Multi-core fiber and method for manufacturing the same

Abstract

A method for manufacturing a multi-core fiber with a complex shape is provided. A plurality (N) of initial optical packages are provided, each optical package having an initial cross-sectional dimension a and including a predetermined number M of optical guiding units. These N optical packages are bundled into a bundle structure, and the bundle structure is subjected to a heat-based treatment to be compressed, obtaining a new multi-core fiber including N×M cores with a cross-sectional dimension c equal to or smaller than the initial cross-sectional dimension a.

Description

Technical Field

[0001] The present disclosure relates to a multi-core optical fiber and a method for manufacturing the same. The technology of the present disclosure is particularly useful for optical computing devices such as those used in artificial neural networks.

Background Art

[0002] Multi-core fibers (MCFs) are attracting increasing attention in various applications such as high-density coupling of optical integrated circuits, spatial division multiplexing (SDM) of optical communication channels, artificial neural networks, and other in-fiber arithmetic processing / tasks.

[0003] Various configurations of neural networks that utilize the propagation and coupling of light between the cores of multi-core fibers have been developed. For example, the paper "Neural networks within multi-core optic fibers", Eyal Cohen et al., Scientific Reports, vol. 6, July 7, 2016, pages 1-14, describes the use of multi-core fibers for the hardware implementation of artificial neural networks that achieve real-time parallel processing of large datasets. According to this technology, optical signals are transmitted laterally between fiber cores by optical coupling.

[0004] Also, patent publication WO2021064727 assigned to the assignee of the present application teaches an artificial neuron network and a corresponding neuron unit based on the use of multi-core fibers.

Summary of the Invention

[0005] In recent years, in the optical communication industry, the demand for various in-fiber operations has been increasing. For this purpose, fibers with complex shapes are required. Specifically, to implement arithmetic processing within a fiber, a multi-core fiber with a large number of cores and, optionally, selective core doping are necessary.

[0006] Therefore, in the art, there is a need for a novel technique that enables the implementation of a multi-core fiber having as many cores as possible while configuring it with a fiber diameter (generally cross-sectional dimension) as small as possible.

[0007] As is well known, a multi-core fiber has a plurality of cores within a common cladding. In the following description, the terms "size" or "lateral size" may be used in relation to the cross-sectional dimension of the multi-core fiber (i.e., the cladding).

[0008] The present disclosure provides a novel method for manufacturing a multi-core fiber with a complex shape, i.e., a multi-core fiber with a large number of cores that allows for the complex pre-design and arrangement of cores with different compositions.

[0009] The multi-core fiber with a complex shape of the present disclosure is fabricated from a plurality of optical packages, each having several (relatively few, e.g., 3 to 19) optical guiding elements (waveguides). Such packages can be simple custom-made multi-core fibers with a small number of cores, standard (commercially available) multi-core fibers, bundles of polymer fibers or glass tubes, or hybrid configurations formed by polymer fibers and glass tubes.

[0010] The multi-core fiber with a complex shape fabricated by the technique of the present disclosure from such a plurality (generally at least two) of packages has a significantly increased number of cores compared to the number of optical guiding elements within the package (e.g., the number of cores increases by at least three times).

[0011] More specifically, the technology of the present disclosure utilizes a multi-core fiber with a relatively small number of cores as an initial package of a plurality of optical guiding units, and the following will be described with respect to this application example. However, the principle of the present disclosure is not limited to this specific example, and thus, the term "initial multi-core fiber" used herein should be broadly interpreted as an "initial package of a plurality of optical guiding units", including multi-core fibers with a small number of cores (single-mode fibers or multi-mode fibers), and optical packages / bundles of optical guiding units such as polymer fibers and / or glass tubes.

