WDM Optical Submarine Network Systems

UDC 621.315.28:621.391.6

VMasuo Suyama VMasato Nagayama VHaruki Watanabe VHaruo Fujiwara VColin Anderson (Manuscript received April 15, 1999)

This paper describes optical submarine network systems that support 160 Gb/s capacity (10 Gb/s ××× 16λλλ) per fiber. These advanced systems enable practical and cost- effective deployment of networks with 4 fiber pair optical submarine cables, and total capacity of 640 Gb/s. A typical network configuration and the relevant equipment for such networks are outlined. The equipment includes submersible wide-band repeaters, optical ADM branching units and line terminal equipment, which we have developed making full use of our advanced optical technology. Our ultra-large capacity (10.7 Gb/s ××× 66λλλ) transmission experiment, and enabling technologies for future Tera-bit transmission systems are also summarized. New network configurations using OADM or Internet Protocol (IP) routers are proposed for next generation WDM submarine networks.

1. Introduction this FEC using the Reed Solomon code (255/ We have already developed and supplied sub- 239) at data rates of 10 Gb/s (SDH STM-64), marine WDM systems for projects such as the based on advanced hardware and software SEA-ME-WE 3 cable system, which features 40 technology. This FEC, together with the in- Gb/s capacity (2.5 Gb/s 8λ 2 fiber pairs). Due creased output power and lower noise figure primarily to the explosive expansion of Internet of the submersible repeaters, has enabled us use, demand for international traffic is currently to minimize the number of repeaters required growing at a high rate, and capacities per fiber for the system, thus minimizing the cost. pair of 10 Gb/s 16 or more are now required. In • Wide optical gain bandwidth order to meet this demand, we have developed the An optical gain bandwidth of at least 12 nm systems outlined in this paper. is required for the 16λ system with channel spacing of 0.8 nm. This is almost twice the 2. Overview of 640 Gb/s submarine bandwidth required for the previous 8λ sys- network utilizing 10 Gb/s ××× 16λλλ WDM tems. We realized the required broad gain Table 1 summarizes major parameters of 640 bandwidth by employing an Erbium Doped Gb/s (10 Gb/s 16λ 4 fiber pair) system. The sys- Fiber (EDF) with optimized dopant concen- tem features the following technical advantages: trations, and a fiber-based gain equalizer • Minimized system cost optimized to compensate for the EDF gain Forward Error Correction (FEC) has been characteristic. employed, using the Reed Solomon 255/239 • Enhanced supervisory functions code, in order to improve system performance. Monitoring the status of each repeater in the We have developed dedicated IC chip sets for network is important for the maintenance of

34 FUJITSU Sci. Tech. J.,35,1,pp.34-45(July 1999) M. Suyama et al.: WDM Optical Submarine Network Systems

Table 1 Major parameters of 640 Gb/s (10 Gb/s ××× 16λλλ ××× 4 fiber pair) system.

Item Parameter Note Capacity per fiber STM-64 16 equivalent to 1935360 telephony voice channels Bit rate per channel 10.664 Gb/s Modulation scheme Return to Zero (RZ) code Signal wavelength 1548 nm ~ 1560 nm Forward error correction Reed Solomon code (255/239) FEC

Maximum system length 10000 km for one hop between SLTE and SLTE Repeater span 40 km ~ 90 km depends upon total hop length Optical fiber type NZ-DSF + DCF NZ-DSF: Non Zero Dispersion Shifted Fiber or LCF: Large Core Fiber LCF + DCF DCF: Dispersion Compensating Fiber Reliability less than 2 ship repairs System life = 25 years Error performamce BER < 1 10-11 After error correction Repeater supervisory • Input power • Output power • Pump laser diode bias • C-OTDR Line powering current 1A DC

Station A Station B REP SIE SIE SIE C C SIE SIE T T SIE SIE SLTE B B SLTE SIE SSE PFE PFE SSE NME NME SLTE SLTE PFE CTB PFE CTB

REP REP

CTB PFE PFE CTB SLTE SLTE

SSE BU SSE NME PFE REP REP PFE NME SIE SLTE C C SLTE SIE SIE T T SIE SIE SIE SIE B B SIE

Station D Station C CTB BU : Branching Unit PFE CTB : Cable Termination Box SLTE NME : Network Management Equipment SSE PFE : Power Feeding Equipment NME REP : Submarine REPeater SIE SIE SIE : SDH Interconnection Equipment SIE SIE SLTE : Submarine Line Terminating Equipment SSE : System Supervisory Equipment Station E

Figure 1 Example network configuration.

