Apparatus and method for coupling laser beam into double-clad optical fiber

Abstract

The invention relates to a device and a method for coupling a laser beam of a laser into a double-clad fiber, comprising a first birefringent optical element which is designed to divide the laser beam entering at a beam entry surface into two sub-laser beams, the two sub-laser beams have a first exit angle and / or a first beam offset relative to a beam exit surface normal; comprising a polarization rotation device configured to adjust the polarization of an incident sub-laser beam and thereby provide a polarization-adjusted sub-laser beam; comprising a second birefringent optical element, the second birefringent optical element being configured to divide each of the polarization-adjusted sub-laser beams into two sub-sub-laser beams, the two sub-sub laser beams have a second exit angle and / or a second beam offset with respect to the beam entry surface normal of the second birefringent optical element; and a coupling-in optical unit, which is designed to couple the sub-sub laser beams having the compensated first exit angle and / or beam offset into the inner core of the double-clad optical fiber and to couple the further sub-sub laser beams into the annular core of the double-clad optical fiber.

Description

Technical Field

[0001] The present invention relates to a device and a method for coupling a laser beam of a laser into a double-clad optical fiber. Background Art

[0002] In recent years, the further development of laser systems has led to new types of material processing, which are based on applying a laser beam of a laser to a workpiece. In order to transmit the laser beam from a usually fixed laser to a target location, the laser beam is usually coupled into a multi-clad optical fiber, in particular a double-clad optical fiber. The target location can be, for example, a processing optical unit, which shapes the laser beam and then applies the shaped laser beam to the workpiece to be processed.

[0003] Important processing operations here are the separation and processing of workpieces, wherein the laser beam can produce perforations in the workpieces along a separation line, along which the workpieces can be separated. Another important processing operation is the joining of two connection partners, wherein a laser beam is applied to the boundary surfaces between adjacent connection partners to produce a melt, which after solidification forms a weld seam between the connection partners.

[0004] Different processing methods usually have different requirements on typical laser beam parameters such as focal diameter, intensity distribution or beam profile characteristics at the processing location. Therefore, changes in processing methods are accompanied by a large modification cost of the optical system.

[0005] From EP2556397 it is known that a laser beam component coupled into the inner core or outer core of a multi-clad optical fiber provides different beam profile characteristics and beam quality in the outcoupled laser beam. For this purpose, the laser beam is split into two sub-laser beams by means of a mechanically retractable wedge switch, which are coupled into different cores of a double-clad optical fiber. However, adjusting the beam quality using a wedge switch is mechanically complex and requires a large number of adjustments.

[0006] US 10914902 shows a different further variant for coupling a laser beam into a double-clad optical fiber, wherein polarization separation of the incident laser beam is achieved by means of a birefringent element and the two resulting sub-laser beams are imaged into different cores of the double-clad optical fiber. Summary of the invention

[0007] Starting from the known prior art, the object of the present invention is to provide an improved device for coupling in a laser beam and a corresponding method.

[0008] This object is achieved by a device for coupling in a laser beam having the features of claim 1. Advantageous further developments are apparent from the dependent claims, the description and the drawings.

[0009] Therefore, a device for coupling a laser beam of a laser into a double-clad optical fiber is proposed, the device comprising a first birefringent optical element, in particular an optical wedge or a plane-parallel plate, which is arranged to split the laser beam incident on a beam entry surface into two sub-laser beams, wherein the two sub-laser beams have a first exit angle and / or a first beam offset relative to a normal to a beam exit surface, wherein the two sub-laser beams are polarized along a basic polarization component of the first birefringent optical element; a polarization rotation device, which is arranged to adjust the polarization of the irradiated sub-laser beam and thus provide a polarization-adjusted sub-laser beam; a second birefringent optical element, wherein a beam exit surface of the second birefringent optical element is first traversed by the polarization-adjusted sub-laser beam, and wherein the first exit angle and / or the first beam offset of the sub-laser beam from the first birefringent optical element is a polarization rotation of the polarization-adjusted sub-laser beam relative to the second birefringent optical element. The invention relates to a method of manufacturing a double-clad optical fiber according to the present invention, wherein the second birefringent optical element is configured to separate the polarization-adjusted sub-laser beams into two sub-sub-laser beams, wherein the two sub-sub-laser beams each have a second exit angle and / or a second beam offset relative to a beam entry surface normal of the second birefringent optical wedge, wherein the second birefringent optical element is configured to separate the polarization-adjusted sub-laser beams into two sub-sub-laser beams, wherein the two sub-sub-laser beams each have a second exit angle and / or a second beam offset relative to a beam entry surface normal of the second birefringent optical wedge, wherein the two sub-sub-laser beams are each polarized along a basic polarization component of the second birefringent optical element, and wherein the second exit angle and / or the second beam offset of the sub-sub-laser beam whose polarization corresponds to the polarization of the original sub-laser beam compensates the corresponding first exit angle and / or the first beam offset; and an incoupling optical unit configured to couple the sub-sub-laser beam with the compensated first exit angle and / or the first beam offset into the inner core of the double-clad optical fiber and to couple the other sub-sub-laser beam into the annular core of the double-clad optical fiber.

[0010] The laser may be a continuous wave laser or a pulsed laser, in particular an ultrashort pulsed laser.

[0011] A continuous wave laser provides a continuous laser beam such that the laser energy is transmitted continuously along the laser beam.

[0012] In contrast, a pulsed laser provides laser energy only during a specific time interval, the length of which is the pulse length. In this case, the energy transmission by the laser pulse also takes place along the laser beam. In particular, the pulsed laser can also be an ultrashort pulse laser, in which case the pulse duration of the laser pulse can be less than 10 ps, ​​preferably less than 1 ps.

[0013] Instead of individual laser pulses, the laser can also, for example, provide bursts, each of which comprises the emission of a plurality of laser pulses. For a specific time interval, the emission of the laser pulses can in this case follow each other very closely, with a spacing of from a few picoseconds to a few hundred nanoseconds. In particular, the burst can be a so-called GHz burst, in which case the sequence of consecutive laser pulses of the burst occurs in the GHz range.

[0014] The wavelength of the laser beam may be, for example, between 200 nm and 2000 nm, preferably 257 nm or 343 nm or 515 nm or 1030 nm.

[0015] The birefringent optical element comprises a beam entry surface and a beam exit surface, and the birefringent optical element itself may comprise or contain a birefringent material. In particular, the birefringent optical element may be configured as a wedge or a plane parallel plate. An optical wedge is transformed into a plane parallel plate by making the beam entry surface parallel to the beam exit surface, and thus an optical wedge may also be understood as a general term for an optical wedge and a plane parallel plate.

