Apparatus and method for laser processing of materials

Abstract

The present invention relates to an apparatus and method for laser processing of materials. The apparatus for laser processing of materials comprises a laser and a beam transmission cable, wherein: the laser is connected to the beam transmission cable; the beam transmission cable is configured to transmit laser radiation emitted from the laser, and the laser radiation is defined by a beam parameter product; and the apparatus is characterized in that: the apparatus comprises at least one squeezing mechanism, the squeezing mechanism comprises a periodic surface defined by a pitch; a section of optical fiber constituting a part of the laser and / or the beam transmission cable is positioned adjacent to the periodic surface; and the squeezing mechanism is configured to squeeze the periodic surface and the section of optical fiber together with a squeezing force; thereby, the beam parameter product can be changed by adjusting the squeezing force.

Description

[0001] This invention patent application is a divisional application of the invention patent application with international application number PCT / GB2017 / 000118, international application date August 3, 2017, application number 201780045160.X entering the Chinese national phase, and name “Device and method for laser processing materials”. Technical Field

[0002] The present invention relates to an apparatus and a method for laser processing of materials. Background Art

[0003] Laser cutting of steel is achieved by directing a laser beam onto the workpiece via a processing head that has optics for collimating and focusing the laser beam and a tapered copper nozzle to provide a high-pressure gas jet coaxial with the beam. The basic cutting operation consists of the laser beam heating and melting the sheet metal workpiece, and a gas jet known as an assist gas jet blowing the molten material out the bottom of the cutting zone. The cutting head moves over the sheet metal while maintaining a constant distance between the nozzle tip and the workpiece surface. The cutting head moves in a programmed path to produce the desired sheet metal contour.

[0004] In the case of cutting stainless steel, an inert auxiliary gas is typically used. This avoids the production of metal oxides on the cut edge face of the workpiece, which can cause problems when working with metal parts. Since the only heat source for this cutting process is provided by the focused laser beam, a smaller focal spot size with a higher energy density will provide more efficient cutting by producing a narrower molten zone. It is advantageous to use a low divergence so that the molten zone is narrowed by the thickness of the metal. The limit on the minimum practical focal spot is determined by the optical depth of field together with the material thickness. This is because the cutting width (kerf) must be wide enough to allow the auxiliary gas to travel to the bottom of the cut with sufficient pressure to cleanly remove the molten material and avoid slag on the lower cut edge, thereby producing a clean cut. For this type of cutting, the auxiliary gas must be applied at a high pressure, typically in the range of 10 to 20 bar. The diameter of the nozzle outlet is typically in the range of 0.5mm to 2.0mm, and generally thicker materials require larger nozzles.

[0005] In the case of cutting mild steel (also known as low carbon steel) with a thickness greater than 5mm, oxygen is typically used as an assist gas, which reacts exothermically with the iron within the workpiece to provide additional heat to speed up the cutting speed. This is typically applied at pressures in the range of 0.25 bar to 1 bar, which is much lower than the pressure used for nitrogen assist gas cutting. For thick profile cutting, typically in the range of 10mm to 30mm thickness, the cut must be wide enough so that the oxygen assist gas can reach the bottom of the cutting area with sufficient airflow to eject the molten material while maintaining a slag-free cut. For thick mild steel cutting, the beam is typically defocused so that the beam waist is located above the sheet metal surface so that the incident beam diameter on the sheet metal surface is larger than the beam waist. As the divergence of the beam increases, better quality cuts with lower edge roughness can be obtained.

[0006] Most general-purpose flatbed laser cutting machines are required to cut a range of metals of various thicknesses that must all have good quality. The choice of focal spot size is usually a compromise of the requirements needed to meet a wide range of process conditions. For cutting thin stainless steel, a small focal spot with low divergence is required, while for cutting thick mild steel, a larger focal spot with higher divergence is required. Such flatbed cutting machines are designed for lasers with fixed beam quality. In order to improve processing capabilities, the cutting head may have an enhanced optical system, firstly to allow limited movement of the focusing lens along the beam path to allow defocusing of the laser beam relative to the workpiece, which can increase the incident spot size, and secondly to allow adjustment of the focal spot diameter. This has limited benefits, because a laser with a constant laser beam quality will have a fixed relationship between focal spot size and divergence, which acts in a manner opposite to that desired by the cutting process.

[0007] Different cutting methods require a small spot with low divergence or a large spot with high divergence, while fixed beam quality lasers can provide small spots with high divergence and large spots with narrow divergence. Therefore, it is impossible to optimize the process parameters for all metal types and thicknesses.

[0008] Similar limitations exist for other material processing equipment such as welding, marking and additive manufacturing. In all of these application areas, there is a need for a laser processing apparatus in which the beam parameter product of the laser can be varied and the diameter of the focused laser beam on the material being processed can be varied.

[0009] It is an object of the present invention to provide an apparatus and a method for laser processing of materials which reduce the above-mentioned problems. Summary of the invention

[0010] According to one non-limiting embodiment of the present invention, there is provided an apparatus for laser processing of a material, the apparatus comprising a laser and a beam transmission cable, wherein:

[0011] The laser is connected to the beam delivery cable;

[0012] a beam delivery cable configured to deliver laser radiation emitted from the laser; and

[0013] Laser radiation is defined by the beam parameter product;

[0014] And the device is characterized in that:

[0015] The device comprises at least one extrusion mechanism comprising a periodic surface defined by a pitch;

[0016] a length of optical fiber forming part of a laser and / or beam delivery cable is positioned adjacent to the periodic surface; and

[0017] The squeezing mechanism is configured to squeeze the periodic surface and the length of optical fiber together with a squeezing force;

[0018] Thus, the beam parameter product can be changed by adjusting the squeezing force.

[0019] By selecting the optical fiber and by changing the squeezing force, it is possible to adjust the beam parameter product of a typical industrial laser in the range of 0.3 mm.mrad to 30 mm.mrad. Advantageously, both the beam radius and the effective numerical aperture of the laser radiation propagating along the optical fiber can be controlled by changing the squeezing force. It is also possible to adjust or switch the output beam profile of the laser radiation, for example from a bell-shaped Gaussian beam profile to a top hat beam profile or an annular profile; this is very desirable for many laser cutting applications. The present invention allows greater freedom in optimizing material processes such as cutting. The focal spot size and divergence can be optimized for each sheet metal type and thickness. The device can be set to produce laser radiation with high beam quality (low beam parameter product) for punching metal and for cutting stainless steel, and laser radiation with low beam quality (higher beam parameter product) for cutting thicker mild steel. In the former case, when focused on the material, the diameter of the laser radiation should be smaller and the divergence lower than the latter.

[0020] The periodic surface may be chirped.Changing the pitch along the length of the squeezing mechanism, either monotonically or in a non-monotonic manner, can reduce the amount of squeezing force required to obtain a desired beam parameter product or output beam profile, thereby improving reliability.

[0021] The squeezing mechanism may include at least two periodic surfaces arranged at an angle to each other. The periodic surfaces may have the same spacing. The angle may be a right angle. The angle may be 60 degrees. The squeezing mechanism may enable one of the periodic surfaces to be squeezed on the optical fiber with a squeezing force different from that of the other periodic surface. The spatial phase of the periodic surface may be configured so that when the squeezing force is applied to the periodic surface, the optical fiber is deformed in a substantially spiral manner. The squeezing force may enable the optical fiber to be pulled through the periodic surface with a force less than 1N, resulting in improved mechanical reliability.

[0022] The device may include a plurality of pressing mechanisms. Having more than one pressing mechanism reduces the pressing force required on each pressing mechanism, thereby increasing reliability.

[0023] At least one of the squeezing mechanisms may have a different pitch than another squeezing mechanism. The different pitches enable coupling between different guided mode groups in the optical fiber. Combining squeezing mechanisms with different pitches provides greater control over the output beam parameter product and the output beam profile.

[0024] The pressing mechanism may be a linear pressing mechanism. This is advantageous if space is at a premium.

[0025] The squeezing mechanism may comprise a cylinder. The optical fiber may be wound around the cylinder. The squeezing force may be applied along the axis of the cylinder. This provides a compact arrangement, makes it easier to apply squeezing force on a longer length of optical fiber than with a linear squeezing mechanism, and allows the use of more than one turn of optical fiber. This enables less squeezing force to be applied, thereby improving long term reliability. The cylinder also helps reduce optical losses in the optical fiber when squeezed.

[0026] The pitch can vary along the radius or circumference of the cylinder. This enables chirped long-period gratings to be fabricated.

[0027] The optical fiber may have a core with a diameter of at least 10 μm. The diameter may be at least 15 μm. The diameter may be at least 50 μm.

