Underwater optical transmission system and switchable underwater repeater

Underwater optical transmission system (1) comprising:

• a first (2) and a second (3) terminal transmission station;
• at least one underwater branching unit (4) located between the said first and second terminal stations;
• a first line (5) connecting the said first station to the said branching unit, comprising at least a first optical fiber connected at one end to the said branching unit;
• a second line (6) connecting the said branching unit to the said second terminal station, comprising at least a second optical fiber connected at one end to the said branching unit;
• a third line (7) connecting the said branching unit to a third terminal station (8), comprising a first pair of optical fibers (71), connected at one end to the said branching unit;
• the said branching unit optically connecting the said first pair of optical fibers of the said third connecting line to the said first and the said second optical fiber respectively;
• characterized in that the said third connecting line comprises
• a switching module (21) comprising at least a first optical switch (22), the said first pair of optical fibers (71) being connected at a second end to two ports (I1, O1) of the said first optical switch (22);
• a second pair of optical fibers (73) connected at a first end to two other ports (I2, O2) of the said first optical switch (22);
• the said first optical switch (22) being adapted to connect the optical fibers of the said first pair (71) together in a short circuit in a first switching state, and to connect the said first pair of optical fibers (71) to the said second pair of optical fibers (73) in a second switching state.