[0012] As described above, the use of cores doped for various applications is required, and furthermore, multi-core fibers doped with only a part of the cores (for example, using a specific pattern of doped cores and passive cores) are required. The process of doping the selected cores (i.e., processing each core or the selected cores individually) becomes more complicated in fibers with closely arranged cores. The method for manufacturing a multi-core fiber of the present disclosure is also particularly useful / advantageous for manufacturing fibers such that the controlled doping of the cores is performed only at the initial stage (i.e., applied to the initial multi-core fiber with a small number of cores) and is maintained during the manufacturing process of the resulting multi-core fiber with a large number of cores, so that at least a part of the cores is appropriately doped and different levels of doping are also performed in some cases (i.e., the desired pattern of doped cores is used).

[0013] According to a broad aspect of the present disclosure, there is provided a method for manufacturing a multi-core fiber having a complex shape, the method comprising: (i) providing a plurality (N) of initial optical packages, each optical package having an initial cross-sectional dimension a and including a plurality (M) of optical guiding units; (ii) bundling the plurality (N) of optical packages into a bundle structure; (iii) subjecting the bundled structure to a heat treatment to obtain a new multi-core fiber having a cross-sectional dimension c equal to or smaller than the initial cross-sectional dimension a and having NxM cores.

[0014] In some embodiments, the initial optical package is a bundle of polymer fibers and / or glass tubes and includes an array of M polymer fibers and / or glass tubes (constituting the optical guiding unit). In some other embodiments, the initial optical package is an initial multi-core fiber including an array of M cores (constituting the optical guiding unit). Such an initial multi-core fiber can be a single-mode fiber or a multi-mode fiber. The bundled structure of the N multi-core fibers can include single-mode multi-core fibers, multi-mode multi-core fibers, or a mixture of single-mode fibers and multi-mode fibers.

[0015] In some embodiments, the method further includes performing a process (ii) and one or more repetitions of (ii) in which a bundling process and a heat-based process applied to a new plurality (K) of multi-core fibers are continuously executed, thereby obtaining a continuous new multi-core fiber including NxMxK cores.

[0016] In some embodiments, the plurality (N) of initial multi-core fibers includes one or more multi-core fibers having doped cores (e.g., a pattern of passive cores and doped cores).

[0017] In addition, the multi-core fiber can be fused into the multimode region by more aggressive tapering, and in this case, the same interaction as that of the photonic lantern occurs. That is, by adiabatically combining a plurality of single-mode cores into one multimode core, a low-loss interface is provided between the single-mode system and the multimode system. Specifically, this enables the multimode system to be converted into a discrete number of single-mode systems with low loss, and vice versa.

[0018] In another broad aspect of the present disclosure, there is provided a multi-core fiber manufactured by the above method. Such a multi-core fiber can have at least 15 cores and a cladding size of at least 50 microns. In some embodiments, the multi-core fiber (manufactured by the above method) includes at least 30 or at least 40 cores.

[0019] The multi-core fiber of the present disclosure presents an optical unit that can be used in various applications as a component / functional block of an optical or electro-optical device such as an artificial neuron unit.

Brief Description of the Drawings

[0020] To better understand the subject matter disclosed herein and to illustrate how it may be actually implemented, embodiments will be described by way of non-limiting examples only with reference to the accompanying drawings.

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0021] Referring to FIG. 1, FIG. 10 of the method of the present disclosure for manufacturing a multi-core fiber with a complex shape is shown. This method can increase the number of cores in the multi-core fiber by at least three times compared to the number of optical guide units (e.g., cores) in the initial optical package (e.g., initial multi-core fiber) of the guide unit. The cladding size (diameter) of the fiber with a relatively large number of cores to be manufactured can be the same as or smaller than the size of a predetermined initial optical package (e.g., initial multi-core fiber) of the guide unit.

[0022] As shown in the figure, the process starts with the step of providing a plurality (N≥2) of optical packages, e.g., multi-core fibers with a small number of cores (step 12). These fibers can be commercially available or custom multi-core fibers with a relatively small number of cores (e.g., 3 to 19 cores).

[0023] Thus, generally, each such initial optical package (e.g., multi-core fiber) has a plurality (M≥3) of optical guide units (cores) within a common cladding of cross-sectional dimension / diameter a.

