Patent Description:
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 workpiece via an optical fiber.

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: (<NUM>) Employ a laser system with fixed beam characteristics that can be used for different tasks but is not optimal for most of them (i.e., a compromise between performance and flexibility); or (<NUM>) 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., optical 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 and shapes 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.

<CIT> discloses an optical delivery waveguide for a material laser processing system.

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,.

Definitions of words and terms as used herein:.

Disclosed herein are methods, systems, and apparatus configured to provide a fiber operable to provide a laser beam having variable beam characteristics (VBC) 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, BPP, intensity distribution, M<NUM> factor, NA, optical intensity, power density, radial beam position, radiance, spot size, or the like, or any combination thereof.

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 beam 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 to its ultimate use (e.g., materials processing). The first and second lengths of fiber may comprise the same or different fibers.

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 the fiber. Important parameters are the fiber core diameter (dcore) and NA. The core diameter is typically in the range of <NUM> - <NUM> microns (although other values are possible), and the NA is typically in the range of <NUM> - <NUM> (although other values are possible). A delivery fiber from the laser may be routed directly to the process head or workpiece, or it may be routed to a fiber-to-fiber coupler (FFC) or fiber-to-fiber switch (FFS), which couples the light from the delivery fiber into a process fiber that transmits the beam to the process head or the workpiece.

Most materials processing tools, especially those at high power (> <NUM> kW), employ multimode (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-to-unit 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.

In one example, the VBC fiber may have a first length and a second length and may be configured to be interposed as an in-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<NUM> factor, NA, optical intensity, power density, radial beam position, radiance, spot size, or the like, or any combination thereof.

<FIG> illustrates an example VBC fiber <NUM> for providing a laser beam having variable beam characteristics without requiring the use of free-space optics to change the beam characteristics. VBC fiber <NUM> comprises a first length of fiber <NUM> and a second length of fiber <NUM>. First length of fiber <NUM> and second length of fiber <NUM> may be the same or different fibers and may have the same or different RIPs. The first length of fiber <NUM> and the second length of fiber <NUM> may be joined together by a splice. First length of fiber <NUM> and second length of fiber <NUM> 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.

A perturbation device <NUM> is disposed proximal to and/or envelops a perturbation region <NUM>. Perturbation device <NUM> may be a device, assembly, in-fiber structure, and/or other feature. Perturbation device <NUM> at least perturbs optical beam <NUM> in first length of fiber <NUM> or second length of fiber <NUM> or a combination thereof in order to adjust one or more beam characteristics of optical beam <NUM>. Adjustment of beam <NUM> responsive to perturbation by perturbation device <NUM> may occur in first length of fiber <NUM> or second length of fiber <NUM> or a combination thereof. Perturbation region <NUM> may extend over various widths and may or may not extend into a portion of second length of fiber <NUM>. As beam <NUM> propagates in VBC fiber <NUM>, perturbation device <NUM> may physically act on VBC fiber <NUM> to perturb the fiber and adjust the characteristics of beam <NUM>. Alternatively, perturbation device <NUM> may act directly on beam <NUM> to alter its beam characteristics. Subsequent to being adjusted, perturbed beam <NUM> has different beam characteristics from those of beam <NUM>, which will be fully or partially conserved in second length of fiber <NUM>. In another example, perturbation device <NUM> need not be disposed near a splice. Moreover, a splice may not be needed at all, for example VBC fiber <NUM> 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).

Perturbed beam <NUM> is launched into second length of fiber <NUM>, where perturbed beam <NUM> characteristics are largely maintained or continue to evolve as perturbed beam <NUM> propagates yielding the adjusted beam characteristics at the output of second length of fiber <NUM>. In one example, the new beam characteristics may include an adjusted intensity distribution. In an example, an altered beam intensity distribution will be conserved in various structurally bounded confinement regions of second length of fiber <NUM>. Thus, the beam intensity distribution may be tuned to a desired beam intensity distribution optimized for a particular laser processing task. In general, the intensity distribution of perturbed beam <NUM> will evolve as it propagates in the second length of fiber <NUM> to fill the confinement region(s) into which perturbed beam <NUM> is launched responsive to conditions in first length of fiber <NUM> and perturbation caused by perturbation device <NUM>. 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 <NUM> are described in greater detail below. Beams <NUM> and <NUM> are conceptual abstractions intended to illustrate how a beam may propagate through a VBC fiber <NUM> for providing variable beam characteristics and are not intended to closely model the behavior of a particular optical beam.

VBC fiber <NUM> may be manufactured by a variety of methods including PCVD (Plasma Chemical Vapor Deposition), OVD (Outside Vapor Deposition), VAD (Vapor Axial Deposition), MOCVD (Metal-Organic Chemical Vapor Deposition. ) and/or DND (Direct Nanoparticle Deposition). VBC fiber <NUM> may comprise a variety of materials. For example, VBC fiber <NUM> may comprise SiO<NUM>, SiO<NUM> doped with GeO<NUM>, germanosilicate, phosphorus pentoxide, phosphosilicate, Al<NUM>O<NUM>, aluminosilicate, 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<NUM>+ (erbium), Yb<NUM>+ (ytterbium), Nd<NUM>+ (neodymium), Tm<NUM>+ (thulium), Ho<NUM>+ (holmium), or the like or any combination thereof. Confinement regions may be bounded by cladding having a lower index than that of the confinement region with fluorine or boron doping. Alternatively, VBC fiber <NUM> may comprise photonic crystal fibers or micro-structured fibers.

VBC fiber <NUM> 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.

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

In an example, first length of fiber <NUM> has a parabolic-index RIP <NUM> as indicated by the left RIP graph. Most of the intensity distribution of beam <NUM> is concentrated in the center of fiber <NUM> when fiber <NUM> is straight or nearly straight. Second length of fiber <NUM> is a confinement fiber having RIP <NUM> as shown in the right RIP graph. Second length of fiber <NUM> includes confinement regions <NUM>, <NUM>, and <NUM>. Confinement region <NUM> is a central core surrounded by two annular (or ring-shaped) confinement regions <NUM> and <NUM>. Layers <NUM> and <NUM> are structural barriers of lower index material between confinement regions (<NUM>, <NUM> and <NUM>), commonly referred to as "cladding" regions. In one example, layers <NUM> and <NUM> may comprise rings of fluorosilicate; in some embodiments, the fluorosilicate cladding layers are relatively thin. Other materials may be used as well, and claimed subject matter is not limited in this regard.

