RELATED APPLICATIONS

[0001] This application is a continuation-in-part of Internationa! application

PCT/US2017/034848, filed May 28, 2017, which claims the benefit of U.S. Provisional Application No. 62/401 ,850, Hied September 29, 2018, This application is a continuation- in-part- of U.S. Patent Application No. 15/807,41 1 , filed May 26, 201 ?, which claims the benefit of U .S. Provisional Application No. 62/401 ,850, filed September 29, 2018. This application is a continuation-in-part of U.S. Patent Application No. 16/607,410, filed May 26, 2017, which claims the benefit of U.S. Provisions! Application No. 62/401 ,650, filed September 29, 2018. This application is a continuation-in-part of U.S. Patent Application No, 18/807,399, filed May 26, 2017, which claims the benefit of U.S. Provisional

Application No. 62/401 ,650, filed September 29, 2018. Ail of the above applications are herein incorporated by reference In their entireties.

TECHNICAL FIELD

[0002] The technology disclosed herein relates to fiber lasers and fiber-coupled lasers. More particularly, the disclosed technology relates to methods of additive manufacturing for tailoring the formation of pores in three-dimensional objects by adjusting laser beam characteristics at an output of a fiber laser or fiber-coupled laser.

BACKGROUND

[0003] The use of high-power fiber-coupled lasers continues to gain popularity for a variety of applications, such as materials processing, cutting, welding, and/or additive

manufacturing. These lasers include, for example, fiber lasers, disk lasers, diode lasers, diode-pumped solid state lasers, and lamp-pumped solid state lasers. In these systems, optical power is delivered from the laser to a work piece via an optical fiber.

[0004] Various fiber-coupled laser materials processing tasks require different beam characteristics {e.g., spatial profiles and/or divergence profiles). For example, cutting thick metal and welding generally require a larger spot size than cutting thin metal. Ideally, the laser beam properties would be adjustable to enable optimized processing for these different tasks. Conventionally, users have two choices: ( 1 ) Employ a laser system with fixed beam characteristics that can be used for different tasks but is not optimal for most of them (he., a compromise between performance and flexibility); or (2) Purchase a laser system or accessories that offer variable beam characteristics but that add significant cost, size, weight complexity, and perhaps performance degradation {e.g., optica ^; loss) or reliability degradation (e.g., reduced robustness or up-time). Currently available laser systems capable of varying beam characteristics require the use of free-space optics or other complex and expensive add-on mechanisms (e.g. , zoom lenses, mirrors,

translatable or motorized lenses, combiners, etc..) in order to vary beam characteristics. No solution exists that provides the desired adjustability in beam characteristics that minimizes or eliminates reliance on the use of free-space optics or other extra

components that add significant penalties in terms of cost, complexity, performance, and/or reliability. What Is needed is an in-fiber apparatus for providing varying beam characteristics that does not require or minimizes the use of free-space optics and that can avoid significant cost, complexity, performance tradeoffs, and/or reliability

degradation.

[0005] Porous structures are commonly used for the creation of lightweight components, filtration, sorption media and acoustic dampening. These properties make porous structures very useful. Often, porosity characteristics within a single bulk material are held relatively constant by the manufacturing process, although this is not so In the case of polymer foams, which may have a non-porous skin created on the outer surfaces.

Manufacturing techniques for porous objects materials often employ assemblage with additional structures to be useful, which raises the cost and complexity of those Items. Furthermore, the porous areas within the assembled structure are limited to the fixed porosity of the individual porous component.

[0006] It is noted that while additive manufacturing techniques, also r-eim&e to as 3D printing, can create voids in material. However, the resolution of the voids. and/or the ability to vary or otherwise tailor the porosity is limited.

[0007] Therefore, manufacturing processes that allow tailoring of pore structures and/or porosity, and thai can efficiently manufacture materials of varied pore structure and/or porosity would be a welcome addition to the art. SUMMARY

[0008] At least disclosed herein are methods, systems and apparatus for varying optical beam characteristics. Methods may include, perturbing an optical beam propagating within a first length of fiber to adjust one or more beam characteristics of the optical beam in the first length of fiber or a second length of fiber or a combination thereof, coupling the perturbed optical beam into a second length of fiber and maintaining at feast a portion of one or more adjusted beam characteristics within a second length of fiber having one or more confinement regions. Methods may further include generating a selected output beam from the second length of fiber having the adjusted beam characteristics responsive to a selection of a first refractive index profile (RIP) of the first length of fiber or a second RIP of the second length of fiber or a combination thereof. In some examples, the one or more beam characteristics of the perturbed optical beam are adjusted based on selection of one or more core dimensions of the first length of fiber or one or more confinement region dimensions of the second length of fiber or a combination thereof to generate an adjusted optical beam responsive to perturbing the first length of fiber, the adjusted optical beam having a particular adjusted: beam diameter, divergence distribution, beam parameter product (BPP), intensify distribution, luminance, M ² value, numerical aperture <NA), optical intensity, power density, radial beam position, radiance, or spot size, or any combination thereof at an output of the second length of fiber, in some example, methods include perturbing the optical beam by bending the first length of fiber to after a bend radius or after a length of a bent region of the first length of fiber or a combination thereof such that one or more modes of the optical beam are displaced radially with respect to a longitudinal axis of the first length of fiber wherein the second length of fiber has an RIP that defines a first confinement region and a second confinement region, in some examples, the adjusted one or more beam characteristics are produced by confining the optical beam in the two or more confinement regions of the second length of fiber. The example methods may further comprise launching the perturbed optical beam from the first length of fiber into the first confinement region or the second confinement region or a combination thereof such that one or more displaced modes of the optical beam are selectively coupled into and maintained in the first confinement region or the second confinement region, or a combination thereof. Disclosed methods may Include, perturbing the one or more beam characteristics of the optical beam by perturbing the first length of fiber or the optical beam In the first length of fiber or a combination thereof to adjust -at least one beam characteristic of the optical beam at an output of the second length of fiber. Perturbing the first length of fiber may include bending, bending over a particular length, micro-bending, applying acousfo-optic excitation, thermal perturbation, stretching, or applying piezo-electfic perturbation, or any combination thereof. The second length of fiber may comprise a first confinement region comprising a central core and a second confinement region comprising an annular core encompassing the first confinement region. Adjusting the one or more beam characteristics of the optica! beam may include selecting a RIP of the first length of fiber to generate a desired mode shape of a lowest order mode, one or more higher order modes, or a combination thereof subsequent to the adjusting. In. some examples, the first length of fiber has a core with a parabolic index profile radially spanning some or all of the core. A RIP of the first length of fiber may be selected to Increase or decrease a width of the. lowest order mode, the higher order modes, or a combination thereof responsive to the perturbing the optical beam. The first- length of fiber or the second length of fiber or a combination thereof may include at least one divergence structure configured to modify a divergence profile of the optical beam. The confinement regions may be separated by one or more cladding structures, wherein the divergence structure may be disposed within at least one confinement region separate from the cladding structure and comprising material having a lower index than the confinement region adjacent to the divergence structure. In some examples, the second length of fiber may be azimufha!iy asymmetric.

[0009] Apparatus disclosed herein may include an optical beam delivery device, comprising a first, length of fiber comprising a first RIP formed to enable modification of one or more beam characteristics of an optical beam by a perturbation device and a second length of fiber having a second RIP coupled to the first length of fiber, the second RIP formed to confine at least a portion of the modified beam characteristics of the optical beam within one or more confinement regions. In some examples., the first RIP and the second RIP are different. In some examples, the second length of fiber comprises a plurality of confinement regions. The perturbation device may be coupled to the first length of fiber or integral with the first length of fiber or a combination thereof. The first length of fiber may comprise a graded-index RIP in at least a radially central portion and the second length of fiber has a first confinement region comprising a central core and a second confinement region that is annular and encompasses the first confinement region. The first confinement region and the second confinement region may be separated by a cladding structure having a refractive index that is lower than the indexes of first confinement region and the second confinement region. The cladding structure may comprise a fluorosiiicate material. The first length of Tiber or the second length of fiber or a

combination thereof may include at least one divergence structure configured to modify a divergence profile of the optical beam and wherein the divergence structure may comprise a first material having a lower index of refraction than a second material encompassing the divergence structure. The second length of fiber may be azimuthaliy asymmetric and may comprise a first confinement region comprising a first core and a second confinement region comprising a second core. In some examples, the first confinement region and the second confinement region may he coaxial, in other examples, the first confinement region and the second confinement region may be non-coaxial The second confinement region may he crescent shaped in some examples. The first RIP may be parabolic in a first portion having a first radius, in some examples, the first RIP may be constant in a second portion having a second radius., wherein the second radius is larger than the first radius. The first RIP may comprise a radially graded index extending to an edge of a core of the first length of fiber, wherein the first RIP Is formed to increase or decrease a width of one or more modes of the optical beam responsive to the modification of the beam characteristics by the perturbation device. The first length of fiber may have a radially graded index core extending to a first radius followed by a constant index portion extending to a second radius, wherein the second radius is larger than the first radius. In some examples, the second length of fiber comprises a central core having a diameter in a range of about 0 to 100 microns, a first annual core encompassing the central core having a diameter in a range of about 10 to .600 microns and a second annuai core having a diameter in a range of about 20 to 1200 microns. The perturbation device may comprise a bending assembly configured to alter a bend radius or alter a bend length of the first length of fiber or a combination thereof to modify the beam characteristics of the optical beam, in some examples, a perturbation assembly may comprise a bending assembly, a mandrel micro-bend in the fiber, an acousto-optic transducer, a thermal device, a fiber stretcher, or a piezo-eleciric device, or any combination thereof. The first length of fiber and the second length of fiber may be separate passive fibers that are spliced together.

[0010] Systems disclosed herein may include,, an optical beam delivery system, comprising an optical fiber including a first, and second length of fiber and an optical system coupled to the second length of fiber including one or more free-space optics configured to receive and transmit an optical beam comprising modified beam characteristics. The first length of fiber may include a first RIP formed to enable, at least in part, modification of one or more beam characteristics of an optical beam by a

perturbation assembly arranged to modify the one or more beam characteristics, the perturbation assembly may be coupled to the first length of fiber or integral with the first length of fiber, or a combination thereof. The second length of fiber may be coupled to the first length of fiber and may include a second RIP formed to preserve at least a portion of the one or more beam characteristics of the optical beam modified by the perturbation assembly within one or more first confinement regions, in some examples, the first RIP and the second RIP are different.

[0011] The optical beam delivery system may further include a first process fiber coupled between a first process head and the optical system, wherein the first process fiber Is configured to receive the optical beam comprising the modified one or more beam characteristics _* The first process fiber may comprise a third RIP configured to preserve at least a portion of the modified one or more beam characteristics of the optical beam within one or more second confinement regions of the first process fiber, in an example, at least a portion of the free-space optics may be configured to further modify the modified one or more beam characteristics of the optical beam. The one or more beam characteristics may include beam diameter, divergence distribution.. BPP, intensity distribution, luminance, W value, NA. optical intensity, power density, radial beam position, radiance, or spot size, or any combination thereof. The third RIP may be the same as or different from the second RIP, The third RIP may be configured to further modify the modified one or more beam characteristics of the optical beam, in some examples, at least one of the one or more second confinement regions includes at least one divergence structure configured to modify a divergence profile of the optical beam. The divergence structure may comprise an area of lower-index material than that of the second confinement region,

[0012] The optical beam delivery system may further include a second process fiber having a fourth RIP that Is coupled between the optical system and a second process head, wherein the second process fiber may be configured to receive the optical beam comprising the modified one or more beam characteristics within one or more second confinement regions of the second process fiber; In some examples, the first process fiber or the second process fiber or a combination thereof may be configured to further modify the modified one or more beam characteristics of the optical beam. The second process fiber may include a! (east one divergence structure configured to modify a divergence profile of the optical beam. The second process fiber may comprise a central core surrounded by at least one of the one or more second confinement regions, wherein the core and the second confinement region are separated by a cladding structure having a first index of refraction that is lower than a second Index of refraction of the central core and a third index of refraction of the second confinement region, wherein the second confinement region may include the at least one divergence structure. The at least one divergence structure may comprise an area of lower-index material than that of the second confinement region, in an example, the second RIP may be different from the third RIP or the fourth RIP or a combination thereof. Alternatively, the second RIP may be the same as the third RIP or the fourth RIP or a combination thereof. The one or more beam

characteristics that may be modified can include beam diameter, divergence distribution, BPP, intensity distribution, luminance, M ² value, NA, optical intensity, power density, radial beam position, radiance, or spot size, or any combination thereof.

