We employ commercial mode-selective photonic lanterns to implement mode multiplexing and demultiplexing for high-capacity free-space optical communications. Moreover, we design a time-division-multiplexed frame structure to efficiently emulate multiple independent transmitters with channelized precoding using only one transmitter. To maximize the throughput of the system, we optimize the modes selected for carrying data, and apply adaptive loading to different channels. By leveraging mode- and polarization-division multiplexing, the free-space optical data link comprising multiple independent channels provides an aggregate net data rate of 1.1 Tbit/s and net spectral efficiency of 28.35 bit/s/Hz. Different from many previous demonstrations based on delayed or partially delayed copies of identical data streams, to the best of our knowledge, ours is a record-high net data rate and net spectral efficiency achieved by a single-wavelength mode-division multiplexed free-space optical communication system with fully independent channels. Moreover, all key devices used in this work, including optical transponder, multiplexer, and demultiplexer are commercially available.
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Funding: EPSRC EP/T009047/1, EP/S003436/1, EP/S016171/1 and H2020 Marie Sklodowska-Curie Actions (713694)