Towards ultra-high capacity space division multiplexed transmission

• Applicant: Professor Dr.-Ing. Peter Krummrich, since 12/2017
• Subject Area: Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
• Term: from 2016 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 289276170

• Final Report Year: 2019

Final Report Abstract

Fundamental capacity limits for mode-division multiplexed optical transmission systems were investigated in this project. Special attention was paid to scaling these systems to high numbers of signal modes and to investigate their upgradability. Existing knowledge of both participating universities was combined to develop a deeper understanding of mode-division multiplexed transmission fibers and erbium-doped fiber amplifiers. Quarterly meetings with all project participants took place in order to share knowledge and present results of each group’s research. We have shown that LP- and vector mode representations yield the same nonlinear coupling coefficients. Therefore, both representations are valid approaches for describing nonlinear effects in multi mode fibers. Furthermore, we developed a multi GPU algorithm for the simulation of nonlinear signal propagation in multi mode fibers with a large number of propagating modes and an acceptable processing time. With this algorithm we have shown numerically that signal degradations due to nonlinear effects in multi mode fibers with more than 100 propagating modes can be weaker than in single mode fibers. We have shown experimentally that losses due to mode coupling in fiber connectors and in bent fibers are mode group dependent and increase with the mode group order. We have shown that the MDG has minima along the EDF for multimode pumped gradedindex fibers and only partial modal load, which can utilized for gain equalization by tweaking the fiber length. Furthermore, the MDG at the fiber output can be decreasing with an increasing number of signal modes, depending on the refractive index profile and fiber length. These effects have to be considered when designing future MDM-EDFA. Furthermore, methods for MDG reduction scaling up to more than 100 modes were developed. We have shown that the gains of all signal modes in a 55 mode fiber and in a 120 signal mode fiber can be equalized in a two-stage EDFA setup using novel pump power optimization techniques. Optimization of the erbium doping profiles was investigated as an approach for MDG reduction. We have shown that for step-index fibers with 50 μm core diameter, the optimal erbium doping profile is strongly oscillating in the radial direction. For graded-index fibers, a single highly doped ring in the outer core area is required. Thus, we show that gain equalization with optimized erbium doping profiles is possible for more than 50 modes in theory, but the obtained doping profiles may be difficult to manufacture. Systems with scalable mode counts for capacity upgrade scenarios were investigated in terms of MDG reduction and the impact of nonlinear effects. We have shown that nonlinear effects are scaling less than proportional with the number of signal modes. The MDG of MDM-EDFA can be minimized for all upgrade steps in a typical OM4 fiber and across the whole C-band for up to 120 modes, demonstrating the feasibility of capacity upgrades. For very high power levels, the transmission fiber can be destroyed due to fiber fuse or selffocusing. We deduce that these effects are not limiting the capacity of MDM systems, because critical power levels for self-focusing are occurring far above the powers for practical mode counts and the rise in temperature required for the fiber fuse effect can be avoided by practical measures.

Publications

• "A GPU-Accelerated Fourth-Order Runge–Kutta in the Interaction Picture Method for the Simulation of Nonlinear Signal Propagation in Multimode Fibers," in J. Lightwave Technol., vol. 35, no. 17, pp. 3622-3628, 1 ( 2017)
  M. Brehler, M. Schirwon, D. Göddeke and P. M. Krummrich
  
• "Impact of WDM channel count on nonlinear effects in MDM transmission systems," in proc. OFC 2017, Los Angeles, paper Th2A.63
  M. Brehler and P. M. Krummrich
  
• "Investigation of LP- and Vector-Modes for the Analysis of Space-Division Multiplexed Systems in the Nonlinear Regime," in J. Lightwave Technol., vol. 35, no. 22, pp. 4859-4864, (2017)
  F. Schmidt and K. Petermann
  
• "Multimode EDFA Designs with Reduced MDG by Considering Spatially Dependent Saturation Effects,", in proc. OFC 2018, San Diego, paper W2A.5
  S. Jeurink and P. M. Krummrich
  
• "Multimode EDFA With Scalable Mode Selective Gain Control at 1480-nm Pump Wavelength," in IEEE Photon. Technol. Lett., vol. 30, no. 9, pp. 849- 852, 1 (2018)
  S. Jeurink and P. M. Krummrich
  
• "Nonlinear impairment scaling with the number of mode groups in mode-multiplexed transmission over a 50 µm multimode fiber," Opt. Express vol. 26, pp. 16393-16401 (2018)
  M. Brehler and P. M. Krummrich
  
• "Numerical Estimation of Nonlinear Impairments in a 62.5 μm MMF for MDM Transmission", in proc. OFC 2018, San Diego, paper W2A.57
  M. Brehler and P. M. Krummrich
  
• "Optimization of the Erbium Doping Profile in Erbium-Doped Fiber Amplifiers for Mode-Division Multiplexing," Photonic Networks; 19th ITG-Symposium, Leipzig, (2018)
  S. Jeurink and P. M. Krummrich
  
• "Experimental Analysis of Inter Mode Group Coupling at Connectors in Graded Index Multimode Fibers," Photonic Networks; 20th ITG- Symposium, Leipzig, Germany, (2019)
  C. M. Spenner, S. Jeurink and P. M. Krummrich
  
• "Impact of MDM-EDFA Saturation Effects on Mode Scaling for Capacity Increases,", in proc. OFC 2019, San Diego, paper Th1B.3
  S. Jeurink and P. M. Krummrich