytic Suzuki cross-coupling reactions on Au-Pd alloy nanoparticles under visible light irradiation

We report herein highly efficient photocatalysts comprising supported nanoparticles (NPs) of gold (Au) and palladium (Pd) alloys, which utilize visible light to catalyse the Suzuki cross-coupling reactions at ambient temperature. The alloy NPs strongly absorb visible light, energizing the conduction electrons of NPs which produce highly energetic electrons at the surface sites. The surface of the energized NPs activates the substrates and these particles exhibit good activity on a range of typical Suzuki reaction combinations. The photocatalytic efficiencies strongly depend on the Au:Pd ratio of the alloy NPs, irradiation light intensity and wavelength. The results show that the alloy nanoparticles efficiently couple thermal and photonic energy sources to drive Suzuki reactions. Results of the density functional theory (DFT) calculations indicate that transfer of the light-excited electrons from the nanoparticle surface to the reactant molecules adsorbed on the nanoparticle surface activates the reactants. The knowledge acquired in this study may inspire further studies of new efficient photocatalysts and a wide range of organic syntheses driven by sunlight.