Metallic coated optical fiber and method of manufacture thereof

Abstract

The optical fiber (100) includes a core (110); a cladding (120) surrounding the core (110); a primary metal coating (130) surrounding the cladding (120) and comprising a noble metal having a melting point of at least 500°C; and a secondary metal coating (140) surrounding the primary coating (130) and having a melting point higher than that of the primary metal coating (130), wherein the thickness of the primary metal coating is greater than the thickness of the secondary metal coating.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of and priority to U.S. Non-provisional Patent Application No. 16 / 590,782, filed October 2, 2019, which is incorporated by reference in its entirety for all purposes.

[0002] In various embodiments, the present invention relates generally to optical fibers, and more specifically, to optical fibers with metallic coatings. [Background technology]

[0003] The amount of light lost as a signal passes through an optical fiber (the "attenuation" of light) is central to the usefulness of optical fiber. The lower the attenuation, the more useful the optical fiber is for long distances or bend-sensitive applications. However, signal attenuation is common in metal-coated optical fibers, especially after thermal cycling. Specifically, optical fibers can exhibit a significant increase in signal attenuation after thermal cycling because the thermal expansion coefficient of metals is much higher than that of glass, and inelastic deformation of the metal creates microbends in the fiber. Additionally, metal-coated optical fibers can be cold welded to a protective metal tube, which also increases the attenuation in the optical fiber due to the expansion / contraction of the protective metal tube. Additionally, when multiple metal-coated fibers are present in the tube, the metal-coated fibers can be cold welded to each other, further increasing the attenuation in the optical fiber.

[0004] Various solutions have been proposed to alleviate this problem of cold welding metal-coated fibers. For example, one solution involves coating the metal-coated optical fiber with a layer of copper metal. However, copper is a corrosion-prone metal that oxidizes easily. Oxidized metals such as copper are brittle and break easily, resulting in a brittle and brittle optical fiber coating. Alternative solutions include coating the metal-coated optical fiber with an oxidation-resistant metal layer such as gold. However, placing a metal tube around the gold-coated optical fiber tends to cause the gold coating to adhere to the tube when heated, resulting in further attenuation within the optical fiber. Some solutions attempt to circumvent this problem of gold adhering to the surrounding tube by coating the metal-coated optical fiber with a powder (e.g., talc powder) before encapsulating it in the tube. However, this solution is rudimentary and may be ineffective as the powder can easily move.

[0005] Therefore, there is a need for improved solutions to reduce or eliminate cold welding of metal coated optical fibers during thermal cycling and to reduce cold weld induced attenuation in metal coated optical fibers. Summary of the Invention

[0006] In one aspect, an embodiment of the invention relates to an optical fiber including a core having a central axis, where the core comprises a silica-based glass and has a refractive index. A cladding region surrounds the core, where the cladding comprises a silica-based glass and has a refractive index lower than that of the core. A primary metal coating surrounds the cladding, where the primary metal coating comprises a precious metal having a melting point of at least 500°C, and a secondary metal coating surrounds the primary metal coating, where the secondary metal coating has a melting point higher than that of the primary metal coating. The thickness of the primary metal coating is greater than the thickness of the secondary metal coating.

[0007] One or more of the following features may be included: The primary metal coating may have a thickness selected from the range of 0.5 microns to 45 microns, for example, 0.5 microns to 30 microns.

[0008] The secondary metal coating may have a thickness selected from the range of 0.005 microns to 2 microns. The secondary metal coating may have a melting point of at least 900°C.

[0009] The secondary metal coating may be porous.

[0010] Precious metals may include gold, ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, and / or any alloys thereof.

[0011] The secondary metal coating may comprise at least 60% by weight of a metal including a precious metal or any alloy thereof.

[0012] The primary metal coating may have a Vickers hardness of 550 MPa or less.

[0013] The secondary metal coating may have a Vickers hardness of greater than 220 MPa.

[0014] The secondary metal coating may include a metal alloyed with phosphorus. It may include a tungsten alloy and / or a metal oxide.

