Light signal transmission system and light signal transmission method

A method for maintaining a desired light signal amplification level between a first terminal and a second terminal, the method comprising:

• transmitting a light signal from the first terminal to the second terminal through a first optical fiber and transmitting the light signal from the second terminal to the first terminal through a second optical fiber, the first and second optical fibers having optical amplification fibers;
• detecting amplification levels of light signals received by the first and the second terminals;
• and
• controlling an excitation level of an excitation light supplied to the optical amplification fibers of the first and second optical fibers in accordance with a difference in the detected amplification levels of the light signals received by the first and second terminals.

A method for transmitting light signals between a first terminal and a second terminal, the method comprising:

• transmitting a light signal from the first terminal to the second terminal through a first optical fiber and transmitting the light signal from the second terminal to the first terminal through a second optical fiber, the first and second optical fibers having optical amplification fibers;
• detecting levels of the light signals received by the first and second terminals;
• and
• determining a section on the first and second optical fibers at which an additional optical fiber was previously inserted in accordance with a difference in the detected levels.

A light signal transmission system for maintaining a desired light signal amplification level between a first terminal and a second terminal, comprising:

• a first optical fiber transmitting the light signal from the first terminal to the second terminal and a second optical fiber transmitting the light signal from the second terminal to the first terminal, the first optical fiber having a first amplification fiber and the second optical fiber having a second amplification fiber;
• a first excitation light source supplying excitation light to the first optical amplification fiber through the first optical fiber from the second terminal;
• a second excitation light source supplying excitation light to the second optical amplification fiber through the second optical fiber from the first terminal;
• and
• a controller controlling an excitation level of the excitation light from at least one of the first and second excitation light sources in accordance with a difference between a level of the light signal received by the first terminal and a level of the light signal received by the second terminal.