Fiber laser-insensitive aiming laser

Abstract

A laser assembly includes: a multi-clad optical fiber optically coupled to a light source configured to emit light radiation of a first wavelength; and a protective element disposed between the light source and the multi-clad optical fiber to prevent a portion of the backward-propagating light radiation of a second wavelength from coupling into the light source.

Description

Technical Field

[0001] The present disclosure relates to methods and apparatus for protecting against backward-propagating radiation in a fiber laser assembly. Background Art

[0002] Users of high-power industrial fiber lasers are accustomed to fiber lasers that emit a visible "aiming beam" as needed for tool alignment using the naked eye. Regulatory requirements for such visible beams typically limit their output power to <1 mW. Desirably, this power is transmitted with less attenuation through the material processing optics selected by the user. The low attenuation requirement encourages incorporation of the alignment beam into the core of the fiber laser.

[0003] In an exemplary fiber laser assembly, the visible beam is injected into the output beam by a combiner. For example, as Figure 1 shown, the laser assembly 100 produces a laser output beam 124 coaxial with the visible beam 134.

[0004] In this embodiment, the assembly 100 includes pump laser beam sources 110, 112 that produce beams 111, 113, respectively. The beams 111, 113 propagate in respective optical fibers 114, 116. The optical fibers 114, 116 are joined to combiner input optical fibers 120, 122. The combiner 102 receives and combines the beams 111 and 113 to form a combined output beam 124 that is coupled into the cladding of the combiner output optical fiber 126. A visible light source 132 produces a visible beam 134 that is coupled via a wavelength division multiplexer (WDM) 136 to an additional input optical fiber 140 and the combiner 102. The combiner 102 couples the visible beam 134 into the core of the output optical fiber 126 that includes a laser 154 having an active optical fiber between a high reflectivity fiber Bragg grating (HR FBG) 152 and a partial reflectivity fiber Bragg grating (PR FBG) 150. The optical fiber 126 transmits the laser output beam 124 to a laser head 128 that directs the beam 124 to a workpiece 130 to perform a machining operation such as cutting, welding, brazing, additive manufacturing, etc. The visible beam 134 is coaxial with the beam 124 and can be used to direct and align the beam 124 on the workpiece 130.

[0005] During active operation, the laser output beam 124 may be reflected from the surface of the workpiece 130 or cause the workpiece 130 to emit radiation in response to the incident beam 124. Both the emitted and reflected radiation can be backward coupled into the core of the laser fiber. This backward-propagating radiation 140 can return through the input fiber and combiner 102 to reach and potentially damage upstream components. Damage caused by backward-propagating radiation can result in catastrophic failure. For example, the backward-propagating radiation may damage or disable the source 132 of the visible aiming beam 134. One way to protect the visible light source 132 is to inject the visible beam 134 through a WDM 136, which is designed to transmit the aiming beam 134 into the core of the fiber laser and transmit the backward-propagating radiation 140 from the fiber laser to an unused port, such as the WDM rejection port 138, where it can be safely dissipated. However, such devices are expensive and add an undesirable cost to the fiber laser.

[0006] The problem is to find a cost-effective method that injects a visible aiming beam into the output of a high-power industrial fiber laser that is reliable under expected backward-propagating radiation. SUMMARY OF THE INVENTION

[0007] Components, devices, and methods for reducing the harmful effects of backward-propagating radiation in a fiber laser are disclosed herein. Such components, devices, and methods include a laser assembly that includes: a multi-clad fiber optically coupled to a light source (e.g., a laser diode) configured to emit light radiation of a first wavelength (e.g., within the visible spectrum); and a protection element disposed between the light source and the multi-clad fiber to prevent a portion of the backward-propagating light radiation of a second wavelength from coupling into the light source.

[0008] In one example, the multi-clad fiber can be a double-clad fiber that includes a core, a cladding, and a buffer layer, where the core has a higher refractive index than the cladding, and the cladding has a higher refractive index than the buffer layer. In different examples, the multi-clad fiber can be a triple-clad fiber that includes a core, a first cladding, a second cladding, and a buffer layer, where the core has a higher refractive index than the first cladding, the first cladding has a higher refractive index than the second cladding, and the second cladding has a higher refractive index than the buffer layer.

