Device and method for optimizing coupling of laser beam into optical waveguide

Abstract

The invention relates to a device and a method for optimizing the coupling of a laser beam (10) of a laser (1) into an optical waveguide (30), having a coupling device (32) arranged to couple the laser beam (10) into the optical waveguide (30); having a mirror device (2) arranged to adjust the illumination angle of the laser beam (10) on the coupling device (32) in order to guide the laser beam (10) centrally onto the fiber core of the optical waveguide (30); and a beam offset device (5) arranged to adjust the irradiation location on the coupling device (32) in the form of a parallel offset (o) of the laser beam (10) in order to direct the laser beam (10) vertically onto the incident surface (300). There is provided a sensor device (6) arranged to detect a measure of the coupling efficiency of the laser beam (10) into the optical waveguide (30), and a control device (7) arranged to receive the measure of the coupling efficiency of the laser beam (10) from the sensor device (6) and to send a control signal to an electrically controllable adjustment device of the mirror device (2) and / or the beam offset device (5).

Description

Technical Field

[0001] The invention relates to a device and a method for optimizing the coupling of a laser beam of a laser into an optical waveguide. Background Art

[0002] In modern laser systems and in material processing using such laser systems, a laser beam generated by a laser beam device is usually coupled into an optical waveguide to transmit the laser beam to a target location. The target location may be, for example, a processing optical device that shapes the laser beam and then applies the shaped laser beam to a workpiece to be processed, thereby processing the workpiece.

[0003] In order to enable the laser energy to be optimally transmitted through the optical waveguide, it is therefore necessary to ensure optimal coupling of the laser beam into the optical waveguide. The coupling is determined in particular by the irradiation angle and irradiation location of the laser beam on the coupling device that transmits the laser beam into the optical waveguide.

[0004] A system of two mirrors is usually used to couple a laser beam into an optical waveguide. When the first mirror is exposed to the laser beam and tilted, the irradiation position and the irradiation angle of the laser beam on the second mirror change. However, if the second mirror is subsequently tilted, the irradiation angle and the irradiation position on the subsequent optical element are adjusted again. The irradiation position and the irradiation angle depend on the settings of the first angle and the second angle, because both mirrors adjust these two parameters. For example, if the laser beam irradiates the coupling-in optical unit perpendicularly, a parallel shift of the laser beam can only be achieved by adjusting the two mirrors together. This has the disadvantage that the mutual dependence and mutual influence of the two mirrors must be compensated for when automatically adjusting the coupling.

[0005] DE 10 2016 11 6 410 discloses a fiber coupling device having a lens and an additional element, which may be a mirror or a prism. Summary of the invention

[0006] Starting from the known prior art, the object of the present invention is to provide an improved method for optimizing the beam quality.

[0007] This object is achieved by a device for optimizing the coupling of a laser beam of a laser into an optical waveguide having the features of claim 1. Advantageous developments are possible according to the dependent claims, the description and the drawings.

[0008] Therefore, a device for optimizing the coupling of a laser beam of a laser into an optical waveguide is proposed, wherein the device comprises a coupling device, which is configured to couple the laser beam into the optical waveguide; wherein the device comprises a mirror device, which is configured to adjust the irradiation angle of the laser beam on the coupling device so as to guide the laser beam centrally onto the optical fiber core of the optical waveguide; wherein the device comprises a beam shifting device, which is configured to adjust the irradiation location onto the coupling device in the form of a parallel shift of the laser beam so as to guide the laser beam vertically onto the incident surface of the optical waveguide.

[0009] The optical waveguide is arranged to guide the laser beam of a laser, such as an ultrashort pulse laser and / or a laser beam of a high power laser, from the incident surface of the optical waveguide to the exit surface of the optical waveguide. Such an optical waveguide can be, for example, a glass optical fiber or another suitable optical fiber. In particular, such an optical waveguide can also be a hollow core optical fiber. The optical waveguide generally also has at least one optical fiber core and an optical fiber cladding, wherein the light is guided in the optical fiber core.

[0010] In order to couple the laser beam of a laser into an optical waveguide, the laser beam must irradiate the optical fiber core of the optical waveguide as centrally as possible. In addition, the laser beam needs to be guided as vertically as possible to the entrance surface of the optical waveguide. This enables particularly large amounts of laser energy to be coupled into the optical waveguide.

[0011] Centrally can mean that the laser beam impinges on the geometric center of the fiber core, such as impinging on the center of a fiber core having a circular cross section. However, centrally can also mean that the laser beam impinges on the surface center of the fiber core cross section. However, centrally can also mean that the laser beam impinges on a specific symmetrical point in the fiber core cross section, such as the focus of an elliptical fiber core cross section.