[0013] In some examples, at least a portion of the free-space optics may be configured to further modify the modified one or more beam characteristics of the optical beam. The first process fiber may be coupled between a first process head and the optical system, wherein the first process fiber is configured to receive the optical beam comprising twice modified one or more beam characteristics. The first process fiber may have a third RIP configured to preserve at least a portion of the twice modified one or more beam

characteristics of the optical beam within one or more second confinement regions of the first process fiber. The third RIP may he different from the second RIP, wherein the third RIP Is configured to further modify the twice modified one or more beam characteristics of the optical beam.

10014] In some examples, the first process fiber may include a divergence structure configured to further modify the twice modified one or more beam characteristics of the optical beam. In some examples,, a second process fiber may be coupled between the optical system and a second process head, wherein the second process fiber is configured to receive the twice modified one or more beam characteristics.

[0015] In some examples, the first process fiber or the second process fiber or a combination thereof is configured to further modify the twice modified one or more beam characteristics of the optical beam. The first process fiber or the second process fiber or a combination thereof may include at least one divergence structure configured to further modify the twice modified one or more beam characteristics of the optica! beam. The optical system may be a fiber-to-fiber coupler, a fiber-to-fiber switch or a process head, or the like or a combination thereof.

[0016] The present disclosure is further directed to a method of making a porous three- dimensional object. The method comprises: a) positioning a first layer of particles on a build plate; b) heating the first layer of particles sufficiently to fuse the particles together to form a first build layer having a first porosity; c) exposing the first build layer to a laser beam to form one or more pores, the exposed first build layer having a first modified porosity, the laser beam being emitted from an optical fiber; d) adjusting one or more beam characteristics of the laser beam prior to or during the exposing of the first build layer, the adjusting of the laser beam occurring prior to the laser beam being emitted from the optical fiber; e) positioning an additional layer of particles on the exposed first build layer; f) heating the additional; layer of particles sufficiently to fuse, the particles together to form a second build layer having a second porosity; g) exposing the second build layer to the laser beam to form one or more pores, the exposed second build layer having a second modified porosity, the laser beam being emitted from the optical fiber; h) adjusting one or more beam characteristics of the laser beam after fusing the particles to form the second build layer and prior to or during the exposing of the second build layer, the adjusting of the laser beam occurring prior to the laser beam being emitted from the optical fiber, and i) repeating e), f) and optionally g) and h) to form a three-dimensional object

[0017] The present disclosure is further directed to a porous three-dimensional object. The object is made by a method comprising: a) positioning a first layer of particles on a build plate; b) heating the first layer of particles sufficiently to fuse the particles together to form a first build layer having a first porosity; c) exposing the first build layer to a laser beam to form one or more pores, the exposed first build layer having a first modified porosity, the laser beam being emitted from an optical fiber; d) adjusting one or more beam

characteristics of the laser beam prior to or during the exposing of the first build layer, the adjusting of the laser beam occurring prior to the laser beam being emitted from the optical fiber; e) positioning an additional layer of ^' particles on the exposed first build layer; 1} heating the additional layer of particles sufficiently to fuse the particles together to form a second build layer having a second porosity: g) exposing the second build layer to the laser beam to form one or more pores, the exposed second build layer having a second modified porosity, the laser beam being emitted from the optical fiber; h) adjusting one or more beam characteristics of the laser beam after fusing the particles to form the second build layer and prior to or during the exposing of the second build layer, the adjusting of the laser beam occurring prior to the laser beam being emitted from the optical fiber, and i) repeating a), f), optionally g) and optionally h) to form a three-dimensional object,

[0018] The present disclosure is aiso directed to a porous three-dimensional object. The porous three-dimensional object comprises: a first layer having one or more pores in a first pore structure: and a second layer on the first layer, the second layer having one or more pores in a second pore structure that is different than the first pore structure. The first layer and the second layer are fused together; and the pore structure in one or more of the first layer and the second layer is not homogenous,

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings, wherein like reference numerals represent like elements, are incorporated in and constitute a part, of this specification and, together with the description, explain the advantages and principles of the presently disclosed technology, in the drawings,

[0020! FIG. 1 illustrates an example fiber structure for providing a laser beam having variable beam characteristics;

[0021] FIG. 2 depicts a cross-sectional view of an example fiber structure for delivering a beam with variable beam characteristics;

[0022] FIG, 3 illustrates an example method of perturbing a fiber structure for providing a beam having variable beam characteristics;

10023] FIG, 4 is a graph illustrating the calculated spatial profile of the lowest-order mode (LPot) for a first length of a fiber for different fiber bend radii;

[0024] FIG. 5 illustrates an example of a two-dimensional intensity distribution at a junction when a fiber for varying beam characteristics is nearly straight; [0025] FIG, 6 illustrates an example of a two-dimensional intensity distribution at a junction when a fiber for varying beam characteristics Is bent with a radius chosen to preferentially excite a particular confinement region of a second length of f iber;

[0026] FIGS. 7 ~ 10 depict experimental results to illustrate further output beams for various hand radii of a fiber for varying beam characteristics shown in FIG. 2;

[0027] FIGS. 11 - 16 illustrate cross-seetionai views of example first lengths of fiber for enabling adjustment of beam characteristics in a fiber assembly;

[0028] FIGS, 17 - 19 illustrate cross-sectional views of example second lengths of fiber ("confinement fibers") for confining adjusted beam characteristics In a fiber assembly;

[0029] F!GS. 20 and 21 Illustrate cross-sectional views of example second lengths of fiber for changing a divergence angle of and confining an adjusted beam in a fiber assembly configured to provide variable beam characteristics;

[0030] FIG. 22A illustrates an example laser system including a fiber assembly configured to provide variable beam characteristics disposed between a feeding fiber and process head;

[0031 j FIG, 228 illustrates an example laser system including a fiber assembly configured to provide variable beam characteristics disposed between a feeding fiber and process head;

[0032] FIG, 23 illustrates an example laser system including a fiber assembly configured to provide variable beam characteristics disposed between a feeding fiber and multiple process fibers;

[0033] FIG. 24 illustrates examples of various perturbation assemblies for providing variable beam characteristics according to various examples provided herein;

[0034] FIG. 25 illustrates an example process for adjusting and maintaining modified characteristics of an optical beam: and

[0035] FIGS. 28-28 are cross-sectional views illustrating example second lengths of fiber ("confinement fibers") for confining adjusted beam characteristics in a fiber assembly,

[0036] FIG. 29 is a flowchart of a method of making a porous three-dimensional object,, according to an example of the present disclosure. [0037] FIG. 30 illustrates a porous three-dimensional object, according to an example of the present disclosure.

[0038] FIG. 31 illustrates a top view of a build layer having regions of differing porosities, according to an example of the present disclosure,

[0039] FIG. 32 illustrates a top view of the build layer of FIG,. 31 showing a laser scan path, according to an example of the present disclosure,

[0040] FIG. 33 illustrates a three-dimensional object having a porous lattice structure, according to an example of the present disclosure.

DETAILED DESCRIPTION

[0041] As used herein throughout this disclosure and in the claims, the singular forms "a," "an,* and "the" include the plural forms unless the context dearly dictates otherwise. Additionally, the term "includes" means "comprises," Further, the term "coupled" does not exclude the presence of Intermediate elements between the coupled items. Also, the terms "modify" and "adjust" are used interchangeably to mean "alter."

[0042] The systems, apparatus, and methods described herein should not he construed as limiting in any way. Instead, the present disclosure is directed toward ail novel and non-obvious features and aspects of the various disclosed embodiments, alone and in various combinations and sub-combinations with one another. The disclosed systems, methods, and apparatus are not limited to any specific aspect or feature or combinations thereof, nor do the disclosed systems, methods, and apparatus require that any one or more specific advantages be present or problems be solved. Any theories of operation are to facilitate explanation, but the disclosed systems, methods, and apparatus are not limited to such theories of operation,

£0043] Although the operations of some of the disclosed methods are described In a particular, sequential order for convenient presentation, it should be understood that, this manner of description encompasses rearrangement, unless a particular ordering is required by specific language set forth below. For example, operations described sequentially may In some cases be rearranged or performed concurrently, Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed systems, methods, and apparatus can be used in conjunction with other systems, methods, and apparatus.. .Additionally, the description sometimes uses terms like "produce" and "provide" to describe the disclosed methods. These terms are high- level abstractions of the actual operations that are performed. The actual operations that correspond to these terms will vary depending on the particular implementation and are readily discernible by one of ordinary skill in the art.

[0044] in some examples, values, procedures, or apparatus are referred to as "lowest", "best", "minimum," or the like. It wiil be appreciated that such descriptions are intended to Indicate that a selection among many used functional alternatives can be made, and such selections need not be better, smaller, or otherwise preferable to other selections, Examples are described with reference to directions indicated as "above:" "below," "upper," lower," and the like. These terms are used for convenient description, but do not imply any particular spatial orientation.

Definitions

[0045] Definitions of words and terms as used herein;

1. The term "beam characteristics" refers to one or more of the following terms used to describe an optical beam, in genera!, the beam characteristics of most interest depend on the specifics of the application or optica! system.

2, The term "beam diameter" is defined as the distance across the center of the beam along an axis for which the irradiance (intensity) equals 1/e ² of the maximum irradiance. While examples disclosed herein generally use beams that propagate in azimuthally symmetric modes, elliptical or other beam shapes can be used, and. beam diameter can be different along different axes. Circular beams are characterized by a single beam diameter. Other beam shapes can have different beam diameters along different axes.

3. The term "spot size" is the radial distance (radius) from the center point of maximum irradiance to the 1/e ² point.

4, The term "beam divergence distribution" is the power vs. the full cone angle. This

quantity is sometimes called the "angular distribution" or "NA distribution." 5, The term "beam parameter product* (BPP) of a laser beam Is defined as the product of the beam radius (measured at the beam waist) and the beam divergence half-angle (measured in the far field). The units of BPP are typically mm-mrad.

6. A "confinement fiber" is defined to be a fiber that possesses .one or more confinement regtons, wherein a confinement region comprises a higher-index region (core region) surrounded by a lower-index region, (cladding region). The RIP of a confinement fiber may include one or more higher-index regions (core regions) surrounded by Sower- index regions (cladding regions), wherein light is guided in the higher-index regions. Each confinement region and each cladding region can have any RIP, including but. not limited to step-index and graded-index. The confinement regions may or may not be concentric and may be a variety of shapes such as circular, annular, polygonal- arcuate, elliptical, or irregular, or the like or any combination thereof. The confinement regions in a particular confinement fiber may ail have the same shape or may be different shapes. Moreover, confinement regions may be co-axial or may have offset, axes with respect to one another. Confinement regions may he of uniform thickness about a central axis in the longitudinal direction, or the thicknesses may vary about the central axis in the longitudinal direction.

7. The term "intensity distribution" refers to optical intensity as a function of position along a line ( 1 D profile) or on a plane {2D profile). The line or plane is usually taken perpendicular to the propagation direction of the light, it is a quantitative property.

8, "Luminance" is a photometric measure of the luminous intensity per unit area of light travelling in a given direction.

