Method for coupling optical fibers and optical coupler

Abstract

A method for optically coupling a first optical fiber and a second optical fiber to one another is described. The method generally comprises bringing a free end of the first optical fiber, a second optical fiber, and a liquid into close proximity to one another in a coupling region, the free end of the first optical fiber having a dimension below a critical dimension, and moving the free end of the first optical fiber through the liquid to contact the second optical fiber along a given coupling length, the contact optically coupling the free end of the first optical fiber and the second optical fiber to one another.

Description

[Technical Field]

[0001] The present improvement relates generally to optical fibers, and more particularly to optically coupling optical fibers to one another. [Background technology]

[0002] In some types of optical couplers, one smaller optical fiber, such as a fiber taper, is optically coupled to a larger optical fiber, or vice versa, so that an optical signal propagating through the optical fiber is transferred to another optical fiber with the highest possible efficiency. In such situations, it can be difficult to bring the smaller optical fiber to the larger optical fiber in a manner that favors continuous optical coupling between the smaller and larger optical fibers. Existing methods for optically coupling a smaller optical fiber to a larger optical fiber generally consist of positioning the smaller and larger optical fibers side-by-side under tension. While tension is maintained on both optical fibers, the smaller and larger optical fibers are brought into contact with each other and then fused or otherwise bonded together, thereby securing the optical coupling between the two fibers. While existing methods for optically coupling optical fibers to each other are somewhat satisfactory, there remains room for improvement. Summary of the Invention [Problem to be solved by the invention]

[0003] It has been discovered that a need exists for optically coupling smaller optical fibers to larger optical fibers, or vice versa, while reducing the risks associated with tensioning, fusing, and / or manipulating the smaller and larger optical fibers, and / or improving the efficiency of the transfer of optical signals from one optical fiber to another. [Means for solving the problem]

[0004] According to a first aspect of the present disclosure, there is provided a method of optically coupling a first optical fiber and a second optical fiber to one another, the method comprising bringing a free end of the first optical fiber, a second optical fiber, and a liquid into close proximity to one another in a coupling region, the free end of the first optical fiber being spaced apart from one another by a critical dimension. wherein the free end of the first optical fiber has a dimension less than 1 mm, and the free end of the first optical fiber moves through the liquid to contact the second optical fiber along a given coupling length, said contact optically coupling the free end of the first optical fiber and the second optical fiber to one another.

[0005] Further according to the first aspect of the present disclosure, during the step of bringing into close proximity, the second optical fiber can, for example, not be under tension.

[0006] Further according to the first aspect of the present disclosure, the step of bringing the free end and the second optical fiber into close proximity may include, for example, bringing the free end and the second optical fiber into close proximity to each other in a bonding region and then injecting a liquid into the bonding region.

[0007] Further according to the first aspect of the present disclosure, the method may further include, for example, bonding the free end of the first optical fiber and the second optical fiber together after the liquid has evaporated.

[0008] Further according to the first aspect of the present disclosure, the method may further include, for example, prior to the bringing into close proximity step, tapering the first optical fiber to leave a waist portion extending between the down-taper portion and the up-taper portion, and removing one of the down-taper portion and the up-taper portion from the first optical fiber to free the waist portion, thereby acting as a free end of the first optical fiber.

[0009] Further according to the first aspect of the present disclosure, the method may further include, for example, applying tension to the second optical fiber during the bringing into close proximity step.

[0010] Further according to the first aspect of the present disclosure, the movement can include, for example, the free end of the first optical fiber helically wrapping around the second optical fiber.

[0011] Further according to the first aspect of the present disclosure, the step of bringing the fibers into close proximity may be performed gradually, for example, in a direction leading to the free tip of the free end of the first optical fiber.

[0012] Further according to the first aspect of the present disclosure, the liquid may be, for example, alcohol.

[0013] Further according to the first aspect of the present disclosure, the first and second optical fibers may be made, for example, from dissimilar materials.

[0014] Further according to the first aspect of the present disclosure, the first optical fiber may be made of, for example, silica, and the second optical fiber may be made of, for example, low phonon energy glass.

[0015] Further according to the first aspect of the present disclosure, the dimensions of the free end of the first optical fiber can be, for example, less than the dimensions of the second optical fiber.

[0016] According to a second aspect of the present disclosure, there is provided an optical coupler comprising a first optical fiber and a second optical fiber optically coupled to the first optical fiber, wherein the first optical fiber has a free end having a dimension below a critical dimension, and wherein the free end of the first optical fiber contacts the second optical fiber along a given coupling length, thereby providing an optical coupling.

[0017] Further according to the second aspect of the present disclosure, the optical coupler can further include a protector, for example, over the free end and the second optical fiber along a given coupling length, the free end having a free tip with a cleaved end face, for example, below the protector. In some embodiments, the protector can extend partially over the free end, which can leave a tip of the free end uncovered by the protector.