In an example, as beam <NUM> propagates along VBC fiber <NUM>, perturbation assembly <NUM> may physically act on fiber <NUM> and/or beam <NUM> to adjust its beam characteristics and generate an adjusted beam <NUM>. In the current example, the intensity distribution of beam <NUM> is modified by perturbation assembly <NUM>. Subsequent to adjustment of beam <NUM>, the intensity distribution of adjusted beam <NUM> may be concentrated in outer confinement regions <NUM> and <NUM> with relatively little intensity in the central confinement region <NUM>. Because each of confinement regions <NUM>, <NUM>, and/or <NUM> is isolated by the thin layers of lower index material in barrier layers <NUM> and <NUM>, second length of fiber <NUM> can substantially maintain the adjusted intensity distribution of adjusted beam <NUM>. Adjusted beam <NUM> will typically become distributed azimuthally within a given confinement region (see e.g., <FIG>, <FIG>, <FIG>, and <FIG>) but will not transition (significantly) between the confinement regions as it propagates along the second length of fiber <NUM>. Thus, the adjusted beam characteristics of adjusted beam <NUM> are largely conserved within the isolated confinement regions <NUM>, <NUM>, and/or <NUM>.

In one example, core confinement region <NUM> and annular confinement regions <NUM> and <NUM> may be composed of fused silica glass, and cladding <NUM> and <NUM> defining the confinement regions may be composed of fluorosilicate glass. Other materials may be used to form the various confinement regions (<NUM>, <NUM> and <NUM>), including germanosilicate, phosphosilicate, aluminosilicate, 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 (<NUM> and <NUM>), including fused silica, borosilicate, 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.

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. For example, confinement regions may be configured to provide stepwise beam displacement.

<FIG> illustrates an example method of perturbing fiber <NUM> 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 <NUM> can be decreased from a first bend radius R<NUM> to a second bend radius R<NUM> about splice junction <NUM> by using a stepped mandrel or cone as perturbation assembly <NUM>. Additionally or alternatively, the engagement length on the mandrel(s) or cone can be varied. Rollers <NUM> may be employed to engage VBC fiber <NUM> across perturbation assembly <NUM>. In an example, an amount of engagement of rollers <NUM> with fiber <NUM> has been shown to shift the distribution of the intensity profile to the outer confinement regions <NUM> and <NUM> of fiber <NUM> with a fixed mandrel radius. There are a variety of other methods for varying the bend radius of fiber <NUM>, 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 <NUM> 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.

Maintaining the bend radius of the fibers across junction <NUM> ensures that the adjusted beam characteristics such as radial beam position and radiance profile of optical beam <NUM> will not return to its unperturbed state before being launched into second length of fiber <NUM>. Moreover, the adjusted radial beam characteristics, including position, divergence angle, and/or intensity distribution, of adjusted beam <NUM> can be varied based on an extent of decrease in the bend radius and/or the extent of the bent length of VBC fiber <NUM>. Thus, specific beam characteristics may be obtained using this method.

In the current example, first length of fiber <NUM> having first RIP <NUM> is spliced at junction <NUM> to a second length of fiber <NUM> having a second RIP <NUM>. 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 <NUM> and to enable conservation of the adjusted beam. Such a RIP may be similar to the RIPs shown in fibers illustrated in <FIG>, and/or <NUM>.

<FIG> is an example graph <NUM> illustrating the calculated profile of the lowest-order mode (LP<NUM>) for a first length of fiber <NUM> for different fiber bend radii <NUM>, wherein perturbation assembly <NUM> involves bending VBC fiber <NUM>. As the fiber bend radius is decreased, an optical beam propagating in VBC fiber <NUM> is adjusted such that the mode shifts radially away from the center <NUM> of a VBC fiber <NUM> core (r = <NUM> micron) toward the core/cladding interface (located at r = <NUM> micron in this example). Higher-order modes (LPIn) also shift with bending. Thus, for a straight or nearly straight fiber (very large bend radius), curve <NUM> for LP<NUM> is centered at or near the center of VBC fiber <NUM>. At a bend radius of about <NUM>, curve <NUM> for LP<NUM> is shifted to a radial position of about <NUM> from the center <NUM> of VBC fiber <NUM>. At a bend radius of about <NUM>, curve <NUM> for LP<NUM> is shifted to a radial position about <NUM> from the center <NUM> of VBC fiber <NUM>. At a bend radius of about <NUM>, curve <NUM> for LP<NUM> is shifted to a radial position about <NUM> from the center <NUM> of VBC fiber <NUM>. At a bend radius of about <NUM>, curve <NUM> for LP<NUM> is shifted to a radial position about <NUM> from the center <NUM> of VBC fiber <NUM>. At a bend radius of about <NUM>, a curve <NUM> for LP<NUM> is shifted to a radial position about <NUM> from the center <NUM> of VBC fiber <NUM>. 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.

In an example, if VBC fiber <NUM> is straightened, LP<NUM> mode will shift back toward the center of the fiber. Thus, the purpose of second length of fiber <NUM> 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 <NUM>. The splice between fibers <NUM> and <NUM> is included in the bent region, thus the shifted mode profile will be preferentially launched into one of the ring-shaped confinement regions <NUM> and <NUM> or be distributed among the confinement regions. <FIG> illustrate this effect.

Initially, in second length of fiber <NUM> shown in the example of <FIG>, confinement region <NUM> has a <NUM> micron diameter, confinement region <NUM> is between <NUM> micron and <NUM> micron in diameter, and confinement region <NUM> is between <NUM> micron and <NUM> micron diameter. Confinement regions <NUM>, <NUM>, and <NUM> are separated by <NUM> thick rings of fluorosilicate, providing an NA of <NUM> for the confinement regions. Other inner and outer diameters for the confinement regions, thicknesses of the rings separating the confinement regions, NA values for the confinement regions, and numbers of confinement regions may be employed.

