Asymmetric combiner with optimal brightness

Abstract

The invention relates to an asymmetric combiner with optimal brightness. In some implementations, an optical system may include a plurality of pumping sources, an output fiber, and a combiner including an input coupled to the plurality of pumping sources and an output coupled to the output fiber. In some implementations, a combiner includes a plurality of pump fibers coupled to a plurality of pump sources and one or more filler fibers made of a cladding material. In some implementations, the number of the plurality of pump fibers is related to an asymmetric build-up geometry, and the plurality of pump fibers and the one or more filler fibers have a symmetric build-up geometry at the input end of the combiner, with a circular cross-section at the output end of the combiner. In some implementations, the plurality of pump fibers and the one or more filler fibers each have a generally circular cross-section.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims priority to U.S. Provisional Patent Application No. 63 / 510,738, entitled “ASYMMETRIC COMBINER WITH OPTIMUM BRIGHTNESS,” filed on June 28, 2023. The disclosure of that prior application is considered a part of and is incorporated by reference into this patent application. Technical Field

[0003] The present disclosure relates generally to pump combiner structures and to pump combiners having one or more filler fibers to achieve a symmetrical and stable stacking geometry. Background Art

[0004] Pump combiners are key components of high-power fiber lasers. Pump combiners are used to combine pump light and signal light to increase the power of the signal light. For example, "optical pumping" of a medium generally refers to a technique that is used to inject light in order to electronically excite the medium or a component of the medium to other (usually higher) energy levels. In the context of a laser or laser amplifier, the goal is to achieve a population inversion in the gain medium, thereby obtaining light amplification via stimulated emission of a range of optical frequencies. In many cases, pump combiners are arranged in a beam configuration that is joined to another optical structure (e.g., a master oscillator power amplifier (MOPA) or a single-pass fiber laser structure) that is configured to deliver hundreds of watts (W) or kilowatts (kW) of pump power. The beam configuration can be achieved by arranging the pump fibers into a specific close-packed configuration (e.g., a hexagonal close-packed configuration, etc.) and fusing and tapering the individual pump fibers into a beam of a target size. Summary of the invention

[0005] In some implementations, a combiner includes: a plurality of pump fibers, wherein the plurality of pump fibers each include: a core; and a cladding surrounding the core; and one or more filling fibers made of the cladding material, wherein the plurality of pump fibers and the one or more filling fibers each have a substantially circular cross-section, wherein a number of the plurality of pump fibers is associated with an asymmetric packing geometry, and wherein the plurality of pump fibers and the one or more filling fibers have a symmetric packing geometry at an input end of the combiner and a circular cross-section at an output end of the combiner.

[0006] In some implementations, an optical system includes: a plurality of pump sources; an output fiber; and a combiner including an input end coupled to the plurality of pump sources and an output end coupled to the output fiber, wherein the combiner includes: a plurality of pump fibers coupled to the plurality of pump sources, wherein the plurality of pump fibers each include: a core; and a cladding surrounding the core; and one or more filling fibers made of a cladding material, wherein the plurality of pump fibers and the one or more filling fibers each have a substantially circular cross-section, wherein a number of the plurality of pump fibers corresponds to a number of the plurality of pump sources and is associated with an asymmetric packing geometry, and wherein the plurality of pump fibers and the one or more filling fibers have a symmetric packing geometry at the input end of the combiner and have a circular cross-section at the output end of the combiner.

[0007] In some implementations, a combiner includes: a plurality of pump fibers, wherein the plurality of pump fibers each include: a core made of a first material having a first refractive index parameter; and a cladding surrounding the core; and one or more filling fibers disposed along a periphery of the combiner and made of a cladding material having a second refractive index parameter less than the first refractive index parameter, wherein the plurality of pump fibers and the one or more filling fibers each have a substantially circular cross-section, and wherein the plurality of pump fibers and the one or more filling fibers have a symmetrical stacking geometry at an input end of the combiner and have a circular cross-section at an output end of the combiner. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1A-Figure 1D is a diagram illustrating an example related to a pump combiner.

