Polarisation stabilisation of vertical cavity surface emitting lasers by minimally invasive focused electron beam triggered chemistry

Local electron triggered reactions of functional surface adsorbates were used as a maskless, dry, and minimally invasive nanolithography concept to stabilize the polarisation of individual vertical cavity surface emitting lasers (VCSELs) on a wafer in a post-processing step. Using a 30 keV focused electron beam of a scanning electron microscope and injecting volatile organo-metallic (CH(3))(2)Au(tfa) molecules, polarisation gratings were directly written on VCSELs by dissociating the surface adsorbed molecules. The electron triggered adsorbate dissociation resulted in electrically conductive Au-C nano-composite material, with gold nanocrystals embedded in a carbonaceous matrix. A resistivity of 2500 μ?cm was measured at a typical composition of 30 at.% Au. This material proved successful in suppressing polarisation switching when deposited as line gratings with a width of 200 nm, a thickness of 50 nm, and a pitch of 500 nm and 1 μm. Refractive index measurements suggest that the optical attenuation by the deposited Au-C material is much lower than by pure Au thus giving a low emission power penalty while keeping the polarisation stable.     

Enhanced in vivo Optical Imaging of the Inflammatory Response to Acute Liver Injury in C57BL/6 Mice Using a Highly Bright Near-Infrared BODIPY Dye

Delving deeper is possible in whole-body in vivo imaging using a super-bright membrane-targeting BODIPY dye ( BD ). The dye was used to monitor homing of ex vivo fluorescently labelled neutrophils to an injured liver of dark-pigmented C57BL/6 mice. In vivo imaging system (IVIS) data conclusively showed an enhanced signal intensity and a higher signal-to-noise ratio in mice receiving neutrophils labelled with the BD dye relative to those labelled with a gold standard dye at 2 h post in vivo administration of fluorescently labelled cells. Fluorescence-activated cell sorting (FACS) confirmed that BD is nontoxic, and an exceptional cell labelling dye that opens up precision deep-organ in vivo imaging of inflammation in mice routinely used for biomedical research. The origin of enhanced performance is identified with the molecular structure and the distinct localisation of the dye within cells that enable remarkable changes in its optical parameters.     

Vertical-Cavity Surface-Emitting 1.55-μm Lasers Fabricated by Fusion

The results of studies on fabrication of vertical-cavity surface-emitting 1.55-μm lasers by fusing AlGaAs/GaAs distributed-Bragg-reflector wafers and an active region based on thin In_0.74Ga_0.26 As quantum wells grown by molecular-beam epitaxy are presented. Lasers with a current aperture diameter of 8 μm exhibit continuous lasing with a threshold current below 1.5 mA, an output optical power of 6 mW, and an efficiency of approximately 22%. Single-mode lasing with a side-mode suppression ratio of 40–45 dB is observed in the entire operating current range. The effective modulation frequency of these lasers is as high as 9 GHz and is limited by the low parasitic cutoff frequency and self-heating.     

Pricing Multicast Communication: A Cost-Based Approach

Multicast and unicast traffic share and compete for network resources. A cost-based approach to multicast pricing, based on accurate characterization of multicast scalability, will facilitate the efficient and equitable resource allocation between traffic types. Through the quantification of link usage, this paper establishes a multicast scaling relationship: the cost of a multicast distribution tree varies at the 0.8 power of the multicast group size. This result is validated with both real and generated networks, and is robust across topological styles and network sizes. Since multicast cost can be accurately predicted given the membership size, there is strong motivation to price multicast according to membership size. Furthermore, a price ceiling should be set to account for the effect of tree saturation. This tariff structure is superior to either a purely membership-based or a flat-rate pricing scheme, since it reflects the actual tree cost at all group membership levels.     

Credits and debits on the Internet

Since the advent of banking in the Middle Ages, bank customers have used paper based instruments to move money between accounts. In the past 25 years (1972-97), electronic messages moving through private networks have replaced paper for most of the value exchanged among banks each day. With the arrival of the Internet as a mass market data network, new technologies and business models are being developed to facilitate electronic credit and debit transfers by ordinary consumers. These new systems include CyberCash (which is a gateway between the Internet and the authorization networks of the major credit cards) and the Secure Electronic Transactions protocol (a standard for presenting credit card transactions on the Internet), as well as First Virtual (a way of using e-mail to secure approval for credit card purchases of information), GC Tech (a payment system that can use credit or debit via an intermediation server), and NetBill (a public private key encryption system for purchasing information)     

Optimized combined harmonic filtering system

This paper presents a thorough analysis of the operation for the combined filtering system consisting of a passive filter with diodes connected in parallel with the capacitors and a low-power inverter. The diodes limit the voltage across the capacitors and the inverter starts to work when disturbances occur in the three-phase network, sending back to the network the excess energy taken by all the capacitors from the network during these disturbances. The proposed combined filtering system has reduced size and cost as well as high efficiency. Laboratory experiments and simulation results proving the effectiveness of the solution are also presented     

Superstars and outsiders in online markets: An empirical analysis of electronic books

Recent rapid growth in electronic book sales has raised a critical question for publishers and bookstores: do e-books cannibalize or increase print sales? In this article, we compare the best-selling titles sold on www.Amazon.com in print or electronic Kindle formats during the period from November 2007 to July 2010. Using econometric methods, we find that the cannibalization of print sales by e-books is more likely to occur for superstar titles written by successful authors. However, we find that a new segment of successful electronic titles that are not best-selling in print format emerge; these books would probably have been unpopular without the new Kindle store and therefore this new distribution channel has expanded the market. We refer to these titles as digital outsiders. The latter are characterized not only by lower prices but also by older release dates. They also include titles that are only released in electronic format. We then argue that electronic books increase the market viability of old print releases. Finally we identify a category that we call print-preferred books that are top sellers in print but not as e-books for reasons of color, graphics, or the need to navigate non-linearly, a style to which the current generation of e-book readers are not well adapted.     

Multichannel Estimation and Equalization Algorithm for Asynchronous Uplink DS/CDMA

This paper addresses the problem of channel estimation andequalization in asynchronous uplink DS/CDMA. We propose a completereceiver structure which contains a multichannel estimator suitablefor time-varying channels, a MMSE equalizer and a propagation delayestimator. The multichannel estimator is a stochastic gradientalgorithm which does not require any knowledge about the propagationdelays. It estimates a matrix which contains a linear combination ofthe impulse response of each channel and the propagation delays. Thisestimate is used to derive a MMSE equalizer. In the despreading stageknowledge on the integer part (chip period multiple) of thepropagation delays is needed. Two reduced complexity schemes forpropagation delay estimation are presented. The channel estimatorconvergence is studied in stationary conditions while the overallalgorithm performance is demonstrated by using simulations intime-varying channel conditions.     

Cathodoluminescence characterization of rare earth doped composite materials based on porous GaP

Porous GaP layers doped with erbium or europium elements have been obtained by electrochemical etching and further impregnation processes. The thermal treatments for optical activation of rare earth (RE) ions lead to partial oxidation of porous GaP skeleton and a composite material is obtained. The presence of ErPO₄ and EuPO₄ oxide nanophases is detected by X-ray diffraction (XRD) analysis. Visible luminescence from RE ions in the composite material has been investigated by means of the cathodoluminescence (CL) technique in the scanning electron microscope. Intense red and green emission lines characteristic from Er³⁺ and Eu³⁺ ions dominate the CL spectra in the case of parallel and regular nanotubes in the samples. The role of the oxygen content and the detected phases in the luminescence results are discussed.