[0012] In a multi-clad fiber, several fiber cores are distributed in concentric rings around a central fiber core. For example, if a laser beam is irradiated into the center of the ring segment in a radial direction, each of the annular fiber cores may be centrally loaded by the laser.

[0013] For this purpose, a mirror arrangement is used to couple the laser beam into the optical waveguide. The mirror arrangement can, for example, comprise one or more mirrors which can deflect the laser beam in different directions. This enables the laser beam to be deflected by the laser in such a way that it is directed as vertically and centrally as possible onto the coupling arrangement, so that the laser beam also strikes the entrance surface of the optical waveguide vertically and centrally.

[0014] For example, the first mirror can deflect the laser beam by a first angle on a first axis and by a second angle on a second axis. By deflecting the laser beam reflected at the first mirror by a certain deflection angle, a specific irradiation point on the second mirror is defined after propagation to the second mirror. From this irradiation point, the second mirror can, for example, steer the laser beam reflected at the first mirror at a further first angle on a further first axis and steer the laser beam at a further second angle on a further second axis.

[0015] The laser beam reflected at the second mirror is finally coupled indirectly into the optical waveguide via a coupling device, such as a lens. In the plane of the coupling device, called the coupling plane, the illumination location is then defined as the position where the laser beam falls on the coupling device. In the coupling plane, the illumination angle is also defined as the angle of the laser beam relative to the surface normal of the coupling plane. The coupling device and the coupling plane can be used synonymously to describe the illumination location and the illumination angle.

[0016] In order to optimize the coupling, a beam deflection device is arranged between the mirror device and the coupling device.

[0017] The beam shifting device is preferably arranged to adjust the irradiation location in the form of a parallel shift of the laser beam. A parallel shift is a displacement of the incident laser beam by a certain displacement length. However, the displaced laser beam remains oriented parallel to the incident laser beam. In other words, the beam shifting device is arranged so that no additional angular shift is applied to the laser beam. Instead, the parallel shift can be adjusted without an angular shift.

[0018] This has the advantage that the degrees of freedom can be adjusted individually via the beam deflection device, so that there is no interaction with the mirror device, i.e., the position adjustment does not require an angle compensation. For example, the mirror device can orient the laser beam exactly perpendicular to the coupling plane, while the beam deflection device individually adjusts the impingement location of the laser beam in the coupling plane.

[0019] The beam deflection of the beam deflection device depends on the relative orientation of the beam deflection device and the laser beam. The beam deflection o is given by:

[0020]

[0021] Wherein α is the angle of incidence relative to the surface normal of the beam deflection device, β is the angle of refraction of the beam deflection device, and d is the thickness of the beam deflection device. The angle of refraction results in particular from the refractive index of air and the material of the beam deflection device according to Snell's law of refraction. By tilting or pivoting the beam deflection device, the angle of incidence is changed, resulting in a change in the deflection.

[0022] Thus, by controlling such a tilt, drift of the laser beam, for example due to ambient temperature fluctuations, can be particularly easily compensated. For this purpose, for example, the last mirror in the mirror arrangement can be used to adjust the illumination angle on the coupling device, while the beam deflection device can be used to adjust the illumination location on the coupling device.

[0023] The coupling device can convert the irradiation position of the laser beam on the coupling device into the irradiation angle of the laser beam on the incident surface of the optical waveguide, and convert the irradiation angle of the laser beam on the coupling device into the irradiation position of the laser beam on the incident surface of the optical waveguide, wherein the coupling device is preferably a lens or a lens system.

[0024] The coupling device can thus perform a position-to-angle transformation or an angle-to-position transformation.

[0025] This means that the irradiation point on the coupling device determines the irradiation angle of the laser beam on the incident surface of the optical waveguide, while the irradiation angle on the coupling device determines the irradiation point on the incident surface of the optical waveguide. In an ideal system, when the laser beam is on the optical axis of the coupling device, the laser beam also irradiates centrally on the optical fiber core and perpendicularly on the incident surface of the optical waveguide, so that particularly efficient coupling into the incident surface of the optical waveguide is possible.

[0026] The irradiation site on the optical fiber core of the optical waveguide may be offset from the center of the optical fiber core of the optical waveguide by less than 10% of the beam diameter of the laser beam, preferably less than 3% of the beam diameter of the laser beam.

[0027] For example, the laser beam may have a beam radius of 30 μm, so that the irradiation location is offset from the center of the optical fiber core of the optical waveguide by less than 3 μm, preferably less than 1 μm.