[0009] Figure 2A-2C is a graph illustrating one or more examples associated with brightness degradation and / or process stability degradation that may occur in a combiner having a number of ports that may result in suboptimal pile-up.

[0010] Figure 3A-3B is a diagram illustrating one or more examples of an asymmetric combiner with optimal brightness. DETAILED DESCRIPTION

[0011] The following detailed description of example implementations refers to the accompanying drawings.The same reference numbers in different drawings may identify the same or similar elements.

[0012] Figure 1A-Figure 1D is a diagram illustrating one or more examples 100 associated with a pump combiner. Figure 1A , reference numeral 105 refers to a pumping configuration, in which a pump fiber is used to deliver pump light from a pump diode so that the pump light can be used to pump a fiber laser. Figure 1AAs shown in , the pump fiber may include a relatively large fused silica core surrounded by a doped fused silica cladding, such as a fluorine-doped (F-doped) fused silica cladding. Additionally, or alternatively, the pump fiber used to deliver the pump light may be a polymer-clad fiber, which includes a fused silica core surrounded by a low-refractive-index polymer (e.g., instead of an F-doped glass cladding). The pump light in a pump configuration is typically contained within the fused silica core, and the brightness or beam parameter product (BPP) of the pump light may be approximated as the product of the numerical aperture (NA) and radius (R) of the pump fiber (e.g., BPP=NA×R).

[0013] In some cases, such as Figure 1A As shown in the reference numeral 110 in FIG. 1 , a pump combiner can be used to combine the power from several pumps to achieve the power that may be required to pump a fiber laser. In particular, a pump combiner is a fiber component that fuses the power from N pumps together and outputs the fused power from the N pumps into a single output fiber, and the pump light can then be converted by the fiber laser. In addition, or alternatively, the output from the pump combiner can be used for a low brightness laser source. For example, reference numeral 110 refers to a 7:1 pump combiner that combines pump light from 7 diodes into a single output, which is then delivered to an output fiber. For example, as shown in cross section, the pump combiner includes 7 optical fibers that are fused together and then spliced ​​to the output fiber.

[0014] In cases where a pump combiner is used to combine power from several pumps, the brightness at the output of the pump combiner generally depends on the brightness of the pumps (e.g., pump diodes) and the brightness drop that occurs when the pumps are combined into a single output fiber. Under perfect adiabatic combining conditions, the brightness drops (and the BPP increases) by the square root of the number of ports in the combiner:

[0015] BPP combiner =√#ports×BPP diode

[0016] BPP combiner refers to the BPP of the light output by the combiner, while BPP diode Refers to the BPP of the light output by the diode.

[0017] For various reasons, pump brightness is often an important parameter to maintain (e.g., minimize its increase) through a pump combiner. For example, pump brightness affects the amount of pump light with a high NA within the fiber laser cladding, where cladding light with a high NA can cause more heating and lower reliability. Additionally, or alternatively, cladding light with a high NA can force laser designs to use larger fibers, which can cause processing and other problems. Furthermore, pump brightness can affect absorptivity in active fibers. For example, a higher NA can result in the generation of more slanted light, which in turn can reduce absorptivity in the fiber core and result in the need for longer active fibers. For at least these reasons, it is often desirable for a pump combiner to operate near the adiabatic limit for brightness conversion.

[0018] In its simplest form, a combiner is often used to transform multiple input fibers into a single output. Therefore, an important design goal of a combiner is often to transform multiple input fibers into a single output as efficiently as possible. For example, one way to efficiently transform multiple input fibers into a single output is to pack the transformed fiber bundles closely together so that when the bundled fibers are fused and tapered, the shape of the bundle approaches a circle, thereby achieving optimal splicing and minimizing brightness degradation. For example, refer to Figure 1B , reference numeral 115 refers to a situation where seven optical fibers are fused together to form a bundle cross section that is circular or as close to circular as possible. For example, in some cases, the glass of each optical fiber in the bundle is heated and provides tension during the melting process, thereby creating surface tension. The surface tension has the effect of minimizing the surface area around the bundle, which begins to change the shape of the bundle from a hexagonal shape to an optimal circular shape. Figure 1B As further shown by reference numeral 120 in FIG. 1 , the resulting structure is a pump combiner having a tapered shape. For example, as shown along a cross section of the combiner along the taper, the input end of the combiner includes individual pump fibers that match (e.g., match in position and area) the input fibers coupled to the corresponding diodes. Near the middle region of the taper, the individual pump fibers begin to become more tightly fused, thereby reducing the space between the individual fibers. At the output end of the combiner, the individual pump fibers are closely packed and close to the core of the output fiber that is spliced ​​to the output end of the tapered combiner.