With the above-noted example dimensions, <FIG> illustrates a simulated example of a two-dimensional intensity distribution at junction <NUM> within second length of fiber <NUM> when VBC fiber <NUM> is nearly straight. A significant portion of LP<NUM> and LPIn is within confinement region <NUM> of fiber <NUM>. When VBC fiber <NUM> is straight (e.g., unperturbed), about <NUM>% of the power is contained within the central confinement region <NUM>, and about <NUM>% of the power is contained within confinement regions <NUM> and <NUM>. In contrast, <FIG> shows a simulated example of a two-dimensional intensity distribution of adjusted optical beam <NUM> applied to junction <NUM> within second length of fiber <NUM> when VBC fiber <NUM> is bent. A significant portion of LP<NUM> and LPIn is within confinement region <NUM> of fiber <NUM> in response to VBC fiber <NUM> being bent with a radius chosen to preferentially excite confinement region <NUM> (the outermost confinement region) of second length of fiber <NUM>. Thus, when fiber <NUM> is bent to preferentially excite second ring confinement region <NUM>, nearly <NUM>% of the power is contained within confinement region <NUM>, and more than <NUM>% of the power is contained within confinement regions <NUM> and <NUM>. These calculations include LP<NUM> and two higher-order modes, which are typical in some <NUM>-<NUM> kW fiber lasers. Specific RIPs, dimensions, and shapes of the confinement regions for the two fibers were assumed for the purpose of the these calculations, but other RIPs, dimensions, and shapes are possible, and claimed subject matter is not limited in this regard.

It is clear from <FIG> that, in the case where perturbation assembly <NUM> acts on VBC fiber <NUM> to bend the fiber, the state of the bend radius establishes the spatial overlap of the modal intensity distribution of the first length of fiber <NUM> with the different confinement regions (<NUM>, <NUM>, and <NUM>) of the second length of fiber <NUM>. Changing the bend radius can thus change the intensity distribution at the output of the second length of fiber <NUM>, thereby changing the diameter, spot size, or intensity profile of the beam, and thus changing its radiance and BPP value. This adjustment of the spot size may be accomplished in an all-fiber structure, involving no free-space optics and consequently may reduce or eliminate the disadvantages of free-space optics discussed above. Such adjustments can also be made with other perturbation assemblies that alter bend radius, bend length, fiber tension, temperature, micro-bending, or other perturbations discussed below.

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 workpiece by the process head. Varying the intensity distribution as shown in <FIG> thus enables variation of the beam profile at the workpiece in order to tune and/or optimize the process, as desired. For example, <FIG>, <FIG>, <FIG>, and <FIG> show, at junction <NUM>, end views of second length of fiber <NUM> as different, progressively increasing amounts of perturbation are applied to VBC fiber <NUM> in response to perturbation assembly <NUM> acting on VBC fiber <NUM> to bend the fiber at various radii (i.e., decreasing of the bend radius). In these prophetic examples, a beam from a laser source could be launched into an input fiber (not shown) with a <NUM> micron core diameter. The input fiber would be spliced to first length of fiber <NUM>. The exact implementation details however, will vary depending on the specifics of the application. In particular, the spatial profile and divergence distribution of the output beam and their dependence on bend radius (or other states of applied perturbation) will depend on the specific RIPs employed, on the splice parameters, and on the characteristics of the laser source launched into the first fiber.

Optical beam <NUM>, whether adjusted or not, has an intensity distribution in which its area spatially overlaps one or more confinement regions. A selectable state of perturbation may be applied to moderately shift optical beam <NUM>, change its BPP, or modify other beam characteristics (i.e., a change in how the aforementioned area spatially overlaps one or more confinement regions) so as to generate adjusted optical beam <NUM>. Thus, different beam shapes may be generated based on the amount of perturbation applied to VBC fiber <NUM>.

<FIG> shows a pictorial view of an input end (the end coupled at splice junction <NUM> to an output end of a first fiber) of fiber <NUM>. Fiber <NUM> is shown receiving in its central coaxial confinement region <NUM> an optical beam <NUM> that is generally unperturbed so as to produce from it, at the output end of fiber <NUM>, a Gaussian intensity distribution shown in <FIG>, which has a corresponding Gaussian intensity profile <NUM> shown in <FIG>. For example, when VBC fiber <NUM> is straight, a nearly Gaussian input beam shown in <FIG> is substantially confined to confinement region <NUM> so as to generate the desired Gaussian intensity distribution at the output. An initial, nominally unperturbed state maintains a generally Gaussian intensity profile having about <NUM>% of its power contained within the central confinement region <NUM>, whereas incremental changes in state may shift the generally Gaussian distribution from lower to higher orders of a generally super-Gaussian distribution. Different states of perturbation may be used to change the Gaussian center, RMS width, or other Gaussian distribution parameters of Gaussian intensity profile <NUM>, or to generate a super-Gaussian beam within central confinement region <NUM>.

Despite excitation of portions of confinement regions from one side at splice junction <NUM>, the results intensity distributions at the opposing side-shown at the output end in <FIG>, <FIG>, <FIG>, and <FIG>-are nearly symmetric azimuthally because of scrambling within confinement regions as the beam propagates within the VBC fiber <NUM>. Although the beam will typically scramble azimuthally as it propagates, various structures or perturbations (e.g., coils) could be included to facilitate this process.

In some embodiments, it may be desirable to have optical power of adjusted optical beam <NUM> divided among confinement regions <NUM>, <NUM>, and/or <NUM> rather than have it concentrated in a single region. In other words, particular confinement regions need not be exclusively excited. For example, as the bend radius is decreased, the intensity distribution at the input shifts to the larger diameters of confinement regions <NUM> and <NUM> located farther away from confinement region <NUM>-see e.g., this shift is visible in <FIG>, <FIG>, and <FIG> and the resulting output is shown in, respectively, <FIG>, <FIG>, and <FIG>. The capability to distribute intensity across one or more confinement regions based on an amount of perturbation advantageously facilitates materials processing applications optimized by having a flatter (or distributed) beam intensity distribution. Other applications expecting more discrete excitation of a particular confinement region are also possible using different fiber RIPs to enable this feature.

<FIG> depicts the intensity distribution when the bend radius of VBC fiber <NUM> is chosen to shift the intensity distribution between confinement regions <NUM> and <NUM>. In one example, the selected amount of applied perturbation is that which simultaneously shifts and expands optical beam <NUM> in forming the adjusted optical beam <NUM> so the area of its intensity distribution spatially overlaps the adjacent confinement regions. Thus, the input end of fiber <NUM> receives adjusted optical beam <NUM> in adjacent portions (e.g., neighboring portions separated by lower-index cladding) of its central coaxial confinement region <NUM> and middle confinement region <NUM> so as to produce an output optical beam having a generally super-Gaussian intensity distribution shown in <FIG>, which has a corresponding super-Gaussian intensity profile <NUM> shown in <FIG>.

