Two-step laterally tapered spot-size converter 1.55-/spl mu/m DFB laser diode having a high slope efficiency

We demonstrate a two-step lateral tapered 1.55-/spl mu/m spot-size converter distributed feedback laser diode (SSC DFB LD) having slope efficiencies as high as 0.457 and 0.319 mW/mA measured at 25 /spl deg/C and 85 /spl deg/C, respectively. The SSC DFB LD fabricated by using a nonselective grating process has a double core waveguide structure including a planar buried heterostructure type active waveguide and a ridge type passive waveguide. The fabricated SSC DFB LD operates at 1.553-/spl mu/m wavelength and shows a far-field pattern in horizontal and vertical directions of 7.3/spl deg/ and 11.6/spl deg/, respectively.     

Modeling growth rate of HfO2 thin films grown by metal-organic molecular beam epitaxy

HfO₂ dielectric layers were grown on the p-type Si (100) substrate by metal-organic molecular beam epitaxy (MOMBE). Hafnium-tetra-butoxide, Hf(O·t-C₄H₉)₄ was used as a Hf precursor and Argon gas was used as a carrier gas. The thickness of the HfO₂ film and intermediate SiO₂ layer were measured by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The properties of the HfO₂ layers were evaluated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high frequency (HF) capacitance-voltage (C-V) measurement, and current-voltage (I-V) measurement. C-V and I-V measurements have shown that HfO₂ layer grown by MOMBE has a high dielectric constant (k) of 20-22 and a low-level of leakage current density. The growth rate is affected by various process variables such as substrate temperature, bubbler temperature, Ar and O₂ gas flows and growth time. Since the ratio of O₂ and Ar gas flows are closely correlated, the effect of variations in O₂/Ar flow ratio on growth rate is also investigated using statistical modeling methodology.     

Energy payback and life‐cycle CO2 emissions of the BOS in an optimized 3·5 MW PV installation

This study is a life‐cycle analysis of the balance of system (BOS) components of the 3·5 MW_p multi‐crystalline PV installation at Tucson Electric Power's (TEP) Springerville, AZ field PV plant. TEP instituted an innovative PV installation program guided by design optimization and cost minimization. The advanced design of the PV structure incorporated the weight of the PV modules as an element of support design, thereby eliminating the need for concrete foundations. The estimate of the life‐cycle energy requirements embodied in the BOS is 542 MJ/m², a 71% reduction from those of an older central plant; the corresponding life‐cycle greenhouse gas emissions are 29 kg CO₂ eq./m². From field measurements, the energy payback time (EPT) of the BOS is 0·21 years for the actual location of this plant, and 0·37 years for average US insolation/temperature conditions. This is a great improvement from the EPT of about 1·3 years, estimated for an older central plant. The total cost of the balance of system components was $940 US per kW_p of installed PV, another milestone in improvement. These results were verified with data from different databases and further tested with sensitivity‐ and data‐uncertainty analyses. Copyright © 2005 John Wiley & Sons, Ltd.     

Theory of Switched RF Resonators

Transient characteristics of switched resonators have been studied. The resonators exhibit controllable impedance and energy storage behaviors during an alternating charging and discharging process. It is discovered that these unique characteristics of switched resonators can lead to novel RF envelope signal processing functions. The paper discusses the basic theory of switched resonators and the designing methodology of relevant RF signal processing applications. Two applications are presented as examples. The first example is a variable, reflective attenuator which uses the controllable impedance of the switched resonators to achieve different attenuation/reflection levels. In the second example, a simple, compact and efficient RF pulse compression technique based on the switched resonator concept is introduced. It utilizes the charging/discharging characteristics of the circuit resonator by varying the resonator's Q-factor. The approach compresses the duration of the modulated pulse without changing the phase characteristics of the RF carrier. The pulse compression technique can also be implemented with other type of resonators including distributed resonators, as demonstrated through the experiments     

Spiral-shaped electromagnetic bandgap structure for simultaneous switching noise suppression

A spiral-shaped electromagnetic bandgap (EBG) structure is proposed to suppress simultaneous switching noise effectively when the power plane drives high-speed ICs. The new EBG structure is locally or periodically utilised on the power plane. Even with reduced unit cell size, its port-to-port transmission characteristic shows a much wider stopband than other conventional EBG structures.     

