Apparatus for laser processing of materials

Abstract

An apparatus for laser processing a material (29), the apparatus comprising at least one first laser (15), at least one second laser (16), an optical coupler (3), and a multi-core fiber (10), wherein each first laser (15) is connected to the optical coupler (3) via a first feed fiber (1), and each second laser (16) is connected to the optical coupler (3) via a second feed fiber (2), the optical coupler (3) connecting the first feed fiber (1) to a first core (11) of the multi-core fiber (10) and connecting the second feed fiber (2) to a second core (12) of the multi-core fiber (10); The optical coupler (3) provides a first optical path (41) from the first laser (15) to the first core (12) of the multicore fiber (10) and a second optical path (42) from the second laser (16) to the second core (12) of the multicore fiber (10), the optical coupler (3) comprising a fiber bundle (4) tapered along its length.

Description

[Technical Field]

[0001] The present invention relates to an apparatus for laser processing materials. [Background technology]

[0002] Lasers are widely used for cutting and welding industrial materials. Different processes and applications have different requirements for laser beam parameters, such as the focal diameter, intensity distribution, or beam quality at the processing point. Laser processing devices are commercially available that can switch the output laser beam between different laser beam parameters, such as a sharply focused, relatively good beam quality required for laser cutting, and a loosely focused, uniform beam quality with a uniform intensity distribution across the beam cross section required for welding or thick-wall cutting.

[0003] It would be desirable if such a laser processing device had more power available with optimal beam quality for laser cutting and other laser material processes, allowing for faster cutting speeds and reducing manufacturing costs, thus being commercially advantageous.

[0004] The present invention seeks to provide an apparatus for laser processing materials that solves the above problems. Summary of the Invention

[0005] According to non-limiting embodiments of the present invention, there is provided an apparatus for laser processing a material, the apparatus comprising at least one first laser, at least one second laser, an optical coupler, and a multicore fiber; each first laser is connected to an optical combiner via a first feed fiber; each second laser is connected to an optical combiner via a second feed fiber; the optical coupler connects the first feed fiber to a first core of the multi-core fiber and the second feed fiber to a second core of the multi-core fiber; the optical coupler provides a first optical path from the first laser to the first core of the multicore fiber; an optical coupler providing a second optical path from the second laser to a second core of the multicore fiber; The optical coupler comprises a fiber bundle that tapers along its length.

[0006] The fiber bundle may include at least one spacing fiber, where the first feed fiber is separated from the second feed fiber by the spacing fiber. This bundle geometry is beneficial in that it allows for the fabrication of separate / non-adjacent first and second feed fibers without the need to introduce an internal capillary into the bundle assembly. Therefore, the bundle geometry can better match the geometry of the multicore fiber. Therefore, it can improve the transmission efficiency of the optical coupler without the additional cost and complexity associated with using an internal capillary to separate the first feed fiber from the second feed fiber.

[0007] The first feed fiber, the second feed fiber, and the spacing fiber may be arranged in a configuration, and the first feed fiber may be offset from the center of the configuration. The configuration may be in the form of a square, a triangle, or a hexagon. Other configurations are possible.

[0008] The fiber bundle may include two first feed fibers, two second feed fibers, and three spacing fibers, and the first feed fibers, second feed fibers, and spacing fibers may be arranged in a hexagonal configuration, and one of the spacing fibers may be at the center of the hexagon.

[0009] The fiber bundle may include at least one first feed fiber, at least two second feed fibers, and at least three spacing fibers arranged in a configuration. One of the spacing fibers may be at the center of the configuration. This configuration allows the first feed fiber to be coupled to a first core of the multicore fiber and the second feed fiber to be coupled to a second core of the multicore fiber. Two, three, four, or more second feed fibers may be provided in this configuration, allowing the optical power emitted by the device to be scaled. The central spacing fiber may have a larger diameter than the other fibers in the configuration.

[0010] The fiber bundle may include one first feed fiber, three second feed fibers, and two spacing fibers. The first feed fiber, second feed fibers, and spacing fibers may be arranged in a hexagonal configuration. Additional second feed fibers may be provided. One of the spacing fibers may be at the center of the configuration. This bundle geometry is similar to the basic LP 0,1 This is advantageous because it allows an optical mode to be coupled from the first feed fiber into the first core of the multicore fiber and then directed toward the material being processed. A mode converter applied to either the first feed fiber and / or the output fiber can convert the fundamental mode into a higher order mode depending on the laser processing being performed on the material.

[0011] The first and second feed fibers may be arranged in a square configuration including the first feed fiber, the second feed fiber, and two spacing fibers, and the first and second feed fibers may be diagonally opposite each other.

[0012] The fiber bundle can include multiple second feed fibers and multiple spacing fibers. The first feed fiber, second feed fiber, and spacing fiber can be arranged in a hexagonal configuration. The first feed fiber can be located at the center of the hexagonal configuration. This bundle geometry also allows for the fabrication of separate / non-adjacent first and second feed fibers without the need to introduce an internal capillary into the bundle assembly. When four second feed fibers are provided, the bundle geometry allows up to four second lasers to be connected to the fiber bundle, which provides power scaling for different fabrication processes depending on how many lasers are required. Additional second feed fibers can be incorporated into the bundle around the central hexagonal configuration, thus allowing additional second lasers to be connected to the fiber bundle, thus enabling additional power scaling.

[0013] The fiber bundle can include multiple first feed fibers that enable power scaling of the laser beam emitted from the first core of the multicore fiber by adding additional first lasers depending on the power required from the first core of the multicore fiber.

[0014] The fiber bundle may include a low-index ring adjacent to the cladding of the first feed fiber, the low-index ring having a refractive index less than the refractive index of the cladding. The low-index ring may be the cladding of the first feed fiber surrounding the cladding.

[0015] The fiber bundle may include an inner capillary. The inner capillary may include at least one groove. Advantageously, the groove aids in assembly of the fiber bundle.

[0016] The fiber bundle may include a first feed fiber and at least one second feed fiber. The first and second feed fibers may be disposed within a capillary. The first feed fiber may be adjacent to the wall of the bore of the capillary. This configuration may simplify the construction of the fiber bundle and may be particularly useful for products with 2-5 second lasers. The bore may be offset from the central axis of the capillary so that the first feed fiber is aligned with the central axis of the capillary.

[0017] The fiber bundle may include an outer capillary surrounding at least one second feed fiber. The outer capillary may be a square capillary. The outer capillary may have other configurations. A square capillary is advantageous for packing the first and second feed fibers when arranged in a square configuration without an inner capillary. Spacing fibers may be included to space adjacent the first and second feed fibers.

[0018] The first laser can include a single-mode laser, which has a higher beam quality than a multi-mode laser of the same wavelength, thus enabling optimization of the laser radiation emitted from the first core of the multi-core fiber. The first laser can include a multi-mode laser.

[0019] The first feed fiber may be a multimode fiber, and the first laser may include an output fiber, and the output fiber and first feed fiber may be fusion spliced together such that a fundamental mode propagating in the output fiber is coupled to a fundamental mode propagating in the first feed fiber. The output fiber and / or the first feed fiber may be tapered at or near the splice to match the profiles of the two fundamental modes, thereby reducing splice loss and coupling to higher order modes.

[0020] The first feed fiber may be tapered such that the core diameter of the first feed fiber at the output of the optical coupler is less than a critical diameter at which the mode field diameter of the fundamental mode of the first feed fiber reaches the minimum mode field diameter of the optical coupler, and preferably the tapering is adiabatic to reduce coupling from the fundamental mode to higher order modes of the first feed fiber.

[0021] The first feed fiber may be a double-clad fiber having an outer cladding with a lower refractive index than the inner cladding, such that optical radiation coupled from the core of the first feed fiber into its inner cladding can be guided by the inner cladding by total internal reflection.

[0022] The second laser may include a single mode laser.

[0023] The second feed fiber may be a multimode fiber, and the second laser may include an output fiber, and the output fiber and second feed fiber may be fusion spliced together such that a fundamental mode propagating in the output fiber is coupled to a fundamental mode propagating in the second feed fiber. The output fiber and / or second feed fiber may be tapered at or near the splice to match the profiles of the two fundamental modes, thereby reducing splice loss and reducing coupling to higher order modes at the splice.

[0024] The second feed fiber may be tapered such that the core diameter of the second feed fiber at the output of the optical coupler is smaller than a critical diameter at which the mode field diameter of the fundamental mode of the second feed fiber reaches a minimum mode field diameter, and preferably the tapering is adiabatic to reduce coupling from the fundamental mode to higher order modes of the second feed fiber.

[0025] The second feed fiber may be tapered such that the core diameter of the second feed fiber at the output of the optical coupler is greater than a critical diameter at which the mode field diameter of the fundamental mode of the second feed fiber reaches a minimum mode field diameter, and preferably the taper is adiabatic to reduce coupling from the fundamental mode to higher order modes of the second feed fiber.

[0026] The second feed fiber may be a double-clad fiber, which has an outer cladding with a lower refractive index than the inner cladding, allowing optical radiation coupled from the core of the second feed fiber into its inner cladding to be guided by the inner cladding by total internal reflection.

[0027] The apparatus can include cladding mode strippers on the first and second feed fibers that can strip unwanted cladding modes from the first or second feed fibers, thereby reducing the possibility of optical damage to optical components and coatings caused by stray light.

[0028] The apparatus may include a cladding mode stripper on the multicore fiber, which may strip unwanted cladding modes from the multicore fiber, thereby reducing the possibility of stray light damaging other equipment or materials being processed.

[0029] The fiber bundle can have an input face at its larger diameter end that is angled θ with respect to its longitudinal axis. The angle θ can be 35°-55°. This ensures that the optical radiation reflected along the fiber bundle is reflected from the fiber bundle by total internal reflection. The angle θ is preferably 45°.

[0030] The apparatus can include a collimator at a distal end of the multi-core fiber, the collimator being connected to a laser processing head including a focusing lens, and the collimator and focusing lens can image the distal end of the multi-core fiber onto the processing material.

[0031] The apparatus may include a control unit connected to the first laser and the second laser and configured to control a power of laser radiation emitted by the first laser and the second laser, thereby independently controlling a power of laser radiation propagating along a first optical path to a first core of the multicore fiber and a power of laser radiation propagating along a second optical path to a second core of the multicore fiber.

[0032] A control unit may be connected to the mode converter to control the beam quality of the laser radiation propagating along the first or second optical path, and thereby to control the beam quality of the laser radiation emitted from the multicore fiber.

[0033] At least one of the first lasers and / or at least one of the second lasers can be connected to a mode converter that can convert a fundamental mode emitted by the first and / or second lasers into at least one higher-order mode that can propagate through the fiber bundle into the multicore fiber. This allows the beam quality of the laser radiation emitted by the multicore fiber to be adjusted before or during laser processing of the material.

[0034] The mode converter is an LP guided by the first feed fiber. 0,1 The mode is one or more LPs of the first feed fiber. p,1 It can be made to couple into an optical mode.

[0035] The device may include a mode converter acting on the multicore fiber.

[0036] The first core of the multicore fiber is an LP p,1The mode may be guided such that the modal content of the first beam (31) emitted by the first core (11) can be selected depending on the laser processing to be performed on the material.

[0037] The mode converter is an LP guided by a second feed fiber. p,1 The mode is one or more LPs of the second feed fiber. p,1 It can be made to couple into an optical mode.

[0038] The taper ratio of the fiber bundle is LP p,1 The mode can be prevented from being guided by the second feed fiber by a minimum taper diameter of the fiber bundle. The minimum taper diameter may be located before the connection between the fiber bundle and the output fiber. This allows the LP p,1 The aperture or divergence angle of the mode or the light rays emitted by the mode can be reduced before coupling into the multicore fiber.

[0039] The multicore fiber can have a taper that connects to the fiber bundle, allowing the fiber bundle to be connected to different beam feed cables with different core diameters.

[0040] The control unit can improve productivity in cutting, welding, and additive manufacturing applications by enabling automatic adjustment of the power and beam quality emitted from the first core, second core, and glass body of the multicore fiber while processing the material. Adjustments can be programmed according to the process being performed, and can be adjusted both before and during the process to account for changes in material thickness, for example.

[0041] The apparatus can include a light analyzer connected to the input of the optical coupler. The light analyzer can enable analyzing optical radiation reflected or emitted from a material to control laser processing of the material. The light analyzer can be used to detect when a material has been perforated, to monitor cutting speed during thin, thick, and variable thickness cuts, to monitor welding and brazing quality, and to monitor the quality of sintered layers of metal powder in additive manufacturing applications. The light analyzer can provide an output to a control unit. The control unit can use information provided by the light analyzer to control at least one of the first laser or lasers, the second laser or lasers, the optical switch (if provided), and the mode converter (if provided).