[0015] The secondary metal coating may have a solubility in the primary metal coating of less than 10% at 20° C. The tube may surround the secondary metal coating. In another aspect, an embodiment of the invention relates to a method for manufacturing an optical fiber, the method comprising placing an optical fiber including a core, a cladding, and a primary metal coating surrounding the cladding in a solution including ions of a secondary metal, where the solution contacts the primary metal coating of the optical fiber, and where the melting point of the secondary metal is higher than the melting point of the primary metal. An electric current is supplied from the solution including ions of the secondary metal to the primary metal coating of the optical fiber, whereby ions of the secondary metal are electrodeposited onto the primary metal coating to form a secondary metal coating surrounding the primary metal coating. The core comprises a silica-based glass and has a refractive index. The cladding comprises a silica-based glass and has a refractive index lower than the refractive index of the core. The primary metal coating comprises a precious metal having a melting point of at least 500° C. The secondary metal coating has a melting point higher than the melting point of the primary metal coating. The thickness of the primary metal coating is greater than the thickness of the secondary metal coating.

[0016] One or more of the following features may be included: The primary metal coating may have a selected thickness of 0.5 microns to 45 microns, e.g., 0.5 microns to 30 microns. The secondary metal coating may have a thickness of 0.005 microns to 2 microns. The secondary metal coating may have a melting point of at least 900°C.

[0017] The secondary metal coating may comprise at least 60% by weight of a metal including a precious metal or any alloy thereof. [Brief description of the drawings]

[0018] These and other features, aspects, and advantages of embodiments of the present invention will become better understood with regard to the following description and accompanying drawings.

[0019] [Figure 1]FIG. 1 shows a cross section of an optical fiber according to an embodiment of the present invention.

[0020] [Diagram 2] FIG. 2 shows a cross section of an optical fiber according to an embodiment of the invention.

[0021] [Diagram 3] FIG. 3 shows a cross section of an optical fiber according to an embodiment of the invention.

[0022] [Figure 4] FIG. 4 shows a cross section of an optical fiber according to an embodiment of the invention.

[0023] [Diagram 5] FIG. 5 shows a graph comparing the attenuation of a first optical fiber including a primary metal coating of gold and a secondary metal coating of ruthenium to the attenuation of a second optical fiber including a primary metal coating of gold and no secondary metal coating, in accordance with an embodiment of the invention.

[0024] These figures depict various embodiments of the present invention for purposes of illustration only, and those skilled in the art will readily recognize from the following detailed description that alternative embodiments of the structures and methods shown herein may be used without departing from the principles of the embodiments of the present invention described herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] An embodiment of the invention includes an optical fiber having two metallic coatings configured to reduce the attenuation of the optical fiber. In particular, as shown in FIG. 1, an optical fiber 100 according to an embodiment of the invention includes a core 110, a cladding 120 surrounding the core 110, a primary metallic coating 130 surrounding the cladding 120, and a secondary metallic coating 140 surrounding the primary metallic coating. The attenuation of the optical fiber 100 is reduced by selecting a material for the secondary metallic coating 140 that is low diffusive to the primary metallic coating 130 while also preventing cold welding despite significant changes in temperature. Thus, the optical fiber 100 is configured to reduce attenuation therein.

[0026] Each of these components of optical fiber 100 is described in turn below. In certain embodiments, described in more detail below with respect to Figures 2 through 4, the optical fiber can further include one or more carbon layers and a seed layer.

[0027] The cross-section of optical fiber 100 shown in FIG. 1, including core 110, cladding 120, primary metallic coating 130, and secondary metallic coating 140, has a diameter D 1 In some embodiments, the optical fiber 100 has a cross-sectional diameter D 1 is in the range of 110 μm to 220 μm, for example, 129 μm to 160 μm.

[0028] Looking initially at the core 110 of the optical fiber 100, the core 110 has a central axis that is perpendicular to the cross-section of the optical fiber 100. The central axis of the core 110 extends along the length (not shown) of the optical fiber 100. The core 110 comprises a silica-based glass, e.g., a germanosilicate, and has a refractive index selected from the range of 1 to 2, e.g., 1.4 to 1.6, or e.g., 1.467.

[0029] Core 110 is D 2 In some embodiments, the core 110 has a diameter D 2is selected from the range of 4 μm to 100 μm, for example, 20 μm to 80 μm.

