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The Nippon Telegraph and Telephone Corporation , commonly known as NTT, is a Japanese telecommunications company headquartered in Tokyo, Japan. Ranked 29th in Fortune Global 500, NTT is the largest telecommunications company in the world in terms of revenue.The company is incorporated pursuant to the NTT Law . The purpose of the company defined by the Law is to own all the shares issued by Nippon Telegraph and Telephone East Corporation and Nippon Telegraph and Telephone West Corporation and to ensure proper and stable provision of telecommunications services all over Japan including remote rural areas by these companies as well as to conduct research relating to the telecommunications technologies that will form the foundation for telecommunications.While NTT is listed on Tokyo, Osaka, New York, and London stock exchanges, the Japanese government still owns roughly one-third of NTT's shares, regulated by the NTT Law. Wikipedia.


Kobayashi M.,Nippon Telegraph and Telephone
IEEE Communications Magazine | Year: 2014

The Great East Japan Earthquake on March 11, 2011, which was the fourth strongest earthquake ever recorded in the world's history, severely damaged telecommunication facilities in unprecedented ways. The large-scale earthquake and tsunami affected many exchange office buildings and facilities. Further damage to services was caused due to the depletion of batteries associated with the prolonged disruption of the commercial power supply. The tremendous disaster caused service disruption to the communications infrastructure; in the case of NTT's facilities, approximately 1.5 million circuits for fixed lines and 4900 mobile base stations stopped working due to direct damage by the earthquake and/or tsunami or subsequent blackouts. However, more than 90 percent of the affected exchange offices and mobile base station equipment was restored by the end of March through an all-out effort by over 11,000 people. Even by the end of April, in areas where customers currently reside, service restoration has mostly been completed except for some areas experiencing construction difficulties, including damaged roads which made it difficult for workers to approach the site. In parallel with the restoration effort, a disaster emergency message service for voice, mobile, and the Internet was quickly provided in order to permit safety confirmation. The NTT Group installed temporary public telephones and Internet access environments, and also lent mobile phones, satellite mobile phones, and tablets free of charge to the affected people and government agencies. Since communication services are vital in modern society, we are making every effort to implement better countermeasures with future disasters in mind. © 2014 IEEE.


Tiemann L.,Nippon Telegraph and Telephone
Nature Physics | Year: 2014

When the motion of electrons is restricted to a plane under a perpendicular magnetic field, a variety of quantum phases emerge at low temperatures, the properties of which are dictated by the Coulomb interaction and its interplay with disorder. At very strong magnetic field, the sequence of fractional quantum Hall liquid phases terminates in an insulating phase, which is widely believed to be due to the solidification of electrons into domains possessing Wigner crystal order. The existence of such Wigner crystal domains is signalled by the emergence of microwave pinning-mode resonances, which reflect the mechanical properties characteristic of a solid. However, the most direct manifestation of the broken translational symmetry accompanying the solidification-the spatial modulation of particles' probability amplitudes-has not been observed yet. Here, we demonstrate that nuclear magnetic resonance provides a direct probe of the density topography of electron solids in the integer and fractional quantum Hall regimes. The data uncover quantum and thermal fluctuations of lattice electrons resolved on the nanometre scale. Our results pave the way to studies of other exotic phases with non-trivial spatial spin/charge order.


Notomi M.,Nippon Telegraph and Telephone
Reports on Progress in Physics | Year: 2010

Recently, strongly modulated photonic crystals, fabricated by the state-of-the-art semiconductor nanofabrication process, have realized various novel optical properties. This paper describes the way in which they differ from other optical media, and clarifies what they can do. In particular, three important issues are considered: light confinement, frequency dispersion and spatial dispersion. First, I describe the latest status and impact of ultra-strong light confinement in a wavelength-cubic volume achieved in photonic crystals. Second, the extreme reduction in the speed of light is reported, which was achieved as a result of frequency dispersion management. Third, strange negative refraction in photonic crystals is introduced, which results from their unique spatial dispersion, and it is clarified how this leads to perfect imaging. The last two sections are devoted to applications of these novel properties. First, I report the fact that strong light confinement and huge light-matter interaction enhancement make strongly modulated photonic crystals promising for on-chip all-optical processing, and present several examples including all-optical switches/memories and optical logics. As a second application, it is shown that the strong light confinement and slow light in strongly modulated photonic crystals enable the adiabatic tuning of light, which leads to various novel ways of controlling light, such as adiabatic frequency conversion, efficient optomechanics systems, photon memories and photons pinning. © 2010 IOP Publishing Ltd.


Takesue H.,Nippon Telegraph and Telephone
IEEE Journal on Selected Topics in Quantum Electronics | Year: 2012

Entangled photon pair generation is an important technology for realizing quantum information systems. Among various entangled photon pair sources, a source based on spontaneous four-wave mixing (SFWM) in a silicon wire waveguide (SWW) is now drawing attention. Thanks to the very large third-order nonlinearity in an SWW, we can realize highly efficient SFWM in a short (∼1 cm) waveguide, which will possibly lead to an integrated entanglement source on a silicon chip. In this paper, we review recent progress on SWW-based entanglement sources. This study reviews the basic theory of SFWM, and then describes correlated and entangled photon generation experiments using SWWs and applications to quantum information experiments. © 2012 IEEE.


Kani J.-I.,Nippon Telegraph and Telephone
IEEE Journal on Selected Topics in Quantum Electronics | Year: 2010

Wavelength-division multiplexing (WDM) technologies are expected to play a key role in realizing the next generation scalable and flexible passive optical networks (PONs). One candidate is WDM-PON, in which each optical network unit (ONU) uses a different wavelength, i.e., a unique wavelength, in each direction to communicate with the optical line terminal. Another candidate is WDM/time-division multiplexing (TDM)-PON; it combines WDM with TDM technology. This paper reviews recent state-of-the-art research on the enabling technologies needed to realize future WDM-PON and WDM/TDM-PON systems, and discusses future directions toward practical PON systems. © 2010 IEEE.

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