Multi-core optical fiber with reduced bubble formation

Abstract

The present disclosure relates to an MCF (200A) that includes multiple cores (102), an outer cladding (101) or tube, a diffusion barrier (202), and a cladding (103). The diffusion barrier (202) and cladding (103) are designed to reduce unwanted dopant migration from the inner cladding to the outer cladding or tube, or to reduce unwanted dopant migration from the core to the outer cladding or tube. The doping levels of various components of the MCF can be controlled to reduce dopant migration. Reducing dopant gradients reduces dopant and gas bubble migration to the interface between the inner cladding, outer cladding or tube, and core.

Description

[Technical Field]

[0001] This application claims the benefit of priority to U.S. Provisional Patent Application No. 62 / 943,352, entitled "MULTI-CORE OPTICAL FIBER WITH REDUCED BUBBLE FORMATION," filed December 4, 2019, inventors Alireza Mirsepassi and Dean Richardson, the entirety of which is incorporated herein by reference as if fully and completely set forth herein. [Background technology]

[0002] Laser light is used in a wide variety of medical procedures to aid in surgery and treat a patient's anatomy. For example, in laser photocoagulation, a laser probe is used to ablate blood vessels in laser burn spots across the retina. Certain types of laser probes burn multiple spots at once, which can result in faster and more efficient photocoagulation. Some of these multi-spot laser probes split a single laser beam into multiple laser beams that exhibit a laser spot pattern and deliver the beams to an array of optical fibers that exhibit a corresponding fiber pattern. Typically, the fibers must be tightly packed so that the fiber pattern matches the laser spot pattern. Furthermore, the laser spot pattern must be precisely aligned with the fiber pattern.

[0003] A fiber can include an outer cladding and multiple cores, which make up a multicore optical fiber (MCF). The cores, the outer cladding, or both can be engineered to transport light. To create an MCF, holes are typically drilled in the outer cladding, and the cores are integrated within the holes. Often, dopants, such as fluorine or germanium, are added to the cores and outer cladding to create the refractive index profile required to support the light-guiding properties of the MCF. Finally, the outer cladding is stretched at high temperatures to the desired diameter and length, resulting in the MCF. Summary of the Invention [Problem to be solved by the invention]

[0004] One drawback of MCFs is that dopants can diffuse from the outer cladding to the core and vice versa, substantially altering the optical properties of the MCF components. Additionally, dopant gradients can cause dopant diffusion, and at high temperatures, gas bubbles can form during MCF fabrication toward the interface between the core and outer cladding. Gas bubbles reduce MCF yield and weaken the MCF, resulting in a brittle fiber. Gas bubbles also degrade the optical performance of MCFs. [Means for solving the problem]

[0005] According to one embodiment, the present disclosure is directed to a multi-core optical fiber including a plurality of cores including a first material, an outer cladding surrounding the cores, the outer cladding including the first material, and diffusion-reducing features that reduce migration of a first dopant between the outer cladding and another element in the MCF.

[0006] Another embodiment is directed to a multicore optical fiber including a rod comprising a first material, a rod inner cladding surrounding the rod, the rod inner cladding comprising the first material and a first dopant, a plurality of cores comprising the first material, a plurality of inner claddings surrounding the cores, the inner claddings comprising the first material and the first dopant, a first portion of each of the inner claddings interfacing with a portion of the rod inner cladding, and an outer tube comprising the first material and the first dopant, a second portion of each of the inner claddings interfacing with a portion of the outer tube.

[0007] A further embodiment is directed to a multi-core optical fiber comprising: a rod comprising a first material; a plurality of cores comprising the first material and a first dopant; a plurality of diffusion barriers surrounding the cores, the diffusion barriers comprising the first material, a first portion of each of the diffusion barriers interfacing with a portion of the rod; and an outer tube comprising the first material, a second portion of each of the diffusion barriers interfacing with a portion of the outer tube.

