Optical transmission apparatus

1. An optical transmission apparatus for adjusting optical intensity of wavelength-multiplexed signal light so as to relay the intensity-adjusted wavelength-multiplexed signal light between optical transmission paths, comprising:

an optical attenuator whose attenuating amount is variable, for attenuating optical intensity of wavelength-multiplexed signal light received from the optical transmission path;

a first optical intensity monitoring unit for demultiplexing an optical signal having a certain wavelength from the wavelength-multiplexed signal light passed through said optical attenuator so as to monitor optical intensity of said demultiplexed optical signal;

a second optical intensity monitoring unit for branching a portion of the wavelength-multiplexed signal light passed through said optical attenuator so as to monitor optical intensity of the branched wavelength-multiplexed signal light;

an optical amplifier for amplifying a portion of the wavelength-multiplexed signal light;

a third optical intensity monitoring unit for branching a portion of the amplified wavelength-multiplexed signal light outputted from said optical amplifier so as to monitor optical intensity of said branched wavelength-multiplexed signal light; and

a control unit for controlling the attenuating amount of said optical attenuator in such a manner that the optical intensity of the optical signal monitored by said first optical intensity monitoring unit is approximated to a first target value, and for controlling a gain of said optical amplifier in such a manner that a ratio of the optical intensity of said wavelength-multiplexed signal light monitored by said second optical intensity monitoring unit to the optical intensity of said wavelength-multiplexed signal light monitored by said third optical intensity monitoring unit is approximated to a second target value;

wherein:

said control unit divides the optical intensity of said wavelength-multiplexed signal light monitored by said second optical intensity monitoring unit by a total wavelength multiplexing number so as to calculate intensity of signal light per 1 wavelength;

said control unit calculates a difference between the intensity of said signal light per 1 wavelength and a third target value; and

said control unit updates said first target value based upon said calculated difference.

2. An optical transmission apparatus as claimed in claim 1 wherein:

said control unit updates said first target value in a periodic manner.

3. An optical transmission apparatus for adjusting optical intensity of wavelength-multiplexed signal light so as to relay the intensity-adjusted wavelength-multiplexed signal light between optical transmission paths, comprising:

an optical attenuator whose attenuating amount is variable, for attenuating optical intensity of wavelength-multiplexed signal light received from the optical transmission path;

a first optical intensity monitoring unit for demultiplexing an optical signal having a certain wavelength from the wavelength-multiplexed signal light passed through said optical attenuator so as to monitor optical intensity of said demultiplexed optical signal;

a second optical intensity monitoring unit for branching a portion of the wavelength-multiplexed signal light passed through said optical attenuator so as to monitor optical intensity of the branched wavelength-multiplexed signal light;

an optical amplifier for amplifying a portion of the wavelength-multiplexed signal light;

a third optical intensity monitoring unit for branching a portion of the amplified wavelength-multiplexed signal light outputted from said optical amplifier so as to monitor optical intensity of said branched wavelength-multiplexed signal light; and

a control unit for controlling the attenuating amount of said optical attenuator in such a manner that the optical intensity of the optical signal monitored by said first optical intensity monitoring unit is approximated to a first target value, and for controlling a gain of said optical amplifier in such a manner that a ratio of the optical intensity of said wavelength-multiplexed signal light monitored by said second optical intensity monitoring unit to the optical intensity of said wavelength-multiplexed signal light monitored by said third optical intensity monitoring unit is approximated to a second target value;

wherein:

said control unit judges whether or not the optical intensity of said wavelength-multiplexed signal light monitored by said second optical intensity monitoring unit is located between a first threshold value and a second threshold value, which are provided in order to detect a change in multiplexed-wavelength numbers;

when said control unit judges that the optical intensity of said wavelength-multiplexed signal light is deviated from a range defined by said first and second threshold values, said control unit controls said optical attenuator by employing said first target value used at a time instant of said judgement made by the control unit for such a time duration until a predetermined time elapses after said judgement was made; and wherein:

when said predetermined time has elapsed, said control unit divides the optical intensity of said wavelength-multiplexed signal light monitored by said second optical intensity monitoring unit by a total wavelength multiplexing number so as to calculate intensity of signal light per 1 wavelength;

said control unit calculates a difference between the intensity of said signal light per 1 wavelength and a third target value; and

said control unit updates said first target value based upon said calculated difference.

4. An optical transmission apparatus as claimed in claim 3 wherein:

when said predetermined time has elapsed, said control unit updates both said first threshold value and said second threshold value based upon the optical intensity of said wavelength-multiplexed signal light monitored by said second optical intensity monitoring unit.

