Examples

Quasi-Single Mode Transmission

  • Description

    In this example, we will be dealing with the principle of quasi-single mode transmission [1], which combines few-mode fibers (FMF) and single-mode fibers (SMF) to reduce nonlinear effects. The considered link consists of 10 spans of 100 km, each including 50 km of FMF supporting LP01 and LP11(a,b) modes followed by 50 km of standard single-mode fiber (Corning VASCADE) and by an EDFA (4 dB noise figure) compensating for the span loss. In the FMF link, strong intragroup coupling [2] is assumed to take place in the fiber while low coupling between LP01 and LP11 groups takes place every 10 km due to non-ideal splices, presenting a random (uniformly distributed) offset.
    The distortion induced by mode coupling and differential group delay in FMF is corrected either using training sequences combined with frequency domain equalization (FDE) or using a classical time domain equalizer (TDE MIMO filter). Low baud-rate multicarrier modulation (11x2 Gbaud) is used to limit the size and complexity of the equalizer.

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  • Typical Results

    The simulation setup is shown in Figure 1. The spectrum of the received signal after 1000 km (3 dBm input power) is displayed in Figure 2 in the cases where splices present 1 um or 2 um maximum offset. We can observe the impact of multipath interference (MPI) in the spectrum as well as in the response of the TDE and FDE equalizer displayed in Figure 3 for max. 2 um offset. Equalization is performed using the DSP Library toolkit. The signal can be successfully detected after 1000 km for 0 dBm and 3 dBm input power ( Figure 4).

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  • Further Information

    Keywords: Few-mode, Kerr, nonlinearities, coupling, MIMO, TDE, data-aided, DSP, HHI

    Similar demonstrations are available in VPItransmissionMaker Optical Systems and on the VPIphotonics Forum.

    [1] F. Yaman et al., "First Quasi-Single-Mode Transmision over Transoceanic Distance using few-mode Fibers", OFC 2015, Th5C.7
    [2] Ho, Keang-Po, and Joseph M. Kahn. "Statistics of group delays in multimode fiber with strong mode coupling." Lightwave Technology, Journal of 29, no. 21 (2011): 3119-3128.

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