Enabling technology for suppressing nonlinear interchannel - - PowerPoint PPT Presentation

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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

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Main topics

Reducing nonlinear inter-channel crosstalk techniques Orthogonal launch

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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/nm2/km

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

1 2 LMF -2 ps/nm/km 9 10 SMF 18 ps/nm/km

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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/nm2/km (M. Vaa, OFC-01 paper WF5) – Dispersion slope-matched map utilizing negative dispersion slope fiber can reduce slope to 0.005 ps/nm2/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.

LMF NZ-DSF A (um2) 70-80 50-55 Dispersion slope 0.05 0.1 LMF NZ-DSF

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5.

Orthogonal launch

– Orthogonal launch reduce XPM effect by half – Orthogonal launch remove FWM effect

0.0 0.2 0.4 0.6 0.8 1.0 1.2

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P3 P2 P1 P4 Pfwm = (P3 + P4)/(P1 + P2) Wavelength Separation ∆λ (nm) PFWM (dB)

A B C

∆λ

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

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Orthogonal launch technique

Receiver 1 2 12

... ...

Combiner Combiner 1 3 63 2 4 64 Data AM PM Data AM PM

....

231-1 223-1 512km

1540.6 nm 1559.5 nm

PC

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

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System Performance Improvement by

• rthogonal Launch

0.0 1.0 2.0 3.0 25 35 45 55 65 channel separation, GHz ∆Q, dB

• 2 dBm
• 4 dBm
• 6 dBm

L=8910Km, PMD=0.06ps/km 1/2

Dmitriy Kovsh, et. al., OFC-01 paper WT1 Bamdad Bakhshi, et. al., OFC-02 paper WP7

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Orthogonally preservation between neighboring channels

0.2 0.4 0.6 0.8 1 3000 6000 9000 System Distance, km <S1.S2> 12.5 GHz 18 GHz 25 GHz 37.5 GHz 50 GHz 100 GHz

PMD=0.06ps/km 1/2

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Polarization controller approach

LiNbO3 polarization controller

can be modeled as a unitary Jones matrix relating the output and input Jones vectors

PBS

ODD ch. EVEN ch. MUX (Nx2) Polarization Controller Polarization Controller DeMUX DeMUX

θ β γ

( )

→ →

= s θ U t γ β, ,

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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

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”.

(a) (b)

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Trans-Atlantic 25 GHz channel spacing Experiment

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Performance of center channel at 1549.715 nm

9 10 11 12 13

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Channel Power (dBm)

Q2(dB)

OPL using PM fiber Random launch OPL using polarization controllers

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5 1 5 3 5 1 5 4 1 5 4 5 1 5 5 1 5 5 5 1 5 6 1 5 6 5 W a ve le n g th (n m ) Optical Power (dBm)

J u ly 9 , 2 2

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 TX spectrum

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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.