Coupling device for coupling hollow-core optical fibres comprising a coupling element
A device for coupling optical fibers, includes a first coupling-inhibited hollow-core optical fiber comprising a first microstructured cladding comprising a plurality of first confining tubular features distributed in a ring and encircling, at least partially, a first core so as to confine at least radiation at a wavelength λop to the first core, a second coupling-inhibited hollow-core optical fiber comprising a second microstructured cladding comprising a plurality of second confining tubular features distributed in a ring and encircling, at least partially, a second core so as to confine the light radiation to the second core, a coupling element arranged between the first and second cores, the coupling element comprising at least one coupling tubular feature comprised at least partially in the first microstructured cladding and/or the second microstructured cladding and having a wall thickness tcp called the coupling thickness and a material index ncp called the coupling index, an arrangement of the coupling element, the coupling thickness tcp and the coupling index ncp being configured so as to create a leakage channel at the wavelength λop allowing the radiation guided by the first optical fiber to be coupled to the second optical fiber and/or the radiation guided by the second optical fiber to be coupled to the first optical fiber.
1 . A device (D) for coupling optical fibers, comprising:
a first coupling-inhibited hollow-core optical fiber (FO 1 ) comprising a first microstructured cladding (SCF 1 ) comprising a plurality of first confining tubular features (MCF 1 ) having a first thickness, being a confining thickness t cf1 , said features being distributed in a ring and encircling, at least partially, a first core (C 1 ) so as to confine at least radiation at a wavelength λ op to said first core,
a second coupling-inhibited hollow-core optical fiber (FO 2 ) comprising a second microstructured cladding (SCF 2 ) comprising a plurality of second confining tubular features (MCF 2 ) having a second thickness, being a confining thickness t cf2 , said features being distributed in a ring and encircling, at least partially, a second core (C 2 ) so as to confine said light radiation to said second core,
a coupling element (SCP) arranged between the first and second cores, said coupling element comprising at least one coupling tubular feature (MCP, MCP 1 , MCP 2 , MTa) comprised at least partially in said first microstructured cladding and/or said second microstructured cladding and having a wall thickness t cp being a coupling thickness and a material index n cp being a coupling index, said coupling thickness t cp being different from said first and second confining thicknesses t cf1 , t cf2 , and
an arrangement of the coupling element, the coupling thickness t cp and the coupling index n cp being configured depending on said wavelength λ op so as to create a leakage channel at said wavelength λ op allowing the radiation guided by the first optical fiber to be coupled to the second optical fiber and/or the radiation guided by the second optical fiber to be coupled to the first optical fiber.
2 . The device as claimed in claim 1 , wherein each coupling tubular feature i∈[1, N] has a coupling thickness t cp,i and a coupling index n cp,i such that
t
cp
,
i
∈
[
100
101
m
(
i
)
2
λ
op
n
cp
,
i
2
-
1
,
100
99
m
(
1
)
2
λ
op
n
cp
,
i
2
-
1
]
,
with m∈ *.
3 . The device as claimed in claim 1 , wherein the coupling tubular features are arranged so that a distance (D 12 ) between the center of a coupling tubular feature and an adjacent coupling tubular feature is less than said wavelength λ op .
4 . The device as claimed in claim 1 , wherein said coupling element comprises at least a first (MCP 1 ) and a second (MCP 2 ) coupling tubular feature.
5 . The device as claimed in claim 4 , wherein the plurality of first and second confining tubular features partially encircle said first and second cores, respectively, said first coupling tubular feature (MCP 1 ) being arranged within the first optical fiber, facing a segment of the first core that is not encircled by the plurality of first confining tubular features, said second coupling tubular feature (MCP 2 ) being arranged within the second optical fiber facing a segment of the second core that is not encircled by the plurality of second confining tubular features, the first and second coupling tubular features being arranged facing each other.
6 . The device as claimed in claim 4 , wherein the plurality of first and second confining tubular features completely encircle the first and second cores, respectively, said first and second coupling tubular features (MCP 1 , MCP 2 ) are nested in one of said first and second confining tubular features, respectively, and the first and second coupling tubular features are arranged facing each other.
7 . The device as claimed in claim 4 , wherein said first coupling tubular feature (MCP 1 ) is arranged within the first optical fiber, facing a segment of the first core that is not encircled by the plurality of first confining tubular features, and wherein the plurality of second confining tubular features completely encircles the second core, said second coupling tubular feature (MCP 2 ) being nested in one of said second confining tubular features and arranged opposite said first coupling tubular feature.
8 . The device as claimed in claim 4 , wherein the coupling element comprises at least one additional tubular feature (MTa) forming one of the coupling tubular features, which feature is arranged between the first and second coupling tubular features.
9 . The device as claimed in claim 1 , wherein said coupling element comprises a single coupling tubular feature (MCP).
10 . The device as claimed in claim 9 , wherein the coupling tubular feature (MCP) is arranged facing a segment of the first core that is not encircled by the plurality of first confining tubular features and facing a segment of the second core that is not encircled by the plurality of first confining tubular features, said tubular feature being placed substantially between said segments.
11 . The device as claimed in claim 9 , wherein the plurality of first confining tubular features completely encircles the first core and the plurality of second confining tubular features partially encircles the second core, said coupling tubular feature (MCP) being arranged within the second optical fiber, facing a segment of the second core that is not encircled by the plurality of second confining tubular features, an azimuthal orientation of the first and second optical fibers within the device being configured to maximize an overlap of said leakage channel with a leakage profile of said first microstructured cladding.
12 . The device as claimed in claim 1 , wherein the coupling thickness or thicknesses t cp and the coupling index or indices nep are configured so that said radiation is guided from the first optical fiber to the second optical fiber by exciting a spatial mode different from a spatial mode of said radiation guided by said first optical fiber.