[0042] The apparatus may include a plurality of second feed fibers. The apparatus may include an optical switch having an input connected to the at least one first laser, a first output for the first feed fiber, and a second output for at least one of the second feed fibers, thus allowing first laser radiation emitted by the at least one first laser to be coupled into either or both of the first feed fiber and the at least one second feed fiber. The optical switch may be between the at least one first laser and the optical coupler.

[0043] The apparatus of the present invention can be used to form a first image by turning on at least one first laser, which can be modified using a mode converter acting on the first laser radiation and / or a mode converter acting on the multicore fiber to increase the beam parameter product of the first beam.

[0044] The first image is modified using a mode converter acting on the first laser radiation and / or a mode converter acting on the multicore fiber, primarily an LP 0,1 The first beam with modal content is mainly LPp,1 can be transformed into a beam with modal content p, where p is an integer.

[0045] The first beam is particularly useful for drilling and micromachining metals.

[0046] The apparatus of the present invention can be used to generate a second image by turning on at least one second laser. The second image can be modified using a mode converter acting on the second laser radiation and / or a mode converter acting on the multicore fiber to increase the beam parameter product of the second beam and / or homogenize the second image. The intensity of the second image can be increased by coupling the first laser radiation into a second feed fiber using an optical switch.

[0047] The second beam is particularly useful for cutting and welding.

[0048] The apparatus of the present invention can be used to form a third image by turning on the first laser and / or the second laser and operating at least one of the mode converters to couple the first and / or second feed fibers into unguided optical modes of the first and / or second feed fibers when tapered in the tapered fiber beam combiner. The third image can be modified using a mode converter acting on the first or second laser radiation and / or a mode converter acting on the multicore fiber to increase the beam parameter product of the third beam and / or homogenize the third image.

[0049] The apparatus of the present invention may be manufactured by a method comprising providing an apparatus for laser processing a material comprising at least one first laser, at least one second laser, an optical coupler, and a multicore fiber; each first laser is connected to an optical combiner via a first feed fiber; each second laser is connected to an optical combiner via a second feed fiber; the optical coupler connects the first feed fiber to a first core of the multi-core fiber and the second feed fiber to a second core of the multi-core fiber; the optical coupler provides a first optical path from the first laser to the first core of the multicore fiber; an optical coupler providing a second optical path from the second laser to a second core of the multicore fiber; the optical coupler comprises a fiber bundle tapered along its length; The power and beam quality of at least one of the first beam, the second beam, and the third beam emitted from the multicore fiber can be controlled in response to the laser processing to be performed on the material.

[0050] The method may be such that it includes one or more method steps for providing any of the above-mentioned components of the device.

[0051] A method of using the apparatus of the present invention may include providing the apparatus of the present invention and switching between a first image, a second image, and a third image depending on the laser processing to be performed on the material.

[0052] In a further aspect, the present invention provides a method for laser processing a material or adjusting a beam profile during material processing using the described method or apparatus. [Brief explanation of the drawings]

[0053] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1] FIG. 1 shows a diagram of an apparatus according to the invention. [Figure 2] FIG. 2 is a cross-sectional view of a fiber bundle having four first feed fibers arranged in a packed square configuration within the inner capillary and fifteen second feed fibers arranged in a ring around the inner capillary and within the outer capillary. [Figure 3]FIG. 3 is a diagram showing a multicore fiber having a first core and a second core. [Figure 4] FIG. 4 is a diagram illustrating the overlap of the first and second cores of the multicore fiber of FIG. 3 and the first and second feed fibers of FIG. [Figure 5] FIG. 5 shows a fiber bundle in which the inner capillary has a groove to aid in assembly of a second feed fiber into the bundle. [Figure 6] FIG. 6 shows a fiber bundle with three first feed fibers arranged in a hexagonal close-packed configuration. [Figure 7] FIG. 7 shows a fiber bundle with seven primary feed fibers arranged in a hexagonal close-packed configuration surrounded by an inner capillary and a ring of secondary feed fibers. [Figure 8] FIG. 8 is a diagram showing a multicore fiber having a first core, an inner core, and an outer core. [Figure 9] FIG. 9 is a diagram illustrating overlapping of the first and second feed fibers in FIG. 7 with the first core, inner ring core, and outer ring core of the multicore fiber in FIG. [Figure 10] FIG. 10 shows a fiber bundle including a single primary feed fiber and six secondary feed fibers arranged in a hexagonal close-packed configuration. [Figure 11] FIG. 11 is a diagram illustrating the overlap of the first and second feed fibers of FIG. 10 with the first and second cores of the multi-core fiber of FIG. [Figure 12] FIG. 12 illustrates the overlap of the first and second feed fibers of FIG. 10 with the first and second cores of the multicore fiber of FIG. 3, where the size of the second core is reduced and the second feed fiber is aligned in a circle within the ring of the second core. [Figure 13] FIG. 13 shows a fiber bundle including a low index ring to avoid coupling to the inner cladding of a multicore fiber. [Figure 14]FIG. 14 shows a fiber bundle including four fibers arranged in a square packing geometry, where the first and second feed fibers are arranged diagonally relative to each other, thus avoiding the use of the low index ring of FIG. [Figure 15] FIG. 15 is a diagram illustrating overlapping of the first and second feed fibers in FIG. 14 with the first and second cores of the multi-core fiber in FIG. [Figure 16] FIG. 16 shows a fiber bundle containing one central primary feed fiber and six secondary feed fibers arranged in a square packing geometry within a square capillary. [Figure 17] FIG. 17 is a diagram illustrating overlapping of the first and second feed fibers in FIG. 16 with the first and second cores of the multi-core fiber in FIG. [Figure 18] FIG. 18 shows a fiber bundle including a first feed fiber and two second feed fibers arranged side by side. [Figure 19] FIG. 19 is a diagram illustrating overlapping of the first and second feed fibers in FIG. 18 with the first and second cores of the multi-core fiber in FIG. [Figure 20] FIG. 20 shows the fiber bundle of FIG. 18, but with offset holes. [Figure 21] FIG. 21 shows the fiber bundle of FIG. 20 but with grooves in the capillary bores. [Figure 22] FIG. 22 shows a fiber bundle comprising a capillary having first and second holes, with a first feed fiber disposed within the first hole and a second feed fiber disposed within the second hole. [Figure 23] FIG. 23 illustrates the overlap of the first and second feed fibers of FIG. 22 with a multicore fiber having a first core aligned with a first hole and a second core aligned with a second hole. [Figure 24]FIG. 24 is a diagram illustrating how the mode field diameter of the fundamental mode of a typical first or second feed fiber decreases as the core diameter decreases until it reaches a minimum mode field diameter at the critical diameter. [Figure 25] FIG. 25 illustrates a device including a fiber bundle tapered along its length, including two first feed fibers and two second feed fibers separated by three spacing fibers. [Figure 26] FIG. 26 shows a fiber bundle including one first feed fiber and three second feed fibers separated by three spacing fibers. [Figure 27] FIG. 27 shows a squeezing mechanism that includes two periodic surfaces. [Figure 28] FIG. 28 is a diagram showing a squeezing mechanism that can deform an optical fiber into a spiral shape. [Figure 29] FIG. 29 shows the individual parts of the squeezing mechanism of FIG. [Figure 30] FIG. 30 is a diagram showing the fundamental LP0,1 mode of the first core of a multicore fiber. [Figure 31-35] 31-35 are diagrams illustrating the individual higher order modes of the first core of a multicore fiber. DETAILED DESCRIPTION OF THE INVENTION

[0054] FIG. 1 shows an apparatus for laser processing a material 29 comprising at least one first laser 15 , at least one second laser 16 , an optical coupler 3 and a multicore fiber 10 . Each first laser 15 is connected to an optical coupler 3 via a first feed fiber 1; Each second laser 16 is connected to an optical coupler 3 via a second feed fiber 2; The optical coupler 3 connects the first feed fiber 1 to a first core 11 of the multi-core fiber 10, and connects the second feed fiber 2 to a second core 12 of the multi-core fiber 10; the optical coupler 3 provides a first optical path 41 from the first laser 15 to the first core 11 of the multi-core fiber 10; the optical coupler 3 provides a second optical path 42 from the second laser 16 to the second core 12 of the multicore fiber 10; The optical coupler 3 comprises a fiber bundle 4 that tapers along its length.

[0055] The apparatus may include an optical switch 20 between the optical coupler 3 and at least one of the first lasers 15. The optical switch 20 has an input 21 connected to the first laser 15, a first output 22 connected to one of the first feed fibers 1, and a second output 23 connected to one of the second feed fibers 2, thus allowing the first laser radiation 18 emitted by the first laser 15 to be coupled into either or both of the first feed fiber 1 and the second feed fiber 2. The optical switch 20 may comprise free-space optical components such as lenses, mirrors, prisms, and wedges that direct the first laser radiation 18 to the first feed fiber 1 and / or the second feed fiber 2. Alternatively, the optical switch 20 may be based on a mechanism in which the optical fiber is bent, thus redirecting the first laser radiation 18 propagating along the optical fiber to the first feed fiber 1 or the second feed fiber 2.

[0056] The optical coupler 3 may comprise free-space optical components such as lenses, mirrors, prisms, and wedges. A free-space coupler capable of controlling and directing an input laser beam into the first core 11 and the second core 12 is described in U.S. Pat. No. 11,215,761, the contents of which are incorporated herein by reference.

[0057] The fiber bundle 4 that is tapered along its length may be fiber bundles 200, 60, 70, 100, 130, 140, 160, 180, 2000, 220, 251, which are described with reference to Figures 2, 6, 7, 10, 13, 14, 16, 18, 20, 22, and 25, respectively. The first feed fiber 1 and the second feed fiber 2 may be tapered individually and then assembled into a fiber bundle. Alternatively, the first feed fiber 1 and the second feed fiber 2 may be assembled into a bundle, and the entire bundle is tapered together to form the tapered input fiber bundle 4.

[0058] FIG. 2 shows a cross section of a fiber bundle 200 at or near its input 5, as shown with reference to FIG. 1. The fiber bundle 200 is tapered along its length. The fiber bundle 200 has two or more first feed fibers 1 and two or more second feed fibers 2. The first feed fibers 1 have a core 205 and a cladding 206. The second feed fibers 2 have a core 207 and a cladding 208. The fiber bundle 200 includes an outer capillary 201 and an inner capillary 202. The outer capillary 201 and the inner capillary 202 are made of glass. The glass is preferably silica or borosilicate glass. More preferably, the glass is fluorine-doped silica, also known as fluorosilicate. Fluorine-doped silica has a lower refractive index than silica. Silica is a preferred material for the claddings 206, 208 of the first and second feed fibers 1, 2; therefore, fluorine-doped silica helps guide optical radiation that may escape from the cores 205, 207 of the first and second feed fibers 1, 2 into their respective claddings 206, 208. Four first feed fibers 1 are disposed within the bore 203 of the inner capillary 202. Fifteen second feed fibers 2 are disposed within the bore 204 of the outer capillary 201. As shown in FIG. 2, the four first feed fibers 1 are arranged in a square configuration, referred to as a square close-packed structure. The second feed fibers 2 are arranged in a circular ring surrounding the first feed fibers 1. Other configurations are also possible.

[0059] The outer capillary 201 may comprise a glass body 223 surrounded by an optional glass cladding 224. The optional glass cladding 224 may have a refractive index less than that of the glass body 223 to guide optical radiation coupled into the glass body 223. The difference in refractive index between the glass body 223 and the glass cladding 224 is preferably sufficient to guide an optical mode that may be coupled from the first feed fiber 1 and the second feed fiber 2 as the optical mode propagates along the fiber bundle 4. Guiding is by total internal reflection.

[0060] The fiber bundle 200 is assembled, tapered, cleaved, and spliced into the multicore fiber 10 shown in Figure 3. The first feed fiber 1 and the second feed fiber 2 can be individually tapered and then assembled. Alternatively, the first feed fiber 1 and the second feed fiber 2 can be assembled into a bundle, and the entire bundle can be tapered together.

