On leaky mode approximations for modal expansion in multilayer openwaveguides

We propose an analytic method to calculate the leaky mode functions to enable modal expansion without encountering the normalization and orthogonality problems of the unphysical mode shape. The wave functions of leaky modes are derived from the explicit formulas of normalized radiation modes. Using leaky modes to approximate a continuum of radiation modes greatly simplifies the analysis of excitation, transitions, propagation, and radiation of light waves in multilayer waveguide structures. Upon comparison with the beam propagation method and modal propagation method, we show that the leaky mode approximation while requiring a much simpler computation is as accurate. This method can also provide better physical insight to device operations     

a-SiC:H/SiO2 Laminated Polarization Splitter for the Wavelength Region Longer Than 1.3 μm Prepared by Plasma-Enhanced Chemical Vapor Deposition

A laminated polarization splitter for the wavelength region longer than 1.3 μm is fabricated for the first time. It is composed of a-SiC:H/SiO₂ alternative multilayers prepared by plasma-enhanced chemical vapor deposition. Splitting behavior is also verified experimentally. It has low absorption loss even for the wavelength region around λ = 1.3 μm because the band-gap energy of a-Sic is larger than that of a-Si. The measured splitting angle is 13.8°, which is 2.4 times larger than the 5.7° splitting angle of rutile. The absorption loss of the multilayer is reduced to 1 × 10^-3 dB/μm at λ = 1.3 μm. The magnitude of the residual stress is 9.45 × 10⁸ dyn/cm², which is about one-third of that prepared by the rf bias sputtering equipment which is used for another project of our group. The deposition rate of SiO₂, is increased to 135 nm/min, which is 27 times larger than that prepared by the sputtering equipment.     

Low-power design techniques for high-performance CMOS adders

A high-performance adder is one of the most critical components of a processor which determines its throughput, as it is used in the ALU, the floating-point unit, and for address generation in case of cache or memory access. In this paper, low-power design techniques for various digital circuit families are studied for implementing high-performance adders, with the objective to optimize performance per watt or energy efficiency as well as silicon area efficiency. While the investigation is done using 100 MHz, 32 b carry lookahead (CLA) adders in a 0.6 μm CMOS technology, most techniques presented here can also be applied to other parallel adder algorithms such as carry-select adders (CSA) and other energy efficient CMOS circuits. Among the techniques presented here, the double pass-transistor logic (DPL) is found to be the most energy efficient while the single-rail domino and complementary pass-transistor logic (CPL) result in the best performance and the most area efficient adders, respectively. The impact of transistor threshold voltage scaling on energy efficiency is also examined when the supply voltage is scaled from 3.5 V down to 1.0 V     

An ARQ scheme using combined QPSK and BPSK transmissions

We propose a hybrid ARQ scheme which uses QPSK modulation for the first transmission and BPSK modulation for retransmissions. The throughput performance of the proposed ARQ scheme is better that those of ARQ schemes purely using QPSK modulation or purely using BPSK modulation for transmissions. Furthermore, the proposed scheme does not require any operation of error correction as usually required in hybrid ARQ schemes. Therefore, the ARQ scheme proposed in this paper can be easily implemented     

Delocalized Electron Accumulation at Nanorod Tips: Origin of Efficient H2 Generation

Photocatalytic hydrogen (H₂) evolution requires efficient electron transfer to catalytically active sites in competition with charge recombination. Thus, controlling charge‐carrier dynamics in the photocatalytic H₂ evolution process is essential for optimized photocatalyst nanostructures. Here, the efficient delocalization of electrons is demonstrated in a heterostructure consisting of optimized MoS₂ tips and CdS nanorods (M‐t‐CdS Nrs) synthesized by amine‐assisted oriented attachment. The heterostructure achieves photocatalytic H₂ activity of 8.44 mmol h^?1 g^?1 with excellent long‐term durability (>23 h) without additional passivation under simulated solar light (AM 1.5, 100 mW cm^?2). This activity is nearly two orders of magnitude higher than that of pure CdS Nrs. The impressive photocatalytic H₂ activity of M‐t‐CdS Nrs reflects favorable charge‐carrier dynamics, as determined by steady‐state PL and time‐correlated single photon counting correlation analysis at low temperature. The MoS₂ cocatalysts precisely located at the end of the CdS Nrs exhibit ultrafast charge transfer and slow charge recombination via spatially localized deeper energy states, resulting in a highly efficient H₂ evolution reaction in lactic acid containing an electrolyte.     

