Mode-Multiplexed Transmission over a 209-km DGD-Compensated Hybrid Few-Mode Fiber Span

We transmitted 5 wavelength channels and 6 spatialand polarization modes over a 209-km long hybrid few-mode fiber span. The fiber supports 6 spatial and polarization modes and consisted of a first section of large effective area depressed-cladding few-mode fiber followed by a graded-index few-mode fiber. The differential group delay was compensated by using fibers spools with opposite differential group delay of opposite sign. Low-loss 3-spot mode couplers are used to couple to the few-mode fiber, and backward pumped distributed Raman amplification to overcome the fiber loss. The 40-Gbit/s QPSK signals with an aggregate line-rate of 1.2 Tbit/s were recovered by coherent multiple-input-multiple-output off-line digital signal processing. The impulse response at various span lengths was compared and analyzed in detail.