In some embodiments, the aforementioned shift and expansion of optical beam <NUM> causes adjusted optical beam <NUM> to possess non-zero ellipticity (this phenomena is also simulated as adjusted optical beam <NUM> of <FIG>. ), which facilitates a more even intensity distribution across confinement regions, resulting in a relatively flat top of a relatively high-order super-Gaussian intensity profile <NUM>. In contrast, less perturbation may be employed to generate a relatively low-order super-Gaussian intensity profile <NUM>. Low-order super-Gaussian intensity profile <NUM> is formed, in some embodiments, by applying less perturbation so as to concentrate more intensity in central coaxial confinement region(s). Conversely, it should be readily appreciated that high-order super-Gaussian intensity profile <NUM> may approach a flat-top (i.e., a top-hat, for circular beams) intensity profile <NUM>.

Skilled persons will appreciate that the higher the order of a super-Gaussian profile, the sharper its corners become as it eventually approximates an ideal flat-top. In practice, however, a flat-top profile maintains at least some rounding in its corners and is typically approximated as a high-order super-Gaussian profile rather than a strictly rectangular profile. Accordingly, a super-Gaussian beam profile having a substantially flat-top and Gaussian fall-off is more generally represented by the following equation: <MAT> where n is the order, r represents radial position, and Ip is peak intensity (on the beam axis) of a Gaussian beam having a Gaussian beam radius w.

Compared to the example of <FIG>, the example of <FIG> shows greater radial shift and less ellipticity, and thereby places more intensity away from region <NUM> and into region <NUM>. As with the previous examples, the optimal amount of shift or ellipticity may be determined empirically, on an application-specific basis. For some applications, the bend radius may be further reduced and chosen to shift the intensity distribution more outward to confinement region <NUM> and confinement region <NUM>, leaving less power density in the center and thereby approximating at the output a saddle-shaped distribution shown in <FIG>, which has a corresponding saddle-shaped intensity profile <NUM> shown in <FIG>. Profile <NUM> is generally defined by a bimodal shape that includes two local maxima <NUM> and a local minimum <NUM> therebetween. In some embodiments, the local minimum may reach about zero intensity (which would be called a "donut" beam), whereas other embodiments maintain residual intensity at the local minimum.

<FIG> shows another pictorial view of the input end of fiber <NUM> primarily receiving in its outer coaxial confinement region <NUM> adjusted optical beam <NUM> so as to produce from it an output optical beam having a so-called donut mode shown in <FIG>, which has a corresponding intensity profile <NUM> shown in <FIG>. In contrast to the previous examples, adjusted optical beam <NUM> also has a smaller diameter so as to concentrate intensity in outer coaxial confinement region <NUM>. The smaller diameter is achieved, for example, using a RIP of a first fiber that is different from the RIP used in connection the previous examples shown in <FIG>, <FIG>, and <FIG>.

Skilled persons will appreciate that the idealized graphs in <FIG>, <FIG>, <FIG>, and <FIG> show smooth transitions. In practice, however, cladding between confinement regions introduces minor disruptions in intensity. These disruptions are, however, not so significant to fundamentally alter the character of selected beam shapes. In other words, a saddle shape, for example, need not possess a perfectly smooth bimodal profile to still serve its intended purpose.

Different fiber parameters from those shown in <FIG> may be used and still be within the scope of the claimed subject matter. Specifically, different RIPs and core sizes and shapes may be 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>, 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>, 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 <FIG>. The designs of <FIG> are also possibble, but are not according to the claimed invention.

Furthermore, VBC fiber <NUM> 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 fiber(s) may not be axially 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 azimuthally 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 glass-polymer interface). In some examples, multiple fiber coatings may be used on VBC fiber <NUM>.

<FIG> 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<NUM> 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 <FIG> 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 <FIG> 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.

In <FIG> first length of fiber <NUM> comprises a step-index profile <NUM>. <FIG> illustrates a first length of fiber <NUM> comprising a "pedestal RIP" (i.e., a core comprising a step-index region surrounded by a larger step-index region) <NUM>. <FIG> illustrates a first length of fiber <NUM> comprising a multiple-pedestal RIP <NUM>.

<FIG> illustrates a first length of fiber <NUM> comprising a graded-index profile <NUM> surrounded by a down-doped region <NUM>. When the fiber <NUM> is perturbed, modes may shift radially outward in fiber <NUM> (e.g., during bending of fiber <NUM>). Graded-index profile <NUM> may be designed to promote maintenance or even compression of modal shape. This design may promote adjustment of a beam propagating in fiber <NUM> 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 donut shaped intensity distribution. A beam spot having a narrow outer confinement region may be useful to enable certain material processing actions.

<FIG> illustrates a first length of fiber <NUM> comprising a graded-index profile <NUM> surrounded by a down-doped region <NUM> similar to that of fiber <NUM>. However, fiber <NUM> includes a divergence structure <NUM> (a lower-index region) as can be seen in profile <NUM>. The divergence structure <NUM> 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 <NUM>, refraction from divergence structure <NUM> causes the beam divergence to increase in first length of fiber <NUM>. The amount of increased divergence depends on the amount of spatial overlap of the beam with the divergence structure <NUM> and the magnitude of the index difference between the divergence structure <NUM> and the core material. Divergence structure <NUM> can have a variety of shapes, depending on the input divergence distribution and desired output divergence distribution. In an example, divergence structure <NUM> has a triangular or graded index shape.

<FIG> illustrates a first length of fiber <NUM> comprising a parabolic-index central region <NUM> surrounded by a constant-index region <NUM>. Between the constant-index region <NUM> and the parabolic-index central region <NUM> is a lower-index annular layer (or lower-index ring or annulus) <NUM> surrounding the parabolic-index central region <NUM>. The lower-index annulus <NUM> helps guide a beam propagating in fiber <NUM>. When the propagating beam is perturbed, modes shift radially outward in fiber <NUM> (e.g., during bending of fiber <NUM>). As one or more modes shift radially outward, parabolic-index region <NUM> promotes retention of modal shape. When the modes reach the constant-index region <NUM> at outer portions of a RIP <NUM>, they will be compressed against the lower-index ring <NUM>, which (in comparison to the first fiber RIP shown in <FIG>) may cause preferential excitation of the outermost confinement region in the second fiber. 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 <NUM> of the RIP <NUM> overlaps with the central step-index core of the confinement fiber. The constant-index portion <NUM> overlaps with the annular core of the confinement fiber. The constant-index portion <NUM> 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.