[0061] The multicore fiber 10 has a first core 11 and a second core 12 separated by an inner cladding 310. The inner cladding 310 is made of glass having a refractive index n4 that is lower than the refractive index n1 of the first core 11 and the refractive index n2 of the second core 12. The inner cladding 310 may be made of silica, borosilicate, or fluorine-doped silica. The first core 11 has a diameter 301, and the second core 12 has an inner diameter 302 and an outer diameter 303. The tapering is such that the first feed fiber 1 overlaps the first core 11 of the multicore fiber 10, and the second feed fiber 2 overlaps the second core 12 of the multicore fiber 10, as shown in FIG. 4. As the fiber bundle 200 tapers, optical radiation propagating from the core 205 of the first feed fiber 1 into the cladding 206 is thereby coupled into the first core 11 of the multicore fiber 10. Similarly, as the fiber bundle 200 tapers, optical radiation radiating from the core 207 into the cladding 208 of the second feed fiber 2 is thereby coupled into the second core 12 of the multicore fiber 10 .

[0062] The tapering may be such that the first feed fiber 1 and the second feed fiber 2 are substantially unstrained at their distal ends, as shown in Figure 4. Alternatively, the tapering in this and other embodiments of the invention may be such that the first feed fiber 1 and / or the second feed fiber 2 collapse together, reducing or eliminating the interstitial space between the fibers at their distal ends.

[0063] The multicore fiber 10 has a glass body 311 that surrounds the second core 12. The glass body 311 may be surrounded by an outer cladding 312. The outer cladding 312 may have a refractive index n6 that is less than the refractive index n3 of the glass body 311. The difference in refractive index n3-n6 is preferably large enough to allow optical radiation coupled into the glass body 311 from the fiber bundle 200 to be guided along the multicore fiber 10 by total internal reflection.

[0064] The glass body 311 may be separated from the second core 12 by a cladding 313 having a refractive index n5 that is lower than both the refractive index n3 of the glass body 311 and the refractive index n2 of the second core 12. Optical radiation coupled into the glass body 311 from the fiber bundle 200 may be guided along the glass body 311 by total internal reflection at the interface between the glass body 311 and the cladding 313 without coupling to the second core 12. The glass body 311 may have a refractive index n3 that is equal to or greater than the refractive index n2 of the second core 12.

[0065] The glass body 311 can have a refractive index n3 that is less than the refractive index n2 of the second core 12. If the cladding 313 between the second core 12 and the glass body 311 is omitted, optical radiation coupled from the fiber bundle 200 into the second core 12 can be guided along the second core 12 via total internal reflection from the boundary between the glass body 311 and the second core 12. However, optical radiation coupled from the fiber bundle 200 into the glass body 311 does not undergo total internal reflection at this boundary. Instead, if the refractive index n3 of the glass body 311 is higher than the refractive index n4 of the inner cladding 310, it can undergo total internal reflection at the boundary between the second core 12 and the inner cladding 310. However, if the refractive index n3 of the glass body 311 is the same as or lower than the refractive index n4 of the inner cladding 310, the optical radiation coupled into the glass body 311 from the fiber bundle 200 will propagate throughout the entire region inside the glass body and can be guided along the multicore fiber 10 by total internal reflection either at the boundary between the glass body 311 and the outer cladding 312 (if provided) or at the outer surface of the multicore fiber 10.

[0066] Thus, the selection of the refractive index n3 of the glass body 311, and whether or not to include the optional cladding 313, can be selected depending on the profile of the third image 36 shown with reference to Figure 1. The third image 36 is formed from optical radiation propagating along the glass body 311 and whether or not this optical radiation is allowed to propagate through the first and second cores 11, 12. If the third image 36 is desired to be an image of only the glass body 311, and not the first and second cores 11, 12, a refractive index profile similar to that shown in Figure 3 can be used.

[0067] Advantageously, the multicore fiber 10 may be tapered before splicing into the fiber bundle 4 of FIG. 1 . This allows the dimensions of the fiber bundle 4 to be independent of the core diameter 301 of the multicore fiber 10. This allows the multicore fiber 10 to have a larger diameter 301 of the first core 11, resulting in an increased stimulated Raman scattering threshold. The increased stimulated Raman scattering threshold is advantageous because it allows higher optical power to be transmitted along the first core 11 before the onset of wavelength conversion caused by Raman scattering. A larger first core 11 may also reduce bending losses of optical radiation propagating along the multicore fiber 10. The multicore fiber 10 may be tapered at its distal end 13, which may reduce the diameter 301 of the first core 11. The degree of tapering at its distal end 13, and therefore the diameter 301 of the first core 11, may be selected depending on the laser processing to be performed on the material 29.

[0068] The multicore fiber 10 of FIG. 1 may comprise two fibers, a high-power coupler output fiber and a process fiber (not shown), which are coupled together. Providing two fibers is advantageous because it simplifies repair and maintenance in the factory. The coupling may include a lens or a fusion splice. The fiber may be tapered at the fusion splice to maintain or modify beam quality. The high-power coupler output fiber and the process fiber may be of the same design as each other, or may be of different designs.

[0069] 1, the multicore fiber 10 may have an end cap 40, which may be made of fused silica, at its distal end 13. The end cap 40 protects the distal end 13 of the multicore fiber 10 from damage by the high-intensity laser radiation used in laser material processing. The end cap 40 may be connected to the multicore fiber 10 by a fusion splice.

[0070] The apparatus of the present invention may include a collimator 7 at the distal end 13 of the multicore fiber 10, which is connected to a laser processing head 8 that includes a focusing lens 9. The collimator 7 may be a lens. The multicore fiber 10 may emit a first beam 31 from the first core 11 and a second beam 32 from the second core 12. The multicore fiber 10 may also emit a third beam 33 from its glass body 311. The collimator 7 and focusing lens 9 form an image of the distal end 13 of the multicore fiber 10 on or near the surface 30 of the material 29. The image includes a first image 34 of the first core 11 formed from the first beam 31 and a second image 35 of the second core 12 formed from the second beam 32. The image may also include a third image 36 of the glass body 311 imaged by the third beam 33. The third beam 33 is generated when optical radiation is coupled into the glass body 311 from the first feed fiber 1 and / or the second feed fiber 2. The third beam 33 therefore also includes optical radiation that is or may be propagating within the first and second cores 11, 12 and inner cladding 310 of the multicore fiber 10 shown in Figure 3. The third image 36 is shown as a large solid circle, but may also include structures within it.

[0071] In certain applications, such as cutting and welding, it is desirable to separate the first core 11 from the second core 12 with the inner cladding 310 so that the second image 35 on the surface 30 of the material has an inner diameter that is larger than the outer diameter of the first image 34. However, there are also applications in cutting and welding applications, as well as in sintering metal powders (additive manufacturing), where it is desirable for the separation to be very small, for example less than 10 μm, preferably less than 1 μm. There may be cases where no separation at all is preferred. Advantageously, the width 304 of the inner cladding 310 shown with reference to FIG. 3 may be reduced in thickness to zero at the distal end 13 of the multicore fiber 10. The reduction in width 304 can be achieved, for example, by dopant diffusion while heating the multicore fiber 10 before or during fusion splicing the end cap 40 and / or before or during tapering the multicore fiber 10 at its distal end 13. The diffusing dopant may be fluorine, which may diffuse into one or more of the first core 11, the second core 12, and the end cap 40. The zero width 304 allows the second image 35 on the surface 30 of the material to have an inner diameter equal to the outer diameter of the first image 34.

[0072] Alternatively or additionally, a reduction in width 304 may be provided at the connection between the multicore fiber 10 and the fused taper beam combiner 4. The reduction in width 304 can be achieved by dopant diffusion while heating the multicore fiber 10, for example, before or during fusion splicing of the multicore fiber 10 to the fused taper beam combiner 4. The dopant may be fluorine, which may diffuse into one or more of the first core 11, the second core 12, and the fused taper beam combiner 4. The reduction in width 304 may be provided in a multicore fiber 10 that is tapered at the end that is connected to the fiber bundle 4, and may be provided in a multicore fiber 10 that is not tapered at the end that is connected to the fiber bundle 4. The reduction in width 304 makes it possible to select a multicore fiber 10 that has a larger width 304 for the same coupling loss. Increasing the width 304 reduces cross-coupling between the optical mode propagating in the first core 11 and the mode propagating in the second core 12.

[0073] The number of first and second lasers 15, 16, the power of the first laser radiation 18 and the second laser radiation 19, and the cross-sectional area of the first core 11 and the second core 12 of the multicore fiber 10 may be selected so that the optical intensities of the first and second images 34 and 35 are equal to each other. This may be advantageous in applications requiring equal optical intensity (power per unit area) on the surface 30 of the material 29 when switching between the first image 34 and the second image 35, or when switching either a single first image 34 or a single second image 35 to a composite image including both the first and second images 34, 35.

[0074] Prior to tapering the first and second feed fibers 1 and 2, the first feed fiber 1 may have a core diameter 209 of 13.5 μm and a cladding diameter 210 of 200 μm. The second feed fiber 2 may also have a core diameter 211 of 13.5 μm and a cladding diameter 212 of 200 μm. The first core 11 of the multicore fiber 10 may have a core diameter 301 of 100 μm. The second core 12 may have an inner core diameter 302 of 125 μm and an outer core diameter 303 of 250 μm. The fiber bundle 200 may have a taper ratio of 5. The taper ratio is defined as the diameter at the input 5 of the fiber bundle 4 divided by the diameter at the output 6 of the fiber bundle 4. The fiber bundle 200 allows for the use of up to four first lasers 15 and up to 15 second lasers 16 in the device shown in FIG. 1 . This design therefore allows for power scaling, allowing the number of first and second lasers 15, 16 to be selected depending on the specific laser processing conditions. Other numbers of first and second feed fibers 1, 2 can be selected with the same or different core and cladding diameters. Other core diameters 301, 302, 303 can also be selected. For example, industry-standard power cables often have cores with diameters of 25 μm, 50 μm, 100 μm, 150 μm, 200 μm, or 300 μm, and these core diameters can be selected for the core diameter 301 of the first core 11 of the multicore fiber 10. First and second feed fibers 1, 2 that are not connected to, or are not intended to be connected to, a laser may be replaced with a glass tube or rod without a core. The glass tube or rod may be made of silica.

[0075] Advantageously, the inner capillary 202 can have a groove 51 on its outer surface, as shown in FIG. 5 . The groove 51 can aid in assembling the fiber bundle 200 when assembling a bundle having both multiple fibers and one or more inner capillaries. This is because the fibers can be difficult to precisely position relative to one another and can fall out of alignment. The groove 51 can be partially circular, as shown, or triangular or U-shaped. Other shapes are also possible. The groove 51 can be made, for example, by machining the inner capillary 202 with a carbon dioxide laser or by acid etching. Preferably, the groove 51 is made by forming it in a larger-diameter glass capillary with a carbon dioxide laser. The larger-diameter glass capillary is then drawn to size by applying heat, preferably in an optical fiber draw tower used for optical fiber manufacturing. Alternatively, or additionally, the groove can be formed in the inner surface of the inner capillary 202 and / or the inner surface of the outer capillary 201.

[0076] FIG. 6 shows an example of a fiber bundle 60 in which the first feed fibers 1 are arranged in a triangular shape. The fiber bundle 60 has three first feed fibers 1. The fiber bundle 60 may have grooves 51 on the surface of the inner capillary 202 and / or the surface of the outer capillary 201, as described with reference to FIG. 5, to assist in assembling the bundle. The same first feed fibers 1 and second feed fibers 2 may be used as described with reference to FIG. 2. The first core 11 of the multicore fiber 10 may have a core diameter 301 of 75 μm. The second core 12 may have an inner core diameter 302 of 100 μm and an outer core diameter 303 of 400 μm. The fiber bundle 60 may have a taper ratio of 6. Other dimensions may also be used.

[0077] 7 shows an example of a fiber bundle 70 in which the feed fibers are arranged in a hexagonal, close-packed configuration. Fiber bundle 70 has a central feed fiber 71 aligned with the central axis of fiber bundle 70 surrounded by feed fibers 72. Fiber bundle 70 may include grooves 51 as described with reference to FIG. 5.

[0078] The fiber bundle 70 may be tapered to the multicore fiber 10 of Figure 3 such that the central feed fiber 71 and feed fiber 72 are coupled to the first core 11 of the multicore fiber 10. In this configuration, the central feed fiber 71 and feed fiber 72 are the first feed fiber 1 described with reference to Figure 1. Preferably, the tapering is adiabatic to reduce coupling between the fundamental mode and higher order modes.