[0008] Various embodiments of the present disclosure may also include one or more of the following features: A concentration of the first dopant in the outer cladding is reduced compared to an MCF without the diffusion-reducing features; A dopant concentration gradient between the outer cladding and another element is reduced compared to an MCF without the diffusion-reducing features; The MCF further includes a plurality of inner claddings surrounding the core, the plurality of inner claddings comprising a first material and the first dopant; The diffusion-reducing features include a plurality of diffusion barriers surrounding the inner cladding, the diffusion barriers comprising the first material; The diffusion-reducing features include a plurality of highly doped regions of the inner cladding doped with the first dopant and a plurality of lightly doped regions of the inner cladding doped with the first dopant, wherein the dopant concentration of the lightly doped regions is less than the dopant concentration of the highly doped regions, and the lightly doped regions surround the highly doped regions. The highly doped region relative to the core has a numerical aperture (NA) of about 0.18 to about 0.28, and the lightly doped region relative to the core has a NA of about 0.08 to about 0.18. The first dopant includes fluorine (F), boron (B), or chlorine (Cl). The diffusion-reducing feature includes an outer cladding having a first dopant concentration. The concentration of the first dopant in the outer cladding is less than the concentration of the first dopant in the plurality of inner claddings. The diffusion-reducing feature includes a plurality of diffusion barriers surrounding the core, the diffusion barriers including a first material. The plurality of cores are doped with the first dopant, and the other element is the plurality of cores. The first dopant increases the refractive index of the first material. The first dopant includes germanium (Ge) or phosphorus (P). Compared to an MCF without a rod inner cladding, the concentration gradient of the first dopant between the outer tube and the rod is reduced. The gradient of the first dopant between the outer tube and the cores is reduced compared to an MCF without diffusion barriers.

[0009] The core is surrounded by various claddings and diffusion barriers that reduce and slow dopant migration and subsequent bubble formation, reducing dopant gradients in the MCF and increasing MCF yield per amount of material, resulting in MCFs with improved material and optical properties.

[0010] For a more complete understanding of the present technology, its features and advantages, reference is now made to the following description taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0011] [Figure 1A] FIG. 1A shows a perspective view of a tip portion of a multi-core optical fiber (MCF) according to an embodiment of the present disclosure. [Figure 1B] FIG. 1B illustrates a front view of the tip of the MCF of FIG. 1A in accordance with certain embodiments of the present disclosure. [Figure 1C] FIG. 1C shows a front view of a tip of an MCF with multiple inner claddings according to certain embodiments of the present disclosure. [Figure 2A] FIG. 2A shows a front cutaway view of an MCF with multiple diffusion barriers and multiple inner claddings, according to certain embodiments of the present disclosure. [Figure 2B] FIG. 2B shows a front cutaway view of an MCF with multiple inner claddings with different regions, according to certain embodiments of the present disclosure. [Figure 2C] FIG. 2C shows a front cutaway view of an MCF with multiple inner claddings and a doped outer cladding, according to certain embodiments of the present disclosure. [Figure 2D] FIG. 2D shows a front cutaway view of an MCF with multiple diffusion barriers according to certain embodiments of the present disclosure. [Figure 2E] FIG. 2E shows a front cutaway view of an MCF with a glass rod and rod inner cladding, according to certain embodiments of the present disclosure. [Figure 2F] FIG. 2F shows a front cutaway view of an MCF with glass rods according to certain embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0012] To facilitate understanding, the same reference numerals have been used, where possible, to refer to identical elements common to the figures, and it is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

[0013] In the following description, details are set forth by way of example to facilitate understanding of the disclosed subject matter. However, it should be apparent to those skilled in the art that the disclosed implementations are illustrative and do not encompass all possible implementations. Therefore, it should be understood that reference to the described examples is not intended to limit the scope of the disclosure. Any changes and further modifications to the described devices, apparatuses, and methods, and any further applications of the principles of the present disclosure, are fully contemplated as would normally occur to one skilled in the art to which the present disclosure pertains. In particular, it is fully contemplated that features, components, and / or steps described with respect to one implementation can be combined with features, components, and / or steps described with respect to other implementations of the present disclosure.

