Method and apparatus for controllably adjusting beam parameters - Patents.com

Abstract

The fiber laser source is comprised of a number of individual fiber lasers coupled together in series, with each subsequent fiber laser being configured to transmit the laser radiation of one of the fiber lasers located upstream from it. Switching among the different operating regimes of the laser source, including SM, MM and various MM, with associated beam shapes, beam qualities and power parameters, is provided at high frequencies corresponding to the on / off switching of each individual fiber laser.

Description

[Technical field]

[0001] The present disclosure relates to fiber laser technology. In particular, the present disclosure relates to a fiber laser source configured to rapidly adjust the spatial and / or divergence beam profile. [Background technology]

[0002] Welding, cutting, and additive manufacturing are just a few widely used applications for industrial fiber lasers. Frequently, tasks involving the use of fiber lasers require dynamic adjustment of numerous beam parameters, including beam diameter and beam shape among others. For example, the beam shapes useful for selected cutting and welding operations often require a combination of beams with respective Gaussian and ring-shaped intensity distributions that lead to high quality welds. A laser source that achieves this combination may include two or more independent laser sources with their respective outputs coupled into a fiber coupler that dynamically controls the beam profile. Termed adjustable mode beam lasers or AMBs, such sources are disclosed in U.S. Patent Application No. 17,299,490 (USPA '490), which is incorporated herein by reference in its entirety. Alternatively, as disclosed in U.S. Patent No. 10,732,440 (US '440), which is also incorporated herein by reference in its entirety, the laser source includes mechanical means for compressing a specially configured fiber to output beams of various characteristics.

[0003] The advantages of an output beam with controllably tunable properties become particularly apparent in laser-based additive manufacturing (LBAM). The latter is a family of various processes including selective laser melting (SLM), where a laser beam melts powder particles in a homogenous mass, and / or selective laser sintering (SLS), where a laser beam fuses powder particles together. Historically achieved by multiple tools used to mill, turn, cast, solder, etc., LBAM uses a single tool that does it all - the laser beam.

[0004] For example, ceramic materials are traditionally processed through a powder metallurgy (PM) process that consists of (1) powder production, (2) primary forming, (3) debinding, (4) furnace sintering, and (5) final forming. Primary forming is traditionally done by slip casting or injection molding, both technically complex and time-consuming techniques. Nowadays, primary forming is done by SLM / SLS, which allows forming ceramic parts into geometries and forms that are not achievable by traditional techniques.

[0005] Clearly, LBAM has a significant number of advantages over traditional techniques, including but not limited to speed, cost and flexibility. One of the greatest advantages of LBAM is rapid prototyping - the ability to design, manufacture and test custom parts in the least amount of time possible. With specific reference to manufacturing / production rate, the build rate of an individual part can be determined according to the following: V b =δ×s×θ, where, δ is the layer thickness, s is the hatch spacing, and θ is the scanning speed.

[0006] The hatch spacing is the distance between the centerlines of two consecutive laser scans, in other words, the hatch spacing determines the resolution of the process. Typically, the hatch spacing is about 70% of the beam diameter on the surface of the laser processing powder. However, some areas of the part to be laser processed require higher resolution, and then require a relatively low scan speed and high quality light that can be focused to a small spot. Others do not require high resolution, and as a result, can only benefit from a higher scan speed and a light with a larger beam spot than that required for the delicate area.

[0007] The industry is, of course, well aware of this and has developed various techniques to address the "non-uniformity" of parts and therefore the laser beam characteristics required to print them at high production rates. For example, one technique utilizes multiple uniformly configured laser sources operating in parallel. The process speed is increased by a factor corresponding to the number of laser sources. If this approach appears to complicate the manufacturing process, that is because it does, and therefore such processes entail high production costs. Yet another approach provides a differently shaped beam delivered to the target by a single multi-clad fiber, as disclosed in USPA '490. In particular, systems implementing this approach are configured with bulk optics that expand the beam diameter when the power of the laser is increased to address selective areas of the part to be laser printed. Conversely, the beam diameter decreases when the output power is decreased such that other areas of the same part require high resolution. In addition to power and optical quality, the system is operable to output differently shaped beams, including, for example, ring-shaped beams, flat-top beams, bell-shaped beams, and others. Structurally, the system requires the use of one or more sophisticated kW power level lasers operating in parallel to output high quality light that, for all practical purposes, can be considered to be a single (transverse) fundamental mode (FM). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] U.S. Application No. 17299490 [Patent Document 2] U.S. Patent No. 10,732,440 Summary of the Invention [Problem to be solved by the invention]