FUJITSU Sci. Tech. J.,35, 1,(July 1999) 35 M. Suyama et al.: WDM Optical Submarine Network Systems

large capacity submarine networks. Our su- for some fiber pairs to terrestrial terminal sta- pervisory system monitors and reports tions, while passing the other fibers through. repeater status including parameters such Optical Add/Drop Multiplexing BU can add/drop as optical input power and output power, as particular wavelengths in one fiber pair. well as pump-laser power and bias current. In addition, a coherent OTDR path is pro- 2.4 Power feeding equipment (PFE) vided in each repeater, enabling precise The PFE equipment provides power to the remote fault localization as far as 10000 km repeaters by applying a DC current of typically from the terminal equipment. 1.0 amp through the center conductor of the submarine cable. Figure 1 is an example network configuration. An overview of the network function of each 2.5 System supervisory equipment type of equipment is given below. A more detailed (SSE) description of some of the equipment including The SSE is an element manager which per- repeaters, OADM and SLTE follows in subsequent forms all necessary submarine system supervisory sections. functions including the element management for the SLTE, the PFE and the repeaters. Surveil- 2.1 Submarine line terminal lance and control of submarine repeaters is equipment (SLTE) achieved by modulation of the main optical The submarine line terminal equipment signal applied at each SLTE. (SLTE) provides the necessary interface between the 9.95 Gb/s signal from the SDH Interconnec- 2.6 Network management equipment tion multiplex Equipment (SIE) and the 10.66 Gb/s (NME) signal (including the FEC overhead), as well as The SSE and the SIE element manager the wavelength division multiplex and de-multi- communicate to the overall Network Management plex functions in optical domain. Equipment (NME), which is comprised of dedicated software running on a UNIX workstation. This 2.2 WDM submarine repeater (REP) NME has the possibility to up-link to other high- WDM submarine repeaters are essential to er network management systems by the ITU-T realize long-distance high-capacity optical fiber Q3 protocol. submarine transmissions. The repeater span is typically 40 to 90 km depending on total system 2.7 Cable termination box (CTB) length. The repeater includes wide-band optical The CTB facilitates the connection between amplifiers equipped with a gain-flattening filter. the optical fibers of the submarine cable and the Typical repeaters are designed for two, three or optical patch cables to the station ODF (optical four fiber pair submarine cable. A repeater for a distribution frame), as well as providing the in- four fiber pair submarine cable includes 8 EDF terface to the center DC power-feed conductor of optical amplifiers, which are powered by DC the submarine cable. Submarine cables with up current from the PFE, fed through the center con- to 4 fiber pairs (8 optical fibers) per cable are typ- ductor of the submarine cable. ically deployed.

2.3 Submarine optical branching unit 2.8 Network protection & SDH (BU) interconnection equipment (SIE) Submersible optical branching units provide The SDH SIE equipment allows application