[0014] In certain embodiments, the term "about" refers to a + / - 10% variation from the nominal value. It is understood that such a variation can be included in any value provided herein.

[0015] The embodiments provided herein generally relate to MCFs with diffusion-reducing features to reduce unwanted dopant migration.

[0016] 1A-1C show various examples of MCFs. More specifically, FIGS. 1A and 1B show an MCF without an inner cladding, while FIG. 1C shows an example of an MCF that includes an inner cladding. Note that, although not shown, MCFs are typically placed within a polyvinyl chloride (PVC) tube to create an MCF cable.

[0017] 1A shows a perspective view of the tip of the MCF 100A. The MCF 100A may be cylindrical, although other shapes are also envisioned.

[0018] FIG. 1B shows a front view of the tip of the MCF 100A of FIG. 1A. As shown, the MCF 100A includes an outer cladding 101 and multiple cores 102. The multiple cores 102 may be made of any transparent material, such as fused silica or glass. In the example of FIGS. 1A and 1B, the cores 102 are doped fused silica. For example, the cores 102 may be germanium-doped fused silica. Doping the cores 102 with germanium or a similar dopant helps to increase the refractive index of the core compared to the fused silica of the outer cladding 101, thereby creating light-guiding properties within the core.

[0019] FIG. 1C shows a front view of the tip of an MCF 100B, which includes multiple inner claddings 103. As shown, the MCF 100B includes an outer cladding 101, multiple cores 102, and multiple inner claddings 103. In contrast to the MCF 100A, in the example of FIG. 1C, the cores 102 of the MCF 100B are undoped and are made of fused silica or a similar transparent material. Each of the cores 102 is surrounded by an inner cladding 103. The inner cladding 103 may include doped fused silica. In some embodiments, the inner cladding 201 is doped with a dopant, such as fluorine (F), chlorine (Cl), or boron (B), that lowers the refractive index of the inner cladding. When doped, the inner cladding 103 has a lower refractive index than the cores 102, thereby creating light-guiding properties within each core 102. The thickness of the inner cladding 103 varies from about 1 μm to about 10 μm, with a core diameter of about 50 μm to about 80 μm.

[0020] Although four cores 102 are shown in the illustrated example, the scope of the disclosure is not so limited. Rather, in other implementations, the MCFs 100A-100B may include fewer than four cores 102. In certain embodiments, the diameter of each core 102 may be between about 50 μm and about 80 μm. In certain embodiments, the centers of any two cores 102 may be between about 100 μm and about 150 μm from each other.

[0021] In certain embodiments, the MCFs 100A-100B are non-illuminating MCFs. In such embodiments, each of the cores 102 is adapted to guide light, such as laser light, while the outer cladding 101 is not configured to guide light. In certain other embodiments, the MCFs 100A-100B may instead be illumination MCFs. An illumination MCF is one in which light for general illumination, as opposed to targeted laser light for treatment, is transmitted through the MCF's outer cladding 101 to provide general illumination to the treatment site. Thus, the outer cladding 101 may be used to transmit light along it to provide general illumination, while the cores 102 are used to transmit laser light for treatment at the treatment site.

[0022] During the fabrication of the MCFs 100A-100B, in certain cases, bubbles may form in the outer cladding 101 or other portions of the MCF, such as in the core 102, in the inner cladding 103, and / or at the interface of the outer cladding 101, the core 102, and / or the inner cladding 103. Bubble formation can cause instabilities during fiber drawing, ultimately resulting in low fiber yields and reduced functionality of the MCFs 100A-100B. With respect to the MCF 100B, one reason for bubble formation is that the dopant concentrations in the outer cladding 101 and the inner cladding 103 are different, and the concentration gradient drives the dopant toward the outer cladding 101, creating bubbles. For example, if the inner cladding 103 of the MCF 100B is made of fluorine-doped silica (SiO 3 / 2When containing fluorine (F), fluorine-doped silica may spontaneously decompose into silicon dioxide (SiO2) and gaseous silicon tetrafluoride (SiF4). The silicon tetrafluoride may then form bubbles in the outer cladding 101 and / or at the interface between the outer cladding 101 and the inner cladding 103. Additionally, the rough interfaces between each of the outer claddings 101 and the core 102 may cause bubbles to form at the respective interfaces.