[0009] Thus, a need exists for a fiber laser source having a simple configuration that is controllably operable to vary, among other things, beam diameter and beam shape. [Means for solving the problem]

[0010] The disclosed laser source is based on a simple concept: two or more fiber lasers are coupled together in series, with each subsequent fiber laser configured to support the propagation of radiation output by one or more preceding upstream fiber lasers. Each of the serially coupled fiber lasers is configured with a set of optical properties including, among others, beam diameter, beam shape, light intensity, emission wavelength, beam divergence (NA) and any combination thereof. The set of optical parameters of each fiber laser is at least partially different from each other, allowing the shape, diameter and quality of the beam from the upstream fiber laser to remain intact as the beam propagates through at least one or more subsequent or downstream fiber lasers. Hence, the laser source operates in different regimes depending on which of the upstream and downstream fiber lasers is in operation. The principle of the disclosed laser source is similar to that of a nesting doll: each subsequent fiber laser has a structure that allows the radiation generated by one or more previous / upstream fiber lasers to propagate through its optical overview and / or to add something uniquely new to the laser source output.

[0011] According to one exemplary implementation of the inventive concept, the laser source includes an upstream multi-clad multimode (MM) fiber laser and a downstream multi-clad single mode (SM) fiber laser. The refractive index profile (RI) of each of the upstream and downstream fiber lasers is configured such that in the MM operation of the laser source, the SM downstream fiber laser transmits the flat-top MM output propagating from the upstream fiber laser without affecting its beam characteristics. In the SM regime of the laser source, only the downstream SM laser outputs a SM / FM bell-shaped beam with a small beam diameter. Yet another regime includes the simultaneous operation of both the downstream and upstream lasers implementing the inventive concept, i.e., the flat-top beam generated by the MM upstream laser is not corrupted during propagation through the downstream laser, along with the bell-shaped beam.

[0012] In another example, two or more MM fiber lasers are optically coupled in series. A laser source with two MM fiber lasers can operate in two different MM regimes characterized by respective flat-top laser source output beams having different diameters, the beam diameter of the downstream fiber laser being smaller than that of the upstream fiber laser. A third regime, involving simultaneous operation of both the upstream and downstream fiber lasers, involves two flat-top source output beams generated simultaneously.

[0013] Yet another example relates to serially coupled MM fiber lasers. However, in contrast to the previously disclosed exemplary optical scheme, here both lasers have respective ring-shaped outputs of different dimensions. Also, the laser source output beams may include one or another ring-shaped beam, or both may output ring-shaped beams concentrically.

[0014] Regardless of the number of fiber lasers that make up the laser source, the RI profile of each is structured such that each subsequent laser transmits light from any of the upstream fiber lasers with minimal impact on the beam optical quality, beam diameter and shape. For the laser source according to the invention to work, the serially coupled fiber lasers should generate respective beams with gradually decreasing beam diameters, the smallest of which is output by the downstream fiber laser.

[0015] Completing the fiber laser source is a delivery fiber with an RI profile that matches the shape of the output beam from any of the fiber lasers, so that the delivery fiber may be configured to deliver SM and / or MM beams as well as various beam shapes according to the desired configuration of the RI index of each of the fiber laser components of the disclosed laser source.

[0016] Based on the above, the fiber lasers of the disclosed laser sources can be configured as multimode and / or single mode sources as well as polarized and unpolarized sources. The disclosed fiber laser configurations may include Fabry-Perot and / or ring resonators. The disclosed laser sources are not limited to any particular power level and therefore operate in a very wide range of powers, from a few watts to several kW, and up to one or more MW, depending on the operating regime of any given laser source. The operating regime may be selected from continuous wave (CW), quasi-CW (QCW) and pulsed laser operation. The active and passive fibers of each fiber laser may have an infinite variety of RI rates, which are specifically tailored to obtain the desired shape and quality of the output beam. In addition to all of the laser configurations disclosed above, the features disclosed above and detailed below may be used in any combination with each other without departing from the claimed subject matter of the present disclosure.