[0030] The cladding 120 surrounds the core 110. Like the core 110, the cladding 120 comprises a silica-based glass and has a refractive index. However, to help confine light within the core and reduce attenuation within the optical fiber 100, the refractive index of the cladding 120 is less than that of the core 110. For example, the cladding 120 may comprise silica doped with fluorine and may have a refractive index selected from the range of 1 to 2, e.g., 1.4 to 1.6, or e.g., 1.452.

[0031] The core 110 and the cladding 120 are 3 In some embodiments, the core 110 and the cladding 120 may have a combined diameter D 3 is typically in the range of 40 μm to 200 μm.

[0032] The primary metal coating 130 surrounds the cladding 120 and comprises a precious metal having a melting point of at least 500° C. Suitable precious metals include, for example, gold, ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, or any alloy thereof.

[0033] There are many advantages to forming the primary metal coating 130 of the optical fiber 100 from a precious metal as opposed to a non-precious metal. First, unlike non-precious metals such as aluminum and copper, precious metals are less reactive and therefore less susceptible to corrosion by mechanisms such as oxidation reactions. Additionally, precious metals are less brittle than non-precious metals, allowing the primary metal coating 130 to be more easily formed from a precious metal and making a primary metal coating 130 made from a precious metal less likely to break. Specifically, in some embodiments, the primary metal coating 130 can be a metal having a Vickers hardness of less than 550 MPa, e.g., 220 MPa or less. An advantage of using a material with such a Vickers hardness is that it reduces the mechanical stress on the glass portion of the optical fiber. In further embodiments, the primary metal coating 130 can be a metal having a ductility of 40% or more. This ductility can be advantageous because it maintains the mechanical integrity of the coating when wrapped into a tight coil.

[0034] In addition to the advantages gained by forming the primary metal coating 130 from a noble metal, there are additional advantages to forming the primary metal coating 130 from a metal having a melting point of at least 500° C. Specifically, by forming the primary metal coating 130 from a metal having a melting point of at least 500° C., the optical fiber 100 can operate at conditions up to 500° C. without experiencing excessive interdiffusion of the optical fiber 100. This resistance to interdiffusion at such high temperatures further enables reduced attenuation of the optical fiber 100.

[0035] In some embodiments, the primary metal coating 130 may include additional features to further reduce the attenuation of the optical fiber 100. For example, in certain embodiments, the primary metal coating 130 has a thickness selected from the range of 0.5 to 45 microns, e.g., 0.5 to 30 microns. At such a thickness, the primary metal coating 130 is thick enough to encapsulate and protect the core 110 and cladding 120 of the optical fiber 100, yet thin enough to avoid increasing the attenuation of the optical fiber 100 as a result of mechanical stress.

[0036] In some additional embodiments, to further reduce attenuation of the optical fiber 100 during thermal cycling, the primary metal coating 130 is 25×10 -6 K -1 With such an expansion coefficient, the primary metallic coating 130 reduces significant expansion and compression during thermal cycling, reducing attenuation of the optical fiber 100 as a result of heating and cooling.

[0037] The secondary metal coating 140 surrounds the primary metal coating 130 and is a metal that has a higher melting point than the melting point of the primary metal coating 130. Additionally, the secondary metal coating 140 has a thickness that is less than the thickness of the primary metal coating 130.

[0038] The secondary metal coating 140 helps to further reduce the attenuation of the optical fiber 100. Specifically, the secondary metal coating 140, which has a higher melting point relative to that of the primary metal coating 130, does not cold weld to other metal-coated fibers or the protective tube surrounding it, and does not diffuse into the primary metal coating 130 during heat treatment. For example, in some embodiments, the secondary metal coating 140 can be a metal having a melting point of at least 900° C. As a result, the secondary metal coating 140 does not easily diffuse into the primary metal coating 130 or the cladding 120, thereby helping to reduce the attenuation of the optical fiber 100.

[0039] Making the secondary metal coating 140 thinner than the primary metal coating 130 is not simply a design choice. Rather, the secondary metal coating 140 is preferably thinner than the primary metal coating to reduce mechanical stresses on both the primary metal coating and the underlying glass.