[0018] Further according to the second aspect of the present disclosure, the protector may be made, for example, from a polymer having a refractive index lower than that of the first and second optical fibers.

[0019] Further according to the second aspect of the present disclosure, the first and second optical fibers may be made, for example, from dissimilar materials.

[0020] Further according to the second aspect of the present disclosure, the first optical fiber may be made of, for example, silica, and the second optical fiber may be made of, for example, a low phonon energy glass.

[0021] Further according to a second aspect of the present disclosure, the free end and the second optical fiber may be, for example, fused to one another along a given coupling length, the free end having a free tip with a rounded end face.

[0022] Further according to the second aspect of the present disclosure, the free end can be wrapped around the second optical fiber, for example, hi some embodiments, the free end can be wrapped around the second optical fiber over a plurality of turns, the number of turns being at least 0.25, preferably at least 0.5, and most preferably at least 1.0.

[0023] Further according to the second aspect of the present disclosure, the free end of the second optical fiber can have a length that is, for example, greater than a given length threshold.

[0024] Further according to the second aspect of the present disclosure, the dimensions of the free end of the first optical fiber can be, for example, less than the dimensions of the second optical fiber.

[0025] It has also been discovered that a need exists for optically coupling smaller optical fibers to larger optical fibers without necessarily using conventional glass processing platforms. Typically, such glass processing platforms group optical fibers together and then fuse them together. While such glass processing platforms are useful in some situations, they can be costly, difficult to operate, and / or cumbersome for customers to take over for repairs. Furthermore, in cases where optical fibers of different materials are to be optically coupled to each other, these glass processing platforms are generally not suitable. This is because different melting points imply that when one of the optical fibers is heated to a desired temperature, the other optical fiber may already be irreversibly melted and / or burned. Therefore, using the above-described method, when a smaller optical fiber and a larger optical fiber are optically coupled to each other and the liquid evaporates from the coupling area, the optical fibers can be glued together instead of and / or in addition to being fused.

[0026] According to a third aspect of the present disclosure, there is provided the use of an optical coupler as defined above as a pump combiner for a fiber-based laser and / or amplifier. Such an optical coupler can enable optical coupling of a pump beam into an active optical fiber used in a communications network or in a fiber-based laser and / or amplifier. More specifically, the method presented herein can enable rapid and reliable fabrication of a pump combiner with high coupling efficiency without complex mechanical or heating steps. The method presented herein can reduce the amount of optical fiber manipulation, which can reduce the risk of breaking any one of the optical fibers when the optical fibers are manipulated. Typical fused fiber combiners tend to disrupt the geometry of the receiving optical fiber, which can reduce the performance of optical fiber communication systems, especially when the core of the receiving optical fiber is near the cladding surface. Additionally, the methods presented herein can enable optical coupling between dissimilar optical fibers that have significantly different melting temperatures (e.g., silica-based glasses with melting temperatures of about 2000°C and fluoride-based glasses with melting temperatures of about 300°C) and therefore cannot be satisfactorily fused together using existing techniques. Thus, the methods presented herein can enable the fabrication of all-fiber pump combiners using such specialized fibers (e.g., low-phonon energy glasses such as fluoride glass fibers) that can transmit in the ultraviolet to mid-infrared regions of the electromagnetic spectrum, while still avoiding the use of complex, bulky, fragile, inefficient, and expensive pump combining systems for these fibers.

[0027] Many additional features and combinations of the present improvements will become apparent to those skilled in the art after reading this disclosure. [Brief explanation of the drawings]