[0028] The illumination angle on the entrance surface of the light guide may deviate from normal incidence on the entrance surface of the light guide by less than 10% of the beam divergence, preferably less than 3% of the beam divergence.

[0029] For example, the beam divergence of the laser beam may be 100 μ°, so that the illumination angle may deviate from normal incidence on the incident surface of the optical waveguide by less than 10 μ°, preferably less than 3 μ°.

[0030] The beam deflection device may be a plane parallel plate. A plane parallel plate is a plate made of a material with a material-dependent refractive index, the front side and the back side of which are oriented parallel to each other. A plane parallel plate has the advantage that it is particularly easy and inexpensive to produce.

[0031] However, the beam deflection device may also be a wedge plate device, wherein the wedge plate device comprises two wedge plates which are displaceable relative to each other and wherein outer sides of the wedge plate device are plane-parallel to each other.

[0032] The wedge plate has a thick end which tapers in the direction of the tapered side. The two wedge plates are oriented to one another in such a way that the tapered side of one wedge plate coincides with the thick end of the other wedge plate. The two outer sides of the wedge plate arrangement are those sides of the wedge plates which do not face one another. If the two outer sides are parallel to one another, the effect of the wedge plate arrangement corresponds to that of a plane-parallel plate. In particular, however, a displaceable wedge can be used to adjust the thickness of the wedge plate arrangement acting on the laser beam. This provides a further possibility of individually adjusting the size of the parallel offset.

[0033] The thickness of the beam deflection device may be less than 20 mm, preferably less than 10 mm. The parallel deviation of the laser beam on the coupling device may be up to 0.5 mm or up to 1 mm.

[0034] This has the advantage that the parallel deviation can be adjusted within a sufficiently large range. If the thickness of the beam deflection device is large, the absorption in the material increases, so that the laser energy deposited in the beam deflection device may damage the beam deflection device.

[0035] The optical waveguide may be a hollow core optical fiber.

[0036] Hollow-core fibers have the advantage that the interaction of the laser beam with the fiber material is lower than with conventional glass fibers based on total reflection. This makes it possible, for example, to achieve longer optical waveguide lengths. In addition, the amplitude of nonlinear effects in hollow-core fibers is reduced, which means that more power can be transmitted through hollow-core fibers than through conventional glass fibers.

[0037] The mirror device and / or the beam deflection device can have an electrically controllable adjustment device and a control device, wherein the control device is configured to control the electrically controllable adjustment device, and the electrically controllable adjustment device is configured to adjust the irradiation angle of the laser beam on the coupling device and / or adjust the irradiation point on the coupling device in the form of a parallel deflection of the laser beam.

[0038] The electrically controllable adjustment device can be, for example, a stepper motor or a piezoelectric adjustment device. A stepper motor control has the advantage that it can adjust the mirror device and / or the beam shift device to a particularly large extent. In particular for the mirror device, this has the advantage that a rough adjustment of the coupling of the laser beam into the optical waveguide is possible. A piezoelectric adjustment device has the advantage that it is particularly suitable for precise adjustment. Therefore, a piezoelectric adjustment device can be used, for example, for a beam shift device to adjust the parallel offset with a certain accuracy so that the coupling is particularly optimal. However, the piezoelectric adjustment device can also be used for the mirror device, for example to ensure a particularly vertical incidence of the laser beam into the incident surface of the optical waveguide. Both the mirror and the beam shift device of the mirror device can have two electrically controllable adjustment devices, so that, for example, a tilt in the x-direction can be achieved with a first adjustment device and a tilt in the y-direction can be achieved with a second adjustment device. The device may include: a sensor device, which is arranged to detect a measure of the coupling efficiency of the laser beam into the optical waveguide, wherein the sensor device is preferably a photodiode.

[0039] With such a sensor device, for example, the intensity can be measured as a measure of the coupling efficiency of the laser light, wherein particularly good coupling is present with particularly high intensities. The sensor device can in particular be a photodiode for measuring the intensity of the laser beam.

[0040] However, the sensor device can also be a camera device, in particular a beam profile camera device, which measures not only the intensity of the laser beam but also detects local information about the shape and form of the laser beam as a measure of the coupling efficiency.

[0041] For this purpose, the device may comprise a beam splitter which is arranged behind the exit surface of the optical waveguide and which is arranged to split a portion of the laser beam behind the optical waveguide and to transmit this portion to the sensor device.