[0040] In some embodiments, the optical fiber 100 may further include an outer tube (not shown) that surrounds the secondary metal coating 140. As noted above, compared to the primary metal coating 130, the secondary metal coating 140 does not easily cold weld or diffuse during thermal cycling due to its higher melting point. Thus, the secondary metal coating 140 does not adhere to the tube as easily as the primary metal coating would if it were an outer coating, and thus the presence of the secondary metal coating similarly reduces the attenuation of the optical fiber 100 in embodiments with an outer tube.

[0041] In some embodiments, the secondary metal coating 140 can include additional features to further reduce adhesion, thereby reducing attenuation of the optical fiber 100. For example, in certain embodiments, the secondary metal coating 140 has a thickness selected from the range of 0.005 microns to 2 microns. At certain thickness values ​​within this range, the secondary metal coating 140 can be porous. The porosity can be 95% or less, for example, 50% or less.

[0042] In further embodiments, the ratio of the thickness of the primary metal coating 130 to the thickness of the secondary metal coating 140 can be 50:1 or more, such as 100:1 or more, or 200:1 or more. At such a thickness, the secondary metal coating 140 is thick enough to act as a barrier to the primary metal coating 130, yet thin enough to prevent cold welding and reduce stress on the primary metal coating and glass.

[0043] The metal forming the secondary metal coating 140 can also be selected to reduce the attenuation of the optical fiber 100. For example, the metal forming the secondary metal coating 140 can be selected to be resistant to corrosion and / or to be ductile and resistant to fracture. For example, in some embodiments, the secondary metal coating 140 can be a metal that includes at least 60% by weight of a precious metal or any alloy thereof. As noted above, compared to non-precious metals, precious metals are less reactive and therefore less susceptible to corrosion by mechanisms such as oxidation reactions. Additionally, precious metals are less brittle than non-precious metals, facilitating the formation of the secondary metal coating 140 from precious metals and making secondary metal coatings 140 made from precious metals less likely to break. Specifically, in some embodiments, the secondary metal coating 140 can be a metal having a Vickers hardness greater than 220 MPa, e.g., greater than 550 MPa. The hardness of the secondary metal coating 140 is preferably greater than the hardness of the primary metal coating 130. The advantage of using a material with such a Vickers hardness is to protect the underlying primary metal coating. In further embodiments, the secondary metal coating 140 can be a metal having a ductility of greater than 30%, such as greater than 40%.

[0044] In addition to being resistant to corrosion and mechanical damage, the metal forming the secondary metal coating 140 may also be selected based on its solubility with the primary metal coating 130. As noted above, diffusion of the secondary metal coating 140 into the primary metal coating 130 may increase the attenuation of the optical fiber 100. Thus, in some embodiments, the metal forming the secondary metal coating 140 may be selected to have a low solubility in the metal forming the primary metal coating 130. For example, in an embodiment in which gold is the primary metal coating 130, nickel may not be selected for the secondary metal coating 140 because although nickel has a high melting point, nickel also has a high solubility with gold and therefore can easily diffuse into gold. In certain embodiments, the secondary metal coating may have a solubility in the primary metal coating of less than 10% at 20° C.

[0045] In some additional embodiments, to further reduce the attenuation of the optical fiber 100, the secondary metallic coating 140 is 25×10 -6 K -1 In some further embodiments, the ratio of the thermal expansion coefficient of the primary metal coating 130 to the thermal expansion coefficient of the secondary metal coating 140 may be, for example, less than 1 to 3, such as 0.5:3 or less. With such an expansion coefficient, the secondary metal coating 140 experiences minimal expansion and compression during thermal cycling, avoiding an increase in attenuation of the optical fiber 100 as a result of heating and cooling.

[0046] In alternative embodiments, the secondary metal coating 140 may be a metal alloyed with phosphorus, a tungsten alloy, or a metal oxide. The advantage of forming the secondary metal coating 140 from these materials is added wear resistance and increased resistance to diffusion into the primary metal coating.