[0009] The protection element can be a reflector or an absorber or a combination thereof. In an example, the protection element can be a dichroic filter configured to transmit light radiation of the first wavelength and reflect light radiation of the second wavelength. Further, the protection element can reflect the light radiation of the second wavelength in a manner that couples a portion of the backward-propagating light radiation into one or more claddings of the multi-clad fiber and / or in a manner that directs the light radiation away from the core of the multi-clad fiber.

[0010] In one example, the protective element can be a dichroic filter. The dichroic filter can be applied to the output end of the multi-clad fiber. In some cases, the output end of the multi-clad fiber can be angled, arcuate, or spherical. Additionally or alternatively, the dichroic filter can be applied to the surface of a window that forms part of an enclosure encapsulating the light source, or to the surface of a protective element disposed adjacent to the output end of the multi-clad fiber.

[0011] The laser assembly can also include focusing optics configured to focus light radiation of a first wavelength into the multi-clad fiber. In such a case, the dichroic filter can include a coating applied to the surface of the focusing optics. In an example, the multi-clad fiber can be a pigtail fiber configured to be optically coupled to an input fiber of a fiber laser. Such a pigtail can be further configured to couple light radiation of the first wavelength from the light source into the input fiber, where the first wavelength is within the visible spectrum and the fiber laser is configured to propagate the light radiation through an output fiber to a workpiece. In an example, the fiber laser can be a diode-pumped fiber laser or a counter-pumped fiber laser.

[0012] The above and other objects, features, and advantages will become more apparent from the following detailed description, which is made with reference to the accompanying drawings that are not necessarily drawn to scale. Description of the Drawings

[0013] The accompanying drawings (where like reference numerals represent like elements) are incorporated into and constitute a part of this specification, and together with the description explain the advantages and principles of the technology of the present disclosure. In the drawings,

[0014] Figure 1 An exemplary laser assembly for guiding a visible beam coaxial with an output high-power laser beam is shown, which includes a WDM for back-reflection protection;

[0015] Figure 2A An exemplary laser assembly for generating and guiding a high-power output laser beam with a coaxial visible beam is shown, which includes a visible light source protection element;

[0016] Figure 2B An exemplary visible light source protection assembly for protecting a visible light source from damage by backward-propagating radiation is shown;

[0017] Figure 2C An exemplary refractive index profile of a double-clad fiber configured to protect a visible light source from damage by backward-propagating radiation is shown;

[0018] Figures 2D - 2HShows a plurality of exemplary visible light source protection components for protecting a visible light source from damage by backward-propagating radiation;

[0019] Figure 3A Shows an exemplary visible light source protection component for protecting a visible light source from damage by backward-propagating radiation;

[0020] Figure 3B Shows an exemplary refractive index profile of a three-cladding optical fiber configured to protect a visible light source from damage by backward-propagating radiation; and

[0021] Figure 4 Shows an exemplary anti-pumping laser assembly for generating and guiding a high-power output laser beam having a coaxial visible light beam, which includes a visible light source protection element. DETAILED DESCRIPTION

[0022] As used in this application and the claims, the singular forms "a", "an", and "the" include the plural forms unless the context clearly dictates otherwise. Further, the term "comprising" means "including". Further, the term "coupled" does not exclude the presence of intermediate elements between the coupled items.

[0023] The systems, devices, and methods described herein should not be construed as being limited in any way. Instead, the present disclosure relates, separately and in various combinations and sub-combinations with each other, to all novel and non-obvious features and aspects of the various disclosed embodiments. The systems, methods, and devices of the present disclosure are not limited to any particular aspect or feature or combination thereof, and the systems, methods, and devices of the present disclosure do not require the presence of any one or more particular advantages or problems to be solved. Any theory of operation is for ease of explanation, but the systems, methods, and devices of the present disclosure are not limited to such theories of operation.

[0024] Although, for convenience of presentation, the operations of some methods of the present disclosure are described in a particular, sequential order, it should be understood that such description includes rearrangements, unless the particular language set forth below requires a particular order. For example, the operations described sequentially may in some cases be rearranged or performed simultaneously. Further, for simplicity, the drawings may not show the various ways in which the systems, methods, and devices of the present disclosure may be used in conjunction with other systems, methods, and devices. Further, the description sometimes uses terms such as "produce" and "provide" to describe the disclosed methods. These terms are high-level abstractions of the actual operations performed. The actual operations corresponding to these terms will vary depending on the particular implementation, and are readily discernible by one of ordinary skill in the art.