[0016] Birefringence refers to the ability of an optical material to split an incident laser beam into two sub-laser beams polarized perpendicular to each other. This is because the refractive index of the optical material is anisotropic depending on the polarization and incident angle of light relative to the optical axis of the optical material.

[0017] If the laser beam impinges on the beam entry surface or the beam exit surface of the birefringent optical element, the polarization of the incident laser beam is projected onto the optical axis of the optical material of the birefringent optical element, whereby the laser beam is split into sub-laser beams according to its polarization components, and the sub-laser beams are polarized along the basic polarization state of the birefringent optical element.

[0018] The sub-laser beams may leave the beam entry surface or the beam exit surface of the birefringent optical element at an exit angle relative to the beam entry surface normal or the beam exit surface normal, such that the sub-laser beams are spatially separated by propagating through the birefringent optical element. In particular, the exit angles of the sub-laser beams may be different such that the sub-laser beams have an angular displacement with respect to each other.

[0019] The exit angles of the sub-laser beams depend on, for example, the anisotropy of the refractive index, and the beam entry surface is preferably parallel to the optical axis of the optical material.

[0020] However, the exit angle may also be affected by the beam exit surface of the birefringent optical element being tilted at an angle to the beam entry surface and / or the optical axis of the optical material.

[0021] However, the sub-laser beams can also leave the birefringent optical element in a beam-shifted manner. The sub-laser beams then extend parallel to the incident laser beam, but are spaced apart from one another perpendicularly to the beam propagation direction. In particular, the first exit angle can also be 0° in such a case.

[0022] In particular, the sub-laser beam may also have a first exit angle and a first beam offset.

[0023] In general, the separation of the sub-laser beams depends on the orientation of the optical axis of the birefringent crystal, the magnitude of the anisotropy, the angular tilt of the beam exit surface relative to the optical axis, and the illumination angle of the laser beam on the beam entry surface and / or the beam exit surface.

[0024] The first birefringent optical element is arranged in front of the polarization rotation device in the beam propagation direction.

[0025] The first birefringent optical element is configured to split a laser beam incident on the beam entry surface into two sub-laser beams having a first exit angle and / or a first beam offset relative to a normal to the beam exit surface and polarized along a base polarization component of the first birefringent optical element.

[0026] For example, the first laser sub-beam may be s-polarized and have an exit angle of -10° relative to the beam exit surface normal, and the second laser sub-beam may be p-polarized and have an exit angle of +20° relative to the beam exit surface normal.

[0027] For example, the first laser sub-beam may be p-polarized and have a beam offset of 0 mm, while the second laser sub-beam is s-polarized and has a beam offset of 2 mm or 5 μm.

[0028] The polarization rotator is arranged after the first birefringent optical element so that the sub-laser beams in the base polarization state and having the first exit angle pass through the polarization rotator. Due to the spatial separation of the sub-laser beams in the first birefringent optical element, the sub-laser beams also impinge on the polarization rotator at different positions. However, the effect of the polarization rotator is independent of the illumination angle and the illumination position.

[0029] The polarization rotation device can modify the polarization of the incident laser sub-beam. The modification can include generating a laser sub-beam in a final polarization state from a laser sub-beam in a defined initial polarization state. In general, the polarization rotation device rotates the electric field vector of the laser sub-beam by a certain angle around the beam propagation direction. By modifying the polarization, the laser sub-beam becomes a polarization-adjusted laser sub-beam.

[0030] For example, a p-polarized polarization-adjusted sub-laser beam can be generated from an s-polarized sub-laser beam. For example, an s-polarized polarization-adjusted sub-laser beam can be generated from a p-polarized sub-laser beam. However, the s-polarized and p-polarized sub-laser beams can also be transferred into a final polarization state in which the two polarization-adjusted sub-laser beams are partially s-polarized and partially p-polarized. The polarization rotation device can also allow the sub-laser beam to pass through without modifying the polarization. Such a sub-laser beam is also a polarization-adjusted sub-laser beam.

[0031] The polarization rotation device may also be a phase element, such as a λ / 4 plate, which generates a circularly polarized laser beam from a linearly polarized laser beam and generates a linearly polarized laser beam from a circularly polarized laser beam.

[0032] The second birefringent optical element is arranged behind the polarization rotating device in the beam propagation direction, and the beam exit surface of the second birefringent optical element is first passed through by the polarization-adjusted sub-laser beam. Therefore, the polarization-adjusted sub-laser beam passes backward through the second optical wedge.

[0033] The polarization-adjusted sub-laser beam is incident on the beam exit surface of the second birefringent optical element at a first exit angle and / or a first beam offset, and the first exit angle and / or the first beam offset of the polarization-adjusted sub-laser beam is a second irradiation angle and / or a second beam offset of the polarization-adjusted sub-laser beam relative to the normal of the beam exit surface of the second birefringent optical element.

[0034] The beam exit surface of the second birefringent optical element is to be understood as a surface of the second birefringent optical element which is arranged at an angle to the optical axis and on which the polarization-adjusted sub-laser beams leaving the first birefringent optical element first impinge.

[0035] In the simplest case, the second birefringent optical element is identical to the first birefringent optical element and is rotated 180° in the beam path. In other words, the beam exit surfaces of the first birefringent optical element and the second birefringent optical element, whose beam exit surfaces are inclined relative to the optical axis, face each other, while the optical axes of the birefringent optical elements are (anti-)parallel relative to each other.

[0036] The second birefringent optical element splits each polarization-adjusted sub-laser beam into two sub-sub-laser beams, and each of the two sub-sub-laser beams has a second exit angle and / or a second beam offset relative to a beam entry surface normal of the second birefringent optical element, and the two sub-sub-laser beams are polarized along a base polarization component of the second birefringent optical element. The description of this effect is similar to that of the first birefringent optical element.

[0037] The second exit angle and / or the second beam offset of the sub-sub-laser beam, whose polarization corresponds to the polarization of the original sub-laser beam, compensates the corresponding first exit angle and / or the first beam offset.

[0038] This means that, for example, a sub-sub-laser beam of the first polarization from a sub-laser beam of the first polarization has a second exit angle at the beam entry surface of the second birefringent optical element that is opposite and equal to the exit angle of the sub-laser beam at the beam exit surface of the first birefringent optical element. The polarization-adjusted sub-laser beams pass through the second birefringent optical element just as they did back through the first birefringent optical element, but only if the polarization and the angle of incidence of the polarization-adjusted sub-laser beams correspond to the components exiting the first birefringent optical element. The description of the beam offset is analogous.

