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

We transmitted five wavelength channels and six spatial and polarization modes over a 209-km-long hybrid few-mode fiber span. The fiber supports six spatial and polarization modes, and consists 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 is compensated by using fiber spools with differential group delay of opposite sign. Low-loss three-spot mode couplers are used to couple to the few-mode fiber, and backward pumped-distributed Raman amplification is used to overcome the fiber loss. The 40-Gb/s QPSK signals with an aggregate capacity of 1.2 Tb/s are recovered by coherent multiple-input–multiple-output off-line digital signal processing. The impulse response at various span lengths is compared and analyzed in detail.