[0028] [Figure 1A] FIG. 1 illustrates steps of an example method for optically coupling a first optical fiber to a second optical fiber, according to one or more embodiments, where the first optical fiber has dimensions that are smaller than the dimensions of the second optical fiber. [Figure 1B] FIG. 1 illustrates steps of an example method for optically coupling a first optical fiber to a second optical fiber, according to one or more embodiments, where the first optical fiber has dimensions that are smaller than the dimensions of the second optical fiber. [Figure 1C] FIG. 1 illustrates steps of an example method for optically coupling a first optical fiber to a second optical fiber, according to one or more embodiments, where the first optical fiber has dimensions that are smaller than the dimensions of the second optical fiber. [Figure 1D] FIG. 1 illustrates steps of an example method for optically coupling a first optical fiber to a second optical fiber, according to one or more embodiments, where the first optical fiber has dimensions that are smaller than the dimensions of the second optical fiber. [Figure 1E] FIG. 1 illustrates steps of an example method for optically coupling a first optical fiber to a second optical fiber, according to one or more embodiments, where the first optical fiber has dimensions that are smaller than the dimensions of the second optical fiber. [Figure 2A] FIG. 2 is a schematic diagram of an example receiving optical fiber, according to one or more embodiments. [Figure 2B] 1 is a schematic diagram of an example delivery optical fiber, according to one or more embodiments. [Figure 3A] FIG. 2C is a cross-sectional view of the delivery optical fiber of FIG. 2B after tapering, illustrating a waist portion extending between the down-tapered portion and the up-tapered portion, according to one or more embodiments. [Figure 3B] 3B is a cross-sectional view of the tapered delivery optical fiber of FIG. 3A after removal of the up-tapered portion, showing its free end, according to one or more embodiments. [Figure 4A] 3B illustrates steps of an example method for optically coupling the receiving optical fiber of FIG. 2A to the free end of the tapered supply optical fiber of FIG. 3B within a coupling region using a liquid, according to one or more embodiments. [Figure 4B] 3B illustrates steps of an example method for optically coupling the receiving optical fiber of FIG. 2A to the free end of the tapered supply optical fiber of FIG. 3B within a coupling region using a liquid, according to one or more embodiments. [Figure 4C] 3B illustrates steps of an example method for optically coupling the receiving optical fiber of FIG. 2A to the free end of the tapered supply optical fiber of FIG. 3B within a coupling region using a liquid, according to one or more embodiments. [Figure 4D] 3B illustrates steps of an example method for optically coupling the receiving optical fiber of FIG. 2A to the free end of the tapered supply optical fiber of FIG. 3B within a coupling region using a liquid, according to one or more embodiments. [Figure 4E] 3B illustrates steps of an example method for optically coupling the receiving optical fiber of FIG. 2A to the free end of the tapered supply optical fiber of FIG. 3B within a coupling region using a liquid, according to one or more embodiments. [Figure 4F] 3B illustrates steps of an example method for optically coupling the receiving optical fiber of FIG. 2A to the free end of the tapered supply optical fiber of FIG. 3B within a coupling region using a liquid, according to one or more embodiments. [Figure 5] FIG. 1 is a schematic diagram of an example optical coupler according to one or more embodiments, in which the free ends of a receiving optical fiber and a tapered supply optical fiber are glued together within a coupling region. [Figure 6]FIG. 1 is a schematic diagram of an example optical coupler according to one or more embodiments, in which the free ends of a receiving optical fiber and a tapered supply optical fiber are fused together within a coupling region. DETAILED DESCRIPTION OF THE INVENTION

[0029] 1A-1E illustrate an example of a method for optically coupling a first optical fiber 10 to a second optical fiber 12, where the first optical fiber 10 has a first dimension D1 that is smaller than a second dimension D2 of the second optical fiber 12.

[0030] In some embodiments, the first optical fiber 10 and the second optical fiber 12 have similar nominal dimensions, e.g., second dimension D2. In such embodiments, the first optical fiber 10 may be tapered down to the first dimension D1 for optical coupling purposes. In some other embodiments, the first optical fiber 10 may have a nominal dimension smaller than the second dimension D2 of the second optical fiber 12. It is noted that in embodiments in which the optical fibers are of circular cross-sectional shape, the dimension may be the diameter of the respective optical fiber. However, in some other embodiments, the optical fibers may not have a circular cross-sectional shape. For example, the optical fibers may have a polygonal cross-sectional shape, an irregular cross-sectional shape, or any other suitable cross-sectional shape.

[0031] In either case, the first dimension D1 is the critical dimension D c Smaller than critical dimension D c can vary from embodiment to embodiment, and the critical dimension D c is generally defined as the dimension below which the free end 14 of the first optical fiber 10 will be free to move and slide over the second optical fiber 12 when in the liquid 16. In some embodiments, the critical dimension D cis less than 50 μm, preferably less than 35 μm, and most preferably less than 20 μm. c depends on the first optical fiber 10. For example, the critical dimension D c may depend on the shape and / or material of the first optical fiber 10.

[0032] As shown in Figure 1A, the first optical fiber 10 and the second optical fiber 12 become optically coupled to one another with the liquid 16 in the coupling region 18. More specifically, Figure 1B shows that when the free end 14 of the first optical fiber 10, the second optical fiber 12, and the liquid 16 are brought into close proximity to one another in the coupling region 18, the free end 14 of the first optical fiber 10 moves within the liquid 16, resulting in a partial coupling length L, as shown in Figure 1C. p 1D, contacting the second optical fiber 12 along a coupling length L c Here, when the liquid 16 evaporates, the bond length L c The contact formed along the coupling length L optically couples the free end 14 of the first optical fiber 10 and the second optical fiber 12 to one another, the result of which is shown in FIG. 1E. c In some embodiments, the bond length L can vary between 5 mm and 100 mm. c can be at least 100 mm, and preferably at least 200 mm or more. In some embodiments, the contact is permanently secured by either fusing or gluing at least the free end 14 and the second optical fiber 12 together within the bonding region 18. Alternatively, the contact can be permanently secured by both fusing and gluing at least the free end 14 and the second optical fiber 12 together within the bonding region 18.