[0039] For example, in a first simple example, the polarization rotation device can rotate the polarization of the sub-laser beam by 0°. Then, according to the above example, the s-polarized sub-laser beam has an exit angle of -10°, and the p-polarized sub-laser beam has an exit angle of +20°. Due to the spatial distance between the first birefringent optical element and the second birefringent optical element, the two sub-laser beams are incident on the second birefringent optical element at different positions. The two sub-laser beams also impinge on the beam exit surface of the second birefringent optical element at angles of -10° and +20°. Therefore, the two sub-laser beams are deflected so that the two sub-laser beams extend parallel to each other but also parallel to the incident laser beam behind the second birefringent optical element. The first exit angle is correspondingly compensated by the second exit angle.

[0040] For example, the polarization rotation device can rotate the polarization of the sub-laser beam by 45°. Then, the first polarization-adjusted sub-laser beam and the second polarization-adjusted sub-laser beam have mixed polarizations, that is, the first polarization-adjusted sub-laser beam and the second polarization-adjusted sub-laser beam have a p-polarization component and an s-polarization component. For example, the first polarization-adjusted sub-laser beam is incident on the beam exit surface of the second birefringent optical element at an irradiation angle of -10°. The component of the laser beam having a polarization corresponding to the polarization of the original laser beam, that is, the s-component, can pass backward through the second birefringent optical element to a certain extent. However, the p-polarization component of the first polarization-adjusted sub-laser beam is deflected. On the contrary, in the second polarization-adjusted sub-laser beam, the p-polarization component is guided backward through the second birefringent optical element, while the s-polarization component is deflected.

[0041] By adjusting the polarization rotation device, the laser power can be distributed between the sub-sub-laser beams having the compensated first exit angle and the other sub-sub-laser beams.

[0042] The coupling-in optical unit can transfer the sub-sub laser beams provided by the second birefringent optical element to different focal regions, in particular, to the inner core or the ring core of the double-clad optical fiber. In particular, the sub-sub laser beams having the compensated first exit angle are introduced into the inner core of the double-clad optical fiber, while the other sub-laser beams are introduced into the ring of the double-clad optical fiber.

[0043] The coupling-in optical unit may comprise a lens and / or a lens system and / or a mirror arrangement. The coupling-in optical unit may also comprise a collimating lens and a focusing lens.

[0044] In this case, the collimator lens is provided for converting a non-parallel sub-beam, in particular a beam bundle of diverging sub-beams, into parallel sub-beams. In particular, sub-sub-laser beams with uncompensated exit angles can be parallelized by the collimator lens.

[0045] The focusing lens can transfer sub-beams of the beam into the focal region. In particular, this can transfer different beams, such as those of the sub-sub-laser beam provided by the second birefringent optical element, into different focal regions.

[0046] Double-clad optical fibers with two cores have an inner core and an intermediate cladding that surrounds the core and is as thin as possible and has a low refractive index. This is followed by a single outer annular core, which is also surrounded by a second cladding of low refractive index. In addition to this, another glass layer may follow, which determines the outer diameter of the fiber but has no influence on its function in terms of beam guidance. The last layer may be a coating made of a plastic material such as silicone and / or nylon, which serves to protect the optical fiber.

[0047] By using double-clad fiber, one can choose between different beam profile characteristics at the fiber output end depending on coupling into the inner core, coupling into the outer ring core, or coupling into both the inner and outer ring cores.

[0048] A double-clad optical fiber is a special case of a multi-clad optical fiber having N cores, the multi-clad optical fiber including at least one double-clad optical fiber. For example, the multi-clad optical fiber may include three cores, namely an inner core, an outer annular core and an intermediate annular core, the intermediate annular core surrounding the inner core and being arranged between the inner core and the outer core. For example, the inner core and the outer core may then form a double-clad optical fiber. However, the intermediate core and the outer core may also form a double-clad optical fiber, or the inner core and the intermediate core may also form a double-clad optical fiber. By combining a plurality of first and second birefringent elements and a polarization rotation device, the intensity of the sub-laser beams in the N cores of the multi-clad optical fiber may also be adjusted.

[0049] Polarization rotation devices can be used to adjust the splitting ratio of coupling laser beams into the core and the inner core and the ring core of the double-clad optical fiber. The splitting ratio can be determined by the ratio of the power of those sub-sub-laser beams having the polarization corresponding to the polarization of the original sub-laser beam to the power of the other sub-sub-laser beams.

[0050] By using the polarization rotation device, in particular a continuous adjustment of the splitting ratio can be achieved. Compared to the prior art, the mechanical effort is drastically reduced, thereby achieving a device that is particularly reliable in terms of adjustment.

[0051] For example, if the polarization rotator does not rotate the polarization of the sub-laser beam, the entire laser power can be coupled into the core of the double-clad fiber. For example, if the polarization rotator rotates the polarization of the sub-laser beam by 90°, the entire laser power can be coupled into the outer core of the double-clad fiber. In particular, all other power ratios can also be adjusted by adjusting the polarization rotator.

[0052] The splitting ratio can be used to adjust the beam quality of the laser beam after the double-clad fiber.

[0053] In the case of material processing using laser radiation, in particular when using high powers in the kW range, switching between coupling variants makes it possible, for example, to choose between: a relatively good beam quality with a sharp focus - as required for laser cutting processes - and a "reduced" beam quality with an almost uniform intensity distribution in the beam cross section - which is particularly suitable for welding processes.

[0054] In order to obtain a high laser beam quality, the laser beam is coupled into the inner core of a double-clad fiber, which in this case behaves like a conventional standard fiber, the core of which is surrounded by an intermediate cladding of low refractive index. However, if a laser beam with a wider profile, e.g. with uniform intensity, is required, the laser beam is coupled into the outer annular core, or into both the inner and outer annular core. Depending on the application, at the output end of the double-clad fiber a laser beam with a filled circular profile according to the inner core, a laser beam with a circular profile according to the outer annular core, a laser beam with a filled circular profile according to both core regions together (with a narrow missing ring due to the first intermediate cladding), or a laser beam of corresponding intermediate order of the profile features mentioned above can be obtained.

[0055] The laser beam can be polarized or unpolarized.

[0056] The exit angle of the laser beam from the birefringent optical element and / or the magnitude of the beam offset is independent of the polarization of the incident laser beam. The polarization of the incident laser beam determines only the amplitude of the individual exiting laser beams. In a sense, the possible spatial paths of the sub-laser beams and sub-sub-laser beams are determined only by the geometry of the elements of the device, while the input polarization determines only how much power is transmitted along each path.

[0057] The first birefringent optical element and / or the second birefringent optical element may include or be formed from quartz glass.

[0058] Quartz glass has a particularly high laser damage threshold, making it particularly suitable for use in laser material processing. In addition, quartz glass is particularly easy to process, which can reduce manufacturing costs.