9. "l ^o thaireL oalso called "beam quality factor" or "beam propagation factor") is a

dimension!ess parameter for quantifying the beam quality of laser beams, with M ² ~ 1 being a diffraction-limited beam, and larger M2 values corresponding to lower beam quality. ^, M ² is equal to the BPP divided by A / ττ, where A is the wavelength of the beam in microns (if BPP Is expressed in- units of mm~mrad}<

10, The term "numerical aperture" or ''NA" of an optical system is a dimensioniess number that characterizes the range of angles over which the system can accept, or emit light,

1 1 , The term "optical intensity" is not an official {SI) unit, but is used to denote Incident power per unit area on a surface or passing through a plane.

12. The term "power density" refers to optical power ^' per unit area, although this is also referred to as "optical intensity." 13. The term "radial beam position" refers to the position of a beam In a fiber measured with respect to the center of the fiber core in a direction perpendicular to the fiber axis.

14. "Radiance" is the radiation emitted per unit solid angle in a given direction by a unit area of an optical source (e.g,, a laser). Radiance may be altered by changing the beam intensity distribution: and/or beam divergence profiie or distribution. The ability to vary the radiance profile of a laser beam implies the ability to vary the BPP.

15. The term ' ^' refractive-index profile" or "RIP" refers to the refractive index as a function of position along a line (ID) or in a plane (2D) perpendicular to the fiber axis, Many fibers are azimuthally symmetric, in which case the ID RIP is identical for any azimuthai angle.

16. A "step-index fiber" has a RIP that is flat (refractive index independent of position) within the fiber core.

17. A "gradecJ-index fiber" has a RIP in which the refractive index decreases with

increasing radial position (i.e., with increasing distance from the center of the fiber cere),

18. A "parabolic-index fiber is a specific case of a graded-index fiber in which the

refractive index decreases quadratically with increasing distance from the center of the fiber core.

19. The term "porosity' is generally defined as the empty space per unit volume in an

object, such as a 3D object, bui!d layer or a region of an object or build layer.

Fiber for Varying Beam Characteristics

[0048] Disclosed herein are methods, systems, and apparatus configured to provide a fiber operable to provide a laser beam having variable beam characteristics. (VBG) that may reduce cost, complexity, optical loss, or other drawbacks of the conventional methods described above. This VBC fiber is configured to vary a wide variety of optical beam characteristics. Such beam characteristics can be controlled using the VBC fiber thus allowing users to tune various beam characteristics to suit the particular requirements of an extensive variety of laser processing applications. For example, a VBC fiber may be used to tune: beam diameter, beam divergence distribution, 8PP, intensity distribution, M ² factor, NA, optica! intensity, power density, radial beam position, radiance, spot size, or the like, or any combination thereof. [G047J In general, the disclosed technology entails coupling a laser beam into a fiber in which the characteristics of the laser beam in the fiber can be adjusted by perturbing the laser beam and/or perturbing a first length of fiber by any of a variety of methods (e.g., bending the fiber or introducing one or more other perturbations) and fully or partially maintaining adjusted seam characteristics in a second length of fiber, The second length of fiber is specially configured to maintain and/or further modify the adjusted beam characteristics.. In some cases, the second length of fiber preserves the adjusted beam characteristics through delivery of the laser beam io its ultimate use (e.g., materials processing). The first and second lengths of fiber may comprise the same or different fibers.

[0048] The disclosed technology is compatible with fiber lasers and fiber-coupled lasers. Fiber-coupled lasers typically deliver an output via a delivery fiber having a step-index refractive index profile: (RIP), i.e., a flat or constant refractive index within the fiber core, in reality, the RIP of the delivery fiber may not be perfectly flat, depending on the design of

diameter Is typically in the range of 10 - 1000 micron (although other values are possible), and the NA is typically in the range of 0,06 - 0,22 (although other values are possible), A delivery fiber from the laser may be routed directly to the process head or work piece, or it may be routed to a fiber-to-fiber coupler (FFC) or fiher-to-fiber switch (FFS), which couples the iight from the delivery fiber Into a process fiber thai transmits the beam to the process head or the work piece,

[0049] Most materials processing tools, especially those at high power (> 1 kW), employ friuitimode (MM) fiber, but some employ single-mode (SM) fiber, which is at the lower end of the dcore and NA ranges. The beam characteristics from a SM fiber are uniquely determined by the fiber parameters. The beam characteristics from a MM fiber, however, can vary {unit-ionmit and/or as a function of laser power and: time), depending on the beam characteristics from the laser source(s) coupled into the fiber, the launching or splicing conditions into the fiber, the fiber RIP, and the static and dynamic geometry of the fiber (bending, coiling, motion, micro- bending, etc). For both SM and MM delivery fibers, the beam characteristics may not be optimum for a given materials processing task, and it is unlikely to be optimum for a range of tasks, motivating the desire to be able to systematically vary the beam characteristics In order to customize or optimize them for a particular processing: task. [0050] In one example, me VBC fiber may have a -first length and a second length: and may be configured to be interposed as an sn-fiber device between the delivery fiber and the process head to provide the desired adjustability of the beam characteristics. To enable adjustment of the beam, a perturbation device and/or assembly is disposed in close proximity to and/or coupled with the VBC fiber and Is responsible for perturbing the beam in a first length such that the beam's characteristics are altered in the first length of fiber, and the altered characteristics are preserved or further altered as the beam propagates in the second length of fiber, The perturbed beam is launched into a second length of the VBC fiber configured to conserve adjusted beam characteristics. The first and second lengths of fiber may be the same or different fibers and/or the second length of fiber may comprise a confinement fiber. The beam characteristics that are conserved by the second length of VBC fiber may include any of: beam diameter, beam divergence distribution, BPP, intensity distribution, luminance, M ² factor, HA, optical intensity, power density, radial beam position, radiance, spot size, or the like, or any combination thereof.

[0051] FIG, 1 illustrates an example VBC fiber 100 for providing a laser beam having variable beam characteristics without requiring the use of free-space optics to change the beam characteristics, VBC fiber 100 comprises a first length of fiber 104 and a second length of fiber 108, First -length of fiber 104 and second length of fiber 108 may be the same or different fibers and may have the same or different RIPs. The first length of fiber 104 and the second length of fiber 108 may be joined together by a splice. First length of fiber 104 and second length of fiber 108 may be coupled in other ways, may be spaced apart, or may be connected via an interposing component such as another length of fiber, free-space optics, glue, index-matching material, or the like or any combination thereof.

[0052] A perturbation device 110 is disposed proximal to and/or envelops perturbation region 106, Perturbation device 1 10 may be a device, assembly, in-fsber structure, and/or other feature. Perturbation device 110 at least perturbs optical beam 102 in first, length of fiber 104 or second length of fiber 108 or a combination thereof in order to adjust one or more beam characteristics of optical beam 102, Adjustment of beam 102 responsive to perturbation by perturbation device 1 10 may occur in first length of fiber 104 or second length of fiber 108 or a combination thereof. Perturbation region 106 may extend over various widths and may or may not extend into a portion of second length of fiber 108. As beam 102 propagates in VBC fiber 100, perturbation device 110 may physically act on VBC fiber 100 to perturb the fiber and adjust the characteristics of beam 102, Alternatively, perturbation device 110 may act directly on beam 102 to alter its beam characteristics. Subsequent to being adjusted, perturbed beam 112 has different beam characteristics than beam 102, which wili be fully or partially conserved in second length of fiber 108. In another example, perturbation device 110 need not be disposed near a splice. Moreover, a splice may not be needed at ail., for example VBC fiber 100 may be a single fiber, first length of fiber and second length of fiber could be spaced apart, or secured with a small gap (air-spaced or filled with an optical material, such as optical cement or an index-matching material).

[0053] Perturbed beam 112 is launched into second length of fiber 108, where perturbed beam 112 characteristics are largely maintained or continue to evolve as perturbed beam 1 12 propagates yielding the adjusted beam characteristics ai the output of second length of fiber 108. In one example, the new beam characteristics may include an adjusted intensify distribution. In an example,, an altered beam intensity distribution will be conserved in various structurally bounded confinement regions of second length of fiber 108. Thus; the beam intensity distribution may he tuned to a desired beam Intensity distribution optimised for a particular laser processing task. In general, the Intensity distribution of perturbed beam 112 will evolve as it propagates in the second length of fiber 108 to fill the confinement reglon(s) into which perturbed beam 112 is launched responsive to conditions in first length of fiber 104 and perturbation caused by perturbation device 1.10. In addition, the angular distribution may evolve as the beam propagates in the second fiber, depending on launch conditions and fiber characteristics. In general, fibers largely preserve the input divergence distribution, but the distribution can be broadened if the input divergence distribution. Is narrow and/or if the fiber has irregularities or deliberate features that perturb the divergence distribution, The various confinement regions, perturbations, and fiber features of second length of fiber 108 are described in greater detail below. Beams 102 and 112 are conceptual abstractions intended to illustrate how a beam may propagate through a VBC fiber 100 for providing variable beam characteristics and are not intended to closely model the behavior of a particular optical beam.

[0064] VBC fiber 100 may he manufactured by a variety of methods including PCVD (Plasma Chemica! Vapor Deposition), OVD (Outside Vapor Deposition), VAD (Vapor Axial Deposition), MOCVD (Metal-Organic Chemical Vapor Deposition.) and/or DND (Direct Nanoparticie Deposition), VBC fiber 100 may comprise a variety of materials. For example, VBC fiber 100 may comprise SiOs, SIOs doped with GeOs, germanosjilcate, phosphorus penioxide, phosphosiffcate, AhOs, alyrninosicat©, or the like or any combinations thereof. Confinement regions may be bounded by cladding doped with fluorine, boron, or the like or any combinations thereof. Other dopants may be added to active fibers, including rare-earth ions such as Er ³⁺ (erbium), Yb ³⁺ {ytterbium}, Nd ³⁺ (neodymlum), Tm ³⁺ (thulium), Ho ³⁺ {hoimium}, or the like or any combination thereof, Confinement regions may be bounded by c!adding having a lower index than the confinement region with fluorine or boron doping. Alternatively, VBC fiber 100 may comprise photonic crystal fibers or micro-structured libers.

[0055] VBC fiber 100 is suitable for use in any of a variety of fiber, fiber optic, or fiber laser devices, including continuous wave and pulsed fiber lasers, disk lasers, solid state lasers, or diode lasers (pulse rate unlimited except by physical constraints). Furthermore, implementations in a planar waveguide or other types of waveguides and not just fibers are within the scope of the claimed technology.

[0058] FIG. 2 depicts a cross-sectional view of an example VBC fiber 200 for adjusting beam characteristics of an optical beam, in an example, VBC fiber 200 may be a process fiber because it may deliver the beam to a process head for material processing. VBC fiber 200 comprises a first length of fiber 204 spliced at junction 206 to a second length of fiber 208, A perturbation assembly 210 Is disposed proximal to junction 206, Perturbation assembly 210 may be any of a variety of devices configured to enable adjustment of the beam characteristics of an optical beam 202 propagating in VBC fiber 200. In an example, perturbation assembly 210 may be a mandrel and/or another device that may provide means of varying the bend radius and/or bend length of VBC fiber 200 near the splice. Other examples of perturbation devices are discussed below with respect to FIG. 24,

[006?] In an example, first length of fiber 204 has a parabolic-index RIP 212 as indicated by the left RIP graph. Most of the intensity distribution of beam 202 is concentrated in the center of fiber 204 when fiber 204 is straight or nearly straight. Second length of fiber 208 is a confinement fiber having RIP 214 as shown in the right RIP graph. Second length of fiber 208 includes confinement regions 216, 218 and 220. Confinement region 216 is a central core surrounded by two annular (or ring-shaped) confinement regions 218 and 220, Layers 222 and 224 are structural barriers of lower Index material between confinement regions (218, 218 and 220), commonly referred to as "cladding" regions.. In one example, layers 222 and 224 may comprise rings of fluorosilicate; in some embodiments, the fluorosilicafe cladding layers are relatively thin. Other materials may be used as wei! and claimed subject matter is not Mmited in this regard.