[0033] 1B and 1C, contact formed between the free end 14 and the second optical fiber 12 may be formed gradually along a direction 20 leading to the free tip 22 of the free end 14 of the first optical fiber 10. However, in some other embodiments, contact is formed along the opposite direction, or simultaneously, along the coupling length L c It can be formed along the entire surface.

[0034] It is contemplated that the order in which the free end 14, second optical fiber 12, and liquid 16 are brought into the bonding region 18 may vary from embodiment to embodiment. For example, the free end 14 and second optical fiber 12 may first be brought into close proximity to one another in the bonding region 18, and then the liquid 16 may be injected into the bonding region 18. The liquid 16 may be injected using a pipette (e.g., a mL pipette, a liquid spray device) or any other liquid injection device. In some other embodiments, the liquid 16 may first be injected onto the free end 14, and then the free end 14 is brought into close proximity to the second optical fiber 12 in the bonding region 18. Alternatively or additionally, the liquid 16 may first be injected onto the second optical fiber 12, and then the second optical fiber 12 is brought into close proximity to the free end 14 in the bonding region 18.

[0035] The type of liquid and its volume can vary from embodiment to embodiment. For example, examples of liquid 16 can include alcohol (e.g., isopropanol, acetone, etc.), solvents (e.g., toluene, water, etc.), and any other clean liquid. In some embodiments, alcohol is preferred because it is a fast-drying liquid, but any other fast-drying liquid can also be used. The volume of liquid used will also depend on the first and second dimensions D1 and D2 of first and second optical fibers 10 and 12, as well as the coupling length L. c The evaporation time of the liquid 16 can depend on the type of liquid used and can also depend on its volume.

[0036] The first optical fiber 10 and the second optical fiber 12 can have different geometries. They can also be of different types, including, but not limited to, single-clad, double-clad, multi-clad, coreless, uni-core, and multi-core optical fibers, and / or any suitable specialty optical fiber. They can also have similar or dissimilar cross sections of any suitable shape, including, but not limited to, D-shaped, circular, and octagonal. Each of the first optical fiber 10 and the second optical fiber 12 can have one, zero, or several cores, depending on the embodiment. As can be appreciated, the first optical fiber 10 and the second optical fiber 12 can be made of similar materials in some embodiments. For example, the first optical fiber 10 and the second optical fiber 12 can both be made of silica-based glass or low-phonon energy glass. In some other embodiments, the first optical fiber 10 and the second optical fiber 12 may be made from dissimilar materials. For example, the first optical fiber 10 may be made from a silica-based glass (having a melting temperature of about 2000°C) and the second optical fiber 12 may be made from a low-phonon energy glass (having a melting temperature of about 300°C), or vice versa.

[0037] In this disclosure, the expression "low phonon energy glass" refers to a glass having a phonon energy lower than that of silica-based glasses (i.e., 800 cm -1The term "low-phonon-energy" is intended to encompass any glass having a maximum phonon energy (lower than 100 kHz). Optical fibers made from low-phonon-energy glasses generally have a transmittance window ranging from the ultraviolet (e.g., 10 nm to 400 nm) to the mid-infrared region (i.e., 2.5 μm to longer wavelengths), unlike fibers made from high-phonon-energy glasses (e.g., silica-based glasses), which instead exhibit a transmittance window only within a given portion of the near-infrared (e.g., up to 2.4 μm). Naturally, using fibers made from low-phonon-energy glasses allows photons at wavelengths in the mid-infrared to propagate along the corresponding length of the fiber, in contrast to fibers made from high-phonon-energy glasses (which instead prevent the propagation of these photons). Thus, the methods described herein may be particularly useful for optical devices intended to operate in the mid-infrared region of the electromagnetic spectrum. Examples of low-phonon energy glasses include fluoride-based, chalcogenide-based, chalcohalide-based, or telluride-based glasses. In some circumstances, some oxide glasses (e.g., tellurite-based glasses) may be considered low-phonon energy glasses. For example, in some embodiments, the low-phonon energy glass is a zirconium fluoride glass having a composition including ZrF4, such as ZBLAN (ZrF4 / HfF4, BaF2, LaF3, NaF, and AlF3). In some other embodiments, the low-phonon energy glass is an indium fluoride glass having a composition including InF3. In alternative embodiments, the low-phonon energy glass is an aluminum fluoride glass having a composition including AlF3. In further embodiments, the low-phonon energy glass is a chalcogenide glass having a composition including As2S3, As2Se3, AsTe, AsSSe, AsSTe, GaLaS, GeAsS, or GeAsSe. Any other suitable low phonon energy glass with a transmittance window in the mid-infrared may be used.

