1. Distributed Raman Amplification for Combating Optical Nonlinearities in Fibre Transmission
Mingming Tan, M. A. Z. Al-Khateeb, Md Asif Iqbal,
Paul Harper, and Andrew Ellis
Aston Institute of Photonic Technologies,
Aston University, Birmingham, B4 7ET, UK

2. Outline
Introduction
Distributed Raman Amplification Techniques for OPC-assisted Nonlinearity Compensation Systems
Evaluation of Nonlinearity Compensation Efficiency Over Different Raman Amplification Schemes
Link Symmetry and Fibre Length
Nonlinearity Compensation Over Realistic Fibre Length
Long-haul OPC-assisted Transmission Using Distributed Raman Amplification
Conclusion

3. Introduction
EDFA has been used widely in optical fibre communication systems.

4. Introduction
Distributed Raman amplification can significantly reduce the signal power variation along the fibre.

5. Quasi-lossless Transmission
Introduction
Ideally, distributed Raman amplification should counteract the fiber attenuation along the path.
Quasi-lossless Transmission
Bidirectional (Forward & Backward) Pumped Distributed Raman Amplification

6. Introduction +/-0.8dB over 80km
Quasi-lossless power profile shows the best balance of ASE noise and nonlinearity.
Is this the best for fibre nonlinearity compensation for a mid-link OPC system?
J. D.Ania-Castañón, "Quasi-lossless transmission using second-order Raman amplification and fibre Bragg gratings," Opt. Express 12, (2004)
M. Tan et al., "Evaluation of 100G DP-QPSK long-haul transmission performance using second order co-pumped Raman laser based amplification," Opt. Express 23, (2015)

7. Introduction
Optical Phase Conjugation (OPC) is one of the promising techniques to compensate the linear dispersive and the nonlinear Kerr impairments.
The nonlinear noise compensation efficiency achieved by mid-link OPC depends on
Dispersion profile symmetry
Signal power profile symmetry
Enabled by Distributed Raman Amplification
P. Rosa et al., "Signal power asymmetry optimisation for optical phase conjugation using Raman amplification," Opt. Express 23, (2015).
M. Al-Khateeb, M. Tan, A. Ellis, “Symmetry Requirements for 34dB Nonlinearity Compensation in OPC Systems,” We3H.3, ECOC 2018

8. Distributed Raman Amplification Techniques for OPC-assisted Nonlinearity Compensation Systems
How the efficiency of nonlinearity compensation is evaluated
First order Raman amplification
Dual order Raman amplification
Raman fibre laser based amplification
First order Raman amplification
Dual order Raman amplification
Raman fibre laser based amplification
M. Al-Kahteeb et al., “Analysis of the nonlinear Kerr effects in optical transmission systems that deploy optical phase conjugation,” Optics Express, Vol. 26, No. 3, 2018.

9. Distributed Raman Amplification Techniques for OPC-assisted Nonlinearity Compensation Systems
First order Raman amplification

10. Distributed Raman Amplification Techniques for OPC-assisted Nonlinearity Compensation Systems
First order Raman amplification
Without mid-link OPC, the nonlinear product power was >-10dBm
M. Al-Kahteeb et al., “Analysis of the nonlinear Kerr effects in optical transmission systems that deploy optical phase conjugation,” Optics Express, Vol. 26, No. 3, 2018.

11. Distributed Raman Amplification Techniques for OPC-assisted Nonlinearity Compensation Systems
First order Raman amplification
Without mid-link OPC, the nonlinear product power was >-10dBm
With mid-link OPC, the nonlinear product was decreased by 27dB
M. Al-Kahteeb et al., “Analysis of the nonlinear Kerr effects in optical transmission systems that deploy optical phase conjugation,” Optics Express, Vol. 26, No. 3, 2018.

12. Distributed Raman Amplification Techniques for OPC-assisted Nonlinearity Compensation Systems
Dual order Raman amplification

13. Distributed Raman Amplification Techniques for OPC-assisted Nonlinearity Compensation Systems
Dual order Raman amplification
Without OPC, the nonlinear product power was >-10dBm
M. Al-Khateeb, M. Tan, A. Ellis, “Symmetry Requirements for 34dB Nonlinearity Compensation in OPC Systems,” We3H.3, ECOC 2018.