[0028] The optical fiber may include glass having an outer diameter of less than or equal to 100 μm. The outer diameter may be less than or equal to 80 μm. In the prior art, the glass diameter of optical fibers used in equipment for laser processing materials exceeds 125 μm. Reducing the diameter enables the optical fiber to be deformed more easily. Reducing the diameter also enables a spacing of 0.5 mm or less to be obtained, thereby enabling coupling between modes with greater propagation constant differences. Therefore, the smaller glass diameter provides a useful advantage over the prior art.

[0029] The spacing may be less than or equal to 8 mm. The spacing may be less than or equal to 6 mm. The spacing may be less than or equal to 5 mm. The spacing may be in the range of 0.5 mm to 4 mm.

[0030] The optical fiber may include a core supporting a first optical mode having a propagation constant β1 and a second optical mode having a propagation constant β2, and when a squeezing force is applied, the spacing is selected to couple the first optical mode to the second optical mode. The spacing may be equal to 2π / (β1–β2). The squeezing mechanism may deform the optical fiber along its length, the deformation may be defined by a symmetry, and the symmetry may be selected so that it couples the first optical mode to the second optical mode. The squeezing mechanism may be configured such that the output of the optical fiber can be switched from the first optical mode to the second optical mode by changing the squeezing force.

[0031] The optical fiber may include one core supporting a first optical mode with a propagation constant β1 and at least one satellite core supporting a second optical mode with a propagation constant β2, and the spacing is selected to couple the first optical mode to the second optical mode. There may be at least two satellite cores surrounding the core. There may be at least four satellite cores surrounding the core. The satellite cores may be ring cores. The spacing may be equal to 2π / (β1–β2). The squeezing mechanism may deform the optical fiber along its length. The deformation may be defined by a symmetry, and the symmetry may be selected to enable the first optical mode to couple to the second optical mode.

[0032] The apparatus may include a transition optical fiber including a central core and at least one satellite core. The satellite cores may be configured to expand the beam diameter of laser radiation propagating in the first optical mode in a different proportion than the expansion of the beam diameter of laser radiation propagating in the second optical mode. There may be at least four satellite cores. The satellite cores may be ring cores.

[0033] The device may include a beam delivery fiber including a central core, the beam delivery fiber including an output end from which laser radiation is emitted. The beam delivery fiber may include a base. The beam delivery fiber may include an annular core surrounding the central core. The device may include a cone, wherein the cone causes the diameter of the central core to increase toward the output end. The device may include two squeezing mechanisms. The second squeezing mechanism may have a periodic surface defined by a pitch, and the periodic surface of the second squeezing mechanism may be applied to the beam delivery fiber. The pitch of the second squeezing mechanism may be greater than the pitch of the first squeezing mechanism.

[0034] The beam delivery fiber may support a fundamental mode with a propagation constant β1 and a second-order optical mode with a propagation constant β2, and the pitch of the second squeezing mechanism is longer than 2π / (β1-β2), and thus the second squeezing mechanism does not couple the fundamental mode and the second-order mode together.

[0035] The spacing of the second squeezing mechanism can be selected to couple higher order modes that can propagate together in the beam delivery fiber, thereby producing a more uniform output beam profile.

[0036] The apparatus may include a lens system positioned to receive laser radiation from the beam delivery cable.The lens system may enable the diameter of the focal spot on the material to be varied.

[0037] The squeezing mechanism may include an actuator.

[0038] The apparatus may comprise a computer, and wherein at least one of the lens system and the actuator is controlled by the computer. The computer may comprise a memory comprising information about material parameters. Preferably, the memory comprises information enabling the lens system and / or the actuator signals to be selected depending on the material parameters, which may comprise the type of material and its thickness. This is a particularly useful aspect of the invention, as it allows the divergence of the laser radiation and the diameter of the focal spot to be controlled by controlling the lens system and the signals to the actuator. Thus, the invention allows automatic tuning of relatively expensive industrial lasers over a wide range of laser processing parameters depending on the material being processed.

[0039] The use of more than one squeezing mechanism simplifies the automated control of the laser radiation parameters. In addition, the use of different squeezing mechanisms on optical fibers with different guiding properties improves the range of control that can be applied.

[0040] The apparatus may include a processing head configured to receive laser radiation from the optical fiber.

[0041] The device may include a first optical fiber and a second optical fiber, the first optical fiber having a first core diameter and the second optical fiber having a second core diameter larger than the first diameter. The second optical fiber may be located between the processing head and the first optical fiber. A first squeezing mechanism may be applied to the first optical fiber and a second squeezing mechanism may be applied to the second optical fiber, so that in use, the spot size of the laser radiation propagating in the first optical fiber can be changed using the first squeezing mechanism, and the profile of the laser radiation can be changed using the second squeezing mechanism. This configuration enables the beam parameter product to be controlled to a large extent independently of the output beam profile. Different beam parameter products with the same output beam profile can be achieved. Thus, for example, it is possible to output a top-hat beam profile with a beam parameter product between 4 and 100 using the device.

[0042] The device may include a vibrating element attached to or forming part of a beam transmission cable. The vibrating element may be configured to vibrate the beam transmission cable. This is advantageous for removing laser speckle from laser radiation. The vibrating element may be a piezoelectric element or an electromagnetic element.

[0043] The present invention also provides a method for laser processing of materials, the method comprising providing a laser and a beam transmission cable, wherein the beam transmission cable is configured to transmit laser radiation from the laser, and the laser radiation is defined by a beam parameter product; the device comprises at least one squeezing mechanism, the squeezing mechanism comprising a periodic surface defined by a spacing; a section of optical fiber constituting a part of the laser and / or the beam transmission cable is positioned adjacent to the periodic surface; and the squeezing mechanism is configured to squeeze the periodic surface and the section of optical fiber together with a squeezing force; and the squeezing force is adjusted to change the beam parameter product.

[0044] The method may include the steps of providing a lens system and positioning the lens system to receive laser radiation from a beam delivery cable.

[0045] The lens system may enable a diameter of a focal spot on the material to be varied, and the method may comprise varying the diameter of the focal spot on the material.

[0046] In the method of the present invention, the pressing mechanism may include an actuator.

[0047] The method may comprise the steps of providing a computer, and controlling at least one of the lens system and the actuator by the computer.The computer may comprise a memory comprising information about material parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:

[0049] Figure 1 An apparatus for laser processing of materials according to the present invention is shown;

[0050] Figure 2 A squeezing mechanism having a chirped periodic surface is shown;

[0051] Figure 3 shows a squeezing mechanism comprising two periodic surfaces at right angles to each other, which enables the optical fiber to be helically deformed;

[0052] Figure 4 shows an extrusion mechanism comprising three periodic surfaces at 60 degrees relative to each other;

[0053] Figure 5 Shows Figure 4 The spatial phase between the three periodic surfaces of ;

[0054] Figure 6 showing an extrusion mechanism having a second periodic surface;

[0055] Figure 7 Shown assembled Figure 6 Extrusion mechanism;

[0056] Figure 8 The extrusion mechanism is shown in cylindrical form;

[0057] Fig. 9 An extruded surface with uniform spacing is shown;

[0058] Fig.10 An extruded surface with a chirped pitch is shown;

[0059] Fig.11 The effective refractive index of the fundamental mode and the second-order mode of the optical fiber is shown;

[0060] Fig.12 The fundamental mode of the optical fiber is shown;

[0061] Fig.13 The second order mode of the optical fiber is shown;

[0062] Fig.14 An optical fiber having a satellite core is shown;

[0063] Fig.15 Shows Fig.14 The optical mode of the optical fiber;

[0064] Fig.16 shows an optical fiber having an annular core surrounding a central core;

[0065] Fig.17 The second-order mode of the ring core is shown;

[0066] Fig.18 The pedestal fiber is shown;

[0067] Fig.19 shows an optical fiber having an annular core surrounding a central core;

[0068] Fig. 20 An example of the present invention is shown, wherein the device includes a first optical fiber, a second optical fiber, and a third optical fiber, and the diameter of the laser radiation guided by the third optical fiber can be switched within 13 μm to 100 μm by applying a squeezing force to a squeezing mechanism;

[0069] Fig.21 An example of the present invention is shown, wherein the device includes a first optical fiber and a second optical fiber, and the diameter of the laser radiation guided by the second optical fiber can be switched within 13 μm to 100 μm by applying a squeezing force to a squeezing mechanism; and

[0070] Fig. 22An example of the present invention is shown, in which the apparatus comprises a first optical fiber, a second optical fiber and a third optical fiber, and the output beam profile of the laser radiation emitted by the third optical fiber can be switched from a central beam with a beam diameter of 50 μm to an annular beam with a beam diameter of 100 μm. DETAILED DESCRIPTION

[0071] Figure 1 An apparatus 10 for laser processing of a material 11 is shown, the apparatus comprising a laser 1 and a beam transmission cable 2, wherein:

[0072] The laser 1 is connected to the beam delivery cable 2;

[0073] The beam transmission cable 2 is configured to transmit the laser radiation 13 emitted by the laser 1; and

[0074] The laser radiation 13 is defined by the beam parameter product 4;

[0075] And the device 10 is characterized in that:

[0076] The device 10 comprises at least one pressing mechanism 5 comprising a periodic surface 6 defined by a spacing 7;

[0077] a length 8 of optical fiber 9 forming part of the laser 1 and / or the beam delivery cable 2 is positioned adjacent to the periodic surface 6; and

[0078] The squeezing mechanism 5 is configured to squeeze the periodic surface 6 and the section 8 of optical fiber 9 together with a squeezing force 12;

[0079] The beam parameter product 4 can thus be varied by adjusting the contact force 12 .