[0023] For MCF 100A, bubbles may form due to differences in dopant concentration between the outer cladding 101 and the core 102. For example, the germanium-doped core 102 of MCF 100A may include germanium dioxide, which may decompose into germanium oxide (GeO) and oxygen gas (O). The oxygen gas may then form bubbles in the outer cladding 101 and / or at the interface between the outer cladding 101 and the core 102. As with MCF 100B, in MCF 100A, the rough interfaces between each of the outer cladding 101 and the inner cladding 103 may also cause bubbles to form at the respective interfaces.

[0024] In either case, reducing these bubbles is desirable to increase the yield of the MCF and improve its material and optical properties. Thus, in the case of MCF 100B, it is desirable to reduce the dopant gradient and dopant diffusion between the outer cladding 101 and the inner cladding 103. It is similarly desirable to reduce the dopant gradient and dopant diffusion between the outer cladding and the core 102 of MCF 100A.

[0025] Accordingly, diffusion-reducing features are included in various embodiments of the present disclosure to reduce undesired migration of dopants into the outer cladding. In some embodiments, the diffusion-reducing features reduce diffusion of dopants between the core and / or inner cladding into the outer cladding. Thus, in such embodiments, the concentration of dopants in the outer cladding is reduced compared to an MCF without diffusion-reducing features. In some embodiments, the diffusion-reducing features reduce the dopant concentration gradient of dopants between the outer cladding and the core and / or inner cladding. Thus, in such embodiments, the dopant concentration gradient between the outer cladding and the core and / or inner cladding is reduced compared to an MCF without diffusion-reducing features.

[0026] FIGS. 2A-2F illustrate different diffusion-reducing features. As described in connection with FIG. 2A, certain embodiments, such as the MCF 100B of FIG. 1C, are related to reducing dopant diffusion between the inner cladding and the outer cladding. In the embodiment of FIG. 2A, the diffusion-reducing feature includes a diffusion barrier. As described in connection with FIG. 2D, certain embodiments, such as the MCF 100A of FIG. 1B, are related to reducing dopant diffusion between the core and the outer cladding. In the embodiment of FIG. 2D, the diffusion-reducing feature includes a diffusion barrier. As described in connection with FIGS. 2B and 2C, certain embodiments, such as the MCF 100B of FIG. 1C, are related to reducing the dopant gradient between the outer cladding and the inner cladding of the MCF. In the embodiments of FIGS. 2B and 2C, the dopant-reducing feature may include a lightly doped inner cladding region, a heavily doped inner cladding region, and / or a doped outer cladding. As described in connection with FIG. 2E, certain embodiments are related to reducing the dopant gradient between the inner cladding and the tube. In these embodiments, the diffusion-reducing features may include the doped tube and the rod inner cladding. As described in connection with FIG. 2F, certain embodiments relate to reducing the diffusion of dopants between the core and the tube. In these embodiments, the diffusion-reducing features may include a diffusion barrier.

[0027] FIG. 2A shows a front cutaway view of an MCF 200A with multiple diffusion barriers 202 and multiple inner claddings 103 according to certain embodiments of the present disclosure. In the example of FIG. 2A, the outer cladding 101 and core 102 comprise undoped fused silica, while the inner cladding 103 comprises doped fused silica (e.g., fluorine-doped fused silica). The diffusion barriers 202 at least partially surround the inner cladding 103. The diffusion barriers 202 comprise fused silica. In certain embodiments, the thickness of the diffusion barriers 202 varies from about 1 μm to about 10 μm. In this embodiment, the diffusion-reducing feature comprises the diffusion barriers 202. The diffusion barriers 202 reduce dopant migration between the inner cladding 103 and the outer cladding 101, reducing the dopant gradient between the inner cladding 103 and the outer cladding 101 and thus reducing bubble migration.