[0079] Alternatively, the fiber bundle 70 can be connected to a multicore fiber 80 of FIG. 8 having a first core 11 surrounded by two second cores formed by an inner ring core 81 and an outer ring core 82. The first core 11 and the inner ring core 81 are separated by a cladding 83. The inner ring core 81 and the outer ring core 82 are separated by a cladding 84. The central feed fiber 71 of FIG. 7 is the first feed fiber 1 of FIG. 1 and is aligned with the first core 11 as shown with reference to FIGS. 8 and 9. The feed fiber 72 is part of the second feed fiber 2 of FIG. 1 and is aligned with the inner ring core 81 as shown with reference to FIG. 9. The other second feed fiber 2 of FIG. 7 is aligned with the outer ring core 82 as shown with reference to FIG. 9. The hexagonal, close-packed configuration of the central feed fiber 71 and feed fibers 72 of the fiber bundle of FIG. 7 avoids the need for an additional capillary separating the central feed fiber 71 from the feed fibers 72. This is advantageous because it is possible to have a smaller diameter and thinner inner ring core 81 which can reduce the beam parameter product and therefore increase the brightness of the light beam emerging from the inner ring core 81. The first and second lasers 15, 16 are individually controlled to cause light radiation to be emitted from the device from one or more of the first core 11, the inner ring core 81 and the outer ring core 82.

[0080] A high-quality beam with the same angular divergence as a low-quality beam can be focused to a smaller diameter beam waist. Therefore, the high-quality beam has a beam parameter product, the beam waist, related to the product of the focused beam waist and the divergence. A high-quality beam with the same optical power as a low-quality beam has a higher brightness.

[0081] 8 can be designed to have a beam with a relatively low beam parameter product emerging from the first core 11, a beam with a relatively low beam parameter product emerging from the inner ring core 81, and a beam with an even higher beam parameter product emerging from the outer ring core 82. The beams emerging from the first core 11 and the inner ring core 81 are useful for keyhole welding and cutting sheet metals of different thicknesses, and the beam emerging from the outer ring core 82 is useful for welding.

[0082] The claddings 83 and 84 can have the same or different refractive indices. The refractive index of the optional outer cladding 312 may be less than the refractive index of the claddings 83 and 84 so that the multicore fiber 80 can direct optical radiation coupled into the cladding 83 and / or the cladding 84 by total internal reflection. The function of the glass body 311 will be described with reference to Figure 3.

[0083] 10 shows an example of a fiber bundle 100 including a single primary feed fiber 1 and six secondary feed fibers 2. The primary feed fiber 1 and secondary feed fibers 2 are arranged in a hexagonal, closed-pack configuration. The fiber bundle 100 has an outer capillary 201 but does not have an inner capillary 202 as described with reference to FIG. 2.

[0084] The first feed fiber 1 may be a double-clad fiber having an outer cladding 101. The outer cladding 101 may have a refractive index lower than the refractive index of the cladding 206. Alternatively or additionally, the second feed fiber 2 may be a double-clad fiber having an outer cladding 102. The outer cladding 102 may have a refractive index lower than the refractive index of the cladding 208. The outer cladding 101 and / or the outer cladding 102 may have a thickness 103.

[0085] FIG. 11 shows how the first and second feed fibers 1 and 2 of FIG. 10 can be coupled to the multicore fiber 10 of FIG. 3. The diameter 301 of the first core 11, the inner and outer diameters 302 and 303 of the second core 12, and the taper ratio of the fiber bundle 100 are selected to ensure that the core 205 of the first feed fiber 1 and the core 207 of the second feed fiber 2 overlap with the first and second cores 11 and 12, respectively, of the multicore fiber 10, but do not overlap with the inner cladding 310. Avoiding overlap reduces splice loss. Preferably, the first and second feed fibers 1 and 2 are weakly tapered so that their fundamental modes do not significantly expand from their respective cores. Higher-order modes can undergo core expansion, thus allowing higher-order modes to be coupled to modes guided by the glass body 223 of the fiber bundle 100. Coupling to the glass body 223 may be increased if the first feed fiber 1 and / or the second feed fiber 2 are single-clad fibers without an outer cladding 101, 102. The first core 11 of the multicore fiber 10 may have a core diameter 301 of 25 μm. The second core 12 may have an inner core diameter 302 of 40 μm and an outer core diameter 303 of 100 μm. The fiber bundle 100 may have a taper ratio of 8. Other dimensions may be used.

[0086] Figure 12 shows an alternative configuration of the first feed fiber 1 and second feed fiber 2 of Figure 10 coupled to the multicore fiber 10 of Figure 3. The multicore fiber 10 is designed so that the cores of the second feed fiber 2 are approximately aligned on a circle 121 having a diameter equal to the average of the inner diameter 302 and outer diameter 303 of the second core 12. The difference between the outer diameter 302 and the inner diameter 303 is smaller in Figure 12 than in Figure 11. The reduced size of the second core 12, together with the central coupling of the second feed fiber 2, results in a lower beam parameter product (higher beam quality) of the laser radiation emitted by the second core 12. This is advantageous for applications requiring higher beam quality, such as cutting or keyhole welding.

[0087] Referring again to Figure 11, the first feed fiber 1 and / or the second feed fiber 2 may be double-clad fibers with outer claddings 101, 102. The diameter 301 of the first core 11, the inner and outer diameters 302, 303 of the second core 12, and the taper ratio of the fiber bundle 100 are selected to ensure that the cladding 206 of the first feed fiber 1 and the cladding 208 of the second feed fiber 2 overlap the first core 11 and the second core 12, respectively, of the multicore fiber 10, but do not overlap the inner cladding 310. Avoiding overlap reduces splice loss. Preferably, the first feed fiber 1 and the second feed fiber 2 are strongly tapered so that their fundamental modes extend from their respective cores 205, 207 and are then guided against their respective outer claddings 101, 102. The fundamental mode has a larger mode field diameter or spot size than when the first and second feed fibers 1 and 2 are weakly tapered. The fundamental mode also diverges less when launched into the multicore fiber 10 when the first and second feed fibers 1 and 2 are strongly tapered. Smaller divergence can reduce the beam parameter product of the first and second beams 31 and 32 launched from the multicore fiber 10, thus improving beam quality, which can be advantageous for applications requiring high beam quality, such as cutting thin sheets of metal or keyhole welding. Higher-order modes also experience mode field expansion and may be guided relative to the outer cladding 101, 102. However, if the outer cladding 101, 102 is sufficiently thin, e.g., less than 5-10 μm, or other thicknesses are possible, or is absent altogether, the tapering allows higher-order modes of the first and second feed fibers 1 and 2 to be coupled into modes guided by the glass body 223 of the fiber bundle 100.

[0088] The core of the second feed fiber 2 in Figure 11 is not aligned with the circle 121 shown with reference to Figure 12. This is advantageous when it is desired that the laser radiation emitted by the second core 12 has a relatively large beam parameter product. Off-center launch into a relatively large area annular core typically launches many optical modes with different radial mode numbers, increasing the beam parameter product of the resulting laser radiation.

[0089] The fiber bundle of Figure 10 is advantageous because it is relatively easy to assemble the first and second feed fibers 1 and 2 with an optimal closed-packing geometry. However, it can be difficult to ensure precise alignment of the first and second cores 11, 12 of the multicore fiber 10 so that optical radiation is not coupled into the inner cladding 310. This can be solved by introducing a low-index ring 131, as shown in the fiber bundle 130 of Figure 13, which has a refractive index smaller than that of the cladding 206 of the first feed fiber 1. The low-index ring 131 can be provided as one or more of: (i) the inner capillary into which the first feed fiber 1 is inserted; (ii) the outer cladding of the first feed fiber 1; and (iii) the outer cladding of the second feed fiber 2. Coupling from the first and second feed fibers 1 and 2 to the inner cladding 310 can be minimized by optimizing the relative dimensions of the first and second feed fibers 1 and 2, the low-index ring 131, the taper ratio of the fiber bundle 100, and the first and second cores 11, 12 of the multicore fiber 10. Referring to Figures 3 and 13, after tapering, the low-index ring 131 preferably has an inner diameter 132 smaller than the diameter 301 of the first core 11 and an outer diameter 133 larger than the inner diameter 302 of the second core 12. The low-index ring 131 may comprise borosilicate glass or fluorine-doped silica.

[0090] FIG. 14 shows a fiber bundle 140 having four fibers assembled in an outer capillary 201. As shown in FIG. 15, one of these fibers can be used as the first feed fiber 1 by radially offsetting the bundle when splicing into the multicore fiber 10 of FIGS. 1 and 3 . The diagonally opposite fiber is then the second feed fiber 2, and the remaining fibers are spacing fibers 141. If the core of the spacing fiber 141 overlaps with the second core 12 rather than the inner cladding 310, the spacing fiber 141 can be used as an additional second feed fiber 2. However, if the core of the spacing fiber 141 overlaps with the inner cladding 310, the spacing fiber 141 can be made of pure silica and its core can be omitted. This bundle geometry is beneficial in that it allows for the fabrication of separate / non-adjacent first and second feed fibers 1 and 2 without the need to introduce an internal capillary into the bundle assembly. Therefore, the geometry of the bundle can be better matched to the geometry of the multicore fiber 10. It can therefore improve the transmission efficiency of the coupler without the additional cost and complexity associated with using an inner capillary separating the first feed fiber 1 from the second feed fiber 2. The same first and second feed fibers 1 and 2 can be used as described with reference to FIG. 2. The first core 11 of the multicore fiber 10 may have a core diameter 301 of 100 μm. The second core 12 may have an inner core diameter 302 of 120 μm and an outer core diameter 303 of 400 μm. The fiber bundle 140 can have a taper ratio of 6. Other dimensions can also be used.

[0091] FIG. 16 shows a fiber bundle 160 including one first feed fiber 1, four second feed fibers 2, and four spacing fibers 141. The outer capillary 161 is a square capillary. FIG. 17 shows the overlap of the first feed fiber 1, the second feed fibers 2, and the four spacing fibers 141 when the fiber bundle 160 is connected to the multicore fiber 10 of FIG. 3. Here, there are four second feed fibers 2 that can be coupled to the second cores 12, each of which allows coupling to the inner cladding 310 to be avoided. Depending on the dimensions of the first cores 11 and the second cores 12, the four spacing fibers 141 in the bundle may not be used, or the spacing fibers 141 can be used as additional second feed fibers 2 if the cores of the spacing fibers 141 overlap with the second cores 12 but not with the inner cladding 310. This geometry of the fiber bundle 160 is beneficial in that it creates a first feed fiber 1 and four second feed fibers 2 that are spatially separated from one another without the need to introduce an internal capillary into the bundle assembly. The bundle geometry can better match the geometry of the multicore fiber 10, thus improving the coupler's transmission efficiency without the added cost and complexity associated with using additional capillaries. Providing four second feed fibers 2 provides up to four times the power handling capability compared to the fiber bundle 140 of FIG. 14 , thus providing power scaling. The same first feed fiber 1 and second feed fiber 2 may be used as described with reference to FIG. 2 . The first core 11 of the multicore fiber 10 may have a core diameter 301 of 100 μm. The second core 12 may have an inner core diameter 302 of 120 μm and an outer core diameter 303 of 400 μm. The fiber bundle 160 may have a taper ratio of 6. Other dimensions may also be used.

[0092] Figure 18 shows a fiber bundle 180 in which a first feed fiber 1 and a second feed fiber 2 are arranged so that the first feed fiber 1 is on one side of the second feed fiber 2 and is arranged against the wall of the hole 181 of the capillary 201. Figure 19 shows how the first feed fiber 1 and the second feed fiber 2 overlap with the first core 11 and second core 12 of the multicore fiber 10 of Figure 3, the arrangement shown requiring a radially offset connection to the multicore fiber 10.

[0093] 20 shows a fiber bundle 2000 comprising a capillary 2001 with an offset hole 2002. The offset hole 2002 is offset by an amount that ensures that the outside of the capillary 2001 is concentric with the outside of the multicore fiber 10 while ensuring that the first and second feed fibers 1 and 2 are aligned with the first and second cores 11, 12. The hole 2002 is preferably non-circular to aid in rotational alignment during splicing to the multicore fiber 10.

[0094] Hole 181 in Figure 18 and hole 2002 in Figure 20 may include grooves 51 as shown in Figure 21. Grooves 51 may be provided by ultrasonic drilling, liquid etching, or vapor etching of the glass capillary prior to reducing the diameter of the capillary in the fiber draw tower.