[0047] As noted above, in certain embodiments, the optical fiber may optionally include one or more carbon layers and a seed layer. Figure 2 illustrates a cross section of an optical fiber 200 according to an embodiment of the invention. The optical fiber 200 is configured to have a secondary metal coating 240 that has low diffusivity to the primary metal coating 230 to reduce attenuation within the optical fiber 200 while also preventing cold welding of the optical fiber 200 despite significant changes in temperature. Thus, the optical fiber 200 is configured to reduce attenuation therein.

[0048] The optical fiber 200 includes a core 210, a cladding 220, a primary metal coating 230, and a secondary metal coating 240, as described above with respect to FIG. 1. However, unlike the optical fiber 100 of FIG. 1, the optical fiber 200 of FIG. 2 further includes a carbon layer 250 deposited between the cladding 220 and the primary metal coating 230 of the optical fiber 200. The carbon layer 250 is a thin layer of carbon and is an optional component of the optical fiber 200. The carbon layer 250 may provide the additional benefit of facilitating electroless deposition and preventing water ingress. The carbon layer may have a thickness of 50 angstroms (5 nm) to 150 angstroms (15 nm), for example, 100 angstroms (10 nm).

[0049] 3 illustrates a cross-section of an optical fiber 300 according to an embodiment of the present invention. The optical fiber 300 is configured to reduce attenuation within the optical fiber 300 by having a secondary metallic coating 340 that resists diffusion into the primary metallic coating 330, while also preventing cold welding of the optical fiber 300 despite significant changes in temperature. Thus, the optical fiber 300 is configured to reduce its attenuation.

[0050] The optical fiber 300 includes a core 310, a cladding 320, a primary metal coating 330, and a secondary metal coating 340, as described above with respect to FIG. 1. However, unlike the optical fiber 100 of FIG. 1, the optical fiber 300 of FIG. 3 further includes a seed layer 360 deposited between the cladding 320 and the primary metal coating 330 of the optical fiber 300. The seed layer 360 may be a thin layer of palladium and is an optional component of the optical fiber 300. The seed layer 360 may provide the added advantage of allowing the fiber to be electroplated. The seed layer may have a thickness of less than 1 μm, for example 0.5 μm. Palladium is a particularly suitable material for the seed layer because it is a noble metal that is commonly deposited using electroless deposition. Other suitable materials for the seed layer are silver and gold.

[0051] 4 illustrates a cross-section of an optical fiber 400 according to an embodiment of the present invention. The optical fiber 400 is configured to reduce the attenuation of the optical fiber 400 by having a secondary metallic coating 440 that resists diffusion into the primary metallic coating 430, while also preventing cold welding of the optical fiber 400 despite significant changes in temperature. Thus, the optical fiber 400 is configured to reduce its attenuation.

[0052] The optical fiber 400 includes a core 410, a cladding 420, a primary metal coating 430, and a secondary metal coating 440, as described above with respect to FIG. 1. However, unlike the optical fiber 100 of FIG. 1, the optical fiber 400 of FIG. 4 further includes a carbon layer 455 and a seed layer 460 deposited between the cladding 420 and the primary metal coating 430 of the optical fiber 400. The carbon layer and the seed layer 455, 460 are optional components of the optical fiber 400. The carbon layer 455 is a thin layer of carbon that surrounds the cladding 420. The seed layer 460 is a thin layer of palladium, silver, or gold that surrounds the carbon layer 455. As described above, the carbon layer 455 facilitates electroless deposition and prevents water ingress, while the seed layer 460 allows for electroplating of the fiber.

[0053] In addition to the optical fiber structures disclosed herein, methods of forming these optical fibers are also disclosed herein. In particular, methods of applying a primary metal coating to an optical fiber and methods of applying a secondary metal coating to the primary metal coating of an optical fiber are disclosed herein. The primary metal coating of an optical fiber can be formed according to any method known to those skilled in the art. For example, in some embodiments, the primary metal coating can be formed on the core and cladding of the optical fiber via electrodeposition. In alternative embodiments, the primary metal coating can be formed via solidification, i.e., melting / solidification.