[0019] Additionally, another important aspect of the process of combining multiple pump fibers into a single output is that as the various fibers are tapered, the NA of the pump light traveling in the core increases inversely proportional to the fiber diameter (e.g., as the fiber diameter decreases, the NA generally increases). For example, pump fibers are often associated with a 0.22 NA, in which case pump light with an NA exceeding 0.22 will escape the core. As the pump light escapes the core and is refracted into the cladding, the NA of the pump light decreases according to Snell's law, which states that for a given pair of media, the sinusoidal ratio of the angle of incidence (θ1) and the angle of refraction (θ2) is equal to the refractive index of the second medium relative to the first medium (n 21 ), which is equal to the ratio of the refractive indices of the two media (n2 / n1), or the ratio of the phase velocities in the two media (v1 / v2). For example, see Figure 1C , reference numeral 125 refers to the state of the pump light at the input end of the 7:1 combiner, where the pump light is initially confined within the individual cores. However, as shown in reference numeral 130, it refers to the state of the pump light near the middle region of the 7:1 combiner, which is only partially confined within the individual cores (e.g., some of the pump light has escaped from the individual cores). In addition, as shown in reference numeral 135, it refers to the state of the pump light near the output end of the 7:1 combiner, which has escaped from the cores.

[0020] refer to Figure 1D , reference numeral 140 refers to a detailed view of the junction between the pump combiner and the output fiber. As shown, the combiner includes multiple optical fibers that are fused or pressed together, and the pump light passes through two different regions, including a first region corresponding to a set of fused silica cores and a second region corresponding to a cladding (e.g., F-doped fused silica or a low refractive index polymer cladding) surrounding the fused silica core. Due to refraction, any light occupying a particular cladding region will have a lower NA than light occupying a core region. According to simulations, the probability of light occupying the core or cladding can be affected by various parameters, which can include the taper ratio, the taper length, and / or the fiber NA, etc. In addition, the probability of light occupying the core or cladding can depend largely on the area of ​​the core or cladding relative to the total area of ​​the combiner. Therefore, as the amount of tapering performed decreases and the core area increases, the probability of pump light entering the core increases. On the other hand, as the amount of tapering increases and the cladding area increases, the probability of pump light entering the cladding increases.

[0021] Figure 1A-Figure 1D are provided as examples. Other examples can be found in the Figure 1A-Figure 1D Different than described. Figure 1A-Figure 1D The number and arrangement of devices shown in the figure are provided as examples. In practice, there may be more than Figure 1A-Figure 1DMore devices, fewer devices, different devices, or differently arranged devices as shown in . In addition, Figure 1A-Figure 1D Two or more of the devices shown in the figure may be implemented in a single device, or Figure 1A-Figure 1D The single device shown in can be implemented as multiple distributed devices. In addition, or alternatively, Figure 1A-Figure 1D The set of devices shown in FIG. 1 may perform the operations described as being performed by Figure 1A-Figure 1D One or more functions performed by another set of devices shown in FIG.

[0022] Figure 2A-2C is a graph illustrating one or more examples 200 related to brightness degradation and / or reduced process stability that may occur in a combiner where the number of ports may result in suboptimal stacking.

