Passive optical network having an optical exchange linked to at least one first optical component (25, 28) by at least one optical fibre (24, 26i) forming a branch of said network, said optical exchange comprising: - means (20, R) for transmitting/receiving at least one optical data signal, - means for transmitting at least one optical amplification signal, - said branch enabling bidirectional transmission of the optical data signal and of the optical amplification signal, characterized in that said branch comprises at least one passive device (3, 3bis) for the amplification of the optical data signal, the device being inserted into the branch by means of a first and a second optical circulator and comprising: - a first passive amplification medium able to amplify the optical power of the optical data signal when the latter travels through the branch in a first direction of transmission, - a second passive amplification medium able to amplify the optical power of the optical data signal when the latter travels through the branch in a second direction of transmission, the first and second passive amplification media being intended to be excited by the optical amplification signal, - means (32, 32bis) for selecting the optical power gain of the first and second amplification media as a function of optical losses respectively associated with the first and second directions of transmission of the optical data signal, - the first three-part optical circulator, the first port being linked to the branch leading to the optical exchange, the second port being linked to the selecting means (32, 32bis), the third port being linked to the second amplification medium, - the second three-part optical circulator, the first port being linked to the branch leading to the first optical component (25, 28), the second port being linked to means for wavelength filtering, the third port being linked to the first amplification medium. - means (20, R) for transmitting/receiving at least one optical data signal, - means for transmitting at least one optical amplification signal, - said branch enabling bidirectional transmission of the optical data signal and of the optical amplification signal, - a first passive amplification medium able to amplify the optical power of the optical data signal when the latter travels through the branch in a first direction of transmission, - a second passive amplification medium able to amplify the optical power of the optical data signal when the latter travels through the branch in a second direction of transmission, the first and second passive amplification media being intended to be excited by the optical amplification signal, - means (32, 32bis) for selecting the optical power gain of the first and second amplification media as a function of optical losses respectively associated with the first and second directions of transmission of the optical data signal, - the first three-part optical circulator, the first port being linked to the branch leading to the optical exchange, the second port being linked to the selecting means (32, 32bis), the third port being linked to the second amplification medium, - the second three-part optical circulator, the first port being linked to the branch leading to the first optical component (25, 28), the second port being linked to means for wavelength filtering, the third port being linked to the first amplification medium.