Optical fibre with reduced polarization mode dispersion and method for obtaining an optical fibre with reduced polarization mode dispersion
View Patent ↗A method for determining at least one parameter of a periodic spin function α(z) with period p, to be applied to an optical fiber along its length z during a drawing process. At least one parameter is selected so that (I) where ε 1 is about 0.05 and y 1 is the first of the three components y 1 (z), y 2 (z), y 3 (z) of a periodic function y(z) of period p such that (II) where L B is an expected beat length of said optical fiber and α(z) is the derivative of the spin function α(z) with respect to the length z. The method is effective for substantially reducing the PMD of optical fibers drawn when applying a spin function.
1. A method for determining at least one parameter of a periodic spin function α(z) with period p, to be applied to an optical fibre along its length z, comprising:
selecting said at least one parameter so that
∫
0
p
y
1
(
z
,
α
′
(
z
)
)
ⅆ
z
∫
0
p
y
1
(
z
,
α
′
(
z
)
)
ⅆ
z
≤
ɛ
1
where ε 1 is about 0.05 and y 1 is the first of the three components y 1 (z), y 2 (z), y 3 (z) of a periodic function {overscore (y)}(z) of a period p such that
ⅆ
y
1
ⅆ
z
=
2
α
′
(
z
)
y
2
ⅆ
y
2
ⅆ
z
=
-
2
π
L
B
y
3
-
2
α
′
(
z
)
y
1
ⅆ
y
3
ⅆ
z
=
2
π
L
B
y
2
where L B is an expected beat length of said optical fibre and α′(z) is the derivative of the spin function α(z) with respect to the length z.
2. A method for making an optical fibre comprising:
(a) heating a fibre preform to a drawing temperature;
(b) providing a periodic spin function α(z) with period p>2 m; and
(c) drawing said optical fibre from said preform, while simultaneously creating a relative spin between said optical fibre and said preform with said spin function;
step (b) further comprising selecting said spin function so that
|
∫
0
p
y
1
(
z
,
α
′
(
z
)
)
ⅆ
z
|
∫
0
p
|
y
1
(
z
,
α
′
(
z
)
)
|
ⅆ
z
≤
ɛ
1
where ε 1 is about 0.05 and yis the first of the three components y 1 (z), y 2 (z), y 3 (z) of a periodic function {overscore (y)}(z) of period p such that
ⅆ
y
1
ⅆ
z
=
2
α
′
(
z
)
y
2
ⅆ
y
2
ⅆ
z
=
-
2
π
L
B
y
3
-
2
α
′
(
z
)
y
1
ⅆ
y
3
ⅆ
z
=
2
π
L
B
y
2
where L B is an expected beat length of said optical fibre and α′(z) is the derivative of the spin function α(z) with respect to the length z.
3. A method as in claim 2 , wherein p is lower than 20 m.
4. A method as in claim 2 , wherein L B is greater than 0.5 m.
5. A method as in claim 4 , wherein L B is greater than 5 m.
6. A method as in claim 2 , wherein an amplitude A of said spin function is lower than 50 turns/m.
7. A method as in claim 6 , wherein A is lower than 10 turns/m.
8. A method as in claim 6 , wherein A is greater than 3 turns/m.
9. A method as in claim 6 , wherein a ratio between an amplitude A and a distance r between two inversion sites of said spin function is lower than 10 turns/m 2 .
10. A method as in claim 2 , wherein said step of drawing is performed at a drawing speed not lower than 5 m/s.
11. A method for making an optical fibre having NA≧0.2 comprising:
(a) heating a fibre preform to a drawing temperature;
(b) providing a periodic spin function α(z) with period p; and
(c) drawing said optical fibre from said preform, while simultaneously creating a relative spin between said optical fibre and said preform with said spin function;
step (b) further comprising selecting said spin function so that
|
∫
0
p
y
1
(
z
,
α
′
(
z
)
)
ⅆ
z
|
∫
0
p
|
y
1
(
z
,
α
′
(
z
)
)
|
ⅆ
z
≤
ɛ
1
where ε 1 is about 0.05 and y 1 is the first of the three components y 1 (z), y 2 (z), y 3 (z) of a periodic function {overscore (y)} (z) of period p such that
ⅆ
y
1
ⅆ
z
=
2
α
′
(
z
)
y
2
ⅆ
y
2
ⅆ
z
=
-
2
π
L
B
y
3
-
2
α
′
(
z
)
y
1
ⅆ
y
3
ⅆ
z
=
2
π
L
B
y
2
where L B is an expected beat length of said optical fibre and α′(z) is the derivative of the spin function α(z) with respect to the length z.