[0042] The beam splitter may be arranged to split only a small portion of the laser beam outcoupled from the optical waveguide and transmit this small portion to the sensor device. For example, less than 20%, preferably less than 5%, of the outcoupled laser beam may be split.

[0043] However, the device may further comprise a reflective element on the exit surface of the optical waveguide, arranged to reflect a portion of the laser beam back to the entrance surface of the optical waveguide and transmit the portion to the sensor device.

[0044] The reflective element may for example be a partially reflective coating on the exit surface of the optical waveguide.The reflective element may also be a partially reflective coating on a portion of the exit surface of the optical waveguide.

[0045] By partially reflecting the laser beam at the exit surface of the optical waveguide and causing it to pass through the optical waveguide again, the sensor device can be arranged at the fixed end of the optical waveguide or on the laser side. This enables the optical waveguide to be used particularly flexibly and in a space-saving manner on the other side, for example on the side of the processing optics.

[0046] The device may comprise a control device which is configured to receive a measure of the coupling efficiency of the laser beam from the sensor device and to send a control signal to an electrically actuatable adjustment device of the mirror device and / or the beam deflection device.

[0047] The control device can be, in particular, a computer and / or a microcontroller and / or an FPGA. If the control device receives the measure of the coupling efficiency and sets the adjustment of the mirror device and / or the beam deflection device, the measure of the coupling efficiency can be optimized fully automatically. In particular, changes in the measure of the coupling efficiency can be detected and compensated by corresponding adjustments. This makes it possible to keep the measure of the coupling efficiency at a particularly high level.

[0048] The control means may be arranged to operate only a single mirror and wedge plate arrangement to optimise coupling.

[0049] This makes it particularly advantageous to adjust the illumination location and the illumination angle independently of one another, so that in particular a simplified optimization of the coupling is possible, since no mutual dependencies have to be taken into account when optimizing the illumination location and the illumination angle.

[0050] The above object is also achieved by the method of claim 14.

[0051] Therefore, a method for optimizing the coupling of a laser beam of a laser into an optical waveguide is proposed, wherein, in a first step, the irradiation angle of the laser beam on the coupling device is adjusted by a first mirror of a mirror device to guide the laser beam centrally onto the optical fiber core of the optical waveguide; wherein, in a second step, the irradiation position on the coupling device is adjusted by a beam shifting device in the form of a parallel shift of the laser beam to guide the laser beam vertically onto the incident surface of the optical waveguide; and wherein the laser beam is coupled into the incident surface of the optical waveguide by the coupling device.

[0052] In a first step, the beam deflection device can be oriented in the beam path in such a way that it does not generate a parallel deviation of the laser beam and / or the beam deflection device can be oriented in a reference position in which the beam deflection device is parallel to the coupling device.

[0053] For example, a coarse adjustment of the mirror arrangement may be performed and fixed during production of the laser system, since such an adjustment is unsuitable and / or complex for the end user due to the interdependence of the optical components in the laser system. In particular, the illumination angle of the laser beam may be adjusted during production such that it is particularly perpendicular to the entrance surface of the optical waveguide. In order to optimize the coupling of the laser beam, it is then only necessary to adjust the illumination angle using a single mirror and to adjust the parallel offset using a beam offset element.

[0054] For example, the beam offset device can be placed in a zero or reference position and the last mirror of the mirror device can be used to adjust the illumination angle. The beam offset position can then be tilted from its zero or reference position to produce a parallel offset.

[0055] A sensor device can be used to detect a measure of the coupling efficiency of the laser beam into the optical waveguide and send this measure to a control device, which can receive and analyze the measure of the coupling efficiency and send a control signal to an electrically controllable adjustment device of a mirror device and / or a beam deflection device, thereby adjusting the irradiation angle and / or the irradiation location in the form of a parallel deflection of the laser beam.

[0056] For example, the control device detects a measure of coupling efficiency that is lower than at an earlier point in time. The control device can then send a control signal to the beam deflection device so that the beam deflection device is tilted a certain amount in one direction so that a certain amount of parallel deflection occurs in this direction. If it is subsequently detected that the measure of coupling efficiency has not improved, a tilt in the opposite direction can be performed. If an improvement is detected, the tilt can be adjusted again in a further step to achieve a further improvement in the measure of coupling efficiency. However, if no improvement is detected, the previous tilt can be adjusted. Subsequently, for example, the tilt can be adjusted in another direction, and the coupling efficiency can thus be further improved, or kept at a high level.

[0057] For example, the same steps can be taken for the last mirror of the mirror arrangement to optimize the illumination angle and improve the measure of coupling efficiency. Since the parallel offset and the illumination angle can be adjusted independently of each other, a particularly simple optimization of the coupling is possible, since no mutual dependencies have to be considered in the optimization algorithm or optimization process.