[0025] In some examples, values, processes, or devices are referred to as "lowest", "best", "minimum", etc. It should be understood that such descriptions are intended to indicate that a choice can be made among many alternative functions in use, and that such a choice need not be better, smaller, or otherwise more preferable than other choices. Examples are described with reference to directions indicated as "above", "below", "upper", "lower", etc. These terms are used for convenience of description and do not imply any particular spatial orientation. Additionally, in the following examples, laser components and assemblies are described at a high level of abstraction and do not include a complete description of all the mechanical, electrical, and optical elements required for operation.

[0026] As described above, a reliable and cost-effective way to inject a visible aiming beam into the output of a high-power industrial fiber laser is an attractive alternative to using an expensive WDM device to handle the backward-propagating radiation at the visible light source. The method proposed herein is to use a visible light source to reflect sufficient backward-propagating radiation back into the fiber laser to reduce the radiation power incident on the light source itself to a safe level without disrupting the operation of the fiber laser.

[0027] Figure 2A An example of a fiber laser assembly 200 for generating and guiding a high-power output laser beam 224 with a coaxial visible beam 234 is shown, where the assembly 200 incorporates a visible light source protection assembly 204 to protect the visible light source 232 from backward-propagating radiation 240. In one example, the assembly 200 includes pump laser beam sources 210, 212 that generate beams 211, 213, respectively. The beams 211, 213 propagate in respective optical fibers 214, 216. The optical fibers 214, 216 are joined to combiner input fibers 220, 222. The combiner 202 receives and combines the beams 211 and 213 to form a combined output beam 224 that is coupled into the cladding of the combiner output fiber 226. The combiner 202 couples a visible beam 234 into the core of the output fiber 226, which includes a laser 274 that includes an active fiber located between an HR FBG 272 and a PR FBG 270.

[0028] The visible light source 232 generates a visible beam 234 that is coupled into an additional input fiber 240 and the combiner 202. The combiner output fiber 226 delivers the laser output beam 224 to a workpiece 230 to perform a desired machining operation. The visible beam 234 is coaxial with the beam 224 and can be used to direct and align the beam 224 on the workpiece 230.

[0029] In one example, the combiner 202 is a pump / signal combiner that is arranged to couple light from an external source (i.e., the visible light source 232) into the core of the fiber laser. The combiner 202 can also couple light from the core of the fiber laser back into the external source. During operation, the workpiece 230 can reflect the incident light when irradiated by the beam 224 and can emit light in response to the incident laser; both the reflected light and the emitted light can be backward coupled into the core of the output fiber 226. Such backward-propagating radiation 240 propagates back through the combiner 202 and into upstream components, such as the visible light source 232. In one example, the visible light source protection assembly 204 is configured to protect the visible light source 232 from the backward-propagating radiation 240, which will be explained in more detail below.

[0030] The visible light source 232 can be a visible light laser diode coupled to the combiner 202 via a visible light pigtail 244, which is coupled to the optical fiber 245 via a connector 260. Laser diodes are typically coupled to single-clad optical fibers in this manner, meaning that the optical fiber confines the light in a glass core surrounded by a low-index glass cladding, which is itself surrounded by a cladding formed of a high-index protective buffer material that does not propagate the light in the glass cladding. Such a structure is not suitable for the visible light source of a fiber laser because the backward fiber laser radiation will not be confined to the core only but will propagate in the cladding. If the visible light pigtail 244 is single-clad, the backward-propagating radiation 240 coupled to the pigtail 244 will be coupled into the buffer, resulting in fiber failure. To avoid such a failure mode, the visible light pigtail 244 includes a double-clad or triple-clad optical fiber.

[0031] Figure 2B An exemplary visible light source protection assembly 204 for protecting the visible light source 232 from damage by the backward-propagating radiation 240 is shown. In this example, the visible light pigtail 244 is a double-clad optical fiber that includes a low-loss buffer 256 having a refractive index lower than that of the intermediate-index glass cladding 254. The cladding 254 is configured to propagate cladding-coupled light with low loss, thus minimizing the risk to the integrity of the buffer 256. The core 252 is a high-index glass including a material having a refractive index higher than that of the cladding 254.

