High-Performance Submarine Line Terminal Equipment for Next-Generation Optical Submarine Cable System: FLASHWAVE S650 V Hiroshi Oikawa V Junichi Yoshimura V Haruki Watanabe (Manuscript received June 20, 2006) Global telecommunications traffic is rapidly growing in response to customer demand for broadband services and more reliable network performance. Thus, the demand for a submarine telecommunications system, which is a backbone infrastructure for international telecommunications, is also steadily increasing. This demand is not only for constructing a new cable system, but also for upgrading capacity by adding extra capacity to existing systems. To meet this demand, we have developed the FLASHWAVE S650, new Submarine Line Terminal Equipment (SLTE), by applying cutting-edge DWDM optical technologies. This equipment features excellent trans- mission performance, improved maintainability, and a flexible configuration suitable for a long-haul system, coupled with upgraded capacity. The FLASHWAVE S650 was successfully deployed in a SEA-ME-WE 4 cable system and certain upgraded systems. This paper describes the various functions, characteristics, and configura- tion of the FLASHWAVE S650. 1. Introduction function necessary for long-distance optical trans- Due to the rapid worldwide expansion of mission, an error correction function, and a communication networks to support broadband, surveillance control function that monitors such there has been a growing need for using submersible equipment as submarine repeaters. submarine optical communication systems as the Moreover, various redundant configurations, main backbone infrastructure of international including an assortment of different options, communications. This has prompted the demand offer the high reliability necessary to support the for upgrade projects that can cope with the laying international communications backbone essential of cable for new systems, as well as expanding the for a submarine communications system. In transmission capacity of existing systems. The addition, the use of a Graphical User FLASHWAVE S650 was developed as cutting-edge Interface (GUI) in combination with submarine Submrine Line Terminal Equipment (SLTE) in communications System Surveillance Equipment response to these needs. (SSE) enables comprehensive control of the The FLASHWAVE S650 can perform a max- submarine communications system. imum of 112-wave multiplex transmissions of This product is employed in Southeast Asia- 10-Gb/s signals through a single optical fiber. Middle East-Western Europe 4 (SEA-ME-WE4), The FLASHWAVE S650 has wavelength a large submarine cable system connecting coun- multiplexing and demultiplexing functions, as tries from Singapore to France, and designed for well as an optical amplification function through a capacity of 10 Gb/s × 68 waves. Moreover, it can the use of an Erbium-Doped Fiber Amplifier be used to improve the existing system to be (EDFA), a wavelength dispersion compensation expanded through upgrade projects. This paper FUJITSU Sci. Tech. J., 42,4,p.469-475(October 2006) 469 H. Oikawa et al.: High-Performance Submarine Line Terminal Equipment for Next-Generation Optical Submarine Cable System: FLASHWAVE S650 first describes an example of the typical 3) SDH Interface Equipment (SIE): Equipment configuration of a submarine communications that interfaces with a terrestrial SDH system, followed by the features and functions of network. the FLASHWAVE S650. Then it explains the 4) Submarine cable and submersible equip- configuration of the equipment in detail. ment: Submarine repeaters that use a high reliability optical amplifier and gain equal- 2. Configuration of submarine ization equipment to rectify the wavelength communications system dependability of gain via a multi-stage con- Figure 1 shows an example of the typical nection of optical fibers and repeaters. configuration of a submarine communications system. This system is composed of various kinds 3. Features and functions of of equipment like SLTE and SSE, and the follow- FLASHWAVE S650 ing equipment described below. The FLASHWAVE S650 enables significant- 1) Power Feeding Equipment (PFE): Power ly improved maintainability compared with supply equipment that supplies electric conventional equipment, while attaining a global- power to such submersible equipment as ly high level of transmission capability using the submarine repeaters. technology shown below. 