36 FUJITSU Sci. Tech. J.,35, 1,(July 1999) M. Suyama et al.: WDM Optical Submarine Network Systems

of the 4-Fiber MS-SPRing (Multiplex Section level and provides optical gain. Since the gain Shared Protection Ring) protection scheme to N depends on the wavelength of an input signal, the 10 Gb/s submarine networks, and includes the EDF limits the transmission wavelength window. special requirements for trans-oceanic submarine A long-period fiber grating (LPG) with an appro- networks. In addition, the SIE allows full access priate loss characteristic is employed to compen- to the protection channel (PCA) for un-protected sate for the gain profile of EDF. Furthermore, a traffic (which may be lost in case the protection high concentration of aluminium is co-doped in scheme acts to protect the main traffic in event of the EDF core, which contributes to a flattened gain a cable or hardware failure). profile.1) Thus, a wide gain bandwidth (12 nm) was achieved, making it suitable for transmission 3. Equipment for 10 Gb/s ××× 16λλλ WDM of 16 wavelengths. submarine links Pump LD’s are duplicated, and supply the This chapter describes details of the equip- EDF’s for both transmit and receive via a coupler ment developed specifically for 10 Gb/s 16λλλ (CPL5). Passive wavelength division multiplex- submarine networks. The equipment includes the ing couplers (WDM) are used to combine the input WDM submarine repeater, the OADM branching line signals at around 1.55 µm with the pump unit (BU) and the WDM submarine line terminal laser signal at 1.48 µm. Dielectric filter technolo- equipment (SLTE). gy was chosen for the WDM coupler, in order to achieve a flat pass-band characteristic. An opti- 3.1 WDM submarine repeater cal isolator (ISO) was designed to ensure very low Figure 2 shows the block diagram of the levels of polarization dependent loss (PDL) and repeater for one sub-system (one fiber pair). polarization mode dispersion (PMD) in the repeat- Table 2 shows the major parameters of the wide- er. The WDM filter and isolator were integrated band WDM repeater. into compact module by making full use of our 3.1.1 Repeater configuration micro-optics technology. A length of optical fibre, whose core is doped 3.1.2 Repeater supervisory system with the rare earth element Erbium, provides op- It is a requirement of the system to be able tical amplification. Optical energy is supplied to to locate faults to within one repeater section. All the Erbium doped fibre (EDF) by pump laser di- hardware faults involving the loss of transmission odes (LD) operating at a wavelength of 1.48 µm, can be located using the input and output moni- which excites the Erbium ions to a higher energy tors of the repeater.

Table 2 EDF1 Input 1 CPL1 WDM1 ISO1 CPL2 Output 1 Major parameters of wideband WDM repeater. LPG1

PD1 PD2 Parameter Value

LD1 Optical output power +10 dBm CPL5 LD2 Noise figure < 6 dB

PD4 PD3 Transmission window > 12 nm EDF2 (optical bandwidth) LPG2 Output 2 ISO2 WDM2 CPL3 Input 2 Remote supervision Optical input power monitor CPL4 Optical output power monitor Pump laser drive current monitor Figure 2 Operating temperature range 0°C to +35°C Configuration of wide-band WDM repeater (sub-system for one fiber pair). System design Iifetime 25 years

FUJITSU Sci. Tech. J.,35, 1,(July 1999) 37 M. Suyama et al.: WDM Optical Submarine Network Systems

Monitoring of the input and output optical in order to eliminate any shift of the center wave- signal level is achieved by using photo diodes (PD) length due to temperature variations. A perfect and couplers (CPL). The pump laser diodes’ con- circulated 3-port optical circulator is used in or- dition can be monitored by remotely monitoring der to still enable fault localization from the their drive current. remote terminals, using coherent optical time domain reflectometry (OTDR). The optical isolator 3.2 Optical add/drop submarine is used to suppress coherent cross-talk, which branching unit might otherwise degrade the transmission perfor- An Optical ADM branching unit (OADM-BU) mance. was developed, which can add or drop any wave- Table 3 summarizes the major parameters lengths to or from the main trunk WDM signal. of the OADM-BU. Figure 4 shows a typical char- Figure 3 shows the optical circuit diagram of the acteristic of the OADM-BU. It can be seen that OADM-BU. It utilizes fiber Bragg gratings, opti- good in-band amplitude flatness and sharp rejec- cal circulators and an optical isolator. The fiber tion characteristics were achieved. grating reflects the specified wavelength, and transmits other wavelengths. The required opti- 3.3 WDM submarine line terminal cal add/drop function is achieved by the combina- equipment (SLTE) for 10 Gb/s ××× 16λλλ tion of the fiber grating and the optical circulator The 10 Gb/s 16λ WDM SLTE is high-speed as shown in Figure 3. The fiber grating is incor- transmission equipment used for transporting a porated into a temperature-compensated package

0 Optical Fiber Fiber Optical 5 circulator grating grating circulator 10 IN OUT 15 λl ~ λn λl ~ λn Optical 20 isolator 25 30 Loss (dB) 35 40 DROP ADD λ λ 45 drop add 1550 1551 1552 1553 1554 1555 1556 1557 1558 1559 1560 λ λ Note: drop = add Wavelength (nm)

