Routing design of tree‐shaped local public communication networks with high reliability and low cost

This paper discusses reliability problems for local public communication networks such as cable television networks and the subscriber‐loops of telecommunication networks. They have tree‐shapes and expand continuously as new customers join. By introducing a simple model, it is shown that most principal reliability measures and cost measures for such networks can be described through the networks' graphical characteristic quantities. Extensive simulations show that the prior provision of trunk pipes and a suitable choice of the route selecting rule for new customers are effective in constructing a highly reliable network with low cost. This revised version was published online in June 2006 with corrections to the Cover Date.     

Driving voltage reduction in a two-phase CCD by suppression ofpotential pockets in inter-electrode gaps

This study reports an optimum design for a two-phase charge-coupled device (CCD) and limitations on its driving voltage reduction. The two-phase CCD to be used as a horizontal-CCD (H-CCD) in a CCD image sensor requires low-voltage and high-speed operation. Reducing the driving voltage, however, may induce potential pockets in the channel under the inter-electrode gaps which results in a fatal decrease in charge-transfer efficiency. In this case it is necessary to optimize the CCD design to be free of pocket generation. For this requirement, we conducted two-dimensional (2-D) device simulations for the two-phase CCD, whose potential barriers are formed by boron ion-implantation. Our simulations indicated that the edge position of the potential barrier region and the dose of boron-ion implantation would be important parameters for controlling the size of potential pockets. At an optimum edge position and a boron dose, the minimum driving voltage appears to be reducible to 1.1 V. Characteristics of potential pockets and methods of their suppression are also discussed     

Dirac Cone Spin Polarization of Graphene by Magnetic Insulator Proximity Effect Probed with Outermost Surface Spin Spectroscopy

The effects of the proximity contact with magnetic insulator on the spin‐dependent electronic structure of graphene are explored for the heterostructure of single‐layer graphene (SLG) and yttrium iron garnet Y₃Fe₅O₁₂ (YIG) by means of outermost surface spin spectroscopy using a spin‐polarized metastable He atom beam. In the SLG/YIG heterostructure, the Dirac cone electrons of graphene are found to be negatively spin polarized in parallel to the minority spins of YIG with a large polarization degree, without giving rise to significant changes in the π band structure. Theoretical calculations reveal the electrostatic interfacial interactions providing a strong physical adhesion and the indirect exchange interaction causing the spin polarization of SLG at the interface with YIG. The Hall device of the SLG/YIG heterostructure exhibits a nonlinear Hall resistance attributable to the anomalous Hall effect, implying the extrinsic spin–orbit interactions as another manifestation of the proximity effect.     

Gain-flattened tellurite-based EDFA with a flat amplificationbandwidth of 76 nm

We describe a tellurite-based Er³⁺-doped fiber amplifier (EDFA) with a flat amplification bandwidth of 76 nm and a noise figure of less than 7 dB. Furthermore, a parallel-type amplifier composed of this EDFA and a 1.45-μm-band Tm³⁺-doped fluoride fiber amplifier achieved a flat amplification bandwidth of 113 nm     

Study on the device characteristics of a quasi-SOI power MOSFETfabricated by reversed silicon wafer direct bonding

The device characteristics of a quasi-SOI power MOSFET were investigated to obtain its optimum device structure. The oxide at the original bottom surface of the bulk power MOSFET of the quasi-SOI power MOSFET formed by reversed silicon wafer direct bonding acts as the buried oxide of the conventional SOI power MOSFET. The short channel effect of the quasi-SOI power MOSFET was larger than that in the conventional SOI power MOSFET. It was suppressed by increasing the width of the oxide in the body region, and the parasitic bipolar effect was suppressed by decreasing it. We also propose a new device structure which can suppress the short channel effect and parasitic bipolar effect of a quasi-SOI power MOSFET based on the results of these experiments     

Fine structures of residual strain distribution in Fe-Doped lnP-100) wafers grown by the LEC and VCZ methods