[0059] The first birefringent optical element and / or the second birefringent optical element may include or be formed from calcite.

[0060] The first birefringent optical element and / or the second birefringent optical element may include barium borate (BBO) or be formed of BBO.

[0061] The substrate thickness of the at least one birefringent optical element may be between 1 mm and 50 mm, preferably between 1 mm and 10 mm.

[0062] The substrate thickness is the length of the longest side in the cross section of the optical element, which is neither the beam entry surface nor the beam exit surface, and in which cross section plane the input laser beam and the generated sub-laser beams are also located.

[0063] Such a substrate thickness enables a particularly robust construction of the optical wedge.

[0064] For a plane-parallel plate, the substrate thickness corresponds to the thickness of the plate.

[0065] The polarization rotator can be controlled electronically.

[0066] This enables the polarisation means to receive and convert electronic control signals.For example, the polarisation rotator may have motorisation such that the polarisation rotator may be rotated.

[0067] The electronic control may for example comprise continuously rotating the polarization of the sub-laser beams from an initial polarization state to a final polarization state by means of a polarization rotation device. In particular, all intermediate polarization states of the two sub-laser beams may be adjusted by means of the polarization rotation device.

[0068] However, it is also possible to use a polarization rotation device to switch the polarization of a sub-laser beam between two states. This may be particularly advantageous when switching between two machining processes.

[0069] The polarization rotation device can be a rotatably mounted λ / 2 plate or a Pockels cell.

[0070] A Pockels cell is an optoelectronic device which can modify the polarization of a laser beam passing through the Pockels cell by applying a control voltage. In particular, the polarization of the laser beam can be rotated. Thus, switching or rotation or modification of the polarization can be performed particularly easily by voltage control.

[0071] In particular, a Pockels cell makes it possible to avoid moving parts in the device so that a certain mechanical stability can be achieved.

[0072] The object specified above is also achieved by a method for coupling in a laser beam having the features according to claim 10. Advantageous further developments of the method are disclosed in the dependent claims, the description and the figures.

[0073] Therefore, a method for coupling a laser beam of a laser into a double-clad optical fiber is proposed, wherein a laser beam incident on a beam entry surface of a first birefringent optical element is split into two sub-laser beams, wherein the two sub-laser beams have a first exit angle and / or a first beam offset relative to a beam exit surface normal, and the two sub-laser beams are polarized along a basic polarization component of the first birefringent optical element, wherein the polarization of the irradiated sub-laser beam is adjusted by a polarization device and thus a polarization-adjusted sub-laser beam is provided, wherein the polarization-adjusted sub-laser beam first passes through a beam exit surface of a second birefringent optical element, wherein the first exit angle and / or the first beam offset of the sub-laser beam from the first birefringent optical element forms a second polarization component of the polarization-adjusted sub-laser beam relative to a beam exit surface normal on the second birefringent optical element. The invention relates to a method for preparing an optical fiber comprising: providing a laser beam having a polarization adjusted portion and a second beam shift, wherein the polarization-adjusted sub-laser beams are each split into two sub-sub-laser beams by a second birefringent optical element, wherein the two sub-sub-laser beams each have a second exit angle and / or a second beam shift relative to a beam entry surface normal of the second birefringent optical element, wherein the two sub-sub-laser beams are each polarized along a basic polarization component of the second birefringent optical element, and wherein the second exit angle and / or the second beam shift of the sub-sub-laser beam whose polarization corresponds to the polarization of the original sub-laser beam compensates for the corresponding first exit angle and / or the first beam shift, and the sub-sub-laser beam having the compensated first exit angle and / or the first beam shift is coupled into the inner core of the double-clad optical fiber by a coupling-in optical unit and the other sub-sub-laser beam is coupled into the annular core of the double-clad optical fiber by the coupling-in optical unit.

[0074] A polarization rotation device can be used to adjust the splitting ratio of coupling the laser beam into the inner core and the ring core of the double-clad optical fiber.

[0075] The beam splitting ratio can be determined by the ratio of the power of those sub-laser beams having the polarization corresponding to the polarization of the original sub-laser beam to the power of the other sub-sub-laser beams.

[0076] The object specified above is also achieved by a system for processing material having the features according to claim 13. Advantageous further developments of the method are described in the dependent claims, the description and the figures.

[0077] Therefore, a system for processing a workpiece using a laser beam of a laser is proposed, the system comprising a laser, a double-clad optical fiber, a device for coupling the laser beam of the laser into the double-clad optical fiber, a processing optical unit and a workpiece, wherein the coupling device is configured to couple the laser beam of the laser into the inner core of the double-clad optical fiber and the annular core of the double-clad optical fiber at a splitting ratio, wherein the double-clad optical fiber is configured to guide the laser beam from the input end of the double-clad optical fiber to the output end of the double-clad optical fiber, wherein the processing optical unit is configured to form a processing laser beam from the laser beam behind the output end of the double-clad optical fiber, focus the processing laser beam, apply the processing laser beam to the workpiece, and thereby process the workpiece.

[0078] The processing optical unit enables the laser beam provided by the double-clad optical fiber to be introduced into the workpiece with appropriate quality. In particular, the laser beam is guided into the workpiece in the focal region for processing the workpiece. Only by focusing using the processing optical unit and converging the generated laser beam into the focal region can an intensity increase be achieved in the focal region by which the workpiece can be processed.

[0079] The processing can, for example, include separating the workpieces along a separation line, or chamfering an edge, or generating a predetermined breaking point, or generating a specifically oriented material stress, etc. However, the system can also be used for processing, in particular cutting, opaque materials, such as metals or metal sheets. In this case, the material can be vaporized and ablated by high-energy excitation of the material of the workpiece.

[0080] However, the workpiece may also comprise two connection partners that are intended to be connected together. In this case, the connection partners may be arranged on top of each other so that the boundary surfaces of the connection partners on which they are to be connected together face each other. The application of the boundary surfaces may result in local melting of the material of the connection partners, the resulting melt bridging the common boundary surface of the connection partners and permanently connecting the connection partners to each other when cooling.

[0081] The system may also have a feeding device which is arranged to move the workpiece and the laser beam relative to each other with a feeding along the trajectory, the feeding preferably taking place perpendicularly or parallel to the separation of the laser beam.

[0082] By feeding, the laser beam and the workpiece are moved relative to one another along the trajectory at a feed rate, which feed rate, for example, results in different impingement positions of the laser beam on the surface of the workpiece over time.