2) Cable Termination Unit (CTU): Cable termi- Table 1 lists the main specifications of this nation equipment that connects terrestrial product. Moreover, the following describes the cable to submarine cable. functions of this equipment in detail. Submarine Line Terminal Equipment Submerged Segment Submarine Line Terminal Equipment (FLASHWAVE S650) (FLASHWAVE S650) STM-64 SIE SIE #1 TRIB WDM CTU CTU WDM TRIB 10.709G × n -wave Submarine Cable Wavelength Submarine multiplexing Repeater STM-64 #n PFE PFE LAN LAN SSE SSE Router Router SSE: System Surveillance Equipment SIE: Synchronous Digital Hierarchy (SDH) Interface Equipment CTU: Cable Termination Unit PFE: Power Feeding Equipment WDM: Wavelength Division Multiplexer TRIB: Tributary LAN: Local Area Network STM: Synchronous Transfer Module Figure 1 Typical Configuration of submarine communications system. 470 FUJITSU Sci. Tech. J., 42,4,(October 2006) H. Oikawa et al.: High-Performance Submarine Line Terminal Equipment for Next-Generation Optical Submarine Cable System: FLASHWAVE S650 Table 1 3.2 Improved level of error correction Main Specifications of FLASHWAVE S650. Higher transmission performance can be Item Specs achieved through the use of an error correction Dimensions 600(W) × 300(D) × 2200(H) mm Wavelength multiplex Max 112 waves function called Ultra-Forward Error Correction Wavelength interval 37.5 GHz (approx. 0.3 nm) (U-FEC). By using the STM-64 signal coupled Error correcting gain 8.2 dB with error correcting compression through the SIE Operational environment Temperature: +5°C to +40°C at a rate of 9.95 Gb/s, the signal is transmitted as requirements Humidity: 5 to 85% a 10.71-Gb/s signal. On the reception side, any Power supply requirement DC -48V errors in the signal are detected and corrected, Submersible-side interface and then reconverted back into a 9.95-Gb/s Optical receiving level -5.0 to +12.5 dBm signal. This is turn reduces the error rate in the Optical transmitting level +7.0 to +15.5 dBm transmission channel from 3.0 × 10-3 to 1.0 × 10-13, Wavelength bandwidth 1533.47 to 1566.83 nm thus allowing for a high correction gain of 8.2 dB. Transmission speed 10.709 Gb/s (U-FEC) Encoding RZ Terrestrial-side interface 3.3 Wavelength dispersion compensation -14.0 to -1.0 dBm When using cables that may extend over sev- Optical receiving level (ITU-T G.957 S64.2b) eral thousands of kilometers, as in submarine -1.0 to +2.0 dBm Optical transmitting level (ITU-T G.957 S64.2b) communications systems, it is essential to reduce Wavelength bandwidth 1530.0 to 1565.0 nm the degradation of wavelength dispersion compen- Transmission speed 9.953 Gb/s (ITU-T G.707) sation for the optical fibers. Especially in the Scrambled binary NRZ Dense Wavelength Division Multiplexing Encoding (ITU-T G.707) (DWDM) system that uses wide-ranging wave- lengths, any difference in wavelength dispersion 3.1 High-density wavelength multiplexing quantity between signals on the short wavelength The use of 37.5-GHz (about 0.3-nm) wave- side and long wavelength side cannot be ignored. length multiplex intervals, coupled with Therefore, by adopting Dispersion Compen- world-class, dense wavelength division multiplex- sation Fiber (DCF), this equipment can ing and demultiplexing technology, enables the compensate the wavelength dispersion of a wide long-distance optical transmission of 10-Gb/s array of signal wavelengths in the wavelength signals through a maximum of 112 waves. In multiplex part of each transmission and reception, addition, by using a colorless Arrayed Waveguide and permit the use of Virtually Imaged Phased Grating (AWG) that can combine waves at a ratio Array (VIPA)1) — variable dispersion compensa- of 8:1 with a thin-film-wave multiplexing/demul- tion technology originally developed by Fujitsu — tiplexing unit that can combine and separate that enables optimal dispersion compensation to waves at a ratio of 14:1, the system becomes ap- each wavelength by performing dispersion com- plicable to multiple wavelength ranges and pensation individually for each wavelength. number of wavelengths systems by simply chang- Furthermore, individual dispersion compen- ing the colorless AWG setting. sation by using VIPA makes automatic At initial setup, for example, sending multi- optimization possible. It controls the dispersion ple DL (Dummy Light) signals on the transmission compensation value to comply with the lowest side to compensate for an inadequate number of error correction value set by FEC through disper- 10-Gb/s signals can stabilize the transmission of sion compensation on the reception-side VIPA. even a single signal. Moreover, by adopting VIPA as an individu- al method of dispersion compensation, the FUJITSU Sci. Tech. J., 42,4,(October 2006) 471 H. Oikawa et al.: High-Performance Submarine Line Terminal Equipment for Next-Generation Optical Submarine Cable System: FLASHWAVE S650 footprint of the device can also be dramatically from submersible equipment through transmis- reduced when compared to devices using the sion using a similar method. conventional DCF and optical amplifier combina- tion