Method for controlling signal gain of a Raman amplifier

1. A method for controlling a signal gain of a pumped Raman amplifier, comprising:

controlling a pump power of a pump signal of said Raman amplifier in response to at least one monitored optical feedback signal reflected back from a transmission line fiber connected to said Raman amplifier,

wherein said monitored optical feedback signal comprises:

at least one optical pilot signal transmitted on an optical supervisory channel and

an optical data signal transmitted on an optical signal channel.

2. The method according to claim 1 ,

wherein the pump power of said optical pump signal is further controlled in response to at least one monitored optical feed-forward signal launched into said transmission line fiber.

3. The method according to claim 1 ,

wherein said at least one monitored optical signal is tapped by means of an optical splitter and converted into a feedback control signal and a feed-forward control signal applied to a pump source unit generating said optical pump signal with the controlled pump power launched into said transmission line fiber connected to said Raman amplifier.

4. The method according to claim 3 ,

wherein the tapped monitored optical signal is converted by a photodetector into an electrical current which is transformed by means of a transimpedance amplifier into a control voltage indicating the signal power of the respective monitored optical signal.

5. The method according to claim 4 ,

wherein a control voltage corresponding to a ratio between the signal power of the monitored optical feedback signal and the signal power of the monitored optical feed-forward signal is supplied to at least one PID control circuit which compares said control voltage with a set voltage read from a look-up table in response to a desired Raman gain set by a user to generate a feedback control signal which controls said pump source unit generating said optical pump signal.

6. The method according to claim 1 ,

wherein said optical supervisory channel comprises a wavelength band between a pump wavelength band of said optical pump signal and a data signal wavelength band of said optical data signal.

7. A pumped Raman amplifier, comprising:

a gain control unit adapted to control a pump power of an optical pump signal in response to at least one monitored optical feedback signal reflected back from a transmission line fiber connected to said pumped Raman amplifier,

wherein said monitored optical feedback signal comprises:

at least one optical pilot signal transmitted on an optical supervisory channel, and

an optical data signal transmitted on an optical signal channel.

8. The pumped Raman amplifier according to claim 7 ,

wherein said gain control unit is further adapted to control said pump power of said optical pump signal in response to at least one monitored optical feed-forward signal launched into said transmission line fiber connected to said pumped Raman amplifier.

9. The pumped Raman amplifier according to claim 7 ,

wherein said gain control unit comprises a PID control circuit which compares a control voltage indicating a ratio between the signal power of the monitored optical feedback signal and the signal power of the monitored optical feed-forward signal with a set voltage read from a look-up table in response to a desired Raman gain set by a user to generate a feedback control signal which controls a pump source unit of said Raman amplifier generating the optical pump signal with the controlled pump power.

10. The pumped Raman amplifier according to claim 9 ,

wherein said pumped Raman amplifier further comprises:

a first monitoring unit adapted to monitor at least one optical pilot signal transmitted in an optical supervisory channel;

a second monitoring unit adapted to monitor an optical data signal transmitted on an optical data channel; and

a third monitoring unit adapted to monitor an optical pump signal generated by said pump source unit being controlled by said gain control unit.

11. The pumped Raman amplifier according to claim 10 ,

wherein each monitoring unit is connected to

an optical splitter adapted to tap the respective monitored optical signal and comprises;

at least one photodetector adapted to convert the tapped optical signal into an electrical current and

at least one transimpedance amplifier adapted to transform said electrical current into a control voltage indicating a signal power of the monitored optical signal.

12. The pumped Raman amplifier according to claim 11 ,

wherein said gain control unit comprises feedback gain adjustment means to adjust the feedback control signal provided by said PID control circuit and feed-forward gain adjustment means to adjust a feed-forward control signal provided by a monitoring unit of said pumped Raman amplifier.

13. The pumped Raman amplifier according to claim 12 ,

wherein said gain control unit further comprises at least one signal adder adapted to add the adjusted feedback control signal and the adjusted feed-forward control signal to generate a signal supplied to a driver amplifier of said pump source unit, wherein said driver amplifier is adapted to amplify the signal and to supply the amplified signal to a laser diode of said pump source unit.

14. A gain control unit for a pumped Raman amplifier,

wherein said gain control unit is adapted to control a pump power of an optical pump signal in response to at least one monitored optical feedback signal reflected back from a transmission line fiber connected to said pumped Raman amplifier,

wherein said monitored optical feedback signal comprises:

at least one optical pilot signal transmitted on an optical supervisory channel, and

an optical data signal transmitted on an optical signal channel.

15. The gain control unit according to claim 14 ,

wherein said gain control unit is further adapted to control said pump power of said optical pump signal in response to at least one monitored optical feed-forward signal launched into said transmission line fiber connected to said pumped Raman amplifier.