[0032] In one example, the core 252, the cladding 254, and the buffer 256 can include a variety of materials known to those skilled in the art to achieve the desired fiber structure and refractive index profile. As a non-limiting example, the core 252 and the cladding 254 can include SiO2, SiO2 doped with GeO2, germanosilicate, phosphorus pentoxide, phosphosilicate, Al2O3, aluminosilicate, etc. or any combination thereof. The buffer 256 can include glass and / or polymer materials, such as fluoropolymers, such as polyvinylidene fluoride (Kynar), polytetrafluoroethylene (Teflon), and polyurethane, etc. or any combination thereof.

[0033] The pigtail 244 can transmit backward-propagating radiation 240 sufficient to damage the visible light source 232. In some cases, even the backward-propagating light 240 guided in the core 252 can damage the visible light source 232. In an example, a protective element including a dichroic coating 248 configured to prevent the backward-propagating radiation 240 from coupling into the visible light source 232 can be applied to the end face 246 of the optical fiber 244. Such a protective element can reflect the incident backward-propagating radiation 240 back into the fiber laser 274. The dichroic filter coating 248 can be designed to fully transmit the visible light 234 to be incident on the core 252 while reflecting the potentially damaging wavelengths of the backward-propagating radiation 240, the wavelength of the backward-propagating radiation 240 being different from the wavelength of the visible light source. Any wavelength within the visible spectrum would be suitable. Typically, the potentially damaging wavelengths will be the main high-power laser wavelengths (e.g., for Yb, 1000 to 1100 nm as a non-limiting example, for Tm, 1900 to 2100 nm), which may be broadened due to non-linear effects such as self-phase modulation, and other wavelengths generated from the main high-power laser wavelength through non-linear effects such as stimulated Raman scattering (SRS).

[0034] The light propagating backward from the fiber laser should not be coupled into the core of the fiber laser by reflection from the visible laser source, otherwise there is a risk of seeding unstable non-linear processes such as SRS or altering the output of the laser or amplifier with an unexpectedly wide seeding bandwidth. The optical return loss (ORL) of the core-coupled light of the visible laser measured from its fiber pigtail 244 should be low. A low ORL can be achieved by angling the end face 246 of the optical fiber 244 with the dichroic coating 248 that interfaces with the visible light source 232, such that the reflection of the backward-propagating radiation 240 leaving the end face 246 is coupled out of the core 252 and into the fiber cladding 254.

[0035] In this example, the return radiation 241 represents light that is reflected back into the optical fiber 244 from one or more reflective components disposed within the assembly 204. The return radiation 241 is reflected from the end face 246 of the optical fiber 244 that has the dichroic coating 248. It propagates back mainly in the cladding 254 of the pigtail optical fiber 244 towards the pump / signal combiner 202. The return radiation 241 will be safely propagated back to the pump / signal combiner 202 through the cladding of a double-clad optical fiber (or a triple-clad optical fiber, see Figure 3A ). The pump / signal combiner 202 couples the return radiation 241 mainly into the cladding of the optical fiber 226 together with any pump light in the fiber laser 274. The cladding-coupled return radiation 241 will propagate through the fiber laser section 274 and can be emitted at the output of the fiber laser, or can be stripped out and safely dissipated in a cladding light stripper (CLS) for removing unwanted fiber laser cladding emissions.

[0036] Figure 2C The relative refractive indices of the core 252, the cladding 254, and the buffer 256 are shown. The refractive index profile 257 works together with the reflective elements of the assembly 204 to safely direct the return radiation 241 in the cladding back to the fiber laser. Other refractive index profiles known to those skilled in the art are also possible, and the claimed subject matter is not limited by this or any other example.

[0037] Figures 2D - 2H Various examples of visible light source protection assemblies 280 - 288 for protecting a visible light source from damage by backward-propagating radiation are shown. The following embodiments are illustrative and are not intended to be exhaustive or limiting of the claimed subject matter. In the examples, the same reference numerals represent the same elements as described above with respect to Figure 2A and Figure 2B described. Additionally, in each of the figures in Figures 2D - 2H , the coating 258 includes a filter or absorber, such as for example a dichroic reflector. The coating 258 is configured to absorb or reflect or otherwise filter the backward-propagating radiation 240. Generally, if the coating 258 is a reflector, it will return the incoming backward-propagating radiation 240 back to the optical fiber 244. As shown in the following examples, such returned radiation 241 can be substantially coupled into the cladding portion 254 of the optical fiber 244, thereby protecting the visible light source 232 from the backward-propagating radiation 240. Coupling the returned radiation 241 into the cladding 254 also minimizes the risk of damaging other components of the fiber laser assembly 200.

