1. distributed versus discrete amplification
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

2. 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

3. Transmission system 40 channels @40 Gbit/s (C band) 6 Raman pumps
TX40
TX1
TX2
RX40
RX1
RX2
TS1
TS2
TSi
TSn
AWG
AWG OR OR
75 km
SSMF
15 km
DCF
75 km
SSMF
15 km
DCF
75 km
SSMF
15 km
DCF
Flattened amplifier
OBPF
CW1
depolarizer
depolarizer
CW6
Transmission Span n°i (TSi)
DRA - backward multi pumping
Transmission Span n°i (TSi)
DRA - forward multi pumping
Transmission Span n°i (TSi)
Discrete flattened amplifier
40 Gbit/s (C band)
100 GHz channel spacing
6 Raman pumps
PMD=0.15ps/km0.5
Up to 5 TS
NRZ, 60% RZ, CS-RZ

4. 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

5. Power evolution with backward pumps10 20 30 40 50 60 70 80
SSMF length in Km
Raman Pumps
40 channel signals
(pumps on)
(pumps off)
ASE noise
DRBS noise
-70
-50
-40
-30
-20
-10
Power in dBm
-60
Highest gain achieved in the second half of the fiber  higher noise
OSNR=25 dB
Signal to DRBS ratio>42 dB for a 18.5 dB on-off gain

6. Power evolution with forward pumps10 20 30 40 50 60 70 80
SSMF length in Km
-60
-50
-40
-30
-20
-10
Power in dBm
40 channel signals
(pumps on)
Raman Pumps
(pumps off)
ASE noise
DRBS noise
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
OSNR=33 dB
Signal to DRBS ratio>42 dB for a 18.5 dB on-off gain

7. 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

8. 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.

9. 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

10. 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 40 Gbit/s
2 total average launched power into the fiber : 3.4 and 6.8 mW
Up to 5 TS, BER > for all formats
When power increases, RZ and CS-RZ have better results

11. 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

12. 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

13. Backward pumped DRA : Tolerance to dispersion slope
NRZ more robust as expected, CS-RZ more robust than RZ when dispersion slope is over estimated

14. 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

15. 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 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