Optical transmission system with optical chromatic dispersion compensator
View Patent ↗An optical transmission system having an optical source, an optical dispersion compensation filter optically connected to the optical source, and a control system. The optical source generates a modulated optical signal having an optical spectrum and a value of dispersion robustness. The optical dispersion compensation filter has at least two cascaded optical resonators and a periodic transfer function rigidly translatable in the frequency spectrum to obtain translation in frequency of the transfer function without a substantial change in shape, and characterized by a free spectral range. The control system acts on the optical dispersion compensation filter in order to rigidly translate the transfer function along the frequency spectrum in first and second positions in the frequency spectrum. The translation of the transfer function between the first and the second positions is smaller than the free spectral range.
1. An optical transmission system comprising:
an optical source generating a modulated optical signal having an optical spectrum and a value of dispersion robustness;
an optical dispersion compensation filter optically connected to the optical source, the optical dispersion compensation filter comprising at least two cascaded optical resonators and having a periodic transfer function rigidly translatable in the frequency spectrum to obtain translation in frequency of the transfer function without a substantial change in shape, and characterized by a free spectral range;
a control system acting on the optical dispersion compensation filter for rigidly translating the transfer function along the frequency spectrum in first and second positions in the frequency spectrum, wherein:
in the first position in the frequency spectrum of the transfer function, a mean chromatic dispersion weighted over the optical spectrum of the modulated signal is greater, in absolute value, than the value of dispersion robustness and a mean slope of the chromatic dispersion weighted on the optical spectrum of the modulated signal is smaller, in absolute value, than 300000 ps/nm 2 ;
in the second position in the frequency spectrum of the transfer function, the mean chromatic dispersion weighted over the optical spectrum of the modulated signal is smaller, in absolute value, than the value of dispersion robustness and mean slope of the chromatic dispersion weighted on the optical spectrum of the modulated signal is smaller, in absolute value, than 300000 ps/nm 2 ; and
wherein translation of the transfer function between the first and second positions is smaller than the free spectral range.
2. The optical transmission system of claim 1 , wherein in the second position, the mean slope of the chromatic dispersion weighted over the optical spectrum of the modulated signal is greater than 1000 ps/nm 2 .
3. The optical transmission system of claim 1 , wherein the optical filter for compensating dispersion comprises at least two optical resonators, not all resonating at the same frequency.
4. The optical transmission system of claim 1 wherein:
the optical source generates a modulated optical signal having an optical spectrum P(ω) where ω is the optical frequency;
the transfer function of the optical compensation filter is such that its chromatic dispersion is expressed by the function β 2 (ω− ω ), ω being a tuneable parameter of the filter, such that:
the function
S
0
(
ϖ
)
=
∫
P
(
ω
)
*
β
2
(
ω
-
ϖ
)
ⅆ
ω
∫
P
(
ω
)
ⅆ
ω
varies in absolute value with an excursion greater than 1000 ps/nm as ω changes within a frequency interval Δν that is smaller than the free spectral range; and
the function
S
1
(
ϖ
)
=
∫
P
(
ω
)
*
ⅆ
β
2
(
ω
-
ϖ
)
ⅆ
ω
ⅆ
ω
∫
P
(
ω
)
ⅆ
ω
remains in absolute value below a predetermined quantity X as ω changes in the spectral region Δν.
5. The optical transmission system of claim 4 , wherein the function
S
2
=
(
ϖ
)
=
∫
P
(
ω
)
*
ⅆ
2
β
2
(
ω
-
ϖ
)
ⅆ
ω
2
ⅆ
ω
∫
P
(
ω
)
ⅆ
ω
remains in absolute value below a predetermined quantity Y as ω changes in the spectral region Δν.
6. The optical transmission system of claim 4 , wherein the quantity X is evaluated considering an ideal filter with transfer function: T(ω)=exp(i*X*ω 3 ) and defining X as the value for which the signal filtered by the filter will have a significant penalty with respect to the unfiltered case.
7. The optical transmission system of claim 5 , wherein the quantity Y is defined as the value for which an ideal filter T(ω)=exp(i*Y*ω 4 ) has a penalty lower than about 1 dB.
8. The optical transmission system of claim 1 , wherein the optical resonators are micro-rings or etalons.
9. An optical telecommunication system comprising:
an optical transmission system comprising:
an optical source generating a modulated optical signal having an optical spectrum and a value of dispersion robustness;
an optical dispersion compensation filter optically connected to the optical source, the optical dispersion compensation filter comprising at least two cascaded optical resonators and having a periodic transfer function rigidly translatable in the frequency spectrum to obtain translation in frequency of the transfer function without a substantial change in shape, and characterized by a free spectral range;
a control system acting on the optical dispersion compensation filter for rigidly translating the transfer function along the frequency spectrum in first and second positions in the frequency spectrum, wherein:
in the first position in the frequency spectrum of the transfer function, a mean chromatic dispersion weighted over the optical spectrum of the modulated signal is greater, in absolute value, than the value of dispersion robustness and a mean slope of the chromatic dispersion weighted on the optical spectrum of the modulated signal is smaller, in absolute value, than 300000 ps/nm 2 ;
in the second position in the frequency spectrum of the transfer function, the mean chromatic dispersion weighted over the optical spectrum of the modulated signal is smaller, in absolute value, than the value of dispersion robustness and the mean slope of the chromatic dispersion weighted on the optical spectrum of the modulated signal is smaller, in absolute value, than 300000 ps/nm 2 ; and
wherein translation of the transfer function between the first and second positions is smaller than the free spectral range;
a transmission system;
a receiver; and
an optical line optically connecting the transmission system to the receiver.
