Bendable and Splitter-Integrated Optical Subassembly Based on a Flexible Optical Board

A bendable and splitter-integrated optical subassembly (OSA) is suggested as a short-distance board-to-board optical interconnection. This OSA was fabricated by simply packaging a vertical-cavity surface-emitting laser on a flexible optical board having an embedded 1 $times$ 8 optical splitter waveguide. Finally, we measured various optical characteristics of the OSA, including insertion, twist, and bending losses.      

A Rigorous 2D Approximation Technique for 3D Waveguide Structures for BPM Calculations

We propose a rigorous 2D approximation technique for the 3D waveguide structures; it can minimize the well‐known approximation errors of the commonly used effective index method. The main concept of the proposed technique is to compensate for the effective cladding index in the equivalent slab model of the original channel waveguide from the modal effective index calculated by the nonuniform 2D finite difference method. With simulations, we used the proposed technique to calculate the coupling characteristics of a directional coupler by the 2D beam propagation method, and the results were almost exactly the same as the results calculated by the 3D beam propagation method.     

Performance analysis of opportunistic CSMA schemes in cognitive radio networks

In this paper, we consider underlay cognitive radio (CR) networks where an amount of interference caused by secondary stations (STAs) has to be kept below a predefined level, which is called interference temperature. We propose opportunistic p-persistent carrier sense multiple access schemes for the CR networks, which opportunistically exploit wireless channel conditions in transmitting data to the secondary access point. We also devise an adaptive interference-level control technique to further improve quality-of-service of a primary network by limiting the excessive interference due to collisions among STAs. The performances of the proposed schemes are mathematically analyzed, and they are validated with extensive computer simulations. The simulation results show that the proposed schemes achieve near optimal throughput of the secondary network while they are backward-compatible to the conventional p-persistent CSMA scheme.     

Low‐Power 512‐Bit EEPROM Designed for UHF RFID Tag Chip

In this paper, the design of a low‐power 512‐bit synchronous EEPROM for a passive UHF RFID tag chip is presented. We apply low‐power schemes, such as dual power supply voltage (VDD=1.5 V and VDDP=2.5 V), clocked inverter sensing, voltage‐up converter, I/O interface, and Dickson charge pump using Schottky diode. An EEPROM is fabricated with the 0.25 μm EEPROM process. Power dissipation is 32.78 μW in the read cycle and 78.05 μW in the write cycle. The layout size is 449.3 μm × 480.67 μm.     

A single-electrode capacitive sensor using incremental delta–sigma architecture

This paper presents a single-electrode capacitive sensor using a single-bit second-order incremental delta–sigma architecture. In order to achieve high accuracy in this capacitance-to-digital converter (CDC), the shielding signal and the digitally controlled offset capacitors are used in combination with the delta–sigma CDC. The designed sensor is suitable for capacitive transducers for ±10 pF input range with sub-fF resolution.     

Organic Phenolic Configurationally Locked Polyene Single Crystals for Electro‐optic and Terahertz Wave Applications

We investigate a configurationally locked polyene (CLP) crystal 2‐(3‐(4‐hydroxystyryl)‐5,5‐dimethylcyclohex‐2‐enylidene)malononitrile (OH1) containing a phenolic electron donor, which also acts as a hydrogen bond donor. The OH1 crystals with orthorhombic space group Pna2₁ (point group mm2) exhibit large second‐order nonlinear optical figures of merit, high thermal stability and very favorable crystal growth characteristics. Higher solubility in methanol and a larger temperature difference between the melting temperature and the decomposition temperature of OH1 compared to analogous CLP crystals, are of advantage for solution and melt crystal growth, respectively. Acentric bulk OH1 crystals of large sizes with side lengths of up to 1 cm with excellent optical quality have been successfully grown from methanol solution. The microscopic and macroscopic nonlinearities of the OH1 crystals are investigated theoretically and experimentally. The OH1 crystals exhibit a large macroscopic nonlinearity with four times larger powder second harmonic generation efficiency than that of analogous CLP crystals containing dimethylamino electron donor. A very high potential of OH1 crystals for broadband THz wave emitters in the full frequency range of 0.1–3 THz by optical rectification of 160 fs pulses has been demonstrated.     

Pixel‐Structured Scintillator with Polymeric Microstructures for X‐Ray Image Sensors

We introduce a pixel‐structured scintillator realized on a flexible polymeric substrate and demonstrate its feasibility as an X‐ray converter when it is coupled to photosensitive elements. The sample was prepared by filling Gd₂O₂S:Tb scintillation material into a square‐pore‐shape cavity array fabricated with polyethylene. For comparison, a sample with the conventional continuous geometry was also prepared. Although the pixelated geometry showed X‐ray sensitivity of about 58% compared with the conventional geometry, the resolving power was improved by about 70% above a spatial frequency of 3 mm^?1. The spatial frequency at 10% of the modulation‐transfer function was about 6 mm^?1.     

Optimized RTL Code Generation from Coarse-Grain Dataflow Specification for Fast HW/SW Cosynthesis

This paper presents a new methodology of automatic RTL code generation from coarse-grain dataflow specification for fast HW/SW cosynthesis. A node in a coarse-grain dataflow specification represents a functional block such as FIR and DCT and an arc may deliver multiple data samples per block invocation, which complicates the problem and distinguishes it from behavioral synthesis problem. Given optimized HW library blocks for dataflow nodes, we aim to generate the RTL codes for the entire hardware system including glue logics such as buffer and MUX, and the central controller. In the proposed design methodology, a dataflow graph can be mapped to various hardware structures by changing the resource allocation and schedule information. It simplifies the management of the area/performance tradeoff in hardware design and widens the design space of hardware implementation of a dataflow graph. We also support Fractional Rate Dataflow (FRDF) specification for more efficient hardware implementation. To overcome the additional hardware area overhead in the synthesized architecture, we propose two techniques reducing buffer overhead. Through experiments with some real examples, the usefulness of the proposed technique is demonstrated.

A CMOS single-pole-four-throw switch

An one-pole-four-throw switch that can be used to switch between the band select filters of four cellular bands and a single input programmable low noise amplifier has been demonstrated in a 0.18-/spl mu/m complementary metal oxide semiconductor process. Its insertion losses are 0.39, 0.61, 0.66, and 0.75dB in the GSM900, DCS1800, PCS1900, and wide-band code division multiple access system bands. IIP3's of the switch are /spl sim/27dBm and isolations are greater than 22dB.     

Designing Thin,Ultrastretchable Electronics with Stacked Circuits and Elastomeric Encapsulation Materials

Many recently developed soft, skin‐like electronics with high performance circuits and low modulus encapsulation materials can accommodate large bending, stretching, and twisting deformations. Their compliant mechanics also allows for intimate, nonintrusive integration to the curvilinear surfaces of soft biological tissues. By introducing a stacked circuit construct, the functional density of these systems can be greatly improved, yet their desirable mechanics may be compromised due to the increased overall thickness. To address this issue, the results presented here establish design guidelines for optimizing the deformable properties of stretchable electronics with stacked circuit layers. The effects of three contributing factors (i.e., the silicone interlayer, the composite encapsulation, and the deformable interconnects) on the stretchability of a multilayer system are explored in detail via combined experimental observation, finite element modeling, and theoretical analysis. Finally, an electronic module with optimized design is demonstrated. This highly deformable system can be repetitively folded, twisted, or stretched without observable influences to its electrical functionality. The ultrasoft, thin nature of the module makes it suitable for conformal biointegration.