[0058] In an example, as beam 202 propagates along VBC fiber 200. perturbation assembly 210 may physically act on fiber 208 and/or beam 202 to adjust its beam characteristics and generate adjusted beam 228. In the current example, the intensity distribution of beam 202 is modified by perturbation assembly 210. Subsequent to adjustment of beam 202 the intensity distribution of adjusted beam 226 may be

concentrated in outer confinement regions 218 and 220 with relatively little intensity in the central confinement region 216. Because each of confinement regions 216, 218, and/or 220 is isolated by the thin layers of lower index material in barrier layers 222 and 224, second length of fiber 208 can substantially maintain the adjusted intensity distribution of adjusted beam 226, The beam will typically become distributed azimuthally within a given confinement region but will not transition (significantly) between the confinement regions as it propagates along the. second length of fiber 208. Thus, the adjusted beam

characteristics of adjusted beam 228 are largely conserved within the isolated

confinement, regions 216, 218, and/or 220. In some cases, it be may desirable to have the beam 226 power divided among the confinement regions 216, 218. and/or 220 rather than concentrated in a single region, and this condition may be achieved by generating an appropriately adjusted beam 226,

[0059] in one example, core confinement region 216 and annular confinement regions 218 and 220 may be composed of fused silica glass, and cladding 222 and 224 defining the confinement regions may be composed of fluorosilicafe glass. Other materials may be used to form the various confinement regions (218, 218 and 220), including

gerrnanosillcate, phosphosliicate, aluminoslicate, or the like, or a combination thereof and claimed subject matter is. not so limited. Other materials may be used to form the barrier rings (222 and 224), including fused silica, foorosilscate, or the like or a combination thereof, and claimed subject matter is not so limited. In other embodiments, the optical fibers or waveguides include or are composed of various polymers or plastics or crystalline materials. Generally, the core confinement regions ^' have refractive indices that are greater than the refractive indices of adjacent barrier/cladding regions.

[0060] In some examples, It may be desirable to increase a number of confinement regions in a second length of fiber to increase granularity of beam control over beam displacements for fine-tuning a beam profile. Far example, confinement regions may be configured to provide stepwise beam displacement.

[0061] FIG. 3 illustrates an example method of perturbing fiber 200 for providing variable beam characteristics of an optical beam. Changing the bend radius of a fiber may change the radial beam position, divergence angle, and/or radiance profile of a beam ^· within the fiber. The bend radius of VBC fiber 200 can be decreased from a first bend radius Ri to a second bend radius F½ about splice junction 208 by using a stepped mandrel or cone as the perturbation assembly 210. Additionally or alternatively, the engagement length on the msndret(s) or cone can be varied. Rollers 250 may be employed to engage VBC fiber 200 across perturbation assembly 210. In an example, an amount of engagement of rollers 250 with fiber 200 has been shown to shift the distribution of the intensity profile to the outer confinement regions 218 and 2.20 of fiber 200 with a fixed mandrel radius. There are a variety of other" methods for varying the bend radius of fiber 200.. such as using a clamping assembly, flexible tubing, or the like, or a combination thereof, and claimed subject matter is not limited In this regard. In another example, for a particular bend radius the length over which VBC fiber 200 is bent can also vary beam characteristics in a controlled and reproducible way. In examples, changing the bend radius and/or length over which the fiber Is bent at a particular bend radius also modifies the intensity distribution of the beam such that one or more modes may be shifted radially away from the center of a fiber core.

[0082] Maintaining the bend radius of the fibers across junction 206 ensures that the adjusted beam characteristics such as radial beam position and radiance profile of optical beam 202 will not return to beam 2G2 ^' s unperturbed state before being launched into second length of fiber 208, Moreover, the adjusted radial beam characteristics, including position, divergence angle, and/or intensity distribution, of adjusted beam 228 can be varied based on an extent of decrease in the bend radius and/or the extent of the bent length of VBC fiber 200. Thus, specific beam characteristics may be obtained using this method.

[0063] In the current example, first length of fiber 204 having first RIP 212 is spliced at junction 206 to a second length of fiber 208 having a second RIP 214. However, it is possible to use a single fiber having a single RIP formed to enable perturbation (e.g., by micro-bending) of the beam characteristics of beam 202 and also to enable conservation of the adjusted beam, Such a RIP may be similar to the RiPs shown in fibers fMustraled in FIGS, 17, 18, and/or 19.

[0084] FIGS, 7 - 10 provide. experimental results for VBC fiber 200 (shown in FIGS. 2 and 3) and illustrate further a beam response to perturbation of VBC fiber 200 when a perturbation assembly 210 acts on VBC fiber 200 to bend the fiber. FIGS, 4 - 6 are simulations and FIGS. 7 - 10 are experimental results wherein a beam from a SM 1050 nm source was launched into an input fiber (not shown) with a 40 micron core diameter. The input fiber was spliced to first length of fiber 204.

[0085] FIG, 4 is an example graph 400 illustrating the calculated profile of the lowest-order mode (LP ₀₁ ) for a first length of fiber 204 for different fiber bend radii 402, wherein a perturbation assembly 210 involves bending VBC fiber 200. As the fiber bend radius is decreased, an optical beam propagating in VBC fiber 200 is adjusted such that the mode shifts radially away from the center 404 of a VBC fiber 200 core (r ~ 0 micron) toward the core/cladding interface (located at r = 100 micron in this example), Higher-order modes (LPin ) also shift with bending. Thus, a straight or nearly straight fiber ^' {very large bend radius), curve 406 for LPsi is centered at or near the center of VBC fiber 200. At a bend radius of about 8 cm, curve 408 for LPQI is shifted to a radial position of about 40 μηη from the center 404 of VBC fiber 200, At a bend radius of about 5 cm,, curve 410 for LPot isShifted to a radial position about 50 pm from the center 404 of VBC fiber 200. At: a bend radius of about 4 cm, curve 412 for LP01 is shifted to a radial position about 60 pm from the center 404 of VBC fiber 200. At a bend radius of about 3 cm, curve 414 for LPoi is shifted to a radial position about 80 pm from the center 404 of VBC fiber 200. At a bend radius of about 2.5 cm, a curve 416 for LP01 is shifted to a radial position about 85 urn from the center 404 of VBC fiber 200. Note that the shape of the mode remains relatively constant {until it approaches the edge of the core), which is a specific property of a parabolic RIP, Although, this property may be desirable in some situations, it is not required for the VBC functionality., and other RIPs may be employed.

[0066] \n an example, if VBC fiber 200 is straightened, IF¾1 mode will shift back toward the center of the fiber. Thus, the purpose of second length of fiber 208 is to "trap" or confine the adjusted intensity distribution of the beam in a confinement region that is displaced from the center of the VBC fiber 200. The splice, between fibers 204 and 208 is included in the bent region, thus the shifted mode profile will be. preferentially launched into one of the ring-shaped confinement regions 218 and 220 or be distributed among the confinement regions. FIGS. 5 and 6 illustrate this effect.

[0067] FIG. 5 illustrates an example two-dimensional intensity distribution at junction 208 within second length of fiber 208 when VBC fiber 200 is nearly straight, A significant portion of U½ and LP _in are within confinement region 218 of fiber 208, FIG, 8 illustrates the two-dimensional intensity distribution at junction 206 within second length of fiber 208 when VBC fiber 200 is bent with a radius chosen to preferentially excite confinement region 220 (the outermost confinement region) of second length of fiber 208. A significant portion of LP ₀₁ and UVare within confinement region 220 of fiber 208.

[0068] in an example, second length of fiber 208 confinement region 216 has a 100 micron diameter, confinement region 218 is between 120 micron and 200 micron in diameter, and confinement region 220 is between 220 micron and 300 micron diameter. Confinement regions 216, 218, and 220 are separated by 10 urn thick rings of

fiuorosicate, providing an HA of 0.22 for the confinement regions, Other inner and outer diameters for the confinement regions, thicknesses of the rings separating the

confinement regions, HA values for the confinement regions, and numbers of confinement regions may be employed.

[0069] Referring again io FIG. 5, with the noted parameters, when VBC fiber 200 is straight about 90% of the power is contained within the central confinement region 216, and about 100% of the power is contained within confinement regions 216 and 218.

Referring now to FIG. 6, when fiber 200 is bent to preferentially excite second ring confinement region 220, nearly 75% of the power is contained, within confinement region 220, and more than 95% of the power is contained within confinement regions 218 and 220. These calculations include LPm and two higher-order modes, which is typical in some 2 - 4 kW fiber iasers.

[0070] It is dear from FIGS. 5 and 6 that in the case where a perturbation assembly 210 acts on V8C fiber 200 to bend the fiber, the bend radius determines the spatial overlap of the modal Intensity distribution of the first length of fiber 204 with the different guiding confinement regions (216, 21.8, and 220} of the second length of fiber 208. Changing the bend radius can thus change the intensity distribution at the output of the second length of fiber 208, thereby changing the diameter or spot size of the beam, and thus also changing its radiance and BPP value. This adjustment of the spot size may be accomplished In an ail-fiber structure, involving no free-space optics and consequently may reduce or eliminate the disadvantages of free-space optics discussed above. Such adjustments can aiso be made with other perturbation assemblies that alter bend radius, bend length, fiber tension, temperature, or other perturbations discussed below.

[0071] In a typical materials processing system (e.g., a cutting or welding tool), the output of the process fiber is Imaged at or near the work piece by the process head, Varying the intensity distribution as shown in FIGS. 5 and 6 thus enables variation of the beam profile at the work piece in order to tune and/or optimize the process, as desired. Specific RIPs for the two fibers were assumed for the purpose of the above calculations, but other RIPs are possible, and claimed subject matter is not limited in this regard.

[0072] FIGS. 7-10 depict experimental results (measured intensity distributions) to illustrate further output beams for various bend radii of VBC fiber 200 shown in FIG. 2.

[0073] In FIG. 7 when VBC fiber 200 is straight, the beam is nearly completely confined to confinement region 216. As the bend radius is decreased, the intensity distribution shifts to higher diameters {FIGS. 8-10). FIG. 8 depicts the intensity distribution when the bend radius of VBC fiber 200 is chosen to shift the intensity distribution preferentially to confinement region 218. FIG. 9 depicts the experimental results when the bend radius is further reduced and chosen to shift the intensity distribution outward to confinement region 220 and confinement region 218. In FIG. 10, at the smallest bend radius, the beam is nearly a "donut mode", with most of the intensity in the outermost confinement region 220.

[0074] Despite excitation of the confinement regions from one side at the splice junction 206, the intensity distributions are nearly symmetric azimuthaily because of scrambling within confinement regions as the beam propagates within the VBC fiber 200. Although the beam will typically scramble azimuthaily as it propagates, various structures or perturbations (e.g., coils) could be included to facilitate this process.

[0075] For the fiber parameters used in the experiment shown in FIGS. 7-10, particular confinement regions were not exclusively excited because some intensity was present in multiple confinement regions. This feature may enable advantageous materials processing applications that are optimized by having a flatter or distributed beam intensity distribution, in applications requiring cleaner excitation of a given confinement region, different fiber RIPs could be employed to enable this feature. [0076] The results shown in FIGS. 7-10 pertain to the particular fibers used in this experiment, and the details will vary depending on the specifics of the implementation. In particular, the spatial profile and divergence distribution of the output beam and their dependence on bend radius will depend on the specific RIPs employed, on the splice parameters, and on the characteristics of the laser source launched into the first fiber,

[0077] Different fiber parameters than those shown in FIG. 2 may be used and still be within the scope of the claimed subject matter. Specifically, different RIPs and core sizes and shapes may he used to facilitate compatibility with different input beam profiles and to enable different output beam characteristics. Example RIPs for the first length of fiber, in addition to the parabolic-index profile shown in FIG. 2, include other graded -index profiles, step-index, pedestal designs (i.e., nested cores with progressively lower refractive indices with increasing distance from the center of the fiber), and designs with nested cores with the same refractive index value but with various NA values for the central core and the surrounding rings. Example RIPs for the second length of fiber, in addition to the profile shown in FIG. 2. Include confinement fibers with different numbers of confinement regions, non-uniform confinement-region thicknesses, different and/or non-uniform values for the thicknesses of the rings surrounding the confinement regions, different and/or non-uniform NA values for the confinement regions, different refractive-index values for the high-index and low-index portions of the RIP, non-circular confinement regions (such as elliptical, oval, polygonal, square, rectangular, or combinations thereof), as well as other designs as discussed in further detail with respect to FIGS. 26-28. Furthermore, VBC fiber 200 and other examples of a VBC fiber described herein are not restricted to use of two fibers. In some examples, implementation may include use of one fiber or more than two fibers, in some cases _. , the flber{s) may not be axiaily uniform; for example, they could include fiber Bragg gratings or long-period gratings, or the diameter could vary along the length of the fiber. In addition, the fibers do not have to be azimuthaliy symmetric, e.g., the core(s) could have square or polygonal shapes. Various fiber coatings (buffers) may be employed, Including high-index or index-matched coatings {which strip light at the glass- polymer Interface) and low-index coatings (which guide light by total internal reflection at the giass-polymer interface). In some examples, multiple fiber coatings may be used on VBC fiber 200.