<FIG> illustrates a first length of fiber <NUM> comprising guiding regions <NUM>, <NUM>, <NUM>, and <NUM> bounded by lower-index layers <NUM>, <NUM>, and <NUM> where the indexes of the lower-index layers <NUM>, <NUM>, and <NUM> are stepped or, more generally, do not all have the same value. The stepped-index layers may serve to bound the beam intensity to certain guiding regions (<NUM>, <NUM>, <NUM>, and <NUM>) when the perturbation assembly <NUM> (see <FIG>) acts on the fiber <NUM>. 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 acousto-optical signals), allowing for a certain degree of perturbation tolerance before a beam intensity distribution is shifted to a more distant radial position in fiber <NUM>. Thus, variation in beam characteristics may be controlled in a step-wise fashion. The radial widths of the guiding regions <NUM>, <NUM>, <NUM>, and <NUM> 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 <NUM> is an example of such a design.

<FIG> depict examples of fibers configured to enable maintenance and/or confinement of adjusted beam characteristics in the second length of fiber (e.g., fiber <NUM>). 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 <FIG> may be combined with any of the second length of fiber described <FIG>.

<FIG> 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 a second length of fiber <NUM>, the second length of fiber <NUM> 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 <NUM>, <NUM>, and/or <NUM>. Fiber <NUM> has a RIP <NUM>. Each of confinement regions <NUM>, <NUM>, and/or <NUM> is bounded by a lower index layer <NUM> and/or <NUM>. This design enables second length of fiber <NUM> to maintain the adjusted beam characteristics. As a result, a beam output by fiber <NUM> 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.

Similarly, <FIG> depicts a cross-sectional view of an example second length of fiber <NUM> for maintaining and/or confining beam characteristics adjusted in response to perturbation in the first length of fiber in a VBC fiber assembly. Fiber <NUM> has a RIP <NUM>. However, confinement regions <NUM>, <NUM>, and/or <NUM> have different thicknesses from the thicknesses of confinement regions <NUM>, <NUM>, and <NUM>. Each of confinement regions <NUM>, <NUM>, and/or <NUM> is bounded by a lower index layer <NUM> and/or <NUM>. 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.

<FIG> depicts a cross-sectional view of an example second length of fiber <NUM> having a RIP <NUM> 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 <NUM>, <NUM>, <NUM>, and <NUM> are different from those of fiber <NUM> and <NUM>; and the barrier layers <NUM>, <NUM>, and <NUM> are of varied thicknesses as well. Furthermore, confinement regions <NUM>, <NUM>, <NUM>, and <NUM> have different indexes of refraction; and barrier layers <NUM>, <NUM>, and <NUM> 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 <NUM>. As the perturbed beam is launched from a first length of fiber to second length of fiber <NUM>, 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 <NUM>, <NUM>, <NUM>, and/or <NUM> of second length of fiber <NUM>.

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 not 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.

<FIG> depicts a cross-sectional view of an example second length of fiber <NUM> having a RIP <NUM> 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 <NUM> 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 <NUM>, <NUM>, and <NUM> and three barrier layers <NUM>, <NUM>, and <NUM>. Second length of fiber <NUM> also has a divergence structure <NUM> situated within the confinement region <NUM>. The divergence structure <NUM> 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 <NUM>, refraction from divergence structure <NUM> causes the beam divergence to increase in second length of fiber <NUM>. The amount of increased divergence depends on the amount of spatial overlap of the beam with the divergence structure <NUM> and the magnitude of the index difference between the divergence structure <NUM> and the core material. By adjusting the radial position of the beam near the launch point into the second length of fiber <NUM>, the divergence distribution may be varied. The adjusted divergence of the beam is conserved in fiber <NUM>, which is configured to deliver the adjusted beam to the process head, another optical system (e.g., fiber-to-fiber coupler or fiber-to-fiber switch), the workpiece, or the like, or a combination thereof. In an example, divergence structure <NUM> may have an index dip of about <NUM>-<NUM> - <NUM>×<NUM>-<NUM> 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.

<FIG> depicts a cross-sectional view of an example second length of fiber <NUM> having a RIP <NUM> for modifying, maintaining, and/or confining beam characteristics adjusted in response to perturbation in the first length of fiber. Second length of fiber <NUM> forms a portion of a VBC fiber assembly for delivering a beam having variable characteristics. In this example, there are three confinement regions <NUM>, <NUM>, and <NUM> and three barrier layers <NUM>, <NUM>, and <NUM>. Second length of fiber <NUM> also has a plurality of divergence structures <NUM> and <NUM>. The divergence structures <NUM> and <NUM> are areas of graded lower index material. As the beam is launched from the first length fiber into second length of fiber <NUM>, refraction from divergence structures <NUM> and <NUM> 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 <NUM> and/or <NUM> and the surrounding core material of confinement regions <NUM> and <NUM> respectively. By adjusting the radial position of the beam near the launch point into the second length of fiber <NUM>, the divergence distribution may be varied. The design shown in <FIG> 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 <NUM>, which is configured to deliver the adjusted beam to the process head, another optical system, or the workpiece. Forming the divergence structures <NUM> and <NUM> with a graded or non-constant index enables tuning of the divergence profile of the beam propagating in fiber <NUM>. 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 it 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 workpiece.

<FIG> are cross-sectional views illustrating examples of fibers and fiber RIPs configured to enable maintenance and/or confinement of adjusted beam characteristics of a beam propagating in an azimuthally asymmetric second length of fiber, wherein 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 <NUM>. These azimuthally asymmetric designs are merely examples and are 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 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 <FIG>).

<FIG> illustrates RIPs at various azimuthal angles of a cross-section through an elliptical fiber <NUM>. At a first azimuthal angle <NUM>, fiber <NUM> has a first RIP <NUM>. At a second azimuthal angle <NUM> that is rotated <NUM>° from first azimuthal angle <NUM>, fiber <NUM> has a second RIP <NUM>. At a third azimuthal angle <NUM> that is rotated another <NUM>° from second azimuthal angle <NUM>, fiber <NUM> has a third RIP <NUM>. First, second, and third RIPs <NUM>, <NUM>, and <NUM> are all different.

