MATERIAL PROCESSING UTILIZING HIGH-FREQUENCY BEAM SHAPING
In various embodiments, laser emissions are steered into different regions of an optical fiber, and/or into different optical fibers, in a temporal pattern such that an output has different spatial output profiles. The temporal pattern has a frequency sufficient such that a workpiece is processed by an effective output shape combining the different spatial output profiles.
This application claims the benefit of and priority to U.S. Provisional Pat. Application No. 62/825,108, filed Mar. 28, 2019, the entire disclosure of which is hereby incorporated herein by reference.
TECHNICAL FIELDIn various embodiments, the present invention relates to the processing (e.g., welding or cutting) of materials utilizing high-power laser devices having shapeable beams.
BACKGROUNDHigh-power lasers are used in many cutting, etching, annealing, welding, drilling, and soldering applications. As in any materials-processing operations, efficiency can be a critical limiting factor in terms of expense and time; the lower the efficiency, the higher will be the cost and/or the slower will be the operation of the laser deployed to process a given material. The properties of the laser beam can influence efficiency, and different materials (such as copper, aluminum, steel, etc.) respond differently to beam properties as they are processed. Moreover, the thicknesses of these materials can affect their response. That is, the nature of a cut or weld may vary with the beam properties depending on the material and/or its thickness.
In addition, even for the same material and thickness thereof, the optical response (and thus optimal beam) of the material may vary depending upon the geometry of the processing. For example, the optical response of a material during a long straight cut may be different compared to an intricate shape with, e.g., sharp corners, curves, or other features.
Furthermore, high-power laser systems often include a laser emitter, the laser light from which is coupled into an optical fiber (or simply a “fiber”), and an optical system that focuses the laser light from the fiber onto the workpiece to be processed. The optical system is typically engineered to produce the highest-quality laser beam, or, equivalently, the beam with the lowest beam parameter product (BPP). The BPP is the product of the laser beam’s divergence angle (half-angle) and the radius of the beam at its narrowest point (i.e., the beam waist, the minimum spot size). The BPP quantifies the quality of the laser beam and how well it can be focused to a small spot, and is typically expressed in units of millimeter-milliradians (mm-mrad). (BPP values disclosed herein are in units of mm-mrad unless otherwise indicated.) A Gaussian beam has the lowest possible BPP, given by the wavelength of the laser light divided by pi. The ratio of the BPP of an actual beam to that of an ideal Gaussian beam at the same wavelength is denoted M2, which is a wavelength-independent measure of beam quality.
Fiber-based laser-processing systems may be configured to select between different beam shapes by, for example, movement of one or more optical elements with respect to (e.g., in, out, or within) the laser beam. However, such systems may be complex and require expensive, specialized optics. Moreover, while conventional systems may be configured to select among multiple beam shapes depending upon, e.g., the material to be processed, the number of possible beam shapes is often limited to a few discrete shapes.
While techniques such as WBC have succeeded in producing laser-based systems for a wide variety of applications, materials-processing challenges remain. For example, lasers having beam shapes optimized for cutting a particular material at a particular thickness may not be suitable for different materials, materials having different thicknesses, materials having variable thicknesses, and even different types and shapes of cuts on that same material. Welding processes present similar challenges. Moreover, conventional systems often enable only the selection among a few different beam shapes, none of which may be completely optimal for the task at hand. Therefore, there is a need for laser systems capable of not only optimizing beam shape for particular materials and processes, but also quickly altering the beam shape during processing, in order to optimize the beam shape “on-the-fly” as the process proceeds.
SUMMARYIn accordance with embodiments of the present invention, laser systems having shapeable output beams are utilized to optimize and simplify materials-processing tasks such as cutting and welding of materials such as metallic materials. In various embodiments, the configuration of the optical fiber utilized to propagate the beam determines, at least in part, the shape of the output beam. For example, the optical fiber may have multiple core regions and/or multiple cladding regions, and in-coupling of the beam into one or more of such regions may determine, at least in part, the shape of the final output beam. In other embodiments, the beam may be steered to different optical fibers, e.g., optical fibers within a shared fiber bundle, where the different fibers (and/or the in-coupling position utilized for one or more of the fibers) determines, at least in part, the shape of the output beam.
In addition, embodiments of the invention feature a switching mechanism configured to steer the laser beam into different regions of the fiber (or into different fibers) at a high rate of speed. The switching speed results in a temporal averaging (or “merging” or “combining”) of the different output profiles enabled by the fiber structure(s) (at least as experienced by the workpiece), thereby enabling a host of different effective output beam profiles utilized for processing. When combined with the relative movement between the output beam and the workpiece being processed, the high-speed beam switching enables material processing having different output shapes optimized for such factors as the material composition, processing geometry, processing type, etc. Advantageously, embodiments of the invention thereby enable the use of all, or substantially all, of the output beam power even while optimizing the final beam profile and processing output shape. Thus, embodiments of the invention represent an improvement over conventional methods in which beam-shape selection depends upon the blocking or non-utilization of portions of the output beam power.
In exemplary embodiments of the invention, the high-speed switching mechanism is utilized to steer the laser beam among two or more different fiber regions (and/or two or more different fibers) in accordance with a control waveform. The control waveform may control a switching device, e.g., a flexure-mounted reflector, which steers the beam into different regions of the fiber (and/or into different fibers). The temporal distribution of laser power between or among the different fiber regions may therefore be varied by varying the duty cycle of the control waveform. That is, the effective shape of the output beam, as experienced by the workpiece during processing, is a weighted average of different spatial output profiles (enabled by the different fibers and/or fiber regions) based on the shape and duty cycle of the control waveform. The control waveform may have any of numerous different shapes, e.g., square wave, sinusoidal, sawtooth wave, etc. Various embodiments of the invention may utilize switching devices other than flexure-mounted reflectors, for example, flexure-mounted and/or actuated optical elements such as lenses and/or prisms or electro-optic elements.
In an example embodiment, the control waveform may dictate steering of the beam between (1) a central core region, whereby the output profile of the beam is a Gaussian-like, focused spot beam, and (2) an outer, annular core region, whereby the output profile of the beam is a larger-area annular beam. In various embodiments, such central and annular core regions may be separated by one or more intermediate layers (e.g., one or more core and/or cladding layers). The control waveform dictates a temporal weighted averaging of the two output beam shapes in accordance with the duty cycle of the waveform. For example, at the workpiece, the final output beam may have a shape representing the average of the spot beam and the annular beam for a duty cycle of 50% (i.e., 50% within the inner core and 50% within the outer core), and that shape may be varied toward one of the extremes or the other by variation of the duty cycle.
Laser systems in accordance with various embodiments of the present invention may also include a delivery mechanism that directs the laser output onto the workpiece while causing relative movement between the output and the workpiece. For example, the delivery mechanism may include, consist essentially of, or consist of a laser head for directing and/or focusing the output toward the workpiece. The laser head may itself be movable relative to the workpiece, and/or the delivery mechanism may include a movable gantry or other platform for the workpiece to enable movement of the workpiece relative to the output, which may be fixed in place.
Embodiments of the invention may incorporate optical fibers having many different internal configurations and geometries. For example, the optical fiber may include, consist essentially of, or consist of a central core region and an annular core region separated by an inner cladding layer. One or more outer cladding layers may be disposed around the annular core region. Embodiments of the invention may be utilized with and/or incorporate optical fibers having configurations described in U.S. Pat. Application Serial No. 15/479,745, filed on Apr. 5, 2017, and U.S. Pat. Application No. 16/675,655, filed on Nov. 6, 2019, the entire disclosure of each of which is incorporated by reference herein.
In accordance with various embodiments of the present invention, the control waveform may dictate steering of the beam between two or more optical fibers of a fiber bundle for beam shaping, as detailed in U.S. Pat. Application Serial No. 15/807,795, filed on Nov. 9, 2017, the entire disclosure of which is incorporated by reference herein. One or more of the optical fibers of the fiber bundle may be multi-clad fibers, i.e., incorporate a central core region with multiple cladding regions concentrically surrounding the core region. In other embodiments, one or more of the optical fibers may be single-clad fibers, i.e., have only one cladding region surrounding the core region. In various embodiments, different optical fibers in the fiber bundle have different core diameters. One or more of the fibers in the fiber bundle may have multiple discrete core regions. In accordance with various embodiments, the laser output beam is directed into two different fibers of the fiber bundle and/or into two or more specific cross-sectional regions of the fiber(s) (e.g., the core region and/or one or more of the cladding regions) in order to vary the beam shape in accordance with the control waveform.