[0083] The beam quality of the processing laser beam downstream of the output end of the double-clad optical fiber is adjusted by means of the splitting ratio for coupling the sub-sub laser beams into the double-clad optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0084] The preferred further embodiments of the present invention are described in more detail by the following description of the accompanying drawings. In the accompanying drawings:

[0085] Figure 1A , Figure 1B , Figure 1C and Figure 1D A schematic representation of a birefringent optical element is shown;

[0086] Figure 2A and Figure 2B shows a schematic representation of the beam path between two birefringent optical elements;

[0087] Figure 3A , Figure 3B , Figure 3C , Figure 3D , Figure 3E and Figure 3F shows a schematic representation of the beam path between two birefringent optical elements when the polarization of a sub-laser beam is adjusted using a polarization rotation device;

[0088] Figure 4A , Figure 4B and Figure 4C shows a schematic representation of coupling a sub-sub laser beam into a double-clad optical fiber using a coupling optical unit; and

[0089] Figure 5A and Figure 5B A schematic representation of a system for processing a material is shown. DETAILED DESCRIPTION

[0090] Preferred exemplary embodiments are described below with reference to the accompanying drawings. In this case, in different figures, identical, similar or elements having the same effect are provided with identical reference numerals, and repeated description of these elements is omitted in some instances to avoid redundancy.

[0091] Figures 1 to 4 show various aspects of a device 1 according to the invention. In particular, without limiting generality, the birefringent optical element is represented as a wedge. However, it is obvious that an optical wedge, as a general implementation of a plane-parallel plate, always includes the properties of a plane-parallel plate.

[0092] Figure 1A Schematically shown is a first optical wedge 10 having a beam entry surface 100 and a beam exit surface 102. The first wedge 10 is arranged to split a laser beam 20 incident on the beam entry surface 100 into two sub-laser beams 200, 202. These sub-laser beams 200, 202 have a first exit angle relative to the beam exit surface normal N102.

[0093] The sub-laser beams 200, 202 are generated by the birefringence property of the first optical wedge 10. In this case, the material of the first wedge 10 has different refractive indices for different polarization directions of the incident laser beam 10, and therefore, the incident laser beam 10 is separated according to the basic polarization components of the material of the first wedge 10. Therefore, the sub-laser beams 200, 202 are polarized along the basic polarization components of the first optical wedge 10. Without limiting generality, it is assumed below that the sub-laser beam 200 is s-polarized and the sub-laser beam 202 is p-polarized.

[0094] On the one hand, the first exit angle can be determined by the entry angle of the incident laser beam 20 and the shape of the beam exit surface 102, in particular the inclination compared to the beam entry surface 100. On the other hand, the first exit angle is also determined by the inclination of the optical axis O of the birefringent medium and the relative inclination of the optical axis with respect to the beam exit surface 102. In the present case, the optical axis of the birefringent medium is oriented parallel to the beam entry surface 100. Therefore, the beam exit surface 102 is at a certain angle with respect to the optical axis O.

[0095] Here, the separation into the sub-laser beams 200, 202 is independent of the polarization of the incident laser beam 20. Therefore, the laser beam 20 can be polarized or unpolarized. In any case, in the birefringent medium, only the electric field vector of the incident laser beam 20 is projected onto the optical axis of the optical wedge 10, so the polarization of the incident laser beam 20 only determines the laser power transmitted along the sub-laser beams 200, 202. However, the size of the spatial separation always remains unchanged.

[0096] Figure 1B A sub-laser beam 200 is shown which impinges on the beam exit surface 102 at the exit angle shown and has a correspondingly selected polarization (here s-polarization) and leaves the optical wedge 10 at the entry angle of the incident laser beam 20. Thus, such a sub-laser beam 200 may pass through the optical wedge 10 backwards.

[0097] For comparison, Figure 1CThe sub-laser beam 200 is shown, which is incident on the beam exit surface 102 at the same exit angle, but has a different base polarization, namely p-polarization, for this exit angle. Therefore, the sub-laser beam 200 is not directed into the path of the incident laser beam 20, but into the path of another laser beam 20'. The p-polarized laser beam 200 cannot simply pass back through the optical wedge, but is deflected.

[0098] like Figure 1D As shown, if the sub-laser beam 200 has both an s-polarization component and a p-polarization component, and is incident on the beam exit surface 102 of the first optical wedge 10 at an exit angle of the s-polarized laser beam, the s-polarization component can pass back through the optical wedge 10. However, the p-polarization component is deflected to a different path, such as Figure 1C The optical wedge 10 shown accordingly separates such a sub-laser beam 200 .

[0099] exist Figure 2A , a first optical wedge 10 and a second optical wedge 12 are schematically shown, wherein, without limiting the generality, it can be assumed at this point that the first wedge 10 and the second wedge 12 have the same construction. The second wedge 12 is simply rotated 180° in the beam path. This ensures that a first exit angle of the sub-laser beams 200, 202 from the beam exit surface 102 of the first optical wedge 10 corresponds to a second angle of the sub-laser beams 200, 202 incident on the beam exit surface 122 of the second optical wedge 12. In a sense, the s-polarized and p-polarized sub-laser beams 200, 202 pass through the second wedge 12 backwards, as Figure 1B As shown.

[0100] However, due to the spatial distance between the first optical wedge 10 and the second optical wedge 12, the sub-laser beams 200, 202 have different irradiation positions on the beam exit surface 122 of the second optical wedge 12. However, the two generated sub-sub-laser beams 2000, 2020 extend parallel to each other after the second optical wedge 12. In a sense, the two sub-sub-laser beams 2000, 2020 extend parallel to the original incident laser beam 20. In other words, the second exit angles of the sub-sub-laser beams 2000, 2020 whose polarization corresponds to the polarization of the original sub-laser beam compensate for the corresponding first exit angles.

[0101] Figure 2BA first optical wedge 10 and a second optical wedge 12 are shown, wherein the two wedges are not identical. In particular, the substrate thickness B of the two optical wedges 10, 12 is different. The substrate thickness B of at least one optical wedge 10, 12 may be between 1 mm and 50 mm, preferably between 1 mm and 10 mm. The substrate thickness B of the first optical wedge 10 may be, for example, 5 mm, and the substrate thickness B of the second optical wedge 12 may be 10 mm. In particular, the first optical wedge 10 and / or the second optical wedge 12 may comprise quartz glass or be made of quartz glass. This enables particularly simple and cost-effective production, while the optical wedges 10, 12 are particularly insensitive to high laser powers.

[0102] exist Figure 2A , Figure 2B In , the sub-laser beams 2000, 2020 have the same polarization as the fundamental polarization component of the optical material of the optical wedge 10, 12 associated with the corresponding path. Figure 3A In the embodiment of the present invention, a polarization rotation device 14 is arranged between the first optical wedge 10 and the second optical wedge 12. The polarization rotation device 14 is configured to rotate the polarization of the sub-laser beams 200, 202 and provide polarization-adjusted sub-laser beams 200', 202'.