Figure 3 (a) "In" to "Out" characteristic Optical circuit diagram of optical ADM branching unit. 0 5 10 λ 15 drop Table 3 20 Major parameters of optical ADM branching unit. 25 30 Loss (dB) Parameter Typical value 35 Operating temperature range 0°C to +35°C 40 45 Signal wavelength 1550 nm to 1560 nm 1550 1551 1552 1553 1554 1555 1556 1557 1558 1559 1560 Insertion loss "In" to "Out": 5.8 dB Wavelength (nm) "In" to "Drop": 4.0 dB (b) "In" to "Drop" characteristic "Add" to "Out": 4.0 dB Insertion loss between "Through" > 36 dB Figure 4 wavelength and "Add/Drop" wavelength Example characteristics of optical ADM branching unit Return loss > 35 dB (Two wavelengths Add and Drop). PDL < 0.3 dB

38 FUJITSU Sci. Tech. J.,35, 1,(July 1999) M. Suyama et al.: WDM Optical Submarine Network Systems

TRIB (λ1) subrack WDM-S rack DCF subrack WDM-S rack STM-64 1 O/E FEC-S NRZ/RZ

TX&LD λ1 units E/O AWG AMP 13 λ4 16

λ5

AWG AMP λ8 CPL AMP To Line λ9 λ TRIB ( 13) subrack AWG AMP λ12 Same as TRIB (λ1) subrack

λ13 TRIB (λ16) subrack AWG λ16 AMP Same as TRIB (λ1) subrack

Figure 5 SLTE block diagram (transmit side).

STM-64 TRIB (λ1) subrack DCF subrack WDM-R rack 1 E/O FEC-R

λ1 RX O/E unit AWG 13 λ4 16

λ5

AWG λ8

CPL AMP From Line λ9 λ TRIB ( 13) subrack AWG λ12 Same as TRIB (λ1) subrack

λ13 TRIB (λ16) subrack AWG λ16 Same as TRIB (λ1) subrack

Figure 6 SLTE block diagram (receive side).

maximum of sixteen STM-64 signals. Figures 5 transmitted to the far end via the submarine re- and 6 are block diagrams of main transmission peaters. The received optical line signal is path of the 10 Gb/s 16λ WDM SLTE. To estab- de-multiplexed to each wavelength signal by the lish higher transmission performance, Reed SLTE, and then converted to an electrical signal. Solomon (255/239) Forward Error Correction The functions of the SLTE are as follows: (FEC) is implemented in the transmission signal 1) Conversion between the 9953.28 Mb/s for each wavelength. Thus, the STM-64 signal is (STM-64) SDH data signal and the subma- converted to a 10.66 Gb/s signal before being mul- rine line signal (10664.22857 Mb/s including tiplexed into WDM optical line signal and the FEC processing)

FUJITSU Sci. Tech. J.,35, 1,(July 1999) 39 M. Suyama et al.: WDM Optical Submarine Network Systems