In various embodiments, the final combined output beam may also include one or more contributions arising from the “transition areas” of the optical fiber (or fiber bundle) between the two or more fiber regions (or optical fibers in a fiber bundle) to which the beam is deliberately steered by the switching mechanism. That is, the shape of the combined beam may correspond to the weighted average of the integral approximation of the dynamic response curve of the system. Particularly at high frequencies (e.g., 50 Hz or more, 100 Hz or more, etc.), a beam steered between two different fiber regions (or fibers in a fiber bundle) may also illuminate the area of the fiber (or fiber bundle) between those regions for a non-negligible amount of the duty cycle. Thus, embodiments of the invention include embodiments in which the combined shape of the output beam is a weighted average of not only the shapes resulting from the fiber regions or fibers to which the beam is deliberately steered, but also one or more regions traversed by the beam as it transitions between or among those regions or fibers. This contribution to the combined beam shape of the shapes resulting from transition regions may decrease as the speed and response of the switching mechanism increases. In other embodiments, the beam may be switched off during transition to the areas to which it is deliberately steered, minimizing or substantially eliminating the contribution of the transition areas. In addition, the contribution of transition areas to the combined shape resulting from a beam steered to two or more optical fibers in a fiber bundle may be smaller, or even substantially absent, if light emitted between the fibers is not coupled into the bundle for transmission from the output end (i.e., if such light is lost rather than transmitted from the output end of the fiber bundle).
Structurally, optical fibers in accordance with embodiments of the invention may include one or more layers of high and/or low refractive index beyond (i.e., outside of) an exterior cladding without altering the principles of the present invention. Various ones of these additional layers may also be termed claddings or coatings, and may not guide light. Optical fibers may also include one or more cores in addition to those specifically mentioned. Such variants are within the scope of the present invention. Optical fibers, and the various core and cladding layers thereof in accordance with various embodiments of the invention may include, consist essentially of, or consist of glass, such as substantially pure fused silica and/or fused silica doped with fluorine, titanium, germanium, and/or boron. Obtaining a desired refractive index for a particular layer or region of an optical fiber in accordance with embodiments of the invention may be accomplished (by techniques such as doping) by one of skill in the art without undue experimentation. Optical fibers utilized in various embodiments of the invention may feature an optional external polymeric protective coating or sheath disposed around the more fragile glass or fused silica fiber itself. Optical fibers described herein may be multi-mode optical fibers.
Optical fibers detailed herein may have at their output ends a laser head configured to focus the output beam from the fiber toward a workpiece to be processed. The laser head may include, consist essentially of, or consist of one or more optical elements for focusing and/or collimating the output beam, and/or controlling the polarization and/or the trajectory of the beam. The laser head may be positioned to emit the output beam toward a workpiece and/or toward a platform or positionable gantry on which the workpiece may be disposed.
Embodiments of the present invention are typically utilized to process a workpiece such that the surface of the workpiece is physically altered and/or such that a feature is formed on or within the surface, in contrast with optical techniques that merely probe a surface with light (e.g., reflectivity measurements). Exemplary processes in accordance with embodiments of the invention include cutting, welding, drilling, and soldering. Various embodiments of the invention also process workpieces at one or more spots or along a one-dimensional processing path, rather than flooding all or substantially all of the workpiece surface with radiation from the laser beam. For example, one or more beam spots may be translated relative to the surface of the workpiece for processes such as cutting or welding. In general, processing paths may be curvilinear or linear, and “linear” processing paths may feature one or more directional changes, i.e., linear processing paths may be composed of two or more substantially straight segments that are not necessarily parallel to each other.
Changing the “shape” of a laser beam herein refers to altering the spatial profile (i.e., 3D shape) and geometric extent of the beam (e.g., at a point at which the beam intersects a surface). Changes in shape may be accompanied by changes in beam size, angular intensity distribution of the beam, and BPP, but mere changes in beam BPP are not necessarily sufficient to change laser beam shape and vice versa. Laser beam shaping is the process of redistributing the intensity (irradiance) and phase of the beam. The intensity distribution defines the beam profile, such as Gaussian, Bessel, annular, multimode, rectangular, top-hat, elliptical or circular, and different intensity profiles may be desirable for specific laser materials processing techniques. (As utilized herein, an “annular” beam is ring-shaped, i.e., having less or substantially no beam intensity in a center portion that is surrounded by a region of higher beam intensity, but not necessarily circular; that is, “annular” beams may be oval-shaped or otherwise quasi-annular.)
Herein, “optical elements” may refer to any of lenses, mirrors, prisms, gratings, and the like, which redirect, reflect, bend, or in any other manner optically manipulate electromagnetic radiation, unless otherwise indicated. Herein, beam emitters, emitters, or laser emitters, or lasers include any electromagnetic beam-generating device such as semiconductor elements, which generate an electromagnetic beam, but may or may not be self-resonating. These also include fiber lasers, disk lasers, non-solid state lasers, etc. Generally, each emitter includes a back reflective surface, at least one optical gain medium, and a front reflective surface. The optical gain medium increases the gain of electromagnetic radiation that is not limited to any particular portion of the electromagnetic spectrum, but that may be visible, infrared, and/or ultraviolet light. An emitter may include or consist essentially of multiple beam emitters such as a diode bar configured to emit multiple beams. The input beams received in the embodiments herein may be single-wavelength or multi-wavelength beams combined using various techniques known in the art. The output beams produced in embodiments of the invention may be single-wavelength or multi-wavelength beams. In addition, references to “lasers,” “laser emitters,” or “beam emitters” herein include not only single-diode lasers, but also diode bars, laser arrays, diode bar arrays, and single or arrays of vertical cavity surface-emitting lasers (VCSELs).
Embodiments of the invention may be utilized with wavelength beam combining (WBC) systems that include a plurality of emitters, such as one or more diode bars, that are combined using a dispersive element to form a multi-wavelength beam. Each emitter in the WBC system individually resonates, and is stabilized through wavelength-specific feedback from a common partially reflecting output coupler that is filtered by the dispersive element along a beam-combining dimension. Exemplary WBC systems are detailed in U.S. Pat. No. 6,192,062, filed on Feb. 4, 2000, U.S. Pat. No. 6,208,679, filed on Sep. 8, 1998, U.S. Pat. No. 8,670,180, filed on Aug. 25, 2011, and U.S. Pat. No. 8,559,107, filed on Mar. 7, 2011, the entire disclosure of each of which is incorporated by reference herein. Multi-wavelength output beams of WBC systems may be utilized as input beams in conjunction with embodiments of the present invention for, e.g., control of beam shape and processing of different workpieces.
In an aspect, embodiments of the invention feature a method of processing a workpiece. A laser and an optical fiber having multiple interior regions are provided. In-coupling of a laser emission into each of the interior regions causes the fiber to produce an output having a different spatial output profile. The laser emission is steered, in a temporal pattern, to different ones of the interior regions of the fiber such that the output has different spatial output profiles. Relative movement between the workpiece and the output is caused while directing the output onto the workpiece to process the workpiece. The temporal pattern has a frequency sufficient such that the workpiece is processed, during the relative movement between the workpiece and the output, by an effective output shape combining the different spatial output profiles.
Embodiments of the invention may include one or more of the following in any of a variety of combinations. The workpiece (e.g., at least the surface thereof) may undergo a time-based response to the output based on the spatial output profile and/or a power density thereof. The relative movement may occur no faster than a maximum processing speed. The maximum processing speed (i) may be selected based on the time-based response of the material and the frequency of the temporal pattern and (ii) may ensure that the response is to the effective output shape. Each interior region of the fiber may be a core region. The interior regions may include at least a central first core and an annular second core surrounding the first core. At least one of the interior regions of the fiber may be a core region. At least one of the interior regions of the fiber may be a cladding region. The laser emission may be steered in response to a control waveform. The control waveform may include, consist essentially of, or consist of a square wave. The effective output shape may be a weighted average of the different spatial output profiles based on a shape and duty cycle of the control waveform.