10. A method for transmitting a modulated optical signal having an optical spectrum and a value of dispersion robustness along an optical line characterized by a dispersion, the method comprising:
generating the modulated optical signal;
rigidly translating a periodic transfer function, characterized by a free spectral range, along a frequency spectrum in first and second positions to obtain translation in frequency of the transfer function without a substantial change in shape, wherein:
in the first position in the frequency spectrum of the transfer function, a mean chromatic dispersion weighted over the optical spectrum of the modulated signal is greater, in absolute value, than the value of dispersion robustness and a mean slope of the chromatic dispersion weighted on the optical spectrum of the modulated signal is smaller, in absolute value, than 300000 ps/nm 2 ;
in the second position in the frequency spectrum of the transfer function, the mean chromatic dispersion weighted over the optical spectrum of the modulated signal is smaller, in absolute value, than the value of dispersion robustness and the mean slope of the chromatic dispersion weighted on the optical spectrum of the modulated signal is smaller, in absolute value, than 300000 ps/nm 2 ; and
the translation of the transfer function between the first and second positions is smaller than the free spectral range;
choosing one of the first and second positions of the frequency spectrum according to the values of dispersion robustness of the modulated optical signal and of the dispersion of the optical line; and
tuning the filter in one of the first and second positions according to the choice.
11. The method of claim 10 , wherein in the second position the mean slope of the chromatic dispersion weighted over the optical spectrum of the modulated signal is greater than 1000 ps/nm 2 .
12. The method of claim 10 , wherein the optical filter for compensating dispersion comprises at least two optical resonators, not all resonating at the same frequency.
13. The method of claim 10 , wherein:
the optical source generates a modulated optical signal having an optical spectrum P(ω) where ω is the optical frequency;
the transfer function of the optical compensation filter is such that its chromatic dispersion is expressed by the function β 2 (ω− ω ), ω being a tuneable parameter of the filter, such that:
the function
S
0
(
ϖ
)
=
∫
P
(
ω
)
*
β
2
(
ω
-
ϖ
)
ⅆ
ω
∫
P
(
ω
)
ⅆ
ω
varies in absolute value with an excursion greater than 1000 ps/nm as ω changes within a frequency interval Δν that is smaller than the free spectral range; and
the function
S
1
(
ϖ
)
=
∫
P
(
ω
)
*
ⅆ
β
2
(
ω
-
ϖ
)
ⅆ
ω
ⅆ
ω
∫
P
(
ω
)
ⅆ
ω
remains in absolute value below a predetermined quantity X as ω changes in the spectral region Δν.
14. The method of claim 13 , wherein the function
S
2
(
ϖ
)
=
∫
P
(
ω
)
*
ⅆ
2
β
2
(
ω
-
ϖ
)
ⅆ
ω
2
ⅆ
ω
∫
P
(
ω
)
ⅆ
ω
remains in absolute value below a predetermined quantity Y as ω changes in the spectral region Δν.
15. The method of claim 13 , wherein the quantity X is evaluated considering an ideal filter with transfer function: T(ω)=exp(i*X*ω 3 ) and defining X as the value for which the signal filtered by the filter will have a significant penalty with respect to the unfiltered case.
16. The method of claim 13 , wherein the quantity Y is defined as the value for which an ideal filter T(ω)=exp(i*Y*ω 4 ) has a penalty lower than about 1 dB.
17. The method of claim 10 , wherein the optical resonators are micro-rings or etalons.
18. The method of claim 11 , wherein:
the optical source generates a modulated optical signal having an optical spectrum P(ω) where ω is the optical frequency;
the transfer function of the optical compensation filter is such that its chromatic dispersion is expressed by the function β 2 (ω− ω ), ω being a tuneable parameter of the filter, such that:
the function
S
0
(
ϖ
)
=
∫
P
(
ω
)
*
β
2
(
ω
-
ϖ
)
ⅆ
ω
∫
P
(
ω
)
ⅆ
ω
varies in absolute value with an excursion greater than 1000 ps/nm as ω changes within a frequency interval Δν that is smaller than the free spectral range; and
the function
S
1
(
ϖ
)
=
∫
P
(
ω
)
*
ⅆ
β
2
(
ω
-
ϖ
)
ⅆ
ω
ⅆ
ω
∫
P
(
ω
)
ⅆ
ω
remains in absolute value below a predetermined quantity X as ω changes in the spectral region Δν.
19. The optical transmission system of claim 2 wherein the optical filter for compensating dispersion comprises at least two optical resonators, not all resonating at the same frequency.
20. The optical transmission system of claim 2 wherein:
the optical source generating a modulated optical signal having an optical spectrum P(ω) where ω is the optical frequency:
the transfer function of the optical compensation filter having the chromatic dispersion expressed by the function β 2 (ω− ω ) being a tuneable parameter of the filter, such that:
the function
S
1
(
ϖ
)
=
∫
P
(
ω
)
*
ⅆ
β
2
(
ω
-
ϖ
)
ⅆ
ω
ⅆ
ω
∫
P
(
ω
)
ⅆ
ω
various in absolute value with an excursion greater than 1000 ps/nm as m changes within a frequency interval ω that is smaller than the free spectral range; and
the function
S
1
(
ϖ
)
=
∫
P
(
ω
)
*
ⅆ
β
2
(
ω
-
ϖ
)
ⅆ
ω
ⅆ
ω
∫
P
(
ω
)
ⅆ
ω
remains in absolute value below a predetermined quantity X as ω changes in the spectral region Δν.