[0054] Similar to the primary metal coating, the secondary metal coating may be formed on the primary metal coating of the optical fiber according to any suitable method known to those skilled in the art. In a preferred embodiment, the secondary metal coating is formed on the primary metal coating via electrodeposition. See, for example, U.S. Patent No. 10,126,493 to Miyamoto et al., entitled "Method and apparatus for fabrication of metal-coated optical fiber, and the resulting optical fiber," which is incorporated herein by reference in its entirety. Specifically, in a preferred embodiment, the secondary metal coating is applied to the primary metal coating of the optical fiber by placing the optical fiber, including the core, cladding, and the primary metal coating surrounding the cladding, in a solution containing ions of the secondary metal such that the ionic solution contacts the primary metal coating of the optical fiber. Then, while the ionic solution remains in contact with the primary metal coating of the optical fiber, an electric current is supplied from the solution containing ions of the secondary metal to the primary metal coating of the optical fiber. This supplied electric current causes ions of the secondary metal to be electrodeposited onto the primary metal coating surrounding the optical fiber, thereby forming a secondary metal coating surrounding the primary metal coating.

[0055] As discussed above with respect to FIG. 1, in some embodiments, the melting point of the secondary metal forming the secondary metal coating is higher than the melting point of the primary metal forming the primary metal coating. For example, in certain embodiments, the primary metal coating can have a melting point of at least 500° C., and the secondary metal coating can have a melting point of at least 900° C. Furthermore, in some embodiments, the thickness of the primary metal coating on the optical fiber is greater than the thickness of the secondary metal coating formed around the primary metal coating by electrodeposition. For example, in certain embodiments, the primary metal coating can have a thickness selected from the range of 0.5 to 45 microns, e.g., 0.5 to 30 microns, and the secondary metal coating can have a thickness selected from the range of 0.005 microns to 2 microns. Furthermore, in certain embodiments, the primary metal coating can be a precious metal and the secondary metal coating can be a metal comprising at least 60% by weight of the precious metal or any alloy thereof.

[0056] Forming a secondary metal coating on an optical fiber via electrodeposition offers many advantages over conventional methods of forming optical fibers to reduce attenuation of the optical fiber. For example, by electrodepositing a secondary metal coating on the primary metal coating, in contrast to coating the core / cladding of the optical fiber with a powder (e.g., talc powder) to reduce friction-induced attenuation of the optical fiber, the secondary metal coating becomes an integral component of the optical fiber and cannot be easily dislodged. Furthermore, in certain embodiments in which the formation of the primary metal coating is also achieved by electrodeposition, the primary metal coating and the secondary metal coating of the optical fiber can be constructed in succession according to the same method, thereby enabling seamless manufacturing of the optical fiber. Such seamless manufacturing of the optical fiber reduces the opportunities for errors that are likely to occur with multiple disjoint manufacturing steps and excessive handling.

[0057] As noted above, each of the optical fiber embodiments shown in Figures 1-4 is configured to reduce the attenuation of the optical fiber by having a secondary metal coating that resists diffusion into the primary metal coating, while also preventing cold welding of the optical fiber despite significant changes in temperature. The secondary metal coating of the optical fiber is important to this reduction in the attenuation of the optical fiber. Figure 5 provides evidence of this importance of the secondary metal coating in reducing the attenuation of the optical fiber. Specifically, Figure 5 shows a graph 500 comparing the attenuation 510 of a first optical fiber that includes a primary metal coating of gold and a secondary metal coating of ruthenium (according to an embodiment of the present invention) to the attenuation 520 of a second optical fiber that includes a primary metal coating of gold and does not include a secondary metal coating. As shown in Figure 5, the attenuation of the first and second optical fibers are compared over a period of 10 days at temperatures 530 ranging from ambient temperature to 500°C.

[0058] As shown in Figure 5, the attenuation 520 of the second optical fiber, which includes only a primary metal coating of gold but no secondary metal coating, increases dramatically as the temperature of the optical fiber is reduced from approximately 500°C to ambient temperature over a period of 8-10 days. In contrast, the attenuation 510 of the first optical fiber, which includes both a primary metal coating of gold and a secondary metal coating of ruthenium, does not increase dramatically as the temperature of the optical fiber is reduced from approximately 500°C to ambient temperature over a period of 8-10 days. Thus, graph 500 illustrates the importance of the secondary metal coating of the optical fiber in reducing the attenuation of the optical fiber through significant changes in temperature. EXAMPLES

[0059] As discussed above with respect to Figure 1, many possible specifications for optical fibers are provided herein. To further support these optical fiber specifications, explicit examples of optical fibers manufactured according to the specifications described herein are provided. Specifically, seven separate examples of optical fibers are provided herein.

