UDC 535.14:621.391

IP Photonic Node

VHaruo Yamashita VTakashi Hatano VSatoshi Nojima VNobuhide Yamaguchi (Manuscript received February 28, 2001)

This paper describes an IP photonic node architecture and its migration based on a single virtual-router view network. The IP photonic node features node cut-through at a various levels such as the wavelength, SONET frame, and/or packet path. Its coordi- nation capability for optical and packet paths enables efficient usage of network re- sources, for example, for the transportation and restoration of very large volumes of IP traffic. This paper also presents some recent photonic technology to make the IP photonic node configurable and expandable.

1. Introduction ing (WDM) transport, an optical amplifier for a The volume of IP traffic is growing exponen- large number of wavelengths, and tunable laser tially because of the widespread use of applications diodes and filters. such as the Internet; virtual private networks (VPNs); and communications between data cen- 2. IP photonic node architecture ters, between collocation facilities, and within based on a single virtual- storage area networks. Photonic networking is router view regarded as an essential and core technology to 2.1 Virtual-router view network cope with this trend. Vigorous efforts to accom- To cope with the ever-increasing IP traffic, modate a huge capacity have been made, and solve the processing bottleneck problem, and meet multi-vendor environment construction has been the demands for Class of Service (CoS) and Qual- promoted by organizations such as the ITU-T, In- ity of Service (QoS), we proposed an IP core ternet Engineering Task Force (IETF), and Optical transport network and transport node architec- Internetworking Forum (OIF). ture based on a single virtual-router view.2) Against this background, we have proposed Figure 1 shows our concept. Users are offered a a virtual network paradigm for the next-generation variety of services through a virtual router core network.1) This paper focuses on an IP photonic transport from application servers. Users do not node architecture based on this concept, its abili- need to know the network structure itself, but re- ty to coordinate between optical paths and packet quire networks to work as one huge virtual server flows, and a migration scenario for the IP photon- which provides requested services at the request- ic node. This paper also describes some of the ed network quality. latest wavelength routing equipment and device IP photonic networks based on a single technologies to realize the IP photonic node, for virtual-router view can configure virtual private example, terabit wavelength division multiplex- networks (VPNs) in a variety of ways to meet us-

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(Virtual server) Data center Application L-SW server User site B SONET Virtual router User site A SONET WDM SONET (Node cut-through User VPN-b Best-effort path WDM WDM by wavelength, frame, router WDM or path) VPN-a User site C Edge Edge node Gateway node L-SW Guaranteed path Access server IP photonic network Access Access Access Cooperation Users Users L-SW: Label switching

Figure 1 Figure 2 Virtual-router view network. Example of main services provided by a virtual router: VPN.

ers’ demands. An example is shown in Figure 2. IP layer Point-to-point path IP-based virtual leased lines in VPNs are set-up IP node IP path: virtual connection between user sites in the point-to-point path or EF-PHB – Priority control (Diff-serve) DiffServ – Mutual interference Router multi-point-to-point paths with a variety of QoS – Abundant logical paths grades in terms of bandwidth, packet loss rate, Link layer priority, delay, delay variation, and so on. Because Label path: virtual connection LSP – MPLS path isolation is required between VPNs, rigid LSR – Mutual interference – Abundant logical paths paths such as wavelengths and SONET frames or SONET layer a f lexible granularity such as groomed IP packet GS8400FUJITSU SONET path: physical connection labels are used as shown in Figure 3. FUJITSU GS8400 GS8400FUJITSU – No interference (TDM) Path

FUJITSU – SONET bandwidth granularity SONET GS8400 node 2.2 IP photonic node architecture The key technology in a single virtual- λ path: physical connection router view is the node cut-through technology – No interference ( λ ) with multiple granularity achieved at 1) the wave- λ – Bandwidth free λ node – Limited to the number of λ length level by wavelength routing, 2) the frame wavelengths ( paths) level (e.g., SONET/SDH ) by electrical ADM and Figure 3 cross connection, and 3) the packet level by layer VPN implementation schemes. 2 label switching. We use the term “IP photonic node” to mean a conceptual node that coordinates optical paths and packet flows and then config- works simpler and enable economic configuration ures a single virtual network. Optical add/drop just by handling the wavelength level. multiplexer (OADM), optical cross-connect (OXC), An example IP photonic node configuration SONET/SDH equipment, and/or layer 2 packet is shown in Figure 4. The node cut through at switches can implement the node cut-through the wavelength level can be done such that only functionality in an IP photonic node. Therefore, the required wavelengths are added or dropped an IP photonic node is a single or composite mod- at the designated node and other wavelengths are ule that provides node cut-through for IP traffic passed through. Similarly, node cut-through will transportation. Especially, node cut-through at be done at the layer 2 packet level. IP packets the wavelength level will make transport net- can be encapsulated with a fixed length label,