[0038] 2A through 4F illustrate another example of a method for coupling a first optical fiber to a second optical fiber. In this example, the first optical fiber is a supply optical fiber 110, i.e., an optical fiber intended to supply an optical signal (e.g., a pump signal) into the second optical fiber. Also in this example, the second optical fiber is a receiving optical fiber 112, i.e., an optical fiber intended to receive an optical signal from the supply optical fiber 110. As shown in the specific example illustrated in FIGS. 2A and 2B, the supply optical fiber 110 and the receiving optical fiber 112 each have a core 130 surrounded by a cladding 132, which in turn is surrounded by one or several layers of coating 134 (typically made of a polymer). As shown in these figures, the supply optical fiber 110 and the receiving optical fiber 112 have a similar nominal dimension D0. In this embodiment, the supply optical fiber 110 has a core 130, although in some other embodiments, the supply optical fiber 110 can be coreless. In this embodiment, the receive optical fiber 112 has a single core, although the receive optical fiber 112 can have multiple cores.

[0039] FIG. 3A shows that the feed optical fiber 110 is uncoated along a given region 136 and then tapered, leaving a waist portion 138 extending between a down-taper portion 140 and an up-taper portion 142. The tapering may be performed by heating the feed optical fiber 110 and pulling both ends. To obtain the free end 114 of the feed optical fiber 110, one of the down-taper portion 140 and the up-taper portion 142 may be removed from the feed optical fiber 110. For example, as shown in FIG. 3B, the feed optical fiber 110 is simply cut or otherwise cleaved proximate the junction of the waist portion 138 and the up-taper portion 142. Preferably, the feed optical fiber 110 is cut to remove most (or, most preferably, the entire) of the up-taper portion 142. It has been found that leaving a portion of the uptaper section 142 can result in undesirable weight at the end of the free end 114, thereby preventing free movement of the free end 114 of the feed optical fiber 110 when in liquid. However, such a portion of the uptaper section 142 can, in some embodiments, be left free-standing at the end of the waist section 138, so long as the undesirable weight is below a given undesirable weight threshold. Preferably, the tip of the free end 114 resides within either the downtaper section 140 or the waist section 138 to avoid undesirable weight at the tip. Cutting the feed optical fiber 110 somewhere along the waist section 138 can be similarly satisfactory. In some embodiments, the waist section 138 is longer than a given length threshold.

[0040] 4A-4F illustrate steps of an example method for optically coupling the receiving optical fiber 112 of FIG. 2A to the free end 114 of the tapered supply optical fiber 110 of FIG. 3B within a coupling region 118 using a liquid 116.

[0041] As shown in FIG. 4A , coating 134 of receive optical fiber 112 is removed along a given portion of the receive optical fiber (hereafter referred to as “uncoated portion 150”). Uncoated portion 150 can have a length extending up to 15 cm in some embodiments. As shown, receive optical fiber 112 is tensioned along its axial orientation. More specifically, in this embodiment, the still-coated end of receive optical fiber 112 is secured onto a separate surface 152, for example, using tape 154. Applying tension to receive optical fiber 112 can facilitate other operations because receive optical fiber 112 can be kept stable.

[0042] 4B, the still-coated portion of the feed optical fiber 110 is secured to one of the surfaces 152 alongside the receive optical fiber, for example, using another tape 154'. In this position, the non-tapered portion 156, the downtapered portion 140, and the waist portion 138 collectively form the free end 114 of the feed optical fiber 110, which is partially free-standing alongside the receive optical fiber 112. The feed optical fiber 110 and the receive optical fiber 112 should be maintained close to each other. As shown, the free end 114 of the feed optical fiber 110 is not secured to anything at this point, so the free end 114 is hanging in the air.

[0043] 4C , a liquid 116 may be injected into the coupling region 118 (in this case, positioned proximate the junction between the downtaper portion 140 and the waist portion 138), thereby causing the waist portion 138 of the supply optical fiber 110 to move toward the receiving optical fiber 112. In some embodiments, it has been found that as the liquid 116 is gradually injected along a first direction 120 and connects with the free tip 122 of the free end 114 of the supply optical fiber 110, the free end 114 of the supply optical fiber 110 spirally wraps itself around the second optical fiber 112. To favor such wrapping, it has been found advantageous to inject the liquid 116 in a back-and-forth sequence (including injecting the liquid 116 along a first direction 120 and then in a reverse direction 160, as shown in FIG. 4D ) until the free end 114 helically wraps itself around the second optical fiber 112 for a desired number of turns. In some embodiments, the desired number of turns can be at least 0.25, preferably at least 0.5, and most preferably at least 1.0. For example, in some preferred embodiments, the desired number of turns varies from two to four turns. Such lasso-type wrapping favors satisfactory contact between the free end 114 and the receiving optical fiber 112. FIG. 4F shows the supply optical fiber 110 and the receiving optical fiber 112 optically coupled to each other according to the methods described herein once the liquid 116 has evaporated (which may require several minutes). It is hypothesized that the free end 114 wraps itself helically around the receive optical fiber 112 and thereafter remains so due to friction and / or intermolecular forces acting between the free end 114 of the supply optical fiber 110 and the receive optical fiber 112. The manner in which the free end 114 wraps itself around the receive optical fiber 112 may be advantageous in at least some circumstances.For example, in embodiments in which the supply optical fiber 110 and / or the receive optical fiber 112 have multiple cores (e.g., multiple cores circumferentially distributed within a cladding), wrapping can bring each one of the cores closer to the other optical fiber, which can enhance the coupling efficiency of the resulting optical coupler. In some embodiments, when the supply optical fiber 110 is brought into the coupling region 118, the receive optical fiber 112 is also free, not under tension, or otherwise slack. In some other embodiments, the free end 114 of the supply optical fiber 110 may not wrap around the receive optical fiber 112. For example, the free end 114 can be parallel to the receive optical fiber 112, at least along a given portion of the receive optical fiber 112.