2) Optical amplification of the transmit and 3.4 Current network protection receive signals architectures 3) Wavelength division multiplexing and de- SDH MS-SPRing network protection config- multiplexing of the signal uration (similar to the BLSR (Bi-directional Line 4) Dispersion compensation using dispersion Switched Ring) configuration in SONET net- compensating fiber, for both transmit and works) is currently the most attractive for large receive high-capacity submarine networks. MS-SPRing 5) Monitoring and displaying of relevant alarms is already widely used in terrestrial networks, and 6) Provision of line supervisory interface. is preferred over unidirectional Path Switched Ring protection schemes, since it allows the re- In the transmit side of the SLTE, the use of circuit capacity on a node-to-node basis and STM-64 SDH signal is converted to an electrical access to the protection channel is possible with signal, and is multiplexed with redundant bits for appropriate SIE equipment. Some specific adap- FEC, thus producing the 10.66 Gb/s signal. This tations to the usual MS-SPRing protocol are is converted to an optical signal with appropriate required for submarine network applications, to wavelength in TRIB sub-rack of the SLTE. A prevent hairpin protection over trans-oceanic maximum 16 channels are multiplexed into one routes. The SDH protection scheme is provided optical line signal using the arrayed waveguide by the SIE equipment. grating (AWG) and CPL blocks in the WDM-S rack of the SLTE. 4. Technologies for future submarine In the receive side of the SLTE, the line sig- network systems nal is amplified and de-multiplexed into separate To meet the increasing demand for network wavelength signals in WDM-R rack. After decod- capacity, which is mainly driven by the growth in ing the FEC bits, each signal is converted to an Internet services, new and advanced technologies STM-64 SDH signal in the TRIB sub-rack of the are required for end-to-end transmission capaci- SLTE. ty and also for network protection architecture. In order to minimize waveform distortion due This chapter discusses some of the enabling tech- to chromatic dispersion, dispersion compensation nologies for Tera-bit transmission and future at both transmit and receive side is necessary.2) network configurations. The necessary dispersion compensating fibers (DCF) to accomplish this are accommodated in the 4.1 Enabling technologies for tera-bit DCF sub-rack of the SLTE. transmission in real networks Overhead bytes in the FEC frame are also Major limiting factors for the realization of used for provision auxiliary plesiochronous data Tera-bit transmission include SNR degradation, channels (2.048 Mb/s), 64 kb/s data channels, and gain bandwidth, and waveform distortion due to voice channels for engineering orderwire. chromatic dispersion and non-linear optical ef- The SLTE equipment also performs surveil- fects. Various technologies seem to hold promise lance and control of submarine repeater and has in addressing these limitations: the alarm and supervisory capability. This equip- • Improved SNR achieved by using lower noise ment has a display interface to indicate relevant repeaters, such as achieved by utilizing 980 alarms and status, which involves receiving and nm pump lasers sending data from or to the System Supervisory • Broad bandwidth achieved by accurate gain Equipment (SSE). equalization and by exploiting L-band EDFA optical amplifiers

40 FUJITSU Sci. Tech. J.,35, 1,(July 1999) M. Suyama et al.: WDM Optical Submarine Network Systems

Transmitter (1537.1 nm to 1563.1 nm) Receiver

Pre-DCF Post-DCF Filter Odd ch. LDs IM CPL OR Even ch. LDs IM SW

SW 3-dB CPL ASE cut FG DSF 50 km 5 4 3 GEQ 2 1 DCF ASE cut DSF 25 km 25 km FG 6 7 GEQ 8 9 GEQ 10

ASE cut FG 15 14 13 GEQ 12 11

ASE cut DSF 25 km FG 16 17 GEQ 18 19 DCF DCF 50 km 10 km

Loop length : 737.6 km

Figure 7 Experiment setup.

22 OSNRs 1.1 dB 20

18 18 OSNR (dB) Q-factors 16

-9 (10 dB/div) 26 nm 14 BER = 10 without FEC 5 dB

Relative intensity BER = 10-11 with FEC 12 Q-factor (dB)

10 1535 1545 1555 1565 1 17334966 Wavelength (nm) Channel

Figure 8 Optical spectrum after 2212 km. Figure 9 Transmission performance (Optical SNR and Q factor).

• Reduced power density and chromatic disper- ogies.3) Figure 7 shows the configuration of the sion compensation achieved by utilizing new relevant transmission experiment. The noise fig- types of optical fiber. ure of the optical amplifiers was as low as 4.9 dB with +13 dBm output power, which was realized We have already successfully demonstrated by efficient pumping at 1.48 µm using a pump re- transmission of 10.7 Gb/s 66λ (= 0.7 Tb/s) over flector. We compensated for the asymmetric gain 2212 km by employing some of the above technol- profile by using GEQs with different free spectral

FUJITSU Sci. Tech. J.,35, 1,(July 1999) 41 M. Suyama et al.: WDM Optical Submarine Network Systems

