This application claims foreign priority to French Application No. 2306988, filed Jun. 30, 2023, the entire contents of which are incorporated by reference herein in its entirety and for all purposes.
The disclosed technology relates to the field of optical data transmission, and more particularly that of the interconnection between a multi-core optical fiber and at least one single-core optical fiber.
Telecommunications networks require large transmission capacities. Thus, multi-core optical fibers may be preferred to single-core optical fibers, because they allow simultaneous transmission of several optical signals in a more compact manner. Interconnection solutions between multi-core fibers and single-core fibers are therefore used to transfer optical signals from one to the other and the other way around.
Thus, there are numerous interconnection methods. For example, the article “Compact Multi-core Fiber Fan-in/out Using GRIN Lens and Microlens Array”, Arao H. et al., 2014, OECC/ACOFT, hereinafter referenced “Arao”, proposes an interconnection method between a multi-core optical fiber and a single-core optical fiber array. Thus, in the Arao article, a discrete microlens array is used after a gradient-index lens and a glass spacer, in order to redirect the optical beams from the multi-core fiber, to the mono-core optical fiber array. However, the use of a glass spacer in order to increase the spacing of the beams, is not a very compact solution. Furthermore, the use of microlenses involves problems of alignment, lack of compactness, and therefore difficulties implementing the system.
Consequently, it is necessary to provide a compact and easy-to-implement solution, making it possible in particular to facilitate the alignment of the different elements of the system.
The disclosed technology addresses this need by providing a coupling system between a multi-core optical fiber and a set of at least one single-core optical fiber, each single-core fiber of said set being coupled with a separate core of the multi-core fiber, said coupling system comprising:
Thus, such a coupling system makes it possible to facilitate the alignment of the different elements. In particular, the use of gradient-index fiber sections having a similar diameter to the diameter of the multi/single-core fibers allows definitive attachment by welding of the gradient-index fibers to the ends of the multi/single-core fibers. The alignment of the elements of such a system is therefore easier than with a microlens array as described in other approaches.
Furthermore, such a coupling system is compact because it does not require the use of a glass spacer, or of a microlens array. Indeed, the gradient-index fiber sections make it possible to gain in compactness by acting both as lens/collimator, enabling precise control of the angle and the diameter of each of the beams in order to guide them correctly from one optical fiber to the other.
According to a particular feature of the disclosed technology, the radial offset of each single-core fiber is defined by a distance h, the distance h being defined as follows:
Thus, the distribution of the single-core fibers, and therefore the distance between them is optimized in order to obtain a compact coupling system. Furthermore, the distance h must be greater than a threshold value selected according to the diameter of the single-core fibers.
According to a particular feature of the disclosed technology, the length l1 of the first gradient-index fiber section of said multi-core fiber is inversely proportional to its quadratic coefficient g1; the length l2 of the gradient-index lens is inversely proportional to its quadratic coefficient g2; and the length l3 of the gradient-index fiber section of said at least one single-core fiber, is inversely proportional to its quadratic coefficient g3.
Thus, the length of the gradient-index fiber sections is adapted in order to correctly transmit the optical beams from one optical fiber to another. These gradient-index fiber sections have a similar role to that of a lens/collimator, and make it possible to direct and control the beams to guide them correctly from one optical fiber to another.
According to an embodiment of the disclosed technology, the cores of the multi-core optical fiber and the set of at least one single-core optical fiber are of single-mode type.
Thus, the coupling system may be used in the context of signal transmission over long distances. Indeed, single-mode optical fibers make it possible to limit noise and losses, and are therefore preferably used over long distances.
According to another embodiment, the cores of the multi-core optical fiber and the set of at least one single-core optical fiber are of multi-mode type, and transmit spatially multiplexed signals.
Thus, the coupling system may be used in the context of simultaneous transmission of several optical signals, often over shorter distances than for single-mode fibers. Indeed, multi-mode optical fibers transmit spatially multiplexed signals composed of a plurality of signals, reflected along different angles to form a plurality of modes (modal multiplexing). The transmitted data speed is therefore increased.
