A method for bidirectional optical communication comprising the steps of:—at a first optical line terminal, directly modulating a laser source to generate a downstream optical signal which has an optical power spectrum comprising two peaks having a frequency separation and a non zero power difference at generation;—propagating said downstream optical signal at a distance along an optical line comprising at least a first optical fiber propagating said downstream optical signal to a second optical line terminal;—at the second optical line terminal: power splitting said downstream optical signal to generate a first and a second power portion of said downstream optical signal, spatially separated; passive filtering said first power portion of said downstream optical signal so as to increase in absolute value a respective power difference of said two peaks, so as to obtain a filtered optical signal which is thereafter detected; and amplitude modulating the second power portion of the downstream optical signal so as to obtain an upstream optical signal having a second amplitude modulation;—propagating back along said optical line the upstream optical signal to the first optical line terminal;—at said first optical line terminal, detecting said upstream optical signal; wherein the method further comprises the step of passive filtering said downstream optical signal and/or said second power portion of the downstream optical signal and/or said upstream optical signal, so as to lower, in absolute value, a respective non zero power difference of said two peaks.