[0103] Here, the polarization of the polarization-adjusted sub-laser beams 200', 202' on the beam exit surface 122 of the second optical wedge 12 only partially corresponds to the basic polarization component of the path. Therefore, similar to the first optical wedge 10, the second optical wedge 12 is configured to split the polarization-adjusted sub-laser beams 200', 202' into two sub-sub-laser beams 2000, 2002 and 2020, 2022, respectively, and the sub-sub-laser beams 2000, 2002, 2020, 2022 are polarized along the basic polarization component of the second wedge 12. In this case, the sub-sub-laser beams 2000, 2002, 2020, 2022 have a second exit angle relative to the beam entry surface normal N120 of the beam entry surface 120 of the second wedge 12.

[0104] In this case, the second exit angles of only those sub-sub-laser beams 2000, 2020 having a polarization corresponding to the polarization of the original sub-laser beam 200, 202 compensate the first exit angle. The other sub-sub-laser beams 2002, 2022 diverge accordingly.

[0105] If the polarization of the sub-laser beams 200, 202 is rotated by the polarization rotation device 14 so that each polarization-adjusted sub-laser beam 200', 202' does not have any component polarized according to the desired basic polarization component, the laser power as a whole is converted into sub-sub-laser beams 2002, 2022 that diverge, i.e., extend not parallel to the incident laser beam 20, as Figure 3B As shown.

[0106] If the polarization of the sub-laser beams 200, 202 is rotated by the polarization rotation device 14 so that each polarization-adjusted sub-laser beam 200', 202' has a polarization component that exactly corresponds to the desired basic polarization component, the laser power is converted as a whole into sub-sub-laser beams 2000, 2020, whose first exit angles are compensated, as Figure 2A As shown.

[0107] For this purpose, the polarization rotation device 14 may be electronically controlled. For example, the polarization rotation device 14 may be a rotatably mounted λ / 2 plate, electronic control of the rotatable bearing enabling adjustment of the rotation angle, and rotation of the λ / 2 plate in turn enabling rotation of the polarization of the sub-laser beams 200, 202. However, the polarization rotation device 14 may also be a Pockels cell, in which case the polarization rotation may be adjusted by electronically controlling the Pockels cell.

[0108] Figure 3C 1 shows a situation in which the incident laser beam 20 impinges on the beam entry surface of the first optical wedge 10 at a certain incident angle. This allows the two sub-laser beams to leave the optical wedge at a certain exit angle and also impinge on the polarization rotation device 14 at the exit angle. Here, the polarization direction of the sub-laser beam can be rotated, and then the polarization-rotated sub-laser beam impinges on the second optical wedge 12 at a corresponding exit angle. By configuring the optical wedges 10 and 12, the size of the distance between the parallel sub-laser beams, in particular the distance between the sub-laser beams, can be adjusted. Figure 3A In comparison, the shape of the daughter-daughter laser beam is better adapted to the double-clad optical fiber.

[0109] exist Figure 3D In the optical wedge and Figure 3A The structure is similar, but the difference is that the optical crystal axis is not oriented antiparallel. This also enables the size of the distance between the parallel sub-sub laser beams to be adjusted.

[0110] exist Figure 3EIn the embodiment of the invention, the birefringent optical elements 10, 12 are constructed as plane parallel plates. Here, the optical crystal axis is, for example, at an angle of 45° to the beam entry surface of the plane parallel plates 10, 12. The incident laser beam 20 is split into two sub-laser beams of orthogonal polarization to each other and leave the first plane parallel plate with only a beam shift and no exit angle. The two sub-laser beams are directed onto the second plane parallel plate, the optical crystal axis of which is rotated relative to the first crystal axis in such a way that the two sub-laser beams are recombined after the second plane parallel plate 12. To a certain extent, the beam shift and the exit angle of 0° are compensated.

[0111] Due to the vertical irradiation of the laser beam, strictly speaking, we can no longer speak of s- and p-polarization components of the incident laser beam, but rather of an ordinary beam and an extraordinary beam. The extraordinary beam contains a beam deviation after passing through the plane-parallel plate, while the ordinary beam passes through the plane-parallel plate without a beam deviation. The magnitude of the beam deviation of the two sub-laser beams from each other depends on the difference in refractive index, the substrate thickness of the plane-parallel plate and the orientation of the optical axis.

[0112] Figure 3F An embodiment according to the invention is shown, in which the polarization rotation device 14 is arranged between the first plane parallel plate 10 and the second plane parallel plate 12. Due to the adjusted polarization of the sub-laser beams, similar to the previous embodiment, the second beam offset now compensates those first beam offsets that associated the sub-laser beams with a polarization corresponding to the original polarization of the sub-laser beams. In other words, for example, in the s-polarized sub-laser beam below, a p-polarization component and an s-polarization component are generated by the polarization rotation device 14. Only the first beam offset of the s-polarization component of the sub-laser beam is compensated by the second plane parallel plate and the second beam offset.

[0113] Figure 4A , Figure 4B and Figure 4C It is shown that a coupling optical unit 16 is arranged behind the second optical wedge 12. The coupling optical unit 16 is configured to couple the sub-sub laser beams 2000, 2020 having the compensated first exit angle into the inner core 30 of the double-clad optical fiber 3, and to couple the other sub-sub laser beams 2002, 2022 into the annular core 34 of the double-clad optical fiber 3.

[0114] The coupling-in optical unit 16 can include a lens and / or a lens system and / or a mirror arrangement, in FIG. 4 the coupling-in optical unit includes only one lens 16 .

[0115] The double-clad optical fiber shown also has a so-called intermediate cladding between the inner core 30 and the annular core 34 , by means of which the sub-sub laser beams coupled into the individual cores of the double-clad optical fiber are retained and guided in the individual cores.

[0116] By means of the polarization rotation device 14 arranged in front of the second optical wedge 12, the total intensity of the sub-sub-laser beams 2020, 2000 with the compensated exit angle can be adjusted relative to the total intensity of the sub-laser beams 2022, 2002 without the compensated exit angle.

[0117] In particular, the individual sub-sub laser beams 2002 and 2022 propagate as a whole in the annular core 34. This means that the sub-sub laser beams 2002, 2022 form a common radiation field and are indistinguishable within the double-clad fiber and also behind the double-clad fiber. The same applies to the sub-sub laser beams 2000, 2020 coupled into the inner core of the double-clad fiber. Thus, the polarization rotation device 14 can be used to adjust the power component of the laser beam 20 to be coupled into the inner core 30 of the double-clad fiber 3 or the annular core 34 of the double-clad fiber 3. Therefore, the polarization rotation device 14 can particularly determine the splitting ratio. In particular, the polarization rotation device 14 can be adjusted so that the entire laser power is coupled into the core 30 of the double-clad fiber, or the entire laser power is coupled into the ring 34 of the double-clad fiber.