[0080] The pitch 7 is the distance between consecutive maxima of the periodic surface 6 and is the inverse of the periodicity or spatial frequency of the periodic surface 6. The periodic surface 6 may be a continuous periodic surface made of a single component, such as Figure 1 Alternatively, the periodic surface 6 may comprise a plurality of components, such as wires or fingers assembled together. The wires or fingers may be adjustable so that the spacing 7 is adjustable.

[0081] Figure 1 The device 10 is shown optically coupled to a lens system 24, a processing head 3 and a focusing lens 25. The lens system 24 may include one or more lenses for collimating and / or amplifying the laser radiation 13. The processing head 3 may include one or more scanning systems for scanning the laser radiation 13 over the material 11. The focusing lens 25 may focus the laser radiation 13 to a focal point 29 on the material 11.

[0082] The beam parameter product 4 is equal to the product of half the beam diameter 2ω21 of the focused laser radiation 13 and the divergence α22. The beam parameter product 4 is a measure of the beam quality of the laser beam, which can also be expressed by its M 2 The beam parameter product 4 is equal to M 2 .λ / π, where λ is the wavelength 23 of the laser radiation 13. Single-mode fiber lasers typically have an M of about 1.1 2 . If the wavelength 23 is 1.06 μm, the beam parameter product 4 is equal to 0.35 mm.mrad. The beam parameter product 4 of the laser beam is maintained in a simple optical system including a lens without aberrations. Therefore, the beam parameter product 4 at the focus 29 is approximately the same as the beam parameter product 34 when the laser radiation 13 emerges from the output end 28 of the beam transmission cable 2 (from which the laser radiation 13 is emitted). The beam diameter 21 at the focus 29 is substantially equal to the product of the beam diameter 27 at the output end 28 of the beam transmission cable 2 and the magnification of the optical system including the lens system 24 and the focusing lens 25. The divergence 22 of the laser radiation 13 is substantially equal to the quotient of the divergence 35 of the laser radiation 13 emitted from the output end 28 of the beam transmission cable 2 and the magnification of the optical system. Therefore, if the beam diameter 21 is larger than the beam diameter 27, the divergence 22 is smaller than the divergence 35.

[0083] The laser radiation 13 is guided along the optical fiber 9, the optical fiber 19 (if present) and the beam transmission cable 2. The laser radiation 13 has a guided beam profile 38 and a guided beam diameter 39 which can be adjusted or switched by the squeezing mechanism 5. Figure 1 As shown, the guided beam profile 38 at the output of the laser 1, depicted as an approximately Gaussian beam profile, has been adjusted to become the output beam profile 14, depicted as having a top-hat beam profile. The output beam diameter 27 is shown to be larger than the guided beam diameter 39.

[0084] By selecting the optical fiber 9 and the squeezing mechanism 5, and by varying the squeezing force 12, it is possible to adjust the beam parameter product 4 of a typical industrial laser within a range of 0.3 mm.mrad to 30 mm.mrad. Advantageously, both the beam diameter 27 and the divergence 35 can be controlled by selecting the squeezing force 12. It is also possible to adjust or switch the output beam profile 14 of the laser radiation 13, for example from a Figure 1 The bell-shaped Gaussian beam profile of the guided beam profile 38 shown in FIG. 3 is transformed into a top-hat beam profile (such as Figure 1) or to an annular profile. The ability to adjust or switch the output beam profile 14 is very desirable for many laser cutting applications. Being able to change the output beam profile 14 is desirable in many laser material processing applications. For example, a Gaussian profile may be advantageous for punching material 11, and a top hat profile or annular profile may be advantageous for cutting material 11. Different output beam profiles 14 are advantageous for different applications, and the optimal output beam profile will depend on the material 11 and its thickness 26.

[0085] The lens system 24 may include collimating optics, a variable beam expander and / or a telescope. The lens system 24 may be configured to vary the diameter 21 of the focused laser radiation 13 on the material 11. The use of the squeezing mechanism 5 in conjunction with the lens system 24 enables the divergence 22 of the laser radiation 13 and the beam diameter 21 of the laser radiation 13 to be varied independently. This is an attractive feature that allows the device to provide a high beam quality (M 21) with a small diameter 21. 2 <4), medium beam quality with medium beam diameter 21 (M 2 between 10 and 20), and low beam quality (M 2 Greater than 30). Furthermore, it is possible to produce a small beam diameter 21 with medium beam quality or low beam quality, and a medium beam diameter 21 with low beam quality or high beam quality. This flexibility allows much greater freedom in optimizing material processes such as cutting. The focal spot size and divergence can be optimized for each sheet metal type and thickness. The device can be set to produce laser radiation 13 with high beam quality (low beam parameter product 4) for cutting stainless steel, and low beam quality (higher beam parameter product 4) for cutting mild steel with a thickness of 26. In the former case, the beam diameter 21 of the laser radiation 13 when focused on the material 11 should be smaller and have a lower divergence than in the latter case.

[0086] The invention is advantageous for cutting metals with lasers. The laser 1 may be a fiber laser, a disk laser or a solid state laser. The laser 1 may be defined by an output power in the range of 500W to 20kW.

[0087] In one experiment, laser 1 was a 3kW ytterbium-doped fiber laser. The wavelength 23 was 1.07 μm. The material 11 was stainless steel. The focused beam diameter 21 was 200 μm, and the output beam profile 14 was a top-hat profile. When cutting stainless steel having a thickness 26 in the range of 2 mm to 8 mm, a higher cutting speed and better cutting quality were obtained with a beam parameter product 4 of approximately 3.0 mm.mrad than with a beam parameter product 4 of approximately 4.8 mm.mrad. In contrast, when material 11 was mild steel having a thickness 26 in the range of 15 mm to 30 mm, better results were obtained with a beam parameter product 4 of approximately 4.8 mm.mrad than with a beam parameter product 4 of 3.0 mm.mrad. The output beam profile 14 was a top-hat profile. The lower beam quality (higher beam parameter product 4) for mild steel improves the quality of the cut edge surface and reduces the surface roughness.

[0088] The laser cutting process begins with punching the material 11 with laser radiation 13. It is advantageous to use a smaller beam diameter 21 with a lower divergence 22 at the focus 29 when punching than when cutting. The output beam profile 14 is preferably a bell-shaped profile such as a Gaussian profile. This improves the quality and speed of the punching. When punching all metals, the beam parameter product 4 should be less than 3 mm.mrad, preferably less than 1 mm.mrad, and more preferably less than 0.5 mm.mrad.

[0089] The advantage of being able to select the beam diameter 27, divergence 35 and output beam profile 14 emitted at the output end 28 of the beam delivery cable 2 enables different beam diameters 21 and divergences 22 to be selected at a focal point 29 that may be above the material 11, within the material 11 or below the material 11. For example, for stainless steel, the focal point 29 may be below the material 11 so that the laser radiation 13 converges at the material 11, while for mild steel, the focal point 29 may be above the material 11 so that the laser radiation diverges at the material 11. Being able to achieve this by adjusting one or more of the squeezing mechanisms 5 is a major advantage over the prior art as it provides a lower cost and simpler system than alternatives that include adjusting the magnification of the focusing optics.

[0090] After punching, the assist gas blows the molten metal and chips out of the punch outlet. At this stage, the beam diameter 28 and divergence 35 can be increased to provide the optimal beam diameter 21 and divergence 22 at the focal point 29. The resulting beam parameter product 4 can be selected depending on the material 11 being processed.

[0091] The pressing mechanism 5 preferably has an opposing periodic surface 42. The periodic surface 6 and the opposing periodic surface 42 are preferably in phase with each other, such as Figure 1As shown. Therefore, when the periodic surface 6 and the opposing periodic surface 42 are squeezed against the optical fiber 9, the optical fiber 9 acts as a spring and bends periodically along its length, so that the strain energy of the optical fiber 9 is minimized. The bend of the optical fiber 9 will have the same pitch 7 as the periodic surface 6, but may include additional harmonics at a higher spatial frequency than the periodicity of the periodic surface 6. As the squeezing force 12 increases, the bend of the optical fiber 9 also increases until the optical fiber 9 is clamped between the periodic surface 6 and the opposing periodic surface 42. Further increases in the squeezing force 12 will cause squeezing stresses through the optical fiber 9.