The laser emission may be a multi-wavelength beam. The laser emission may be steered to different ones of the interior regions of the fiber based on (i) a type of processing performed on the workpiece, (ii) a property of the workpiece, and/or (iii) a processing path along which the workpiece is processed. The type of processing may be selected from the list consisting of cutting, welding, etching, annealing, drilling, soldering, and brazing. The property of the workpiece may include, consist essentially of, or consist of a thickness of the workpiece, a composition of the workpiece, a reflectivity of the workpiece, and/or a topography of the workpiece. The laser emission may be steered to different ones of the interior regions of the fiber based on one or more directional changes in the processing path. The laser may include, consist essentially of, or consist of (i) one or more beam emitters emitting a plurality of discrete beams, (ii) focusing optics for focusing the plurality of beams toward a dispersive element, (iii) the dispersive element for receiving and dispersing the received focused beams, and (iv) a partially reflective output coupler positioned to receive the dispersed beams, transmit a portion of the dispersed beams therethrough as the laser emission, and reflect a second portion of the dispersed beams back toward the dispersive element. The laser emission may be composed of multiple wavelengths. The dispersive element may include, consist essentially of, or consist of a diffraction grating.
The optical fiber may include, consist essentially of, or consist of a fiber core, a first cladding region surrounding the fiber core, and a second cladding region surrounding the first cladding region. The optical fiber may include, consist essentially of, or consist of a fiber core, a first cladding region surrounding the fiber core, an annular core surrounding the first cladding region, and a second cladding region surrounding the annular core. The optical fiber may include, consist essentially of, or consist of (i) a central core having a first refractive index, (ii) surrounding the central core, a first cladding having a second refractive index, (iii) surrounding the first cladding, an annular core having a third refractive index, and (iv) surrounding the annular core, a second cladding having a fourth refractive index. The first refractive index may be larger than the fourth refractive index. The third refractive index may be larger than the fourth refractive index. The second refractive index may be smaller than the first refractive index and/or larger than the fourth refractive index. The third refractive index may be larger than the first refractive index.
The optical fiber may include, consist essentially of, or consist of (i) a center core having a first refractive index, (ii) surrounding the center core, a first cladding having a second refractive index smaller than the first refractive index, (iii) an annular core surrounding the first cladding, and (iv) surrounding the annular core, a second cladding having a third refractive index smaller than the first refractive index. The annular core may include, consist essentially of, or consist of (i) a first region having a fourth refractive index greater than the second refractive index, and (ii) a second region, a refractive index of the second region varying between (i) a fifth refractive index less than or equal to the fourth refractive index and (ii) a sixth refractive index greater than or equal to the second refractive index. The first region may be disposed between the second region and the second cladding. The second region may be disposed between the first region and the second cladding.
The optical fiber may include, consist essentially of, or consist of (i) a center core having a first refractive index, (ii) an annular core surrounding the center core, and (iii) surrounding the annular core, a first cladding having a second refractive index smaller than the first refractive index. The annular core may include, consist essentially of, or consist of (a) a first region having a third refractive index greater than the second refractive index, and (b) a second region, a refractive index of the second region varying between (i) a fourth refractive index less than or equal to the third refractive index and (ii) a fifth refractive index less than the fourth refractive index. The first region may be disposed between the second region and the first cladding. The second region may be disposed between the first region and the first cladding.
The optical fiber may include, consist essentially of, or consist of (i) a center core having a first refractive index, (ii) surrounding the center core, a first cladding having a second refractive index smaller than the first refractive index, (iii) an annular core surrounding the first cladding, and (iv) surrounding the annular core, a second cladding having a third refractive index smaller than the first refractive index. The annular core may include, consist essentially of, or consist of (i) a first region having a fourth refractive index greater than the second refractive index, and (ii) a second region having a fifth refractive index greater than the second refractive index and smaller than the fourth refractive index. The first region may be disposed between the second region and the second cladding. The second region may be disposed between the first region and the second cladding.
The optical fiber may include, consist essentially of, or consist of (i) a center core having a first refractive index, (ii) surrounding the center core, a first cladding having a second refractive index smaller than the first refractive index, (iii) an annular core surrounding the first cladding, and (iv) surrounding the annular core, a second cladding having a third refractive index smaller than the first refractive index. The annular core may include, consist essentially of, or consist of (i) a first region having a fourth refractive index greater than the second refractive index, (ii) a second region having a fifth refractive index greater than the second refractive index, and (iii) a third region, disposed between the first and second regions, having a sixth refractive index smaller than the fourth and fifth refractive indices. The annular core may include, consist essentially of, or consist of (i) a fourth region having a seventh refractive index greater than the second refractive index, and (ii) a fifth region, disposed between the second and fourth regions, having an eighth refractive index smaller than the fifth and seventh refractive indices.
In another aspect, embodiments of the invention feature a method of processing a workpiece. A laser and a fiber bundle having multiple optical fibers are provided. In-coupling of a laser emission into each of at least two (or even each) of the optical fibers causes the fiber to produce an output having a different spatial output profile. The laser emission is steered, in a temporal pattern, to different ones of the optical fibers of the fiber bundle such that the output has different spatial output profiles. Relative movement between the workpiece and the output is caused while directing the output onto the workpiece to process the workpiece. The temporal pattern has a frequency sufficient such that the workpiece is processed, during the relative movement between the workpiece and the output, by an effective output shape combining the different spatial output profiles.
Embodiments of the invention may include one or more of the following in any of a variety of combinations. The workpiece (e.g., at least the surface thereof) may undergo a time-based response to the output based on the spatial output profile and/or a power density thereof. The relative movement may occur no faster than a maximum processing speed. The maximum processing speed (i) may be selected based on the time-based response of the material and the frequency of the temporal pattern and (ii) may ensure that the response is to the effective output shape. The laser emission may be steered in response to a control waveform. The control waveform may include, consist essentially of, or consist of a square wave. The effective output shape may be a weighted average of the different spatial output profiles based on a shape and duty cycle of the control waveform.
The laser emission may be a multi-wavelength beam. The laser emission may be steered to different ones of the optical fibers based on (i) a type of processing performed on the workpiece, (ii) a property of the workpiece, and/or (iii) a processing path along which the workpiece is processed. The type of processing may be selected from the list consisting of cutting, welding, etching, annealing, drilling, soldering, and brazing. The property of the workpiece may include, consist essentially of, or consist of a thickness of the workpiece, a composition of the workpiece, a reflectivity of the workpiece, and/or a topography of the workpiece. The laser emission may be steered to different ones of the optical fibers based on one or more directional changes in the processing path. The laser may include, consist essentially of, or consist of (i) one or more beam emitters emitting a plurality of discrete beams, (ii) focusing optics for focusing the plurality of beams toward a dispersive element, (iii) the dispersive element for receiving and dispersing the received focused beams, and (iv) a partially reflective output coupler positioned to receive the dispersed beams, transmit a portion of the dispersed beams therethrough as the laser emission, and reflect a second portion of the dispersed beams back toward the dispersive element. The laser emission may be composed of multiple wavelengths. The dispersive element may include, consist essentially of, or consist of a diffraction grating.
At least one of the optical fibers may include, consist essentially of, or consist of a fiber core, a first cladding region surrounding the fiber core, and a second cladding region surrounding the first cladding region. At least one of the optical fibers may include, consist essentially of, or consist of a fiber core, a first cladding region surrounding the fiber core, an annular core surrounding the first cladding region, and a second cladding region surrounding the annular core. At least one of the optical fibers may include, consist essentially of, or consist of (i) a central core having a first refractive index, (ii) surrounding the central core, a first cladding having a second refractive index, (iii) surrounding the first cladding, an annular core having a third refractive index, and (iv) surrounding the annular core, a second cladding having a fourth refractive index. The first refractive index may be larger than the fourth refractive index. The third refractive index may be larger than the fourth refractive index. The second refractive index may be smaller than the first refractive index and/or larger than the fourth refractive index. The third refractive index may be larger than the first refractive index.
At least one of the optical fibers may include, consist essentially of, or consist of (i) a center core having a first refractive index, (ii) surrounding the center core, a first cladding having a second refractive index smaller than the first refractive index, (iii) an annular core surrounding the first cladding, and (iv) surrounding the annular core, a second cladding having a third refractive index smaller than the first refractive index. The annular core may include, consist essentially of, or consist of (i) a first region having a fourth refractive index greater than the second refractive index, and (ii) a second region, a refractive index of the second region varying between (i) a fifth refractive index less than or equal to the fourth refractive index and (ii) a sixth refractive index greater than or equal to the second refractive index. The first region may be disposed between the second region and the second cladding. The second region may be disposed between the first region and the second cladding.