[0118] It is particularly advantageous here that a particularly uniform power distribution on the entry surface of the double-clad optical fiber can be achieved by splitting the polarization-adjusted laser sub-beams 200', 202' into sub-laser sub-beams 2000, 2002, 2020, 2022. This can reduce the thermal load on the entry surface.

[0119] By adjusting the splitting ratio using the polarization rotator, it is also possible to adjust the beam quality behind the double-clad fiber 3. If a portion of the laser radiation in the annular core 34 of the double-clad fiber 3 provides a planar laser beam behind the double-clad fiber, and a portion of the laser radiation in the inner core 30 of the double-clad fiber provides a collimated laser beam, the overall beam quality can be configured by adjusting the polarization rotator 14.

[0120] Figure 4A It is also shown that the laser power is coupled into the annular core 34 at 25% via daughter-daughter laser beams 2002, 2022, respectively, while the laser power is also coupled into the inner core 30 of the double-clad optical fiber at 25% via daughter-daughter laser beams 2020, 2000, respectively.

[0121] Figure 4B It is shown that the laser power is coupled into the annular core 34 at 50% via the daughter-daughter laser beams 2002, 2022, respectively, while no laser power is coupled into the inner core 30 of the double-clad optical fiber.

[0122] Figure 4CIt is shown that no laser power is coupled into the annular core 34, while the laser power is coupled into the inner core 30 of the double-clad optical fiber at 50% via the daughter-daughter laser beams 2020, 2000, respectively.

[0123] Figure 5A A system according to the invention for machining a workpiece 5 is schematically shown. In particular, the machining of the workpiece may comprise the joining of two connection partners. In this case, the connection partners 50, 52 are arranged on top of each other at a common boundary surface.

[0124] In this case, the laser 2 provides, for example, ultrashort laser pulses, which can be introduced into the boundary layer of the connection partners 50 , 52 in the form of a sequence of individual pulses or in the form of a sequence of pulse bursts.

[0125] The laser beam 20 of the laser 2 is guided through the device 1 for coupling the laser beam 20 into the double-clad optical fiber, and the device 1 couples the laser beam 20 into the annular core 34 and the inner core 30 of the double-clad optical fiber 3 according to the splitting ratio predetermined by the polarization rotation device 14.

[0126] The double-clad optical fiber guides the laser beam 20 to the processing optical unit 4. The processing optical unit may include an outcoupling optical unit, with which the laser beam 20 is coupled out of the ring 34 and the core 30 of the double-clad optical fiber 3. However, the processing optical unit 4 can also be arranged after the outcoupling optical unit. For example, the processing optical unit 4 focuses the laser beam 20 with a beam quality determined by the splitting ratio into the common boundary surface of the two connection partners 50, 52.

[0127] In order to focus the laser beam 20 into the common boundary surface of the connection partner 50, 52, the first connection partner 50 must be transparent to the wavelength of the laser 2 in the beam propagation direction. For example, the first connection partner 50 can be glass, crystal, ceramic or plastic. For example, the second connection partner 52 can be opaque or transparent. For example, the second connection partner 52 can be metal, semiconductor, plastic or ceramic.

[0128] At the boundary surface, the laser pulse is absorbed so that the material of the connection partner 50, 52 melts and joins the other connection partner 52, 50 at the boundary surface. Once the melt cools, a permanent connection is formed between the two connection partners 50, 52. In other words, the two connection partners 50, 52 are connected together in this area by welding.

[0129] The laser beam and the connection partner can be moved and / or positioned relative to each other by means of a feed device 6, wherein the feed V is between 0.01 mm / s and 1000 mm / s, preferably between 0.1 mm / s and 300 mm / s. For this purpose, the connection partner can be positioned, for example, on the feed device 6. This can achieve the following result: the laser beam 20 is moved along the connection seam on the connection partner 50, 52, so that the connection partner 50, 52 can be connected along the connection seam.

[0130] Figure 5B A system for machining a workpiece 5 according to the invention is schematically shown, wherein the machining here comprises separating the workpiece 5. In this case, Figure 5A Similarly, the laser beam 20 is introduced into the workpiece 5 along a trajectory 54 along which the material is to be separated. By introducing the laser beam 20, the workpiece 5 is damaged in a targeted manner along this trajectory, so that the workpiece 5 can be separated along the trajectory 54.

[0131] In order to Figure 5A and Figure 5B To switch between the processing operations, the polarization rotation device 14 only needs to be adjusted once, so no modification work is required.

[0132] To the extent applicable, all the individual features presented in the exemplary embodiments may be combined with one another and / or interchanged without departing from the scope of the present invention.