[0044] To verify that the optical coupling is satisfactory, a coupling efficiency test can be performed. If the coupling efficiency is not satisfactory, the supply optical fiber 110 and the receive optical fiber 112 can be separated from each other and the method can be repeated until the coupling efficiency is deemed satisfactory.

[0045] FIG. 5 illustrates a portion of an optical coupler 200 in which contact between the free end 214 of the supply optical fiber 210 and the receive optical fiber 212 is secured by applying a protector 262 (e.g., adhesive, a polymer (e.g., Cytop CTX-109 AE, Defensa EXP OP-255), glass, or any other protective material) along the coupling region 118. In such an embodiment, the free tip 222 of the free end 214 preserves its cleaved end face 264. The cleaved end face 264 can be a regular cleavage or an irregular cleavage, depending on the embodiment. In the illustrated embodiment, the cleaved end face 264 is beneath the protector 262. However, in some other embodiments, the cleaved end face 264 may not be beneath the protector 262. This is because the protector 262 may only partially cover the free end 214. In some embodiments, the adhesive and / or polymer may have a refractive index lower than that of the supply optical fiber 210 and the receive optical fiber 212, guiding the light that is trapped within the optical fibers and improving coupling efficiency. However, in some other embodiments, the refractive index of the adhesive and / or polymer may be equal to or greater than that of the supply optical fiber 210 and the receive optical fiber 212. In some embodiments, the polymer may be UV-curable. In some other embodiments, the protector may be provided in the form of two glass slides that sandwich the supply optical fiber 210 and the receive optical fiber 212. In some embodiments, a polymer may be used in addition to the two glass slides. As shown in this particular embodiment, the protector 262 may be in physical contact with the heat sink 263.

[0046] For example, an optical coupler in which a supply optical fiber 110 and a receiving optical fiber 112 are optically coupled, such as shown in FIG. 4F (without adhesive or polymer), achieved a coupling efficiency of approximately 92%, while the optical coupler 200 of FIG. 5 achieved a coupling efficiency of approximately 95%.

[0047] In addition to being time consuming, such fuseless optical couplers have been found to be useful in applications where the shape of the receiving optical fiber is to be preserved, such as in optical communications applications, and in applications where light is to be optically coupled between two fibers of different materials that cannot be fused together due to their different melting temperatures.

[0048] 6 illustrates an alternative optical coupler 300 in which contact between the free end 314 of the supply optical fiber 310 and the receiving optical fiber 312 is secured by fusing the free end 314 and the receiving optical fiber 312 together. In such an embodiment, the free tip 322 of the free end 314 is slightly melted and thus has a melted appearance, for example, with a rounded end face 366. In some embodiments, only a portion of the free end 314 can be fused to the receiving optical fiber 312, thereby leaving the free tip 322 with a cleaved end face.

[0049] Such optical couplers find application in cladding-pumped fiber lasers and fiber amplifiers. In these lasers, the fiber core contains active ions, and energy must be provided to the active ions to place them in an excited state, which provides gain for the laser or amplifier. The energy can be provided by a lower wavelength pump laser. In the case of high-power multicore or multimaterial fiber lasers or amplifiers, it can be beneficial to inject the pump into the fiber cladding. Such optical couplers provide a means for injecting the pump into the cladding that has very good efficiency, is simple, easy to use, and is compatible with multicore fibers and coupling between different fiber materials (e.g., silica feed fiber to fluoride receive fiber).

[0050] In some embodiments, the length of the downtaper portion can be at least 4.0 cm, preferably at least 5.0 cm, and most preferably at least 7.0 cm. The length of the waist portion can be at least 1.0 cm, preferably at least 2.0 cm, and most preferably at least 4.0 cm. In some embodiments, the diameter of the waist portion can range from 15 μm to 44 μm. These exemplary values ​​are provided by way of example only, as other dimensions for the length of the downtaper portion, the length of the waist portion, and their dimensions can also be used in some other embodiments. Considering several experiments, it has been found that increasing the length of the downtaper portion and reducing the diameter of the waist portion can lead to improved coupling efficiency.

