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 and N. Bergano April 2005 1/12
Main topics 2/13 Reducing nonlinear inter-channel crosstalk techniques Orthogonal launch 2/12
Techniques for reducing nonlinear interchannel crosstalk 1. Large effective area transmission fibers Nonlinear phase shift is inversely proportional to Aeff Unfortunately, large Aeff fiber has a large dispersion slope to > 0.1ps/nm 2 /km 3/13 2. Standard dispersion management 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 2 9 10 3/12
4/13 3. Modern dispersion management 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) 4. Chirped Return-to-Zero (CRZ) transmission format - Suppress nonlinear interaction by broadening the spectrum of launched signal. 4/12
5/13 5. Orthogonal launch Orthogonal launch reduce XPM effect by half Orthogonal launch remove FWM effect P FWM (db) 0-10 -20-30 -40 P fwm = (P 3 + P 4 )/(P 1 + P 2 ) A B C P 1 P 2 P 3 λ P4 TWO-tone FWM vs λ in a 500 km amplifier chain for; A) conventional WDM fiber, B) hybrid spans using large mode fiber, and C) orthogonal polarization launch. N. Bergano, OFC98 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Wavelength Separation λ (nm) 5/12
Orthogonal launch technique 6/13 1540.6 nm 1559.5 nm 1 3...... 63 2 4 64 Combiner Combiner Data AM PM 2 31-1 Data AM PM 12... 2 23-1 512km 2 Receiver PC 1 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
System Performance Improvement by orthogonal Launch 7/13 Q, db 3.0 2.0 1.0 L=8910Km, PMD=0.06ps/km 1/2-2 dbm -4 dbm -6 dbm 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
Orthogonally preservation between neighboring channels 8/13 PMD=0.06ps/km 1/2 1 0.8 <S1.S2> 0.6 0.4 0.2 0 12.5 GHz 18 GHz 25 GHz 37.5 GHz 50 GHz 100 GHz 0 3000 6000 9000 System Distance, km 8/12
Polarization controller approach 9/13 LiNbO3 polarization controller can be modeled as a unitary Jones matrix relating the output and input Jones vectors θ β γ ODD ch. EVEN ch. Polarization Controller Polarization Controller DeMUX MUX (Nx2) PBS t = (,β, γ ) s U θ DeMUX 9/12
Loss control problem 10/13 (a) 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 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
11/13 Trans-Atlantic 25 GHz channel spacing Experiment 11/12
12/13-15 -20-25 TX spectrum July 09, 2002 13 12 Performance of center channel at 1549.715 nm OPL using PM fiber Random launch OPL using polarization controllers Optical Power (dbm) -30-35 -40-45 Q 2 (db) 11 10-50 -55 1535 1540 1545 1550 1555 1560 1565 Wavelength (nm) 9-12 -11-10 -9-8 -7-6 -5-4 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
Conclusion 13/13 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