We report successful transmission of dual-LP(11) mode (LP(11a) and LP(11b)), dual polarization coherent optical orthogonal frequency-division multiplexing (CO-OFDM) signals over two-mode fibers (TMF) using all-fiber mode converters. Mode converters based on mechanically induced long-period grating with better than 20 dB extinction ratios are realized and used for interfacing single-mode fiber transmitter and receivers to the TMF. We demonstrate that by using 4×4 MIMO-OFDM processing, the random coupling of the two LP(11) spatial modes can be successfully tracked and equalized with a one-tap frequency-domain equalizer. We achieve successful transmission of 35.3 Gb/s over 26-km two-mode fiber with less than 3 dB penalty.

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In addition to the dimensions of time, frequency, complex constellation, and polarization, spatial mode can be the fifth dimension to be explored for modulation and multiplexing in optical fiber communications. In this paper, we demonstrate successful transmission of 107-Gb/s dual-mode and dual-polarization coherent optical orthogonal frequency-division multiplexing (CO-OFDM) over a 4.5-km two-mode fiber. A mechanically-induced LP01/LP11 mode converter is used as the mode selective element in a spatial-mode multiplexed system.

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