[0028] FIG. 2B shows a front cutaway view of an MCF 200B having multiple inner claddings 103 with different regions according to certain embodiments of the present disclosure. Each of the inner claddings 103 includes a heavily doped region 103h and a lightly doped region 103l. The heavily doped region 103h has a higher concentration of dopant (e.g., F dopant) than the lightly doped region 103l. According to some embodiments, the lightly doped region 103l is doped such that the numerical aperture (NA) of the lightly doped region is about 0.08 to about 0.18 relative to the core 102, and the heavily doped region 103h is doped such that the NA of the heavily doped region is about 0.18 to about 0.28 relative to the core. The NA is given by the following equation:

number

[0029] The thickness of the region is about 1 μm to about 10 μm with a core diameter of about 50 μm to about 80 μm. In the example of FIG. 2B, the highly doped region 103 h of each inner cladding 103 serves to reduce the amount of laser light that escapes from the respective core 102. In this embodiment, the diffusion-reducing feature includes a lightly doped region 103 l and a highly doped region 103 h, and the combination of the lightly and highly doped regions of each cladding 103 also serves to reduce bubble formation from the respective inner cladding 103 because there is a more gradual dopant gradient between the highly doped region 103 h, the lightly doped region 103 l, and the outer cladding 101.

[0030] 2C shows a front cutaway view of an MCF 200C with multiple inner claddings 103 and a doped outer cladding 201, according to certain embodiments of the present disclosure. The outer cladding 201 is doped with a dopant including fluorine (F), boron (B), or chlorine (Cl). In some embodiments, the doped outer cladding 201 has a lower dopant concentration relative to the inner cladding 103, reducing the dopant gradient between the doped outer cladding and the inner cladding. In such embodiments, the NA of the doped outer cladding 201 relative to the core 102 is between about 0.08 and about 0.18, and the NA of the inner cladding 103 relative to the core 102 is between about 0.18 and about 0.28. In this embodiment, the diffusion-reducing feature comprises the doped outer cladding 201. The reduced dopant gradient between the doped outer cladding 201 and the inner cladding 103 reduces bubble migration between the doped outer cladding 201 and the inner cladding 103 .

[0031] FIG. 2D shows a front cutaway view of an MCF 200D with multiple diffusion barriers 202 according to certain embodiments of the present disclosure. In the example of FIG. 2D, the core 102 is doped with a dopant that increases the refractive index of the core, thereby enabling light-guiding properties within the core 102. According to some embodiments, the dopant includes any dopant that increases the refractive index of the core 102, such as germanium (Ge) or phosphorus (P). Thus, in the example of FIG. 2D, the inner cladding 103 is not required because the doped core 102 can create a refractive index gradient with the surrounding material (e.g., the outer cladding 101), thereby enabling the light-guiding properties of the core. In this embodiment, the diffusion-reducing features include the diffusion barriers 202. In the example of FIG. 2D, the outer cladding 101 can include fused silica. Therefore, to prevent bubbles from forming in the outer cladding 101, in the embodiment of FIG. 2D, a diffusion barrier 202 made of the same material as the outer cladding 101 is used to create a dopant diffusion shield and reduce bubble formation at the interface to the outer cladding 101.