[0060] A first exemplary optical fiber manufactured according to the specifications described herein is a multimode optical fiber having a diameter of 131 μm, a numerical aperture (NA) of 0.2, and including a graded-index core with a diameter of 50 μm, a cladding with a thickness of 37.5 μm, a primary metal coating of gold with a thickness of 3 μm, and a secondary metal coating of ruthenium with a thickness of 150 angstroms (15 nm).

[0061] A second exemplary optical fiber manufactured according to the specifications described herein is a single mode optical fiber having a diameter of 131 μm, a 0.12 NA, and including a 9 μm diameter step-index core, a 58 μm thick cladding, a 3 μm thick primary metal coating of gold, and a 150 angstrom (15 nm) thick secondary metal coating of ruthenium.

[0062] A third exemplary optical fiber manufactured according to the specifications described herein is a multimode optical fiber having a diameter of 155 μm, a 0.2 NA, and including a graded-index core of 50 μm diameter, a cladding of 37.5 μm thickness, a primary metal coating of gold of 15 μm thickness, and a secondary metal coating of ruthenium of 150 angstroms (15 nm) thickness.

[0063] A fourth exemplary optical fiber manufactured according to the specifications described herein is a multimode optical fiber having a diameter of 260 μm, a 0.2 NA, and including a graded-index core of 50 μm diameter, a cladding of 75 μm thickness, a primary metal coating of gold of 30 μm thickness, and a secondary metal coating of ruthenium of 150 angstroms (15 nm) thickness.

[0064] A fifth exemplary optical fiber manufactured according to the specifications described herein is a single mode optical fiber having a diameter of 260 μm, a 0.12 NA, and including a step-index core having a diameter of 9 μm, a cladding having a thickness of 95.5 μm, a primary metal coating of gold having a thickness of 30 μm, and a secondary metal coating of ruthenium having a thickness of 150 angstroms (15 nm).

[0065] A sixth exemplary optical fiber manufactured according to the specifications described herein is a multimode optical fiber having a diameter of 260 μm, a 0.22 NA, and including a step-index core of 200 μm diameter, a cladding of 10 μm thickness, a primary metal coating of gold of 20 μm thickness, and a secondary metal coating of ruthenium of 150 angstroms (15 nm) thickness.

[0066] A seventh exemplary optical fiber manufactured according to the specifications described herein is a multimode optical fiber having a diameter of 131 μm, a 0.275 NA, and including a graded-index core having a diameter of 62.5 μm, a cladding having a thickness of 31.25 μm, a primary metal coating of gold having a thickness of 3 μm, and a secondary metal coating of ruthenium having a thickness of 150 angstroms (15 nm).

[0067] The above exemplary optical fibers are intended to provide illustrative examples only and are not inclusive of all possible embodiments of the optical fibers disclosed herein. In particular, alternative optical fiber configurations not expressly disclosed herein may be provided in accordance with the specifications described throughout this disclosure.

[0068] Additional Considerations Upon reading this disclosure, those skilled in the art will appreciate further alternative structural and functional designs through the principles disclosed herein. Thus, while specific embodiments and applications have been illustrated and described, it should be understood that the disclosed embodiments are not limited to the precise structures and components disclosed herein. Various modifications, changes and variations, which will be apparent to those skilled in the art, can be made in the arrangement, operation and details of the methods and apparatus disclosed herein without departing from the spirit and scope as defined by the appended claims.

[0069] As will be apparent to those skilled in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has distinct components and features which may be readily separated or combined with the features of any of the other several embodiments without departing from the scope or spirit of the embodiments of the invention. Any described method may be carried out in the order of events described or in any other order which is logically possible.

[0070] As used herein, a reference to "one embodiment" or "an embodiment" means that a particular element, feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment. The appearances of the phrase "in one embodiment" in various places in the specification do not necessarily all refer to the same embodiment.