[0024] In some embodiments, all M cores of the multi-core fiber are so-called "passive cores", and in some other embodiments, at least a part (one or more) of the M cores of the N multi-core fibers are doped (i.e., P cores are doped (P≤M) (optional step 14). When the multi-core fiber includes passive cores and doped cores, they are arranged in a specific pattern. Generally, the N multi-core fibers can have the same or different numbers / patterns of passive cores and doped cores.

[0025] Next, the N multi-core fibers are bundled (step 16) into a bundle with a lateral dimension b (b>>a). The step of bundling the N multi-core fibers can be performed using known suitable techniques, such as capillaries or holders (e.g., ring-shaped holders), or other techniques that firmly hold the plurality of multi-core fibers together.

[0026] The multi-core fiber bundle of size b obtained in this way is then subjected to a processing technique (step 18) aimed at compressing the bundle to a significantly smaller size than b and to a size c of the multi-core fiber close to the original size a of the initial multi-core fiber. Such processing may include heating and / or tapering of the bundle. By this processing, a new multi-core fiber (MCF) of size c (compared to the bundle size b) containing NxM cores is obtained (step 20).

[0027] It should be noted that the above-described processing process may include arc heating for tapering the fiber. The process parameters to be controlled include arc power and drawing speed (e.g., about 0.05 mm / sec). Another suitable method is the burner method of heating the fiber bundle to about 1600 - 1800 °C.

[0028] If the initial multi-core fiber has a pattern formed of passive cores and doped cores, the resulting multi-core fiber has a multiplication of this pattern.

[0029] If necessary, the above process (steps 12 - 18) can be applied and repeated to a plurality of NxM core fibers of size c (constituting a new initial package). Specifically, a plurality of multi-core fibers of size c are bundled and processed (heated and drawn) again. It should be understood that for the size (cladding diameter) of the final new multi-core fiber, tapering is performed at a ratio of about 3 - 10 at each stage, and the size of the final multi-core fiber with multiple cores becomes relatively small.

[0030] It should be understood that the principle of the technology of the present disclosure is not limited to the number of fibers (packages) to be bundled nor to the number of cores (optical guiding units) of each fiber. Also, the technology of the present disclosure has no limit on the number of repetitions of the bundling stage and the processing stage. Generally, the number of repetitions depends on the size of the initial multi-core fiber to be used.

[0031] The overall process parameters are selected such that a desired final core size (diameter) of, for example, about 3 to 10 microns and a desired final cladding size (diameter) of, for example, at least 50 microns are obtained.

[0032] Considering commercially available multi-core fibers, typical dimensions are, for multi-core fibers with passive cores, a core diameter of 10 microns, a core pitch of 50 microns, and a cladding diameter of 125 microns, and for multi-core fibers with doped cores (Er / Yb doped), a core diameter of 6 microns, a core pitch of 35 microns, and a cladding diameter of 187.5 microns may be obtained.

[0033] As described above, another option is to start the process from an initial package / bundle of glass tubes (optical guide units) held by a capillary or a specially made holder.

[0034] Referring to FIGS. 2A and 2B, specific but non-limiting examples of the above-described techniques of the present disclosure are schematically shown.

[0035] FIG. 2A illustrates a process 100 for manufacturing a multi-core fiber having a complex shape. As shown in FIG. 2A, a plurality (N = 7) of initial multi-core fibers MCF (packages of optical guide units), each having M cores (M = 7) and a lateral dimension (cladding diameter) a, are bundled to form a fiber bundle structure FBS having a lateral dimension b (b >> a), with or without a capillary (step 101). Next, the bundled MCF structure FBS is processed (e.g., heated and / or tapered) to compress this structure FBS, resulting in another (new) multi-core fiber MCF' having a lateral dimension c that is significantly smaller than size b and having 7x7 (NxM) cores (step 102).