[0038] Figure 2DAn exemplary visible light source protection assembly 280 is shown, where a focusing lens 242 for coupling light from a visible light source 232 into an optical fiber 244 includes a coating 258 on a surface 259, and the coating is a filter such as a dichroic filter. The coating 258 is depicted as facing the optical fiber surface 246. In another example, the coating 258 may be applied to a portion of the surface 259 facing the visible light source 232. The optical fiber surface 246 of the assembly 280 may or may not be angled and may optionally include a filter coating 248. The angled surface 246 may inhibit the coupling of return radiation into the core 252.

[0039] Figure 2E An exemplary visible light source protection assembly 282 is shown, where a filter coating 258 is applied to a surface of a protective element such as a window 261 in an enclosure 262 to protect the visible light source 232 from the surrounding environment.

[0040] Figure 2F An exemplary visible light source protection assembly 284 is shown, where a filter coating 258 (such as a dichroic filter) is applied to a surface 265 of a protective element 264 dedicated to filtering backward-propagating radiation 240. The protective element 264 may be positioned at various locations within the assembly 284 to protect the visible laser source 232, its optical fiber pigtail 244, and any intervening optical devices 242.

[0041] In another example, the coating 258 may be a light absorber configured to absorb a portion of the radiation 240 rather than reflect the radiation 240. This method may have a more limited power handling capacity than other methods described herein.

[0042] Additionally or alternatively, other reflective surfaces may be provided between the end face 246 of the optical fiber pigtail 244 and the visible light source 232 to minimize the return radiation 241 reflected back into the core of the optical fiber.

[0043] Figure 2G An exemplary visible light source protection assembly 286 is shown, where the protective element 264 may be angled and / or shaped to help minimize the coupling of reflected backward-propagating radiation 240 into the core 252. The surface may be arcuate or spherical (see Figure 2H ). The tilt angle θ must be small enough (e.g., 3 - 12 degrees) to couple the light back into the optical fiber cladding and close enough to the optical fiber (e.g., 75 - 125um) to couple into the cladding 254. If the distance is too far, the light will be diffused out and it will not couple well into the cladding 254. The return radiation 241 reflected back to the optical fiber 244 by the protective element 264 may be coupled into the cladding 254 to be safely transmitted back towards the fiber laser 274.

[0044] Figure 2H An exemplary visible light source protection assembly 288 is shown, where the end face 268 of the optical fiber 244 can be shaped such that reflection of core-guided light is weakly coupled back into the core 252 of the optical fiber. It is known to those skilled in the art that the surface can be arcuate or spherical or other known shapes to help control the reflection angle on the backward-propagating radiation 240. Additionally, a filter coating 248 can be applied to the arcuate end face 268 and can allow visible light 234 to couple into the core 252 of the optical fiber and reflect a portion of the backward-propagating radiation 240, thereby sending the return radiation 241 to the fiber laser 274. In some examples, the surface shape of the end face 268 can be selected to facilitate the coupling of the visible light beam 234, thus eliminating the need for the lens 242.

[0045] In some examples, including Figures 2A - 2H those depicted in Figure 3A An exemplary visible light source protection assembly 304 for protecting a visible light source 332 from damage by backward-propagating radiation 340 is shown, where the visible light source pigtail 344 is a triple-clad optical fiber.

[0046] In one example, the backward-propagating radiation 340 is reflected by a dichroic coating 348 on the angled end face 346 and is preferentially coupled back into the cladding of the optical fiber 344 as return radiation 341.