[0092] The periodic surface 6 and the opposing periodic surface 42 may have a non-zero phase relative to each other. This design may introduce additional harmonics into the deformation of the optical fiber 9, which may induce coupling between additional optical modes supported by the optical fiber 9.

[0093] The phase between the periodic surface 6 and the opposite periodic surface 42 may be anti-phase, so that the optical fiber 9 is clamped between the periodic surface 6 and the opposite periodic surface 42. Mode coupling is then induced by the periodic perturbation caused by the photoelastic effect.

[0094] Figure 1 The device in FIG. 1 is shown with a second squeezing mechanism 15, which includes a periodic surface 16 defined by a spacing 17. The periodic surface 16 can be squeezed against a section 18 of optical fiber 19. The use of the second squeezing mechanism 15 can reduce the squeezing force 12 required to obtain the desired beam diameter 27, divergence 35 and output beam profile 14, thereby reducing the risk of fiber 9 breakage and improving mechanical reliability. The second squeezing mechanism 15 can also be used to couple higher order optical modes together, in which case the spacing 17 is preferably longer than the spacing 7.

[0095] like Figure 1 As shown, the periodic surface 16 can be chirped, that is, its pitch 17 can vary along the length of the second squeezing mechanism 15. The pitch 17 can vary in a monotonic manner (as shown) or in a non-monotonic manner. The chirp reduces the amount of squeezing force 12 required to obtain the desired beam parameter product 4 or output beam profile 14, thereby improving reliability. Figure 2 An example of a chirped second squeezing mechanism 15 is shown. The second squeezing mechanism 15 has opposing periodic surfaces 41, and an optical fiber 19 (not shown) is squeezed between the periodic surface 16 and the opposing periodic surface 41. The squeezing force 12 may be applied via at least one hole 43, which may be a threaded hole. The opposing periodic surface 41 may be fixed in place using a fixing screw installed through at least one hole 44.

[0096] The periodic surface 16 and the opposing periodic surface 41 are preferably in phase with respect to each other, such as Figure 1Therefore, when the periodic surface 16 and the opposite periodic surface 41 are pressed against the optical fiber 19, the reference Figure 1 As shown, the optical fiber 19 acts as a spring and bends along its length so that the strain energy of the optical fiber 19 is minimized. The bend will have the same pitch 17 as the periodic surface 16, but may include additional harmonics that are desired to couple together the additional modes guided by the optical fiber 19. As the squeezing force 12 increases, the bending of the optical fiber 19 also increases until the optical fiber 19 is clamped between the periodic surface 16 and the relative periodic surface 41. Further increases in the squeezing force 12 will cause further squeezing stress through the optical fiber 19. Alternatively, the periodic surface 16 and the relative periodic surface 41 may have a non-zero phase relative to each other. Such a design may introduce additional harmonics into the deformation of the optical fiber 19, which may cause coupling between additional optical modes supported by the optical fiber 19. The phase between the periodic surface 16 and the relative periodic surface 41 may be anti-phase, so that the optical fiber 19 is clamped between the periodic surface 16 and the relative periodic surface 41. The mode coupling is then caused by the periodic perturbations caused by the photoelastic effect.

[0097] The pressing mechanism 5 may comprise two periodic surfaces 6 arranged at an angle 45 to each other, such as Figure 3 As shown in the extrusion mechanism 40 shown in FIG. Each periodic surface 6 has an opposite periodic surface 42 of the same or similar design. Figure 1 and Figure 2 As described, the periodic surfaces 6 may have the same phase as their respective opposite periodic surfaces 42. When each periodic surface 6 is squeezed against the optical fiber 9, the section of optical fiber 9 acts as a spring and deforms along its length. The periodic surfaces 6 of the squeezing mechanism 40 may have the same spacing 7 as each other or different spacing 7 from each other. The angle 45 may be a right angle. The squeezing mechanism 40 is shown in cross section, where the optical fiber 9 is shown as offset from the centerline of the squeezing mechanism 40 by one periodic surface 6.

[0098] The squeezing mechanism 40 can enable each periodic surface 6 to be squeezed against the optical fiber 9 with a different squeezing force 12. The spatial phases of the two periodic surfaces 6 can be 90 degrees out of phase with each other, so that when the squeezing force 12 is applied to the two periodic surfaces 6, the optical fiber 9 can be deformed in a generally helical manner. Figure 1 and Figure 2 As described, the optical fiber 9 will act as a spring and deform so as to minimize its strain energy. Therefore, the deformation of the optical fiber 9 may not be a precise spiral, but may contain harmonics. These harmonics may be beneficial in coupling between certain optical modes guided by the optical fiber 9. This arrangement provides great control over which guided modes of the optical fiber 9 are coupled to which guided modes.

[0099] The pressing mechanism 5 may include an odd number of periodic surfaces 6 arranged at an angle 51 to each other, such as Figure 4 The angle 51 is preferably the product of 180 degrees and (n-2) / n, where n is the number of periodic surfaces 6. Figure 5 As shown, the periodic surfaces 6 preferably have a relative spatial phase 55 with respect to each other which is equal to 360 degrees divided by the number of periodic surfaces 6. The odd number is preferably 3 and the angle 51 is preferably 60 degrees. Figure 5 The length of the extrusion mechanism 50 is shown. Figure 4 The amplitudes 52, 53, 54 of each of the three periodic surfaces 6 shown in FIG. The periodic surfaces 6 have a relative spatial phase 55 of 120 degrees relative to each other. When each of the periodic surfaces 6 is pressed against the optical fiber 9, the section of optical fiber 9 acts as a spring and deforms in a generally helical manner along its length. As shown in FIG. Figure 1 , 2 As described with respect to 3, the optical fiber 9 will act as a spring and deform so as to minimize its strain energy. Therefore, the deformation of the optical fiber 9 along its length may not be an exact helical shape, but may contain harmonics of the helical periodicity (defined as the inverse of the pitch 7). These harmonics may be advantageous in coupling between certain optical modes guided by the optical fiber 9.

[0100] The squeezing mechanism 5 may be a reference Figure 6 The extrusion mechanism 60 shown in FIG. 1 includes at least three components 66, each component 66 having a second periodic surface 61 designed to be aligned with a periodic surface 6 of another component 66. Figure 4 and Figure 5 As mentioned, the three periodic surfaces 6 preferably have a relative spatial phase 55 of 120 degrees relative to each other. In order for the components 66 to be assembled together, the second periodic surface 61 of each of the components 66 has a relative spatial phase 55 of 120 degrees relative to the periodic surface 6 of the same component 66. Figure 7 An arrangement is shown in which three components 66 have been assembled together and a compressive force 12 is applied. The optical fiber 9 is shown as being bent by one of the components 66. Other arrangements of assembling the components 66 together are possible, including where one of the second periodic surfaces 61 is pressed against the optical fiber 9. Experimentally, it has been observed that the LP guided by the optical fiber 9 01 mode can be preferentially coupled to the LP 31 and LP 32 This may be due to the three-fold symmetry of the squeezing mechanism 50. Advantageously, in order to achieve the fundamental mode LP guided by the optical fiber 9 01 Similar mode coupling levels of Figures 3 to 7The squeezing force in the squeezing mechanism 40, 50, 60 needs to be much smaller than the reference Figure 2 The squeezing force 12 of the second squeezing mechanism 15 is shown. In the experiment, the squeezing force 12 is small enough so that the optical fiber 9 can be squeezed out with a force less than 1N. Figure 7 The squeeze mechanism shown in FIG. 1 is pulled despite the presence of a large amount of mode coupling. The ability to reduce the squeeze force 12 to achieve the same level of mode coupling improves reliability.

[0101] The device may include a plurality of pressing mechanisms 5. Including a plurality of pressing mechanisms can reduce the pressing force 12 required on each of the pressing mechanisms 5, thereby improving reliability.

[0102] At least one of the squeezing mechanisms 5 may have a different pitch 7 than another of the squeezing mechanisms 5. The different pitches 7 induce coupling between different sets of guided modes in the optical fiber 9. Combining squeezing mechanisms 5 with different pitches 7 provides greater control over the output beam parameter product 4 and the output beam profile 14.

[0103] The squeezing mechanism 5 may be, for example, Figures 1 to 4 , 6 and 7. This is advantageous if space is at a premium.

[0104] The squeezing mechanism 5 may include Figure 8 The cylinder 81 is shown. The optical fiber 9 (not shown) can be wound around the cylinder 81. The compressive force 12 can be applied along the axis of the cylinder 81, for example by compressing the optical fiber 9 with the ring 82. The ring 82 is shown as having opposite periodic surfaces 42, but this is not necessarily the case. The spacing 7 can be uniform or chirped, respectively. Fig. 9 and Fig.10 The top surface of an example of a periodic surface 6 is shown in FIG. 8 , where each period is shown by line 83. The periodic surface 6 can be configured as follows: Figure 8 The cylinder 81 may be circular or elliptical. Other shapes are also possible. The spacing 7 may vary along the radius 84 of the circumference 85 of the cylinder 81. This enables chirped long period gratings to be manufactured.