[0032] FIG. 2E shows a front cutaway view of an MCF 250A with a rod 210 and a rod inner cladding 230 according to a specific embodiment of the present disclosure. In the example of FIG. 2E, each of the cores 102 comprises fused silica or a similar material, while the inner cladding 103 comprises fused silica doped with a dopant including F, B, or Cl. The rod 210 is surrounded by the rod inner cladding 230, which comprises fused silica, glass, or a similar material. A first portion 211 of each of the inner claddings 103 interfaces with the inner surface of a tube 251 that surrounds all of the cores 102. A second portion 212 of each of the inner claddings 103 also interfaces with the rod inner cladding 230. In the example of FIG. 2E, the tube 251 is doped with a dopant including F, B, or Cl to reduce the dopant gradient between the outer shell 101 and the inner cladding 103. Additionally, as shown, in the second portion 212, the rod inner cladding 230 also surrounds the rod 210 to reduce the dopant gradient between the glass rod 210 and the inner cladding 103. Because the rod inner cladding 230 has the same material as the inner cladding 103 surrounding the core 102, the likelihood of bubbles forming in the rod 210 is reduced. In contrast, if the rod inner cladding 230 were not used around the rod 210, bubbles could form in the rod 210 due to the dopant gradient between the rod 210 and the inner cladding 103. In this embodiment, the diffusion-reducing feature includes the doped tube 251 and the rod inner cladding 230.

[0033] FIG. 2F shows a front cutaway view of an MCF 250B with rods 210 according to a specific embodiment of the present disclosure. In the example of FIG. 2F, each of the cores 102 includes fused silica or a similar material doped with a first dopant, such as germanium (Ge) or phosphorus (P), that increases the refractive index of the core. Diffusion barriers 202 include fused silica and surround the cores. A first portion 214 of each of the diffusion barriers 202 interfaces with the inner surface of the tube 251. A second portion 213 of each of the diffusion barriers 202 interfaces with the rod 210. In the example of FIG. 2F, the diffusion barriers 202 have the same composition as the outer shell to reduce the dopant gradient between the tube 251 and the core 102. In the example of FIG. 2F, the tube 251 may include fused silica. 2F , in order to prevent bubbles from forming in tube 251, diffusion barrier 202 is made of the same material as tube 251 to reduce the dopant gradient between doped core 102 and tube 251. In this embodiment, the diffusion-reducing feature includes diffusion barrier 202.

[0034] As described above, an MCF includes one or more of multiple cores, an outer shell, a diffusion barrier, a cladding, and a dopant. The diffusion barrier and cladding at least partially surround the core. The diffusion barrier and cladding are designed to reduce unwanted migration of dopants from the inner cladding to the outer cladding or tube. The doping levels of various components of the MCF can be controlled to reduce dopant migration. In some embodiments, the inner cladding is undoped and the core is doped instead, eliminating the need to dope the inner cladding.

[0035] The reduction of dopant gradients reduces dopant migration and the likelihood of bubble formation at the interface between the core and the outer cladding or tube. Additionally, the cladding and diffusion barriers help to delay and reduce dopant migration between the various components of the MCF. The dopant type and dopant profile can be tailored to maintain the desired material and optical properties of the MCF.