<FIG> illustrates RIPs at various azimuthal angles of a cross-section through a multicore fiber <NUM> not useful to implement the claimed invention. At a first azimuthal angle <NUM>, fiber <NUM> has a first RIP <NUM>. At a second azimuthal angle <NUM>, fiber <NUM> has a second RIP <NUM>. First and second RIPs <NUM> and <NUM> are different. In an example, perturbation device <NUM> may act in multiple planes in order to launch the adjusted beam into different regions of an azimuthally asymmetric second fiber.

<FIG> illustrates RIPs at various azimuthal angles of a cross-section through a fiber <NUM> not useful to implement the claimed invention, the fiber having at least one crescent shaped core. In some cases, the corners of the crescent may be rounded, flattened, or otherwise shaped, which may minimize optical loss. At a first azimuthal angle <NUM>, fiber <NUM> has a first RIP <NUM>. At a second azimuthal angle <NUM>, fiber <NUM> has a second RIP <NUM>. First and second RIPs <NUM> and <NUM> are different.

<FIG> illustrates an example of a laser system <NUM> including a VBC fiber assembly <NUM> configured to provide variable beam characteristics. VBC fiber assembly <NUM> comprises a first length of fiber <NUM>, a second length of fiber <NUM>, and a perturbation device <NUM>. VBC fiber assembly <NUM> is disposed between feeding fiber <NUM> (i.e., the output fiber from the laser source) and VBC delivery fiber <NUM>. VBC delivery fiber <NUM> may comprise second length of fiber <NUM> or an extension of second length of fiber <NUM> that modifies, maintains, and/or confines adjusted beam characteristics. Beam <NUM> is coupled into VBC fiber assembly <NUM> via feeding fiber <NUM>. Fiber assembly <NUM> is configured to vary the characteristics of beam <NUM> in accordance with the various examples described above. The output of fiber assembly <NUM> is adjusted beam <NUM>, which is coupled into VBC delivery fiber <NUM>. VBC delivery fiber <NUM> delivers adjusted beam <NUM> to a free-space optics assembly <NUM>, which then couples beam <NUM> into a process fiber <NUM>. Adjusted beam <NUM> is then delivered to process head <NUM> by process fiber <NUM>. 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), and/or beam scan assemblies (such as galvanometer scanners, polygonal mirror scanners, or other scanning systems) that are used to shape the beam <NUM> and deliver the shaped beam to a workpiece.

In laser system <NUM>, one or more of the free-space optics of assembly <NUM> may be disposed in an FFC or other beam coupler <NUM> to perform a variety of optical manipulations of an adjusted beam <NUM> (represented in <FIG> with different dashing from that of beam <NUM>). For example, free-space optics assembly <NUM> may preserve the adjusted beam characteristics of beam <NUM>. Process fiber <NUM> may have the same RIP as VBC delivery fiber <NUM>. Thus, the adjusted beam characteristics of adjusted beam <NUM> may be preserved all the way to process head <NUM>. Process fiber <NUM> may comprise a RIP similar to any of the second lengths of fiber described above, including confinement regions.

Alternatively, as illustrated in <FIG>, free-space optics assembly <NUM> may change the adjusted beam characteristics of beam <NUM> by, for example, increasing or decreasing the divergence and/or the spot size of beam <NUM> (e.g., by magnifying or demagnifying beam <NUM>) and/or otherwise further modifying adjusted beam <NUM>. Furthermore, process fiber <NUM> may have a different RIP than VBC delivery fiber <NUM>. Accordingly, the RIP of process fiber <NUM> may be selected to preserve additional adjustment of adjusted beam <NUM> made by the free-space optics of assembly <NUM> to generate a twice adjusted beam <NUM> (represented in <FIG> with different dashing from that of beam <NUM>).

<FIG> illustrates an example of a laser system <NUM> including VBC fiber assembly <NUM> disposed between a feeding fiber <NUM> and a VBC delivery fiber <NUM>. During operation, a beam <NUM> is coupled into VBC fiber assembly <NUM> via feeding fiber <NUM>. Fiber assembly <NUM> includes a first length of fiber <NUM>, a second length of fiber <NUM>, and a perturbation device <NUM> and is configured to vary characteristics of beam <NUM> in accordance with the various examples described above. Fiber assembly <NUM> generates an adjusted beam <NUM> output by VBC delivery fiber <NUM>. VBC delivery fiber <NUM> comprises a second length of fiber <NUM> of fiber for modifying, maintaining, and/or confining adjusted beam characteristics in a fiber assembly <NUM> in accordance with the various examples described above (see <FIG>, for example). VBC delivery fiber <NUM> couples adjusted beam <NUM> into a beam switch (FFS) <NUM>, which then couples its various output beams to one or more of multiple process fibers <NUM>, <NUM>, and <NUM>. Process fibers <NUM>, <NUM>, and <NUM> deliver adjusted beams <NUM>, <NUM>, and <NUM> to respective process heads <NUM>, <NUM>, and <NUM>.

In an example, beam switch <NUM> includes one or more sets of free-space optics <NUM>, <NUM>, and <NUM> configured to perform a variety of optical manipulations of adjusted beam <NUM>. Free-space optics <NUM>, <NUM>, and <NUM> may preserve or vary adjusted beam characteristics of beam <NUM>. Thus, adjusted beam <NUM> may be maintained by the free-space optics or adjusted further. Process fibers <NUM>, <NUM>, and <NUM> may have the same or a different RIP as that of VBC delivery fiber <NUM>, depending on whether it is desirable to preserve or further modify a beam passing from the free-space optics assemblies <NUM>, <NUM>, and <NUM> to respective process fibers <NUM>, <NUM>, and <NUM>. In other examples, one or more beam portions of beam <NUM> are coupled to a workpiece 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 workpiece processing. Alternatively, beam <NUM> can be switched to one or more of a set of VBC fiber assemblies.

Routing adjusted beam <NUM> through any of free-space optics assemblies <NUM>, <NUM>, and <NUM> enables delivery of a variety of additionally adjusted beams to process heads <NUM>, <NUM>, and <NUM>. Therefore, laser system <NUM> 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").