[0095] As described with reference to Figure 2, the same first feed fiber 1 and second feed fiber 2 can be used in the fiber bundles 180 and 2000. The first core 11 of the multicore fiber 10 can have a core diameter 301 of 25 µm. The second core 12 may have an inner core diameter 302 of 40 µm and an outer core diameter 303 of 100 µm. The fiber bundle 180 may have a taper ratio of 6. Other dimensions can also be used.

[0096] 22 shows a fiber bundle 220 comprising a capillary 225 having a first hole 221 and a second hole 222. A first feed fiber 1 is disposed within the first hole 221, and a second feed fiber 2 is disposed within the second hole 222. The capillary 225 comprises a glass body 223 having first and second holes 221, 222 surrounded by an optional glass outer cladding 224. Advantageously, the refractive index of the outer cladding 224 may be smaller than the refractive index of the glass body 223, allowing the glass body 223 to guide light that may be coupled from the first feed fiber 1 and / or the second feed fiber 2 into the glass body 223 as the light propagates through the fiber bundle 220. The glass body 223 may alternatively guide air. The fiber bundles 200, 60, 70, 100, 130, 140, 160, 180, 2000 and 251 described with reference to Figures 2, 6, 7, 10, 13, 14, 16, 18, 20 and 25 may have a glass outer cladding 224 for guiding light that may be coupled from the first feed fiber 1 and / or the second feed fiber 2.

[0097] The fiber bundle 220 is assembled, tapered, cleaved, and spliced into a multicore fiber 230 shown in FIG. 23 . The first feed fiber 1 and the second feed fiber 2 can be individually tapered and then assembled. Alternatively, the first feed fiber 1 and the second feed fiber 2 can be assembled into a bundle, and the entire bundle can be tapered together. The multicore fiber 230 has a glass body 311. The glass body 311 is made of glass having a refractive index lower than that of both the first core 11 and the second core 12. The glass body 311 may be made of silica or fluorine-doped silica. The glass body 311 may be surrounded by an outer cladding 312 having a refractive index lower than that of the glass body 311. The outer cladding 312 may be glass. 22 , as the fiber bundle 220 tapers, optical radiation that radiates from the core 205 of the first feed fiber 1 into the cladding 206 is thereby coupled into the first core 11 of the multicore fiber 10. Similarly, optical radiation that radiates from the core 207 of the second feed fiber 2 into the cladding 208 as the fiber bundle 220 tapers is thereby coupled into the second core 12 of the multicore fiber 230. As optical radiation propagates along the fiber bundle 220, optical radiation that is coupled into the glass body 223 from the first feed fiber 1 and / or the second feed fiber 2 is thereby coupled into the glass body 311 of the multicore fiber 230. 3 and 8 may also have an outer cladding 312 for guiding optical radiation that may be coupled from the first feed fiber 1 and / or the second feed fiber 2. If the outer cladding 312 has a refractive index lower than that of the glass body 311, this optical radiation may be guided along the glass body 311 to the distal end 13 of the multicore fiber 10, 80 or 230, as shown in FIG.

[0098] 1, the first laser 15, or at least one of the first lasers 15 if multiple first lasers 15 are used, may comprise a single-mode laser that emits a single transverse or fundamental optical mode. Alternatively or additionally, one or more of the first lasers 15 may comprise a multimode laser that emits multiple transverse optical modes.

[0099] The second laser 16, or at least one of the second lasers 16 if multiple second lasers 16 are used, may comprise a single mode laser or a multimode laser.

[0100] The first laser 15 and the second laser 16 may each have an output fiber 38 that is fusion spliced at splices 37 to the first feed fiber 1 and the second feed fiber 2. The first feed fiber 1 and the second feed fiber 2 may be single mode or multimode fibers.

[0101] Each first laser 15 may be a single-mode laser, and the output fiber 38 connected to the first laser 15 may be either a single-mode fiber or a multimode fiber, with the splice 37 being such that the fundamental mode of the output fiber 38 is coupled to the fundamental mode of the first feed fiber 1. Tapering the output fiber 38 and / or the first feed fiber 1 at the splice 37 can be used to match the profiles of the fundamental modes of the output fiber 38 and the first feed fiber 1 at the splice 37, thereby increasing the coupling efficiency of the fundamental mode when there is a mismatch in mode field diameter. Preferably, the tapering is adiabatic to reduce coupling from the fundamental mode of the first feed fiber 1 to higher-order modes of the first feed fiber 1. Configuring the first feed fiber 1 to propagate substantially in its fundamental mode through the fiber bundle 4 can reduce optical loss and increase the brightness of the first beam 31. This is advantageous for applications requiring high brightness, such as cutting and keyhole welding.

[0102] When the second laser 16 is a single-mode laser, the output fiber 38 connected to the second laser 16 can be either a single-mode fiber or a multimode fiber, and the splice 37 couples the fundamental mode of the output fiber 38 to the fundamental mode of the second feed fiber 2. Tapering the output fiber 38 and / or the second feed fiber 2 at the splice 37 can be used to match the profiles of the fundamental modes of the output fiber 38 and the second feed fiber 2 at the splice 37, thereby increasing the coupling efficiency of the fundamental mode when there is a mismatch in mode field diameter. Preferably, the tapering is adiabatic to reduce coupling from the fundamental mode of the second feed fiber 2 to higher-order modes of the second feed fiber 2. Configuring the second feed fiber 2 to propagate substantially in its fundamental mode through the fiber bundle 4 can reduce optical loss and increase the brightness of the second beam 32. This is advantageous for applications requiring high brightness, such as cutting and keyhole welding.

[0103] The first and second lasers 15 and 16 can be diode lasers, fiber lasers, disk lasers, or solid-state lasers. Preferably, the first and second lasers 15 and 16 are fiber lasers. The first and second lasers 15 and 16 may be continuous-mode, quasi-continuous-mode, or pulsed lasers. The first and second lasers 15 and 16 may be master oscillator power amplifier lasers. At least one of the first and second lasers 15 and 16 may emit visible laser radiation that can be used to align at least one of the collimator 7, processing head 8, and focusing lens 9 with the material 29 being processed. The first and second lasers 15 and 16 are preferably kilowatt lasers capable of emitting an average power of 1 kW to 10 kW. At least one of the first and second lasers 15 and 16 may emit infrared radiation. The infrared radiation may be in the wavelength range of 700 nm to 2500 nm, preferably 1000 nm to 1100 nm. At least one of the first and second lasers 15, 16 can emit visible light, which may be in the wavelength range of 400 nm-650 nm, more preferably in the wavelength range of 500 nm-560 nm.

[0104] The first laser 15, or at least one of the first lasers 15 if multiple first lasers 15 are used, may be connected to a mode converter 17. Alternatively or additionally, the second laser 16, or at least one of the second lasers 16 if multiple second lasers 16 are used, may be connected to the mode converter 17. The mode converter 17 may be an internal component of the first laser 15 or the second laser 16. The mode converter can couple optical modes propagating along the optical fiber and can be used to control the beam quality or intensity of the first laser radiation 18 emitted by the first laser 15 and the second laser radiation 19 emitted by the second laser 16. The mode converter can be made using a mechanism to compress or bend the optical fiber, as taught, for example, in U.S. Patent Application Publication No. 2019 / 262949 and U.S. Patent No. 10,295,845. The optical fiber can be a step-index fiber or a graded-index fiber that can be connected to a step-index fiber at its output. The amount of modal coupling provided by the modal converter 17 can be controlled by an actuator (not shown).

[0105] The mode converter 17 may couple the fundamental mode to a single higher-order mode in the first feed fiber 1 or the second feed fiber 2. Such a mode converter is taught in U.S. Patent Application Publication No. 2021 / 0362269. The single higher-order mode can be experimentally selected by selecting the optical mode that is coupled from the first feed fiber 1 or the second feed fiber 2 as the optical mode propagates along the fiber bundle 4, and is then guided by the glass body 223 of the fiber bundle 4 and the glass body 311 of the multicore fiber 10. Such a higher-order mode may be a mode that experiences cutoff in the first feed fiber 1 or the second feed fiber 2 as its core diameter decreases along the taper. The cutoff occurs because the smaller diameter core is too small to guide the higher-order mode. The higher-order mode can be guided by the glass body 223 due to its large diameter.

[0106] The higher order modes may be coupled to other higher order modes within the fiber bundle 4 .

[0107] The mode converter 17 may couple the fundamental mode to multiple higher order modes of the first feed fiber 1 or the second feed fiber 2. The amount of coupling can be selected experimentally by ensuring that the mode converter couples only to higher order modes that can propagate along the fiber bundle 4 and glass body 311 of the multicore fiber 10 without loss.

[0108] As shown in FIG. 1, the device of the present invention may also comprise a mode converter 2511, as described with reference to FIG. 25, for coupling optical modes propagating in at least one of the first core 11 and the second core 12 of the optical fiber 10.

[0109] The device of the present invention may include a cladding mode stripper 24 in at least one of the first feed fibers 1 and in at least one of the second feed fibers 2 .

[0110] The device of the present invention may include a cladding mode stripper 39 in the multicore fiber 10 .

[0111] The cladding mode strippers 24 and 39 may each be configured such that the fiber is surrounded by a polymer with a higher refractive index than its outer glass cladding. Alternatively or additionally, the cladding mode strippers 24 and 39 may comprise grooves cut or etched into the outer glass cladding of the fiber. A laser-etched cladding mode stripper is described by Imen et al. (Opt. Lett 15(17), p950-2, 1990). A cladding mode stripper may remove light propagating along the cladding of an optical fiber, which may cause heating or optical problems in downstream components such as optical beam combiners or beam delivery optics.

[0112] During operation, each first laser 15 may be a single-mode laser, and the first laser radiation 18 may propagate in the fundamental mode of the output fiber 38. The first feed fiber 1 may be a multimode fiber, e.g., a fiber supporting a fundamental, second-order, and third-order mode. The fiber may support modes with mode orders higher than three. Each splice 37 is preferably configured so that the fundamental mode of the output fiber 38 is coupled to the fundamental mode of the first feed fiber 1. The fundamental mode of the first feed fiber 1 propagates along the core 205 of the first feed fiber 1 through the fiber bundle 4 and is coupled to the first core 11 of the multicore fiber 10, from which it is directed to the first image 34 on the surface 30 of the material 29. Turning each of the first lasers 15 on and off turns the first image 34 on and off. Varying the output power from all or some of the first lasers 15 changes the intensity of the first image 34, and can also change the beam quality and, therefore, the size of the first image 34.

[0113] The mode converter 17 at the output of the first laser 15 can be operated to couple at least one higher-order mode into the first feed fiber 1. These higher-order modes can propagate through the fiber bundle 4 and initiate higher-order modes within the first core 11. A light beam with a high proportion of higher-order modes will be less bright than a light beam with a low proportion of higher-order modes. The mode converter 17 can therefore be used to control the brightness, and therefore the beam quality and size, of the first image 34.

[0114] The first feed fiber 1 may be such that, when tapered, higher order modes couple from the core 205 of the first feed fiber 1 into its cladding 206. Such coupling into cladding modes can increase the brightness, beam quality, and size variation of the first image 34 that can be achieved with the mode converter 17.

[0115] The fiber bundle 4 and the first feed fiber 1 may be such that, when tapered, certain higher order modes couple from the core 205 of the first feed fiber 1 to the glass body 311. For example, the LP p,qA mode (described with reference to Figures 30-35) cuts off at the taper if (i) the azimuthal mode number p is greater than the normalized frequency V of the first feed fiber 1 divided by the taper ratio, or (ii) the radial mode number q is greater than the normalized frequency V of the first feed fiber 1 divided by the product of the taper ratio and π. In the case of a double-clad fiber with a fluorine-doped outer cladding, the inner cladding acts as the core, and its radius should be used to calculate the normalized frequency V. Alternatively, or additionally, the mode that cuts off at the taper and thus couples to the glass body 311 can be found using beam propagation theory or through experimentation. Thus, the mode converter 17 can switch the laser radiation emitted by the multicore fiber 10 from the first beam 31 to the third beam 33 by coupling from the core 205 of the first feed fiber 1 to one or more higher-order modes that couple to the glass body 311. The third beam 33 may have a beam parameter product that is 10-100 times larger than the beam parameter product of the first beam 31. Larger variations in the beam parameter products are also possible.

[0116] By varying the mode order of the first laser radiation 18 coupled into the first feed fiber 1 using the mode converter 17, a large variation in the brightness, beam quality and dimensions of the achievable first image 34 and third image 36 is provided.