[0071] As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that includes a list of elements is not necessarily limited to only those elements, but may include other elements not expressly listed or inherent in such process, method, article, or apparatus. Furthermore, unless expressly stated to the contrary, "or" refers to an inclusive or and not an exclusive or. For example, a condition A or B is satisfied by any of the following: A is true (or present) and B is false (or absent), A is false (or absent) and B is true (or present), or both A and B are true (or present).

[0072] Finally, the use of "a" or "an" is used to describe elements and components of the embodiments herein. This is done merely for convenience and to give a general sense of the embodiments of the invention. This description should be understood to include one or at least one, and the singular also includes the plural, unless it is clear that another is meant.

Claims

1. a core having a central axis, where the core comprises a silica-based glass and has a refractive index; a cladding surrounding the core, where the cladding comprises a silica-based glass and has a refractive index lower than that of the core; a layer surrounding the cladding, said layer comprising at least one of (i) a seed layer comprising palladium, or (ii) a carbon layer; a primary metal coating surrounding said layer, wherein the primary metal coating comprises a precious metal selected from the group consisting of gold, ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, or any alloy thereof, having a melting point of at least 500° C.; and a secondary metal coating surrounding the primary metal coating, where the secondary metal coating has a melting point higher than the melting point of the primary metal coating; wherein the thickness of the primary metal coating is greater than the thickness of the secondary metal coating; Including optical fiber.

2. The optical fiber of claim 1 , wherein the primary metal coating has a thickness selected from the range of 0.5 μm to 45 μm.

3. 10. The optical fiber of claim 1, wherein the secondary metallic coating has a thickness selected from the range of 0.005 μm to 2 μm.

4. The optical fiber of claim 1 , wherein the secondary metallic coating has a melting point of at least 900° C.

5. The optical fiber of claim 1 , wherein the secondary metallic coating is porous.

6. 10. The optical fiber of claim 1, wherein the secondary metallic coating comprises at least 60% by weight of a metal comprising a precious metal or any alloy thereof.

7. 10. The optical fiber of claim 1, wherein the primary metal coating has a Vickers hardness of 550 MPa or less.

8. The optical fiber of claim 1 , wherein the secondary metallic coating has a Vickers hardness greater than 220 MPa.

9. The optical fiber of claim 1 , wherein the secondary metallic coating comprises a tungsten alloy.

10. The optical fiber of claim 1 , wherein the secondary metallic coating is a metal oxide.

11. 10. The optical fiber of claim 1, wherein the secondary metal coating has a solubility in the primary metal coating of less than 10% at 20°C.

12. The optical fiber of claim 1 further comprising a tube surrounding the secondary metallic coating.

13. 1. A method for producing an optical fiber, comprising the steps of: placing an optical fiber including a core, a cladding surrounding the core, a layer surrounding the cladding, said layer including at least one of (i) a seed layer including palladium, or (ii) a carbon layer, and a primary metal coating surrounding said layer, in a solution including ions of a secondary metal, wherein the solution contacts the primary metal coating of the optical fiber, and wherein the melting point of the secondary metal is greater than the melting point of the primary metal; and supplying an electric current from a solution containing ions of a secondary metal to a primary metal coating of the optical fiber, thereby electrodepositing ions of the secondary metal onto the primary metal coating to form a secondary metal coating surrounding the primary metal coating; wherein (i) the core has a central axis, comprises a silica-based glass, and has a refractive index, (ii) the cladding comprises a silica-based glass and has a refractive index lower than that of the core, (iii) the primary metal coating comprises a precious metal selected from the group consisting of gold, ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, or any alloy thereof, having a melting point of at least 500° C., (iv) the secondary metal coating has a melting point higher than that of the primary metal coating, and (v) the thickness of the primary metal coating is greater than the thickness of the secondary metal coating. The method includes:

14. The method of claim 13 , wherein the primary metal coating has a thickness selected from the range of 0.5 μm to 45 μm.

15. The method of claim 13, wherein the secondary metal coating has a thickness selected from the range of 0.005 μm to 2 μm.

16. The method of claim 13, wherein the secondary metal coating has a melting point of at least 900°C.

17. The method of claim 13 , wherein the secondary metal coating comprises a metal comprising at least 60% by weight of a precious metal or any alloy thereof.

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