Bidirectional optical amplifying apparatus and optical gain controlling method in a bidirectional WDM optical communication network

In a bidirectional WDM optical communication network, a bidirectional optical amplifying apparatus for amplifying a bidirectional optical input signal of a WDM channel, input from the bidirectional WDM optical communication network in forward and backward directions, to a predetermined level according to an optical output of a pump laser, and outputting an amplified bidirectional optical output signal, the bidirectional optical amplifying apparatus comprising:

• a bidirectional optical amplifier for amplifying a forward WDM optical input signal and a backward WDM optical input signal, and outputting an amplified forward WDM optical output signal and an amplified backward WDM optical output signal, respectively;
• an optical signal measurement means for measuring a total input intensity of the bidirectional optical input signal to the bidirectional optical amplifying apparatus by adding the forward WDM optical input signal and the backward WDM optical input signal, and for measuring a total output intensity of the bidirectional optical output signal from the bidirectional optical amplifying apparatus by adding the forward WDM optical output signal and the backward WDM optical output signal;
• and
• a control means for determining a variation of the WDM channel due to a branching or coupling of the WDM channel by calculating an optical gain from the total input intensity and the total output intensity, controlling a level of the bidirectional optical output signal according to the determination, and thereby uniformly maintaining a transmission gain of the bidirectional WDM optical communication network.

In a bidirectional WDM optical communication network, a method of controlling an optical gain of a bidirectional WDM optical amplifying apparatus amplifying a bidirectional WDM optical signal of a WDM channel to a predetermined level according to an optical output of a pump laser and outputting an amplified bidirectional WDM optical signal, the method comprising:

• dividing, in a constant ratio, forward WDM optical input signal and backward WDM optical input signal, and dividing, in a constant ratio, forward WDM optical output signal and backward WDM optical output signal in the bidirectional WDM optical amplifying apparatus and branching a portion of the bidirectional WDM optical signal from the optical communication network;
• converting the branched forward WDM optical input signal, the branched forward WDM optical output signal, the branched reverse WDM optical input signal, and the branched reverse WDM optical output signal to an electrical signal respectively;
• detecting a forward WDM optical input signal and a backward WDM optical input signal, and detecting a forward WDM optical output signal and a backward WDM optical output signal;
• calculating a total input intensity and a %total output intensity of the bidirectional WDM optical signal by adding the detected forward WDM optical input signal to the detected backward WDM optical input signal, and by adding the detected forward WDM optical output signal to the detected backward WDM optical output signal respectively;
• and
• compensating a gain error of the bidirectional WDM optical amplifying apparatus caused by a variation in the WDM channel, using the detected forward WDM optical input signal, the detected backward WDM optical input signal, the detected forward WDM optical output signal and the detected backward WDM optical output signal.