For example, free-space optics in beam switch <NUM> may direct adjusted beam <NUM> to free-space optics assembly <NUM> configured to preserve the adjusted characteristics of beam <NUM>. Process fiber <NUM> may have the same RIP as that of VBC delivery fiber <NUM>. Thus, the beam delivered to process head <NUM> will be a preserved adjusted beam <NUM>.

In another example, beam switch <NUM> may direct adjusted beam <NUM> to free-space optics assembly <NUM> configured to preserve the adjusted characteristics of adjusted beam <NUM>. Process fiber <NUM> may have a different RIP from that of VBC delivery fiber <NUM> and may be configured with divergence altering structures as described with respect to <FIG> to provide additional adjustments to the divergence distribution of beam <NUM>. Thus, the beam delivered to process head <NUM> will be a twice adjusted beam <NUM> having a different beam divergence profile from that of adjusted beam <NUM>.

Process fibers <NUM>, <NUM>, and/or <NUM> may comprise a RIP similar to any of the second lengths of fiber described above, including confinement regions or a wide variety of other RIPs, and claimed subject matter is not limited in this regard.

In yet another example, free-space optics switch <NUM> may direct adjusted beam <NUM> to free-space optics assembly <NUM> configured to change the beam characteristics of adjusted beam <NUM>. Process fiber <NUM> may have a different RIP from that of VBC delivery fiber <NUM> and may be configured to preserve (or alternatively further modify) the new further adjusted characteristics of beam <NUM>. Thus, the beam delivered to process head <NUM> will be a twice adjusted beam <NUM> having different beam characteristics (due to the adjusted divergence profile and/or intensity profile) from those of adjusted beam <NUM>.

In <FIG>, the optics in the FFC or FFS may adjust the spatial profile and/or divergence profile by magnifying or demagnifying the beam <NUM> before launching into the process fiber. They may also adjust the spatial profile and/or divergence profile via other optical transformations. They may also adjust the launch position into the process fiber. These methods may be used alone or in combination.

<FIG> 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 <NUM> and <NUM>. The examples provided above are not exhaustive and are meant for illustrative purposes only. Thus, claimed subject matter is not limited in this regard.

<FIG> illustrates various examples of perturbation devices, assemblies or methods (for simplicity referred to collectively herein as "perturbation device <NUM>") for perturbing a VBC fiber <NUM> and/or an optical beam propagating in VBC fiber <NUM> according to various examples provided herein. Perturbation device <NUM> may be any of a variety of devices, methods, and/or assemblies configured to enable adjustment of beam characteristics of a beam propagating in VBC fiber <NUM> in response to application of one or more of various states of perturbation. Some examples of various states of perturbation that may be applied to VBC fiber <NUM> include, but are not limited to, amount or direction of bending, lateral mechanical stress, acoustic wave oscillation-induced mechanical pressure, temperature variation, piezo-electric transducer displacement, and varying periodicity or amplitude of refractive grating. A variation in one or more states establishes a different state of perturbation. To vary one or more of these states, perturbation device <NUM> may be a mandrel <NUM>, a micro-bend <NUM> in the VBC fiber, flexible tubing <NUM>, an acousto-optic transducer <NUM>, a thermal device <NUM>, a piezo-electric device <NUM>, a grating <NUM>, a clamp <NUM> (or other fastener), or the like, or any combination thereof. These are merely examples of perturbation devices <NUM> and not an exhaustive listing of perturbation devices <NUM>, and claimed subject matter is not limited in this regard.

Mandrel <NUM> may be used to perturb VBC fiber <NUM> by providing a form about which VBC fiber <NUM> may be bent. As discussed above, reducing the bend radius of VBC fiber <NUM> moves the intensity distribution of the beam radially outward. In some examples, mandrel <NUM> may be stepped or conically shaped to provide discrete bend radii levels. Alternatively, mandrel <NUM> 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 <NUM> may be constant (e.g., a cylindrical form) or non-constant (e.g., an oval-shaped form). Similarly, flexible tubing <NUM>, clamps <NUM> (or other varieties of fasteners), or rollers <NUM> may be used to guide and control the bending of VBC fiber <NUM> about mandrel <NUM>. 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 <NUM> and mandrel <NUM> 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 <NUM> may move up and down along a track <NUM> on a platform <NUM> to change the bend radius of VBC fiber <NUM>.

Clamps <NUM> (or other fasteners) may be used to guide and control the bending of VBC fiber <NUM> with or without a mandrel <NUM>. Clamps <NUM> may move up and down along a track <NUM> or a platform <NUM>. Clamps <NUM> may also swivel to change bend radius, tension, or direction of VBC fiber <NUM>. A controller <NUM> may control the movement of clamps <NUM>.

In another example, perturbation device <NUM> may be flexible tubing <NUM> and may guide bending of VBC fiber <NUM> with or without a mandrel <NUM>. Flexible tubing <NUM> may encase VBC fiber <NUM>. Tubing <NUM> may be made of a variety of materials and may be manipulated using piezoelectric transducers controlled by a controller <NUM>. In another example, clamps or other fasteners may be used to move flexible tubing <NUM>.

Micro-bend <NUM> 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 VBC fiber <NUM>. Mechanical stress may be applied by an actuator <NUM> that is controlled by controller <NUM>. However, this is merely an example of a method for inducing mechanical stress in fiber <NUM> and claimed subject matter is not limited in this regard.

Acousto-optic transducer (AOT) <NUM> 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 <NUM> including AOT <NUM> may be configured to vary the beam characteristics of a beam propagating in the fiber. In an example, a piezo-electric transducer <NUM> may create the acoustic wave and may be controlled by a controller or driver <NUM>. The acoustic wave induced in AOT <NUM> may be modulated to change and/or control the beam characteristics of the optical beam in VBC <NUM> in real-time. However, this is merely an example of a method for creating and controlling an AOT <NUM>, and claimed subject matter is not limited in this regard.

Thermal device <NUM> 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 <NUM> including thermal device <NUM> may be configured to vary a range of beam characteristics. Thermal device <NUM> may be controlled by a controller <NUM>.

Piezo-electric transducer <NUM> 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-electric device <NUM>. Thus, a perturbation assembly <NUM> including piezo-electric transducer <NUM> may be configured to vary the beam characteristics over a particular range.

