A method of superimposing N optical transmission modes for collective transmission along a multimode optical fiber, where N > 1, and the method comprises: launching N optical signals for propagation over a data transmission network comprising a multimode optical fiber, wherein each of the N propagating optical signals comprises N distinct superimposed transmission modes (M1, M2,...); optically sampling a portion of each of the N propagating optical signals at a receiving end of the data transmission network; splitting the N distinct superimposed transmission modes (M1, M2,...) of the N propagating optical signals into N optical detection channels; deriving N 2 -1 distinct measurement conditions from a transmission matrix T and a special unitary matrix group SU corresponding to the N distinct superimposed transmission modes (M1, M2,...) at the receiving end of the data transmission network; extracting N 2 -1 measurements from the optically sampled signals at the receiving end of the data transmission network, wherein the N 2 -1 measurements correspond to the N 2 -1 distinct measurement conditions; using the extracted N 2 -1 measurements to solve the matrix equation T ⋅ Λ | V 〉 = τ | V 〉 where A represents generated SU matrices, τ represents the extracted measurements, and |V> represents principal state eigenvectors of an output matrix corresponding to the N propagating optical signals at the receiving end of the data transmission network; transposing the output matrix and generating principal state launch conditions from the eigenvectors of the transposed output matrix; and controlling the phase and amplitude of the N distinct superimposed transmission modes (M1, M2,...) of each of the N propagating optical signals in accordance with the principal state launch conditions to form a principal state in each of the N propagating optical signals. launching N optical signals for propagation over a data transmission network comprising a multimode optical fiber, wherein each of the N propagating optical signals comprises N distinct superimposed transmission modes (M1, M2,...); optically sampling a portion of each of the N propagating optical signals at a receiving end of the data transmission network; splitting the N distinct superimposed transmission modes (M1, M2,...) of the N propagating optical signals into N optical detection channels; deriving N 2 -1 distinct measurement conditions from a transmission matrix T and a special unitary matrix group SU corresponding to the N distinct superimposed transmission modes (M1, M2,...) at the receiving end of the data transmission network; extracting N 2 -1 measurements from the optically sampled signals at the receiving end of the data transmission network, wherein the N 2 -1 measurements correspond to the N 2 -1 distinct measurement conditions; using the extracted N 2 -1 measurements to solve the matrix equation T ⋅ Λ | V 〉 = τ | V 〉 where A represents generated SU matrices, τ represents the extracted measurements, and |V> represents principal state eigenvectors of an output matrix corresponding to the N propagating optical signals at the receiving end of the data transmission network; transposing the output matrix and generating principal state launch conditions from the eigenvectors of the transposed output matrix; and controlling the phase and amplitude of the N distinct superimposed transmission modes (M1, M2,...) of each of the N propagating optical signals in accordance with the principal state launch conditions to form a principal state in each of the N propagating optical signals.