Numerical simulation of point to point transmission in a 40 channel 40 Gbit/s system :

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Numerical simulation of point to point
transmission in a 40 channel 40 Gbit/s system
distributed versus discrete amplification
Gadi Eisenstein, David Dahan Electrical
Engineering Dept. TECHNION
Abstract
This poster describes a numerical simulation of
fourty - 40 Gbit/s channel transmission at 100
GHz detuning. Discrete and distributed
amplification are compared for three possible
modulation formats for various powers and
distances
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Outlines

• Transmission system
• Distributed Raman Amplification (DRA)
• Backward versus forward pumping
• Gain and Noise figure of DRA
• Discrete versus distributed amplifiers
• total launched power of 3.4 mW
• total launched power of 6.8 mW
• Backward pumped DRA
• Tolerance to dispersion slope
• Tolerance to PMD
• Conclusion

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Transmission system
TSi
TSn
TS2
TS1
AWG
AWG
OR
OR
15 km DCF
75 km SSMF
15 km DCF
15 km DCF
75 km SSMF
75 km SSMF
Flattened amplifier
OBPF
CW1
depolarizer
depolarizer
CW6
Transmission Span ni (TSi) DRA - backward multi
pumping
Transmission Span ni (TSi) Discrete flattened
amplifier
Transmission Span ni (TSi) DRA - forward
multi pumping

• 40 channels _at_40 Gbit/s (C band)
• 100 GHz channel spacing

• Up to 5 TS
• NRZ, 60 RZ, CS-RZ

• 6 Raman pumps
• PMD0.15ps/km0.5

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Power evolution in DRA
Performances of DRA limited by Raman amplified
spontaneous emission (ASE), Rayleigh scattering
of ASE and double Rayleigh backscattering (DBRS)
of the signal which leads to multipath
interference
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Power evolution with backward pumps
Highest gain achieved in the second half of the
fiber ? higher noise
Signal to DRBS ratiogt42 dB for a 18.5 dB on-off
gain
OSNR25 dB
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Power evolution with forward pumps
Highest gain achieved in the first half of the
fiber where the signal power are the highest
maximum near the first quarter noise ? lower
nonlinear tolerance
OSNR33 dB
Signal to DRBS ratiogt42 dB for a 18.5 dB on-off
gain
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Gain and Noise Figure in DRA
To make suitable comparisons between discrete and
distributed amplifiers, the Raman gain has to be
considered as lumped at the end of the
transmission distance the total fiber loss is
removed We define the gain and the noise figure
of the distributed Raman amplifier with respect
to the signal at a reference unpumped fiber
PASE amplified simultaneous emission power
measured over the bandwidth Bm
Comparisons are made for both backward and
forward configurations to achieve more than 18 dB
flattened gain over 33 nm with less than 0.8 dB
peak ripple
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Gain and Noise Figure in backward DRA
18.2 dB flat gain achieved over 33 nm with a peak
ripple of 0.65 dB for total average input
launched power of 3.4 mW.
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Gain and Noise Figure in forward DRA
18.5 dB flat gain achieved over 33 nm with a peak
ripple of 0.8 dB for total average input launched
power of 3.4 mW.
NF is better than in the backward case because of
the higher output OSNR
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Discrete versus Distributed amplifiers (1/3)
Backward DRA
Ideal Discrete amplifier with frequency
independent gain (18.2 dB) and NF (4 dB) 3
modulation formats NRZ, RZ, CS-RZ with 128
length PRBS _at_ 40 Gbit/s 2 total average launched
power into the fiber 3.4 and 6.8 mW
Up to 5 TS, BER gt10-12 for all formats When
power increases, RZ and CS-RZ have better results
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Discrete versus Distributed amplifiers (2/3)
Forward DRA
Good performances for low launched power, CS-RZ
has the best results because of this
configuration is higher sensitive to nonlinear
effects For higher power, the high nonlinear
regime makes NRZ and RZ performances drop after
respectively 150 and 225 km, CS-RZ still good
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Discrete versus Distributed amplifiers (3/3)
Ideal discrete amplifier
For low launched power, not possible to exceed
225 km with all formats Higher launched power
leads to higher OSNR, good performances for NRZ
up to 300 km, up to 375 km for RZ and CS-RZ
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Backward pumped DRA Tolerance to dispersion
slope
NRZ more robust as expected, CS-RZ more robust
than RZ when dispersion slope is over estimated
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Backward pumped DRA Tolerance to PMD
NRZ more sensitive than RZ and CS-RZ to PMD For
a given distance RZ better than CS-RZ but for a
given PMD value Cs-RZ reaches longer distances
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Conclusion

• Comparison between DRA and discrete ideal
  amplifier have been performed with NRZ, RZ and
  CS-RZ modulation formats
• Benefit of using backward pumped distributed
  Raman amplification in term of OSNR improvement.
• Backward DRA allows to reach error free distances
  with low input power at distances where the most
  ideal discrete amplifier fails
• Typical NRZ distance limitation _at_ 40 Gbit/s can
  be increased
• In the backward DRA case, there is a balance
  between the good tolerances of NRZ for dispersion
  slope and robustness of RZ and CS-RZ to PMD