We experimentally demonstrate a degenerate mode-division multiplexing transmission system with single-sideband Nyquist pulse-shaped pulse amplitude modulation-4 and direct detection techniques. Hilbert superposition cancellation (HSC) processing is applied to cancel the first-order cross talk at the receiver side. A least mean square Volterra-based multiple-input, multiple-output (MIMO) nonlinear equalizer (NLE) is used to compensate the second-order distortion. Experimental results show that compared with the MIMO linear equalizer without HSC processing, the MIMO NLE with HSC processing can help improve the bit error rate performance by almost 1 order of magnitude at the received optical power of -10 dBm. (C) 2020 Optical Society of America
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