[0078] FIGS, 11-16 illustrate cross-sectional views of examples of first lengths of fiber for enabling adjustment of beam characteristics in a VBC fiber responsive to perturbation of an optical beam propagating in the first lengths of fiber. Some examples of beam characteristics that may be adjusted in the first length of fiber are: beam diameter, beam divergence distribution, BPP, intensity distribution, luminance, M ² factor, NA, optical intensity profile, power density profile, radial beam position, radiance, spot size, or the like, or any combination thereof. The first lengths of fiber depicted in FIGS. 11-16 and described below are merely examples and do not provide an exhaustive recitation of the variety of first lengths of fiber that may be utilized to enable adjustment of beam

characteristics in a VBC fiber assembly. Selection of materials, appropriate RIPs, and other variables for the first lengths of fiber illustrated In FIGS. 11-16 at least depend on a desired beam output A wide variety of fiber variables are contemplated and are within the scope of the claimed subject matter. Thus, claimed subject matter is not limited by examples provided herein,

[0079] In FIG. 11 first length of fiber 1100 comprises a step-Index profile 1 102. FIG. 12 illustrates a first length of fiber 1200 comprising a "pedestal RIP" (i.e., a core comprising a step-index region surrounded by a larger step-Index region) 1202. f 10. 13 illustrates first length of fiber 1300 comprising a multiple-pedestal RIP 1302.

[0080] FIG. 14A illustrates first length of fiber 1400 comprising a graded-index profile 141.8 surrounded by a down-doped region 1404, When the fiber 1400 is perturbed, modes may shift radially outward In fiber 1400 (e.g., during bending of fiber 1400), Graded-index profile 1402 may be designed to promote maintenance or even compression of modal shape. This design may promote adjustment of a beam propagating in fiber 1400 to generate a beam having a beam intensity distribution concentrated in an outer perimeter of the fiber (i.e., in a portion of the fiber core that is displaced from the fiber axis), As described above, when the adjusted beam is coupled Into a second length of fiber having confinement regions, the intensity distribution of the adjusted beam may be trapped in the outermost confinement region, providing a donui shaped intensity distribution, A beam spot having a narrow outer confinement region may be useful to enable certain material processing actions.

[0081] FIG, 14B illustrates first length of fiber 1408 comprising a graded-index profile 1414 surrounded by a down-doped region 1408 similar to fiber 1400. However, fiber 1408 includes a divergence structure 1410 (a lower-Index region) as can be seen in profile 1412, The divergence structure 1410 is an area of material with a lower refractive index than that of the surrounding core. As the beam is launched into first length of fiber 1406, refraction from divergence structure 1410 causes the beam divergence to increase in first length of fiber 1406. The amount of increased divergence depends on the amount of spatial overlap of the beam with the divergence structure 1410 and the magnitude of the Index difference between the divergence structure 1410 and the core material.

Divergence structure 1410 can have a variety of shapes, depending on the input divergence distribution and desired output divergence distribution, in an example, divergence structure 1410 has a triangular or graded index shape,

[0082] FIG, 15 illustrates a first length of fiber 1500 comprising a parabolic-index central region 1502 surrounded by a constant-index region 1504, and the constant-index region 1504 is surrounded by a lower-index annular layer 1506. The lower-index annular layer 1506 helps guide a beam propagating in fiber 1500. When the propagating beam is perturbed, modes shift radially outward in fiber 1500 (e.g., during bending of fiber 1500}- As one or more modes shift radially outward, parabolic-index region 1502 promotes retention of modal shape,. When the modes reach the constant-index region of the RIP 1510, they will be compressed against the low-index annular layer 1506, which may cause preferential excitation of the outermost confinement region in the second fiber (in comparison to the first fiber RIP shown in FIG, 14). In one implementation, this fiber design works with a confinement fiber having a central step-index core and a single annular core. The parabolic-index portion 1502 of the RIP overlaps with the central step- index core of the confinement fiber. The constant-index portion 1504 overlaps with the annular core of the confinement fiber. The constant-index portion 1504 of the first fiber is Intended to make it easier to move the beam into overlap with the annular core by bending. This fiber design also works with other designs of the confinement fiber.

[0083] FIG, 18 illustrates a first length of fiber 1800 comprising guiding regions 1604, 1606, 1608, and 1616 bounded by lower-index layers 1610, 1612, and 1614 where the indexes of the lower-index layers 1610, 1612, and 1614 are stepped or, more generally, do not. all have the same value, as illustrated by RIP 1602, The lower-index layers may serve to bound the beam intensity to certain guiding regions (1604, 1606, 1606, and 1616) when the perturbation assembly 210 (see FIG, 2) acts on the fiber 1600. In this way, adjusted beam light may be trapped in the guiding regions over a range of perturbation actions (such as over a range of bend, radii, a range of bend lengths, a range of micro- bending pressures, and/or a range of aoousto-opticai signals), allowing for a certain degree of perturbation tolerance before a beam intensity distribution is shifted to a more distant radial position in fiber 1600. Thus, variation In beam characteristics may be controlled in a step-wise fashion. The radial widths of the guiding regions 180.4, 1606, 1608, and 1818 may be adjusted to achieve a desired ring width, as may be required by an application. Also, a guiding region can have a thicker radial width to facilitate trapping of a larger fraction of the incoming beam profile if desired. Region 1806 is an example of such a design.

[0084] FIGS. 17-21 depict examples of fibers configured to enable maintenance and/or confinement of adjusted beam characteristics in the second length of fiber (e.g., fiber 208). These fiber designs are referred to as "ring-shaped confinement fibers" because they contain a central core surrounded by annular or ring-shaped cores. These designs are merely examples and not an exhaustive recitation of the variety of fiber RIPs that may be used to enable maintenance and/or confinement of adjusted beam characteristics within a fiber. Thus, claimed subject matter is not limited to the examples provided herein.

Moreover, any of the first lengths of fiber described above with respect to FIGS. 11-16 may be combined with any of the second length of fiber described FIGS. 17-21 ,

[0085] FIG. 17 illustrates a cross-sectional view of an example second length of fiber for maintaining and/or confining adjusted beam characteristics in a VBC fiber assembly. As the perturbed beam is coupled from a first length of fiber to second length of fiber 1700, the second length of fiber 1700 may maintain at least a portion of the beam characteristics adjusted in response to perturbation in the first length of fiber within one or more of confinement regions 1704, 1708, and/or 1708. Fiber 1700 has a RIP 1702. Each of confinement regions 1704, 1706, and/or 1708 is bounded by a lower index layer 1710 and/or 1712. This design enables second length of fiber 1700 to maintain the adjusted beam characteristics. As a result, a beam output by fiber 1700 will substantially maintain the received adjusted beam as modified in the first length of fiber giving the output beam adjusted beam characteristics, which may be customized to a processing task or other application.

[0086] Similarly, FIG , 18 depicts a cross -sectional view of an example second length of fiber 1600 for maintaining and/or confining beam characteristics adjusted in response to perturbation in the first length of fiber in a VBC fiber assembly. Fiber 1800 has a RIP 1802. However, confinement regions 1808, 1810, and/or 1812 have different thicknesses than confinement regions 1704, 170.8, and 1708. Each of confinement regions 1808, 1810, and/or 1812 is hounded by a lower index layer 1804 and/or 1806. Varying the thicknesses of the confinement regions (and/or barrier regions) enables tailoring or optimization of a confined adjusted radiance profile by selecting particular radial positions within which to confine an adjusted beam.

[0087] FIG. 19 depicts a cross-sectional view of an example second length of fiber 1900 having a RIP 1902 for maintaining and/or confining an adjusted beam in a VBC fiber assembly configured to provide variable beam characteristics-. In this example, the number and thicknesses of confinement regions 1904, 1906, 1908, and 1910 are different from fiber 1700 and 1800 and the barrier layers -1912, 1914, and 1916- are of varied thicknesses as well. Furthermore, confinement regions 1904. 1906, 1908, and 1910 have different indexes of refraction and barrier layers 1912, 1914, and 1916 have different indexes of refraction as well. This design may further enable a more granular or optimized tailoring of the confinement and/or maintenance of an adjusted beam radiance to particular radial locations within fiber 1900. As the perturbed beam Is launched from a first length of fiber to second length of fiber 1900 the modified beam characteristics of the beam (having an adjusted intensity distribution, radial position, and/or divergence angle, or the like, or a combination thereof) is confined within a specific radius by one or more of confinement regions 1904, 1906, 1908 and/or 1910 of second length of fiber 1900.

[0088] As noted previously, the divergence angle of -a beam may be conserved or adjusted and then conserved in the second length of fiber. There are a variety of methods to change the divergence angle of -a beam. The following _, are examples of fibers configured to enable adjustment of the divergence angle of a beam propagating from a first length of fiber to a second length of fiber in a fiber assembly for varying beam characteristics.. However, these are merely examples and ml an exhaustive recitation of the variety of methods that may be used to enable adjustment of divergence of a. beam. Thus, claimed subject matter is not limited to the examples provided herein.

[00891 Π6. 20 depicts a cross-sectional view of an example second length of fiber 2000 having RIP 2002 for modifying, maintaining, and/or confining beam characteristics adjusted in response to perturbation in the first length of fiber, in this example, second length of fiber 2000 is similar to the previously described second lengths of fiber and forms a portion of the VBC fiber assembly for delivering variable beam characteristics as discussed above, There are three confinement regions 2004, 2008, and 2006 and three barrier layers 2010, 2012, and 2016. Second length of fiber 2000 also has a divergence structure 2014 situated within the confinement region 2008. The divergence structure 2014 is an area of material with a lower refractive Index than that of the surrounding confinement region. As the beam is launched into second length of fiber 2000 refraction from divergence structure 2014 causes the beam divergence to increase in second length of fiber 2000, The amount of increased divergence depends on the amount of spatial overlap of the beam with the divergence structure 2014 and the magnitude of the index difference between the divergence structure 2014 and the core material. By adjusting the radial position of the beam near the launch point Into the second length of fiber 2000, the divergence distribution may be varied. The adjusted divergence of the beam is conserved in fiber 2000, which is configured to deliver the adjusted beam to the process head, another optica! system (e.g., fiber-to-fiber coupler or fiber-to-fiber -switch), the work piece, or the like, or a combination thereof . In an example, divergence structure 2014 may have an index dip of about 10 ^-5 0 3x10 ^-2 with respect to the surrounding material. Other values of the index dip may be employed within the scope of this disclosure and claimed subject matter is not so limited.

