Optical fiber amplifier with improved performance
View Patent ↗A method for controlling a variation in gain in an optical amplifier stage and an optical amplifier. The optical amplifier stage includes a pumping device for providing pumping power and a control unit for determining a change in an input power of the optical amplifier. The method includes the steps of determining a change in an input power of the optical amplifier, adjusting a pumping power of the pumping device to a first power level for a predetermined period of time and adjusting the pumping power of the pumping device to a second power level. The second power level is able to drive the amplifier gain to a predetermined gain value after the change in the input power occurred.
1. A method for controlling a variation in gain of an amplifier stage of an optical amplifier, the amplifier stage receiving an input signal with non-zero input power and including a pumping device, the method comprising:
detecting a change in the input power of the amplifier stage to a changed input power;
determining from the changed input power a second power level, the second power level being able to drive the amplifier gain to a predetermined gain value after the change in the input power occurred;
adjusting a pumping power of the pumping device to a first power level for a predetermined period of time, wherein the first power level is different from the second power level; and later
adjusting the pumping power of the pumping device to the second power level.
2. The method according to claim 1 , wherein the predetermined gain value is substantially equal to a first gain value, the first gain value being a gain of the amplifier stage prior to the change in the input power.
3. The method according to claim 2 , which further comprises determining a third power level which maintains the gain of the amplifier stage at the first gain value.
4. The method according to claim 1 , wherein the change in the input power of the amplifier stage is an abrupt change.
5. The method according to claim 4 , which further comprises determining the predetermined period of time based on the following equation:
Δ
t
opt
zero
=
τ
3
ln
{
α
fit
P
pump
eff
|
before
+
1
α
fit
P
pump
eff
|
after
+
1
}
,
where τ 3 stands for a lifetime of the pump level, α fit , is a parameter including
a density of the erbium ions, P pump eff | before is given by the equation
P
pump
eff
|
before
=
P
0
ESA
ln
(
P
pump
|
before
P
0
ESA
+
1
)
,
where P pump | before is the third power level and P pump eff | after is given by the equation
P
pump
eff
|
after
=
P
0
ESA
ln
(
P
pump
|
after
P
0
ESA
+
1
)
,
where P pump | after is the second power level and P 0 ESA is the characteristic power.
6. The method according to claim 1 , wherein the change in the input power of the amplifier stage is a substantially linear change with time.
7. The method according to claim 5 , which further comprises adjusting successively and alternatively the pumping power of the pumping device to intermediate power levels and at the first power level for predetermined periods of time.
8. The method according to claim 7 , which further comprises determining the intermediate power levels P pump | (i) by using means for measuring or means for calculating, said means for measuring or means for calculating including digital signal processors.
9. The method according to claim 8 , wherein the step of determining the intermediate power levels P pump | (i) further includes calculating the effective power levels P pump eff | (i) .
10. The method according to claim 8 , wherein the step of determining the intermediate power levels P pump eff | (i) and P pump | (i) is effected with a sampling rate of approximately 1 MHz.
11. The method according to claim 7 , which further comprises determining the predetermined periods of time (Δt opt zero | (i) ) based on an iterative equation:
Δ
t
opt
zero
|
(
i
)
=
τ
3
ln
{
α
fit
P
pump
eff
|
(
i
-
1
)
+
1
α
fit
P
pump
eff
|
(
i
)
+
1
}
,
wherein τ 3 stands for a lifetime of the pump level and α fit is a parameter including a density of erbium ions.
12. The method according to claim 1 , wherein the change in the input power of the amplifier stage is based upon one or more events selected from the group consisting of:
removing a channel of a wavelength division multiplex signal transmitted,
a fiber break,
protection switching, and
component failures.
13. The method according to claim 12 , wherein the first power level is lower than the second power level.
14. The method according to claim 13 , wherein the first power level is approximately zero.
15. The method according to claim 1 , wherein the change in the input power of the stage amplifier is based on adding a channel of a wavelength division multiplex signal transmitted.
16. The method according to claim 15 , wherein the second power level is lower than the first power level.
17. The method according to claim 1 , wherein the optical amplifier is a multistage amplifier.
18. An amplifier stage of an optical amplifier for amplifying a wavelength division multiplexing signal received by the amplifier stage and having non-zero input power, the amplifier stage comprising:
a pumping device for providing pumping power;
a control unit for detecting a change in the input power of the amplifier stage;
wherein said control unit is operable, on detecting a change in the input power of the amplifier stage to a changed input power, to determine from the changed input power a second power level which is able to drive an amplifier gain to a predetermined gain value after the change in the input power occurred, and to adjust a pumping power of the pumping device to a first power level for a predetermined period of time and later to the second power level, wherein the first power level is different from the second power level.
19. The amplifier stage according to claim 18 , wherein said control unit is adjustable to operate a feed-forward control.
20. The amplifier stage according to claim 19 , wherein said control unit is adjustable to operate a feed-forward and a feedback control.