Method for controlling an erbium doped fiber amplifier (EDFA) and amplifier arrangement

1. A method for controlling an optical fiber amplifier with a first amplifier stage and a second amplifier stage, pumped by a single pump light source generating a primary pump signal, the method which comprises:

splitting the primary pump signal in a tunable splitter into a first pump signal and a second pump signal according to a splitting factor, for pumping the first amplifier stage and the second amplifier stage, respectively;

determining a primary actuating variable for controlling a second pump power of the second pump signal and therefore an output power of the amplifier;

adjusting a total pump power of the primary pump signal according to the primary actuating variable while maintaining a maximum splitting factor if the total pump power of the primary pump signal is less than an available maximum total pump power of the primary pump signal; and

adjusting the splitting factor of the tuneable splitter according to the primary actuating variable if the total pump power equals the maximum total pump power of the primary pump signal.

2. The method according to claim 1 , which comprises:

calculating secondary actuating variables according to the primary actuating variable determining the pump power of the primary pump signal and the splitting factor;

converting the secondary actuating variables into electrical control signals; and

adjusting the total pump power of the pump light source and the splitting factor of the tuneable splitter according to the electrical control signals.

3. The method according to claim 1 , which comprises:

determining the output power of the amplifier output signal;

comparing a reference value with the output power; and

generating the primary actuating variable according to a difference between the reference value and the output power.

4. The method according to claim 2 , which comprises:

comparing the maximum pump power with the current pump power; or

comparing a total pump power reference value with a calculated total pump power value; and

generating the secondary actuation variables according to a comparison result of the pump power reference value and the calculated pump power reference value.

5. The method according to claim 4 , which comprises combining a forward control component, derived from an input signal, with the primary actuating variable determining the output power of the output signal.

6. The method according to claim 1 , which comprises:

checking whether or not the total pump power is less than the maximum pump power and the splitting factor is less than the maximum splitting factor; and

if both conditions are fulfilled, increasing the total pump power and the splitting factor until a characteristic control line is obtained.

7. An optical amplifier, comprising:

a single pump light source for generating a primary pump signal;

a tuneable splitter having a variable splitting factor for dividing the primary pump signal into a first pump signal and a second pump signal;

a first amplifier stage and a second amplifier stage connected to receive the first pump signal and the second pump signal, respectively; and

a control unit for monitoring an output power of the amplifier and for controlling the primary pump signal, said control unit being configured to:

determine a primary actuating variable for controlling a second pump power of the second pump signal and therefore the output power of the amplifier;

adjust a total pump power of the primary pump signal according to the primary actuating variable while maintaining a maximum splitting factor if a total pump power of the primary pump signal is less than a maximum total pump power of the primary pump signal; and

adjust the splitting factor of said tuneable splitter according to the primary actuating variable if the total pump power equals the maximum total pump power of the primary pump signal.

8. The optical amplifier according to claim 7 , wherein said control unit is configured for:

calculating secondary actuating variables according to the primary actuating variable determining the pump power of the primary pump signal and the splitting factor;

converting the secondary actuating variables into electrical control signals; and

adjusting the total pump power of said pump light source and the splitting factor of said tuneable splitter according to the electrical control signals.

9. The optical amplifier according to claim 7 , wherein said control unit is configured for:

determining the output power of the amplifier;

comparing a reference value with the output power; and

generating the primary actuating variable according to a difference of the reference value and the output power.

10. The optical amplifier according to claim 7 , wherein said control unit is configured for:

comparing the maximum pump power with the pump power; or

comparing a total pump power reference value with a calculated total pump power value; and

generating the secondary actuation variables according to a result of the respective comparing step.

11. The optical amplifier according to claim 7 , which comprises a feed forward unit connected to the amplifier input via a first splitter and a first optical-electrical converter monitoring an input signal and generating a feed-forward component from a power variation of an input signal and feeding the feed-forward component to said control unit.

12. The optical amplifier according to claim 7 , wherein passive parts of the amplifier are integrated on a Planar Lightwave Circuit chip.