According to another embodiment, the cores of the multi-core optical fiber and the set of at least one single-core optical fiber support WDM (Wavelength Division Multiplexing) type transmissions, and therefore transmit wavelength multiplexed signals.
Thus, the coupling system may be used in the context of simultaneous transmission of several optical signals, often over shorter distances than for single-mode fibers. Indeed, like multi-mode type fibers, WDM transmissions make it possible to increase the data transmission speed on an optical fiber, compared to a single-mode optical fiber only comprising a single-mode optical fiber only comprising a single signal, because wavelength multiplexed signals are composed of a plurality of signals each having a separate wavelength.
Alternatively, the coupling system comprises at least two different types of single-core fibers and multi-core fiber cores from the single-mode type, multi-mode type and type supporting WDM transmission, i.e. a compatible coupling for all of the wavelengths from 1260 nm to 1675 nm.
Thus, the coupling system may use single-core fibers and multi-core fibers of different types. For example, a multi-core fiber may include a single-mode type code and a multi-mode type core, each of the cores being respectively associated with a single-mode fiber and a multi-mode fiber within the coupling system.
According to a particular embodiment, said first and second microlensed ends are coupled directly at the input and output of said gradient-index lens.
Thus, the coupling system is simple and compact, with easier implementation, in particular such a system makes it possible to facilitate the alignment of the different elements composing it.
According to another particular embodiment, at least one of said first and second microlensed ends is coupled at the input and output of said gradient-index lens via an optical component belonging to the group comprising:
Thus, the system may have additional elements, making it possible to obtain a more elaborate system with additional optical functions, the system remaining compact and easy to implement.
According to an alternative of the disclosed technology, the end of the multi-core fiber and the first corresponding microlensed end are comprised in an independent ferrule; each end of single-core fiber of said set and the second corresponding microlensed end are comprised in an independent ferrule; and the gradient-index lens is independent.
According to another alternative of the disclosed technology, the end of the multi-core fiber, the first corresponding microlensed end and the gradient-index lens are comprised in a same ferrule, on one hand; and each single-core fiber end of said set and the second corresponding microlensed end are comprised in an independent ferrule, on the other.
According to another alternative of the disclosed technology, the end of the multi-core fiber and the first corresponding micro-lensed end are comprised in a first independent ferrule, on one hand; and the set of at least one single-core fiber end, each second corresponding microlensed end, and the gradient-index lens are comprised in a second ferrule, on the other.
Thus, different coupling modes may be used for the implementation of the coupling system. Different element blocks may thus be interconnected via independent ferrules, these ferrules forming separate element blocks (independent blocks) and allowing removable mechanical assembly between these different blocks. The term “independent” specifies the separate nature of the different element blocks, as well as the removable nature of any connection between these blocks.
The disclosed technology also relates to a method for coupling a multi-code optical fiber and a set of at least one single-core optical fiber, said method comprising:
Thus, such a coupling method allows a simple assembly of the system where the alignment of the different elements is facilitated. In particular, the use of gradient-index fiber sections having a similar diameter to the diameter of the multi/single-core fibers allows definitive attachment by welding. The system thus obtained and compact and easy to implement.
Other aims, features and advantages of the technique will appear upon reading the following description, given as a merely illustrative and non-limiting example, and which refers to the appended figures, wherein:
The disclosed technology relates to a compact and easy-to-implement coupling technique, between a multi-core optical fiber and at least one single-core optical fiber.
More particularly, as illustrated by
The multi-core and single-core fibers used according to the technique of the disclosed technology may be multi-mode and/or single-mode type and/or capable of supporting WDM type transmission. In the case of single-mode fibers, optical beam propagation within multi-core and single-core fibers may be performed according to an axial mode (zero angle of incidence at the fiber core input).
According to a first embodiment, the coupling system may be used to transmit optical beams from at least one single-core optical fiber to the cores of a multi-core optical fiber.