[0051] Optical Coupler - Example 1 The optical coupler was formed by optically coupling a coreless optical fiber made of silica-based glass, with a length of 75 mm and a down-tapered section of 2.0 cm, to a double-clad optical fiber (with a waist diameter of 22 μm) made of silica-based glass. The contacts were fixed using a low-refractive-index polymer. A coupling efficiency of approximately 92% was achieved with this coupler.

[0052] Optical Coupler - Example 2 The optical coupler was formed by optically coupling a coreless optical fiber made from silica-based glass and a taper with a length of 75 mm to a double-clad optical fiber made from low-phonon energy glass (and more specifically, ZBLAN). The contacts were secured using a low-refractive-index polymer. A coupling efficiency of approximately 90% was achieved with this coupler.

[0053] Optical Coupler - Example 3 An all-fiber-silica-to-fluoride glass fiber combiner was formed by optically coupling a coreless optical fiber made from silica-based glass (to which a 90 mm long coreless fiber taper was fusion-spliced) to a double-clad optical fiber made from 7% erbium-doped ZBLAN. The contact was fixed using a low-refractive-index polymer. A coupling efficiency of approximately 90% was achieved with this coupler.

[0054] As can be understood, the examples described and illustrated above are intended to be merely illustrative. For example, it can be appreciated that in some embodiments, the supply optical fiber will be optically coupled to the cladding of the receive optical fiber. In some embodiments, the liquid need not be evaporated before gluing and / or fusing the receive and supply optical fibers together, as the liquid can be easily removed using a cloth. Moreover, in some embodiments, the supply optical fiber can be cut at several points along the downtaper, thereby removing the downtaper, waist, and portions of the uptaper. In such embodiments, the free end of the supply optical fiber can be moved toward the receive optical fiber in the liquid, as long as its dimensions are below the critical dimension. It is contemplated that the first and second optical fibers can be moved toward each other along a transverse orientation. More specifically, in some other embodiments, the first and second optical fibers can be moved toward each other at an angle. The scope is indicated by the appended claims. It should be noted that the present invention includes the following aspects. [Aspect 1] 1. A method of optically coupling a first optical fiber and a second optical fiber, the method comprising bringing a free end of the first optical fiber, the second optical fiber, and a liquid into close proximity to one another in a coupling region, the free end of the first optical fiber having a dimension below a critical dimension, the free end of the first optical fiber moving in the liquid to contact the second optical fiber along a given coupling length, the contact optically coupling the free end of the first optical fiber and the second optical fiber to one another. [Aspect 2] 2. The method of claim 1, wherein the second optical fiber is not under tension during the bringing into close proximity step. [Aspect 3] The method of aspect 1, wherein the step of bringing the free end and the second optical fiber into close proximity includes bringing the free end and the second optical fiber into close proximity to each other within the bonding region and then injecting the liquid into the bonding region. [Aspect 4] 2. The method of embodiment 1, further comprising the step of adhering the free end of the first optical fiber and the second optical fiber to one another after the liquid has evaporated. [Aspect 5] 2. The method of aspect 1, further comprising, prior to the bringing into close proximity step, tapering the first optical fiber to leave a waist portion extending between a down-taper portion and an up-taper portion, and removing one of the down-taper portion and the up-taper portion from the first optical fiber to free the waist portion, thereby acting as the free end of the first optical fiber. [Aspect 6] The method of embodiment 5, further comprising the step of further removing the waist portion, thereby leaving the other of the downtaper portion and the uptaper portion to act as the free end of the first optical fiber. [Aspect 7] 10. The method of embodiment 1, further comprising tensioning the second optical fiber during the bringing into close proximity step. [Aspect 8] 2. The method of claim 1, wherein the moving comprises helically wrapping the free end of the first optical fiber around the second optical fiber. [Aspect 9] 2. The method of claim 1, wherein the step of bringing into close proximity is performed gradually in a direction leading to a free tip of the free end of the first optical fiber. [Aspect 10] 2. The method of claim 1, wherein the liquid is an alcohol. [Aspect 11] 2. The method of embodiment 1, wherein the first and second optical fibers are made of dissimilar materials. [Aspect 12] 12. The method of embodiment 11, wherein the first optical fiber is made from silica and the second optical fiber is made from a low-phonon energy glass. [Aspect 13] 2. The method of embodiment 1, wherein the second optical fiber is a multicore optical fiber. [Aspect 14] 2. The method of claim 1, wherein the dimension of the free end of the first optical fiber is less than a dimension of the second optical fiber. [Aspect 15] 1. An optical coupler comprising a first optical fiber and a second optical fiber optically coupled to the first optical fiber, the first optical fiber having a free end having a dimension below a critical dimension, the free end of the first optical fiber contacting the second optical fiber along a given coupling length, thereby providing an optical coupling. [Aspect 16] 16. The optical coupler of claim 15, further comprising a protector on the free end and the second optical fiber along the given coupling length, the free end having a free tip with a cleaved end face. [Aspect 17] 17. The optical coupler of embodiment 16, wherein the protector is made of at least one of a polymer and a glass having a refractive index lower than that of the first and second optical fibers. [Aspect 18] 17. The optical coupler of embodiment 16, wherein the protector is in physical contact with the heat sink. [Aspect 19] 16. The optical coupler of embodiment 15, wherein the first and second optical fibers are made of dissimilar materials. [Aspect 20] 16. The optical coupler of embodiment 15, wherein the first optical fiber is made of silica and the second optical fiber is made of a low-phonon energy glass. [Aspect 21] 16. The optical coupler of claim 15, wherein the free end and the second optical fiber are fused to each other along the given coupling length, and the free end has a free tip with a rounded end face. [Aspect 22] 16. The optical coupler of embodiment 15, wherein the free end is wrapped around the second optical fiber. [Aspect 23] 16. The optical coupler of embodiment 15, wherein the free end of the first optical fiber has a length that is greater than a given length threshold. [Aspect 24] 16. The optical coupler of embodiment 15, wherein the dimension of the free end of the first optical fiber is less than the dimension of the second optical fiber. [Aspect 25] 25. Use of the optical coupler of any one of embodiments 15 to 24 as a pump combiner for fiber-based cladding-pumped lasers and / or amplifiers. [Explanation of symbols]