[0017] Various aspects of at least one embodiment are described below with reference to the accompanying drawings, which are not intended to be drawn to scale. The drawings are included to provide illustration and further understanding of the various features and overviews and embodiments, and are incorporated into and constitute a part of this specification, but are not intended as a definition of the scope of any particular embodiment. The drawings, together with the remainder of the specification, serve to explain the principles and operation of the described and claimed aspects and embodiments. In the drawings, each identical or nearly identical part illustrated in the various figures is represented by a similar numeral. For purposes of clarity, every part may not be labeled in every figure. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 illustrates an example schematic of the disclosed laser source including serially coupled upstream MM and downstream SM fiber lasers. [Diagram 2] FIG. 14 illustrates another exemplary schematic of the disclosed laser source configured with serially coupled upstream and downstream MM fiber lasers. [Diagram 3]3 illustrates an exemplary RI index profile of the MM active fiber of FIGS. 1 and 2, respectively. FIG. [Figure 4] 4 illustrates an exemplary RI index profile of a MM passive fiber utilized in combination with the active MM fiber of FIG. 3. [Diagram 5] FIG. 5 illustrates exemplary RI index profiles of each of the input and output SM passive fibers operating in combination with the MM fiber lasers of FIGS. 3 and 4. [Figure 6] FIG. 6 illustrates an exemplary RI index profile of the active SM fiber of FIG. 1 combined with the RI profiles of FIGS. 3, 4 and 5, respectively. [Figure 7] FIG. 3 illustrates a ring-shaped RI profile of the MM fiber of FIGS. 1 and 2. [Figure 8] FIG. 3 illustrates yet another RI profile of the MM fiber of FIGS. 1 and 2. [Figure 9] FIG. 3 illustrates an example ring-shaped RI profile of the MM fiber laser of FIGS. 1 and 2. [Figure 10] 10 illustrates the RI profile of the SM fiber laser of FIG. 1 that can be operated in combination with the MM fiber laser of FIG. 9. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The disclosed laser source provides flexibility in structuring differently configured fiber lasers to tailor the source output beam to existing needs. The concept underlying the laser source according to the present invention provides serially coupled fiber lasers, where each subsequent fiber laser is configured to guide the beam generated by any of the upstream fiber lasers without substantially affecting the optical properties of the beam. In addition, each subsequent laser is structured to output its own beam with a smaller beam diameter than the one transmitted by this fiber laser. Each of the fiber lasers can operate in a regime selected from CW, QCW and pulsed regimes. The disclosed laser source can include at least two or more fiber lasers operating in respective regimes that are the same or different from each other. Also, the multiple fiber lasers of the disclosed laser source may generate light with the same or different emission wavelengths and / or the same or different powers.

[0020] 1, the disclosed configuration of laser source 10 is merely one example of an otherwise limitless overview that one skilled in the art of fiber laser technology can design utilizing the disclosed concepts. In particular, laser source 10 includes two light generators or fiber lasers 12 and 14, the former being an upstream MM fiber laser and the latter being a SM downstream fiber laser. In the illustrated overview, SM downstream laser 14 is coupled to a passive delivery fiber 24.

[0021] The lasers 12, 14 each have a respective all-fiber Fabry-Perot resonant cavity in which a respective set of three fibers are comprised: a gain medium or active fiber 25, 35, an input passive fiber 26, 32, and an output passive fiber 28, 34. The active fiber of each set is butt-spliced ​​at its opposite end to a respective input / output passive fiber and is doped with ions of a laser-active rare earth element. The following non-exclusive list of typical glassy lanthanides includes ions of ytterbium (Yb), erbium (Er), thulium (Tm), neodymium (Nd), holmium (Ho), praseodymium (Pr), cerium (Ce), various co-doping combinations, and others. Passive fibers are commonly utilized for fiber lasers because it is technically easier to write fiber Bragg gratings (FBGs) in passive fibers. Thus, each of the resonant cavities shown is defined between an upstream highly reflective FBG and a downstream weak FBG. In particular, the MM upstream laser 12 has its resonant cavity defined between FBGs 16 and 18, while the SM laser 14 has its resonant cavity defined between FBGs 20 and 22. Two pairs of FBGs 16, 18 and 20, 22, respectively, are configured differently, with FBGs 16 and 18 being MM while the other pair of FBGs 20 and 22 are SM. A delivery fiber 24 is spliced ​​to the output passive fiber 34 of the SM laser 14 and configured to output a SM or MM or both SM and MM source output beam as disclosed below.