According to a second embodiment, the coupling system may be used to transmit optical beams from the cores of a multi-core optical fiber to at least one single-core optical fiber. This second embodiment is used to support the description hereinafter, it being understood that the technique according to the disclosed technology is not limited thereto.
Thus, the coupling system according to the disclosed technology uses a multi-core optical fiber comprising n cores, n being a natural integer greater than or equal to 2, on one hand; and m single-core optical fibers, m being a natural integer greater than or equal to 1, and less than or equal to n, on the other. Thus, with reference to
According to a particularly advantageous embodiment, a single-core fiber corresponds to each core of the multi-core fiber, i.e. n=m.
On one hand, the coupling system according to the disclosed technology therefore uses a multi-core optical fiber. This multi-core optical fiber comprises at least two cores. As mentioned above, the cores of the multi-core fiber may be single-mode and/or multi-mode and/or capable of supporting WDM type transmission.
As illustrated by
The axis O0 corresponding to the center of the multi-core optical fiber defines the main optical axis of the system. The axis OMCF-i is therefore parallel with the main axis of the system, and spaced by a distance ei relative to this main axis.
The coupling system according to the disclosed technology makes it possible to transmit the optical beam from the core CMCF-i of the multi-core optical fiber to the core of the single-core optical fiber SCF-j, it being understood that the beam may also be transmitted in the opposite direction.
According to a first example embodiment illustrated by
According to a second example embodiment illustrated by
Furthermore, the coupling system uses at least one single-core optical fiber. As mentioned above, the core of the single-core fiber may be single-mode, multi-mode or capable of supporting WDM type transmission.
As illustrated by
This distance h; makes it possible to optimize the placement of the single-core optical fibers, thus making it possible to obtain a compact coupling system. Furthermore, this distance is selected so as be greater than a threshold value predefined according to the diameter of the single-core fibers.
As illustrated by
The diameter of the gradient-index fiber section is dGRIN-MCF. This diameter dGRIN-MCF may be between 80 and 400 μm, and more particularly between 80 and 250 μm. According to an example embodiment, the diameter dGRIN-MCF is advantageously similar to the diameter of the multi-core fiber dMCF. However, a tolerance of a few hundred micrometers may be applied between dGRIN-MCF and dMCF. Indeed, it is possible to weld (assemble) fibers of different diameters with a tolerance of the order of a few 100 μm. More particularly, the following tolerance may be applied: dGRIN-MCF=dMCF±200 μm. For example, a multi-core optical fiber, having a diameter dMCF equal to 125 μm, may be coupled with a gradient-index fiber section having a diameter dGRIN-MCF equal to 250 μm. Or according to another example, illustrated by the examples of
This coupling may thus be performed for welding on account of the dimensional similarity of the diameters of these two elements.
Furthermore, the gradient-index fiber section has a central axis OGRIN-MCF. According to a particular embodiment, this axis OGRIN-MCF is aligned with the main optical axis of the system O0, with a tolerance of <±1 μm. Thus, according to a particular example embodiment illustrated by
The gradient-index fiber section (GRIN-MCF) may be composed of organic or mineral glass. The material used may be doped to obtain a specific refractive index profile. According to an example embodiment, this profile declines from the center of the section toward its circumference. Thus, the refractive index at the center of the gradient-index fiber section is n1. According to an example embodiment wherein the section is made of pure silica, this index n1 is greater than the refractive index of the silica nsi, where nsi=1.457 to 632.8 nm (for an HeNe laser). In this case, the refractive index profile may be obtained by doping silica with one or more elements making it possible to increase or decrease the refractive index of silica (Ge, P, Al, Cl, Ti, Br, B, F).
The quadratic coefficient of the gradient-index section is g1. This quadratic coefficient g1 has values typically between 0.5 and 10 mm−1.
