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Arai M.,Nippon Telegraph and Telephone | Arai M.,Japan Society of Applied Physics | Kobayashi W.,Nippon Telegraph and Telephone | Kobayashi W.,Institute of Electronics and Information and Communication Engineers IEICE | Kohtoku M.,Nippon Telegraph and Telephone
NTT Technical Review | Year: 2012

In this article, we review our efforts to reduce the power consumption of optical transmitter modules for Ethernet and telecommunications use. To reduce the power consumption, we aim to eliminate the light source's temperature controller and improve the stability of the output power and modulation characteristics under ambient temperature conditions. We describe a 1.3-μm-range metamorphic laser on a GaAs substrate that exhibits improved temperature characteristics. It has a characteristic temperature of 220 K and is capable of lasing up to 200°C. In addition, the bias current for 10-Gbit/s modulation at high temperature has been reduced. This laser is promising for uncooled light sources operating with low power consumption. Source

Hashimoto D.,Nippon Telegraph and Telephone | Hashimoto D.,Japan Society of Applied Physics | Shimizu K.,Nippon Telegraph and Telephone
NTT Technical Review | Year: 2014

We have been investigating hyperfine sublevels of 167Er3+ ions doped in a silicate glass fiber with the objective of demonstrating quantum memory in the 1.5-μm telecommunication band. Memory time is determined by the stability of hyperfine sublevels (the lifetime) of 167Er3+ ions, so it is therefore necessary to clarify the lifetime properties. This article describes (i) the anomalous temperature dependence of the lifetime that was unexpectedly discovered in the lifetime measurements and (ii) the physical properties of glass that resulted in the anomalous phenomenon. Copyright 2014 NTT Technical Review All Rights Reserved. Source

Sun L.,Tokyo University of Information Sciences | Shibata T.,Japan Society of Applied Physics
IEEE Transactions on Circuits and Systems for Video Technology | Year: 2014

This paper presents an unsupervised object extraction system that extracts a single object from natural scenes without relying on color information. The contour information and texture information are analyzed through separate oriented-edge-based processing channels and then combined to complement each other. Contour candidates are extracted from multiresolution edge maps, whereas the local texture information is compactly represented by an oriented-edge-based feature vector and then analyzed by K-means clustering. The object region is determined by merging the results of two separate analysis channels based on the simple assumption that the object is located centrally in the scene. As a result, the object region has been successfully extracted from the scene with a well-defined single boundary line. Both subjective and objective evaluations were carried out and it is shown that the proposed algorithm handles the challenges of complex background well, using only gray-scale images. © 2013 IEEE. Source

Zhu H.,University of Tokyo | Shibata T.,Japan Society of Applied Physics | Shibata T.,Japan Aerospace Exploration Agency
IEEE Transactions on Circuits and Systems for Video Technology | Year: 2014

A very-large-scale integration capable of extracting motion features from moving images in real time has been developed employing row-parallel and pixel-parallel architectures based on the digital pixel sensor technology. Directional edge filtering of input images is carried out in row-parallel processing to minimize the chip real estate. To achieve a real-time response of the system, a fully pixel-parallel architecture has been explored in adaptive binarization of filtered images for essential feature extraction as well as in their temporal integration and derivative operations. As a result, self-speed-adaptive motion feature extraction has been established. The chip was designed and fabricated in a 65-nm CMOS technology and used to build an object detection system. Motion-sensitive target image localization was demonstrated as an illustrative example. © 1991-2012 IEEE. Source

Nakatsugawa M.,A+ Network | Nakatsugawa M.,Japan Society of Applied Physics
NTT Technical Review | Year: 2012

This report summarizes the activities and outcomes of the Radiocommunication Assembly 2012 (RA- 12) and World Radiocommunication Conference 2012 (WRC-12), which were held from January to February 2012 in Geneva, Switzerland. RA and WRC are the major conferences of ITU-R (International Telecommunication Union, Radiocommunication Sector). Source

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