Intensity surface stretching technique for contrast enhancement of digital photography

In this paper we propose a contrast enhancement technique which stretches the intensity surfaces of an image to improve the quality of a digital photo. The proposed method enhances the contrast of an image by stretching the intensity surface of the original image to the maximum range of the output image. This is done in proportion to the distances between the original intensity surface, and the upper and lower intensity surfaces respectively. The upper and lower intensity surfaces are generated adaptively from the original intensity surface by gaussian smoothing and gamma transform. In our experiments, digital color images in a variety of illumination conditions were used, and the proposed method was compared with other algorithms such as histogram stretching, histogram equalization, gamma correction, and retinex. From the results of the experiments, it was proven that the proposed algorithm further enhanced the contrast more than other methods and resulted in a more natural image without deterioration of gradation.

A simple SNR representation method for AMC schemes of MIMO systems with ML detector

Adaptive modulation and coding (AMC) is a powerful technique to enhance the link performance by adjusting the transmission power, channel coding rates and modulation levels according to channel state information. In order to efficiently utilize the AMC scheme, an accurate signal-to-noise ratio (SNR) value is normally required for determining the AMC level. In this paper, we propose a simple method to represent the SNR values for maximum likelihood (ML) detector in multi-input multi-output (MIMO) systems. By analyzing the relation between the upper bound and the lower bound of the ML detector performance, we introduce an efficient way to determine the SNR for the ML receiver. Based on the proposed SNR representation, an AMC scheme for single antenna systems can be extended to MIMO systems with ML detector. From computer simulations, we confirm that the proposed SNR representation allows us to achieve almost the same system throughput as the optimum AMC systems in frequency selective channels with reduced complexity.     

Wavelength‐Dependent Photosensitivity in a Germanium‐Doped Sol–Gel Hybrid Material for Direct Photopatterning

Photosensitivity, as evident in permanent changes in refractive index and volume upon light exposure, is observed in a germanium‐doped methacrylate hybrid material (hybrimer) and found to depend on the wavelength of the UV light. Exposure to short‐wavelength UV illumination (220–260 nm) results in very high photosensitivity with changes in refractive index (Δn ≈ 0.0164) and film thickness (Δt ≈ –40 %) that are mainly a result of photopolymerization and Ge‐related densification. In contrast, the hybrimer is hardly photosensitive to light in the long UV‐wavelength range (350–390 nm). Direct photopatterning of a single circle on the hybrimer film creates a concave lens‐like topography upon illumination with UV light of short wavelength and a convex lens‐like one upon illumination with UV light of long wavelength.     

Design,Implementation, and Validation of KOMPSAT‐2 Software Simulator

In this paper, we present design features, implementation, and validation of a satellite simulator subsystem for the Korea Multi‐Purpose Satellite‐2 (KOMPSAT‐2). The satellite simulator subsystem is implemented on a personal computer to minimize costs and trouble on embedding onboard flight software into the simulator. An object‐oriented design methodology is employed to maximize software reusability. Also, instead of a high‐cost commercial database, XML is used for the manipulation of spacecraft characteristics data, telecommand, telemetry, and simulation data. The KOMPSAT‐2 satellite simulator subsystem is validated by various simulations for autonomous onboard launch and early orbit phase operations, anomaly operation, and science fine mode operation. It is also officially verified by successfully passing various tests such as the satellite simulator subsystem test, mission control element system integration test, interface test, site installation test, and acceptance test.     

Pipelined Scheduling of Functional HW/SW Modules for Platform‐Based SoC Design

We developed a pipelined scheduling technique of functional hardware and software modules for platform‐based system‐on‐a‐chip (SoC) designs. It is based on a modified list scheduling algorithm. We used the pipelined scheduling technique for a performance analysis of an MPEG4 video encoder application. Then, we applied it for architecture exploration to achieve a better performance. In our experiments, the modified SoC platform with 6 pipelines for the 32‐bit dual layer architecture shows a 118% improvement in performance compared to the given basic SoC platform with 4 pipelines for the 16‐bit single‐layer architecture.