At least one of the optical fibers may include, consist essentially of, or consist of (i) a center core having a first refractive index, (ii) an annular core surrounding the center core, and (iii) surrounding the annular core, a first cladding having a second refractive index smaller than the first refractive index. The annular core may include, consist essentially of, or consist of (a) a first region having a third refractive index greater than the second refractive index, and (b) a second region, a refractive index of the second region varying between (i) a fourth refractive index less than or equal to the third refractive index and (ii) a fifth refractive index less than the fourth refractive index. The first region may be disposed between the second region and the first cladding. The second region may be disposed between the first region and the first cladding.
At least one of the optical fibers may include, consist essentially of, or consist of (i) a center core having a first refractive index, (ii) surrounding the center core, a first cladding having a second refractive index smaller than the first refractive index, (iii) an annular core surrounding the first cladding, and (iv) surrounding the annular core, a second cladding having a third refractive index smaller than the first refractive index. The annular core may include, consist essentially of, or consist of (i) a first region having a fourth refractive index greater than the second refractive index, and (ii) a second region having a fifth refractive index greater than the second refractive index and smaller than the fourth refractive index. The first region may be disposed between the second region and the second cladding. The second region may be disposed between the first region and the second cladding.
At least one of the optical fibers may include, consist essentially of, or consist of (i) a center core having a first refractive index, (ii) surrounding the center core, a first cladding having a second refractive index smaller than the first refractive index, (iii) an annular core surrounding the first cladding, and (iv) surrounding the annular core, a second cladding having a third refractive index smaller than the first refractive index. The annular core may include, consist essentially of, or consist of (i) a first region having a fourth refractive index greater than the second refractive index, (ii) a second region having a fifth refractive index greater than the second refractive index, and (iii) a third region, disposed between the first and second regions, having a sixth refractive index smaller than the fourth and fifth refractive indices. The annular core may include, consist essentially of, or consist of (i) a fourth region having a seventh refractive index greater than the second refractive index, and (ii) a fifth region, disposed between the second and fourth regions, having an eighth refractive index smaller than the fifth and seventh refractive indices.
In yet another aspect, embodiments of the invention feature a laser system that includes, consists essentially of, or consists of a beam source for emission of an input laser beam, an optical fiber having multiple interior regions, a switching mechanism, and a delivery mechanism. In-coupling of an input laser emission into each of the interior regions causes the fiber to produce an output having a different spatial output profile. The switching mechanism steers the input laser emission to different ones of the interior regions of the fiber to produce different spatial output profiles in a temporal pattern having a frequency. The delivery mechanism directs the output onto the workpiece while causing relative movement therebetween, thereby processing the workpiece. The frequency is sufficient such that the workpiece is processed, during the relative movement between the workpiece and the output, by an effective output shape combining the different spatial output profiles.
Embodiments of the invention may include one or more of the following in any of a variety of combinations. The switching mechanism may include, consist essentially of, or consist of a flexure-mounted reflector. The workpiece (e.g., at least the surface thereof) may undergo a time-based response to the output based on the spatial output profile and/or a power density thereof. The switching mechanism may be configured to limit the relative movement to a maximum processing speed. The maximum processing speed (i) may be selected based on the time-based response of the material and the frequency of the temporal pattern and (ii) may ensure that the response is to the effective output shape. Each interior region of the fiber may be a core region. The interior regions may include at least a central first core and an annular second core surrounding the first core. At least one of the interior regions of the fiber may be a core region. At least one of the interior regions of the fiber may be a cladding region. The system may include a waveform generator for generating a control waveform. The switching mechanism may be configured to steer the input laser emission in response to the control waveform. The control waveform may include, consist essentially of, or consist of a square wave. The effective output shape may be a weighted average of the different spatial output profiles based on a shape and duty cycle of the control waveform.
The laser emission may be a multi-wavelength beam. The switching mechanism may be configured to steer the laser emission to different ones of the interior regions of the fiber based on (i) a type of processing performed on the workpiece, (ii) a property of the workpiece, and/or (iii) a processing path along which the workpiece is processed. The type of processing may be selected from the list consisting of cutting, welding, etching, annealing, drilling, soldering, and brazing. The property of the workpiece may include, consist essentially of, or consist of a thickness of the workpiece, a composition of the workpiece, a reflectivity of the workpiece, and/or a topography of the workpiece. The switching mechanism may be configured to steer the laser emission to different ones of the interior regions of the fiber based on one or more directional changes in the processing path. The beam source may include, consist essentially of, or consist of (i) one or more beam emitters emitting a plurality of discrete beams, (ii) focusing optics for focusing the plurality of beams toward a dispersive element, (iii) the dispersive element for receiving and dispersing the received focused beams, and (iv) a partially reflective output coupler positioned to receive the dispersed beams, transmit a portion of the dispersed beams therethrough as the input laser emission, and reflect a second portion of the dispersed beams back toward the dispersive element. The input laser emission may be composed of multiple wavelengths. The dispersive element may include, consist essentially of, or consist of a diffraction grating.
The optical fiber may include, consist essentially of, or consist of a fiber core, a first cladding region surrounding the fiber core, and a second cladding region surrounding the first cladding region. The optical fiber may include, consist essentially of, or consist of a fiber core, a first cladding region surrounding the fiber core, an annular core surrounding the first cladding region, and a second cladding region surrounding the annular core. The optical fiber may include, consist essentially of, or consist of (i) a central core having a first refractive index, (ii) surrounding the central core, a first cladding having a second refractive index, (iii) surrounding the first cladding, an annular core having a third refractive index, and (iv) surrounding the annular core, a second cladding having a fourth refractive index. The first refractive index may be larger than the fourth refractive index. The third refractive index may be larger than the fourth refractive index. The second refractive index may be smaller than the first refractive index and/or larger than the fourth refractive index. The third refractive index may be larger than the first refractive index.
The optical fiber may include, consist essentially of, or consist of (i) a center core having a first refractive index, (ii) surrounding the center core, a first cladding having a second refractive index smaller than the first refractive index, (iii) an annular core surrounding the first cladding, and (iv) surrounding the annular core, a second cladding having a third refractive index smaller than the first refractive index. The annular core may include, consist essentially of, or consist of (i) a first region having a fourth refractive index greater than the second refractive index, and (ii) a second region, a refractive index of the second region varying between (i) a fifth refractive index less than or equal to the fourth refractive index and (ii) a sixth refractive index greater than or equal to the second refractive index. The first region may be disposed between the second region and the second cladding. The second region may be disposed between the first region and the second cladding.
The optical fiber may include, consist essentially of, or consist of (i) a center core having a first refractive index, (ii) an annular core surrounding the center core, and (iii) surrounding the annular core, a first cladding having a second refractive index smaller than the first refractive index. The annular core may include, consist essentially of, or consist of (a) a first region having a third refractive index greater than the second refractive index, and (b) a second region, a refractive index of the second region varying between (i) a fourth refractive index less than or equal to the third refractive index and (ii) a fifth refractive index less than the fourth refractive index. The first region may be disposed between the second region and the first cladding. The second region may be disposed between the first region and the first cladding.
The optical fiber may include, consist essentially of, or consist of (i) a center core having a first refractive index, (ii) surrounding the center core, a first cladding having a second refractive index smaller than the first refractive index, (iii) an annular core surrounding the first cladding, and (iv) surrounding the annular core, a second cladding having a third refractive index smaller than the first refractive index. The annular core may include, consist essentially of, or consist of (i) a first region having a fourth refractive index greater than the second refractive index, and (ii) a second region having a fifth refractive index greater than the second refractive index and smaller than the fourth refractive index. The first region may be disposed between the second region and the second cladding. The second region may be disposed between the first region and the second cladding.
The optical fiber may include, consist essentially of, or consist of (i) a center core having a first refractive index, (ii) surrounding the center core, a first cladding having a second refractive index smaller than the first refractive index, (iii) an annular core surrounding the first cladding, and (iv) surrounding the annular core, a second cladding having a third refractive index smaller than the first refractive index. The annular core may include, consist essentially of, or consist of (i) a first region having a fourth refractive index greater than the second refractive index, (ii) a second region having a fifth refractive index greater than the second refractive index, and (iii) a third region, disposed between the first and second regions, having a sixth refractive index smaller than the fourth and fifth refractive indices. The annular core may include, consist essentially of, or consist of (i) a fourth region having a seventh refractive index greater than the second refractive index, and (ii) a fifth region, disposed between the second and fourth regions, having an eighth refractive index smaller than the fifth and seventh refractive indices.
