Fabrication and characteristics of high-speed implant-confined index-guided lateral-current 850-nm vertical cavity surface-emitting lasers

Process technology of high-speed implant-apertured index-guide lateral-current-injection top dielectric-mirror quantum-well 850-nm vertical cavity surface-emitting lasers (VCSELs) has been developed. Oxygen and helium implantation for aperture definition and extrinsic capacitance reduction, dielectric mirror formation, p- and n-ohmic contact formation, VCSEL resistance, and thermal analysis were investigated. Employing this technology, GaAs/AlGaAs-based 850-nm VCSELs with small signal modulation bandwidths up to 11.5 Gb/s and an eye diagram generated at 12 Gb/s by a pseudorandom bit sequence of 2/sup 31/-1 were achieved. The bit-error rates were below 10/sup -13/. The threshold current is as low as 0.8 mA for 7-/spl mu/m-diameter current apertures and typical slope efficiencies of 0.45-0.5 mA/mW were obtained.     

A 5 mW and 5% efficiency 210 GHz InP-based heterostructure barrier varactor quintupler

This letter reviews the design, construction, and measurement of a 210 GHz heterostructure barrier varactor frequency quintupler. The quintupler utilizes planar heterostructure barrier varactors (HBVs) based on the InGaAs/InAlAs/AlAs material system and has produced a measured output power of 5.2 mW with 5.2% conversion efficiency at 210 GHz. This performance is comparable to the state-of-the-art results reported in the literature for HBV frequency triplers operating at millimeter and submillimeter wavelengths.     

A digital quadrature modulator with on-chip D/A converter

The first analog IF mixer stage of a transmitter can be replaced with this digital quadrature modulator. The modulator interpolates orthogonal input carriers by 16 and performs digital quadrature modulation at carrier frequencies f/sub s//4, -f/sub s//4,f/sub s//2 (f/sub s/ is the sampling frequency). A 12-b digital-to-analog (D/A) converter is integrated with the digital quadrature modulator. A segmented current source architecture is combined with a proper switching technique to reduce spurious components and to enhance dynamic performance. The digital quadrature modulator is designed to fulfill the spectral, phase, and EVM specifications of GSM, EDGE, and WCDMA base stations. The die area of the chip is 27.09 mm/sup 2/ (0.35-/spl mu/m CMOS technology) and the total power consumption is 1.02 W with 2.8 V at 500-MHz output sampling rate (0.78-W digital modulator, 0.24-W D/A converter).     

Design of radiation-emission measurements of an air-traffic surveillance radar

The current work presents the procedure of designing and carrying out measurements of radiation emission from an air-traffic surveillance radar. The system requirements are first given, and then the equipment used is described. The steps to determine the operating characteristics of the radar are specified in detail. The necessary methods for manual power measurements and calculations are next explained. Since the final measurement system was fully automated, its main features (topology, protocol of operation) are also given. Finally, some measurement results taken during the initial phase of system operation are presented and discussed.     

An adaptive Gaussian model for satellite image deblurring

The deconvolution of blurred and noisy satellite images is an ill-posed inverse problem, which can be regularized within a Bayesian context by using an a priori model of the reconstructed solution. Since real satellite data show spatially variant characteristics, we propose here to use an inhomogeneous model. We use the maximum likelihood estimator (MLE) to estimate its parameters and we show that the MLE computed on the corrupted image is not suitable for image deconvolution because it is not robust to noise. We then show that the estimation is correct only if it is made from the original image. Since this image is unknown, we need to compute an approximation of sufficiently good quality to provide useful estimation results. Such an approximation is provided by a wavelet-based deconvolution algorithm. Thus, a hybrid method is first used to estimate the space-variant parameters from this image and then to compute the regularized solution. The obtained results on high resolution satellite images simultaneously exhibit sharp edges, correctly restored textures, and a high SNR in homogeneous areas, since the proposed technique adapts to the local characteristics of the data.     