The length of the gradient-index section is l1. This length l1 is between 100 μm and 10 mm, for example equal to 500 μm. This length l1 is defined according to the quadratic coefficient of the section g1. More particularly, this length is defined by the formula:
As illustrated by
As illustrated by
Thus, the gradient-index section makes it possible to replace the microlens assemblies of other approaches. This section has a lensing and collimation function in order to direct and control the optical beam transmitted. All of the parameters mentioned above are co-dependent and may be adapted to obtain the desired dimensions and orientations, and thus optimize the transmission of the optical beam. Furthermore, on account of the dimensions of this gradient-index fiber section, it may be welded directly to the multi-core optical fiber. Welding thus making it possible to definitively set a specific alignment of the elements. Therefore, this makes it possible to limit alignment errors and facilitate the use of the coupling system, while obtaining a compact assembly.
As illustrated by
The diameter of the gradient-index fiber section is dGRIN-SCF-j. This diameter dGRIN-SCF-j may be between 80 and 400 μm, and more particularly between 80 and 250 μm. According to an example embodiment, the diameter dGRIN-SCF-j is advantageously similar to the diameter of the single-core fiber dSCF-j. However, a tolerance of a few hundred micrometers may be applied between dGRIN-SCF-j and dSCF-j. Indeed, it is possible to weld/assemble fibers of different diameters with a tolerance of the order of a few 100 μm. More particularly, the following tolerance may be applied: dGRIN-SCF-j=dSCF-j±200 μm. For example, a multi-core optical fiber, having a diameter dSCF-j equal to 125 μm, may be coupled with a gradient-index fiber section having a diameter dGRIN-SCF-j equal to 250 μm. Or according to another example, illustrated by the examples of
This coupling may thus be performed for welding on account of the dimensional similarity of the diameters of these two elements.
Furthermore, the gradient-index fiber section has a central axis OGRIN-SCF-j. According to a particular embodiment, this axis OGRIN-SCF-j is aligned with the axis of the single-core fiber OSCF-j, with a tolerance of <±1 μm. Thus, according to a particular example embodiment illustrated by
The gradient-index fiber section (GRIN-SCFj) may be composed of organic or mineral glass. The material used may be doped to obtain a specific refractive index profile. According to an example embodiment, this profile declines from the center of the section toward its circumference. Thus, the refractive index at the center of the gradient-index fiber section is n3-j. According to an example embodiment wherein the section is made of pure silica, this index n3-j is greater than the refractive index of the silica nsi, where nsi=1.457 to 632.8 nm (for an HeNe laser). In this case, the refractive index profile may be obtained by doping silica with one or more elements making it possible to increase or decrease the refractive index of silica (Ge, P, Al, Cl, Ti, Br, B, F).
The quadratic coefficient of the gradient-index section is g3-j. This quadratic coefficient g3 has values typically between 0.5 and 10 mm−1.
The length of the gradient-index fiber section (GRIN-SCFj) is l3-j. This length l3-j is between 100 μm and 10 mm, for example equal to 500 μm. This length l3-j is defined according to the quadratic coefficient of the section g3-j. More particularly, this length is defined by the formula:
As illustrated by
According to the example illustrated by
As mentioned above relative to the single-core optical fiber, the gradient-index fiber section associated with a single-core fiber has a radial offset relative to the multi-core optical fiber and the associated gradient-index fiber section, according to a core parameter of the multi-core fiber. More particularly, this radial offset may be defined by the distance hj between the center of the single-core fiber and/or the center of the associated gradient-index section (corresponding respectively to an axis OSCF-j and/or an OGRIN-SCF-j), on one hand, and the main optical axis of the system O0, on the other.
Thus, the gradient-index section makes it possible to replace the microlens assemblies of other approaches. This section has a lensing and collimation function in order to direct and control the optical beam transmitted. All of the parameters mentioned above are co-dependent and may be adapted to obtain the desired dimensions and orientations, and thus optimize the transmission of the optical beam. Furthermore, on account of the dimensions of this gradient-index fiber section, it may be welded directly to the multi-core optical fiber. Welding thus making it possible to definitively set a specific alignment of the elements. Therefore, this makes it possible to limit alignment errors and facilitate the implementation of the coupling system, while obtaining an extremely compact assembly.
As illustrated by
These couplings may be performed by removable mechanical assembly, by bonding, or any other suitable assembly.