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

Gratings <NUM> may be used to induce perturbation of a beam propagating in a VBC fiber <NUM>. A grating <NUM> can be written into a fiber by inscribing a periodic variation of the refractive index into the core. Gratings <NUM> 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 <NUM> having gratings <NUM> may be coupled to a stage <NUM>. Stage <NUM> may be configured to execute any of a variety of functions and may be controlled by a controller <NUM>. For example, stage <NUM> may be coupled to VBC fiber <NUM> with fasteners <NUM> and may be configured to stretch and/or bend VBC fiber <NUM> using fasteners <NUM> for leverage. Stage <NUM> may have an embedded thermal device and may change the temperature of VBC fiber <NUM>.

<FIG> illustrates an example process <NUM> for adjusting and/or maintaining beam characteristics within a fiber without the use of free-space optics to adjust the beam characteristics. In block <NUM>, a first length of fiber and/or an optical beam are perturbed to adjust one or more optical beam characteristics. Process <NUM> moves to block <NUM>, where the optical beam is launched into a second length of fiber. Process <NUM> moves to block <NUM>, where the optical beam having the adjusted beam characteristics is propagated in the second length of fiber. Process <NUM> moves to block <NUM>, 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.

<FIG> shows a beam shaper system <NUM> implemented with an optical beam delivery device <NUM> in the form of a VBC fiber <NUM>, which is constructed in accordance with the disclosed paradigm represented by example VBC fiber <NUM> (see e.g., <FIG> for additional details). For conciseness, some previously described details of <FIG> are further simplified and, therefore, not reproduced in <FIG>. Note also that subscripts "A," "B," "C," and "D" represent different selectable configurations of beam shaper system <NUM>, which are explained in the following paragraphs.

A laser source <NUM> emits optical beam <NUM> (<FIG>) propagating in a first length of fiber <NUM>, which corresponds to first length of fiber <NUM> (<FIG>). Optical beam <NUM> is incident on VBC fiber <NUM>. Perturbation device <NUM> operating in combination with, and applying different states (e.g., different amounts or directions) of perturbation to, VBC fiber <NUM> directs the fiber mode to different corresponding confinement regions of a second length of fiber <NUM>, which corresponds to second length of fiber <NUM> (<FIG>).

As described previously with reference to <FIG>, a controller <NUM> enables beam shaper system <NUM> to selectively move the fiber mode, i.e., the intensity distribution, of optical beam <NUM> to different areas at an input of second length of fiber <NUM>. In some embodiments, controller <NUM> comprises a computer workstation having input-output (I/O) devices suitable for establishing a signal interface with perturbation device <NUM> so as to signal states of perturbation that correspond to desired beam shapes indicated through, e.g., user input. Skilled persons will appreciate that controller <NUM> may include a central processing unit (CPU), field-programmable gate array (FPGA), or other control devices suitable for performing logic operations. Controller <NUM> may also include a non-transitory machine readable storage medium storing instructions thereon that, when executed, cause controller <NUM> to perform any methods or operations described in this disclosure.

In a first "A" configuration, controller <NUM> signals perturbation device <NUM> to apply a first state of perturbation to VBC fiber <NUM> and thereby establish a first selected intensity profile <NUM>A at an output end of second length of fiber <NUM>. An output beam having first selected intensity profile <NUM>A is then delivered by a process head <NUM> to a workpiece <NUM>.

In a subsequent "B" configuration, controller <NUM> signals perturbation device <NUM> to apply a second state of perturbation, different from the first state, to VBC fiber <NUM> and thereby establish a second selected intensity profile <NUM>B, different from first selected intensity profile <NUM>A, at the output end of second length of fiber <NUM>. Thus, perturbation device <NUM>, in response to control signals from controller <NUM>, applies to VBC fiber <NUM> a selected amount or direction of bend that shifts the fiber mode to a different area of confinement regions (c. , different areas shown in <FIG>, <FIG>, <FIG>, and <FIG>) and thereby provides a means of establishing, at an output of second length of fiber <NUM>, different selectable intensity profiles <NUM>.

Different intensity profiles <NUM> are selectable based on different material properties. According to some embodiments, a change from one perturbation state to another state is configured indirectly, e.g., in response to a selected change <NUM> in either a type of material to be processed or an indirectly related calibration setting for material of the same or different types than that of workpiece <NUM>. In other embodiments, a change from one perturbation state to another state is configured directly, e.g., by a direct selection <NUM> of a desired beam shape (i.e., potentially irrespective of material). Thus, a user may simply select a material or a beam shape through a selection interface <NUM> provided by, e.g., controller <NUM>, so as to dynamically change beam shape. The change may also be made fully or partly autonomously. For conciseness, a resulting intensity profile selected directly or indirectly is simply referred to as a selected intensity profile. Furthermore, skilled persons will appreciate that a selection of an intensity distribution is equivalent to a selection of an intensity profile-particularly since, in an azimuthally symmetric set of confinement regions, a given intensity profile is generally the same across any radial cross-sectional position among of the set of confinement regions.

Claim 1:
An optical beam delivery device (<NUM>) configured to generate, from an optical beam (<NUM>), selectable intensity profiles, the optical beam delivery device (<NUM>) comprising:
a first length of fiber (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>) having a first refractive index profile (RIP) (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>), the first RIP enabling, in response to an applied perturbation, modification of the optical beam to form an adjusted optical beam, the adjusted optical beam defining, at an output end of the first length of fiber, different intensity distributions based on different states of the applied perturbation; and
a second length of fiber (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>) having an input end coupled to the output end of the first length of fiber, the second length of fiber formed with coaxial confinement regions (<NUM>, <NUM>, <NUM>; <NUM>, <NUM>, <NUM>; <NUM>, <NUM>, <NUM>; <NUM>, <NUM>, <NUM>, <NUM>; <NUM>, <NUM>, <NUM>; <NUM>, <NUM>, <NUM>) defining a second RIP (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>) that is different from the first RIP, wherein a first confinement region and a second confinement region of the coaxial confinement regions are separated by a cladding structure having a refractive index that is lower than the indexes of the first confinement region and the second confinement region, the coaxial confinement regions arranged to confine at least a portion of the adjusted optical beam, the confined portion corresponding to an intensity distribution of the different intensity distributions, and in which the intensity distribution is established by a corresponding state of the different states of the applied perturbation such that the confined portion is configured to provide, at an output of the second length of fiber, a selected intensity profile (<NUM>) of the selectable intensity profiles (<NUM>A, <NUM>B, <NUM>C, <NUM>D).