FUJITSU Sci. Tech. J.,37, 1,(June 2001) 23 H. Yamashita et al.: IP Photonic Node

λ Backbone network λ Hierarchical network MUX/DMUX for network scalability

Packet SW + OXC/OADM OXC Packet aggregation for full usage Fiber of λ bandwidth

(Edge node) (Edge node) Optical SW IP traffic transport by λ cut-through path

Figure 5 λ Network Network Collaborated work in and electrical levels. INF IP INF label SW Tributary Tributary INF INF network edges, as shown in Figure 5. The IP pho- Figure 4 tonic node aggregates and grooms IP packets sent Example configuration of IP photonic node. by connected nodes into the same destination or QoS and then accommodates them into the same which is used as a switching label between ingress optical path by a packet switch. The CoS/QoS and egress edge nodes/routers. This type of la- during packet aggregation/grooming should be beled packet can be dropped or added at the considered. In the future, if the economically avail- designated node and passed through the interme- able wavelength count increases, a more flexible diate nodes. In some cases, cut-through at the usage of wavelengths would be applicable, for ex- frame level can be applied such that payload in- ample, different QoS packets could be assigned to formation in only designated frames is added or different wavelengths. dropped at the designated node and others are Some of the advantages of coordinating opti- passed through. cal paths and packet flows from the viewpoint of optical path restoration or protection are described 2.3 Coordination function in the IP below.3) photonic nodes A simple IP photonic node is composed of a A wavelength or an optical path basically separate optical path switch and packet switch. works as a point-to-point path, so the wavelength In this case, if the utilization of each optical path count increases with the number of connected is low, the number of restored wavelengths be- points or nodes. An increase in the wavelength comes large. As a result, the optical path switch count requires an increase in the number of re- will need to be large. On the other hand, some lated optical transmitters/receivers and WDM integrated IP photonic nodes can be configured filters. The cost of a node will depend on how many by using an integrated optical-path and packet wavelengths need to be handled. Therefore, to switch, which replaces a part of the optical path make it possible to provide an economical service switch with packet switches, thereby reducing the to users, a highly-efficient bandwidth utilization hardware size. If we coordinate the operation of per wavelength should be considered. An aggre- the optical path and packet layer, the number of gation and grooming function for converting IP restored wavelengths can be reduced. Figure 6 packets into an appropriate wavelength or opti- shows a simple optical path protection scheme and cal path is essential for the IP photonic node at a coordinated optical path and packet layer pro-

24 FUJITSU Sci. Tech. J.,37, 1,(June 2001) H. Yamashita et al.: IP Photonic Node

λ 1 (0.5) λ 1 (1.0) C C C C λ 3 (1.0) λ 2 (1.0) E E λ 2 (0.5) B D B D λ 1 (0.5) λ 2 (1.0) λ 3 (0.5) λ 3 (0.5) λ 2 (1.0) λ 1 (0.5) λ 1 (1.0) λ 2 (1.0) λ 2 (1.0) λ 1 (1.0)

B D B D λ 2 (1.0) λ 2 (1.0) E E λ 1 (0.5) λ 1 (0.5) A A A A

(Numbers in parentheses indicate utilization of optical path λ k) *low utilization of restored optical path *high utilization of restored optical path (reduced wavelength counts)

(a) Simple optical-path protection (b) Coordinated optical path and packet layer protection

Figure 6 Protection schemes in IP photonic nodes.