The diameter of the gradient-index fiber section is dGRIN-L. This diameter dGRIN-L may be between 125 μm and 4 mm, typically equal to 1 mm.
The alignment of the lens with the other elements of the system is limited by any defects present on the edges of the lens. More specifically, the gradient-index lens has a central axis OGRIN-L. According to an embodiment, this axis OGRIN-L is aligned with the main axis of the system O0, with a tolerance of 3 μm, or with a tolerance of 1 μm. Thus, according to a particular example embodiment illustrated by
The gradient-index lens (GRIN-L) may be composed of organic or mineral glass. The material used may be doped to obtain a specific refractive index profile. According to an example embodiment, this profile declines from the center of the lens toward its circumference. Thus, the refractive index at the center of the gradient-index lens is n2. According to an example embodiment wherein the lens is made of pure silica, this index n2 is greater than the refractive index of the silica nsi, where nsi=1.457 to 632.8 nm (for an HeNe laser). In this case, the refractive index profile may be obtained by doping silica with one or more elements making it possible to increase or decrease the refractive index of silica (Ge, P, Al, Cl, Ti, Br, B, F).
The quadratic coefficient of the gradient-index section is g2. This quadratic coefficient g2 has values typically between 0.5 and 10 mm−1.
The length of the gradient-index fiber section (GRIN-L) is l2. This length l2 is between 500 μm and 10 mm, typically of the order of one millimeter. This length l2 is defined according to the quadratic coefficient of the lens g2. More particularly, this length is defined by the formula:
Thus, this gradient-index lens has a lensing and collimation function in order to control the radius and angle of the optical beam transmitted. All of the parameters mentioned above are co-dependent and may be adapted to obtain the desired dimensions and orientations, and thus optimize the transmission of the optical beam.
The coupling method according to the disclosed technology may use different types of assemblies such as welding, removable mechanical assembly, bonding mechanical assembly, etc.
More particularly, the method comprises welding of the gradient-index sections (GRIN-MCF, GRIN-SCF) to the corresponding multi-core (MCF) and single-core fibers (SCF). Thus, as illustrated by
The gradient-index fiber sections having preferably a similar diameter to that of the corresponding optical fibers, welding is thus facilitated, and this makes it possible to create correctly aligned microlensed ends definitively attached to the multi-core and single-core optical fibers.
Furthermore, each of the microlensed ends thus formed may be mechanically assembled with the gradient-index lens (GRIN-L), for example by bonding, via a removable mechanical connection such as ferrules, etc. More particularly, as illustrated by
Thus, such a coupling method allows a simple assembly where the alignment of the different elements is facilitated. In particular, the use of gradient-index fiber sections having a similar diameter to the diameter of the multi/single-core fibers allows definitive attachment by welding. The system thus obtained and compact and easy to implement.
It is understood that the elements described relative to the system may be applied to the method and conversely. More particularly, the radial offset of a single-core fiber (and of the corresponding microlensed end) relative to the multi-core fiber (and to the corresponding microlensed end) is dependent on a core parameter of the multi-core fiber. More specifically, the optical axis of the assembled single-core fiber advantageously has an offset of a distance h with the main optical axis of the system, the distance h being defined according to the distance e between the main optical axis of the system and the optical axis of the core of the multi-core optical fiber, the beam of which is transmitted to the assembled single-core optical fiber. This distance h is greater than a threshold value according to the diameter of the single-core fibers, typically a minimum threshold value facilitating the coupling of the single-core fibers on the lens GRIN-L.
A first particular example of a coupling system according to the disclosed technology is represented by
According to this example, the optical beam from the core CMCF-1 is intended to be transmitted to the single-core fiber SCF1, the beam from the core CMCF-2 is intended to be transmitted to the fiber SCF2, the beam from the core CMCF-3 is intended to be transmitted to the fiber SCF3, the beam from the core CMCF-4 is intended to be transmitted to the fiber SCF4,
Furthermore, the center of each of these cores is spaced by a distance ei (e1, e4) relative to the main axis of the system (O0). More specifically,
In this example, the wavelength A selected is equal to 380 μm. The diameter of all of the optical fibers and gradient-index fiber sections is equal to 125 μm. Furthermore, each gradient-index section is perfectly aligned with the optical fiber with which it is coupled.