[0105] The squeezing mechanism 5 in the form of a cylinder 81 provides a compact arrangement, making it easier to apply the squeezing force 12 to a longer section 8 of optical fiber 9 than with a linear squeezing mechanism, and allows the use of more than one turn of optical fiber 9. This enables a smaller squeezing force 12 to be applied, thereby improving long-term reliability. It also helps to reduce optical losses in the optical fiber 9 when being squeezed.

[0106] Optical fiber 9 and / or optical fiber 19 may be a reference Fig.11First optical fiber 90 is shown. First optical fiber 90 has a core 91, a glass cladding 94 and a polymer coating 95. Core 91 preferably has a diameter 92 of at least 10 μm. Diameter 92 may be at least 15 μm. Diameter 92 may be at least 50 μm. Increasing core diameter 92 enables first optical fiber 90 to guide more and more optical modes.

[0107] The core 91 has a refractive index 96 greater than the refractive index 99 of the glass cladding 94. Preferably, the optical fiber 9 supports at least Fig.12 The base model 121 shown and the reference Fig.13 The second order mode 122 is shown. The fundamental mode 121 may be an LP mode occurring in two orthogonal polarization states. 01 The second order mode 122 may be an LP mode that can occur in two directions. 11 Therefore, there are two fundamental modes 121 and four second-order modes 122, respectively. Fig.12 and 13 shown.

[0108] LP 01 and LP 11 The module is more generally described as LP p,q modulus, where p is the azimuthal modulus and q is the radial modulus. 2p is the number of lobes around the azimuth, and q is the number of lobes along the radius. Therefore, LP 01 The mode has zero lobes around the azimuth and one lobe along the radius. 11 The mode has two lobes around the azimuth and one lobe along the radius. If the overlap integral of the product of the electric field of the first mode and the electric field of the second mode integrated over the section 8 of optical fiber 9 due to the perturbation of the optical fiber 9 caused by the squeezing mechanism 5 is non-zero, then the squeezing mechanism 5 couples the first mode to the second mode. As described below, this places requirements on the propagation constants of the first and second modes and the periodicity of the periodic surface 6. It also places requirements on the symmetry of the electric fields of the first and second modes compared to the perturbation of the optical fiber.

[0109] Reference Fig.11 , the fundamental mode 121 has an effective refractive index 97 of β1 / k, and the second-order mode 122 has an effective refractive index 98 of β2 / k, where β1 and β2 are propagation constants of the fundamental mode 121 and the second-order mode 122, respectively, and k is a wave number related to the wavelength 23 of the laser radiation 13 by k=2π / λ. It is useful to consider the difference in propagation constants Δβ=β1–β2. In order to make reference to Figures 1 to 7 The squeezing mechanism 5 shown in FIG. 01 Mode coupling to LP 11To obtain a mode, there needs to be a spatial frequency component in the deformation of the fiber 9 along its length that is equal to Δβ / 2π. This occurs if the periodicity (defined as the inverse of the pitch 7) is equal to Δβ / 2π, or a harmonic of the periodicity is equal to Δβ / 2π. However, it is also important to consider the symmetry of the perturbation of the fiber 9 compared to the optical mode.

[0110] If p is not zero, then each LP guided by the core of the optical fiber 9 p,q The azimuthal dependence of the electric field of the mode can be expressed as follows:

[0111] E(r,θ)=E(r).cos(pθ)

[0112] E(r,θ)=E(r).sin(pθ)

[0113] where E(r) is the radial dependence of the electric field, and cos(pθ) and sin(pθ) represent Fig.13 (for p=1) in the two directions shown.

[0114] When the optical fiber 9 or optical fiber 19 has a uniform spacing along its length (e.g., such as where the spacing 7 is uniform along the length 8) Figure 1 and Figure 2 When the linear sinusoidal bending is caused by the linear compression mechanism shown, then by symmetry considerations, when the spacing 7 is equal to 2π / Δβ, only one of the two directions will be coupled. This assumes Fig.13 The second-order mode 122 in is degenerate. More generally, if p is an odd integer and the spacing 7 is equal to 2π / (β A – Beta B ), then the LP guided by the core 01 Mode can be coupled to LP guided by the same core p,q Module, where β A and β B is the propagation constant of the optical modes being coupled together. However, unless significant harmonics are present in the sinusoidal bending, the LP 11 The coupling of the modes will be strongest. If p is an even integer, then the symmetry of the perturbation is not correct. By a similar symmetry argument, if the fiber has a sinusoidal bend along its length, then the linear squeezing mechanism will not pull the LP 01 Mode coupling to LP 0q As described below, the LP guided by the central core 01 The mode and other optical modes can also couple to the optical modes guided by the satellite cores adjacent to the central core. This coupling occurs if the overlap integral mentioned above is not zero.

[0115] If the periodic surface 6 and the opposing periodic surface 42 are in anti-phase (with Figure 1), the fiber 9 will be compressed periodically along its length. Mode coupling will then be induced via the photoelastic effect. By symmetry considerations, LP 01 Mode will not couple to LP 11 module, because the symmetry is incorrect. However, if the spacing 7 is equal to 2π / (β A – Beta B ), where β A and β B is the propagation constant of the optical modes coupled together, then LP 01 mode can couple to LP 21 mode, or more generally coupled to the LP p,q modes, where p = 2, 4, 8, etc. However, this arrangement is generally not preferred because the squeezing force 12 required to obtain appreciable mode coupling is generally much greater than when the periodic surface 6 and the opposing periodic surface 42 are as shown in FIG. Figure 1 The required extrusion force 12 when in phase is shown.

[0116] When the optical fiber 9 or the optical fiber 19 has (for example, Figure 3 , 4 , 6 and 7) when the spiral deformation is caused by one of the extrusion mechanisms shown in Figure 6, then when the spacing 7 is equal to 2π / Δβ, LP 01 The mode can be coupled to the LP in two directions by symmetry argument p,q However, if p is an even integer, then LP 01 Modes will not couple, or LP 01 Mode will not couple to LP 0q Therefore, Figure 3 , 4 , 6 and 7 provide a mode coupling amount that is at least Figure 1 and Figure 2 The squeezing mechanism shown in provides twice the amount of mode coupling. Figure 5 As discussed, the compression mechanism 60 includes three components 66 that deform the first optical fiber 90 into a helical shape. 01 Mode coupling to LP 31 and LP 32 This means that there is a triple azimuthal perturbation along the first optical fiber 90 caused by the squeezing mechanism 60 that provides the required symmetry for coupling.

[0117] As before, if the periodic surface 6 and the opposing periodic surface 42 of the squeezing mechanism 40, 50 and 60 are anti-phase, so that the optical fiber 9 is periodically compressed along its length, the mode coupling is between different optical modes. From the perspective of symmetry, LP 01 mode will couple to the LP 0qThis arrangement is generally not preferred because it requires a greater extrusion force 12 for comparable effect.

[0118] Once from LP 01 Mode coupling, light can more easily couple or scatter into other higher-order modes because (i) the difference in propagation constants between these modes, Δβ, is usually smaller than that of the LP 01 The difference in propagation constant between the mode and the first mode to which it couples, Δβ, and (ii) statistically, there will be perturbations in the optical fiber 9 occurring at longer spatial frequencies than the periodicity.

[0119] Therefore, refer to Figure 3 , 4 The spiral extrusion mechanism 30, 40, 50, 60 shown in , 6 and 7 in which the optical fiber 9 is perturbed in a spiral manner is advantageous because it is similar to the reference Figure 1 and Figure 2 The linear squeezing mechanism shown couples more mode orientations together than the one shown, and further, the squeezing force 12 required to provide the coupling and thus the maximum bending of the fiber 9 is smaller, which results in less stress applied to the fiber 9 and thus higher reliability. Experimentally, it has been observed that the fiber 9 can be pulled from a fiber such as Figure 7 Where the spiral squeeze mechanism and the linear squeeze mechanism induce similar levels of mode coupling in the optical fiber 9, this is much less than that obtained from, for example, Figure 2 The linear squeezing mechanism shown pulls the required pulling force on the optical fiber 9. Therefore, a smaller squeezing force 12 is applied to the optical fiber in the spiral squeezing mechanism, which means higher mechanical reliability.