In another aspect, embodiments of the invention feature a laser system that includes, consists essentially of, or consist of a beam source for emission of an input laser beam, a fiber bundle having multiple optical fibers, a switching mechanism, and a delivery mechanism. In-coupling of an input laser emission into each of at least two (or even all) of the optical fibers causes the fiber bundle to produce an output having a different spatial output profile. The switching mechanism steers the input laser emission to different ones of the optical fibers of the fiber bundle to produce different spatial output profiles in a temporal pattern having a frequency. The delivery mechanism directs the output onto the workpiece while causing relative movement therebetween, thereby processing the workpiece. The frequency is sufficient such that the workpiece is processed, during the relative movement between the workpiece and the output, by an effective output shape combining the different spatial output profiles.
Embodiments of the invention may include one or more of the following in any of a variety of combinations. The switching mechanism may include, consist essentially of, or consist of a flexure-mounted reflector. The workpiece (e.g., at least the surface thereof) may undergo a time-based response to the output based on the spatial output profile and/or a power density thereof. The switching mechanism may be configured to limit the relative movement to a maximum processing speed. The maximum processing speed (i) may be selected based on the time-based response of the material and the frequency of the temporal pattern and (ii) may ensure that the response is to the effective output shape. The system may include a waveform generator for generating a control waveform. The switching mechanism may be configured to steer the input laser emission in response to the control waveform. The control waveform may include, consist essentially of, or consist of a square wave. The effective output shape may be a weighted average of the different spatial output profiles based on a shape and duty cycle of the control waveform.
The laser emission may be a multi-wavelength beam. The switching mechanism may be configured to steer the laser emission to different ones of the optical fibers based on (i) a type of processing performed on the workpiece, (ii) a property of the workpiece, and/or (iii) a processing path along which the workpiece is processed. The type of processing may be selected from the list consisting of cutting, welding, etching, annealing, drilling, soldering, and brazing. The property of the workpiece may include, consist essentially of, or consist of a thickness of the workpiece, a composition of the workpiece, a reflectivity of the workpiece, and/or a topography of the workpiece. The switching mechanism may be configured to steer the laser emission to different ones of the optical fibers based on one or more directional changes in the processing path. The beam source may include, consist essentially of, or consist of (i) one or more beam emitters emitting a plurality of discrete beams, (ii) focusing optics for focusing the plurality of beams toward a dispersive element, (iii) the dispersive element for receiving and dispersing the received focused beams, and (iv) a partially reflective output coupler positioned to receive the dispersed beams, transmit a portion of the dispersed beams therethrough as the input laser emission, and reflect a second portion of the dispersed beams back toward the dispersive element. The input laser emission may be composed of multiple wavelengths. The dispersive element may include, consist essentially of, or consist of a diffraction grating.
At least one optical fiber may include, consist essentially of, or consist of a fiber core, a first cladding region surrounding the fiber core, and a second cladding region surrounding the first cladding region. At least one optical fiber may include, consist essentially of, or consist of a fiber core, a first cladding region surrounding the fiber core, an annular core surrounding the first cladding region, and a second cladding region surrounding the annular core. At least one optical fiber may include, consist essentially of, or consist of (i) a central core having a first refractive index, (ii) surrounding the central core, a first cladding having a second refractive index, (iii) surrounding the first cladding, an annular core having a third refractive index, and (iv) surrounding the annular core, a second cladding having a fourth refractive index. The first refractive index may be larger than the fourth refractive index. The third refractive index may be larger than the fourth refractive index. The second refractive index may be smaller than the first refractive index and/or larger than the fourth refractive index. The third refractive index may be larger than the first refractive index.
At least one optical fiber may include, consist essentially of, or consist of (i) a center core having a first refractive index, (ii) surrounding the center core, a first cladding having a second refractive index smaller than the first refractive index, (iii) an annular core surrounding the first cladding, and (iv) surrounding the annular core, a second cladding having a third refractive index smaller than the first refractive index. The annular core may include, consist essentially of, or consist of (i) a first region having a fourth refractive index greater than the second refractive index, and (ii) a second region, a refractive index of the second region varying between (i) a fifth refractive index less than or equal to the fourth refractive index and (ii) a sixth refractive index greater than or equal to the second refractive index. The first region may be disposed between the second region and the second cladding. The second region may be disposed between the first region and the second cladding.
At least one optical fiber may include, consist essentially of, or consist of (i) a center core having a first refractive index, (ii) an annular core surrounding the center core, and (iii) surrounding the annular core, a first cladding having a second refractive index smaller than the first refractive index. The annular core may include, consist essentially of, or consist of (a) a first region having a third refractive index greater than the second refractive index, and (b) a second region, a refractive index of the second region varying between (i) a fourth refractive index less than or equal to the third refractive index and (ii) a fifth refractive index less than the fourth refractive index. The first region may be disposed between the second region and the first cladding. The second region may be disposed between the first region and the first cladding.
At least one optical fiber may include, consist essentially of, or consist of (i) a center core having a first refractive index, (ii) surrounding the center core, a first cladding having a second refractive index smaller than the first refractive index, (iii) an annular core surrounding the first cladding, and (iv) surrounding the annular core, a second cladding having a third refractive index smaller than the first refractive index. The annular core may include, consist essentially of, or consist of (i) a first region having a fourth refractive index greater than the second refractive index, and (ii) a second region having a fifth refractive index greater than the second refractive index and smaller than the fourth refractive index. The first region may be disposed between the second region and the second cladding. The second region may be disposed between the first region and the second cladding.
At least one optical fiber may include, consist essentially of, or consist of (i) a center core having a first refractive index, (ii) surrounding the center core, a first cladding having a second refractive index smaller than the first refractive index, (iii) an annular core surrounding the first cladding, and (iv) surrounding the annular core, a second cladding having a third refractive index smaller than the first refractive index. The annular core may include, consist essentially of, or consist of (i) a first region having a fourth refractive index greater than the second refractive index, (ii) a second region having a fifth refractive index greater than the second refractive index, and (iii) a third region, disposed between the first and second regions, having a sixth refractive index smaller than the fourth and fifth refractive indices. The annular core may include, consist essentially of, or consist of (i) a fourth region having a seventh refractive index greater than the second refractive index, and (ii) a fifth region, disposed between the second and fourth regions, having an eighth refractive index smaller than the fifth and seventh refractive indices.
These and other objects, along with advantages and features of the present invention herein disclosed, will become more apparent through reference to the following description, the accompanying drawings, and the claims. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and may exist in various combinations and permutations. As used herein, the term “substantially” means ±10%, and in some embodiments, ±5%. The term “consists essentially of” means excluding other materials that contribute to function, unless otherwise defined herein. Nonetheless, such other materials may be present, collectively or individually, in trace amounts. Herein, the terms “radiation” and “light” are utilized interchangeably unless otherwise indicated. Herein, “downstream” or “optically downstream,” is utilized to indicate the relative placement of a second element that a light beam strikes after encountering a first element, the first element being “upstream,” or “optically upstream” of the second element. Herein, “optical distance” between two components is the distance between two components that is actually traveled by light beams; the optical distance may be, but is not necessarily, equal to the physical distance between two components due to, e.g., reflections from mirrors or other changes in propagation direction experienced by the light traveling from one of the components to the other. Distances utilized herein may be considered to be “optical distances” unless otherwise specified.
In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the present invention are described with reference to the following drawings, in which:
An exemplary laser system 100 for varying laser beam shape using a fiber 105 in accordance with embodiments of the invention is depicted in
Optical fiber 105 may have many different internal configurations and geometries. For example, optical fiber 105 may include, consist essentially of, or consist of a central core region and an annular core region separated by an inner cladding layer. One or more outer cladding layers may be disposed around the annular core region. Embodiments of the invention may be utilized with and/or incorporate optical fibers having configurations described in U.S. Pat. Application Serial No. 15/479,745, filed on Apr. 5, 2017, and U.S. Pat. Application No. 16/675,655, filed on Nov. 6, 2019, the entire disclosure of each of which is incorporated by reference herein.
All or a portion of the laser system 100 may be disposed optically upstream of the laser-processing head that is utilized to deliver the output beam to the workpiece. The delivery head may include one or more optical elements for focusing or otherwise directing the output beam to the workpiece. Optical fiber 105 may be optically coupled to the processing head and deliver the output beam thereto.