With respect to the multi-core fiber (MCF), the center of each of its cores is at a distance e=10 μm from the center of the multi-core fiber (corresponding to the main optical axis of the system O0). Furthermore, the diameter of the optical beam ω0 is equal to 5 μm at the output of the multi-core fiber.
With respect to the gradient-index fiber section of the multi-core fiber (GRIN-MCF), as illustrated by
Furthermore, the diameter of the beams ω1 at the output of the gradient-index fiber section is determined as follows:
And finally, as indicated by
With respect to the gradient-index lens (GRIN-L), as illustrated by
Furthermore, the diameter of the beams ω1 at the output of the gradient-index fiber section is determined as follows:
Finally, the angle of the optical beam relative to the main optical axis at the output of the lens is zero.
With respect to the gradient-index fiber sections of the single-core fibers (GRIN-SCF1, GRIN-SCF2, GRIN-SCF3, GRIN-SCF4), as illustrated by
With respect to the single-core optical fibers (SCF1, SCF2, SCF3, SCF4), they are centered on the gradient-index fiber sections with which they are coupled, and are therefore also offset by a distance h=71 μm relative to the main axis of the system O0.
In the case of a multi-core optical fiber according to this first example, the optical parameters are selected so that the distance h complies with the following inequality:
In this case: h>62.5 μm.
Finally, in the case of this first example, the gradient-index fiber sections and the gradient-index lens used have specific refractive index profiles. Thus,
A second particular example of a coupling system according to the disclosed technology is represented by
According to this example, a multi-core optical fiber may have a central core (CMCF-5), and peripheral cores (CMCF-1, CMCF-2, CMCF-3, CMCF-4).
By applying the technique described above, the beam from the central core of the multi-core fiber is not deflected, to be transmitted to a single-core optical fiber. Indeed, because e5=0, then: θ5=e×g1=0 and h=0.
Therefore, there is no offset of the single-core optical fiber to which the beam from the central core of the multi-core fiber is transmitted. The single-core optical fiber SCF5 is centered on the same main axis as the multi-core optical fiber.
More specifically,
Additional optical functions may be added to the system, they may be implemented by adding at least one of the following optical components:
These components may be disposed between two elements of the coupling system, in particular, between the gradient-index lens and one of the gradient-index fiber sections of the multi-core fiber and/or a single-core fiber.
According to an embodiment illustrated by
Thus, according to a particular embodiment, at least one of the gradient-index fiber sections of the multi-core fiber or a single-core fibers is coupled at the input and/or at the output of said gradient-index lens via an additional optical component.
Moreover, in order to add such an additional element, it is possible to adjust the choice of parameters of the gradient index, the external diameter and the length of the gradient-index fiber sections.
These additional components may be fitted in the system according to different methods, for example the so-called “V-groove” method, or a method using fibers mounted in cylindrical ferrules with an alignment sleeve. The “V-groove” method uses V-shaped grooves wherein the elements to be aligned and assembled are placed, the groove making it possible to facilitate alignment; whereas the “sleeve” method uses a sleeve wherein ferrules are inserted in order to align the fibers (or other elements) present in these ferrules. These methods may also be used for the alignment of the other elements of the coupling system.
Furthermore, adding such additional optical components makes it possible to obtain a more elaborate and complete system with additional optical functions, the system remaining compact and easy to implement.
4.2. Implementation with Ferrule-Type Connectors
The coupling system according to the disclosed technology may be implemented via the use of specific connectors such as ferrules, making it possible to form blocks of elements to be interconnected.
Thus, according to a first example,
According to a second example,
Finally,
Thus, the use of such connectors makes it possible to facilitate the implementation of the coupling system, by facilitating the alignment of the elements and their interconnection.
Number | Date | Country | Kind |
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2306988 | Jun 2023 | FR | national |