[0120] like Fig.14 As shown, optical fiber 9 and optical fiber 19 may have at least one satellite core 141 adjacent to core 91. Second optical fiber 140 has four satellite cores 141 symmetrically spaced around core 91. Each satellite core 141 may have a refractive index 142 and a diameter 143 such that the reference Fig.15 The optical mode 151 shown has the same Fig.11 and Fig.13 The effective refractive index β2 / k 98 of the second order mode 122 is shown to be substantially the same as the effective refractive index 143. Then, the optical mode 151 will resonantly couple to the second order mode 122. The resonant coupling is Fig.15 Therefore, refer to Figure 1 , 2 , 3, 4, 6 and 7 shown in the squeezing mechanism 5 can be configured to LP core 91 01 Mode coupled to LP core 91 11 mode, and then the LP of the core 91 11mode will be coupled to the optical mode 151 of the satellite core 141. Alternatively or additionally, if reference is made to Figure 1 , 2 , 3, 4, 6 and 7 shown in the squeezing mechanism 5 is applied to the second optical fiber 140, the squeezing force 12 can be selected, such as to cause the LP 01 Direct coupling of the fundamental mode 121 to the optical mode 151 of the satellite core 141, even if the design of the core 91 is such that the core 91 does not support the second-order LP 11 mode. As discussed above, if the optical fiber 9 is deformed sinusoidally in a linear manner, coupling will be strongest in only one azimuthal direction. If deformed in a helical manner, coupling will occur in all azimuthal directions. Advantageously, the inclusion of satellite cores 141 enables laser radiation 13 to be coupled from core 91 to satellite cores 141, thereby increasing the guided beam diameter 39 of the laser radiation 13 as it propagates along the optical fiber 9.

[0121] like Fig.16 As shown, optical fiber 9 and optical fiber 19 may be a second optical fiber 160 having an annular core 161 surrounding core 91. Annular core 161 may have a refractive index 162 and a thickness 164 such that reference Fig.17 The second order mode 171 shown has the same Fig.11 and Fig.13 The effective refractive index β2 / k 98 of the second order mode 122 is shown to be substantially the same as the effective refractive index 163. If the second order mode 122 of the core 91 is launched into the second optical fiber 160, the second order mode 122 will be resonantly coupled to the second order mode 171. Alternatively or additionally, if reference is made to Figure 1 , 2 , 3, 4, 6 and 7 shown in the squeezing mechanism 5 is applied to the second optical fiber 160, the squeezing force 12 can be selected, such as to cause the LP 01 Direct coupling of the fundamental mode 121 to the second order mode 171 of the annular core 161, even if the design of the core 91 is such that the core 91 does not support the second order LP 11 mode. According to the previous discussion, if the optical fiber 9 is deformed sinusoidally in a linear manner, coupling will be strongest in only one azimuthal direction. If deformed in a helical manner, coupling will occur in all azimuthal directions. Advantageously, the inclusion of the annular core 161 enables the laser radiation 13 to be coupled directly or indirectly from the core 91 to the annular core 161 via the second order mode 122, thereby increasing the guided beam diameter 39 of the laser radiation 13 as it propagates along the optical fiber 9.

[0122] Reference Fig.11 , 14and 16, the glass cladding 94 may have a diameter 93 between 70 μm and 500 μm. The diameter 93 may be between 70 μm and 200 μm. The diameter 93 is preferably less than or equal to 125 μm. The diameter 93 is more preferably less than or equal to 80 μm. Reducing the diameter 93 enables the optical fiber 9 to be deformed more easily. Reducing the diameter 93 also enables a spacing 7 of 0.5 mm or less to be obtained, thereby enabling coupling between modes with greater propagation constant differences. Therefore, a smaller glass diameter 93 combined with a smaller spacing 7 provides a useful advantage over the prior art.

[0123] Reference Figures 1 to 4 ,as well as Figures 6 to 10 , the spacing 7 may be less than 12 mm. The spacing 7 may be less than 5 mm. The spacing 7 may be in the range of 0.5 mm to 5 mm.

[0124] Reference Figure 1 , the optical fiber 9 or the optical fiber 19 (if present) is coupled to the beam delivery cable 2. The beam delivery cable 2 may include a reference Fig.18 The third optical fiber 180 is shown. The third optical fiber 180 has a core 181 having a diameter 182 and a refractive index 183. The third optical fiber 180 also includes a base 184 having a diameter 185 and a refractive index 186. The diameters 182 and 185 and the refractive indices 183 and 186 can be selected to maintain the ratio of the laser radiation 13 propagating in the core 91 of the optical fiber 9 or the optical fiber 19 (if present). Thus, for example, if the third optical fiber 180 is spliced ​​to Fig.14 For the second optical fiber 140 of the satellite core 141, the diameter 182 can be selected to be substantially equal to the diameter 92, and the diameter 185 can be selected to be substantially equal to or greater than the outer edge to outer edge distance 149. The refractive index 186 can be selected to be substantially equal to or greater than the refractive index 142. The refractive index 183 can be selected to be substantially equal to the refractive index 142 plus the difference between the refractive indices 96 and 99. Thus, the laser radiation 13 coupled from the core 91 of the second optical fiber 140 to one or more of the satellite cores 141 can be coupled into the base 184 of the third optical fiber 180 and propagated along the beam transmission cable 2.

[0125] The beam transmission cable 2 may include a reference Fig.19 190 is shown. The third optical fiber 190 has a core 191 having a diameter 192 and a refractive index 193. The third optical fiber 190 also includes an annular core 194 having a diameter 195, a refractive index 196, and a thickness 199. The diameters 192 and 195, the thickness 199, and the refractive indices 193 and 196 are selected to maintain the ratio of the laser radiation 13 propagating in the core 91 of the optical fiber 9 or the optical fiber 19 (if present). Thus, for example, if the third optical fiber 190 is spliced ​​to Fig.16For the second optical fiber 160, the diameter 192 can be selected to be substantially equal to the diameter 92, the thickness 199 can be selected to be substantially equal to the thickness 164, and the diameter 195 can be selected to be substantially equal to the diameter 169. The refractive index 196 can be selected to be substantially equal to or higher than the refractive index 162. The refractive index 193 can be selected to be substantially equal to the refractive index 96. Therefore, the laser radiation 13 coupled from the core 91 of the second optical fiber 160 into the ring core 161 can be coupled into the ring core 194 of the third optical fiber 190 and propagated along the beam transmission cable 2.

[0126] Refer again Figure 1 , the squeezing mechanism 5 may include at least one actuator 31. The actuator 31 may include a motor and / or an electromagnet. The actuator may include a ratchet. The application of an electrical signal may be used to provide the squeezing force 12 via the actuator 31.

[0127] The apparatus 10 may comprise a computer 32. At least one of the lens system 24 and the actuator 31 may be controlled by the computer 32. The computer 32 may comprise a memory 33 comprising information about material parameters. Preferably, the memory 33 contains information enabling the signals driving the lens system 24 and / or the at least one actuator 31 to be selected depending on the parameters of the material 11. The parameters may comprise the type of material and its thickness 26. This is a particularly useful aspect of the invention as it allows the divergence 22 of the laser radiation 13 and the diameter 21 of the focused laser radiation 13 to be controlled by controlling the lens system 24 and the signals to the actuator 31. Thus, the invention allows the automatic tuning of a relatively expensive industrial laser 1 over a wide range of laser 1 processing parameters depending on the material being processed.

[0128] Example 1

[0129] Fig. 20 A first example of the present invention is shown. Figure 1 The extrusion mechanism 5 shown in FIG. Fig.11 The first optical fiber 90. The fiber core 91 supports Fig.12 The base model 121 and Fig.13 The fundamental mode 121 propagates in the core 91 as indicated above and below the first optical fiber 90 at point A. The core 91 has a diameter 92 of the order of 15 μm and a refractive index 96 that is 0.0034 greater than the refractive index 99 of the cladding. The squeezing mechanism 5 has a spacing 7 that matches the difference in effective refractive indices 97 and 98 of the fundamental mode 121 and the second-order mode 122, such that the spacing 7=2π / Δβ. By adjusting the squeezing force 12 applied by the squeezing mechanism 5, the laser radiation 13 output by the first optical fiber 90 can be adjusted as shown in FIG. Fig. 20Switching between the fundamental mode 121 and the second-order mode 122 indicated above and below the first optical fiber 90 at point B is also possible. Switching between combinations of the fundamental mode 121 and the second-order mode 122 is also possible. These combinations are Fig. 20 Not shown.

[0130] The first optical fiber 90 is spliced ​​to Fig.14 The second optical fiber 140 is shown. The core 91 of the second optical fiber 140 has the same design as the core 91 of the first optical fiber 90. The four satellite cores 141 have a diameter 143 of 6.6 μm, a refractive index 142 that is the same as the refractive index 96 of the core 91, and an outer edge to outer edge distance 149 of 36.6 μm. When the squeezing mechanism 5 is adjusted so that the output of the first optical fiber 90 is the fundamental mode 121, the fundamental mode 121 is successfully coupled to the core 91 of the second optical fiber 140 and propagates along the second optical fiber 140 without coupling to other higher order optical modes. Therefore, the second optical fiber 140 emits Fig. 20 140 above the second optical fiber 140. When the squeezing mechanism 5 is adjusted so that the output of the first optical fiber 90 is the second-order mode 122, the second-order mode 122 is converted to Fig.15 The optical mode(s) 151 output from the satellite core 141 at the output end of the second optical fiber 140 are shown in FIG. The optical mode 151 is Fig. 20 1 is shown below the second optical fiber 140 at point C in FIG. Thus, the second optical fiber 140 is used as a transition fiber to expand the guided beam diameter 39 of the laser radiation 13 propagating in the fundamental mode 121 in a different proportion than the expansion of the guided beam diameter 39 of the laser radiation 13 propagating in the second-order mode 122.