tection scheme. In the figure, when there are no Coordinated protection Simple optical path protection link failures, optical paths A and E are set as 120 116 Conditions: 30% shown by the dotted lines. The line rate conver- × 87 – 6 6- 80 sion is assumed to be 0.5, 0.5, 0.5, and 1.0 for paths 58 82 62 A, B, C, and E, respectively. In a coordinated 40 29 41 protection scheme, the number of required Maximum wavelength count 21 wavelengths can be reduced as compared to the 12 34 × Demand simple optical path protection scheme. This is – Number of paths: 630 N (36C2 = 630, Demand N=1 to 4) because, in the coordinated protection scheme, – Path set up according to Dijkstra’s algorithm paths A and B can be accommodated on a single – Utilization per optical path: 0.25 optical path. Figure 7 To confirm the effects of coordination on pro- Evaluation of number of required wavelengths. tection schemes, the number of wavelengths required for a photonic network was evaluated in 3. IP photonic node migration a 6 × 6-grid network. Figure 7 shows the evalu- The IP photonic node architecture based on ation results. Firstly, 630 routes, which connect a single virtual-router view will migrate as all nodes in a full-mesh configuration, were de- photonic technology advances. It is expected that fined as demand 1 and then additional routes were networking in the virtual route core transport will assigned up to demand 4. Here, demand k (k=1, be simpler in the future because there will be an 2, 3, or 4) means the number of connection paths abundance of wavelengths that can be flexibly between nodes. The traffic load of each optical assigned. Generally, we can categorize the devel- path in the normal state was assumed to be 0.25. opment into the three stages shown in Figure 8. The evaluation results show that, regardless of – 1st stage: Wavelength paths are used as demand, the required maximum number of wave- point-to-point paths or as virtual fibers be- lengths in the coordinated protection scheme can tween nodes. be reduced by about 30% compared with the sim- – 2nd stage: Wavelengths are flexibly assigned ple optical path protection scheme. among nodes on demand.

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Photonic routing IP IP IP IP IP IP IP 3rd stage IP in core NW L2 label LA LB LB LB LC Tera/Peta bit λ λ λ 1 P router/node λ label 1 2 3 Photonic Consolidation of SW and λ paths routing Core – BW/root dynamic control Edge WDM IP Edge IP NW 100 T IP LS IP Router 2nd stage LS OADM/OXC LS IP OXC LS Edge node Phy λ Phy λ LS Phy IP WDM MPLS OXC LS node λ path set-up Phy 10 T Large transmission BW MPLS network Network capacity (b/s) MPLS Router Edge node Router node Edge node 1st stage (a) Initial stage 2

WDM IP IP IP IP IP IP λ λ λ λ λ λ 2000 2003-5 2005-10 label 1 2 3 4 5

Figure 8 Core WDM node IP photonic network development. IP Edge λ OXC NW OXC node OXC IP Edge OXC λ node λ path set-up – 3rd stage: Optical packets can be transport- ed in the network, for example, using (b) Mature stage 2 wavelength or optical coding information. Figure 9 These stages will be completed in sequence IP photonic node processing in the stage 2. or they may overlap in certain areas. In the 1st stage, optical paths are used as semi-permanent paths between nodes. For IP traf- can flexibly handle wavelengths for re-routing, fic transportation, wavelength transparency or dropping and/or adding, will play an important independency is used for different transmission role in wavelength networking. Because of the protocols. situation in stage 2, the IP packet handling pro- In the 2nd stage, the IP transport core net- cess and optical path handling in IP photonic works become simpler as the number of available nodes will be migrated as shown in Figure 9. IP wavelengths increases. Wavelengths are flexibly photonic nodes at the edge will handle more IP- used for protection or network restoration when related functionality, and IP photonic nodes at the faults occur in the transmission. Also, to secure core will focus on flexible wavelength switching traffic load balancing and/or Cos/Qos, optical paths to configure simpler transport networks. As a re- are flexibly re-assigned or re-routed on demand. sult, OXC/OADMs will work mainly in the In this stage, some optical paths are pre-assigned transport core networks. to provide logically direct paths conveying huge In the 3rd stage, IP packets may be handled amounts of traffic between nodes. Other optical in the form of optical packets, which have their paths are utilized on-demand by traffic engineer- destinations as wavelengths or optical coding in- ing, restoration, and so on. To use optical paths formation. Currently, the key technologies for flexibly on-demand, nodes should have the poten- optical recognition, optical memory, and so on are tial to change transmitter wavelengths and/or in the infant phase and there is an extremely high receive dynamically changed wavelengths. Tun- barrier in front of us that needs to be overcome. able laser diodes which can change transmitter An example IP photonic node for handling optical wavelengths on demand and tunable filters which packets is outlined below. Figure 10 shows its can receive wavelengths that are dynamically and schematic diagram. selectively designated are therefore considered to Some areas, for example, metropolitan areas, be key functional devices. OXC/OADMs, which are considered to be candidates for the optical

