Reconfigurable optical amplifier, reversible optical circulator, and optical signal transmission system

An optical signal transmission system, comprising:

• a first communication terminal, having a first optical switch unit connected to a first receiver and a first transmitter;
• a second communication terminal, having a second optical switch unit connected to a second receiver and a second transmitter;
• an optical first path, connected between the first receiver and the second transmitter through the first optical switch unit and the second optical switch unit;
• an optical second path, connected between the first transmitter and the second receiver through the first optical switch unit and the second optical switch unit;
• and
• a protection path, connected between the first receiver and the second transmitter or between the second receiver and the first transmitter through the first optical switch unit and the second optical switch unit, wherein the protection path comprises at least one reconfigurable optical amplifier, and the reconfigurable optical amplifier comprises:
• a first reversible optical circulator, having four I/O ports which are respectively a first terminal, a second terminal, a third terminal, and a fourth terminal, wherein the first terminal, the second terminal, the third terminal, and the fourth terminal sequentially transmit a first optical signal in a first transmission direction of a forward circulation or a backward circulation according to a control signal, and the first terminal is isolated from the adjacent fourth terminal;
• and
• an optical gain device, connected between the first terminal and the adjacent fourth terminal, wherein the second terminal and the third terminal are respectively connected to a first node and a second node, and the first node and the second node are respectively connected to the first communication terminal and the second communication terminal either directly or through a second reversible optical circulator.