Katsumi Iwatsuki

Convergence of WDM Access and Ubiquitous Antenna Architecture for Broadband Wireless Services

This paper proposes a novel network architecture for Giga-bit throughput in broad- band ubiquitous networks. A convergence of WDM access and RoF ubiquitous antenna archi- tecture can realize universality of remote base stations for various types of air interfaces and the scalabilities of WDM technologies are expected to improve the throughput in wireless service area covered by RoF-MIMO antenna. We discusse distribution of MIMO antenna, method of RoF MIMO signals over WDM PON, and conflgurations of center station and remote base stations.

Multiport power router and its impact on future smart grids

We propose a Y configuration power router as a unit cell to easily construct a power delivery system that can meet many types of user requirements. The Y configuration power router controls the direction and magnitude of power flows between three ports regardless of DC or AC. We constructed a prototype three-way isolated DC/DC converter that is the core unit of the Y configuration power router. The electrical insulation between three ports assures safety and reliability for power network systems. We then tested the operation of power flow control. The experimental results revealed that our methodology based on a governing equation was appropriate to control the power flow of the three-way DC/DC converter. In addition, a distribution network composed of power routers had the ability to easily enable interchanges of electrical power between autonomous microgrid cells. We also explored the requirements for communication between energy routers to achieve dynamic adjustments of energy flows in a coordinated manner and their impact on resilient power grid systems.

Transmission Performance Investigation of RF Signal in RoF-DAS Over WDM-PON With Bandpass-Sampling and Optical TDM

The radio over fiber (RoF)-distributed antenna system (DAS) over a wavelength division multiplexing-passive optical network (WDM-PON) with multiple input multiple output (MIMO) employing bandpass-sampling and optical time division multiplexing (TDM) techniques has been proposed to realize next generation broadband wireless access with higher throughput and its preliminary feasibility has been confirmed. To investigate the performance of bandpass-sampled and time domain multiplexed optical signals, and enhance the transmission performance in the wireless link of the RoF-DAS over WDM-PON, we perform two-tone signal transmission experiments with 2.4 GHz band radio frequency (RF) signals and analyze the RF carrier power, third-order intermodulation distortion (IMD) power and noise power. The analysis results confirmed that the nonlinearity of the proposed system is mainly caused by a lithium niobate-Mach-Zehnder modulator (LN-MZM) as with the other RoF systems and that the dominant noise components are the signal-spontaneous beat noise arising from the amplified spontaneous emission (ASE) of two erbium doped fiber amplifiers (EDFAs) and the signal-signal beat noise caused by the interference between the optical TDM pulses. The latter is the specific noise component in the proposed system. In addition, we clarify the principle of the signal-signal beat noise generation and report that the signal-spontaneous beat noise can be reduced by the gain optimization of the two EDFAs.

Next-generation resilient access networks

After the East Japan Great Earthquake, the construction of resilient network has been strongly required. On the other hand, the technical convergence with wired and wireless plays an important role to achieve the next generation access networks beyond bandwidth of current optical access. In this paper, we discuss next generation resilient access networks, handling the download of huge data, images, and videos, as well as to upload of a large number of sensor data, any time and anywhere.

Cyber physical system based on resilient ICT

While development of science and technology has built up the sophisticated civilized society, it has also resulted in quite a few disadvantages in global environment and human society. The common recognition has been increasingly shared worldwide on sustainable development society attaching greater importance to the symbiotic relationship with nature and social ethics. After the East Japan Great Earthquake, it is indispensable for sustainable social development to enhance capacity of resistance and restoration of society against natural disaster, so called resilient society. Our society consists of various Cyber Physical Systems (CPSs) that make up the physical systems by fusing with an Information Communication Technology (ICT). We describe the proposed structure of CPS in order to realize resilient society. The configuration of resilient CPS consisting of ICT and physical system is discussed to introduce autonomous, distributed, and cooperative structure, where subsystems of ICT and physical system are simultaneously coordinated and cooperated with Business Continuity Planning (BCP) engine, respectively. We show the disaster response information system and energy network as examples of BCP engine and resilient CPS, respectively. We also propose the structure and key technology of resilient ICT.

Photonic Frequency Double-Mixing Conversion Over the 120-GHz Band Using InP- and Graphene-Based Transistors

InP-based high electron mobility transistors (InP-HEMTs) and graphene-channel FETs (G-FETs) are experimentally examined as photonic frequency converters for future broadband optical and wireless communication systems. Optoelectronic properties and three-terminal functionalities of the InP-HEMTs and G-FETs are exploited to perform single-chip photonic double-mixing operation over the 120 GHz wireless communication band. A 10 Gbit/s-class data signal on a 112.5 GHz carrier is mixed down to a 25 GHz IF band with an 87.5 GHz LO signal that is simultaneously self-generated from an optically injected photomixed beat note. The results suggest that the intrinsic channel of the G-FET can achieve a speed performance that is superior to that of an InP-HEMT having an equivalent device feature size. The reduction of the extrinsic parasitic resistances and the implementation of an efficient photo-absorption structure in the G-FET may allow a millimeter-wave and sub-THz photonic frequency conversion with a sufficiently high conversion gain for practical purposes.

The projects of Disaster-Resistant Information Communication Network at the Research Organization of Electrical Communication, Tohoku University

After the East Japan Great Earthquake, Tohoku University has established Research Organization of Electrical Communication to achieve the most advanced disaster-resistant information communication network in the world. In this paper, we will introduce our projects of “Disaster-Resistant Information Communication Network” based on industry-academia-government collaboration.

Multi-port power router and its impact on resilient power grid systems

We propose a Y-configuration power router as a unit cell to easily construct a power delivery system that can meet many types of user requirements. The Y-configuration power router controls the direction and magnitude of power flow among three ports regardless of DC and AC. We constructed a prototype three-way isolated DC/DC converter that is the core unit of the Y-configuration power router and tested the power flow control operation. Experimental results revealed that our methodology based on the governing equation was appropriate for the power flow control of the three-way DC/DC converter. In addition, the hexagonal distribution network composed of the power routers has the ability to easily interchange electric power between autonomous microgrid cells. We also explored the requirements for communication between energy routers to achieve dynamic adjustments of energy flow in a coordinated manner and its impact on resilient power grid systems.

Sub-THz photonic frequency conversion using optoelectronic transistors for future fully coherent access network systems

This paper reviews advances in sub-THz photonic frequency conversion using optoelectronic transistors for future fully coherent access network systems. Graphene-channel field effect transistors (G-FETs) and InP-based high electron mobility transistors (inP-HEMT) are experimentally examined as photonic frequency converters. Optoelectronic properties and three-terminal functionalities of the G-FETs and InP-HEMTs are exploited to perform single-chip photonic double-mixing operation over the 120 GHz wireless communication band. A single transistor can photomix the optical subcarriers to generate LO and mix down the RF data on the sub-THz carrier to the IF band.

Photonic frequency conversion using graphene FETs for future fully coherent access network

We report on the possibilities of graphene channel FET (G-FET) as a photonic frequency double-mixing conversion device for future fully coherent access network systems. A 112.5-GHz RF signal whose amplitude was coded with a 5-GHz rectangular signal was input to the gate, concurrently a 1.58-μm wavelength photomixed dual CW laser beam having a beat frequency of 87.5 GHz was incident to the FET, generating the local (LO) signal. The RF and LO signals were mixed to reproduce the down-converted 5-GHz signal onto the 25-GHz intermediate frequency (IF) signal successfully.