[0022] For operation in SM, only the downstream SM fiber laser 14 is pumped to generate a signal beam O14. Alternatively, to generate only an MM output beam O12 at the output of the laser source 10, the MM upstream laser 12 generates an MM signal that is coupled into the downstream SM laser 14, which is de-energized during operation of the laser 12. The SM fiber laser 14 transmits the combined MM beam along an optical path that further includes a delivery fiber 24 without affecting the beam optical properties. Simultaneous operation of the fiber lasers 12, 14 provides both MM and SM source outputs, respectively. Based on the above, alternative or simultaneous pumping of the fiber laser components 12 and 14 provides a laser source output beam O12 / O14 with at least two or more desired optical properties. In particular, the properties may include, among others, M 2 Factors include the beam shape, for example bell-shaped or flat-top or ring-shaped, and power, which is adjusted by individually controlling the pump power of each fiber laser.

[0023] FIG. 2 illustrates another exemplary scheme configured according to the disclosed concept. Similar to FIG. 1, the laser source 10′ includes two fiber lasers 12 and 12′, but in contrast to the configuration of FIG. 1, both fiber upstream and downstream lasers 12 and 12′ are MM, respectively. The working principle of the illustrated laser 10′ is similar to that of FIG. 1: the downstream fiber laser 12′ transmits the output beam O12 of the upstream MM fiber laser 12. Alternatively, the downstream MM fiber laser 12′ generates its own MM output beam O14, but the beam diameter is smaller than that of the beam O12 from the upstream MM fiber laser 12. Finally, both MM fiber lasers 12 and 12′ can operate simultaneously, respectively, and contribute to the laser source output beam including the beam O12 from the upstream MM laser 12 and the beam O14 from the downstream MM laser 12′.

[0024] Both Fig. 1 and Fig. 2 each illustrate the use of a pump 55 including a diode laser or other type of pump laser. Typically, the pumping configuration involves side pumping, where pump light is coupled into the outer cladding of the double clad active fibers 25, 25' and 35 and propagates in a zigzag fashion across the fiber region, as is well known to those skilled in the art of fiber technology. However, end pumping schemes can also be used. The pump light may be coupled into the gain medium such that it co-propagates or counter-propagates or both with the generated signal light. The pumps 55 can excite only the designated fiber lasers and are therefore individually controlled. Control can also be realized by a central processing unit to achieve a desired combination of SM and MM optical power. Those skilled in the art will readily recognize that combinations of more than two fiber lasers, such as multiple upstream MM and downstream SM or all MM lasers, can be readily constructed based on the disclosed concepts.

[0025] The remainder of this application discloses fiber structures that put the disclosed concepts into practice. One of the salient design features that realizes the disclosed concepts is the RI profile of the fiber components, which is adjusted to obtain the desired output beam characteristics of the laser source 10.

[0026] 3 and 4 in combination with FIG. 1, the active fiber 25 of the upstream MM fiber laser 12 may have a single or multi-clad configuration. As shown, the RI of the fiber 25 includes a core 40, which may be doped with ions of a rare earth element and concentrically surrounded by a cladding 42, which in turn may be surrounded by a polymeric protective sleeve, not shown here. Pumped according to a parallel or end-pump configuration, light generated in the core 40 of the active fiber 25 is coupled into a core 40' of an output passive fiber 28, as illustrated in FIG. 4. The cores 40 and 40' of the respective active and passive fibers 25, 28 are dimensioned with suitable core diameters and NAs to prevent optical losses. The optical output from the passive fiber 28 of the laser 12 is coupled into an input passive fiber 32 of the SM downstream fiber laser 14.