[0023] For example, refer to Figure 2A , reference numeral 205 refers to a typical 7:1 capillaryless combiner with optimal symmetry (e.g., 7 input fibers form a hexagonal shape at the input end of the combiner). In this case, the bundle is deformed from a hexagonal shape to a circular or near-circular output cross-section. However, in cases where only 6 ports are needed instead of 7 ports and the design goal is to optimize brightness, using a 7-port combiner will result in brightness being discarded from the additional ports, even in cases where the additional ports are not used. Alternatively, reference numeral 210 refers to a combiner configuration with only 6 ports, which can be created by removing the center port in the bundle. However, the stacking geometry shown in reference numeral 210 is unstable, and the fibers may be difficult or impossible to keep together during the melting and tapering process.

[0024] Therefore, reference Figure 2B , reference numeral 215 refers to another possible approach in which the fibers are stacked in a different geometry (e.g., a triangle) to stabilize the bundle melting process. Although the bundle is stable in this case, the alternative geometry does not deform well into the circular or near-circular shape required when spliced ​​with the output fiber. For example, the shaded area between the fiber core and the outer circular shape of the output fiber substantially represents the area where brightness waste occurs. In addition, removing one of the outer fibers from a bundle having a hexagonal shape (as shown in reference numeral 220) can also result in a mismatch at the splice between the combiner and the output fiber, thereby exacerbating brightness degradation.

[0025] refer to Figure 2C, reference numerals 225 and 230 refer to alternative approaches to addressing the brightness degradation and / or reduced beam stability issues in which capillaries are used in the beam process. However, there are various disadvantages to using capillaries. For example, reference numeral 225 refers to an example in which a fused silica capillary is used, which stabilizes the beam for processing. However, the addition of fused silica results in a drop in output brightness (e.g., using fused silica is similar to having a larger core area), possibly to a greater extent than using 7 fibers. Alternatively, reference numeral 230 refers to an example using F-doped fused silica, which is similar to using more cladding area. Therefore, if the combiner is tapered far enough and long enough, a brightness advantage can be observed. However, the use of thin-walled F-doped capillaries presents processing problems due to the much lower melting point, and the material tends to bubble during the tapering process, making it more difficult to join.

[0026] Figure 2A-2C are provided as examples. Other examples can be found in the Figure 2A-2C Different than described. Figure 2A-2C The number and arrangement of devices shown in the figure are provided as examples. In practice, there may be more than Figure 2A-2C More devices, fewer devices, different devices, or differently arranged devices are shown in . In addition, Figure 2A-2C Two or more of the devices shown in the figure may be implemented in a single device, or Figure 2A-2C The single device shown in can be implemented as multiple distributed devices. In addition, or alternatively, Figure 2A-2C The set of devices shown in FIG. 1 may perform the operations described as being Figure 2A-2C One or more functions performed by another set of devices shown in .

[0027] Some implementations described herein involve the use of filler fibers to stabilize stacking and improve brightness conversion in combiners that otherwise have suboptimal stacking geometries. For example, the filler fibers described herein typically have a dn that is less than the dn of the pump fiber core used, where dn refers to the difference between the refractive index of the core and the refractive index of the cladding. For example, if the pump fiber core is standard fused silica, the filler fiber can be fluorosilicate glass, borosilicate glass, or any other glass whose dn is less than the fused silica core. On the other hand, in the case where the core of the glass is germanium (Ge)-doped fused silica, the filler fiber can be fused silica fiber or other suitable material. Furthermore, another important property of the filler fiber is that the filler fiber is not limited by the geometry and size of the pump fiber, but can be any geometry or size that stabilizes the beam. The examples described herein illustrate the specific case of using a standard fused silica pump fiber and a filling fiber having the same material as the pump fiber cladding (e.g., F-doped fused silica or a low-refractive-index polymer), but the filling fiber described herein can be doped with any suitable dopant having a dn less than that of fused silica, such as boron, fluorine, phosphorus, and aluminum.

