Steigerung der Übertragungskapazität optisch verstärkter faseroptischer Übertragungssysteme durch Modenmultiplexbetrieb
Zusammenfassung der Projektergebnisse
Space Division Multiplexing (SDM) was investigated as a very promising approach to increase fiber capacity. The goal of this project was to benefit from the knowledge at both participating institutions to develop a deep understanding of the signal propagation effects in multi-mode transmission fibers and multi-mode Erbium Doped Fiber Amplifiers. Frequent meetings between all participating researchers helped to share the knowledge and to profit from it for the research activities. We discovered that splice-induced Mode-Dependent Loss (MDL) can severely impair the transmission capacity. Strong mode mixing can reduce MDL. Furthermore, we discovered that intermodal nonlinear effects can occur between different fiber modes. The effect of intermodal nonlinear interaction can have the same magnitude as intramodal nonlinear effects. We showed that the maximum transmission capacity of a graded-index 10 mode multi-mode fiber is larger than the capacity of 10 single-mode fiber systems when the SMF and the MMF have equal power density in the fiber core. Furthermore we discovered that the capacity of a 55 mode fiber exceeds the capacity of 55 standard single-mode fiber systems. We demonstrated that small variations of the group-velocity difference between the two LP-modes of a few-mode fiber leads to a strong fluctuation of the system performance. Finally, we showed that DMD management that has been introduced to reduce the complexity of the required MIMO receivers, increases the intermodal nonlinear signal distortion. Regarding amplifiers suitable for SDM operation, it has been shown that erbium doped fiber amplifiers (EDFAs) with multi mode active fibers are potentially more energy efficient than amplifiers with multi core active fibers due to denser mode packing. Since mode-dependent gain (MDG) can have a significant impact on system performance, investigations of EDFAs have been carried out to minimize MDG. It has been shown that gain equalization over the full C-band can be realized by using different pump modes. Furthermore, it was possible to operate the amplifier with different mode and wavelength channel counts, which is important in flexible capacity upgrade scenarios. Pump modes with rotationally symmetric intensity distributions help to avoid angular dependences of signal mode launch conditions. Also, if gain values at a given wavelength are equalized properly for all signal modes, a single gain flattening filter suffices to flatten the gain spectrum for all modes. Beating effects between modes can be observed which result from different propagation constants. Simulation results have shown that beating effects between pump modes have a significant impact on amplifier performance. Experimental investigations have been carried out to demonstrate that beating effects between signal modes should be considered, too, as they can result in different gain values of modulated and unmodulated signals.
Projektbezogene Publikationen (Auswahl)
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“Analytical Description of Cross-Modal Nonlinear Interaction in Mode Multiplexed Multimode Fibers,” IEEE Photonics Technology Letters, vol. 24, no. 21, pp. 1929–1932, September 2012
G. Rademacher, S. Warm, and K. Petermann
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“Impact of Mode Beating Effects in Optical Multi-Mode Amplifiers for Space Division Multiplexing”, IEEE Photonics Technology Letters, Vol. 25, no. 24, pp. 2482 – 2485, November 2013
S. Akhtari, P. M. Krummrich
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“Influence of Discrete Mode Coupling on the Nonlinear Interaction in Mode-Multiplexed Systems,” IEEE Photonics Technology Letters, vol. 25, no. 13, pp. 1203–1206, May 2013
G. Rademacher, S. Warm and K. Petermann
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“Multi mode optical amplifiers with flexible wavelength and spatial channel count“, Optical Fiber Communication Conference (OFC), paper JTh2A.21, March 2013
S. Akhtari, P. M. Krummrich
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“Splice loss requirements in multi-mode fiber mode-divisionmultiplex transmission links,” Optics Express, vol. 21, no. 1, pp. 519–532, January 2013
S. Warm and K. Petermann
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“Intermodal Nonlinear Performance Fluctuation due to WDM Channel Granularity in MDM Systems,” IEEE Summer Topicals, pp. 194-195, July 2014
G. Rademacher, S. Warm and K. Petermann
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“Selection of energy optimized pump concepts for multi core and multi mode erbium doped fiber amplifiers”, Optics Express, vol. 22, no. 24, December 2014
P. M. Krummrich, S. Akhtari
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“Experimental Analysis of the Impact of Beating between Signal Modes on Few-Mode Erbium Doped Fiber Amplifier Performance”, Optical Fiber Communication Conference (OFC), paper Tu3C.4, March 2015
S. Akhtari, M. Finkenbusch, R. Winfield, P.M. Krummrich
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“Nonlinear Interaction in Differential Mode Delay Managed Mode-Division Multiplexed Transmission Systems,” Optics Express, vol. 23, no. 1, pp. 55-60, January 2015
G. Rademacher, S. Warm and K. Petermann