[0027] FIG. 5 illustrates the RI of the fibers 32, 35, and 34 of the downstream SM fiber laser 14 seen in FIG. 1. In other words, all three fibers have a uniform RI, and although the following description is based on the input passive fiber 32, it always refers to the other two fibers 35 and 34, respectively. Based on the example, the input passive fiber 32 of the SM fiber laser 14 has a core 52 that receives the MM radiation from the core 40' of the output passive fiber 28 of the upstream fiber laser 12 of FIG. 1 and FIG. 4. The cores 40' and 52 of each fiber laser 12, 14 are configured with a uniform numerical aperture (NA) and a uniform outer diameter to minimize and preferably completely prevent coupling optical losses. The annular dip 54 in the RI of the SM input fiber 32 of FIG. 5 is formed by SiO 2 , with F as fluorine. 2 3. The fiber optics 12 is formed of a glass, such as SiO.sub.2 / SiF, and acts as a barrier to confine the guided emission to the inner core 52. The cores of all three fibers of the downstream laser 14 each have a central core region 50 with an enhanced RI compared to that of the core 52.

[0028] Referring to FIG. 6 in addition to all of the above figures, the MM radiation guided into the core 52 including the central region 50 of the input passive fiber 32 of the downstream laser 14 is further coupled into the inner cladding 52′ and central region 50 of the active fiber 35. Due to the uniformity of all fiber components of the downstream fiber laser 14, internal cavity losses of light propagating through these fibers are substantially eliminated. As will be readily appreciated by those skilled in the fiber laser art, the central core region 50 of each of the passive and active fibers of the downstream SM fiber laser 14 does not affect the output of the upstream MM fiber laser 12, which has a flat-top shape. Further guided through the delivery fiber 24, the configuration of which is disclosed below, the MM radiation with a flat-top beam shape is output from the laser source 10.

[0029] 1 in SM is achieved by pumping only the downstream fiber laser 14. The central core region 50 of each of the input and output passive fibers 32, 34, respectively, may be made of glass, e.g., Ge, for germanium or other known elements, or SiO 2 / GeO 2 6 to provide an elevated RI in this central core region. In addition, the central core region 50 of the active fiber 35 in FIG. 6 is doped with luminescent ions. Each of the FBGs 20 and 22 in FIG. 1 is written into the central core region 50 of each of the input and output passive fibers 32, 34 of the SM fiber laser 14. Thus, when operation of the laser source in FIG. 1 is required to be SM only, the upstream MM fiber laser 14 is switched off. When operation of the laser source 10 requires a source output that includes an outer MM flat-top and an inner SM bell-shaped beam, both the upstream and downstream fiber lasers 12, 14, respectively, are operated simultaneously.

[0030] With reference to Figures 1 and 6, a few words should be said about SM fiber lasers. Within the context of this disclosure, all of the fibers - passive and active - are MM fibers, i.e., all fiber cores are capable of supporting multiple modes. What makes the SM fiber laser 14 output radiation substantially in the fundamental mode (FM) at the desired wavelength is the selection of the waveguide geometry and NA, as known to those skilled in the art, that allows the waveguide to support substantially only FM. Among the multiple modes reflected from the FBGs 20, 22 to the resonator, the FM has the highest reflection coefficient. Therefore, the FM reaches the oscillation threshold first. Thus, the SM fiber laser 14 is an MM fiber that is for all practical purposes considered and referred to as SM. 2 Effectively outputs a beam with a single FM of ≦1.3.

[0031] The MM-MM configuration of the laser source 10' illustrated in Fig. 2 can be realized by the combination of the RIs of Figs. 3-4 and Figs. 7 and 8, respectively. As particularly illustrated in Fig. 7, the active fiber 25' of the downstream MM fiber laser 12' may have a double clad configuration in which the central core region 52 is provided within the inner cladding 54. The input and output passive fibers 26' and 28' of Fig. 2 each include a central core region 62 within the inner cladding 64 (Fig. 8). In order for the downstream MM fiber laser 12' of Fig. 2 to transmit radiation from the upstream MM laser 12 of Figs. 2-4, the input and output passive fibers 26', 28' and the active fiber 25' (Figs. 8 and 7) have respective inner claddings 64, 54 provided with diameters matching those of the respective cores 40 of Figs. 4 and 3.