[0058] Thus, the coupling efficiency may be adjusted by a control loop, wherein a reading of the measure of the coupling efficiency is performed for each change of the adjustment and further changes of the adjustment are then performed depending on the changed measure of the coupling efficiency.

[0059] The method can be carried out in particular during ongoing laser operation and can thereby compensate for angular and parallel drifts of the laser beam and keep the coupling of the laser beam optimal during ongoing laser operation.

[0060] In particular, an automated method for rescaling a measure of coupling efficiency to ensure optimal system performance is provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] 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:

[0062] FIG1 shows a schematic representation of an apparatus for coupling a laser beam into an optical waveguide according to the prior art;

[0063] Figure 2A , Figure 2B A schematic representation of the optimization of the coupling of the laser beam is shown;

[0064] Figure 3 A schematic representation of an apparatus according to the invention is shown;

[0065] Figure 4 A schematic representation of a beam deflection device is shown;

[0066] Figure 5 A schematic representation of a wedge plate arrangement is shown;

[0067] Figure 6 shows a further schematic representation of a wedge plate arrangement; and

[0068] Figure 7 A further schematic representation of the device according to the invention is shown. DETAILED DESCRIPTION

[0069] 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 descriptions of these elements are omitted in some instances to avoid redundancy.

[0070] 1 schematically shows a device according to the prior art for coupling a laser beam 10 of a laser 1 into an optical waveguide 30. The laser beam 10 is provided by a laser 1, which is, for example, an ultrashort pulse laser. The laser beam 10 is then deflected via a mirror device 2 so that it can be coupled into an incident surface 300 of an optical waveguide 30 using a coupling device 32. The mirror device 2 here has, for example, two mirrors 20, 22.

[0071] The first mirror 20 reflects the laser beam 10 in the negative y direction, in which direction the laser beam impinges on the second mirror 22 after a certain distance. The reflection angle of the first mirror 20 and the distance between the first mirror 20 and the second mirror 22 define the impingement location of the laser beam 10 on the second mirror 22. From the impingement location on the second mirror 22, the laser beam 10 is guided in the direction of the optical waveguide 30, in which direction the laser beam is coupled into the incident surface 300 of the optical waveguide 30 by a coupling device 32 (e.g., a lens). After passing through the optical waveguide 30, the laser beam 10 can finally be coupled out from the exit surface 302 of the optical waveguide 30 by the outcoupling optical unit 34.

[0072] In order to achieve the best possible coupling, the laser beam 10 must be centered on the fiber core of the optical waveguide and perpendicular to the incident surface 300 of the optical waveguide 30, such as Figure 2A , Figure 2B shown.

[0073] Figure 2A The case where the laser beam 10 falls on the incident surface 300 at a certain angle, for example, at an angle pair relative to the xy plane and relative to the yz plane. Here, the irradiation angle of the laser beam 10 is measured relative to the surface normal of the incident surface 300. The irradiation location of the laser beam 10 on the optical fiber core can also be defined in the incident surface 300. Figure 2A In the case shown, the incident surface 300 and the optical fiber core completely overlap, and the laser beam 10 is directed non-centrally and at an angle onto the incident surface 300. This results in the laser beam being coupled into the optical waveguide by the coupling device with little or no efficiency.

[0074] In order to achieve the best possible coupling, according to the prior art, both the illumination angle and the illumination location on the coupling device 32 must be adjusted via the mirror device 2. However, due to the use of mirrors, these two quantities can only be adjusted simultaneously. Figure 2B Optimized coupling of the laser beam 10 into the optical waveguide 30 via the coupling device 32 is shown, wherein the irradiation angle relative to the surface normal of the incident surface 300 vanishes and wherein the irradiation point of the laser beam 10 coincides with the center of the incident surface 300 or with the fiber core.

[0075] from Figure 2B Based on the ideal situation in FIG. 1 , a drift of the laser beam 10 may occur during laser operation. Such a drift may be, for example, a drift of the irradiation angle or a drift of the irradiation location. In order to achieve an optimized coupling and compensate for possible drifts, according to the invention, a beam deflection element 5 is arranged between the mirror arrangement 2 and the coupling-in optical unit 32, such as Figure 3 shown.

[0076] The beam shifting element 5 is arranged to apply a parallel shift to the laser beam 10. By means of the parallel shift, the impingement point of the laser beam 10 on the coupling device can be adjusted independently of the impingement angle. This enables an optimized coupling of the laser beam 10.

