Adaptive optics Digital signal processing Eigenvalue and eigenfunctions Eigenvalues and eigenfunctions Equalizers Estimation Estimation methods MIMO systems Mean square error Mode-dependent gain Mode-dependent loss Network-based Neural networks Optical coupling Optical couplings Optical fiber communication Optical fibers Optical polarization Optical receivers Optical signal to noise ratio Optical-fiber communication Signal receivers Signal to noise ratio Signalto- noise ratio estimations Space division multiple access Space division multiplexing Transfer matrix method mode-dependent gain optical fiber communications space division multiplexing