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 m.tan1@aston.ac.uk

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

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

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

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

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, 4372-4377 (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, 22181-22189 (2015)

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, 31772-31778 (2015). M. Al-Khateeb, M. Tan, A. Ellis, “Symmetry Requirements for 34dB Nonlinearity Compensation in OPC Systems,” We3H.3, ECOC 2018

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.

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

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.

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.

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

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.

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.

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.

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

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.

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.

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

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

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, 2215-2221 (2016)

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.

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

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

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.

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

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)

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.

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.

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.

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