Effective Polysulfide Rejection by Dipole‐Aligned BaTiO3 Coated Separator in Lithium–Sulfur Batteries

Although the exceptional theoretical specific capacity (1672 mAh g^?1) of elemental sulfur makes lithium–sulfur (Li–S) batteries attractive for upcoming rechargeable battery applications (e.g., electrical vehicles, drones, unmanned aerial vehicles, etc.), insufficient cycle lives of Li–S cells leave a substantial gap before their wide penetration into commercial markets. Among the key features that affect the cyclability, the shuttling process involving polysulfides (PS) dissolution is most fatal. In an effort to suppress this chronic PS shuttling, herein, a separator coated with poled BaTiO₃ or BTO particles is introduced. Permanent dipoles that are formed in the BTO particles upon the application of an electric field can effectively reject PS from passing through the separator via electrostatic repulsion, resulting in significantly improved cyclability, even when a simple mixture of elemental sulfur and conductive carbon is used as a sulfur cathode. The coating of BTO particles also considerably suppresses thermal shrinkage of the poly(ethylene) separator at high temperatures and thus enhances the safety of the cell adopting the given separator. The incorporation of poled particles can be universally applied to a wide range of rechargeable batteries (i.e., metal‐air batteries) that suffer from cross‐contamination of charged species between both electrodes.     

Predictive Validity of an Empirical Approach for Selecting Promising Message Topics: A Randomized‐Controlled Study

Several message topic selection approaches propose that messages based on beliefs pretested and found to be more strongly associated with intentions will be more effective in changing population intentions and behaviors when used in a campaign. This study aimed to validate the underlying causal assumption of these approaches which rely on cross‐sectional belief–intention associations. We experimentally tested whether messages addressing promising themes as identified by the above criterion were more persuasive than messages addressing less promising themes. Contrary to expectations, all messages increased intentions. Interestingly, mediation analyses showed that while messages deemed promising affected intentions through changes in targeted promising beliefs, messages deemed less promising also achieved persuasion by influencing nontargeted promising beliefs. Implications for message topic selection are discussed.     

S/W Based Frame‐Level Synchronization for Irregular Screen Processing System

A multi‐screen environment provides a new opportunity for digital signage applications, where various irregularly shaped screens are employed as an effective means for advertisements and information. A formation method applicable to numerous irregularly shaped screens is proposed to provide a new perspective on digital signage applications. The crucial part of the proposed method comes from the geometric sensing of each screen and the formation of a virtual screen where geometrically aligned content extraction and encoding are employed for content transmission to each screen. In addition, a software‐based synchronization method for the proposed system is proposed to address the frame‐level synchronization between screens. The experimental results of the proposed method show an improved performance of the frame‐level synchronization, where the inconsistency between frames is not identified.     

An alternative method to fabricate the planar-type resonant-cavity light-emitting diodes by using silicon oxide for short-reach communications

In this article, the silicon oxide (SiO_x) planarization technique is presented to fabricate the 650-nm resonant-cavity light-emitting diodes (RCLEDs). The performances of RCLEDs are characterized by forward voltage, light output power, external quantum efficiency, emission spectrum, and dynamic response. As a result, the device with the SiO_x-planarized layer exhibits a low operating voltage of 2.3 V at 20 mA, a maximum light output power of 304 μW at 15 mA, and the best external quantum efficiency of 3% at 1.2 mA. In addition, the SiO_x-planarized device exhibits temperature insensitivity as compared to the device without it. The RCLED with a 30-μm diameter shows the maximum 3 dB frequency bandwidth of 275 MHz at a driving current of 40 mA. Finally, the RCLED with a SiO_x-planarized layer shows a clear eye-opening feature as operating at 100 Mbit/s at 20 mA. These results indicate that such LEDs are excellent candidates for use in high-speed short-reach plastic optical fiber communications.