[0117] Similarly, the second laser 16 may be a single-mode laser, and the second laser radiation 19 may propagate in the fundamental mode of the output fiber 38. The second feed fiber 2 may be a multimode fiber, e.g., a fiber supporting the fundamental, second, and third modes. The fiber may support modes with mode orders higher than three. The splice 37 is preferably such that the fundamental mode of the output fiber 38 is coupled to the fundamental mode of the second feed fiber 2. This propagates along the core 207 of the second feed fiber 2, through the fiber bundle 4, and is coupled to the second core 12 of the multicore fiber 10, from where it is directed to a second image 35 on the surface 30 of the material 29. Turning each of the second lasers 16 on and off turns the second image 35 on and off. Varying the output power from all or some of the first lasers 15 changes the intensity of the first image 34. Varying the output power from all or some of the second lasers 16 changes the intensity of the second image 35.

[0118] The mode converter 17 at the output of the second laser 16 can be operated to emit at least one higher-order mode into the second feed fiber 2. These higher-order modes can propagate through the fiber bundle 4 and initiate higher-order modes in the second core 12. A light beam with a high proportion of higher-order modes will be less bright than a light beam with a low proportion of higher-order modes. Therefore, the mode converter 17 can be used to control the brightness of the second image 35.

[0119] The fiber bundle 4 and the second feed fiber 2 may be such that, when tapered, certain higher order modes are coupled from the core 207 of the second feed fiber 2 to the glass body 311. For example, LP p,qA mode (described with reference to Figures 30-35) cuts off at the taper if (i) the azimuthal mode number p is greater than the normalized frequency V of the second feed fiber 2 divided by the taper ratio, or (ii) the radial mode number q is greater than the normalized frequency V of the second feed fiber 2 divided by the taper ratio times π. In the case of a double-clad fiber with a fluorine-doped outer cladding, the inner cladding acts as the core, and its radius should be used to calculate the normalized frequency V. Alternatively or additionally, the mode that cuts off at the taper and thus couples to the glass body 311 can be found using beam propagation theory or through experimentation. Thus, the mode converter 17 can switch the laser radiation emitted by the multicore fiber 10 from the second beam 32 to the third beam 33 by coupling to one or more of the higher-order modes that couple from the core 207 of the second feed fiber 2 to the glass body 311. The third beam 33 may have a beam parameter product that is 10-100 times larger than the beam parameter product of the second beam 32. Larger variations in the beam parameter products are also possible.

[0120] Therefore, varying the mode order of the second laser radiation 19 coupled into the second feed fiber 2 by the mode converter 17 provides a large variation in the brightness, beam quality, and dimensions of the second image 35 and the third image 36 that can be achieved.

[0121] The fiber bundle 4 may include an outer cladding 224 as shown in FIGS. 2 and 22, so that optical radiation that is not guided along the cladding 206 of the first feed fiber 1 or the cladding 208 of the second feed fiber 2 may be guided along the fiber bundle 4 and delivered to the multicore fiber 10.

[0122] The multicore fiber 10 may include a glass body 311 and an outer cladding 312 as shown with reference to FIG. 3. When the first feed fiber 1 shown in FIG. 2 is tapered, higher order modes may be coupled from the core 205 of the first feed fiber 1 to the outer capillary 201 and / or inner capillary 202 (if provided) of the fiber bundle 4. Similarly, the second feed fiber 2 in FIG. 2 may be tapered such that higher order modes couple from the core 207 of the second feed fiber 2 to the outer capillary 201 and / or inner capillary 202 (if provided) of the fiber bundle 4. These higher order modes then propagate through the fiber bundle 4 of the multicore fiber 10 as shown in FIG. 3 to the glass body 311. The glass body 311 of the multicore fiber 10 may have a larger cross-sectional area than the first core 11 or the second core 12 and therefore output a beam with a much lower beam quality than that emitted by the first core 11 or the second core 12. Therefore, the mode converter 17 can be used to greatly control the output beam emitted by the multicore fiber 10, from changing the beam quality of the beams emitted from the first core 11 and the second core 12, to coupling that changes the ratio of power between the first core 11, the second core 12 and the glass body 311 of the multicore fiber 10.

[0123] Therefore, the control unit 28 can control the power, intensity, spot size, and beam parameter product of the first, second, and third beams 31, 32, 33 emitted from the first core 11, the second core 12, and the glass body 311 by individually controlling the first laser 15 or each of the multiple first lasers 15, the second laser 16 or each of the multiple second lasers 16, the optical switch 20 or each of the multiple optical switches 20, and the mode converter 17 or each of the multiple mode converters 17.

[0124] FIG. 24 shows how the mode field diameter 241 of the fundamental mode of a typical first feed fiber 1 or second feed fiber 2 decreases with decreasing core diameter 240 until it reaches a minimum mode field diameter 242 at a critical diameter 243. Reducing the core diameter 240 below the critical diameter 243 increases the mode field diameter 241. A tapering such that the core diameter 240 is smaller than the critical diameter 243 can be referred to as a strong tapering. A strong tapering can be advantageous because as the mode field diameter 241 increases, the divergence angle of the laser radiation emitted from the first feed fiber 1 and / or the second feed fiber 2 decreases. A strong tapering can help maintain the beam quality of the laser radiation propagating along the first feed fiber 1 and the second feed fiber 2 after the first feed fiber 1 and the second feed fiber 2 are spliced into the multicore fiber 10. A weak taper, i.e., a taper in which the core diameter 240 tapers so that it remains above the critical diameter 243, can be used to minimize the mode field diameter 241 at the tapered end. A weak taper can be advantageous when it is desired to achieve a smaller mode field diameter 241 at the tapered end. The smaller mode field diameter 241 can be used to excite a larger number of higher-order modes of a multimode core, such as the second cores 12 and 82 of the multicore fibers 10, 80, and 230 shown in FIGS. 3, 8, and 23, respectively, thus obtaining a more uniform power distribution of the laser radiation emitted from the multicore fiber 10. The power distribution can be made even more uniform by using two or more core diameters 240 in the first feed fiber 1 and / or the second feed fiber 2.

[0125] 1, 2, 5, 6, 10, 13, 14, 16, 18, 20, 21 and 22, the first feed fiber 1 and feed fibers 71 and 72 of Figure 7 may have a core 205 as shown with reference to Figure 2 having a core diameter 209, and a cladding 206 having a cladding diameter 210. Similarly, the second feed fiber 2 may have a core 207 as shown with reference to Figure 2 having a core diameter 211, and a cladding 208 having a cladding diameter 212.

[0126] The core diameter 209 of the first feed fiber 1 before tapering can be in the range of 10 μm-50 μm, preferably in the range of 15 μm-35 μm. The cladding diameter 210 before tapering can be in the range of 125 μm-250 μm, preferably in the range of 200 μm-250 μm. For cutting applications or applications involving both cutting and welding, the first feed fiber 1 before tapering is a multimode fiber, preferably having a core diameter 209 of approximately 25 μm-35 μm, which can be operated under appropriate launch conditions to deliver the fundamental mode of the first feed fiber 1 to the first core 11 of the multicore fiber 10. The taper of the first feed fiber 1 is preferably a strong taper to maintain beam quality. A mode converter 17 can be used to induce coupling from the fundamental mode to higher-order modes, thus providing control over the beam quality of the first image 34 on the material 29. For welding applications, the first feed fiber 1, before tapering, is preferably a multimode fiber with a core diameter 209 in the range of 50 μm-400 μm, more preferably 100 μm-200 μm.

[0127] The core diameter 211 of the second feed fiber 2 before tapering can be in the range of 10 μm-50 μm, preferably in the range of 15 μm-35 μm. The cladding diameter 212 before tapering can be in the range of 125 μm-250 μm, preferably in the range of 200 μm-250 μm. The second feed fiber 2 with a different core diameter 211 can be provided to couple into more optical modes within the second core 12 of the multicore fiber 10, which improves the uniformity of the output power distribution of the laser radiation emitted from the multicore fiber 10. For cutting applications or applications involving both cutting and welding, the second feed fiber 2 before tapering is a multimode fiber, preferably having a core diameter 211 of about 25 μm-35 μm, and can be operated under appropriate emission conditions to deliver the fundamental mode of the second feed fiber 2. The first feed fiber 1 is preferably strongly tapered to maintain beam quality. The mode converter 17 can be used to induce coupling from the fundamental mode to higher order modes, thus providing control over the beam quality of the second image 35 on the material 29. For welding applications, the second feed fiber 2 before tapering is preferably a multimode fiber with a core diameter 211 in the range of 50 μm-100 μm. The second feed fiber 2 is preferably weakly tapered.

[0128] The first feed fiber 1 and the second feed fiber 2 may be single-clad fibers having a single cladding 206, 208, as shown with reference to Figure 2. Alternatively, one or more of the claddings 206, 208 may be surrounded by a low-index ring 131, as shown in Figure 13. Such a fiber with a low-index ring 131 may be called a double-clad fiber. Double-clad fibers may be preferred when a strong taper is used, because the low-index ring 131 may help to contain the fundamental mode or higher-order modes as the mode expands from the core along the taper.

[0129] Prior to tapering, the individual first and second feed fibers 1, 2 can be acid etched to reduce their cladding diameters 210, 212. Reducing the cladding diameters 210, 212 can increase the brightness of the laser radiation emitted from the fiber bundle 4. A suitable acid is hydrofluoric acid.

[0130] Referring to Figures 1, 3, 8, and 23, the multicore fibers 10, 80, and 230 may have a core diameter 301 of the first core 11 of 15 μm-200 μm. Referring to Figures 1, 3, and 8, the multicore fibers 10 and 80 may have an inner diameter 302 of the second core 12 of 30 μm-220 μm and an outer diameter 303 of the second core 12 of 45 μm-400 μm. The inner cladding 310 may have a width 304, as shown in Figure 3. The width 304 is the difference between the inner diameter 302 and the core diameter 301. The width 304 is preferably in the range of 10 μm-25 μm. The first core 11 may have a numerical aperture in the range of 0.08-0.24. The second core 12 may have a numerical aperture in the range of 0.12-0.24. The glass body 311 may have a numerical aperture in the range of 0.1-0.48, preferably 0.2-0.48, relative to the outer cladding 312. The numerical aperture of a dielectric waveguide having a core with refractive index n1 and a cladding with refractive index n2 is (n1 2 -n2 2 ) The numerical aperture is related to the acceptance angle of a dielectric waveguide and the angle of total internal reflection of a ray of light propagating along the waveguide. Increasing the numerical aperture increases the acceptance angle of the waveguide and also increases the maximum angle at which a ray of light propagating along the waveguide undergoes total internal reflection. The multicore fiber 10, 80 may also be coated with a coating (not shown) having a lower refractive index than the glass body 311 of the multicore fiber.

[0131] The first feed fiber 1 and the second feed fiber 2 can have a circular, square, or rectangular core and cladding. The multicore fiber 10 can have a circular, square, or rectangular core and cladding. Other shapes are possible.

[0132] The device shown in Figure 25 has a fiber bundle 251 with an input face 258 at its large diameter end that has an angle θ 257 relative to its longitudinal axis. Angle 257 between 35°-55° ensures that optical radiation reflected along fiber bundle 251 is reflected from fiber bundle 251 by total internal reflection. Angle 257 is preferably 45°. Fiber bundles 200, 60, 70, 100, 130, 140, 160, 180, 2000, or 220, as described with reference to Figures 2, 6, 7, 10, 13, 14, 16, 18, 20, and 22, respectively, can have angle 257.

[0133] A fiber bundle 251 is shown having two first feed fibers 1, two second feed fibers 2, and three spacing fibers 141 arranged in a hexagonal formation. The fibers are tapered and connected to the multicore fiber 10 using an offset splice 252, with the first feed fiber 1 coupled to the first core 11 and the second feed fiber 2 coupled to the second core 12 of the multicore fiber 10. The alignment of the first and second feed fibers 1 and 2 with the first and second cores 11 and 12 of the multicore fiber 10 at the splice 252 is shown by the dashed line on the right of FIG. 25. As explained with reference to FIG. 14, the use of spacing fibers 141 allows for the fabrication of separate / non-adjacent first and second feed fibers 1 and 2 without the need to introduce an inner capillary into the bundle assembly.