Dangerous liaisons? Component-based development and organizational subcultures

This paper presents an exploratory case study of the investment banking arm of a multinational banking corporation (Invebank) and its attempt to introduce component-based development (CBD). Based on a logic of opposition and utilizing literature on organizational culture and metaphors as an analytical device, issues confronting Invebank in CBD adoption are identified. In particular, problems in CBD implementation were encountered because, while CBD requires extensive knowledge sharing and collaboration, subcultural differences in Invebank meant that this proved difficult to enact. Thus, the paper considers the complexities of subcultural differences in firms and provides a salutary reminder that the implementation of corporate-wide integrative "solutions" such as CBD, may be problematic. Further, there is more to the issue of organizational subcultural differences than the oft-cited business-information technology (IT) divide. Nevertheless, the case demonstrates that subcultural differences should not simply be viewed as a threat. Rather, the recognition and discussion of these differences can provide a stimulus for identifying limitations of the policies surrounding technology implementation and use that if changed could help to maximize the benefits of the technology. Simplistic entreaties to knowledge sharing and the nurture of collaboration and consensus are, thus, brought into question. Implications for further research into the implementation of integrative software solutions like CBD in multifunctional and multifarious organizations are also considered.     

Block Copolymer Surface Reconstuction: A Reversible Route to Nanoporous Films

Thin films of block copolymers have been used as templates and scaffolds for the fabrication of arrays of nanostructured materials. In general, a chemical modification of the film or the removal of one of the components by photodegradative methods is required to produce a nanoporous film that serves as a template or scaffold. Here, however, the preferential interaction of one of the components with a solvent is shown to produce a reconstruction of the block copolymer film that, upon drying, leads to the generation of a nanoporous template. The area density of the pores is identical to that of the original copolymer thin film. Since no chemical reactions occurr, the process is fully reversible. Upon heating the copolymer film above its glass‐transition temperature, mobility is imparted to the copolymer and the original copolymer film with oriented domains is recovered. The film reconstruction significantly simplifies the generation of nanoporous templates.     

Parasitic-aware RF circuit design and optimization

RF circuit synthesis techniques based on particle swarm optimization and adaptive simulated annealing with tunneling are described, and comparisons of parasitic-aware designs of an RF distributed amplifier and a nonlinear power amplifier are presented. Synthesized in 0.35-/spl mu/m digital CMOS using a single 3.3-V power supply, the designs provide an 8-dB gain and 8-GHz bandwidth for a four-stage distributed amplifier, and 1.2-W output power with 55% drain efficiency at 900 MHz for a three-stage power amplifier. A standard circuit simulator, HSPICE or SPECTRE, embedded in an optimization loop is used to evaluate cost functions. The proposed design and optimization methodology is computationally efficient and robust in searching complex multidimensional design spaces.     

On Schur stable multivariate polynomials

The class of stable multivariate polynomials, recently introduced by Kaczorek (1985), is the largest class of polynomials preserving the stability property under small coefficient variations. The principal goal of the contribution is to show that the class of Schur stable multivariate polynomials is the Moebius transformation of the latter one. This fundamental relation provides a vehicle to translate results known for one class to the other one.     

High temperature transport kinetics in heteroepitaxial LaFeO3 thin films

Heteroepitaxial LaFeO₃(1 1 0) thin films with a thickness of 150 nm were grown on LaAlO₃(0 0 1) by reactive sputtering in an inverted cylindrical magnetron geometry. Equilibrium conductivity was measured as a function of partial pressure of oxygen at T=1000 °C, and logσ plotted vs. logP(O₂) showed a minimum in conductivity for P(O₂)=10⁻¹¹ atm and a linear response between 10⁻¹⁰ and 1 atm. This linear response makes thin films of LaFeO₃ a promising material for oxygen sensor applications. We have also measured the time response of the film conductivity upon an abrupt change in the partial pressure of ambient oxygen from 10⁻² to 10⁻³ atm, which was determined at 60 s for T=700 °C and <3.5 s at T=1000 °C.