The configuration of the switching mechanism 110 and/or the optical element 120 and/or the fiber 105 may be controlled via a controller 140 and/or one or more actuators (not shown) operatively connected thereto. Thus, the switching mechanism 110 and/or the optical element 120 and/or the fiber 105 and/or the one or more actuators may be responsive to the controller 140. The controller 140 may be responsive to a desired target spatial output beam profile (e.g., input by a user and/or based on one or more properties of a workpiece to be processed such as the distance to the workpiece, the composition of the workpiece, thickness of the workpiece, reflectivity of the workpiece, topography of the workpiece, etc., and/or based on the type of processing and/or the desired processing path on the workpiece) and configured to position switching mechanism 110 and/or the optical element 120 and/or the fiber 105 to cause the beam 115 to strike the input face of the fiber 105 such that the output beam output from the fiber 105 has the target spatial output beam profile. The output beam thus produced may be directed to a workpiece for processes such as annealing, cutting, welding, drilling, etc. The controller 140 may be programmed to achieve the desired power distribution and/or output BPP and/or beam quality via, e.g., a particular switching mechanism tilt and/or position (and/or tilt) of optical element 120 and/or fiber 105 as detailed herein.
The controller 140 may be provided as either software, hardware, or some combination thereof. For example, the system may be implemented on one or more conventional server-class computers, such as a PC having a CPU board containing one or more processors such as the Pentium or Celeron family of processors manufactured by Intel Corporation of Santa Clara, Calif., the 680×0 and POWER PC family of processors manufactured by Motorola Corporation of Schaumburg, Ill., and/or the ATHLON line of processors manufactured by Advanced Micro Devices, Inc., of Sunnyvale, Calif. The processor may also include a main memory unit for storing programs and/or data relating to the methods described herein. The memory may include random access memory (RAM), read only memory (ROM), and/or FLASH memory residing on commonly available hardware such as one or more application specific integrated circuits (ASIC), field programmable gate arrays (FPGA), electrically erasable programmable read-only memories (EEPROM), programmable read-only memories (PROM), programmable logic devices (PLD), or read-only memory devices (ROM). In some embodiments, the programs may be provided using external RAM and/or ROM such as optical disks, magnetic disks, as well as other commonly used storage devices. For embodiments in which the functions are provided as one or more software programs, the programs may be written in any of a number of high level languages such as FORTRAN, PASCAL, JAVA, C, C++, C#, BASIC, various scripting languages, and/or HTML. Additionally, the software may be implemented in an assembly language directed to the microprocessor resident on a target computer; for example, the software may be implemented in Intel 80×86 assembly language if it is configured to run on an IBM PC or PC clone. The software may be embodied on an article of manufacture including, but not limited to, a floppy disk, a jump drive, a hard disk, an optical disk, a magnetic tape, a PROM, an EPROM, EEPROM, field-programmable gate array, or CD-ROM.
The controller 140 may also be operatively connected to, or may incorporate, a waveform generator 150 (e.g., a variable frequency controller or variable frequency generator) configured to generate a control waveform utilized to control the configuration (e.g., tilt and/or translation) of the switching mechanism 110 and/or the optical element 120, and thus the spatial output profile emitted from the fiber 105. Waveform generators are conventional and may be supplied by one of ordinary skill in the art without undue experimentation. The control waveform may be utilized to control the switching mechanism 110 and/or the optical element 120 via, e.g., application of the waveform to the actuator(s) and/or stage(s) controlling the configuration of the switching mechanism 110 and/or the optical element 120. For example, such components may incorporate piezoelectric materials that deform in response to applied electric fields. Such materials, actuators, and stages are conventional and may be provided by one of ordinary skill in the art without undue experimentation.
The controller 140 may also operate a conventional positioning system configured to cause relative movement between the output laser beam and the workpiece being processed. For example, the positioning system may be any controllable optical, mechanical or opto-mechanical system for directing the beam through a processing path along a two- or three-dimensional workpiece. During processing, the controller 140 may operate the positioning system and the laser system 100 so that the laser beam traverses a processing path along the workpiece. The processing path may be provided by a user and stored in an onboard or remote memory, which may also store parameters relating to the type of processing (cutting, welding, etc.) and the beam parameters (e.g., beam shapes) necessary to carry out that processing. In this regard, a local or remote database may maintain a library of materials and thicknesses that the system will process, and upon user selection of material parameters (type of material, thickness, etc.), the controller 140 queries the database to obtain the corresponding parameter values. The stored values may include beam shapes suitable to the material, the type of processing, and/or the geometry of the processing path.
As is well understood in the plotting and scanning art, the requisite relative motion between the beam and the workpiece may be produced by optical deflection of the beam using a movable mirror, physical movement of the laser using a gantry, leadscrew or other arrangement, and/or a mechanical arrangement for moving the workpiece rather than (or in addition to) the beam. The controller 140 may, in some embodiments, receive feedback regarding the position and/or processing efficacy of the beam relative to the workpiece from a feedback unit, which will be connected to suitable monitoring sensors.
The duty cycle of the control waveform may be selected to produce an output shape of the laser beam, at least as experienced by the workpiece, that is a weighted average of two or more spatial output profiles resulting from in-coupling of beam 115 into one or more regions of fiber 105. That is, the duty cycle of the control waveform may determine the temporal pattern in accordance with which the beam 115 is steered into the various regions of the fiber 105, and, thus, the overall averaged output shape of the beam delivered to and experienced by the workpiece. Because, in various embodiments, the switching frequency of the control waveform is greater than the time-response of the workpiece to the beam, the effect of the laser beam on the workpiece corresponds to the weighted average of the various spatial output profiles of the beam, even if those output profiles are discrete from each other at the beam output. Thus, herein “merged” or “averaged” or “combined” output beam shape refers to the average beam profile experienced at the workpiece.
For a given relative rate of movement between the laser beam and the workpiece, the frequency of the control waveform may be increased in order to produce a new, averaged output beam shape as the beam is applied to the workpiece.
Embodiments of the invention may enable a user to process (e.g., cut or weld) a workpiece along a desired processing path, and the optimal beam shape and maximum processing speed is selected based on factors such as, but not limited to, the composition of the workpiece, the thickness of the workpiece, the reflectivity of the workpiece, the geometry of the processing path, etc. For example, a user may select or preprogram the desired processing path into the system using any suitable input device or by means of file transfer. Thereafter, the controller 140 may analyze the different output beam shapes enabled by the optical fiber of the system, the processing path, and the type and features (e.g., thickness) of the workpiece, querying its database as necessary. Based on this information, the system may determine optimum output beam shape as a function of location along the processing path, the control frequency and rate of relative motion required to produce the beam shape, and thus the maximum processing speed. In operation, the controller 140 may operate the laser system and positioning of the workpiece to process the workpiece along the preprogrammed path, maintaining the proper average beam shape to be experienced at the workpiece. If the composition and/or thickness of the material being processed changes, the location and nature of the change may be programmed, and the controller 140 may adjust the laser beam shape and/or the rate of relative motion between the workpiece and the beam accordingly.
In addition, the laser system may incorporate one or more systems for detecting the thickness of the workpiece and/or heights of features thereon. For example, the laser system may incorporate systems (or components thereof) for interferometric depth measurement of the workpiece, as detailed in U.S. Pat. Application Serial No. 14/676,070, filed on Apr. 1, 2015, the entire disclosure of which is incorporated by reference herein. Such depth or thickness information may be utilized by the controller to control the output beam shape to optimize the processing (e.g., cutting or welding) of the workpiece, e.g., in accordance with records in the database corresponding to the type of material being processed.
As mentioned above, embodiments of the invention may be utilized with and/or incorporate optical fibers having many different configurations. For example,
In addition, embodiments of the invention may utilize optical fibers described in U.S. Pat. Application Serial No. 15/479,745, filed on Apr. 5, 2017, the entire disclosure of which is incorporated by reference herein. Thus, embodiments of the invention involve coupling of the laser beam into a multi-clad optical fiber herein termed a “step-clad fiber.” One exemplary step-clad fiber includes, consists essentially of, or consists of a center core, a first cladding disposed around the center core, the first annular core disposed around the first cladding, and a second cladding disposed around the first annular core. Step-clad fibers in accordance with embodiments of the invention are not limited to having only a single annular core and two claddings - one or more additional annular cores and associated claddings may be disposed around the second cladding. As utilized herein, the term “annular core” is defined as a ring-shaped region having a higher refractive index than both the inner and outer layers adjacent thereto. Layers other than the center core and the annular core(s) are typically claddings in a step-clad fiber. Such claddings have lower refractive indices than at least one layer adjacent thereto.