[0028] Figure 3A-3B is a diagram illustrating one or more examples 300 of an asymmetric combiner with optimal brightness. For example, Figure 3A The figure illustrates filler fibers that can be used in combiners in situations where the number of ports in the combiner does not produce a symmetrical and stable stacking geometry. In some implementations, the filler fiber can enable a stable combiner construction process without sacrificing the brightness of the combiner. Essentially, the filler fiber is an optical fiber made entirely of fused silica or a low index polymer material doped with a suitable material such that the dn of the filler fiber is less than the dn of the pump fiber core. For example, if the pump fiber core is standard fused silica, the filler fiber can be a fluorosilicate glass, a borosilicate glass, a low index polymer, or any glass whose dn is less than the dn of the fused silica core. In another example, where the core of the glass is germanium-doped fused silica, the filler fiber can be a fused silica fiber or another suitable material. Furthermore, another important property of the filler fiber is that the filler fiber is not limited by the geometry and size of the pump fiber, but can be any geometry or size that makes the beam stable. For example, as Figure 3A As shown in , the outer diameter of the fill fiber can be equal to the outer diameter of the individual pump fibers.

[0029] Therefore, if Figure 3AAs shown in FIG. 305 , filler fibers can enable a stable packing geometry to be used even when the number of input ports is different from the number of input ports that results in a hexagonal shape that typically produces a stable packing geometry. For example, reference numeral 305 refers to an example of using filler fibers at the center of a 6:1 combiner to produce a stable 7:1 packing geometry. Figure 3A The examples refer to the use of filler fibers at the center of the combiner bundle, but the filler fibers can be substituted for any position of the pump fibers. In some implementations, adding filler fibers to an otherwise asymmetric combiner bundle is similar to adding more cladding material. Therefore, as long as the bundle is tapered and light is squeezed out of the core of the pump fiber, the brightness advantages of a stable 7:1 stacking geometry can be achieved. Additionally, relative to techniques using capillaries, the use of filler fibers is less prone to blistering due to their location and relative heat exposure.

[0030] In addition, despite Figure 3A An example of a combiner based on a stable 7:1 stacking geometry is illustrated, but filler fibers can be used for combiners with any suitable number of ports. For example, the optimal stacking geometry for a capillaryless combiner with one center port is 7 ports, 19 ports, 37 ports, 61 ports, etc. For example, refer to Figure 3B , reference numeral 310 refers to an optimal packing geometry of a capillary-free combiner with one central port and seven total ports, reference numeral 315-1 refers to a 6:1 combiner configuration with six pump fibers and a filling fiber used as a central fiber, and reference numeral 315-2 refers to a 4:1 combiner configuration with four pump fibers and three filling fibers located at various positions within a hexagonal packing geometry. In another example, reference numeral 320 refers to an optimal packing geometry of a capillary-free combiner with one central port and 19 total ports, and reference numeral 325 refers to a 15:1 combiner configuration with 15 pump fibers and four filling fibers located at various positions within a hexagonal packing geometry. In another example, reference numeral 330 refers to an optimal packing geometry of a capillary-free combiner with one central port and 37 total ports, and reference numeral 335 refers to a 34:1 combiner configuration with 34 pump fibers and three filling fibers located at various positions within a hexagonal packing geometry. However, in general, the optimal location for the filler fiber may be around the periphery of the combiner, since higher drops typically occur in the outer layers of the bundle configuration.

[0031] Thus, as described herein, a combiner with optimal brightness may include a plurality of pump fibers, each pump fiber including a core and a cladding surrounding the core. In addition, in the case where the number of the plurality of pump fibers is associated with an asymmetric (e.g., non-hexagonal) packing geometry, the combiner may include one or more filling fibers made of a cladding material such that the plurality of pump fibers and the one or more filling fibers form a bundle without a surrounding capillary structure, having a symmetrical packing geometry at the input end of the combiner (e.g., a single central port and one or more hexagonal rings concentrically surrounding the single central port). In addition, the bundle has a circular cross-section at the output end of the combiner. In some implementations, the outer diameter of the one or more filling fibers is equal to the outer diameter of the pump fiber. Additionally, or alternatively, the one or more filling fibers may have a different geometry and / or size than the pump fiber (e.g., the filling fiber is not limited to the geometry and / or size of the pump fiber, but may have any geometry or size that stabilizes the fiber bundle).