26 FUJITSU Sci. Tech. J.,37, 1,(June 2001) H. Yamashita et al.: IP Photonic Node

#n Receive λ 4

Addressing: λ Ring throughput Ring network O/E , E/O reduction Node #1 Receive λ 3 #2 #3 Receive λ 1 Receive λ 2 Filter O/E LDb Optical SW / Shutter LDa Standby LD for next λ Dynamically assigned Tunable LD ( i) operation time-slot similar to Tg 1 (~ms) assignment in slotted ring … LDa λ n λ k #2 #3 #n LDb λ m λ j λ packet (TDM-slot) burst reception From node #k From node #n Output to ring Input from ring λ n λ m λ k λ j (after filter) λ 1 λ 1 λ 1 λ 1 Tg 2 (~µs) Tg 2 (~µs)

Figure 10 Example scheme of wavelength packet handling. packet transportation scheme. In a conventional wavelength to another in a tunable LD is rela- two-fiber ring network with N nodes, each node tively long, so standby tunable LDs are required shares its line traffic capacity with the other nodes. to compensate for the transition time-gap. In this If each node can use multiple wavelengths, then example, a ring network with N nodes requires N the communication traffic can be increased at the wavelengths and the available bandwidth between cost of providing each node with multiple optical two nodes is limited to the transmission line rate transmitter/receivers that can send different per wavelength. Also, a burst packet optical re- wavelengths. The optical packet transportation ceiver operating at, for example, 10 Gb/s, is scheme, however, has the potential to reduce the required. However, a highly efficient utilization number of optical transmitter/receivers and of the wavelength bandwidth, for example, a uti- achieve a high traffic capacity. lization equal to the number of nodes N times the A certain wavelength for each node is as- transmission line rate, can be attained with a sin- signed as a destination flag, and then the node gle pair of optical tunable transmitter/receivers. assigned by its wavelength extracts its designat- A similar scheme can also be applied if a fixed ed wavelength. Each node prepares the packets wavelength is assigned to each node for sending to be sent to other nodes, and at an appropriate packets and tunable filters are used to detect pack- time, these packets are issued on designated wave- ets from a designated node. lengths by using a tunable laser diode (TLD). To avoid a collision of the same wavelength packet 4. Wavelength routing equipment on the ring, as in a network, a time and device technology domain multiplexing access scheme or time-slot The salient features of the photonic network assignment scheduling method can be applied technology are fully utilized to configure the for each wavelength that a node uses to send its proposed IP photonic node architecture and its packets. Currently, the switching time from one migration described above. The rest of this

FUJITSU Sci. Tech. J.,37, 1,(June 2001) 27 H. Yamashita et al.: IP Photonic Node

section describes various advanced photonic combined C + L-band optical amplifier was devel- networking systems and devices: the recently oped (the C band is from 1530 to 1570 nm, and developed terabit WDM equipment (FLASHWAVE- the L band is from 1570 to 1610 nm). The block OADX); a wide-band optical amplifier for diagram of the combined C + L-band optical am- combined C-band and L-band operation; and an plifier is shown in Figure 11. By using this type acousto-optic tunable filter (AOTF), tunable of optical amplifier in the FLASHWAVE-OADX, laser diode, and other key devices for wavelength 88 wavelengths in each band are available with a routing. wavelength spacing of 0.4 nm (50 GHz). R&D is continuing towards the target of 1000 4.1 Terabit WDM transport systems wavelengths by further narrowing the wavelength We have developed and reported two types spacing to 0.2 nm and also by developing an opti- of WDM systems:4) the FLASHWAVE 320 G for cal amplifier which can cover the shorter and long-haul networks and the FLASHWAVE Metro longer wavelength regions. Figure 12 shows the for metro networks. We developed FLASHWAVE- WDM spectrum of this amplifier after a 7221 km OADX to meet the demand for further capacity transmission of 211 wavelengths separated by and long-distance transmission.5) This system 0.3 nm. provides a transmission capacity of 176 wave- lengths × 10 Gb/s = 1.76 Tb/s per fiber. We applied Conventional band EDFA leading edge device technologies such as Raman optical amplifiers and tunable laser diodes. To AGC VAT AGC DCF compensate for degradation due to optical noise 1.55/1.58 1.55/1.58 accumulation and non-linearity and to secure the WDM WDM required system gain, we implemented forward AGC VAT AGC error correction (FEC) based on ITU-T Recommen- DCF dation G.975. The system specifications are shown L-band EDFA in Table 1. • Simple upgrade configuration • Directional flexibility (Uni-/Bi-directional) • ALC operation for wide input power range 4.2 Optical amplifier for large number of wavelengths Figure 11 Configuration of C+L-band optical amplifier. To increase the number of wavelengths, a