[0077] For example, the laser beam 10 may exhibit a drift of the illumination angle and the illumination location after a certain operating duration. By adjusting, for example, the second mirror 22 of the mirror arrangement 2, the illumination location on the fiber core can be easily corrected. Finally, the subsequent beam shifting element 5 can be used to adjust the illumination angle by means of a parallel shift of the laser beam 10 before the coupling optical unit 32, so that the laser beam 10 is directed perpendicularly onto the incident surface 300 and is thus coupled into the center of the incident surface 300 of the optical waveguide 30.

[0078] The coupling device 32 can thus convert the irradiation position of the laser beam 10 on the coupling device 32 into the irradiation angle of the laser beam 10 on the incident surface 300 of the optical waveguide 30, and convert the irradiation angle of the laser beam 10 on the coupling device 32 into the irradiation position of the laser beam 10 on the incident surface 300 of the optical waveguide 30, wherein the coupling device 32 is preferably a lens or a lens system.

[0079] The irradiation location on the incident surface 300 of the optical waveguide 30 can be offset from the center of the incident surface 300 of the optical waveguide 30 and thus also from the center of the optical fiber core by less than 10% of the beam diameter of the laser beam 10, preferably less than 3% of the beam diameter of the laser beam.

[0080] For example, the laser beam 10 may have a beam radius of 1 μm, so that the irradiation location deviates from the center of the optical fiber core of the optical waveguide 30 by less than 0.1 μm, preferably less than 0.033 μm.

[0081] The illumination angle on the entrance surface of the optical waveguide may deviate from normal incidence on the entrance surface of the optical waveguide by less than 10% of the beam divergence, preferably less than 3% of the beam divergence.

[0082] For example, the beam divergence of the laser beam may be 600 μ°, so that the illumination angle may deviate from normal incidence on the incident surface 300 of the optical waveguide 30 by less than 60 μ°, preferably less than 18 μ°.

[0083] The mirrors 20, 22 of the mirror device 2 and also the beam shifting assembly 5 can be equipped with electrically controllable adjustment devices so that the tilt of these elements indicated by the double arrows can be adjusted electronically. In addition, the device has a sensor device 6 and a beam splitter 4, which are both arranged on one side of the outcoupling optical unit 34 in this embodiment. The beam splitter 4 can deflect a portion of the outcoupled laser beam 10 and provide this portion to the sensor device 6. The measurement of the coupling efficiency can be determined by the intensity measured at the sensor device or by the beam profile measured at the sensor device or the beam quality measured at the sensor device. The sensor device 6 sends a measure of the coupling efficiency to the control device 7. Finally, the control device 7 can control the electrically controllable adjustment devices of the mirrors 20, 22 and the beam shifting device 5 by electronic control. This enables the mirrors 20, 22 and the beam shifting device 5 to be tilted and the coupling to be optimized.

[0084] For this purpose, the control device 7 may for example tilt one after the other the last mirror 22 of the mirror arrangement 2 and the beam deflection device 5. In particular, the control device may be arranged to control only a single mirror 22 and the wedge plate arrangement to optimize the coupling.

[0085] By determining a measure of the coupling efficiency after each adjustment, the control device 7 can draw conclusions whether the coupling has improved or deteriorated or whether the coupling has remained unchanged by comparing this measure with previously measured values. The coupling efficiency can be optimized by systematically adjusting the tilt.

[0086] For example, in a first step, only the irradiation angle of the laser beam 10 in the coupling plane can be adjusted, wherein the beam shifting device 5 is arranged in the beam path so that the parallel offset is zero. However, the beam shifting device 5 can also be moved to a reference position, for example parallel to the coupling plane. Therefore, the irradiation angle of the laser beam 10 on the beam shifting device 5 corresponds to the irradiation angle of the laser beam 10 in the coupling plane. Subsequently, the parallel offset of the laser beam 10 can be adjusted by tilting the beam shifting device 5 so that the laser beam 10 is irradiated perpendicularly onto the incident surface 300 of the optical waveguide 30.

[0087] For example, a fully automatic optimization of the coupling of the laser beam 10 can be realized during ongoing laser operation. This enables compensation of temporal drifts, for example angular drifts or parallel drifts.

