Apparatus and method to calculate a noise figure of an optical amplifier for wavelength channels in a partial-fill scenario to account for channel loading
An apparatus comprising a processor configured to calculate a noise figure of an optical amplifier for a plurality of selected wavelength channels in a partial-fill scenario that accounts for channel loading. The noise figure is calculated using a plurality of corresponding noise figure correction values at a plurality of wavelengths based on an effective number of channels.
1. An apparatus comprising:
a processor configured to calculate a noise figure of an optical amplifier for a plurality of selected wavelength channels, wherein the noise figure is calculated using a plurality of corresponding noise figure correction values at a plurality of wavelengths, wherein the noise figure correction values are based on an effective number of channels, but are not based on power, and wherein the effective number of channels accounts for a plurality of different actual numbers of the selected wavelength channels for different channel loading scenarios; and
a memory coupled to the processor and configured to store the noise figure.
2. The apparatus of claim 1 , wherein the optical amplifier is an Erbium Doped Fiber Amplifier (EDFA) that is positioned on an optical link.
3. The apparatus of claim 1 , wherein the noise figure is calculated for the wavelengths at one or more gain levels of the optical amplifier, and wherein the noise figure is more sensitive to at least one of smaller wavelengths and lower gain levels.
4. The apparatus of claim 1 , wherein the noise figure correction values represent a plurality of differences between the noise figure that accounts for channel loading and a corresponding second noise figure that does not account for channel loading.
5. The apparatus of claim 4 , wherein a spread of the plurality of differences decreases as the effective number of channels for a same actual number of selected wavelength channels, and wherein the same actual number of selected wavelength channels may not correspond to a same set of selected wavelength channels.
6. The apparatus of claim 4 , wherein the noise figure is reduced across the wavelengths when fewer wavelength channels are selected for channel loading, and wherein the differences are also reduced across the wavelengths when fewer wavelength channels are selected for channel loading.
7. The apparatus of claim 1 , wherein the processor is further configured to calculate a gain correction of the optical amplifier for the selected wavelength channels, and wherein the gain correction is calculated for the plurality of wavelengths based on an actual number of the selected wavelength channels that correspond to a channel loading scenario.
8. The apparatus of claim 7 , wherein the gain correction, the noise figure, or both are used to design one or more components that interact with the optical amplifier in an optical communications system.
9. The apparatus of claim 7 , wherein the gain correction, the noise figure, or both are used to estimate an optical signal to noise ratio (OSNR) for an optical link, a power ripple on the optical link, a dynamic range requirement of a channel actuator for OSNR equalization, or combinations thereof.
10. A computer implemented method comprising:
calculating with a processor an effective number of channels for a plurality of wavelengths, wherein the effective number of channels accounts for a relative contribution in reducing a noise figure at different wavelengths and is calculated based on a reference wavelength, but not based on power;
calculating with the processor a noise figure correction for the wavelengths based on the effective number of channels; and
adjusting with the processor a noise figure that corresponds to all optical amplifier using the noise figure correction.
11. The computer implemented method of claim 10 , wherein the effective number of channels is calculated as follows:
n eff (λ)= c 1 (λ ref −λ)+ c 0 ,
wherein λ ref is a reference wavelength, λ is a wavelength, and c 0 and c 1 are empirical constants, wherein the noise figure is calculated as follows:
Δ
NF
dB
=
p
1
n
eff
+
p
3
exp
(
-
p
2
n
eff
)
,
and wherein p 1 , p 2 , and p 3 are fitting constants.
12. The computer implemented method of claim 10 , further comprising:
calculating a gain correction for the plurality of wavelengths; and
adjusting a gain that corresponds to the optical amplifier using the gain correction.
13. The computer implemented method of claim 12 , wherein the gain correction is calculated as follows:
Δ
G
(
λ
)
=
-
α
g
(
n
)
∑
i
=
1
n
exp
(
-
(
λ
-
λ
i
)
w
2
-
(
λ
i
-
λ
SHB
)
W
2
)
,
wherein λ is a wavelength, λ i is a selected wavelength channel, and λ SHB is a spectral hole burning wavelength, wherein α, w, and W if are empirical constants, and wherein g(n) is a function of a number of channels (n) that accounts for the fact that as the number of channels increases, a spectral hole depth decreases.
14. The computer implemented method of claim 10 , wherein the optical amplifier is an Erbium Doped Fiber Amplifier (EDFA) that is positioned on an optical link.
15. A method comprising:
monitoring an optical-to-signal noise ratio (OSNR) of an optical amplifier positioned on an optical link;
calculating a gain correction of the optical amplifier for a plurality of selected wavelength channels, wherein the gain correction is based on a selected wavelength channel, but is not based on power; and
forwarding the gain correction to a channel actuator coupled to the optical amplifier for OSNR equalization.
16. The method of claim 15 , wherein the gain correction is calculated as follows:
Δ
G
(
λ
)
=
-
α
g
(
n
)
∑
i
=
1
n
exp
(
-
(
λ
-
λ
i
)
w
2
-
(
λ
i
-
λ
SHB
)
W
2
)
,
wherein λ is a wavelength, λ i is the selected wavelength channel, and λ SHB is a spectral hole burning wavelength, wherein α, w, and W are empirical constants, and wherein a function g(n) is a function of a number of channels (n) that accounts for the fact that as the number of channels increases, a spectral hole depth decreases.
17. The method of claim 15 , further comprising:
calculating a noise figure of the optical amplifier for the selected wavelength channels in a partial-fill scenario (partial-fill noise figure) that accounts for channel loading, wherein the noise figure is calculated using a plurality of corresponding noise figure correction values at a plurality of wavelengths based on an effective number of channels; and
forwarding the calculated partial-fill noise figure to the channel actuator coupled to the optical amplifier for OSNR equalization.
18. The method of claim 17 , wherein the partial-fill noise figure is calculated for the selected wavelength channels at one or more gain levels of the optical amplifier, and wherein the partial-noise noise figure is more sensitive to at least one of smaller wavelengths and lower gain levels.
19. The method of claim 15 , wherein the optical amplifier is an Erbium Doped Fiber Amplifier EDFA), and wherein the optical link comprises at least one optical filter.
20. A method comprising:
identifying, using a processor, a full-fill scenario that implements a first number of wavelengths;
identifying, using the processor, a partial-fill scenario that implements a second number of wavelengths that is less than the first number of wavelengths;
calculating, using the processor, a noise figure correction associated with the partial-fill scenario;
calculating, using the processor, a noise figure associated with the full-fill scenario; and
adjusting, using the processor, the noise figure using the noise figure correction.
21. The method of claim of claim 20 , wherein the noise figure correction is calculated using an effective channel number that accounts for a relative contribution in reducing the noise figure at different wavelengths.
22. The method of claim 20 , further comprising:
calculating, using the processor, a gain correction associated with the partial-fill scenario;
calculating, using the processor, a gain associated with the full-fill scenario; and
adjusting, using the processor, the gain using the gain correction.