[0133] Reference numerals list

[0134] 1 Device

[0135] 10 The first birefringent optical element

[0136] 100 Beam enters surface

[0137] 102 beam exit surface

[0138] 12 Second birefringent optical element

[0139] 120 Beam enters surface

[0140] 122 beam exit surface

[0141] 14 Polarization Rotation Device

[0142] 16 Coupling optical unit

[0143] 2 Laser

[0144] 20 Incident laser beam

[0145] 200 laser beams

[0146] 200' polarization-adjusted laser beam

[0147] 2000 sub-sub laser beams

[0148] 2002 Sub-sub laser beam

[0149] 202 laser beams

[0150] 202' Polarization-adjusted sub-laser beam

[0151] 2020 sub-sub laser beam

[0152] 2022 sub-sub laser beam

[0153] 22 Processing laser beam

[0154] 3 Double-clad optical fiber

[0155] 30 Inner core

[0156] 32 Intermediate cladding

[0157] 34 Ring core

[0158] 4 Processing optical unit

[0159] 5 Workpiece

[0160] 50 First connection partner

[0161] 52 Second connection partner

[0162] 54 Track

[0163] 6 Feeding device

[0164] B Base thickness

[0165] N1 Beam exit surface normal

[0166] O Optical axis of birefringent medium

Claims

1. A device (1) for coupling a laser beam (20) of a laser (2) into a double-clad optical fiber (3), A first birefringent optical element (10), in particular an optical wedge or a plane-parallel plate, is provided for splitting the laser beam (20) incident on the beam entry surface (100) into two sub-laser beams (200, 202), wherein: The two sub-laser beams (200, 202) have a first exit angle and / or a first beam offset relative to a beam exit surface normal (N102), wherein the two sub-laser beams (200, 202) are polarized along a basic polarization component of the first birefringent optical element (10); A polarization rotation device (14) is provided, which is configured to adjust the polarization of the irradiating sub-laser beams (200, 202) and thereby provide polarization-adjusted sub-laser beams (200', 202'); A second birefringent optical element (12), in particular an optical wedge or a plane-parallel plate, wherein a beam exit surface (122) of the second birefringent optical element (12) is first traversed by the polarization-adjusted sub-laser beams (200', 202'), and wherein the first exit angle and / or the first beam offset of the sub-laser beams (200, 202) from the first birefringent optical element (10) is a second irradiation angle and / or a second beam offset of the polarization-adjusted sub-laser beams (200', 202') relative to a normal (N122) to the beam exit surface of the second birefringent optical element (12), wherein the second birefringent optical element (12) is configured to split each of the polarization-adjusted sub-laser beams (200, 202′) into two sub-sub-laser beams (2000, 2002, 2020, 2022), wherein each of the two sub-sub-laser beams (2000, 2002, 2020, 2022) has a second exit angle and / or a second beam offset relative to a beam entry surface normal (N120) of the second optical wedge (12), wherein each of the two sub-sub-laser beams (2000, 2002, 2020, 2022) is polarized along a fundamental polarization component of the second birefringent optical element (12), and wherein the second exit angle and / or the second beam offset of a sub-sub laser beam (2000, 2002, 2020, 2022) whose polarization corresponds to the polarization of the original sub-laser beam (200, 202) compensates for the corresponding first exit angle and / or the first beam offset; and A coupling optical unit (16) is provided, which is configured to couple a sub-sub laser beam (2000, 2020) having a compensated first exit angle and / or a first beam offset into the inner core (30) of the double-clad optical fiber (3), and to couple other sub-sub laser beams (2002, 2022) into the annular core (34) of the double-clad optical fiber (3).

2. The device (1) according to claim 1, characterized in that The laser beam (20) is polarized or unpolarized.

3. The device (1) according to claim 1 or 2, characterized in that The first birefringent optical element (10) and / or the second birefringent optical element (12) include quartz glass or are formed of quartz glass.

4. Device (1) according to any one of the preceding claims, characterized in that The substrate thickness (B) of at least one birefringent optical element (10, 12) is between 1 mm and 50 mm, preferably between 1 mm and 10 mm.

5. Device (1) according to any one of the preceding claims, characterized in that The first birefringent optical element (10) and the second birefringent optical element (12) are identically designed.

6. Device (1) according to any one of the preceding claims, characterized in that The polarization rotation device (14) is electronically controllable.

7. Device (1) according to any one of the preceding claims, characterized in that The coupling optical unit (14) comprises a lens and / or a lens system and / or a mirror arrangement.

8. Device (1) according to any one of the preceding claims, characterized in that The double-clad optical fiber (3) comprises an intermediate cladding (32).

9. A method for coupling a laser beam (20) of a laser (2) into a double-clad optical fiber (3), in, The laser beam (20) incident on the beam entry surface (100) of the first birefringent optical element (10) is divided into two sub-laser beams (200, 202), wherein the two sub-laser beams (200, 202) have a first exit angle and / or a first beam offset relative to a beam exit surface normal (N102), wherein the two sub-laser beams (200, 202) are polarized along a fundamental polarization component of the first birefringent optical element (10), wherein the polarization of the sub-laser beams (200, 202) for irradiation is adjusted using a polarization rotating device (14), thereby providing sub-laser beams (200', 202') with adjusted polarization, wherein the polarization-adjusted sub-laser beams (200', 202') first pass through a beam exit surface (122) of a second birefringent optical element (12), wherein a first exit angle and / or a first beam offset of the sub-laser beams (200', 202') from the first birefringent optical element (10) is a second irradiation angle and / or a second beam offset of the polarization-adjusted sub-laser beams (200', 202') relative to a normal (N122) of the beam exit surface on the second birefringent optical element (12), wherein the polarization-adjusted sub-laser beams (200, 202′) are each split into two sub-sub-laser beams (2000, 2002, 2020, 2022) by the second birefringent optical element (12), wherein the two sub-sub-laser beams (2000, 2002, 2020, 2022) each have a second exit angle and / or a second beam offset relative to a beam entry surface normal (N120) of the second optical wedge (12), wherein the two sub-sub-laser beams (2000, 2002, 2020, 2022) are each polarized along a fundamental polarization component of the second optical wedge (12), and wherein the second exit angle and / or the second beam offset of a sub-sub laser beam (2000, 2002, 2020, 2022) whose polarization corresponds to the polarization of the original sub-laser beam (200, 202) compensates for the corresponding first exit angle, and A sub-sub laser beam (2000, 2020) having a compensated first exit angle and / or a first beam offset is coupled into the inner core (30) of the double-clad optical fiber (3) using a coupling optical unit (16), and other sub-sub laser beams (2002, 2022) are coupled into the annular core (34) of the double-clad optical fiber (3) using the coupling optical unit (16).

10. The method according to claim 9, characterized in that The polarization rotation device (14) is used to adjust the splitting ratio of coupling the laser beam (20) into the inner core (30) and the annular core (34) of the double-clad optical fiber (3).

11. The method according to claim 10, characterized in that The beam splitting ratio is determined by the ratio of the power of those sub-sub-laser beams (2000, 2020) whose polarization corresponds to the polarization of the original sub-laser beam (200, 202) to the power of the other sub-sub-laser beams (2002, 2022).

12. A system for processing a workpiece (5) using a laser beam (20) of a laser (2), the system comprising a laser (2), a double-clad optical fiber (3), a device (1) for coupling the laser beam (20) of the laser (2) into the double-clad optical fiber (3) according to any one of claims 1 to 8, a processing optical unit (4) and a workpiece (5), in, The device (1) for coupling is configured to couple the laser beam (20) of the laser (2) into the inner core (30) of the double-clad optical fiber (3) and the annular core (34) of the double-clad optical fiber (3) at a splitting ratio. The double-clad optical fiber (3) is configured to guide the laser beam (20) from an input end of the double-clad optical fiber (3) to an output end of the double-clad optical fiber. The processing optical unit (4) is configured to: form a processing laser beam (22) from the laser beam (20) behind the output end of the double-clad optical fiber (3), focus the processing laser beam (22), and apply the processing laser beam (22) to the workpiece (5), thereby processing the workpiece (5).

13. The system according to claim 12, characterized in that The beam quality of the processing laser beam (22) after the output end of the double-clad optical fiber (3) is adjusted by means of the splitting ratio.

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