[0036] As shown in this non-limiting example, the above process is repeated to bundle a number (K) of new multi-core fibers MCF' (where K can be equal to or different from N) (in this example, seven such new multi-core fibers MCF') into a new bundle structure FBS' (step 103), which is then processed / compressed, for example via heating and tapering (step 104), to obtain a new multi-core fiber MCF'' of size d having (NxMxK) cores.

[0037] The example of Fig. 2B shows a schematic process 200 for manufacturing a complex-shaped multi-core fiber with a pattern of doped cores. The process 200 is generally similar to the previous example of Fig. 2A. However, in the embodiment of Fig. 2B, the process starts with a plurality (e.g., N=7) of initial multi-core fibers MCF with heterogeneous core composition, which have a pattern of passive cores PC (e.g., silica cores) and doped cores DC (e.g., Er / Yb doped). The initial multi-core fibers MCF each having a size a are bundled (step 101) into a fiber bundle structure FBS with a size b (b>>a), and the structure FBS is processed (e.g., heated and / or tapered) to create a new multi-core fiber MCF' with a smaller size c and an increased number of cores to 7x7 (NxM) (step 102). Optionally, the new plurality (K) of multi-core fibers MCF' are bundled (step 103) into a new bundle structure FBS' and processed (step 104) to obtain a new multi-core fiber MCF'' of size d having (NxMxK) cores. The disclosed technique allows for controlled doping of selected cores only at an early stage and is maintained during the manufacturing process of the resulting multi-core fiber MCF' (or MCF'').

Claims

1. A method for manufacturing a multi-core fiber having a complex shape, comprising: providing a plurality (N) of initial optical packages, each optical package having an initial cross-sectional dimension a and including a predetermined number M of optical guiding units; bundling the plurality (N) of optical packages into a bundle structure; performing a heat treatment on the bundle structure to obtain a new multi-core fiber having a cross-sectional dimension c equal to or smaller than the initial cross-sectional dimension a and having NxM cores.

2. The method according to claim 1, wherein the initial optical package is a bundle including the predetermined number M of glass tubes.

3. The method according to claim 1, wherein the initial optical package is a bundle including the predetermined number M of polymer fibers.

4. The method according to claim 1, wherein the initial optical package is a bundle including the predetermined number M of polymer fibers and glass tubes.

5. The method according to claim 1, wherein the initial optical package is an initial multi-core fiber having the predetermined number M of cores.

6. The method according to claim 5, wherein the multi-core fiber is a single-mode or multi-mode multi-core fiber.

7. Further, for a new plurality (K) of the new multi-core fibers, performing one or more repetitions of a process of continuously performing the bundling step and the heat-based treatment step, thereby obtaining a continuous new multi-core fiber including NxM x K cores.

8. The method according to claim 1, wherein the initial optical package has any one of a configuration of a bundle of glass tubes including the predetermined number M of glass tubes, a bundle of polymer fibers including the predetermined number M of polymer fibers, a bundle of polymer fibers and glass tubes, and an initial multi-core fiber having the predetermined number M of cores.

9. Further, for a new plurality (K) of the new multi-core fibers, performing eight or more repetitions of a process of continuously performing the bundling step and the heat-based treatment step, thereby obtaining a continuous new multi-core fiber including NxM x K cores.

10. The method according to claim 5, wherein the plurality (N) of initial multi-core fibers comprises one or more multi-core fibers including doped cores.

11. The method according to claim 5, wherein the plurality (N) of initial multi-core fibers comprises one or more multi-core fibers having a pattern of passive cores and doped cores.

12. The method according to claim 5, wherein the multi-core fiber is fused into the multi-mode region.

13. A multi-core fiber, characterized in that it is manufactured by the method according to claim 1.

14. A multi-core fiber, characterized in that it is manufactured by the method according to claim 9.

15. A multi-core fiber comprising at least 15 cores within a common cladding having a cross-sectional dimension of at least 50 microns.

16. The multi-core fiber according to claim 15, wherein the core comprises a doped core.

17. The multi-core fiber according to claim 15, wherein the core comprises a passive core and a doped core.

18. An optical device comprising at least one multi-core fiber having the configuration according to claim 15.

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