5. An optical transmission apparatus configured to adjust an optical intensity of a wavelength-multiplexed signal light so as to relay the intensity-adjusted wavelength-multiplexed signal light between optical transmission paths, the optical transmission apparatus comprising:

an optical attenuator with a variable attenuating amount, configured to attenuate an optical intensity of a wavelength-multiplexed signal light received from the optical transmission path;

a first optical intensity monitoring unit, configured to demultiplex an optical signal having a certain wavelength from the wavelength-multiplexed signal light passed through said optical attenuator so as to monitor optical intensity of said demultiplexed optical signal;

a second optical intensity monitoring unit, configured to branch a portion of the wavelength-multiplexed signal light passed through said optical attenuator so as to monitor optical intensity of the branched wavelength-multiplexed signal light;

an optical amplifier, configured to amplify a portion of the wavelength-multiplexed signal light;

a third optical intensity monitoring unit, configured to branch a portion of the amplified wavelength-multiplexed signal light outputted from said optical amplifier so as to monitor optical intensity of said branched wavelength-multiplexed signal light; and

a control unit, configured to control the attenuating amount of said optical attenuator in such a manner that the optical intensity of the optical signal monitored by said first optical intensity monitoring unit is approximated to a first target value, and configured to control a gain of said optical amplifier in such a manner that a ratio of the optical intensity of said wavelength-multiplexed signal light monitored by said second optical intensity monitoring unit to the optical intensity of said wavelength-multiplexed signal light monitored by said third optical intensity monitoring unit is approximated to a second target value;

wherein said control unit is configured to divide the optical intensity of said wavelength-multiplexed signal light monitored by said second optical intensity monitoring unit by a total wavelength multiplexing number so as to calculate intensity of signal light per 1 wavelength;

wherein said control unit is configured to calculate a difference between the intensity of said signal light per 1 wavelength and a third target value; and

wherein said control unit is configured to update said first target value based upon said calculated difference.

6. An optical transmission apparatus as claimed in claim 5 , wherein said control unit is configured to update said first target value in a periodic manner.

7. An optical transmission apparatus configured to adjust an optical intensity of a wavelength-multiplexed signal light so as to relay the intensity-adjusted wavelength-multiplexed signal light between optical transmission paths, the optical transmission apparatus comprising:

an optical attenuator with a variable attenuating amount, configured to attenuate an optical intensity of a wavelength-multiplexed signal light received from the optical transmission path;

a first optical intensity monitoring unit, configured to demultiplex an optical signal having a certain wavelength from the wavelength-multiplexed signal light passed through said optical attenuator so as to monitor optical intensity of said demultiplexed optical signal;

a second optical intensity monitoring unit, configured to branch a portion of the wavelength-multiplexed signal light passed through said optical attenuator so as to monitor optical intensity of the branched wavelength-multiplexed signal light;

an optical amplifier, configured to amplify a portion of the wavelength-multiplexed signal light;

a third optical intensity monitoring unit, configured to branch a portion of the amplified wavelength-multiplexed signal light outputted from said optical amplifier so as to monitor optical intensity of said branched wavelength-multiplexed signal light; and

a control unit, configured to control the attenuating amount of said optical attenuator in such a manner that the optical intensity of the optical signal monitored by said first optical intensity monitoring unit is approximated to a first target value, and configured to control a gain of said optical amplifier in such a manner that a ratio of the optical intensity of said wavelength-multiplexed signal light monitored by said second optical intensity monitoring unit to the optical intensity of said wavelength-multiplexed signal light monitored by said third optical intensity monitoring unit is approximated to a second target value;

wherein said control unit is configured to judge whether or not the optical intensity of said wavelength-multiplexed signal light monitored by said second optical intensity monitoring unit is located between a first threshold value and a second threshold value, the first threshold value and the second threshold value being provided in order to detect a change in multiplexed-wavelength numbers;

wherein when said control unit judges that the optical intensity of said wavelength-multiplexed signal light is deviated from a range defined by said first and second threshold values, said control unit is configured to control said optical attenuator by employing said first target value used at a time instant of said judgment made by the control unit for such a time duration until a predetermined time elapses after said judgment was made; and

wherein when said predetermined time has elapsed, said control unit is configured to divide the optical intensity of said wavelength-multiplexed signal light monitored by said second optical intensity monitoring unit, by a total wavelength multiplexing number, so as to calculate intensity of signal light per 1 wavelength, said control unit is configured to calculate a difference between the intensity of said signal light per 1 wavelength and a third target value, and said control unit is configured to said first target value based upon said calculated difference.

8. An optical transmission apparatus as claimed in claim 7 ,

wherein when said predetermined time has elapsed, said control unit is configured to update both said first threshold value and said second threshold value based upon the optical intensity of said wavelength-multiplexed signal light monitored by said second optical intensity monitoring unit.