A method for transmitting digital data by a primary optical signal between a transmitter terminal and a receiver terminal, involves the following steps: determining a magnitude characterizing optical-wave degradation between the transmitter terminal and the receiver terminal, determining a number of transmission channels by a decreasing function of the magnitude characterizing optical-wave degradation, distributing the digital data over the transmission channels, modulating optical signals of different wavelengths using digital data distributed over the transmission channels, generating the primary optical signal by wavelength multiplexing of the optical signals, and sending a transmission configuration, including at least the number of transmission channels, from the transmitter terminal to the receiver terminal.