Embodiments of the invention may also utilize and/or incorporate optical fibers having configurations detailed in U.S. Pat. Application No. 16/675,655, filed on Nov. 6, 2019, the entire disclosure of which is incorporated by reference herein. For example, optical fibers in accordance with embodiments of the invention feature an annular core region incorporating (i) a sub-region of graded refractive index, (ii) subregions having different refractive indices in a stepped profile, or (iii) a low-refractive-index barrier layer.
In various embodiments, the annular core 820 includes, consists essentially of, or consists of two different regions. As shown in
In accordance with various embodiments of the invention, the diameters of core and cladding regions may depend at least in part on various properties (e.g., output power) of the laser source and/or on the desired BPP range of the output beam to be transmitted by the optical fiber. For example, a center core diameter D0 of approximately 100 µm, matched with a laser source having a BPP of about 3.5 mm-mrad, will typically result in a relatively low output NA (approximately 0.09) with a minimum BPP of approximately 4 mm-mrad. Continuing the example, if the desired BPP variation range is about a factor of 6, the diameter D2 of the annular core 320 may be approximately 600 µm, not considering NA enlargement that may occur when some laser power is in-coupled into the first cladding 815 and/or into a portion (e.g., the lower-index portion) of the graded-index region 820g. Assuming the NA of the center core 810 is approximately 0.12 and the laser input NA is approximately 0.085, the enlarged NA will be approximately 0.147 (=sqrt(0.12×0.12 + 0.085 × 0.085)), which is larger than the input NA by a factor of 1.7. As mentioned, the effective enlargement of the overall output NA may be smaller than this factor of 1.7 because, in various embodiments, not all of the input power is coupled into low-index regions or exits from high-index regions. Assuming that the overall NA enlargement is approximately 1.5, then the annular core diameter may be reduced to approximately 400 µm to achieve the same desired range of BPP variation. A smaller diameter of the annular core may result in higher intensity of the output beam, which may be beneficial in many high-power laser applications. In various embodiments, the ratio of the diameter D2 to the diameter D0 ranges from approximately 2.5 to approximately 8, or approximately 3 to approximately 6. This ratio may be applied to all different optical-fiber embodiments detailed herein.
In various embodiments, the thickness of the first cladding 815 (i.e., ((D1-D0)/2) may be less than approximately one-half of the diameter D0 (i.e., less than approximately D0/2). This thickness of the first cladding may be applied to all different optical-fiber embodiments detailed herein. For optical fiber 800, the thickness of the first cladding 815 may be even smaller, e.g., less than approximately 25%, less than approximately 10%, or even less than approximately 5% of the diameter D0, due to, e.g., the presence of the lower-index portion of the graded-index region 820g.
Advantageously, laser energy coupled into the refractive-index profile of the annular core 820, including the graded-index region 820g, will result in output beams having annular beams with different effective diameters and widths, depending upon the input location in annular core 820. Thus, when the beam shape is altered in response to the control waveform, as detailed above, the use of fiber 800 enables a variety of different average beam shapes experienced at the workpiece. In various embodiments, the graded-index region 820g provides and enables different critical-angle interface locations of total internal reflection of input beams having different NAs. For example, laser power with an input NAin in-coupled into the constant-index region of annular core 820 will typically not spread within the entire annular core 820, but will rather be contained within a more limited area having a refractive index larger than nx (which is greater than n1) that satisfies sqrt(n22 - nx2)= NAin. In other words, the portion of annular core 820 having refractive index nx acts as a ray stopper. Similarly, different portions of the input power in the NA domain will have different input NA ranging from 0 to NAin, and these different portions will therefore be “blocked” by different portions (i.e., cylindrical “interfaces”) within the annular core 820. In general, a z-portion of power having an input NAz (which is less than or equal to NAin) in-coupled into the annular core 820 at position y having a relatively high refractive index ny will be confined within a volume in the annular core 820 having refractive index larger than nx and that satisfies sqrt(ny2 - nx2)= NAz. This equation applies to all the embodiments of the invention. This general proposition may be applied to any and all different embodiments of the invention detailed herein.
In various embodiments, compared to the step-clad optical fiber 700 depicted in
In addition, as indicated by the double-headed arrow between locations A and B in
In various embodiments, the refractive-index profile (i.e., the variation of the refractive index as a function of position) of the graded-index region 820g may be a substantially linear gradient, as shown in
In various embodiments, the annular cladding 820 may entirely consist of the graded-index region 820g; that is, the width of the constant-index region of annular cladding 820 may be approximately zero. In addition or instead, the graded-index region 820g may extend such that it interfaces with the center core 810, i.e., the width of the first cladding 815 may be approximately zero. In various embodiments, the refractive index n2 and/or nH within the annular core 820 may be smaller, larger, or approximately equal to n0, i.e., the refractive index of the center core 810. Finally, although not depicted in
In various embodiments, the annular core 920 includes, consists essentially of, or consists of two different regions. As shown in
For multi-step clad optical fiber 900, in accordance with various embodiments, the thickness of interior step-index region 920s may be greater than or equal to approximately 10% of the center core diameter D0, or even greater than or equal to approximately 25% of D0. Such values may be applied to the thickness of the first cladding 915 as well. In various embodiments, the thickness of one or more layers of the optical fiber depends on the center-core diameter D0 because the spot size of the input laser beam may be, for example, approximately 60% to approximately 90% of D0.
In various embodiments, compared to the step-clad optical fiber 700 depicted in
In various embodiments, the annular core 920 may include, consist essentially of, or consist of more than two different regions having different refractive indices. In addition, in various embodiments, the refractive index n2 of the exterior step-index region 920e may be larger than refractive index n2s of the interior step-index region 920s, as shown in
In various embodiments, the annular core 1020 includes, consists essentially of, or consists of three different regions. As shown in
In various embodiments of the invention, the barrier region 1020b, together with the first cladding 1015 and the exterior cladding 1025, will substantially stop laser power from spreading over to other regions of fiber 1000 when the power is initially coupled into either the inner region 1020a or the outer region 1020c; therefore, output beams in accordance with embodiments of the invention may feature two discrete annular rings at the fiber exit, at least prior to averaging in response to a desired output waveform. That is, fiber 1000 enables the formation of output beams having two annular rings with different output intensities via distribution of input laser power between regions 1020a, 1020c. Such output beams are typically not enabled via the use of fibers 600, 700 detailed above. Moreover, laser power in-coupled into the barrier region 1020b will typically not be lost from the output beam but will instead spread throughout the annular core 1020.
In various embodiments, of the invention, laser power coupled into the first cladding 1015 will tend to spread over to the entire annular core region 1020, and such power may also spread over to the center core 1010. Thus, coupling beam energy into the first cladding 1015 may result in a larger effective beam size at the fiber exit than coupling into inner region 1020a. Therefore, in embodiments of the invention a non-monotonic increase in output beam size results as the laser energy is coupled into the various regions of fiber 1000, resulting in dynamic BPP variations not enabled via use of fibers 600, 700.
In various embodiments of the invention, the annular core region 1020 may include more than one barrier region 1020b, and each barrier region may have a different thickness and/or a different refractive index, although the refractive indices of such barrier layers are typically smaller than refractive index n2 and larger than or approximately equal to refractive index n1. That is, the annular core region 1020 may be divided into N+1 regions (e.g., regions 1020a, 1020c) by N barrier regions 1020b. The thickness and/or refractive index of two or more (or even all) of the multiple barrier regions 1020b may be equal to each other or different from each other.
As shown in
As with optical fiber 1000 of
In embodiments of the invention, the beam is steered into two or more different optical fibers (e.g., fibers within a fiber bundle) instead of or in addition to being steered into two or more different locations within the fiber(s).
In various embodiments of the invention, in order to reduce the risk of damage to the fibers 105, the input side of the fiber bundle 1110 is attached (e.g., via fusion) to a glass endcap. That is, the input side of the fiber bundle may be a unitary segment within which the different fibers 105 are coupled to different areal portions of the glass endcap. The glass endcap (not shown in
As shown in
Laser systems and laser delivery systems in accordance with embodiments of the present invention and detailed herein may be utilized in and/or with WBC laser systems. Specifically, in various embodiments of the invention, multi-wavelength output beams of WBC laser systems may be utilized as the input beams for laser beam delivery systems for waveform-based control as detailed herein.
In various embodiments, each of the diode bars 1205 is associated with (e.g., attached or otherwise optically coupled to) a fast-axis collimator (FAC)/optical twister microlens assembly that collimates the fast axis of the emitted beams while rotating the fast and slow axes of the beams by 90°, such that the slow axis of each emitted beam is perpendicular to the WBC dimension downstream of the microlens assembly. The microlens assembly also converges the chief rays of the emitters from each diode bar 1205 toward a dispersive element 1210. Suitable microlens assemblies are described in U.S. Pat. No. 8,553,327, filed on Mar. 7, 2011, and U.S. Pat. No. 9,746,679, filed on Jun. 8, 2015, the entire disclosure of each of which is hereby incorporated by reference herein.
