August 2010 Vol. 8 No. 8

View from the Top

• Mitsunobu Komori, Executive Vice President of NTT DOCOMO, Chief Technical Officer, Member of the Board of Directors, and Managing Director of R&D Center

  

  Driving Innovation Continually to Turn Our Dreams into Reality

  Overview
  NTT DOCOMO is set to become one of the first mobile communications operators in the world to launch Long Term Evolution (LTE) services, with the start scheduled for December 2010. As the mobile communications market is generally perceived to be approaching maturity, what issues are on the agenda of the mobile industry? Executive Vice President and Chief Technical Officer of NTT DOCOMO, Mitsunobu Komori, clarifies the status of the mobile industry, sharing with us his insights on the social mission of NTT DOCOMO as a world-leading enterprise and describing the future that mobile technology is expected to bring forth.

Special Feature: Front-line Materials Research

• Materials Research Activities

  

  Abstract
  NTT Laboratories performs materials research because it plays a fundamental role in the development of information and communication systems. This Special Feature introduces our work on four materials: aluminum nitrides, diamond, graphenes, and nanowires. The research is proceeding in three directions: composition control, high crystal quality, and low dimensionality.

• Improved Emission Efficiency of 210-nm Deep-ultraviolet Aluminum Nitride Light-emitting Diode

  

  Abstract
  We describe technology developed to improve the emission efficiency of our aluminum nitride (AlN) deep-ultraviolet light-emitting diode, which has a wavelength of 210 nm: the shortest wavelength ever observed from any semiconductor. The improvement utilizes the unique characteristic that the emission intensity greatly changes depending on the crystal plane of the emitting surface.

• Diamond Field-effect Transistors as Microwave Power Amplifiers

  

  Abstract
  This article reviews the present status and future prospects of diamond transistors for microwave power amplifiers. NTT has been developing a technology for growing high-quality diamond film and has successfully fabricated diamond field-effect transistors (FETs) using the film. These diamond FETs exhibit the highest reported frequency limit in the millimeter wave range and the highest reported radio-frequency power capability in the microwave range.

• Graphene Growth on Silicon Carbide

  

  Abstract
  With the aim of developing a single-crystal graphene substrate, which is indispensable for practical applications of graphene, we are experimentally and theoretically investigating the structural and physical properties of graphene grown on silicon carbide by thermal decomposition.

• Towards New Low-dimensional Semiconductor Nanostructures and New Possibilities

  

  Abstract
  This article introduces our research on the bottom-up growth of semiconductor nanowires and an advanced investigation of their optical and electrical properties. We also describe the fabrication of various novel nanostructures that will help to promote nanowire applications and open up new opportunities.

Regular Papers

• Direct Actuation of GaAs Membrane Resonator by Scanning Probe

  

  Abstract
  A method for evaluating the mechanical properties of microresonators and nanoresonators with high spatial resolution is described. Mechanical vibration is directly induced into a circular resonator by voltage applied from a conductive microprobe, and the nanometer-order amplitude of the resonator is simultaneously measured by a scanning probe microscopy system. The resonant properties of 200-nm-thick GaAs circular membranes with a diameter of 14–64 μm were measured and the resonant frequencies were found to range from 0.65 to 5.18 MHz. The minimum detectable amplitude was about 1 nm. The amplitude distributions of the fundamental mode and higher modes were successfully observed with nanometer resolution.

Letters

• 40-km Single-mode-fiber Transmission for 100-Gbit/s Ethernet System Based on 25-Gbit/s 1.3-μm Εlectroabsorption Μodulator Ιntegrated with Distributed Feedback Laser

  

  Abstract
  We have developed a 1.3-μm electroabsorption modulator integrated with a distributed feedback laser for medium- and long-distance 100-Gbit/s Ethernet. To ensure a sufficient extinction ratio in the 1.3-μm band, we used a tensile-strained quantum well absorbing layer made with InGaAlAs-based material, which has a larger conduction band offset than InGaAsP. The modulator was coupled to the laser by butt jointing to optimize the structure separately. The fabricated device packaged in a butterfly module has a small-signal 3-dB bandwidth of 33 GHz. With this module, we demonstrated 10- and 40-km transmission on a single-mode fiber at the modulation speed of 25 Gbit/s at 40°C.

• Uncooled Operation of 10-/40-Gbit/s 1.55-μm Electroabsorption Modulator Integrated with Distributed Feedback Laser

  

  Abstract
  We have developed two types of 1.55-μm-wavelength electroabsorption modulator integrated with a distributed feedback laser diode by using InGaAlAs material. One has a twin waveguide structure, which has the advantage of a simple fabrication process. Its output power reached 4 mW at 85°C. The other has a butt-joint structure, which has the advantage of design flexibility. Its measured power penalties were less than 2 dB after 10-Gbit/s 80-km single-mode-fiber transmission in the range from –25 to 100°C and 40-Gbit/s 2-km single-mode-fiber transmission from –15 to 80°C.

Global Standardization Activities

• Establishment of New Focus Groups in ITU-T

  

  Abstract
  Two new Focus Groups concerning smart grids and cloud computing were established in the ITU-T TSAG (International Telecommunication Union, Telecommunication Standardization Sector Telecommunication Standardization Advisory Group) meeting held in Geneva, Switzerland, between February 8th and 10th, 2010.

External Awards/Papers Published in Technical Journals and Conferences Proceedings

• External Awards/Papers Published in Technical Journals and Conferences Proceedings