[0032] When operation of the laser source 10' is required, for example, with MM radiation output only from the downstream MM fiber laser 12', the latter is pumped and the upstream MM fiber laser 12 is switched off. The only difference in the described schematic of FIG. 2 between the upstream and downstream MM lasers 12, 12', respectively, is the diameter of the cores 52, 62 of the respective active fibers 25, 25', the core of the downstream MM laser 12' being somewhat smaller than that of the upstream MM laser 12. When only the upstream MM fiber laser 12 operates, the downstream MM fiber laser 12' is turned off. Alternatively, both MM fiber lasers 12 and 12' can operate in concert, with the flat-top beam O14 of the upstream MM laser 12 in FIG. 2 surrounding the output flat-top beam O12 of the downstream MM laser 12'.

[0033] With reference to FIG. 9 and FIG. 1, the above-mentioned flat-top shaped MM beam is not the only shape that the upstream MM fiber laser 12 of FIG. 1 and FIG. 2 can output. In particular, the RI profile illustrated in FIG. 9 is fabricated in the fiber when the output beam is required to have a ring shape. The ring core 48 contains RI enhancing additives and luminescent dopants. The upstream MM fiber laser 12 with the RI profile of FIG. 9 can be used in combination with the SM downstream fiber laser 14 with the RI profile as illustrated in FIG. 10. In particular, the ring-shaped beam from the upstream MM laser 12 is transmitted through the ring core 42 of the downstream SM laser 14. Thus, the combination of the upstream and downstream fiber lasers 12 and 14 with the corresponding RI profiles of FIG. 9 and FIG. 10, respectively, provides a ring-shaped laser source 10 output beam when only the MM laser 14 is operated, and a bell-shaped beam when the downstream laser 14 is operated alone or both. One skilled in the art would be able to select appropriate passive fiber RI profiles to provide the desired optical connections between the MM and SM lasers of FIGS. 9 and 10, respectively, and the SM fiber laser 12 and delivery fiber 24 based on the inventive concepts underlying this disclosure.

[0034] The aspects disclosed herein in accordance with the present invention are not limited in their application to the details of construction and the arrangement of parts set forth in the following description or illustrated in the accompanying drawings. These aspects may assume other embodiments and be practiced or carried out in various ways. Examples of specific implementations are provided herein for illustrative purposes only and are not intended to be limiting. In particular, acts, parts, elements and features described in connection with any one or more embodiments are not intended to be excluded from a similar role in any other embodiment. For example, while this disclosure focuses primarily on beam shape, light quality and power, obvious derivations of the disclosed parameters are readily apparent to one of ordinary skill in the art. For example, knowing the beam shape, it is easy to determine the beam diameter and, as a result, the beam divergence, etc. for any given wavelength.

[0035] Also, the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. Reference to the singular or plural is not intended to limit the disclosed systems or methods, their parts, acts or elements. Additionally, in the event of a conflicting usage of terms between this document and a document incorporated herein by reference, the usage of the terms in the incorporated references is supplementary to that of this document, and to the extent of any inconsistent conflict, the usage of the terms in this document will control.

[0036] Although some aspects of at least one example have been described in this manner, those skilled in the art will readily recognize that various changes, modifications, and improvements will readily occur to those skilled in the art. The number of fiber lasers can, of course, be well beyond two. In fact, the disclosed laser source is modular, so that additional fiber laser components can be added to the above disclosed, and then substituted as necessary. For example, the number of concentric cores in the illustrated RI profile is only limited by common sense. Additional examples of RI profiles are disclosed in U.S. Pat. No. 1,073,240, which is fully incorporated herein by reference. The disclosed examples, as well as obvious changes, modifications, and improvements thereof, are all part of this disclosure and are applicable to various industrial applications. Therefore, the above description and drawings are merely exemplary. [Explanation of symbols]