In embodiments of the invention in which both a FAC lens and an optical twister (e.g., as a microlens assembly) are associated with each of the beam emitters and/or emitted beams, and SAC lenses (as detailed below) affect the beams in the non-WBC dimension. In other embodiments, the emitted beams are not rotated, and FAC lenses may be utilized to alter pointing angles in the non-WBC dimension. Thus, it is understood that references to SAC lenses herein generally refer to lenses having power in the non-WBC dimension, and such lenses may include FAC lenses in various embodiments. Thus, in various embodiments, for example embodiments in which emitted beams are not rotated and/or the fast axes of the beams are in the non-WBC dimension, FAC lenses may be utilized as detailed herein for SAC lenses.
As shown in
Also depicted in
For the welding process utilized in this example, the control frequency may be varied to vary the distance between “pierce points” at which the laser beam is utilized to penetrate through one or more layers of the workpiece to create spot welds. Equivalently, the processing speed (i.e., the relative rate of translation between the workpiece and the beam) may be varied while the control frequency is held constant. For example, this process may be utilized to replace the need for rivets between workpieces incorporating layers of dissimilar materials as the spot welds are formed through the various layers. The averaged/merged beam profile enabled by the high-frequency beam switching yields superior results, because the averaged beam size (which has a larger beam size than the pierce point) will pre-heat the workpiece, reducing thermal stress when the workpiece is penetrated at the pierce points. The thermal gradients in the workpiece are reduced, reducing the risk of cracking or fracture during processing. The use of the averaged beam shape also reduces material splattering, resulting in cleaner weld seams that do not require additional processing (e.g., grinding of weld seams prior to painting or other finishing processes).
The terms and expressions employed herein are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.
Claims
1-61. (canceled)
62. A laser system comprising:
- a beam source for emission of an input laser beam;
- an optical fiber having multiple interior regions, in-coupling of an input laser emission into each of the interior regions causing the fiber to produce an output having a different spatial output profile;
- a switching mechanism for steering the input laser emission to different ones of the interior regions of the fiber to produce different spatial output profiles in a temporal pattern having a frequency; and
- a delivery mechanism for directing the output onto the workpiece while causing relative movement therebetween, thereby processing the workpiece,
- wherein the frequency is sufficient such that the workpiece is processed, during the relative movement between the workpiece and the output, by an effective output shape combining the different spatial output profiles.
63. The system of claim 62, wherein the switching mechanism comprises a flexure-mounted reflector.
64. The system of claim 62, wherein the workpiece undergoes a time-based response to the output based on the spatial output profile and a power density thereof, the switching mechanism being configured to limit the relative movement to a maximum processing speed (i) selected based on the time-based response of the material and the frequency of the temporal pattern and (ii) ensuring that the response is to the effective output shape.
65-67. (canceled)
68. The system of claim 62, further comprising a waveform generator for generating a control waveform, the switching mechanism being configured to steer the input laser emission in response to the control waveform.
69. The system of claim 68, wherein the control waveform is a square wave.
70. The system of claim 68, wherein the effective output shape is a weighted average of the different spatial output profiles based on a shape and duty cycle of the control waveform.
71-75. (canceled)
76. The system of claim 62, wherein the beam source comprises:
- one or more beam emitters emitting a plurality of discrete beams;
- focusing optics for focusing the plurality of beams toward a dispersive element;
- the dispersive element for receiving and dispersing the received focused beams; and
- a partially reflective output coupler positioned to receive the dispersed beams, transmit a portion of the dispersed beams therethrough as the input laser emission, and reflect a second portion of the dispersed beams back toward the dispersive element,
- wherein the input laser emission is composed of multiple wavelengths.
77. The system of claim 76, wherein the dispersive element comprises a diffraction grating.
78-79. (canceled)
80. The system of claim 62, wherein the optical fiber comprises (i) a central core having a first refractive index, (ii) surrounding the central core, a first cladding having a second refractive index, (iii) surrounding the first cladding, an annular core having a third refractive index, and (iv) surrounding the annular core, a second cladding having a fourth refractive index, wherein (i) the first refractive index is larger than the fourth refractive index, (ii) the third refractive index is larger than the fourth refractive index, and (iii) the second refractive index is smaller than the first refractive index and larger than the fourth refractive index.
81. The system of claim 80, wherein the third refractive index is larger than the first refractive index.
82. The system of claim 62, wherein the optical fiber comprises (i) a center core having a first refractive index, (ii) surrounding the center core, a first cladding having a second refractive index smaller than the first refractive index, (iii) an annular core surrounding the first cladding, and (iv) surrounding the annular core, a second cladding having a third refractive index smaller than the first refractive index,
- wherein the annular core comprises: a first region having a fourth refractive index greater than the second refractive index, and a second region, a refractive index of the second region varying between (i) a fifth refractive index less than or equal to the fourth refractive index and (ii) a sixth refractive index greater than or equal to the second refractive index.
83. The system of claim 82, wherein the first region is disposed between the second region and the second cladding.
84. The system of claim 82, wherein the second region is disposed between the first region and the second cladding.
85. The system of claim 62, wherein the optical fiber comprises (i) a center core having a first refractive index, (ii) an annular core surrounding the center core, and (iii) surrounding the annular core, a first cladding having a second refractive index smaller than the first refractive index,
- wherein the annular core comprises: a first region having a third refractive index greater than the second refractive index, and a second region, a refractive index of the second region varying between (i) a fourth refractive index less than or equal to the third refractive index and (ii) a fifth refractive index less than the fourth refractive index.
86. The system of claim 85, wherein the first region is disposed between the second region and the first cladding.
87. The system of claim 85, wherein the second region is disposed between the first region and the first cladding.
88. The system of claim 62, wherein the optical fiber comprises (i) a center core having a first refractive index, (ii) surrounding the center core, a first cladding having a second refractive index smaller than the first refractive index, (iii) an annular core surrounding the first cladding, and (iv) surrounding the annular core, a second cladding having a third refractive index smaller than the first refractive index,
- wherein the annular core comprises: a first region having a fourth refractive index greater than the second refractive index, and a second region having a fifth refractive index greater than the second refractive index and smaller than the fourth refractive index.
89. The system of claim 88, wherein the first region is disposed between the second region and the second cladding.
90. The system of claim 88, wherein the second region is disposed between the first region and the second cladding.
91. The system of claim 62, wherein the optical fiber comprises (i) a center core having a first refractive index, (ii) surrounding the center core, a first cladding having a second refractive index smaller than the first refractive index, (iii) an annular core surrounding the first cladding, and (iv) surrounding the annular core, a second cladding having a third refractive index smaller than the first refractive index,
- wherein the annular core comprises: a first region having a fourth refractive index greater than the second refractive index, a second region having a fifth refractive index greater than the second refractive index, and a third region, disposed between the first and second regions, having a sixth refractive index smaller than the fourth and fifth refractive indices.
92. The system of claim 91, wherein the annular core comprises:
- a fourth region having a seventh refractive index greater than the second refractive index; and
- a fifth region, disposed between the second and fourth regions, having an eighth refractive index smaller than the fifth and seventh refractive indices.
93. The system of claim 62, wherein the optical fiber comprises (i) a center core, wherein a refractive index of the center core (a) is equal to a first refractive index at a center portion of the center core and (b) decreases, over at least a portion of a radius of the center core, to a second refractive index smaller than the first refractive index, (ii) surrounding the center core, a first cladding having a third refractive index smaller than the first refractive index, (iii) an annular core surrounding the first cladding, and (iv) surrounding the annular core, a second cladding having a fourth refractive index smaller than the first refractive index,
- wherein the annular core comprises: a first region having a fifth refractive index greater than the third refractive index, a second region having a sixth refractive index greater than the third refractive index, and a third region, disposed between the first and second regions, having a seventh refractive index smaller than the fifth and sixth refractive indices.
94-122. (canceled)
Type: Application
Filed: Jun 22, 2023
Publication Date: Oct 19, 2023
Inventors: Mark MORDARSKI (Tewksbury, MA), Bryan Lochman (Nashville, TN), Francisco Villarreal-Saucedo (Middleton, MA)
Application Number: 18/339,563