12. A method as in claim 11 , wherein L B is lower than 5 m.
13. A method as in claims 1 , 2 or 11 , wherein p<L B .
14. A method as in claims 1 , 2 , or 11 , wherein ε 1 is about 0.01.
15. A method as in claim 14 , wherein ε 1 is about 0.008.
16. A method as in claim 15 , wherein ε 1 is about 0.002.
17. A method as in claims 1 , 2 or 11 , wherein said spin function is a sinusoidal function.
18. A method as in claims 1 , 2 or 11 , wherein said spin function is a triangular function.
19. A method as in claims 1 , 2 or 11 , wherein said spin function is a trapezoidal function.
20. An optical fibre comprising at least a section having a beat length L B and a periodic spin function α(z) with period p>2 m impressed therein,
said spin function being such that
|
∫
0
p
y
1
(
z
,
α
′
(
z
)
)
ⅆ
z
|
∫
0
p
|
y
1
(
z
,
α
′
(
z
)
)
|
ⅆ
z
≤
ɛ
1
where ε 1 is about 0.05 and y 1 is the first of the three components y 1 (z), y 2 (z), y 3 (Z) of a periodic function {overscore (y)}(z) of period p such that
ⅆ
y
1
ⅆ
z
=
2
α
′
(
z
)
y
2
ⅆ
y
2
ⅆ
z
=
-
2
π
L
B
y
3
-
2
α
′
(
z
)
y
1
ⅆ
y
3
ⅆ
z
=
2
π
L
B
y
2
and α′(z) is the derivative of the spin function α(z) with respect to the length z.
21. An optical fibre as in claim 20 , wherein said optical fibre has a PMD coefficient, and said PMD coefficient is lower than or equal to 0.05 ps/km 1/2 .
22. An optical fibre as in claim 20 , wherein a length of said section of optical fibre is higher than or equal to 10 times the period p of the spin function.
23. An optical fibre having NA≧0.2, comprising at least a section having a beat length L B and a periodic spin function α(z) with period p impressed therein,
said spin function being such that
|
∫
0
p
y
1
(
z
,
α
′
(
z
)
)
ⅆ
z
|
∫
0
p
|
y
1
(
z
,
α
′
(
z
)
)
|
ⅆ
z
≤
ɛ
1
where ε 1 is about 0.05 and y 1 is the first of the three components y 1 (z), y 2 (z), y 3 (z) of a periodic function {overscore (y)}(z) of period p such that
ⅆ
y
1
ⅆ
z
=
2
α
′
(
z
)
y
2
ⅆ
y
2
ⅆ
z
=
-
2
π
L
B
y
3
-
2
α
′
(
z
)
y
1
ⅆ
y
3
ⅆ
z
=
2
π
L
B
y
2
and α′(z) is the derivative of the spin function α(z) with respect to the length z.
24. An optical fibre having a length tower than 1 km, comprising at least a section having a beat length L B and a periodic spin function α(z) with period p impressed therein,
said spin function being such that
|
∫
0
p
y
1
(
z
,
α
′
(
z
)
)
ⅆ
z
|
∫
0
p
|
y
1
(
z
,
α
′
(
z
)
)
|
ⅆ
z
≤
ɛ
1
where ε 1 is about 0.05 and y 1 is the first of the three components y 1 (z), y 2 (z), y 3 (z) of a periodic function {overscore (y)}(z) of period p such that
ⅆ
y
1
ⅆ
z
=
2
α
′
(
z
)
y
2
ⅆ
y
2
ⅆ
z
=
-
2
π
L
B
y
3
-
2
α
′
(
z
)
y
1
ⅆ
y
3
ⅆ
z
=
2
π
L
B
y
2
and α′(z) is the derivative of the spin function α(z) with respect to the length z.
25. An optical fibre as in claim 24 , wherein said fibre length is lower than 500 m.
26. An optical fibre as in claim 24 , wherein said fibre length is lower than 200 m.
27. An optical telecommunication system comprising:
an optical transmission line;
at least one transmitter for adding a signal to said transmission line; and
at least one receiver for receiving said signal from said transmission line;
said transmission line comprising at least one optical fibre according to any one of claims 20 to 26 .
28. An article comprising at least one optical fibre according to any one of claims 20 to 26 .