[0088] Figure 4 , Figure 5 and Figure 6 Various possible embodiments of the beam deflection device 5 are shown. Figure 4, the beam deflection device 5 is a plane parallel plate. The plane parallel plate has two plane parallel outer surfaces 500, 502, through which the laser beam 10 passes. If the laser beam 10 enters the plane parallel plate 5 through the outer surface 500 at an illumination angle to the surface normal n, the laser beam 10 is refracted toward the surface normal n. When the laser beam 10 leaves the plane parallel plate, the laser beam 10 is refracted away from the surface normal n'. Therefore, the outgoing laser beam has only a parallel offset o with the incident laser beam. The parallel offset o depends on the input angle relative to the surface normal n and the thickness D of the plane parallel plate.

[0089] Figure 5 An alternative embodiment of a beam deflection device 5 is shown. The beam deflection device 5 is a wedge plate device 5'. The wedge plate device 5' comprises two wedge plates 50, 52, which taper from a thick end to a tapered side. The two wedge plates 50, 52 are placed and / or oriented relative to each other in such a way that the outer surfaces 500, 502 and also the inner surfaces extend parallel to each other. Accordingly, a parallel deviation o can also be generated with the wedge plate device 5'.

[0090] The two wedges 50, 52 of the wedge plate device 5' can be displaced relative to each other, such as Figure 6 As shown. This makes it possible to adjust the thickness of the wedge plate device 5' through which the laser beam 10 is displaced in parallel. If the wedge plates 50, 52 are moved away from each other, the thickness d becomes smaller, whereby the parallel offset o also becomes smaller. If the wedge plates 50, 52 are moved one above the other, the thickness d becomes larger, whereby the parallel offset o also becomes larger.

[0091] Figure 7 A further embodiment of the device according to the invention is shown. Here, the exit surface 302 of the optical waveguide 30 at least partially has a partially reflective coating, which reflects the laser beam 10 back to the incident surface 300 of the optical waveguide 30. The exit surface 302 of the optical waveguide 30 in particular also includes further components attached to the fiber end of the optical waveguide 30. For example, a so-called end cap can be spliced ​​or fused to the fiber end with such a coating. For example, at the fiber end of a hollow-core fiber, a glass block can be held at a certain distance from the fiber end via a ferrule and a nozzle brick, wherein the glass block, in particular a glass block made of quartz glass, can have such a coating. When using ultrashort laser pulses, the use of a hollow-core fiber with a coated glass block is particularly preferred. The laser beam coupled out of the exit surface 302 can be deflected, for example, by a beam splitter 4 and transmitted to a sensor device 6. This embodiment has the advantage that the detection of the measure of the coupling efficiency is arranged on the fixed side, i.e. the laser side of the device. The optical waveguide 30 can therefore be used particularly flexibly without requiring installation space for the beam splitter 4 and the sensor device 6 , for example on the side of the process optics.

[0092] 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.

[0093] Reference numerals list

[0094] 1 Laser

[0095] 10 Laser beam

[0096] 2 mirror device

[0097] 20 First Mirror

[0098] 22 Second Mirror

[0099] 3 Optical waveguide device

[0100] 30 Optical waveguide

[0101] 32 Coupling Optical Unit

[0102] 34 Decoupling optical unit

[0103] 300 Incident surface

[0104] 302 exit surface

[0105] 4 Beam splitters

[0106] 5 Beam Deflection Device

[0107] 5' Wedge Plate Assembly

[0108] 50 first wedge

[0109] 52 Second wedge

[0110] 6 Sensor device

[0111] 7 Control Devices

[0112] d Beam deflection device thickness o Parallel deflection

[0113] n, n' surface normal

Claims

1. A device for optimizing the coupling of a laser beam (10) of a laser (1) into an optical waveguide (30), A coupling device (32) is provided, which is configured to couple the laser beam (10) into the optical waveguide (30), A mirror device (2) is provided, wherein the mirror device is configured to adjust the irradiation angle of the laser beam (10) on the coupling device (32) so as to guide the laser beam (10) centrally onto the optical fiber core of the optical waveguide (30); and A beam deflection device (5) is provided, the beam deflection device being configured to adjust the irradiation location on the coupling device (32) in the form of a parallel deviation (o) of the laser beam (10) so as to guide the laser beam (10) vertically onto the incident surface (300) of the optical waveguide (30), Features A sensor device (6) is arranged to detect a measure of the coupling efficiency of the laser beam (10) into the optical waveguide (30), and a control device (7) is arranged to receive the measure of the coupling efficiency of the laser beam (10) from the sensor device (6) and to send a control signal to an electrically controllable adjustment device of the mirror device (2) and / or the beam deflection device (5).

2. The device according to claim 1, characterized in that The beam deflection device (5) is configured to adjust the irradiation location in the form of a parallel deviation (o) of the laser beam (10) without changing the irradiation angle.