[0036] The subject matter disclosed above is considered to be illustrative and not limiting, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments that fall within the spirit and scope of the present disclosure. Accordingly, to the maximum extent permitted by law, the scope of the present disclosure shall be determined by the broadest possible interpretation of the following claims and their equivalents, and shall not be limited or constrained by the foregoing detailed description. According to aspect (1), there is provided a multi-core optical fiber (MCF), a plurality of cores comprising a first material; an outer cladding surrounding the core, the outer cladding comprising the first material; a diffusion-reducing feature that reduces migration of a first dopant between the outer cladding and another element in the MCF; The multi-core optical fiber (MCF) includes: According to aspect (2), the concentration of the first dopant in the outer cladding is reduced compared to an MCF without the diffusion-reducing features. According to aspect (3), the dopant concentration gradient between the outer cladding and the other element is reduced compared to an MCF without the diffusion-reducing features. According to aspect (4), the laser further includes a plurality of inner claddings surrounding the core, the plurality of inner claddings including the first material and the first dopant. According to aspect (5), the diffusion-reducing feature includes a plurality of diffusion barriers surrounding the inner cladding, and the diffusion barriers include the first material. According to aspect (6), the diffusion-reducing feature is: the plurality of heavily doped regions of the inner cladding doped with the first dopant; lightly doped regions of the inner cladding doped with the first dopant, the dopant concentration of the first dopant in the lightly doped regions being less than the dopant concentration of the first dopant in the heavily doped regions, the lightly doped regions surrounding the heavily doped regions; Includes. According to aspect (7), the numerical aperture (NA) of the heavily doped regions relative to the cores is about 0.18 to about 0.28, and the NA of the lightly doped regions relative to the cores is about 0.08 to about 0.18. According to embodiment (8), the first dopant includes fluorine (F), boron (B), or chlorine (Cl). According to aspect (9), the diffusion-reducing feature includes the outer cladding having a first dopant concentration. According to aspect (10), the concentration of the first dopant in the outer cladding is less than the concentration of the first dopant in the plurality of inner claddings. According to aspect (11), the diffusion-reducing feature includes a plurality of diffusion barriers surrounding the core, and the diffusion barriers include the first material. According to aspect (12), the plurality of cores are doped with the first dopant, and the other element is the plurality of cores. According to aspect (13), the first dopant increases the refractive index of the first material. According to the fourteenth aspect, the first dopant includes germanium (Ge) or phosphorus (P). According to an aspect (15), there is provided a multi-core optical fiber (MCF), a rod including a first material; a rod inner cladding surrounding the rod, the rod inner cladding comprising the first material and a first dopant; a plurality of cores comprising the first material; a plurality of inner claddings surrounding the core, the plurality of inner claddings comprising the first material and the first dopant, a first portion of each of the plurality of inner claddings interfacing with a portion of the rod inner cladding; an outer tube comprising the first material and the first dopant, wherein a second portion of each of the inner claddings interfaces with a portion of the outer tube; The multi-core optical fiber (MCF) includes:

Claims

1. A multi-core optical fiber (MCF), a plurality of cores comprising a first material; an outer cladding surrounding the core, the outer cladding comprising the first material; a plurality of inner claddings surrounding the core, the plurality of inner claddings including the first material and a first dopant, each of the cores being surrounded by one of the plurality of inner claddings; a diffusion-reducing feature that reduces migration of the first dopant from the inner cladding to the outer cladding; a multi-core optical fiber (MCF) in which the diffusion-reducing feature comprises a plurality of diffusion barriers surrounding the inner cladding, the diffusion barriers comprising the first material, and each of the inner claddings is surrounded by one of the plurality of diffusion barriers.

2. the diffusion-reducing feature comprises: the plurality of heavily doped regions of the inner cladding doped with the first dopant; the plurality of lightly doped regions of the inner cladding doped with the first dopant, the dopant concentration of the first dopant in the lightly doped regions being less than the dopant concentration of the first dopant in the heavily doped regions, the lightly doped regions surrounding the heavily doped regions; 2. The MCF of claim 1, comprising:

3. 3. The MCF of claim 2, wherein the numerical aperture (NA) of the highly doped regions relative to the plurality of cores is from about 0.18 to about 0.28, and the NA of the lightly doped regions relative to the plurality of cores is from about 0.08 to about 0.

18.

4. The MCF of claim 3 , wherein the first dopant comprises fluorine (F), boron (B), or chlorine (Cl).

5. The MCF of claim 1 , wherein the diffusion-reducing feature comprises the outer cladding of a first dopant concentration.

6. The MCF of claim 5 , wherein the first dopant concentration in the outer cladding is less than the first dopant concentration in the plurality of inner claddings.

7. The MCF of claim 1 , wherein the diffusion-reducing feature comprises a plurality of diffusion barriers surrounding the core, the diffusion barriers comprising the first material.

8. The MCF of claim 1 , wherein the first dopant increases the refractive index of the first material.

9. The MCF of claim 8 , wherein the first dopant comprises germanium (Ge) or phosphorus (P).

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