SubOptic2010 Poster Session: System Design & Applications - SD14 Extremely Narrow Channel Spacing 10Gb/s-DWDM Transmission for Advanced Submarine Cable System Takehiro Nakano, Taketo Onuma, Takanori Inoue, Yoshihisa Inada, Takaaki Ogata NEC Corporation
Introduction ▐ To cope with the increasing capacity requirements, we have been investigating to increase the number of 10Gb/s channels. ▐ To date, we have already deployed 33GHz spaced 10Gb/s DWDM submarine cable systems. ▐ This paper describes our recent development of 10Gb/s DWDM transmission technologies with extremely narrow channel spacing of 25GHz for submarine cable systems to achieve over Tb/s capacity. Page 1
Extremely Narrow Channel Spacing ▐ Figure1 shows the optical spectrum of the commercial modulation formats of 10Gb/s. ▐ Their spectrum widths are approximately 20~25GHz. NRZ RZ RZ-DPSK Vertical axis:10dB/div, Horizontal axis: 25GHz/div Figure 1: Optical Spectra of 10Gb/s signals ▐ We have confirmed the possibility of reducing the channel spacing of 10Gb/s signals down to 25GHz as shown in Figure2. 33GH-spacing 25GH-spacing Modulation formats : RZ-DPSK Figure 2: Channel spacing of 10Gb/s signals Page 2
Receiver Sensitivity of 25GHz-spaced 10Gb/s signal ▐ In order to confirm the Q performance with narrow channel spacing of 25GHz, we compared the difference of receiver sensitivity between the RZ-DPSK signal and the RZ signal with 25GHz and 33GHz channel spacing . Back-to-back Performance 18 RZ-DPSK (25GHz-spacing) 17 RZ-DPSK (33GHz-spacing) 16 15 Q value [dB] 14 3dB 13 12 11 RZ (25GHz-spacing) 10 RZ (33GHz-spacing) 9 8 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 OSNR [dB] This result indicates that the RZ-DPSK signal keeps its excellent receiver sensitivity with 25GHz channel spacing. Page 3
Assessment of Transmission Performance ▐ A narrow channel spacing enhances the nonlinear effects, such as the cross-phase modulation (XPM) and the four-wave- mixing (FWM), in the optical fiber transmission, and it degrades the transmission performances. ▐ To make an assessment of the transmission performance with a narrow channel spacing, we compared the Q values between 25GHz and 33GHz channel spacing after long distance transmission over the dispersion managed fiber (DMF). Page 4
(1) Experimental Setup ▐ To make an assessment, we prepared long distance transmission line with the re-circulating technique and RZ-DPSK signals of 25GHz and 33GHz channel spacing . LD1 PM-AWG × N × N LD3 RZ-DPSK DCF DCF MUX Transmitter LD5 (Odd) LD7 SW1 DMUX LD2 25GHz or 33GHz PM-AWG LD4 RZ-DPSK Pol. spacing 8WDM DPSK Transmitter Scr. LD6 Receiver (Even) SW2 LD8 41CW Lights Block Pol. BEQ Scr. 1075km x 11 times circulation =11833km DMF1075km Transmission Line Page 5
(2) Transmission Line Configuration ▐ For very long distance transmission, we employed the Dispersion Managed Fiber (DMF) as transmission line. ▐ The DMF can achieve excellent dispersion flatness and greatly reduce nonlinearity effects. � Combination of DMF+ and DMF- in a span DMF+ : Large effective core area DMF- : Slope-matched DCF � Average dispersion adjustment to avoid optical phase noise accumulation 1 DMF1075km Transmission Line 0.8 NZ-DSF 0.6 Dispersion [ps/nm/km] 0.4 DMF Repeater output power 0.2 73km span +16.5dBm 0 -0.2 DMF -0.4 Dispersion slope: -0.6 Block < 0.01ps/nm 2 /km -0.8 D+ D- D+ D- DCF -1 1540 1545 1550 1555 1560 1565 Wavelength [nm] Page 6
(3) Result ▐ We measured the Q value performance dependency on the transmission distance with channel spacings of 25GHz and 33GHz in order to confirm the impacts of narrowing channel spacing . Channel Power : -4dBm/ch 17 33GHz-Spacing 16 33GHz-spacing 25GHz-Spacing 15 14 Q value [dB] 13 12,000km 12 25GHz-spacing 11 > 3 3dB Margin dB Margin > 10 9 FEC Detection Limit : 8.8dB 8 4000 6000 8000 10000 12000 14000 16000 Transmission Distance [km] 10Gb/s 25GHz-DWDM RZ-DPSK is feasible with almost the same performance as the case of 33GHz channel spacing. Page 7
Demonstration: 132x10Gb/s-6,500km transmission ▐ To demonstrate the extremely narrow channel spacing transmission using the fully-established 10Gb/s technologies, we conducted 132x10Gb/s-6,500km transmission experiment adopting RZ-DPSK modulated 132 signals with a 25GHz channel spacing. Q value Spectrum 18 10 16 0 Power [dBm] Q value [dB] 14 -10 > 6dB Margin > 6dB Margin 12 -20 10 -30 8 -40 FEC Detection Limit : 8.8dB 6 -50 1535 1540 1545 1550 1555 1560 1565 1570 Wavelength [nm] All 132CHs have sufficient Q margins against FEC detection limit. Page 8
10Gb/s Line Terminal Equipments ▐ We have developed the Submarine Line Terminal Equipment supported 25GHz-spaced DWDM system. TPND Rack WME Rack Main features � RZ-DPSK / RZ / NRZ modulation formats � Enhanced FEC (Coding Gain 10dB) � Various channel grid (25/33/50/100GHz) with Tunable Light Source Various tributary interfaces � STM-64/OC-192, 10GbE LAN PHY STM-16/OC-48 x 4 Tunable Dispersion Compensation Module � (TDCM) 32ch x 10G Transponders in one TPND Rack � Maximum Capacity : 180ch DWDM � OADM system support � 2200mm(H) x 600mm(W) x 300mm(D) � Page 9
Conclusion ▐ We showed our recent development of 10Gb/s DWDM transmission technologies with extremely narrow channel spacing of 25GHz for submarine cable systems to achieve over Tb/s capacity. ▐ It has been verified that transmission over 12,000km with 25GHz-spaced RZ-DPSK signal is feasible with a performance comparable with that of 33GHz channel spacing. Page 10
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