ranges, resulting in a bandwidth of 26 nm after tion, an Optical ADM developed for use in terres- transmission over 2212 km (Figure 8). A good trial networks can easily be deployed in submarine transmission performance was confirmed in terms networks using this configuration. of optical SNR and Q factor (Figure 9). 4.2.2 Network configurations These technologies combined with the new using OPSW without OADM optical fiber featuring large effective area, and dis- In case of the fixed connection of the wave- persion compensation up to the third order,4) will lengths in the optical layer, it is possible to connect enable the practical realization of Tera-bit trans- the OPSW to the SLTE directly, without using the mission in networks over transoceanic distances. OADM (Figure 11). This configuration allows the deployment of systems at a lower cost, while still 4.2 Future high capacity network maintaining the high network reliability offered architectures by the OPSW. Telecommunication backbone networks will 4.2.3 Network configurations in the near future evolve into data networks which using an IP router accommodate voice, video, IP and other telecom- Recently, telecommunication services using munications services. A submarine network Internet protocol (IP) are developing very quick- system which can satisfy the requirements of this ly. It is now important to apply the IP technology evolution, and also features more economical and to the submarine cable networks, as the interna- flexible configuration is described. tional backbone network also shifts towards an 4.2.1 Network configurations IP based network. Figure 12 shows a possible using OADM and OPSW network configuration using IP routers, where a Figure 10 shows a ring-configuration sub- high capacity IP router is connected directly to marine network configuration using an Optical the SLTE. In the event of a network failure, traf- Add / Drop Multiplexer (OADM) at the terminals. fic can be restored by the routing protocol of the The OADM can add or drop and pass through any IP router. The system has the following features: desired wavelength signals in optical layer, by us- 1) Efficient transportation of IP traffic ing appropriate optical filters. The OADM sends 2) Lower cost for network equipment the wavelength multiplexed signal on to the SLTE. 3) Easy integration with other networks using For protection against possible line or equipment IP protocols failure, the optical protection switch (OPSW) with 4) Simplified network architecture and protection Transoceanic Ring Protection mode, is supported 5) The possibility to protect the network using in this configuration. the routing protocol. The special features in this configuration are as follows: Therefore, this configuration seems promis- 1) Transparency to any digital hierarchy ing for future submarine networks. 2) High reliability by using the OPSW 3) Add/Drop and Through any wavelength in 5. Conclusions the optical layer We have described a practical and cost-effec- 4) Effective use of the wavelength in the ring tive 640 Gb/s (10 Gb/s 16λ 4 fiber pair) optical network. submarine network system, together with the network configuration and relevant equipment. In This configuration can exclusively assign particular, the new submersible wide-bandwidth wavelengths for various telecommunication optical repeater, optical ADM branching unit, and services and signals in the optical layer. In addi- submarine line terminal equipment were detailed.

42 FUJITSU Sci. Tech. J.,35, 1,(July 1999) M. Suyama et al.: WDM Optical Submarine Network Systems

Station A Station B REP OADM OADM

/ PSW SLTE CTB CTB SLTE / PSW SSE SSE NME PFE PFE SLTE NME SLTE CTB PFE PFE CTB

REP REP

CTB PFE PFE CTB SLTE SSE SSE SLTE PFE BU PFE NME REP REP NME OADM SLTE SLTE OADM

/ PSW CTB / PSW CTB

Station D Station C BU : Branching Unit CTB PFE CTB : Cable Termination Box SLTE NME : Network Management Equipment OADM: Optical Add Drop Multiplexer SSE PFE : Power Feeding Equipment OADM NME PSW : Protection Switch / PSW REP : Submarine REPeater SLTE : Submarine Line Terminating Equipment Station E

OADM

WORKING O-Filter SLTE O-Filter O-Filter SLTE

O-Filter

O-Filter O-Filter PROTECTION

SLTE SLTE

O-Filter : Optical Filter

OPSW λλ

Figure 10 Ring submarine network configuration using OADM.

Through

Add SLTE SLTE Through Drop Through

SLTE SLTE

Fixed wirning

: Working : Protection OPSW λλ Figure 11 Connection configuration between SLTE and OPSW.

FUJITSU Sci. Tech. J.,35, 1,(July 1999) 43 M. Suyama et al.: WDM Optical Submarine Network Systems Station A Station B REP

ROUTER ROUTER

SLTE CTB CTB SLTE SSE SSE NME PFE PFE SLTE NME SLTE CTB PFE PFE CTB

REP REP

CTB PFE PFE CTB SLTE SSE SSE SLTE PFE BU PFE NME REP REP NME SLTE SLTE ROUTER ROUTER CTB CTB

Station D Station C BU : Branching Unit CTB PFE CTB : Cable Termination Box SLTE NME : Network Management Equipment PFE : Power Feeding Equipment SSE REP : Submarine REPeater NME ROUTER : IP ROUTER ROUTER SLTE : Submarine Line Terminating Equipment SSE : System Superviously Equipment Station E

Figure 12 Ring submarine network configuration using the IP Router.

