We demonstrate digital turbulence compensation using a 12-spatial mode digital coherent receiver with a multimode preamplifier that provides a 6-dB sensitivity improvement. This combination acts similarly to ideal lossless adaptive optics. Coherent superposition of 12 spatial-modes reduced median BER from 0.1 to 1×10-5 compared to traditional single-mode detection.

We show mode-multiplexed transmission over individual mode groups up to 9 groups of a 27 km long graded-index multimode fiber. We also investigate transmission distances up to 500 km using a recirculating loop arrangement for the first 6 mode groups using QPSK and 16-QAM signals.

We demonstrate mode-multiplexed 90×90 MIMO transmission over all nine mode groups of a 26.5-km graded-index multimode fiber span, achieving a record spectral efficiency of 202 bit/s/Hz.

We show mode-multiplexed transmission over the 6 th mode group of a 50-μm graded-index multimode fiber using a multi-plane light conversion device, for transmission distances up to 90 km.

We show 72×72 MIMO based transmission over a 2 km long 50μm graded-index multimode fiber with a spectral efficiency of 72 bitls/Hz.