[0090] FIG. 21 depicts a cross-sectional view of an example second length of fiber 2100 having a RIP 2102 for modifying, maintaining, and/or confining beam characteristics adjusted in response to perturbation in the first length of fiber. Second length of fiber 2100 forms a portion of a VBC fiber assembly for delivering a beam having variable

characteristics. In this example, there are three confinement regions 2104, 2108, and 2108 and three barrier layers 2110, 2112, and 2118. Second length of fiber 2100 also has a plurality of divergence structures 2114 and 2118. The divergence structures 21 14 and 2118 are areas of graded tower index material As the beam is launched from the first, length fiber into second length of fiber 2100, refraction from divergence structures 2114 and 2118 causes the beam divergence to increase. The amount of increased divergence depends on the amount of spatial overlap of the beam with the divergence structure and the magnitude of the Index difference between the divergence structure 2114 and/or 2118 and the surrounding core material of confinement regions 2108 and 2104 respectively. By adjusting the radial position of the beam near the launch point Into the second length of fiber 2100, the divergence distribution may be varied. The design shown in FIG.. 21 allows the intensity distribution and the divergence distribution to be varied somewhat independently by selecting both a particular confinement region and the divergence distribution within that confinement region (because each confinement region may include a divergence structure}.. The adjusted divergence of the beam is conserved in fiber 2100,· which is configured to deliver the adjusted beam to the process head, another optical system, or the work piece. Forming the divergence structures 2114 and 2118 with a graded or non-constant index enables tuning of the divergence profile of the beam propagating in fiber 2100. An adjusted beam characteristic such as a radiance profile and/or divergence profile may be conserved as it is delivered to a process head by the second fiber. Alternatively, an adjusted beam characteristic such as a radiance profile and/or divergence profile may be conserved or further adjusted as ft is routed by the second fiber through a fiber-to-fiber coupler (FFC) and/or fiber-to-fiber switch (FFS) and to a process fiber, which delivers the beam to the process head or the work piece.

[0091] FIGS. 26-28 are cross-sectional views illustrating examples of fibers and fiber R!Ps configured to enable maintenance and/or confinement of adjusted beam characteristics of a beam propagating in an azlmuthaily asymmetric second length of fiber wberein the beam characteristics are adjusted responsive to perturbation of a first length of fiber coupled to the second length of fiber and/or perturbation of the beam by a perturbation device 110. These azlrouthaiiy asymmetric designs are merely examples and are not an exhaustive recitation of the variety of fiber RIPs thai may be used to enable maintenance and/or confinement of adjusted beam characteristics within an azimuthally asymmetric fiber. Thus, claimed subject matter is not limited to the examples provided herein.

Moreover, any of a variety of first lengths of fiber (e.g., like those described above) may be combined with any azimuthally asymmetric second length of fiber (e.g., like those described in FIGS. 26-28).

[0092] FIG. 26 illustrates RIPs at various azimuthai angles Of a cross-section through an elliptical fiber 2600. At a first azimuthai angle 2602, fiber 2600 has a first RIP 2604. At a second azimuthai angle 2606 that is rotated 45" from first azimuthai angle 2602, fiber 2600 has a second RIP 2608. At a third azimuthai angle 2610 that is rotated another 45° from second azimuthai angle 260.6, fiber 2600 has a third RIP 2612. First, second and third RIPs 2804, 2608 and 2612 are all different.

[0003} FIG. 2? illustrates RIPs at various azimuthai angles of a cross-section through a multfcore fiber 2700. At a first azimuthai angle 2702, fiber 2700 has a first RIP 2704. At a second azimuthal angle 2706, fiber 2700 has a second RIP 2708. First and second RIP ^' S 2704 and 2708 are different In an example, perturbation device 110 may act in multiple planes in order to launch the adjusted beam into different regions of an azimulhaliy asymmetric second fiber.

[0094] FIG, 28 illustrates RIPs at various azimuthai angles of a cross-section through a fiber 2800 having at least one crescent shaped core. In some eases, the corners of the crescent may be rounded, flattened, or otherwise shaped, which may minimize optical loss. At a first azimuthai angle 2802, fiber 2800 has a first RIP 2804. At a second azimuthai angle 2806, fiber 2800 has a second RIP 2808. First and second RIPs 2804 and 2808 are different.

10095] FIG. 22A illustrates an example of a laser system 2200 including a VBC fiber assembly 2202 configured to provide variable beam characteristic?. VBC fiber assembly 2202 comprises a first length of fiber 104, second length of fiber 108, and a perturbation device 110. VBC fiber assembly 2202 is disposed between feeding fiber 2212 (i.e., the output fiber from the laser source) and VBC delivery fiber 2240. VBC delivery fiber 2240 may comprise second length of fiber 108 or an extension of second length of fiber 108 that modifies, maintains, and/or confines adjusted beam characteristics. Beam 2210 is coupled into VBC fiber assembly 2202 via feeding fiber 2212. Fiber assembly 2202 is configured to vary the characteristics of beam 2210 in accordance with the various examples described above. The output of fiber assembly 2202 Is adjusted beam 2214 which is coupled into VBC delivery fiber 2240. VBC delivery fiber 2240 delivers adjusted beam 2214 to free- space optics assembly 2208, which then couples beam 2214 into a process fiber 2204. Adjusted beam 2214 Is then delivered to process head 2206 by process fiber 2204. The process head can include guided wave optics (such as fibers and fiber coupler), free space optics such as lenses, mirrors, optical filters, diffraction gratings), beam scan assemblies such as galvanometer scanners, polygonal mirror scanners, or other scanning systems that are used to shape the beam 2214 and deliver the shaped beam to a workpiece,

[0096] In laser system 2200, one or more of the free-space optics of assembly 2208 may be disposed in an FFC or other beam coupler 2216 to perform a variety of optical manipulations of an adjusted beam 2214 (represented in FIG. 22A with different dashing lhan beam 2210). For example, free-space optics assembly 2208 may preserve the adjusted beam characteristics of beam 2214, Process fiber 2204 may have the same RIP as VBC delivery fiber 2240. Thus, the adjusted beam characteristics of adjusted beam 2214 may be preserved all the way to process head 2308. Process fiber 2204 may- comprise a RIP similar to any of the second lengths of fiber described above, including confinement regions.

[0097] Alternatively, as illustrated In FIG. 22B _S free-space optics assembly 2208 may change the adjusted beam characteristics of beam 2214 by, for example, increasing or decreasing the divergence and/or the spot size of beam 2214 (e.g.,. by magnifying or demagnifying beam 2214} and/or otherwise further modifying adjusted beam 2214.

Furthermore, process fiber 2204 may have a different RiP than VBC delivery fiber 2240. Accordingly, the RIP of process fiber 2204 may be selected to preserve additional adjustment of adjusted beam 2214 made by the free-space optics of assembly 2208 to generate a twice adjusted beam 2224 (represented in FIG. 228 with different dashing than beam 2214),

[0098] FIG. 23 illustrates an example of a laser system 2300 including VBC fiber assembly 2302 disposed between feeding fiber 2312 and VBC delivery fiber 2340. During operation, beam 2310 is coupled into VBC fiber assembly 2302 via feeding fiber 2312. Fiber assembly 2302 includes a first length of fiber 104, second length of fiber 108, and a perturbation device 110 and is configured to vary characteristics of beam 2310 in accordance with the various examples described above. Fiber assembly 2302 generates adjusted beam 2314 output by VBC delivery fiber 2340, VBC delivery fiber 2340 comprises a second length of fiber 108 of fiber for modifying, maintaining, and/or confining adjusted beam characteristics in a fiber assembly 2302 in accordance with the various examples described above (see FIGS. 17-21, for example). VBC delivery fiber 2340 couples adjusted beam 2314 into beam switch (FFS) 2332, which then couples its various output beams to one or more of multiple process fibers 2304, 2320, and 2322. Process fibers 2304, 2320, and 2322 deliver adjusted beams 2314, 2328, and 2330 to respective process heads 2308, 2324, and 2328.

[0099] in an example, beam switch 2332 includes one or more sets of free-space optics 2303, 2316, and 2318 configured to perform a variety of optical manipulations of adjusted beam 2314. Free-space optics 2308, 2316, and 2318 may preserve or vary adjusted beam characteristics of beam 2314. Thus, adjusted beam 2314 may be maintained by the free-space optics or adjusted further. Process fibers 2304, 2320, and 2322 may have the same or a different RIP as VBC delivery fiber 2340, depending on whether it is desirable to preserve or further modify a beam passing from the free-space optics assemblies 2308, 2316, and 2318 to respective process fibers 2304, 2320, and 2322, in other examples, one or more beam portions of beam 2310 are coupled to a workplace without adjustment, or different beam portions are coupled to respective VBC fiber assemblies so that beam portions associated with a plurality of beam characteristics can be provided for

simultaneous workpieee processing. Alternatively, beam 2310 can be switched to one or more of a set of VBC fiber assemblies.

[00100] Routing adjusted beam 2314 through any of free-space optics assemblies 2308, 2316, and 2318 enables delivery of a variety of additionally adjusted beams to process heads 2308, 2324, and 2328. Therefore, laser system 2300 provides additional degrees of freedom for varying the characteristics of a beam, as well as switching the beam between process heads ("time sharing") and/or delivering the beam to multiple process heads simultaneously ("power sharing"),

[00101] For example, free-space optics in beam switch 2332 may direct adjusted beam 2314 to free-space optics assembly 2318 configured to preserve the adjusted

characteristics of beam 2314. Process fiber 2304 may have the same RIP as VBC delivery fiber 2340, Thus, the beam delivered to process head 2306 will be a preserved adjusted beam 2314.

100102] in another example, beam switch 2332 may direct adjusted beam 2314 to free- space optics assembly 2318- configured to preserve the adjusted characteristics of adjusted beam 2314, Process fiber 2320 may have a different RIP than VBC delivery fiber 2340 and may be configured with divergence altering structures as described with respect to FIGS. 20 and 21 to provide additional adjustments to the divergence distribution of beam 2314, Thus, the beam delivered to process head 2324 will be a twice adjusted beam 2328 having a different beam divergence profile than adjusted beam 2314.

[00103] Process fibers 2304, 2320, and/or 2322 may comprise a RIP similar to any of the second lengths of fiber described above, including confinement regions or a wide variety of other RfPs, and claimed subject matter is not limited in this regard.

[00104] In yet another example, free-space optics switch 2332 may direct adjusted beam 2314 to free-space optics assembly 2:308 confiaured to -change the beam characteristics of adjusted beam 2314, Process fiber 2322 may have a different RIP than VBC delivery fiber 2340 and may be configured to preserve (or alternatively further modify) the new further adjusted characteristics of beam 2314, Thus, the beam delivered to process head 2328 will be a twice adjusted beam 2330 having different beam characteristics (due to the adjusted divergence, profile and/or intensity profile) than adjusted beam 2314,

[001051 In FIGS. 22A, 22B, and 23, the optics in the FFC or FFS may adjust the spatial profile -and/or divergence profile by magnifying or demagnifylng the beam 2214 before launching into the process fiber. They may also adjust the spatial profile arid/or divergence profile via other optical transformations. They may also adjust the launch position into the process fiber. These methods may he used alone or in combination.

[00106] FIGS. 22A, 22B, and 23 merely provide examples of combinations of adjustments to beam characteristics using free-space optics and various combinations of fiber RIPs to preserve or modify adjusted beams 2214 and 2314. The examples provided above are not exhaustive and are meant for illustrative purposes only. Thus, claimed subject matter is not limited in this regard.