[0047] The visible light source pigtail 344 includes a low-loss buffer section 356 having a refractive index lower than that of the first glass cladding 354 and the second glass cladding 358. In one example, the refractive index of the cladding 354 is lower than that of the cladding 358 to confine a portion of the cladding light in the second (inner) cladding 358 to prevent it from interacting sufficiently with the buffer section 356. The core 352 includes a material having a refractive index higher than that of the first cladding 358 and the second cladding 354. The triple-clad optical fiber also uses a buffer section 356 having a refractive index lower than that of the first (outer) cladding 354 to facilitate low-loss propagation of the portion of the light confined in the outer cladding 354, thereby further reducing the likelihood of damage to the fiber buffer section 356 by heating.

[0048] In one example, the core 352, the first cladding 358, the second cladding 354, and the buffer 356 may include a variety of materials known to those skilled in the art to achieve the desired refractive index profile. As a non-limiting example, the core 352, the first cladding 358, and the second cladding 354 may include SiO2, SiO2 doped with GeO2, germano-silicate, phosphorus pentoxide, phospho-silicate, Al2O3, alumino-silicate, etc., or any combination thereof. The buffer 356 may include glass and / or polymer materials, such as fluoropolymers, e.g., polyvinylidene fluoride (Kynar), polytetrafluoroethylene (Teflon), and polyurethane, etc., or any combination thereof.

[0049] Figure 3B An exemplary refractive index profile 360 is depicted, which shows the relative refractive indices of the core 352, the first cladding 358, the second cladding 354, and the buffer 356. The refractive index profile 360 works with the reflective elements of the assembly 304 to safely direct the return radiation 341 in the cladding back into the fiber laser. Other refractive index profiles known to those skilled in the art are possible, and the claimed subject matter is not limited by this or any other example.

[0050] The anti-pumping architecture will use a pump / signal combiner at the output of the fiber laser to couple pump light that propagates backward relative to the expected fiber laser output direction into the fiber laser. In such an architecture, the visible light source pigtail can still be spliced into the fiber laser behind the high-reflection fiber Bragg grating that forms the back end of the fiber laser oscillator.

[0051] Figure 4 An exemplary anti-pumping fiber laser assembly 400 for generating and guiding a high-power output laser beam 424 with a coaxial visible beam 434 is shown, where the assembly 400 incorporates a visible light source protection assembly 404 to protect the visible light source 432 from backward-propagating radiation 440. In the example, the assembly 400 includes pump laser beam sources 410, 412 that generate beams 411, 413, respectively. The beams 411, 413 propagate in respective optical fibers 414, 416. The optical fibers 414, 416 are spliced to combiner input optical fibers 420, 422. The combiner 402 receives and combines the beams 411 and 413 to form a combined output beam 424 that is coupled into a combiner gain fiber 426. The combiner gain fiber 426 includes a laser 474 that includes an active fiber between an HR FBG 452 and a PR FBG 450.

[0052] A visible light source 432 generates a visible light beam 434 that is coupled into the core of a gain fiber 426 via an additional input fiber 445 and from there is coupled to an output fiber 427 via a combiner 402. The combiner output fiber 426 delivers a laser output beam 424 having a coaxial visible light aiming beam 434 to a workpiece 430 to perform a desired machining operation. Back-propagating radiation 440 is reflected and emitted from the workpiece 430 and propagates back to the visible light source pigtail 444 via the fiber 427, the combiner 402, the gain fiber 426, and the fiber 445.

[0053] In this example, the visible light source pigtail 444 is a double-clad or triple-clad fiber as described with respect to Figure 2B or 3A. According to the above method, the visible light source protection assembly 404 protects the visible light source 432 from damage by the back-propagating radiation 440 by reflecting and / or absorbing all or a portion of the radiation 440. Specifically, the angled fiber end face 446 includes a filter material and the coating 448 is configured to reflect the back-propagating radiation 440. The reflection of the back-propagating radiation 440 leaving the end face 446 is coupled out of the core 452 and into the cladding of the visible light source pigtail 444. The visible light source protection assembly 404 may include different or additional reflective elements that are configured to reflect the radiation 440 back into the pigtail 444. In Figure 4 , the returned radiation 441 represents such reflected radiation. The returned radiation 441 will propagate safely back through the cladding of the fiber pigtail 444 through the laser 474 to the combiner 402. This cladding-coupled returned radiation 441 may propagate through the fiber laser section 474 and may be emitted at the output or may be stripped and safely dissipated in the CLS.

