1/13 Enabling technology for suppressing nonlinear interchannel crosstalk in DWDM transoceanic systems H. Zhang R.B. Jander C. Davidson D. Kovsh, L. Liu A. Pilipetskii B. Bakhshi and N. Bergano April 2005 1/12 Tyco Telecommunications Proprietary Equipment for performance evaluation of DWDM systems B. Bakhshi
2/13 Main topics � Reducing nonlinear inter-channel crosstalk techniques � Orthogonal launch 2/12 Tyco Telecommunications Proprietary Equipment for performance evaluation of DWDM systems B. Bakhshi
3/13 Techniques for reducing nonlinear interchannel crosstalk Large effective area transmission fibers 1. – Nonlinear phase shift is inversely proportional to Aeff Unfortunately, large Aeff fiber has a large dispersion slope to > 0.1ps/nm 2 /km – Standard dispersion management 2. – Reducing XPM effect by avoiding propagating over zero-dispersion wavelength – Reducing FWM effect by reducing phase-matching length – However, Have non-zero dispersion slope, and interaction between large accumulated dispersion and nonlinear effects results in signal distortion in edge channels LMF -2 ps/nm/km SMF 18 ps/nm/km 1 9 10 2 3/12 Tyco Telecommunications Proprietary Equipment for performance evaluation of DWDM systems B. Bakhshi
4/13 Modern dispersion management 3. – Combination of Large-Mode (LMF) and Non-Zero Dispersion shifted fiber (NZ-DSF) reduces overall dispersion slope to 0.058 ps/nm 2 /km (M. Vaa, OFC-01 paper WF5) LMF NZ-DSF LMF NZ-DSF A (um 2 ) 70-80 50-55 Dispersion slope 0.05 0.1 – Dispersion slope-matched map utilizing negative dispersion slope fiber can reduce slope to 0.005 ps/nm 2 /km, realize > 1Tb/s submarine transmission (C. Davidson, OFC-00 PD-25) Chirped Return-to-Zero (CRZ) transmission format 4. - Suppress nonlinear interaction by broadening the spectrum of launched signal. 4/12 Tyco Telecommunications Proprietary Equipment for performance evaluation of DWDM systems B. Bakhshi
5/13 Orthogonal launch 5. – Orthogonal launch reduce XPM effect by half – Orthogonal launch remove FWM effect 0 P fwm = (P 3 + P 4 )/(P 1 + P 2 ) P 1 P 2 P 3 P 4 -10 A P FWM (dB) ∆λ -20 B TWO-tone FWM vs ∆λ in a 500 km amplifier chain for; -30 A) conventional WDM fiber, B) hybrid spans using large mode fiber, and C) orthogonal polarization launch. C N. Bergano, OFC98 -40 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Wavelength Separation ∆λ (nm) 5/12 Tyco Telecommunications Proprietary Equipment for performance evaluation of DWDM systems B. Bakhshi
6/13 Orthogonal launch technique 1540.6 nm 1 Receiver Combiner Data AM PM 3 ... 63 2 31 -1 PC 2 Combiner Data AM PM 4 .... ... 12 2 1 64 1559.5 nm 2 23 -1 512km Neal Bergano, et. al. “ 320 Gb/s WDM Transmission (64x5 Gb/s) over 7,200 km using Large Mode Fiber Spans and Chirped Return-to-Zero signal,” OFC-98, paper PD-12 6/12 Tyco Telecommunications Proprietary Equipment for performance evaluation of DWDM systems B. Bakhshi
7/13 System Performance Improvement by orthogonal Launch L=8910Km, PMD=0.06ps/km 1/2 3.0 -2 dBm -4 dBm 2.0 -6 dBm ∆ Q, dB 1.0 0.0 25 35 45 55 65 channel separation, GHz Dmitriy Kovsh, et. al., OFC-01 paper WT1 Bamdad Bakhshi, et. al., OFC-02 paper WP7 7/12 Tyco Telecommunications Proprietary Equipment for performance evaluation of DWDM systems B. Bakhshi
8/13 Orthogonally preservation between neighboring channels PMD=0.06ps/km 1/2 1 0.8 0.6 <S1.S2> 12.5 GHz 18 GHz 0.4 25 GHz 37.5 GHz 0.2 50 GHz 100 GHz 0 0 3000 6000 9000 System Distance, km 8/12 Tyco Telecommunications Proprietary Equipment for performance evaluation of DWDM systems B. Bakhshi
9/13 Polarization controller approach � LiNbO3 polarization controller can be modeled as a unitary Jones matrix relating the output and input Jones vectors β γ θ DeMUX → → ( ) = β , γ PBS t U θ , s Polarization ODD ch. Controller MUX (Nx2) Polarization EVEN ch. Controller DeMUX 9/12 Tyco Telecommunications Proprietary Equipment for performance evaluation of DWDM systems B. Bakhshi
10/13 Loss control problem Local gradient is searched by dithering � the control parameters. There always exists an input � polarization to the controller that is insensitive to dithering the control parameter. – W. Shieh and H. Kogelnik, IEEE Photonics Technology Letters, 2001 Small change of input or output � (a) polarization requires large change of control variables – Fred Heismann. JLT 1994 (a) Tyco’s Solution (b): � – Intelligent dither algorithm changes the control variable by a large angle when there exists a “dead spot”. (b) 10/12 Tyco Telecommunications Proprietary Equipment for performance evaluation of DWDM systems B. Bakhshi
11/13 Trans-Atlantic 25 GHz channel spacing Experiment 11/12 Tyco Telecommunications Proprietary Equipment for performance evaluation of DWDM systems B. Bakhshi
12/13 Performance of center channel at 1549.715 nm TX spectrum 13 OPL using PM fiber -1 5 J u ly 0 9 , 2 0 0 2 Random launch -2 0 OPL using polarization 12 controllers -2 5 Q 2 ( dB ) Optical Power (dBm) -3 0 11 -3 5 -4 0 10 -4 5 -5 0 9 -5 5 1 5 3 5 1 5 4 0 1 5 4 5 1 5 5 0 1 5 5 5 1 5 6 0 1 5 6 5 -12 -11 -10 -9 -8 -7 -6 -5 -4 W a ve le n g th (n m ) Channel Power (dBm) � 9 data channels together with 25 depolarized CW loading tones. � Data channel spacing is 25 GHz � Data channel is RZ modulated with 13 dB spectral size band suppression 12/12 Tyco Telecommunications Proprietary Equipment for performance evaluation of DWDM systems B. Bakhshi
13/13 Conclusion � DWDM system with narrow channel spacing (<0.3 nm) needs suppress nonlinear interchannel crosstalk. � Orthogonal launch reduce XPM effect by one half and eliminates FWM effect, � Practical orthogonal launch method exists. 13/12 Tyco Telecommunications Proprietary Equipment for performance evaluation of DWDM systems B. Bakhshi
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