[0131] The output of the second optical fiber 140 is spliced ​​to Fig.18 The third optical fiber 180 is a beam transmission fiber. The core 181 of the third optical fiber 180 has the same diameter 92 as the core 91 of the first optical fiber 90. The difference between the core refractive index 183 and the base refractive index 186 is 0.0034. The base 184 has a diameter 185 of 100um, and the difference between the base refractive index 186 and the cladding refractive index 99 is 0.014. When the squeezing mechanism 5 is adjusted to select the fundamental mode 121 in the first optical fiber 90, the output of the third optical fiber 180 has an output beam diameter 27 of 13μm, and a beam quality M of about 1.1 2This corresponds to an output beam profile 14 that is approximately Gaussian and a beam parameter product 4 of approximately 0.37 mm.mrad. When the squeezing mechanism 5 is adjusted to select the second-order mode 122 in the first optical fiber 90, the laser radiation 13 is directed primarily in the base 184 of the third optical fiber 180 as a laser beam 2001 of a combination of many higher-order modes (not shown separately). The laser beam 2001 has an output beam diameter 27 of approximately 100 μm and a beam quality M of approximately 12. 2 This corresponds to an output beam profile 14 that approximates a top-hat and a beam parameter product 4 of about 4 mm.mrad.

[0132] It is observed that the laser beam 2001 does not have a stable output beam profile 14. Therefore, referring to Figure 2 The second squeezing mechanism 15 is shown to be applied to the third optical fiber 180. The pitch 17 of the second squeezing mechanism 15 is longer than the pitch 7 of the squeezing mechanism 5 because it is desired to couple higher order optical modes propagating along the third optical fiber 180 having a closer spacing of effective refractive indexes (not shown). The use of the second squeezing mechanism 15 ensures a beam quality M of approximately 15. 2 factor, and a uniform distribution of power over the area of ​​the base 184. The beam parameter product 4 is approximately 5. Fig. 20 As shown, the laser radiation 13 emitted from the third optical fiber 180 can then be switched from an output beam profile 14 of a Gaussian profile having an output beam diameter 27 of 13 μm and a beam parameter product of 0.37 mm.mrad to an output beam profile 14 of approximately a top hat having an output beam diameter 27 of approximately 100 μm and a beam parameter product 4 of 5 mm.mrad by selecting the squeezing force 12 applied to the squeezing mechanism 5. The Gaussian profile is usually preferably used for punching the material 11 with the laser beam before cutting. The top hat profile is usually preferably used for cutting the material 11 with the laser beam 3.

[0133] Example 2

[0134] Fig.21 A second example of the invention is shown, in which the first optical fiber 90 of the first example has been replaced by a second optical fiber 140 . Figure 1 The extrusion mechanism 5 shown in FIG. Fig.14The second optical fiber 140 is shown in . The core 91 has a diameter 92 of about 15 μm and a refractive index 96 that is 0.0034 greater than the cladding refractive index 99. The core 91 can support a fundamental mode 121 with an effective refractive index 97. The four satellite cores 141 each have a diameter 143 of 6.6 μm, a refractive index 142 that is 0.003 greater than the cladding refractive index 99, and an outer edge to outer edge distance 149 of 36.6 μm. The satellite cores 141 can propagate optical modes 151 having an effective refractive index 143. The squeezing mechanism 5 has a spacing 7 designed to match the difference in the effective refractive indices 97 and 143, so that the spacing 7 = 2π / Δβ. As Fig.21 As shown, by adjusting the squeezing force 12 applied by the squeezing mechanism 5 , the fundamental mode 121 or the optical mode 151 can be selected at the output of the second optical fiber 140 .

[0135] The output end of the second optical fiber 140 is spliced ​​to Fig.18 The third optical fiber 180 has the same parameters as the third optical fiber in Example 1. When the squeezing mechanism 5 is adjusted to select the fundamental mode 121 in the second optical fiber 140, the output end of the third optical fiber 180 is substantially in the fundamental mode 121. When the squeezing mechanism 5 is adjusted to select the optical mode 151 in the second optical fiber 140, the laser radiation 13 is mainly guided in the base 184 of the third optical fiber 180 and has an output beam diameter 27 of about 100 um and a beam quality M of about 12 corresponding to a beam parameter product 4 of about 4 mm.mrad. 2 As described in Example 1, refer to Figure 2 The second squeezing mechanism 15 shown is applied to the third optical fiber 180 to stabilize the output beam profile 14 at the output end 28 of the third optical fiber 180. Fig.21 As shown, the laser radiation 13 emitted from the third optical fiber 180 can then be switched from a Gaussian profile having an output beam diameter 27 of 13 μm and a beam parameter product of 0.37 mm.mrad to an approximate top-hat profile having an output beam diameter 27 of approximately 100 μm and a beam parameter product 4 of 5 mm.mrad by selecting the squeezing force 12 applied to the squeezing mechanism 5.

[0136] Example 3

[0137] Fig. 22 A third example of the present invention is shown, in which the second optical fiber 140 of the first example has been replaced by Fig.16 The second optical fiber 160 of the first example has been replaced by the third optical fiber 180 of the reference Fig.19 The design of the first optical fiber 90 is similar to that of the first example and Fig. 20 Same as described.

[0138] The first optical fiber 90 is spliced ​​to Fig.16 The second optical fiber 160 is shown. The core 91 of the second optical fiber 160 is of the same design as the core 91 of the first optical fiber 90. The annular core 161 has an outer diameter 169 of 40 μm, a thickness 164 of 5 μm, and a refractive index 162 that is 0.0026 greater than the cladding refractive index 99. When the squeezing mechanism 5 is adjusted so that the output of the first optical fiber 90 is the fundamental mode 121, the fundamental mode 121 is successfully coupled to the core 91 of the second optical fiber 160 and propagates along the second optical fiber 160 without coupling to other higher-order optical modes. When the squeezing mechanism 5 is adjusted so that the output of the first optical fiber 90 is the second-order mode 122, the second-order mode 122 is converted to Fig.17 The second-order mode(s) 171 output from the ring core 161 at the output end of the second optical fiber 160 are shown in FIG.

[0139] Fig.19 The core 191 of the third optical fiber 190 has a diameter 192 of 50 μm. The core refractive index 193 is 0.014 greater than the base refractive index 99. The annular core 194 has an outer diameter 195 of 100 μm, a thickness 199 of 20 μm, and a refractive index 196 that is 0.014 greater than the cladding refractive index 99. The core diameter 192 is approximately 2.5 times greater than the core diameter 92 of the second optical fiber 160. Therefore, the third optical fiber must be tapered with a taper ratio of about 2.5 so that the respective transverse dimensions of the second optical fiber 160 and the third optical fiber 190 at the input end 221 of the third optical fiber 190 match.

[0140] When the squeezing mechanism 5 is adjusted to select the fundamental mode 121 in the first optical fiber 90, the output of the third optical fiber 180 has an output beam diameter 27 of 50 μm and a beam quality M of about 4 corresponding to a beam parameter product of about 1.35 mm.mrad. 2 When the squeezing mechanism 5 is adjusted to select the second-order mode 122 in the first optical fiber 90, the laser radiation 13 is guided in the annular core 194 of the third optical fiber 190 and has an output beam diameter 27 of about 100 um and a beam quality M of about 12 corresponding to a beam parameter product 4 of about 4 mm.mrad. 2 factor.