3. The device according to claim 1 or 2, characterized in that: The coupling device (32) converts the irradiation position of the laser beam (10) on the coupling device (32) into the irradiation angle of the laser beam (10) on the incident surface (300) of the optical waveguide (30), and converts the irradiation angle of the laser beam (10) on the coupling device (32) into the irradiation position of the laser beam (10) on the optical fiber core of the optical waveguide (30), Therein, the coupling device (32) is preferably a lens or a lens system.

4. A device according to any one of the preceding claims, characterised in that The irradiation location on the optical fiber core of the optical waveguide (30) is offset from the center of the optical fiber core of the optical waveguide (30) by less than 10% of the beam diameter of the laser beam (10), preferably less than 3% of the beam diameter of the laser beam, and / or The illumination angle on the incident surface (300) of the optical waveguide (30) deviates from normal incidence on the incident surface (300) of the optical waveguide (30) by less than 10% of beam divergence, preferably less than 3% of beam divergence.

5. A device according to any one of the preceding claims, characterised in that The beam deflection device (5) - is a plane parallel plate, or - is a wedge plate device (5'), wherein the wedge plate device (5') comprises two wedge plates (50, 52) that can be displaced relative to each other, and wherein the outer sides (500, 502) of the wedge plate device (5') are plane-parallel to each other.

6. A device according to any one of the preceding claims, characterised in that The thickness (d) of the beam deflection device (5) is less than 20 mm, preferably less than 10 mm.

7. A device according to any one of the preceding claims, characterised in that The parallel deviation (o) of the laser beam (10) on the coupling device (32) is not higher than 0.5 mm or not higher than 1 mm.

8. A device according to any one of the preceding claims, characterised in that The optical waveguide (30) is a hollow core optical fiber or a multi-clad optical fiber.

9. A device according to any one of the preceding claims, characterised in that The mirror device (2) and / or the beam deflection device (5) have an electrically controllable adjustment device and a control device, wherein the control device is configured to control the electrically controllable adjustment device, and the electrically controllable adjustment device is configured to adjust the irradiation angle of the laser beam (10) on the coupling device (32) and / or adjust the irradiation point on the coupling device (32) in the form of a parallel offset (o) of the laser beam (10).

10. The device according to any one of the preceding claims, characterized in that a beam splitter (4) arranged behind the exit surface of the optical waveguide (30) and configured to separate a portion of the laser beam behind the optical fiber and to transmit the portion to the sensor device, and / or A reflective element on the exit surface (302) of the optical waveguide (30), the reflective element being arranged to reflect a portion of the laser beam (10) back to the incident surface (300) of the optical waveguide (30) and to transmit the portion to the sensor device (6).

11. A device according to any one of the preceding claims, characterised in that A control device (7) is arranged to actuate only a single mirror (22) and the beam deflection device (5) to optimize the coupling.

12. A method for optimizing the coupling of a laser beam (10) of a laser (1) into an optical waveguide (30), in, In a first step, the radiation angle of the laser beam (10) on the coupling device (32) is adjusted by means of a first mirror (22) of the mirror device (2) so as to guide the laser beam (10) centrally onto the optical fiber core of the optical waveguide (30). wherein, in a second step, the irradiation location on the coupling device (32) is adjusted in the form of a parallel deviation (o) of the laser beam by means of a beam deviation device (5) so as to guide the laser beam (10) vertically onto the incident surface of the optical waveguide (300), and The laser beam (10) is coupled into the incident surface (300) of the optical waveguide (30) by means of the coupling device (32).

13. The method according to claim 12, characterized in that In the first step, the beam deflection device (5) is oriented in the beam path in such a way that it does not generate a parallel deviation (o) of the laser beam and / or the beam deflection device (5) is oriented in a reference position, wherein the beam deflection device (5) is parallel to the coupling device (32).

14. The method according to any one of claims 12 or 13, characterized in that detecting a measure of the coupling efficiency of the laser beam (10) into the optical waveguide (30) by means of a sensor device (6) and sending the measure of the coupling efficiency to a control device (7), The control device (7) receives and evaluates the measure of the coupling efficiency and sends a control signal to an electrically controllable adjustment device of the mirror device (2) and / or the beam deflection device (5), thereby adjusting the irradiation angle and / or the irradiation point in the form of a parallel deflection of the laser beam (10).

15. The method according to any one of claims 12 to 14, characterized in that The method is performed during ongoing laser operation and thereby compensates for angular drift and parallel drift of the laser beam (10) and optimally maintains coupling of the laser beam (10) during ongoing laser operation.

Images