Enabling technologies for future Tera-bit trans- over 4,760 km straight line using pre- and mission networks were discussed, referring to our post-dispersion compensation and FWM 0.7 Tb/s (10.7 Gb/s 16 66λ) transmission cross talk reduction. OFC’96, San Jose, WM3, experiment, and new network configurations February, 1996. using OADM or IP routers were proposed for next- 3) T. Terahara, T. Naito, N. Shimojo, T. Tanaka, generation of WDM submarine networks. T. Chikama, and M. Suyama: 0.7 Tbit/s (66 10.66 Gbit/s) WDM transmission over 2,212 References km using broadband, high-power EDFAs 1) T. Naito, N. Shimojo, T. Terahara, T. Tanaka, with pump reflector. Electron. Lett. 34, 10, T. Chikama, and M. Suyama: Long-haul pp.1001-1002 (May 1998). WDM transmission system by use of high 4) M. Murakami, H. Maeda, and T. Imai: Long- Aluminum codoped EDFAs and gain-equal- haul 16 10 WDM transmission experiment izers. GLOBECOM’98, Sydney, pp.993-997, using higher order fiber dispersion manage- November, 1998. ment technique. ECOC’98, Madrid, TuC28, 2) T. Naito, T. Terahara, T. Chikama, and M. September, 1998. Suyama: Four 5-Gb/s WDM transmission

44 FUJITSU Sci. Tech. J.,35, 1,(July 1999) M. Suyama et al.: WDM Optical Submarine Network Systems

Masuo Suyama received B.E. and M.E. Haruo Fujiwara received B.S. and M.S. degrees in Applied Physics from the degrees in Electrical Engineering from University of Tokyo, Tokyo, Japan, in Osaka University, Osaka, Japan in 1973 1980 and 1982, respectively. He joined and 1975, respectively. He joined Fujitsu Laboratories Ltd., Kawasaki in Fujitsu Laboratories Ltd., Kawasaki in 1983 and was engaged in research and 1975 and transferred to Fujitsu Ltd. in development of optical amplifiers and 1985. He has been engaged in the their system applications. Since 1994, development of optical submarine re- he has been with submarine telecom- peaters and branching units. He is a munications division of Fujitsu Ltd., member of the Institute of Electronics, working on system design. He is a mem- Information and Communication Engi- ber of the Institute of Electronics, Information and Communica- neers (IEICE) of Japan. tion Engineers (IEICE) of Japan.

Masato Nagayama received a B.E. de- Colin Anderson received a B.Sc. gree in Electrical Engineering from the degree, majoring in Physics from Science University of Tokyo, Tokyo, Victoria University, Wellington, New Japan in 1989. He joined Fujitsu Ltd., Zealand in 1975. In 1988 he received Kawasaki, in 1989 and has been en- an MBA degree from the Victoria Uni- gaged in the research and development versity Graduate School of Business of data communication network sys- and Government. After 12 years with tems for 9 years. Since 1998 he has Philips NZ Ltd., in both engineering and been engaged in the research and de- marketing roles, he joined Fujitsu NZ velopment of submarine cable network Ltd. in 1986. In 1992 he moved to Tokyo systems. Japan, to take up a position in the Inter- national Telecommunications Business Group of Fujitsu Limit- ed. He is currently Business Development Manager for Submarine Networks Sales & Marketing in the International Telecommuni- cations Business Group. He is a member of the IEEE Commu- nications Society. Haruki Watanabe received B.E. and M.E. degrees in Electronics Engineer- ing from Nihon University, Tokyo, Japan in 1980 and 1982, respectively. He joined Fujitsu Ltd., Kawasaki in 1982, where he was engaged in research and development of submarine line terminal equipment. He joined Fujitsu Kyushu Digital Technology Ltd., Fukuoka in 1999. He is a member of the Institute of Electronics, Information and Commu- nication Engineers (IEICE) of Japan.

FUJITSU Sci. Tech. J.,35, 1,(July 1999) 45