[0134] The fiber bundle 251 is an example of a fiber bundle including at least one first feed fiber 1, at least two second feed fibers 2, and at least three spacing fibers 141 arranged in a configuration. One of the spacing fibers 141 may be at the center of the configuration. This configuration allows the first feed fiber 1 to be coupled to the first core 11 of the multicore fiber 10, and the second feed fiber 2 to be coupled to the second core 12 of the multicore fiber 10. Two, three, four, or more second feed fibers 2 may be provided in this configuration, allowing the optical power emitted by the device to be scaled. The central spacing fiber 141 may have a larger diameter than the other fibers in the configuration.

[0135] The use of spacing fibers 141 to separate at least one first feed fiber 1 coupled only to the first core 11 and at least one second feed fiber 2 coupled to the second core 12 provides advantages in assembling a fiber bundle 251. For example, a fiber bundle 251 may have one first feed fiber 1 aligned with the center of the first core 11 and only three second fibers 2 aligned with the second cores 12, as shown in Figure 26. Three spacing fibers 141 separate the first feed fiber 1 from the second feed fiber 2.

[0136] 25 shows a fiber bundle 251 mounted on a substrate 256 that acts as a heat sink to remove thermal energy caused by optical losses in the splices. Advantageously, the substrate 256 preferably has a high thermal conductivity to spread and remove heat so that temperature increases do not damage the fiber coatings, and a low thermal expansion to reduce stresses applied to the fiber bundle 251. The thermal conductivity is preferably greater than 100 ppm / °C, more preferably greater than 200 ppm / °C. The thermal expansion is preferably less than 5×10 -6 / °C, more preferably less than 3 × 10 -6 / °C. Suitable materials for the heat sink include copper-tungsten. It is also advantageous to use a relatively soft material to secure fiber bundle 251 to substrate 256, as this reduces the forces transmitted to the coupler as the package expands and contracts. For example, a silicone material (not shown) can be used. Each of fiber bundles 200, 60, 70, 100, 130, 140, 160, 180, 2000, or 220 shown in Figures 2, 6, 7, 10, 13, 14, 16, 18, 20, and 22 can be provided on substrate 256.

[0137] The multicore fiber 10 is shown connected to an optional beam-delivery fiber 254 at a splice 2510 to deliver laser radiation to the material 29 shown in FIG. 1 . The beam-delivery fiber 254 preferably has the same optical design as the multicore fiber 10. More preferably, the second core 12 of the beam-delivery fiber may have a diameter 1 μm–10 μm larger than the second core 12 of the multicore fiber 10 to reduce splice loss. When transmitting optical powers exceeding 1 kW over distances exceeding 5 m, it may be preferable for the beam-delivery fiber 254 to have as large a diameter as possible while maintaining beam quality. Increasing the diameter can reduce wavelength conversion and other undesirable optical effects caused by nonlinear processes such as stimulated Raman scattering, thus enabling the transmission of higher optical powers over longer distances. The beam-delivery fiber 254 may be tapered at its output end with a taper 255. This can be advantageous for adjusting the output beam divergence and spot size of the laser radiation to match the beam requirements of processing optics such as a cutting or welding head. The beam delivery fiber 254 preferably has a strong outer jacket that is abrasion and chemical resistant, a metal shield to withstand punctures, and may include part of an optional fracture detection system to shut down the laser in the event of damage.

[0138] The multicore fiber 10 connects the fiber bundle 251 to the beam-delivery fiber 254. This may require providing a taper 253 to reduce the diameters 301, 302, and 303 of the multicore fiber 10, as shown in FIG. 3 , so that at least one first feed fiber 1 is aligned with only the first core 11 and thus couples the laser radiation, and at least one second feed fiber 2 is aligned with only the second core 12 of the multicore fiber 10 and thus couples the laser radiation. Connecting the fiber bundle 251 to the beam-delivery fiber 254 with the multicore fiber 10 has manufacturing advantages, as it allows beam-delivery fibers 254 with different core diameters to be connected to the fiber bundle 251 by changing the design of the taper 253. It also allows the beam-delivery fiber 254 to be more reliably replaced if damaged during operation. The splice 2510 can be located in the same housing or container as the fiber bundle 251, or in a separate housing 259. The beam delivery fiber 254 can be more easily repaired or replaced when the splice 2510 is in a separate housing 259 .

[0139] The device shown in FIG. 25 may include a mode converter 2511 for coupling optical modes propagating in at least one of the first core 11 or the second core 12 of the optical fiber 10 and / or the beam delivery fiber 254.

[0140] The mode converter 2511 can include a squeezing mechanism, such as the squeezing mechanism 270 shown in FIG. 27 . The squeezing mechanism 270 includes a first periodic surface 271 and a second periodic surface 272 arranged out of phase such that the optical fiber 10 is periodically bent along its length at a pitch 277. The pitch 277 can be uniform, as shown, or can be chirped. The chirp can be monotonic or non-monotonic. A squeezing force can be applied by an actuator 275 to squeeze the optical fiber 10 between the first periodic surface 271 and the second periodic surface 272.

[0141] The mode converter 2511 may comprise a squeezing mechanism 280 shown in FIG. 28, which comprises three sections 285, each having two periodic surfaces 281 and 282, as shown with reference to FIGS. 28 and 29. The sections 285 are arranged at 120° relative to each other. The periodic surfaces 281 and 282 are spatially 120° out of phase with each other along their lengths, such that the optical fiber 10 is deformed into a substantially helical shape when the periodic surfaces are squeezed together. The squeezing force can be applied by an actuator 275.

[0142] Pitch 27 is 2π / (β A -β B ), optical modes can be coupled together, and β A and β B is the propagation constant of the optical modes coupled together. In experiments, when the pitch 277 is chirped from at least 7.5 mm at its input end (the end closest to the fiber bundle 251) to 2.9 mm or less at its output end (the end farthest from the fiber bundle 251), the individual linearly polarized light LP of the first core 11 can be chirped by increasing the squeezing force applied to the multicore fiber 10 using either the squeezing mechanism 270 or the squeezing mechanism 280. p,q It has been found that the modes can be combined together in ascending order. Thus, the LP shown in FIG. 30 has a single bright spot 320. 0,1 When modes are input to the mode converter 2511, the single higher order modes of the first core 11 shown in Figures 31-35 can be obtained alone or in combination. 1,1 The mode has two high-intensity spots 321, and the LP 2,1 The mode has four high-intensity spots 322, and the LP 3,1 The mode has six high-intensity spots 323, and the LP 4,1 The mode has eight high-intensity spots 324, and the LP 5,1The mode has ten bright spots 325. The absolute value and range of pitch 277 depends on the design of optical fiber 10. Pitch 277 is preferably selected according to the design of optical fiber 10 and the number of optical modes that are desired to couple into and that can be found experimentally.

[0143] The mode converter 2511 can be used to increase the beam parameter product of the optical radiation propagating in the first core 11 of the multicore fiber 10, including by generating a flattened top profile. This can be achieved by using two or more first feed fibers 1 to launch multiple optical modes of the first core 11, and / or by launching at least one optical mode of the first core 11, in each case by increasing the squeezing force applied by the squeezing mechanism 270 or 280. The pitch 277 is preferably chirped along the length of the squeezing mechanism 270 or 280. The pitch 277 at the input end closest to the fiber bundle 251 is preferably longer than the pitch 277 at the output end further away from the fiber bundle 251.

[0144] The mode converter 2511 may also be used to increase the beam parameter product of the optical radiation propagating within the second core 12 of the multicore fiber 10, including creating a flattened top profile. This can be achieved by increasing the squeezing force applied by the squeezing mechanism 270 or 280. The pitch 277 is preferably chirped along the length of the squeezing mechanism 270 or 280.

[0145] 1 , the apparatus of the present invention may include a control unit 28 connected to the first laser 15, or at least one of the first lasers 15 if multiple first lasers 15 are used. Alternatively or additionally, the control unit 28 may be connected to the second laser 16, or at least one of the second lasers 16, if multiple second lasers 16 are used. The control unit 28 may comprise electronic circuitry and a computer or microprocessor / microcontroller and may send control signals to the first laser 15 and the second laser 16 to control their output power or to switch their output power on and off, and thus control the intensities of the first image 34, the second image 35, and the third image 36. The control unit 28 may send control signals to the optical switch 20 to control the switching of the first laser radiation 18 between the first feed fiber 1 and the second feed fiber 2. The control unit 28 can send control signals to the mode converter 17 to control the coupling of the fundamental mode into higher-order modes of the first feed fiber 1 and the second feed fiber 2. The control unit 28 can send control signals to the processing head 8 to control the flow of assist or process gas. Such gases can be used for cutting and welding metals. The control unit 28 can be configured to control the first laser 15, the second laser 16, the mode converter 17 (if provided), the optical switch 20 (if provided), and the processing head 8 to select one or more of the first image 34, the second image 35, and the third image 36 depending on the laser processing being performed on the material 29. The relative optical power in the first image 34, the second image 35, and the third image 36 can be varied or turned on and off, as indicated by the double arrows in FIG. 1 . The control unit can include two or more control units.

[0146] As described with reference to FIG. 3 , the optical fiber 10 may include a glass body 311 surrounding the second core 12, the glass body 311 having a refractive index lower than that of the second core 12. The glass body 311 may be surrounded by a cladding 313 having a refractive index lower than that of the glass body 311. As described with reference to FIG. 1 , the mode converter 17 can switch the laser radiation emitted by the multicore fiber 10 from the first beam 31 and / or the second beam 32 into the third beam 33 by coupling into one or more of the higher-order modes of the first feed fiber 1 and / or the second feed fiber 2. A minimum taper diameter 2512 of the fiber bundle 251 may be located before the splice 252. This can reduce the numerical aperture of the third beam 33 before the optical radiation enters the multicore fiber 10. Preferably, the minimum taper diameter 2512 and its relative position with respect to the splice 252, the first feed fiber 1 and the second feed fiber 2 and the output fiber 10 are such that the first beam 31, the second beam 32 and the third beam 33 are within the acceptance angle of the processing optics shown in Figure 1. The minimum taper diameter 2512 and its relative position can be found by experimentation.

[0147] A method of using the apparatus of the present invention may include providing the apparatus of the present invention and switching between first image 34, second image 35, and third image 36 in response to laser processing to be performed on material 29. The method may also include one or more method steps for providing optional components of the apparatus.

[0148] As also shown in FIG. 1 , the apparatus may include a light analyzer 25 connected to the input 5 of the optical coupler 3. As shown in FIG. 1 , optical radiation 26 reflected or emitted from the material 29 is analyzed by the light analyzer 25, and the results are input to the control unit 28. Alternatively or additionally, the light analyzer 25 may be connected to the mode stripper 24 or the mode stripper 29. The light analyzer 25 may include a photodetector and an optical and / or electronic filter. The light analyzer 25 allows for analyzing the optical radiation reflected or emitted from the material 29 to control laser processing of the material 29. The light analyzer 25 can be used to detect when the material 29 is perforated, monitor cutting speed during thin, thick, and variable thickness cutting, monitor welding and brazing quality, and monitor the quality of sintered layers of metal powder in additive manufacturing applications. The light analyzer 25 may output to the control unit 28. When the light analyzer 25 is used to detect when the material 29 has been perforated, the control unit 28 can adjust the light intensity in the first beam 31 and the second beam 32 from a high intensity beam suitable for perforating to a low intensity beam suitable for cutting. The light analyzer 25 is shown connected to the second feed fiber 2. Alternatively or additionally, the light analyzer 25 can be connected to the first feed fiber 1 or to the spacing fiber 141 as shown with respect to FIG. 14.

[0149] 1, the apparatus of the present invention can be used to form a first image 34 by turning on at least one first laser 15. The first image 34 can be modified using a mode converter 17 acting on the first laser radiation 18 and / or the mode converter 2511 to increase the beam parameter product of the first beam 31. The mode converter 17 can switch between a first image 34 comprising a fundamental mode 320 and a first image 34 comprising one or more higher-order annular core modes 321-325.

[0150] The first beam 31 is particularly useful for drilling and micromachining metals.

[0151] The apparatus of the present invention can be used to form a second image 35 by turning on at least one second laser 16. The second image 35 can be modified using the second laser radiation 19 and / or the mode converter 17 acting on the mode converter 2511 to increase the beam parameter product of the second beam 32 and / or homogenize the second image 35. The second image 35 can be increased in intensity by coupling the first laser radiation 18 into the second feed fiber 2 using the optical switch 20.

[0152] The second beam 31 is particularly useful for cutting and welding.