[0054] The general and specific principles of examples of the presently disclosed technology have been described and illustrated, and it is apparent that the examples may be modified in arrangement and detail without departing from such principles. We claim all modifications and variations that come within the spirit and scope of the appended claims.

Claims

1. A laser assembly comprising: a first light source configured to emit first optical radiation at a first wavelength, wherein the first wavelength is within the visible spectrum; a second light source configured to emit second optical radiation as laser light at a second wavelength; a first multi-clad optical fiber optically coupled to the first light source, wherein the first multi-clad optical fiber transmits the first optical radiation toward a workpiece; a second optical fiber optically coupled to the second light source, wherein the second optical fiber transmits the second optical radiation toward the workpiece and the first multi-clad optical fiber receives backward propagating optical radiation at the second wavelength reflected from the workpiece; a protection element disposed between the first light source and the first multi-clad optical fiber, wherein the protection element prevents at least a portion of the backward propagating optical radiation at the second wavelength from coupling into the first light source; a combiner connected to the first multi-clad optical fiber and the second optical fiber; and A third optical fiber connected to the combiner, The combiner combines the first optical radiation and the second optical radiation into the third optical fiber, so that the first optical radiation is coupled into the core of the third optical fiber and the second optical radiation is coupled into the cladding of the third optical fiber, and the first optical radiation is coaxial with the second optical radiation and is used to guide and align the second optical radiation on the workpiece.

2. The laser assembly according to claim 1, wherein, The second light source is a diode laser.

3. The laser assembly according to claim 1, wherein, The first multi-clad optical fiber is a double-clad optical fiber including a core, a cladding, and a buffer layer, the core having a higher refractive index than the cladding, and the cladding having a higher refractive index than the buffer layer.

4. The laser assembly according to claim 1, wherein, The first multi-clad optical fiber is a triple-clad optical fiber including a core, a first cladding, a second cladding, and a buffer layer, the core having a higher refractive index than the first cladding, the first cladding having a higher refractive index than the second cladding, and the second cladding having a higher refractive index than the buffer layer.

5. The laser assembly according to claim 1, wherein, The protection element is a reflector or an absorber or a combination thereof.

6. The laser assembly according to claim 1, wherein, The protection element is a dichroic filter configured to transmit the first optical radiation at the first wavelength and to reflect the second optical radiation at the second wavelength.

7. The laser assembly according to claim 1, wherein, The protection element is a dichroic filter configured to reflect the second optical radiation at the second wavelength in a manner that couples a portion of the backward propagating optical radiation to one or more claddings of the first multi-clad optical fiber.

8. The laser assembly according to claim 7, wherein, The dichroic filter is applied to the output end of the first multi-clad optical fiber.

9. The laser assembly according to claim 8, wherein, The output end of the first multi-clad optical fiber is angled.

10. The laser assembly according to claim 8, wherein, The output end of the first multi-clad optical fiber is spherical.

11. The laser assembly according to claim 7, wherein, The laser assembly also includes focusing optics configured to focus the first optical radiation at the first wavelength into the first multi-clad optical fiber, wherein the dichroic filter is a coating applied to a surface of the focusing optics.

12. The laser assembly according to claim 7, wherein, The dichroic filter is applied on a surface of a window forming part of a package enclosing the first light source.

13. The laser assembly according to claim 7, wherein, The dichroic filter is applied on a surface of a protective element disposed adjacent to an output end of the first multi-clad optical fiber.

14. The laser assembly according to claim 13, wherein, The output end is coated with a dichroic filter.

15. The laser assembly according to claim 14, wherein, The output end is angled.

16. The laser assembly according to claim 7, wherein, The first multi-clad optical fiber is a fiber pigtail configured to be optically coupled to an input fiber of a fiber laser.

17. The laser assembly according to claim 16, wherein, The pigtail is further configured to couple the first optical radiation of the first wavelength from the light source to the input fiber, wherein the fiber laser is configured to propagate the first optical radiation through an output fiber to a workpiece.

18. The laser assembly according to claim 17, wherein, The fiber laser is a diode-pumped fiber laser.

19. The laser component according to claim 17, wherein, The fiber laser is a backward-pumped fiber laser.

20. The laser assembly according to claim 3, wherein, The protective element is configured to reflect the second optical radiation of the second wavelength in a manner that guides the second optical radiation away from the core.

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