[00107] FIG. 24 illustrates various examples of perturbation devices, assemblies or methods (for simplicity referred to collectively herein as "perturbation device 1 10") for perturbing a VBC fiber 200 and/or an optical beam propagating in VBC fiber 200 according to various examples provided herein. Perturbation device i 10 may he any of a variety of devices, methods, and/or assemblies configured to enable adjustment of beam characteristics of a .beam propagating in VBC fiber 200. In an example, perturbation device 1 10 may foe a mandrel 2402, a micro-bend 2404 in the VBC fiber, flexible tubing 2408, an acousto-optic transducer 2408, a thermal device 2410, a piezo-elecihe device 2412, a grating 2414, a clamp 2418 (or other fastener), or the like, or any combination thereof. These are merely examples of perturbation devices 110 and not an exhaustive listing of perturbation devices 110 and claimed subject matter is not limited in this regard,

[00108] Mandrel 2402 may be used to perturb VBC fiber 200 by providing a form about which VBC fiber 200 may be bent. As discussed above, reducing the bend radius of VBC fiber 200 moves the intensity distribution of the beam radially outward . In some examples, mandrel 2402 may be stepped or conicaliy shaped to provide discrete bend radii levels. Alternatively, mandrel 2402 may comprise a cone shape without steps to provide continuous bend radii for more granular control of the bend radius. The radius of curvature of mandrel.2402 may be constant (e.g,, a cylindrical form) or non-constant (e.g., an oval- shaped form). Similarly, flexible tubing 2408, clamps 2418 (or other varieties of fasteners), or rollers 250 may bo used to guide and control the bending of VBC fiber 200 about mandrel 2402. Furthermore, changing the length over which the fiber is bent at a particular bend radius also may modify the intensity distribution of the beam. VBC fiber 200 and mandrel 2402 may be configured to change the intensity distribution within the first fiber predictably (e.g., in proportion to the length over which the fiber is bent and/or the bend radius). Rollers 250 may move up and down along a track 2442 on platform 2434 to change the bend radius of VBC fiber 200.

[00109] Clamps 2416 (or other fasteners) may he used to guide and control the bending of VBC fiber 200 with or without a mandrel 2402. Clamps 2416 may move up and down along a track. 2442 or platform 2448, Clamps 2416 may also swivel to change bend radius, tension, or direction of VBC fiber 200. Controller 2448 may control the movement of clamps 2416,

[00110] In another example, perturbation device 110 may he flexible tubing 2406 and may guide bending of VBC fiber 200 with or without a mandrel 2402, Flexible tubing 2406 may encase VBC fiber 200, Tubing 2406 may be made of a variety of materials and may be manipulated using piezoelectric transducers controlled by controller 2444, In another example, clamps or other fasteners may be used to move flexible tubing 2406,

100111} Micro-bend 2404 in VBC fiber is a local perturbation caused by lateral mechanical stress on the fiber. Micro-bending can cause mode coupling and/or transitions from one confinement region to another confinement region within a fiber, resulting in varied beam characteristics of the beam propagating in a V8C fiber 200. Mechanical stress may be applied by an actuator 2436 that is controlled by controller 2440. However, this is merely an example of a method for inducing mechanical stress in fiber 200 and claimed subject matter is not limited in this regard.

[00112] Acousto-optic transducer (ACT) 2408 may be used to induce perturbation of a beam propagating In the VBC fiber using an acoustic wave. The perturbation is caused by the modification of the refractive index of the fiber by the oscillating mechanical pressure of an acoustic wave. The period and strength of the acoustic wave are related to the acoustic ^' wave frequency and amplitude, allowing dynamic control of the acoustic perturbation. Thus, a perturbation assembly 110 including AOT 2408 may be configured to vary the beam characteristics of a beam propagating in the fiber. In an example, piezoelectric transducer 2418 may create the- acoustic wave and may he controlled by con.tr.oHer or driver 2420, The acoustic wave Induced in AOT 2408 may he modulated to change and/or control the beam characteristics of the optical beam in VBC 200 in real-time.

However, this is merely an example of a method for creating and controlling an AOT 2408 and claimed subject matter is not limited in this regard,

[00113] Thermal device 2410 may be used to induce perturbation of a beam propagating in VBC fiber using heat. The perturbation is caused by the modification of the RIP of the fiber induced by heat. Perturbation may be dynamically controlled by controlling an amount of heat transferred to the fiber and the length over which the heat is applied.. Thus, a perturbation assembly 110 including thermal device 2410 may be configured to. vary a range of beam characteristics. Thermal device 2410 may be controlled by controller 2450.

[00114] PiezO-etectric transducer 2412 may be used to induce perturbation of a beam propagating in a VBC fiber using piezoelectric action. The perturbation is caused by the modification of the RIP of the fiber induced by a piezoelectric material attached to the fiber. The piezoelectric material in the form of a Jacket around the bare fiber may apply tension or compression to the fiber, modifying its refractive index via the resulting changes in density. Perturbation may be dynamically controlled by controlling a voltage to the piezo-eiectric device 2412. Thus, a perturbation assembly 110 including ^' piezo-eiectric transducer 2412 may be configured to vary the beam characteristics over a particular range.

[00115] In an example* piezo-eiectric transducer 2412 may be configured to displace VBC fiber 200 in a variety of directions (e.g., axia!!y, radially, and/or laterally) depending on a variety of factors, including how the piezo-eiectric transducer 2412 is attached to VBC fiber 200, the direction of the polarization of the piezo-eiectric materials, the applied voltage, etc. Additionally, bending of VBC fiber 200 is possible using the piezo-eiectric transducer 2412, For example, driving a length of piezo-eiectric material having multiple segments comprising opposing electrodes can cause a piezoelectric transducer 2412 to bend in a lateral direction. Voltage applied to piezoelectric transducer 2412 by electrode 2424 may be controlled by controller 2422 to control displacement of VBC fiber 200, Displacement may be modulated to change and/or control the beam characteristics of the optical beam in VBC 200 in real-time. However, this is merely an example of a method of controiiing displacement of a VBC fiber 200 using a piezoelectric transducer 2412 and claimed subject matter is not limited in this regard.

[00116] Gratings 2414 may be used to Induce perturbation of a beam propagating in a VBC fiber 200. A grating 2414 can be written into a fiber by inscribing a periodic variation of the refractive index into the core. Gratings 2414 such as fiber Bragg gratings can operate as optical filters or as reflectors. A long-period grating can induce transitions among co-propagating fiber modes. The radiance, intensity profile, and/or divergence profile of a beam comprised of one or more modes can thus be adjusted using a long- period grating to couple one or more of the original modes to one or more different modes having different radiance and/or divergence profiles. Adjustment is achieved by varying the periodicity or amplitude of the refractive index grating. Methods such as varying the temperature, bend radius, and/or length (e.g., stretching) of the fiber Bragg grating can be used for such adjustment. VBC fiber 200 having gratings 2414 may be coupled to stage 2428. Stage 2426 may he configured to execute any of a variety of functions and may be controlled by controller 2428. For example, stage 2426 may be coupled to VBC fiber 200 with fasteners 2430 and may be configured to stretch and/or bend VBC fiber 200 using fasteners 2430 for leverage. Stage 2426 may have an embedded thermal device and may change the temperature of VBC fiber 200.

[00117] FIG. 25 illustrates an example process 2500 for adjusting and/or maintaining beam characteristics within a fiber without the use of free-space optics to adjust the beam characteristics. In block 2502, a first length of fiber and/or an optical beam are perturbed to adjust one or more optical beam characteristics. Process 2500 moves to block 2504, where the optical beam is launched into a second length of fiber. Process 2500 moves to block 2506, where the optical beam having the adjusted beam: characteristics is propagated in the second length of fiber. Process 2500 moves to block 2508, where at least a portion of the one or more beam characteristics of the optical beam are maintained within one or more confinement regions of the second length of fiber. The first and second lengths of fiber may be comprised of the same fiber, or they may be different fibers.

100118] An embodiment of the present disclosure is directed to a method of making a porous three-dimensional object by additive manufacturing techniques. During the creation of a layer-based 3D printed item, there exists a time at which every portion of the material is either exposed or lies immediately under the surface of the thinly deposited or processed layer, which is often referred to as a "build layer' in Ihe additive manufacturing art. This level of access to the material of the build layer allows for additional laser processing that can be used to tailor the porosity, pore size and/or overall pore structure of each successive build layer during the accessible period, thereby allowing the porosity, pore size and/or pore structure to be tailored throughout the entire 3D object as it is printed.

[001191 Referring to FIG, 29, the method comprises positioning a first layer of particles on a build plate, as shown in block 2902, The particles can be free-flowing {e,g., a dry powder), In the form of a paste or in any other form suitable for additive manufacturing. The particles may comprise metals or non-metal materials or mixtures of both. Particles comprising metal material can include any metals or metal containing compounds, including alloys and mixtures of various metallic compounds (e.g., metal oxides, metal carbides, metal nitrides and so forth) that are suitable for additive manufacturing, Non- metals can include any non-metal materials suitable for additive manufacturing, such as, for example, polymers or waxes.

[00120] The first layer of particles is heated sufficiently to fuse the particles together to form a first build layer having a first porosity; as shown in block 2904, The first build layer is exposed to a laser beam to form one or more pores, the exposed first build layer having a first modified porosity, as shown at block 2906. As will be discussed in greater detail below, the processes of blocks 2904 and 2008 can be performed simultaneously (e.g., in a single pass of the iaser) or sequentially (e.g., the particles of the entire build layer are first fused, followed by exposing the build layer to a laser beam to form pores), as can the processes of blocks 2912 and 2914. Fusing of the particles is defined, as used herein, to include sintering, melting (e.g., partially or fully melting) or any other phenomena in which the particles are joined together (e.g., by coalescing) through heating.

[00121] The Iaser beam employed for exposing the first build ^' layer is emitted from an optical fiber, such as any of the optical fiber lasers disclosed herein, At block 2908, one or more beam characteristics of the iaser beam are adjusted prior to or during the exposing of the first build layer. As described herein, the adjusting of the laser beam occurs prior to the iaser beam being emitted from the optical fiber, such as by perturbing a first fiber coupled to a second fiber, or by any of the other techniques set forth in the present disclosure. After forming the one or more pores at block 2908, an additional layer of particles is positioned on the exposed first build layer, as shown at block 2910. The additional layer of particles is heated sufficiently to fuse the particles together to form a second build layer Having a second porosity, as shown at block 2912. The second build layer Is exposed to the laser beam to form one or more pores, the exposed second build layer having a second modified porosity, as shown at block 2914. One or more beam characteristics of the laser beam are adjusted after fusing the particles to form the second buiid layer and prior to or during the exposing of the second build layer. Further, the adjusting of the laser beam occurs prior to the laser beam being emitted from the optical fiber, as shown at block 2918. As shown at 2918, the steps illustrated at blocks 2910, 2912 and optionally those at 2914 and 2916 can be repeated one or more times, such as 1 to 1,000,000 times, or 10 to 100,000 limes, or 100 to 50,000 times to form a three- dimensional object,

[00122] The adjusting of the one or more beam characteristics of the optical beam can be performed by any of the techniques described herein. For example, adjusting the one or more beam characteristics can comprise adjusting one or more of a beam diameter, divergence distribution, beam parameter product (BPP), intensity distribution, luminance, M2 value, numerical aperture (NA), optical Intensity, power density, radial beam position, radiance or spot size, or any combination thereof. In an embodiment, adjusting the one or more beam characteristics is carried out without ^' the use of free-space optics, as also described herein. In an example, adjusting the one or more beam characteristics of the optical beam comprises adjusting a beam parameter product of the laser beam. In yet another example, adjusting the one or more beam characteristics of the optical beam comprises adjusting one or both of a divergence distribution, BPP or an intensity distribution of the laser beam. Varying these beam characteristics can produce numerous different beam profiles suited for fusing the particle layer and/or for generating tailored pore shapes. The ability to adjust the beam parameters quickly can allow switching among beam shapes on the fly, thereby allowing efficient tailoring of porosity and/or pore size.

[0O123j In an example, the same laser is used for both heating to fuse the particles and to expose the first and second build layers, in this example, the characteristics of the laser beam can be adjusted using any of the above described techniques to provide a laser beam that is suitable for fusing the particles; followed by adjusting the laser beam again to provide a laser beam that is suitable for forming pores. In an embodiment adjusting the characteristics of the laser beam comprises adjusting one or more of a beam diameter, divergence distribution, beam parameter product (BPP), intensity distribution, luminance. U2 value, numerical aperture (NA), optica! intensity, power density, radial beam position, radiance or spot size, or any combination thereof. For example, a first set of laser beam characteristics, such as a first divergence distribution and/or intensify distribution, can be used to fuse the particles of the first build layer and the second build layer together; and a second set of laser beam characteristics, such as a second divergence distribution and/or intensity distribution, can be used to form the one or more pores of the exposed first buiid layer and exposed second build layer, where the first set of laser beam characteristics is different from the second set of laser beam characteristics.