[0037] 10 Laser light source 10' Laser Light Source 12 Fiber laser 12' Fiber Laser 14 Fiber laser 16 Fiber Bragg Grating 18 Fiber Bragg Grating 20 Fiber Bragg Grating 22 Fiber Bragg Grating 24 Delivery Fiber 25 Active Fiber 25' Active Fiber 26 Input Passive Fiber 26' input passive fiber 28 Output Passive Fiber 28' output passive fiber 32 Input Passive Fiber 34 Output Passive Fiber 35 Active Fiber 40 cores 40' Core 42 Clad 48 Ring Core 50 Central Core Region 52 cores 52' Inner Cladding 54 Annular Dip 55 Pump 62 Central Core Region 64 Inner Cladding O12 Beam O14 Beam

Claims

1. an upstream fiber laser and a downstream fiber laser optically coupled in series with each other and controllable to generate respective first and second beams, the downstream fiber laser configured to deliver a first beam, the first and second beams each characterized by parameters including beam shape, beam quality, power, wavelength or a combination thereof; a delivery fiber optically coupled to an output of the downstream fiber laser and configured to deliver the first beam, or the second beam, or the first and second beams simultaneously; A fiber laser light source comprising:

2. 10. The fiber laser source of claim 1, further comprising an additional upstream fiber laser that generates a third laser beam, alone or in combination with the first beam or the second beam or with the first and second beams, that is transmitted through the upstream and downstream fiber lasers and the delivery fiber.

3. 2. The fiber laser source of claim 1, wherein at least one or more of the beam shape, beam quality, wavelength and power of each of the first, second and third beams are different from each other.

4. 2. The fiber laser source of claim 1, wherein the downstream fiber laser is configured to generate the second beam in a fundamental transverse mode (FM) or in a multiple transverse mode (MM), and the first beam output by the upstream fiber laser is in MM.

5. 10. The fiber laser source of claim 1, wherein the upstream and downstream fiber lasers are configured to generate respective first and second beams each having a bell, flat top or ring shape.

6. 2. The fiber laser source of claim 1, wherein the upstream and downstream lasers are configured to generate respective first and second beams, the beam diameter of the second beam being smaller than the beam diameter of the first beam.

7. The fiber laser source of claim 1 , further comprising a plurality of optical pumps designated to excite respective upstream and downstream fiber lasers.

8. 8. The fiber laser source of claim 7, wherein the optical pumps are individually controlled and each is selected from a diode laser or a fiber laser or a combination thereof.

9. The fiber laser source of claim 7 , further comprising a central processing unit operatively connected to said optical pumps and configured to control an on / off state of each of said optical pumps.

10. 2. The fiber laser source of claim 1, wherein the upstream and downstream fiber lasers are each configured with spaced apart input and output passive fibers and active fibers, with opposite ends of the active fiber spliced ​​to respective opposite ends of the input and output passive fibers, the input and output passive fibers flanking each of the upstream and downstream fiber lasers with respective Fiber Bragg Gratings (FBGs), each pair of FBGs defining a resonator cavity therebetween that includes the active fiber.

11. 11. The fiber laser source of claim 10, wherein the input and output passive fibers and the active fiber of the upstream fiber laser are each configured to transmit MM laser radiation, and the input and output passive fibers and the active fiber of the upstream fiber laser have respective cores configured with uniform core diameters.

12. 12. The fiber laser source of claim 11, wherein the downstream fiber laser includes the active fiber and the input / output passive fibers each having a multi-clad configuration including a central core and an inner cladding, the inner cladding is sized with a cladding diameter that matches the uniform core diameter of the active fiber and the input / output passive fibers of the upstream fiber laser, and the cores of the active fiber and the input / output passive fibers of the downstream fiber laser, respectively, are sized to transmit FM or MM.

13. The fiber laser source of claim 12 , wherein the input and output passive fibers and the active fiber of the downstream fiber laser operating in FM have respective mode field diameters that are matched to each other.

14. The fiber laser source of claim 1 , wherein the fiber laser source outputs a source beam at FM, MM, or FM and MM, or multiple MM.

15. 13. The fiber laser source of claim 12, wherein the core and the inner core of each active fiber are selectively doped with ions of one or more rare earth metals.

16. The fiber laser source of claim 1 , wherein the upstream and downstream fiber lasers operate at the same or different respective wavelengths from each other.

17. 10. The fiber laser source of claim 1, wherein the delivery fiber is a multi-clad passive fiber.

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