[0153] The apparatus of the present invention can be used to form a third image 36 by turning on the first laser 15 and / or the second laser 16 and operating at least one of the mode converters 17 to couple the first laser radiation 18 and / or the second laser radiation 19 into unguided optical modes of the first feed fiber 1 and the second feed fiber 2 when the fiber bundle 4 is tapered. The third image 36 can be modified using the mode converter 17 acting on the first laser radiation 18 or the second laser radiation 19 and / or the mode converter 2511 to increase the beam parameter product of the third beam 33 and / or homogenize the third image 36.

[0154] The apparatus of the present invention is capable of delivering a number of different energy profiles that are advantageous for material processing applications, including laser metal cutting, welding, selective laser melting, and additive manufacturing.

[0155] Referring to FIG. 1, the at least one first laser 15 and the at least one second laser 16 can operate independently of each other.

[0156] The device of the present invention can be switched between a high intensity source, ideal for cutting, drilling and perforating highly reflective materials, and a large area annular beam, ideal for cutting thick walled mild steel.

[0157] The apparatus of the present invention can provide spatter-free welding of reflective and coated materials. The outer annular beam from the second core 12 acts to preheat the material, while one or more higher order ring beams generated within the core precisely control the molten pool that is formed.

[0158] The inventive apparatus offers distinct advantages for powder bed additive manufacturing. Metal powder fusion requires precise energy control to prevent defects and porosity that can compromise the structural integrity of the part. A single laser can only operate in one regime, with either processing speed or feature size compromised. The inventive laser can be switched between a first image 34 containing either a single mode for high precision and / or one or more higher-order annular core modes for medium precision; a second image 35 containing an annular beam ideal for fusing materials at high rates with low defects; and a third image 36 containing a larger beam ideal for fusing materials at high speeds with low defects. Uniquely, the source can be switched between these operating regimes to optimize productivity and quality.

[0159] It should be understood that the embodiments of the present invention described above with reference to the accompanying drawings are given by way of example only, and that modifications and additional steps and components may be provided to improve performance. Individual components shown in the drawings are not limited to use in those drawings and specific embodiments, but may be used interchangeably in other embodiments and in all aspects of the present invention. The present invention extends to any of the above-described features taken alone or in any combination. Figure 1 shows an apparatus for laser processing a material 29, comprising at least one first laser 15, at least one second laser 16, an optical coupler 3, and a multicore fiber 10.

Claims

1. An apparatus for laser processing a material (29), comprising: The device comprises at least one first laser (15), at least one second laser (16), an optical coupler (3), and a multi-core fiber (10); Each first laser (15) is connected to the optical coupler (3) via a first feed fiber (1); Each second laser (16) is connected to the optical coupler (3) via a second feed fiber (2); the optical coupler (3) connects the first feed fiber (1) to a first core (11) of the multi-core fiber (10) and connects the second feed fiber (2) to a second core (12) of the multi-core fiber (10); the optical coupler (3) provides a first optical path (41) from the first laser (15) to the first core (11) of the multicore fiber (10); the optical coupler (3) provides a second optical path (42) from the second laser (16) to the second core (12) of the multicore fiber (10); The optical coupler (3) comprises a fiber bundle (4) tapered along its length.

2. at least one spacing fiber (141); 2. The device according to claim 1, wherein the first feed fiber (1) or first feed fibers (1) are separated from the second feed fiber (2) or second feed fibers (2) by the spacing fiber (141) or spacing fibers (141).

3. 3. The apparatus of claim 2, wherein the first feed fiber (1), the second feed fiber (2) and the spacing fiber (141) are arranged in a predetermined configuration, and the first feed fiber (1) is offset from the center of the configuration.

4. 4. The device of claim 3, wherein the configuration is a square, triangular, or hexagonal configuration.

5. 4. The apparatus of claim 3, wherein the fiber bundle (4) comprises two first feed fibers (1), two second feed fibers (2), and three spacing fibers (141), and the two first feed fibers (1), the two second feed fibers (2), and the three spacing fibers (141) are arranged in a hexagonal form.

6. 4. The apparatus of claim 3, wherein the fiber bundle (4) comprises at least one first feed fiber (1), at least two second feed fibers (2), and three spacing fibers (141) arranged in a predetermined configuration.

7. 4. The apparatus of claim 3, wherein the fiber bundle (4) comprises one first feed fiber (1), three second feed fibers (2), and two spacing fibers (141), and wherein the one first feed fiber (1), the three second feed fibers (2), and the two spacing fibers (141) are arranged in a hexagonal form.

8. 3. The apparatus of claim 2, wherein the first feed fiber (1) and the second feed fiber (2) are arranged in a square configuration, including two of the first feed fiber (1), the second feed fiber (2), and the spacing fiber (141), and the first feed fiber (1) and the second feed fiber (2) are diagonally opposite each other.

9. 2. The apparatus of claim 1, wherein the fiber bundle (4) comprises a plurality of the first feed fibers (1).

10. 2. The apparatus of claim 1, wherein the fiber bundle (4) comprises a low-index ring (131) adjacent to the cladding (206) of the first feed fiber (1), the low-index ring (131) having a refractive index less than that of the cladding (206).

11. 11. The device of claim 10, wherein the low index ring (131) is the cladding of the first feed fiber (1) surrounding the cladding (206).

12. The device of claim 1, wherein the fiber bundle (4) comprises an inner capillary (202).

13. 13. The device of claim 12, wherein the inner capillary (202) comprises at least one groove (51).

14. 2. The device of claim 1, wherein the fiber bundle (4) comprises the first feed fiber (1) and at least one second feed fiber (2), the first feed fiber (1) and the second feed fiber (2) being arranged in a capillary (201), and the first feed fiber (1) contacting a wall of a hole (181) of the capillary (201).

15. 15. The apparatus of claim 14, wherein the hole (181) is offset from a central axis of the capillary (201), and the first feed fiber (1) is aligned with the central axis of the capillary (2001).

16. 2. The device of claim 1, wherein the fiber bundle (4) comprises an outer capillary (201) surrounding at least one second feed fiber (2).

17. 17. The device of claim 16, wherein the outer capillary (201) is a square capillary (161).

18. 2. The apparatus of claim 1, wherein the first laser (15) comprises a single mode laser.

19. 19. The apparatus of claim 18, wherein the first feed fiber (1) is a multimode fiber, and the first laser (15) has an output fiber (38), the output fiber (38) and the first feed fiber (1) being fusion spliced with a splice (37) such that a fundamental mode propagating in the output fiber (38) is coupled to a fundamental mode propagating in the first feed fiber (1).

20. 2. The device of claim 1, wherein the first feed fiber is tapered, and the core diameter of the first feed fiber at the output of the optical coupler is smaller than a critical diameter at which a mode field diameter of a fundamental mode of the first feed fiber reaches a minimum mode field diameter.

21. 2. The device according to claim 1, wherein the first feed fiber (1) is a double-clad fiber.

22. The apparatus of claim 1 , wherein the second laser (16) comprises a single mode laser.

23. 23. The apparatus of claim 22, wherein the second feed fiber (2) is a multimode fiber, and the second laser (16) has an output fiber (38), the output fiber (38) and the second feed fiber (2) being fusion spliced with a splice (37) such that a fundamental mode propagating in the output fiber (38) is coupled to a fundamental mode propagating in the second feed fiber (2).

24. 24. The device of claim 23, wherein the second feed fiber is tapered, and the core diameter of the second feed fiber at the output of the optical coupler is smaller than a critical diameter at which the mode field diameter of the fundamental mode of the second feed fiber reaches a minimum mode field diameter.

25. 24. The device of claim 23, wherein the second feed fiber is tapered, and the core diameter of the second feed fiber at the output of the optical coupler is smaller than a critical diameter at which the mode field diameter of the fundamental mode of the second feed fiber reaches a minimum mode field diameter.

26. 2. The device of claim 1, wherein the second feed fiber (2) is a double-clad fiber.

27. 27. The device according to any one of the preceding claims, comprising cladding mode strippers (24) in the first feed fibre (1) and in the second feed fibre (2).

28. The apparatus of claim 1 , further comprising a cladding mode stripper (24) in the multicore fiber (10).

29. 2. The apparatus of claim 1, wherein the fiber bundle (4) has, at its larger diameter end, an input face (258) that has an angle (257) of 35°-55° relative to its longitudinal axis.

30. 2. The apparatus according to claim 1, further comprising a collimator (7) at the distal end (13) of the multicore fiber (10), the collimator (7) being connected to a laser processing head (8) having a focusing lens (9).

31. 2. The apparatus according to claim 1, further comprising a control unit (28) connected to the first laser (15) and the second laser (16), the control unit (28) controlling the power of laser radiation emitted by the first laser (15) and the second laser (16) to thereby independently control the power of laser radiation propagating along the first optical path (41) to the first core (11) of the multicore fiber (10) and the power of laser radiation propagating along the second optical path (41) to the second core (12) of the multicore fiber (10).

32. 32. The apparatus of claim 31, wherein the control unit (28) is connected to a mode converter (17), which controls the beam quality of the laser radiation propagating along the first optical path (41) or the second optical path (42), thereby controlling the beam quality of the laser radiation emitted from the multicore fiber (10).

33. 2. The apparatus of claim 1, wherein when a plurality of the first lasers (15) are used, the or at least one of the first lasers (15) is connected to a mode converter (17).

34. The mode converter (17) is a LP fiber guided by the first feed fiber (1). ０．１ The mode is one or more LP of said first feed fiber (1). ｐ，１ 34. The apparatus of claim 33 adapted to be coupled into an optical mode.

35. The device of claim 1 , comprising a mode converter (2511) acting on the multicore fiber (10).

36. The first core (11) of the multicore fiber (10) is an LP ｐ，１ 36. The apparatus of claim 35, wherein the apparatus is capable of mode steering, thereby enabling modal components of a first beam (31) emitted by the first core (11) to be selected according to the laser processing to be performed on the material (29).

37. 2. The apparatus of claim 1, wherein when multiple second lasers (16) are used, the or at least one of the second lasers (16) is connected to a mode converter (17).

38. The mode converter (17) is a LP guided by the second feed fiber (2). ０．１ The mode is one or more LP of said second feed fiber (2). ｐ，１ 38. The apparatus of claim 37 adapted to be coupled into an optical mode.

39. Said LP ０．１ 39. The apparatus of claim 38, wherein no mode is guided by the second feed fiber (2) at a minimum taper diameter (2512) of the fiber bundle (251).

40. 40. The apparatus of claim 39, wherein the minimum taper diameter (2512) is located before a splice (252) between the fiber bundle (251) and the multicore fiber (10).

41. The device of claim 1 , wherein the multicore fiber (10) has a taper (253) that joins with the fiber bundle (4).

42. 2. The device according to claim 1, further comprising an optical analyzer (25) connected to the input (5) of the optical coupler (3), which makes it possible to analyze optical radiation reflected or emitted from the material (29) in order to control laser processing of the material (29).

43. 2. The apparatus of claim 1, further comprising an optical switch (20) having a plurality of the second feed fibers (2) and having an input (21) connected to the at least one first laser (15), a first output (22) for the first feed fiber (1), and a second output (23) for at least one of the second feed fibers (2), thus enabling first laser radiation (18) emitted by the at least one first laser (15) to be coupled into either or both of the first feed fiber (1) and at least one second feed fiber (2).

44. 44. The apparatus of claim 43, wherein the optical switch (20) is between the at least one first laser (15) and the optical coupler (3).

45. 10. The apparatus of claim 1, wherein the optical radiation can be switched between a first image (34) having a fundamental mode (320), a first image (34) having one or more higher-order annular core modes (321-325), a second image (35) having an annular beam, and a third image (36) comprising a solid beam depending on the laser processing being performed on the material (29).

46. 1. A method comprising providing an apparatus for laser processing a material, the apparatus comprising: the apparatus comprises at least one first laser, at least one second laser, an optical coupler, and a multi-core fiber; Each first laser (15) is connected to the optical coupler (3) via a first feed fiber (1); Each second laser (16) is connected to the optical coupler (3) via a second feed fiber (2); the optical coupler (3) connects the first feed fiber (1) to a first core (11) of the multi-core fiber (10) and connects the second feed fiber (2) to a second core (12) of the multi-core fiber (10); the optical coupler (3) provides a first optical path (41) from the first laser (15) to the first core (11) of the multicore fiber (10); the optical coupler (3) provides a second optical path (42) from the second laser (16) to the second core (12) of the multicore fiber (10); The optical coupler (3) comprises a fiber bundle (4) tapered along its length; A method for controlling the power and beam quality of at least one of a first beam, a second beam, and a third beam emitted from a multicore fiber in response to laser processing to be performed on a material.

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