[00124] In an embodiment, exposing the first buiid. layer at block 2908 (FIG, 29} removes portions of the fused particles from the first build layer so that the first modified porosity is greater than the first porosity. Similarly, exposing the second buiid layer at block 2914 removes portions of the fused particles from the second build layer so that the second modified porosity is greater than the second porosity. The mechanisms of pore creation with the laser may be likened to piercing or hole drilling, or may also Involve ablation or vaporization of portions of the fused particles in order to create the pores.

[00125] By employing the laser systems of the present disclosure, the porosity can be tailored in any desired manner. FIG, 30 shows an example of a 3D object 3000 comprising pores 3001. As illustrated, the object 3000 and the huM layers that form it have a. non- homogenous pore structure. As illustrated in FIG. 30, the porosity within a single build, layer 3010 can be varied, so that the exposed first build layer has a first region 3002 and a second region 3004, a porosity of the first region being different than a porosity of the second region. Exposing of the first region 3002 can be carried out using the laser having a first set of adjusted beam characteristics and the exposing of the second region 3004 can be carried out using the laser having a second set of adjusted beam characteristics that are different from the first set of adjusted beam characteristics. Multiple regions of a similar or the same porosity can be employed in a buiid layer. For example, region 3002 has a porosity similar to that of region 3006, as illustrated in FIG. 30. Further, the pores can vary continuously in a region, such as the graded porosity shown at region 3008 of FIG, 30. Any number of regions of differing porosity can be incorporated into a build layer using the techniques of the present disclosure. For example, the exposed buiid layers can comprise 2, 3 or more regions, such as 2 to 10,000 regions, or S to 500 regions, of differing porosity, with each region having a different porosity than other regions adjacent thereto in the build layer. In an example, the build layer can have a substantially ^' infinite number of regions of differing porosity, as in the case of a continuously graded porosity across the entire build layer.

[00126] In an embodiment the adjusting of the one or more beam characteristics of the laser beam prior to or during the exposing of the first build layer comprises perturbing an optical beam propagating within a first length of fiber to adjust one or more of the beam characteristics of the laser beam in the first, length of fiber or a second length of fiber or a combination thereof. As described herein, the perturbed optical beam is coupled into the second length of fiber. At least a portion of one or more adjusted beam characteristics is maintained within the second length of fiber. The first length of fiber and the second length of fiber have different refractive index profiles (RIPs). [00127] Any of the fiber designs described herein can be employed. In an example, the second length of fiber can be azimutha!ly asymmetric, such as the fibers in FIGS, 26 to ^' 28, or azSmuthatly symmetric, such as the fibers in FIGS. 14A to 21 , Employing different refractive index profile configurations for the second length of fiber, example, azlmuihaiiy asymmetric configurations or azimutha!iy symmetric configurations, or varying the optical beam distribution within the chosen fiber configuration, may affect the laser beam characteristics emitted from the fiber, and In torn, potentially affect the pore sizes and/or pore shapes that are formed in the build layer being exposed by the resulting laser beam that is emitted from the second fiber. Any of the refractive index profile configurations described herein for use in the second fiber can potentially be employed; and may be combined with any of the first fiber configurations described herein to provide a desired system for modifying pore structure in a build layer.

[00128] As described above, heating at blocks 2904 and 2912 can be is carried out using a first laser and the exposing of the build layers at 2906 and 2914 can be carried out using a second laser, where the first laser and the second laser are the same laser. Because beam characteristics can. be adjusted very quickly (e.g., many times a second, such as 10, 100, 1000 or as high as 100,000 times per second, depending on the adjustments ^' being made) heating to fuse the particles and exposing the build layer to form pores can be accomplished together during a single pass of the same laser, where changes in pore density can be accomplished by changing one or more of the beam characteristics, as described above, during the single pass. Thus, for example, the Heating at 2904 and exposing at 2908 can be performed simultaneously or sequentially during a single pass of the laser, as cars the heating at 2912 and exposing at 2914. For example, FIG. 31 illustrates a top view of a build layer ^' 3100 having different porosity regions 3102, 3104 and 3108. The regions can have any desired porosity. For illustrative purposes, region 3102 can be a fully dense layer, region 3104 can have a sintered structure with a porosity formed by interstitial spaces between fused particles; and region 3106 can have a tailored porosity that is greater than both the porosity of regions 3102 and 3104. The term "fully dense" as used herein is a term of art and is defined herein to mean the native density of the material. Such native densities can generally be found in the literature. FIG. 32 illustrates the same build layer 3100 with an overlay of an example path of a laser beam as if travels across a surface area of the build layer 31.00. While only a single pass is illustrated, multiple passes can be made across ail or a portion of the build layer 3100, as desired for heating and/or forming pores in the various regions. For example, a single pass car) be made to melt the particles of region 3102 to form a fully dense region; a single pass can also be made to fuse the particles in regions 3104 so as to form a sintered region: and first and second passes can be made over region 3106, the first pass to sinter or fully melt that region, as desired, and the second pass to form a desired pore structure, Alternatively, a single pass of the laser beam can be employed to form each of regions 3102, 3104 and 3108.

[00129] in FIG. 32, the path of the laser is illustrated as going horizontally, from right to left or left to right across the build layer 3100, as shown by laser path segments 3202. 3204 and 3206. However, the path of the laser can be in any desired direction across the build layer (e.g., vertical, diagonal and so forth), and/or can follow a linear or non-linear pattern, as desired. Thus, the path of the laser can be any suitable path that will accomplish the desired degree of fusing of the particles, porosity and/or pore structure.

[00130] In addition, as the laser is scanned across the build layer, the beam

characteristics can be adjusted as described herein to provide the desired fusing of the particles, porosity and/or pore structure, For example, a first set of laser beam

characteristics, can be employed with scanning region 3102, a second set of laser characteristics may be used when scanning region 3104 and a third set of characteristics may be used when scanning region 3108. Using the techniques for adjusting the laser beam characteristics described herein, the beam emitted from the fiber is switched between the first set of characteristics, the second set of characteristics and the third set of characteristics, Thus,, for example, as the laser beam follows path segment 3204 in FIG.. 32 and passes from region 3102 to region 3104, the beam can be adjusted from the first set of characteristics to the second set of characteristics, Then, as the laser beam continues along the path segment 3204 and passes from region 3104 back to region 3104, the beam can be adjusted from the second set of characteristics to the first set of characteristics. Likewise, as the laser beam travels along the path segment 3206 and passes from region 3104 to region 3108, the beam can be adjusted from the second set of characteristics to the third set of characteristics. During the laser scanning process, the adjustments to the beam characteristics can optionally be made on the fly, without stopping or slowing the scanning motion of the laser as it passes over the build layer 3100.

[00131] In an embodiment, the heating at blocks 2904 and 2912 of FIG. 28 is carried out using a first laser and a second laser is used to form the laser beam employed for the process at blocks 2908 and 2914, where the second laser Is different than the first laser. During the heating at blocks 2904, 2912 and 2906, 2914, the beam characteristics of either -or both of the first laser and the second laser can optionally be adjusted in any manner as described herein.

[00132] In an embodiment, the porosity can be varied from build layer to build layer within a 3D object. Referring to FIG. 30, for example,, the modified porosity of an exposed build layer 3016 can be different than a modified porosity of an exposed build layer 3014 that is formed on the build layer 3016. in an embodiment, each of the build layers 3010, 3012, 3014, 3016 and 3018 have a different porosity and/or different pore shapes than the build layer on which it Is formed, thereby resulting in different pore structures for some or each of the layers. Therefore, the porosity and/or pore size can be varied as desired across each build layer. Additionally, the porosity and/or pore size can be varied as the layers are built, thereby providing a three ^' dimensional porosity/pore size variability within the matrix of the 3D monolithic object being formed. Thus, the porous three-dimensional object of FIG. 30 comprises a first build layer 3010 having one or more pores in a first pore structure; and a second build 3012 layer on the first build iayer 3010, the. second layer having one or more pores in a second pore structure that is different than the first pore structure. The three dimensional object of FIG. 30 is illustrated with five build layers. However, the object may include any number of build layers having differing pore structures and/or differing porosities, such as 1 to 1,000,000 build layers, or 3 to 100,000 bulk! layers, or 5 to 50,000 build layers. While some of the build layers may have a homogenous pore structure, at least one of the build layers, such as 2 to 10 of the build layers, has a non-homogenous pore structure. Further, because the object of FIG., 30 is made fey additive manufacturing, each, build layer is joined to the adjacent layer or layers by fusing of the particles that are used to make the build layer to the adjacent layer or layers (e.g., by sintering or melting to coalesce the particles to the adjacent layer or layers ),

[00133] The pores formed by the methods of the present disclosure can have any desired shape. As an example, the one or more pores can have an asymmetric or symmetric non- spherical shape, as illustrated by pores 3001-1 and 3001-2 of FIG. 30, respectively.

Further, the shape of the pores can be varied within a build layer or from build layer to build layer within a 3D object, as also illustrated by FIG, 30, The pore size can be large enough to span two or more build layers, if desired. Thus, the methods of the present disclosure can comprise forming one or more pores having a first shape and one or more pores having a second shape that is different than the first shape. The different shapes can optionally be formed by employing a process that comprises adjusting beam characteristics, including any of the beam characteristics described herein. For example, a first set of beam characteristics can be employed io form pores 3001-1 and a second set of beam characteristics can be employed to form pores 3001-2.

[00134] In an embodiment, the build layer can be exposed to a laser beam to form a lattice structure therein, FIG, 33 shows on example of a 3D object 3.300 comprising pores 3302 that are arranged is a lattice structure that can be made using the methods of the present disclosure. One advantage of employing the methods of the present disclosure is that the lattice structure can be tailored in a nearly infinite variety of ways and/or may be produced in a relatively efficient manner by adjusting the beam characteristics as described herein. For instance, lattice structures with very small or very large pore sizes, non-symmetrical and/or non-spherical pore shapes and/or with pores arranged In a wide variety of lattice patterns can be achieved. Because the feature size of the pores made by the laser techniques of the present disclosure can be very small, lattice structures and other 3D objects can advantageously be made with very large numbers of very small pores {e.g., micron or nanometer s¾ed pores), In an embodiment, the average pore size can be, for example, about 500 nm to about 10 microns, or -about 1 micron to about 5 microns.. However, a benefit of the laser techniques of the present disclosure is that a wide variety of desired pore sizes can be selectively incorporated into the objects made thereby. As an example, the pore sizes of the lattice structures (or any other 3D objects) can range from the nanometer scale, such as, for example, from about 500 nm or 800 nm, to any desired upper limit, such as a millimeter, a centimeter or larger. Average pore sizes can range, for example, from about 500 nm to about 5 millimeters, such as about 1 micron to about 500 microns or 1 millimeter.

[00135] An embodiment of the present disclosure is directed to a porous three- dimensional object, made by the methods of the present disclosure, such as the methods shown and described above with respect to FIG. 29. The resulting three-dimensional object can have two or more regions of differing porosity in a single build layer. For example, one or more build layers In a 3D object can each comprise 2, 3 or more regions, such as 2 to 1,000 regions, or 5 to 50 regions of differing porosity, with each region having a different porosity than other regions adjacent thereto in the build layer. The 3D objects can include pores of any desired shape, including any of the pore shapes described herein. The pores can result in novel lattice structures thai have any of the pore sized described herein.

[00138] Having described and illustrated the general and specific principles of examples of the presently disclosed technology, it should be apparent that the examples may be modified in arrangement and detail without departing from such principles, We claim all modifications and variation coming within the spirit and scope of the following claims.