Techniques for reducing crosstalk in multicore fibers
An optical fiber has two or more core regions disposed within a common cladding region. Each of the core regions is configured to guide a respective light transmission comprising at least one optical mode along the length of the fiber. The cores are arranged within the common cladding region according to a core configuration that substantially prevents crosstalk between modes of neighboring cores in the fiber, in a deployment of the fiber in which cross-coupling between neighboring cores is affected by perturbations arising in the deployed fiber.
1. A multicore optical fiber, comprising: two or more core regions disposed within a common cladding region, wherein each of the core regions is configured to guide a respective light transmission comprising at least one optical mode along the length of the fiber, wherein the cores are arranged within the common cladding region according to a core configuration that prevents crosstalk between modes of neighboring cores in the fiber in a deployment of the fiber in which cross-coupling between neighboring cores is affected by a perturbations arising in the deployed fiber, wherein the cross talk <|dU| 2 > accumulates per unit length L, substantially in accordance with a relationship:
〈
dU
2
〉
/
L
≈
2
π
C
λ
2
S
ff
(
Δ
β
)
;
wherein λ is the wavelength, C is the coupling coefficient, Δβ is the length-average mismatch between the propagation constants of the modes of neighboring cores, and S ƒƒ is the power spectral density of the phase mismatch induced by the length v-varying part of said perturbations.
2. The fiber of claim 1 , wherein the cores are further configured so as to result in a phase mismatch between neighboring cores that is sufficiently large so as to result in a low power spectral density.
3. The fiber of claim 2 , wherein the perturbations occurring in the fiber deployment are configured to reduce crosstalk below a threshold value.
4. The fiber of claim 1 , wherein the fiber deployment is configured such that, in a fiber having a Δβ below a selected level, the perturbations are sufficiently large so as to result in a desired crosstalk between neighboring cores.
5. The fiber of claim 4 , wherein the desired crosstalk is low.
6. The fiber of claim 4 , wherein the desired crosstalk is high along a specified length.
7. The fiber of claim 1 , wherein the cores are arranged in a configuration that minimizes the probability of phase-matching events between neighboring cores.
8. The fiber of claim 7 , wherein the fiber is deployed such that there are gradual variations in the perturbations.
9. The fiber of claim 1 , wherein the deployed fiber is configured to have perturbations resulting from at least one of:
bends in the fiber,
variations in fiber orientation around the axis of propagation,
preform-derived variations,
draw-induced variations,
stress-induced variations,
thermally-induced variations,
chemically-induced variations, and
radiation-induced variations.
10. A method for estimating average crosstalk <|dU| 2 > between cores in a multicore fiber subject to perturbations, comprising:
modeling accumulated crosstalk per unit length L as
〈
dU
2
〉
/
L
≈
2
π
C
λ
2
S
ff
(
Δ
β
)
wherein λ is the wavelength, C is the coupling coefficient, Δβ is the length-averaged mismatch between the propagation constants of the two modes, and S ff is the power spectral density of the phase mismatch induced by the length-varying part of perturbations.
11. The method of claim 10 , wherein the perturbations result from at least one of:
bends in the fiber,
variations in fiber orientation around the axis of propagation,
preform-derived variations,
draw-induced variations,
stress-induced variations,
thermally-induced variations,
chemically-induced variations, and
radiation-induced variations.