By using a high-spatial-resolution scanning infrared polariscope, in-plane components of residual strain have been characterized quantitatively in 2′Φ wafers of Fe-doped InP( 100) single crystals grown by the liquid-encapsulated Czochralski (LEC) and the vapor pressure controlled Czochralski (VCZ) methods. The twodimensional distribution maps of LEC-grown wafers reveal characteristic fine structures such as slip-like patterns originated from crystallographic glides during the crystal growth process, highly strained spots and filaments due to inclusions or voids inside the wafer, or due to scratches on the surface. The sliplike patterns are seldom observed in the VCZ-grown wafers. The residual strain value averaged over the whole region of wafer is also examined, together with etch pit density and resistivity, as a function of the solidified fraction. It is found that the residual strain in the Fe-doped InP crystals grown by the LEC and VCZ methods mainly depends on the thermal stress during the growth process rather than on the impurity-hardening effect of Fe.Key words: InP, infrared polariscope, liquid-encapsulated Czochralski (LEC) method, residual strain, vapor pressure controlled Czochralski (VCZ) method     

Design and performance evaluation of amplifier modules in stackable ROADMs for low-cost CWDM access networks

Coarse wavelength division multiplexing (CWDM) network has proven to be promising lower cost network architecture for a significant cost advantage over dense wavelength division multiplexing due to the lower cost of lasers and the filters used in CWDM modules. A compatible amplifier module having bidirectional amplification capability was deployed for introducing inside stackable reconfigurable optical add/drop multiplexers in realizing large-scale CWDM networks. The amplifier module for use in the bidirectional IP transmission confirmed that the insertion losses of the nodes and the losses of the fibers connecting the nodes can be compensated effectively, allowing the network administrator to increase the number of nodes and fiber length of the network. However, the noise generated from the amplification due to amplified spontaneous emission must be considered in network design issues. In this paper, optical power penalties due to the bidirectional amplification were estimated by conducting experimentation on minimum detectable power of optical transceivers. After analyzing the power penalty issue, an IP-over-CWDM ring network was implemented and the performance of network was evaluated by monitoring the power and packet transmissions before and after the amplifier module was turned on.     

A 128-kb FeRAM macro for contact/contactless smart-card microcontrollers

This paper describes a 128-kb FeRAM macro for smart-card microcontrollers. This macro, which was designed and fabricated using a 0.35-/spl mu/m three-metal CMOS and a Capacitor-on-Metal/Via-stacked-Plug (CMVP) process technology, is ideally suited for recent system LSIs such as smart-card microcontrollers. It has a flexible memory size ranging from 32 to 128 kb, a low consumption current of 0.3 mA, and endurance of more than 10/sup 8/ write/read cycles under a wide range of supply voltages, from 2.7 to 5.5 V. These characteristics, which are required of not only contact-type smart-card microcontrollers but also contactless-type ones, were achieved by using four newly developed circuit technologies: 1) a three-metal CMVP memory cell; 2) a voltage-regulating architecture; 3) a main/sub bitline and wordline structure; and 4) a dynamic-type offset sense amplifier.     

Efficient use of frequencies in terrestrial ISDB system

Requirements for a terrestrial ISDB system and the schemes for efficiently using frequencies to fulfil the requirements are discussed. One requirement of a terrestrial ISDB system is the efficient allocation of frequencies using a SFN (single frequency network). The SFN incorporates the great advantages of OFDM, which has excellent performance under multi-path conditions. The transmission characteristics of 64QAM-OFDM and the SFN capability using 64QAM-OFDM in the Kanto area, including the Tokyo metropolitan area, are analyzed. The results show that more than a 97% coverage ratio can be obtained even by using a single channel while the same area is covered currently by more than 30 analog channels. The other requirement is a scheme for efficiently using the available frequency band for various services. A transmission scheme concept called BST-OFDM (band segmented transmission-orthogonal frequency division multiplexing) is proposed as a transmission scheme for meeting the requirements of a terrestrial ISDB system. In the BST-OFDM scheme, data are transmitted in a number of OFDM blocks called a BST-segment, for which channel coding and modulation schemes can be independently defined to provide robustness in the transmission environment according to stationary, portable and mobile reception     

Mechanism of the noise reduction method by superposition ofhigh-frequency current for semiconductor injection lasers

Semiconductor injection lasers sometimes reveal excess noise called the mode hopping noise, which is associated with the mode hopping phenomena among longitudinal modes. The mode hopping phenomena are caused by coupling effects among lasing modes. To reduce this kind of noise superposition of high-frequency (HF) current on the injection current is frequently used. This reduction method is theoretically analyzed based on the mode competition theory and is compared with experimental measurements. It is confirmed that the coupling effect among the longitudinal modes is released with the HF superposition because of enhanced vibration of the injected electron, resulting in reduction of the mode hopping noise