Total signal bandwidth: 64.4 nm

Table 1 103 waves (30.6 nm) 108 waves (33.8 nm) Main features of FLASHWAVE-OADX. Item Parameters Multiplexed wavelength 1 to 176 Wavelength range 1528.77 to 1607.04 nm (0.4 nm spacing) Fiber SMF/NZDSF Signal rate 9.95382 Gb/s

Signal format Scrambled NRZ Intensity (10 dB/div.) Maximum distance SMF: 500 km (100 km × 5) NZDSF: 600 km (100 km × 6) 1530 1550 1570 1590 1610 System gain SMF: 25 dB × 5 NZDSF: 25 dB × 6 Wavelength (nm) (Res.: 0.1 nm) Dispersion compensation Dispersion compensator BER < 1E-15 Figure 12 Spectrum after 7221 km transmission using C + Supervisory Optical supervisory channel L-band optical amplifier.

28 FUJITSU Sci. Tech. J.,37, 1,(June 2001) H. Yamashita et al.: IP Photonic Node

4.3 Tunable filter 4.4 Tunable laser modules We have developed advanced tunable filter When the WDM network wavelength count devices based on the acousto-optic tunable filter reaches a certain level, it becomes essential to use (AOTF) design.6) The AOTF is the ideal compo- tunable wavelength laser devices (TLDs). These nent for OADM systems because its inherent devices can greatly reduce the cost of network own- flexibility, bit rate/format transparency, and ership because it is not necessary to keep a large single device structure enable single or multi- number of spare optical transmitters in stock and wavelength add, through, and drop functions to they simplify network maintenance. Additional- be realized in a single integrated device. ly, TLDs provide enhanced wavelength allocation Figure 13 shows the structure and the key pa- flexibility. Wavelength interchange can be readi- rameters of our AOTF. By adding a high-frequency ly achieved, remotely, without the need to change control signal of around 170 MHz to the AOTF, hardware. Wavelength stability is crucial within the wavelength corresponding to the control sig- a WDM network, and wavelength-locking technol- nal is dropped out at the drop port and the ogy has been employed to guarantee that the remaining wavelengths travel to the through port. wavelength variation of any source is maintained Multiple wavelengths can be selected by simulta- within the desired operating tolerance. neously adding multiple control signals. This Figure 14 shows the structure of our tunable LD. AOTF has a good performance and is suitable for In this example, eight LD arrays, an optical cou- use in practical systems. pler, and a semiconductor optical amplifier are monolithically integrated on a chip. Each LD has a tunable range of more than 400 GHz, and the total module can cover 32 wavelengths with a 100 GHZ spacing. Recently, we have developed a TLD which can 0 -10 cover more than 20 wavelengths with a 50 GHz -20 -30 -40 spacing. By using just eight of these devices in -50 1540 1548 1556 Transmission (dB) our FLASHWAVW-OADX, we can cover 176 wave- Configuration Wavelength (nm) Tilted thin-film SAW guide lengths, which will lead to a reduction in the

LiNbO3 Optical signal Through number of maintenance packages that must be input SAW Drop kept in stock. PBS Control signal (RF) IDT

0 -10 Configuration Feature -20 -30 • Wide tuning range and high output power -40 Tunable laser diode module -50 by 8 DFB-LD array chip with SOA Multi-wavelength • High wavelength stability for ITU-T grid Transmission (dB) 1540 1548 1556 locker Wavelength (nm) by built-in multi-wavelength locker λ 1 Lens isolator Output