14. Distributed Raman Amplification Techniques for OPC-assisted Nonlinearity Compensation Systems
Dual order Raman amplification
Without OPC, the nonlinear product power was >-10dBm
With OPC, the nonlinear product power was decreased by ~39dB
M. Al-Khateeb, M. Tan, A. Ellis, “Symmetry Requirements for 34dB Nonlinearity Compensation in OPC Systems,” We3H.3, ECOC 2018.

15. Distributed Raman Amplification Techniques for OPC-assisted Nonlinearity Compensation Systems
Raman fibre laser based amplification
Random distributed feedback laser formed by fibre Rayleigh backscattering and FBG
M. Tan et al., “Extended reach of 116 Gb/s DP-QPSK transmission using random DFB fiber laser based Raman amplification and bidirectional second-order pumping,” Optical Fiber Communication Conference (OFC) 2015.
M. Tan et al., “Transmission performance improvement using random DFB fiber laser based Raman amplification and bidirectional second-order pumping,” Optics Express, Vol. 24, No.3, 2016.

16. Distributed Raman Amplification Techniques for OPC-assisted Nonlinearity Compensation Systems
Raman fibre laser based amplification
Without OPC, the nonlinear product power was >-10dBm

17. Distributed Raman Amplification Techniques for OPC-assisted Nonlinearity Compensation Systems
Raman fibre laser based amplification
Without OPC, the nonlinear product power was >-10dBm
With OPC, the nonlinear product power was decreased by 20dB, due to the worst link power symmetry.

18. Distributed Raman Amplification Techniques for OPC-assisted Nonlinearity Compensation Systems
The symmetry of the link power profile is related to the fibre length.
50km RFL BW-pumping
75km RFL BW-pumping
100km RFL BW-pumping
Shorter link length doesn’t necessarily mean better symmetry.
To achieve the best symmetry, the Raman pumping configuration matters.

19. Distributed Raman Amplification Techniques for OPC-assisted Nonlinearity Compensation Systems
How can we improve the link symmetry with realistic fibre length (i.e. 80km)
80km SSMF
Signal at 1550nm
WDM
WDM
BW-pump
at 1455nm

20. Distributed Raman Amplification Techniques for OPC-assisted Nonlinearity Compensation Systems
How can we improve the link symmetry with realistic fibre length (i.e. 80km)
80km SSMF
FBG at 1455nm
Signal at 1550nm
WDM
WDM
Random DFB fibre laser
BW-pump
at 1366nm

21. Distributed Raman Amplification Techniques for OPC-assisted Nonlinearity Compensation Systems
How can we improve the link symmetry with realistic fibre length (i.e. 80km)
80km SSMF
FBG at 1455nm
Signal at 1550nm
WDM
WDM
Random DFB fibre laser
FW-pump
at 1366nm
>700mW
BW-pump
at 1366nm
M. Tan et al., “Extended reach of 116 Gb/s DP-QPSK transmission using random DFB fiber laser based Raman amplification and bidirectional second-order pumping,” Optical Fiber Communication Conference (OFC) 2015
M. Tan et al., "Transmission performance improvement using random DFB laser based Raman amplification and bidirectional second-order pumping," Opt. Express 24, (2016)

22. Distributed Raman Amplification Techniques for OPC-assisted Nonlinearity Compensation Systems
How can we improve the link symmetry with realistic fibre length (i.e. 80km)
80km SSMF
FBG at 1455nm
Signal at 1550nm
WDM
WDM
Random DFB fibre laser
FW-pump
at 1455nm
~100mW
Significant RIN Transfer
BW-pump
at 1366nm
Broadband coherent fibre laser
Broadband incoherent ASE pump
M. Tan et al., “RIN Mitigation and Transmission Performance Enhancement with Forward Broadband Pump,” IEEE Photonics Technology Letter, Vol. 30, No. 3, 2018.
M. Iqbal, M. Tan, P. Harper, “On the Mitigation of RIN Transfer and Transmission Performance Improvement in Bidirectional Distributed Raman Amplifiers,” Journal of Lightwave Technology, Vol. 36, No. 13, 2018.
M. Iqbal, M. Tan*, P. Harper, “Enhanced Transmission Performance Using Backward-Propagated Broadband ASE Pump,” IEEE Photonics Technology Letters, Vol. 30, No. 9, 2018.

