Abstract
Limited-size receiver (Rx) apertures and transmitter- Rx (Tx-Rx) misalignments could induce power loss and. modal crosstalk in a mode-multiplexed free-space link. We experimentally demonstrate the mitigation of these impairments in a 400 G bids four-data-channel free-space optical link. To mitigate the above degradations, our approach of singular-value-decomposition-based (SVD-based) beam orthogonalization includes (1) measuring the transmission matrix H for the link given a limited-size aperture or misalignment; (2) performing SVD on the transmission matrix to find the U, Sigma, and V complex matrices; (3) transmitting each data channel on a beam that is a combination of Laguerre-Gaussian modes with complex weights according to the V matrix; and (4) applying the U matrix to the channel demultiplexer at the Rx. Compared with the case of transmitting each channel on a beam using a single mode, our experimental results when transmitting multi-mode beams show that (a) with a limited-size aperture, the power loss and crosstalk could be reduced by similar to 8 and similar to 23 dB, respectively; and (b) with misalignment, the power loss and crosstalk could be reduced by similar to 15 and , similar to 40 dB, respectively. (C) 2020 Optical Society of America