[0055] 10 First Optical Fiber 12 Second optical fiber 14 Free end 16 liquid 18 Combined area 20 directions 22 Free tip 110 Supply optical fiber 112 Receiving optical fiber 114 Free end 116 Liquid 118 Combined area 120 First Direction 122 Free tip 130 cores 132 Cladding 134 Coating 136 Given Area 138 Waist 140 Down taper part 142 Up tapered part 150 Uncoated area 152 Surface 154 Tape 154' Another Tape 156 Non-tapered part 160 opposite direction 200 Optical Coupler 210 Supply optical fiber 212 Receiving optical fiber 214 Free end 222 Free tip 262 Protector 263 Heatsink 264 Cleaved end face 300 Optical Coupler 310 Supply optical fiber 312 Receiving optical fiber 314 Free end 322 Free tip 366 Rounded Ends D0 nominal dimensions D1 First dimension D2 Second dimension D c Critical dimensions L c Bond Length Lp Partial bond length

Claims

1. 1. A method for optically coupling a first optical fiber and a second optical fiber to each other, comprising: The method includes bringing the free end of the first optical fiber, the second optical fiber, and a liquid into close proximity to one another in a coupling region; the free end of the first optical fiber has a dimension that is less than a critical dimension; the free end of the first optical fiber moves through the liquid to contact the second optical fiber along a given coupling length; the moving includes wrapping the free end at least partially around the second optical fiber along the given coupling length; The method, wherein the contact optically couples the free end of the first optical fiber and the second optical fiber to one another.

2. The method of claim 1 , wherein no tension is applied to the second optical fiber during the bringing into close proximity step.

3. 2. The method of claim 1, wherein the step of bringing the free end and the second optical fiber into close proximity includes bringing the free end and the second optical fiber into close proximity to each other in the bonding region and then injecting the liquid into the bonding region.

4. The method of claim 1 , further comprising the steps of evaporating the liquid and adhering the free end of the first optical fiber and the second optical fiber together.

5. 2. The method of claim 1, further comprising, prior to the step of bringing into close proximity, tapering the first optical fiber to leave a waist portion extending between a down-taper portion and an up-taper portion, and removing one of the down-taper portion and the up-taper portion from the first optical fiber to free the waist portion, thereby acting as the free end of the first optical fiber.

6. 6. The method of claim 5, further comprising the step of further removing the waist portion, thereby leaving the other of the downtapered portion and the uptapered portion to act as the free end of the first optical fiber.

7. The method of claim 1 , further comprising the step of applying tension to the second optical fiber during the step of bringing into close proximity.

8. The method of claim 1 , wherein the wrapping comprises wrapping the free end around the second optical fiber at least one turn.

9. 2. The method of claim 1, wherein the step of bringing into close proximity is performed gradually in a direction leading to a free tip of the free end of the first optical fiber.

10. The method of claim 1 , wherein the liquid is alcohol.

11. The method of claim 1 , wherein the first and second optical fibers are made from a plurality of dissimilar materials.

12. The method of claim 11 , wherein the first optical fiber is made from silica and the second optical fiber is made from a low phonon energy glass.

13. The method of claim 1 , wherein the second optical fiber is a multicore optical fiber.

14. The method of claim 1 , wherein the dimension of the free end of the first optical fiber is less than the dimension of the second optical fiber.

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