λ ...... 2 ... λl 88 SOA Main functions Characteristics Temperature Characteristics control Wavelength selective optical switch Parameters Characteristics Parameters Characteristics • Simultaneous ADD/DROP of Bandwidth > 0.4 nm Wavelength tunable 26 nm 8 DFB-LD array chip multi-wavelength signal Sidelobe < - 37 dB range (1535 to 1561 nm ITU-T grid) with SOA Rejection < - 40 dB Wavelength stability < ± 0.05 nm Tuning range > 80 nm SOA: Semiconductor optical amplifier Output power > +10 dBm Insertion loss < 9 dB RIN < - 140 dB/Hz

Figure 13 Figure 14 Acousto-optic tunable filter (AOTF). Tunable LD structure.

FUJITSU Sci. Tech. J.,37, 1,(June 2001) 29 H. Yamashita et al.: IP Photonic Node

5. Conclusion 2) A. Hakata, M. Katoh, H. Yamashita, and This paper introduced an IP photonic node S. Nojima: IP Core Transport Network. architecture based on a virtual-router view net- FUJITSU Sci. Tech. J., 37, 1, pp.12-21 (2001). work proposed for the next-generation IP 3) T. Nishi and S. Kuroyanagi: Photonic IP node transport network and discussed its future migra- with integrated optical-path and packet tion. An example of an IP photonic node with switch. ITU-T Telecom Asia 2000 Forum, coordination for wavelength paths and packet INF-3, Dec. 2000. paths was described and its effect on restoration 4) D. Maruhashi, K. Yamane, H. Sumiya, and Y. was evaluated. Lastly, this paper described some Nagai: WDM Optical Fiber Transmission advanced photonic network systems and devices Systems. FUJITSU Sci. Tech. J., 35, 1, that can form the foundation of the proposed node pp.25-33 (1999). architecture and migration. 5) N. Yamaguchi: Photonic Network. (In Japanese), FUJITSU, 51, 6, pp.413-418 References (2000). 1) T. Tsuda, Y. Mochida, and H. Kuwahara: 6) T. Nakazawa et al.: Ti:LiNbO3 AOTF for Photonic Solution for Next Generation IP 0.8 nm channel spaced WDM. post deadline Transport Network. ITU-T Telecom Asia paper, PD-1, OFC’98, 1998. 2000 Forum, INF-11, Dec. 2000.

Haruo Yamashita received the B.S. Satoshi Nojima received the B.S. and degree in Physics from the University M.S. degrees in Electrical Engineering of Tokyo, Tokyo, Japan in 1978 and the from Waseda University, Tokyo, Japan M.S. degree from Tokyo Institute of in 1976 and 1978, respectively. He Technology, Tokyo, Japan in 1980. In joined Fujitsu Laboratories Ltd., 1980 he joined Fujitsu Limited, Kawasaki, Japan in 1978, where he has Kawasaki, Japan. been engaged in research and devel- From 1983 to 2000 he was with Fujitsu opment of computer communication Laboratories Ltd., and he is currently network systems. He is a member of Director of the Optical Access Systems the Institute of Electronics, Information, Division in Fujitsu Limited. and Communication Engineers (IEICE) He has been engaged in research and development of broad- of Japan. band optical access and backbone systems. He is a member of the Institute of Electronics, Information, and Communication Engineers (IEICE) of Japan.

Takashi Hatano received the B.E. de- Nobuhide Yamaguchi received the B.E. gree in Electrical Engineering from degree in Electronic Engineering and Waseda University, Tokyo, Japan in the M.E. degree in Physical Information 1980. He joined Fujitsu Limited, Processing from Tokyo Institute of Kawasaki, Japan, in 1980 and has been Technology, Tokyo, Japan in 1974 and engaged in development of switching 1976, respectively. He joined Fujitsu and transmission systems. He is cur- Laboratories Ltd., Kawasaki, Japan in rently a Director of the Advanced Pho- 1976, where he was engaged in tonic Core Systems Development in research and development of optical Fujitsu Limited. transmission systems until 1982. Then he was with Fujitsu Ltd., Kawasaki, Japan and engaged in development of optical fiber transmission systems and digital transmission systems until 2000. Since 2000 he has been engaged in research of next-generation photonic systems. He is a member of the Institute of Electronics, Information, and Communication Engineers (IEICE) of Japan.

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