23. Distributed Raman Amplification Techniques for OPC-assisted Nonlinearity Compensation Systems
How can we improve the link symmetry with realistic fibre length (i.e. 80km)
First order BW-pumping
RFL based amplification with BW-pumping
RFL based amplification with bidirectional pumping

24. Distributed Raman Amplification Techniques for OPC-assisted Nonlinearity Compensation Systems
How can we improve the link symmetry with realistic fibre length (i.e. 80km)
First order BW-pumping
RFL based amplification with BW-pumping
RFL based amplification with bidirectional pumping

25. Long-haul OPC-assisted Transmission Using Raman Fibre Laser Based Amplification Technique
I. Phillips, M. Tan, M. Stephens, M. McCarthy, E. Giacoumidis, S. Sygletos, P. Rosa, S. Fabbri, S. Le, T. Kanesan, S. Turitsyn, N. Doran, P. Harper, and A. Ellis, "Exceeding the Nonlinear-Shannon Limit using Raman Laser Based Amplification and Optical Phase Conjugation," OFC 2014, paper M3C.1.
M. Stephens, M. Tan, I. Phillips, S. Sygletos, P. Harper, N. Doran, “1.14 Tb/s DP-QPSK WDM polarization-diverse optical phase conjugation,” Optics Express, Vol. 22, No. 10, 2014.

26. Long-haul OPC-assisted Transmission Using Raman Fibre Laser Based Amplification Technique

27. Long-haul OPC-assisted Transmission Using Raman Fibre Laser Based Amplification Technique
Q factors versus signal launch powers without and with OPC
EDFA
RFL based amplification with BW-pumping
RFL based amplification with bidirectional pumping
(quasi-lossless)

28. Long-haul OPC-assisted Transmission Using Raman Fibre Laser Based Amplification Technique
Transmission performance enhancement with OPC
EDFA
RFL amplification with BW-pumping only
RFL amplification with bidirectional pumping
(quasi-lossless)
Max reach without OPC
4671km
7833km
4287km
Max reach with OPC
10059km
5112km
Improvement in reach 0%
28%
(Up to 72%)
19%
A. Ellis, M. Tan, M. Iqbal, M. Al-Khateeb, V. Gordienko, G. Saavedra, S. Fabbri, M. Stephens, M. McCarthy, A. Perentos, I. Phillips, D. Lavery, G. Liga, R. Maher, P. Harper, N. Doran, S. Turitsyn, S. Sygletos, P. Bayvel, “4 Tbit/s transmission reach enhancement using 10x400 Gbit/s super-channels and polarization insensitive dual band optical phase conjugation,” JLT, Vol.34, No.8, 2016.
M. Al-Khateeb, M. Tan, M. Iqbal, A. Ali, M. McCarthy, P. Harper, A. Ellis, “Experimental demonstration of 72% reach enhancement of 3.6Tbps optical transmission system using mid-link Optical Phase Conjugation,” accepted by Optics Express, 2018.

29. Conclusion
What would be the best link power profile for OPC-assisted transmission over realistic length of fibre?
Without OPC, it should achieve very good balance between ASE noise and nonlinear impairment (small signal power variations)
With OPC, the link power profile has to be very symmetrical.
This can be only enabled by higher order RIN-penalty-free bidirectional pumped distributed Raman amplification.

30. Acknowledgement
The work was funded by UK EPSRC programme grant PEACE (EP/L000091/1) and Photonic Phase Conjugation Systems (PHOS, EP/S003436/1)
We thank the contributions from Pawel Rosa from National Institute of Telecommunications, Warsaw, Poland.
We thank Sterlite Technologies for providing the fiber.

31. Thank you ! Mingming Tan m.tan1@aston.ac.uk
Aston Institute of Photonics Technologies, Aston University, Birmingham, UK