[0032] In addition, the core of each pump fiber is made of a first material having a first refractive index parameter (e.g., a first dn value), and the one or more filling fibers are made of a second material having a second refractive index parameter (e.g., a second dn value) less than the first refractive index parameter. In other words, the one or more filling fibers are made of any suitable material having a dn value less than the dn value of the core of the pump fiber used. In addition, or alternatively, the cladding of each pump fiber can be made of a cladding material (e.g., F-doped fused silica or a low refractive index polymer) used for one or more filling fibers. In addition, although the position along the periphery of the combiner provides the lowest pump attenuation (because the attenuation is generally highest at the outer layer), the filling fiber can be located at any suitable position within the fiber bundle. Therefore, as described herein, the combiner can be used in an optical system (e.g., a pump system) including multiple pump sources (e.g., diodes) and output fibers, wherein the combiner is joined or otherwise arranged between the pump sources and the output fibers. For example, in this case, the number of pump fibers included in the bundle can generally correspond to the number of pump sources.

[0033] Figure 3A-3B are provided as examples. Other examples are similar to those regarding Figure 3A-3B Different than described. Figure 3A-3B The number and arrangement of devices shown in the figure are provided as examples. In practice, there may be more than Figure 3A-3B The devices shown in the figure may be more devices, fewer devices, different devices, or devices arranged differently. In addition, Figure 3A-3B Two or more of the devices shown in the figure may be implemented in a single device, or Figure 3A-3B The single device shown in can be implemented as multiple distributed devices. In addition, or alternatively, Figure 3A-3B The set of devices shown in FIG. 1 may perform the operations described as being Figure 3A-3B One or more functions performed by another set of devices shown in .

[0034] The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit the implementations to the precise forms disclosed. Modifications and variations may be made in accordance with the foregoing disclosure or may be obtained from the practice of the implementations. In addition, unless the foregoing disclosure clearly provides a reason why one or more implementations cannot be combined, any implementation described herein may be combined.

[0035] Even if a specific combination of features is recorded in the claims and / or disclosed in the specification, these combinations are not intended to limit the disclosure of various implementations. In fact, many of these features can be combined in ways that are not specifically recorded in the claims and / or not disclosed in the specification. Although each dependent claim listed below may directly depend on only one claim, the disclosure of various implementations includes the combination of each dependent claim with all other claims in the claim set. As used herein, the phrase "at least one" of a list of items refers to any combination of these items, including single members. For example, "at least one of: a, b or c" is intended to cover a, b, or c, ab, ac, bc and abc, and any combination with multiple identical items.

[0036] Unless clearly described, any element, action or instruction used herein should not be interpreted as key or necessary. In addition, as used herein, the article "one" and "an" are intended to include one or more projects, and can be used interchangeably with "one or more". In addition, as used herein, the article "the" is intended to include one or more projects related to the article "the", and can be used interchangeably with "one or more". In addition, as used herein, the term "set" is intended to include one or more projects (for example, a combination of related projects, unrelated projects, or related and unrelated projects), and can be used interchangeably with "one or more". If only intended to a project, the phrase "only one" or similar language is used. In addition, as used herein, the term "have", "have", "have" etc. are intended to be open terms. In addition, unless otherwise clearly stated, the phrase "based on" is intended to mean "at least partially based on". In addition, as used herein, the term "or" is intended to be inclusive when used in a series, and can be used interchangeably with "and / or", unless otherwise clearly stated (for example, if used in combination with "either" or "only one"). In addition, for ease of description, spatially relative terms (such as "below," "lower," "above," "upper," etc.) may be used herein to describe the relationship of one element or feature illustrated in the figures to another element or feature. In addition to the orientations depicted in the figures, spatially relative terms are also intended to cover different orientations of devices, equipment, and / or elements in use or operation. Devices may be oriented in other ways (rotated 90 degrees or in other orientations), and the spatially relative descriptors used herein may also be interpreted accordingly.

Claims

1. A combiner, comprising: A plurality of pump optical fibers, wherein each of the plurality of pump optical fibers comprises: core; and a cladding surrounding the core; and One or more filled optical fibers, made of cladding material, wherein the plurality of pump fibers and the one or more filling fibers each have a substantially circular cross-section, wherein the number of the plurality of pump fibers is associated with an asymmetric stacking geometry, and The plurality of pump fibers and the one or more filling fibers have a symmetrical stacking geometry at the input end of the combiner and a circular cross-section at the output end of the combiner.

2. The combiner of claim 1, wherein the outer diameter of the one or more filling fibers is equal to the outer diameter of the plurality of pump fibers.

3. The combiner of claim 1 , wherein the core of each of the plurality of pump fibers is made of a first material having a first refractive index parameter, and wherein the one or more filling fibers are made of a second material having a second refractive index parameter that is less than the first refractive index parameter.

4. The combiner of claim 1, wherein the one or more filler fibers are disposed along a periphery of the combiner.

5. The combiner of claim 1, wherein the cladding of each of the plurality of pump fibers is made of the cladding material used for the one or more fill fibers.

6. The combiner of claim 1, wherein the one or more filling fibers have one or more of the following that are different from the plurality of pump fibers: geometry, or size.

7. The combiner of claim 1, wherein the symmetrical stacking geometry comprises: A single central port, and one or more hexagonal rings concentrically surrounding the single central port.

8. The combiner of claim 1, wherein the plurality of pump fibers and the one or more filling fibers form a fiber bundle without a surrounding capillary.

9. An optical system comprising: Multiple pump sources; Output optical fiber; as well as A combiner, comprising an input end and an output end, wherein the input end is coupled to the plurality of pump sources, and the output end is coupled to the output optical fiber, wherein the combiner comprises: A plurality of pump fibers are coupled to the plurality of pump sources, wherein each of the plurality of pump fibers comprises: core; and a cladding surrounding the core; and One or more filled optical fibers, made of cladding material, wherein the plurality of pump fibers and the one or more filling fibers each have a substantially circular cross-section, wherein the number of the plurality of pump fibers corresponds to the number of the plurality of pump sources and is associated with an asymmetric stacking geometry, and The plurality of pump fibers and the one or more filling fibers have a symmetrical stacking geometry at the input end of the combiner and a circular cross-section at the output end of the combiner.

10. The optical system of claim 9, wherein the outer diameter of the one or more filling fibers is equal to the outer diameter of the plurality of pump fibers.

11. The optical system of claim 9, wherein the core of each of the plurality of pump fibers is made of a first material having a first refractive index parameter, and wherein the one or more filling fibers are made of a second material having a second refractive index parameter that is less than the first refractive index parameter.

12. The optical system of claim 9, wherein the one or more filler fibers are disposed along a periphery of the combiner.

13. The optical system of claim 9, wherein the cladding of each of the plurality of pump fibers is made of the cladding material used for the one or more fill fibers.

14. The optical system of claim 9, wherein the one or more filling fibers have one or more of the following that are different from the plurality of pump fibers: geometry, or size.

15. The optical system of claim 9, wherein the symmetrical packing geometry comprises: A single central port, and one or more hexagonal rings concentrically surrounding the single central port.

16. The optical system of claim 9, wherein the plurality of pump fibers and the one or more filling fibers form a fiber bundle without a surrounding capillary.

17. A combiner comprising: A plurality of pump optical fibers, wherein each of the plurality of pump optical fibers comprises: a core made of a first material having a first refractive index parameter; and a cladding surrounding the core; and one or more filled optical fibers disposed along the periphery of the combiner and made of a cladding material having a second refractive index parameter that is less than the first refractive index parameter, wherein the plurality of pump fibers and the one or more filling fibers each have a substantially circular cross-section, and The plurality of pump fibers and the one or more filling fibers have a symmetrical stacking geometry at the input end of the combiner and a circular cross-section at the output end of the combiner.

18. The combiner of claim 17, wherein the cladding of each of the plurality of pump fibers is made of the cladding material used for the one or more fill fibers.

19. The combiner of claim 17, wherein the symmetrical stacking geometry comprises: A single central port, and one or more hexagonal rings concentrically surrounding the single central port.

20. The combiner of claim 17, wherein the plurality of pump fibers and the one or more fill fibers form a fiber bundle without a surrounding capillary.

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