[0141] Reference Figure 2The second squeezing mechanism 15 shown is applied to the third optical fiber 190. The spacing 17 of the second squeezing mechanism 15 is longer than the spacing 7 of the squeezing mechanism 5 because it is desired to couple higher order optical modes propagating along the third optical fiber 190 having a closer spacing of effective refractive indices (not shown). The second squeezing mechanism 15 is adjusted by adjusting the squeezing force 12. When the fundamental mode 121 is selected at the output of the first optical fiber 90 by applying the squeezing force 12 to the squeezing mechanism 5, the laser radiation 13 at the output of the third optical fiber 190 has a beam quality M of about 7 corresponding to a beam parameter product 4 of about 2.36 mm.mrad. 2 The laser radiation 13 is approximately uniformly distributed in the fiber core 191. When the second-order mode 122 is selected at the output of the first optical fiber 90, the beam quality M at the output end 28 of the third optical fiber 190 is 2 The factor is about 15, which corresponds to a beam parameter product 4 of about 5 mm.mrad. The optical power is approximately uniformly distributed in the ring core 194. When a combination of the fundamental mode 121 and the second-order mode 122 is selected in the first optical fiber 90 by adjusting the squeezing force 12 applied to the squeezing mechanism 5, any relative distribution of the total power between the core 191 and the ring core 194 between about 0% and about 100% can be achieved. Fig. 22 As shown, the output beam profile 14 of the laser radiation 13 emitted from the third optical fiber 190 can then be switched from a top-hat-like profile having an output beam diameter 27 of 50 μm and a beam parameter product of 2.36 mm.mrad to a top-hat-like annular profile having an output beam diameter 27 of about 100 μm and a beam parameter product 4 of 5 mm.mrad by selecting the squeezing force 12 applied to the squeezing mechanism 5. For cutting the material 11 with the laser beam 13, an output beam profile 14 having a top-hat annular profile is generally preferred over an output beam profile 14 having a top-hat profile or a bell-shaped Gaussian beam profile. It should be noted that if it is desired to switch from a bell-shaped Gaussian profile (M 2 ~1.1) Switching to a top-hat annular profile, the cone 225 can be designed to be thermally insulated so that the fundamental mode 121 propagates along the first optical fiber 90, the second optical fiber 160, the cone 255 and the third optical fiber 190 without mode coupling.

[0142] Examples 1 and 2 both use a third optical fiber 180 and a second squeezing mechanism 15. However, these may be omitted if it is desired to switch the laser radiation 13 emitted from the device 10 from the fundamental mode 121 and the optical mode 151 of the satellite core 141. This is advantageous for certain welding applications where multiple closely spaced beams are required.

[0143] The extrusion mechanism 5 and the second extrusion mechanism 15 used in Examples 1-3 are reference Figure 1 and Figure 2The linear change. Either or both of the extrusion mechanism 5 and the second extrusion mechanism 15 can be referred to Figures 3 to 10 Preferably, the extrusion mechanism 5 and the second extrusion mechanism 15 are reference Figures 3 to 7 The spiral squeezing mechanism described. This squeezing mechanism enables a lower squeezing force 12 to be applied to achieve the same amount of mode conversion, and thereby improves reliability. This squeezing mechanism also couples optical modes of all orientations, and thus reduces the formation of hot spots sometimes seen in the output beam profile 14. When coupling between two defined optical modes such as the fundamental mode 121 and the second-order mode 122, a uniform spacing 7 or 17 is preferred. When coupling between various optical modes, such as when the second squeezing mechanism 15 is applied to the third optical fiber 180 and the third optical fiber 190 in Examples 1 to 3, a chirped spacing 7 or 17 is preferred. Preferably, the spacing 7 or 17 is longer when coupling between various higher-order optical modes than when coupling between the fundamental mode 121 and the second-order mode 122.

[0144] The use of more than one squeezing mechanism 5 simplifies the automatic control of the parameters of the laser radiation 13. The beam divergence 22, the diameter 21 and the output beam profile 14 can be controlled. In addition, the use of different squeezing mechanisms 5 with different guiding characteristics on the optical fiber 9 improves the range of control that can be applied. For example, the optical fiber 9 and the optical fiber 19 can each be Fig.11 The diameter 93 of the first optical fiber 90 may be 75 μm, so that the pitch 7 can be as small as 0.5 mm. The diameter 93 of the optical fiber 19 may be 250 μm, and the core 91 may be more multimode than the core 91 of the optical fiber 9. Then, the pitch 17 is preferably longer than the pitch 7, for example in the range of 2 mm to 8 mm. In addition, at least one of the squeezing mechanisms 5 and 15 may be Figure 3 The form shown, in which the optical fiber 9 or 19 can be deformed into a helix which can have a uniform or chirped pitch 7 or 17. It should be noted that one of these mechanisms 5 can be replaced by another mode coupling device such as a connector with an offset core.

[0145] As reference Figure 1 As shown, the device 10 may include a vibrating element 36 attached to or forming part of the beam delivery cable 2. The vibrating element 36 may be configured to vibrate the beam delivery cable 2. This may be advantageous for removing laser speckle from the laser radiation 13 or removing hot spots from the output beam profile 14 of the laser radiation 13. The vibrating element 36 may be a piezoelectric element or an electromagnetic element.

[0146] Figure 1 The optical fibers 9 and 19 shown in FIG. 1 may be reference Fig.11 , 14, 16, 18 and 19. Optical fiber 9 and optical fiber 19 may have a solid core and cladding, may have additional cores and claddings (including depressed claddings), and may have longitudinally extending holes in the core and / or cladding. This discussion focuses on LP 01 Fundamental mode to LP 11 Coupling of the Second Order Mode However, the squeezing mechanism 5, the second squeezing mechanism 15, the squeezing mechanism 40, the squeezing mechanism 50 and the squeezing mechanism 60 may be used to induce mode coupling between other optical modules.

[0147] It should be appreciated that the embodiments of the invention described above with reference to the accompanying drawings have been given by way of example only, and modifications and additional components may be provided to enhance performance. The individual components shown in the accompanying drawings are not limited to their use in the accompanying drawings, and may be used in other drawings and in all aspects of the invention. The invention also extends to the individual components mentioned and / or shown above, either alone or in any combination.

Claims

1. An apparatus for laser processing of materials, the apparatus comprising a laser and a beam transmission cable, wherein: The laser is connected to the beam delivery cable; The beam transmission cable is configured to transmit laser radiation emitted from the laser; and the laser radiation is defined by a beam parameter product; And the device is characterized in that: The device comprises at least one squeezing mechanism comprising a periodic surface defined by a pitch and a lens system; a length of optical fiber forming part of at least one of the laser and the beam delivery cable is positioned adjacent to the periodic surface; The squeezing mechanism is configured to squeeze the periodic surface and the section of optical fiber together with a squeezing force; Thus, the beam parameter product can be changed by adjusting the squeezing force; the squeezing mechanism is an adjustable squeezing mechanism operable to provide iterative adjustment of the beam parameter product and the output beam profile of the laser radiation to achieve an optimal output beam profile dependent on the laser processing to be performed on the material; as well as the lens system being positioned to receive the laser radiation from the beam delivery cable, The apparatus is configured to punch the material using laser radiation having a bell-shaped beam profile, adjust the output beam profile to a top hat or ring profile, and cut the material using laser radiation having the top hat or ring profile.

2. The device according to claim 1, characterized in that The periodic surface is chirped.

3. The device according to claim 1 or claim 2, characterized in that: The squeezing mechanism comprises at least two periodic surfaces arranged at an angle to each other, and wherein the spatial phases of the periodic surfaces are configured such that when the squeezing force is applied to the periodic surfaces, the optical fiber is deformed in a helical manner.

4. The device according to claim 1 or claim 2, characterized in that: The optical fiber includes a core supporting a first optical mode having a propagation constant β1 and a second optical mode having a propagation constant β2, and the pitch is selected to couple the first optical mode to the second optical mode when the squeezing force is applied.

5. The device according to claim 1 or claim 2, characterized in that: The optical fiber includes a core supporting a first optical mode having a propagation constant β1 and at least one satellite core supporting a second optical mode having a propagation constant β2, and the spacing is selected to couple the first optical mode to the second optical mode.

6. A method for laser processing a material, the method comprising providing an apparatus comprising a laser and a beam transmission cable, wherein: The beam transmission cable is configured to transmit laser radiation emitted from the laser; and the laser radiation is defined by a beam parameter product; The device comprises at least one pressing mechanism comprising a periodic surface defined by a pitch; a length of optical fiber forming part of at least one of the laser and the beam delivery cable is positioned adjacent to the periodic surface; as well as The squeezing mechanism is configured to squeeze the periodic surface and the section of optical fiber together with a squeezing force, whereby the beam parameter product can be changed by adjusting the squeezing force; The squeezing mechanism is an adjustable squeezing mechanism operable to provide iterative adjustment of the beam parameter product and the output beam profile of the laser radiation; as well as adjusting the squeezing force to change the beam parameter product and the output beam profile of the laser radiation emitted from the beam delivery cable to achieve an optimal output beam profile depending on the laser processing to be performed on the material, Wherein the method further comprises: providing a lens system, positioning the lens system to receive the laser radiation from the beam delivery cable, punching the material using the laser radiation having a bell-shaped beam profile, adjusting the output beam profile to a top-hat or donut profile, and cutting the material using the laser radiation having the top-hat or donut profile.

7. The method according to claim 6, characterized in that The step of selecting a diameter of a focal spot on said material is included.

8. The method according to claim 7, characterized in that The step of selecting a divergence of a focal spot on said material is included.

9. The method according to claim 6, characterized in that The step of selecting a divergence of a focal spot on said material is included.

10. The method according to claim 6, characterized in that The method comprises providing a computer, providing an actuator for providing the squeezing force, and controlling at least one of the lens system and the actuator by the computer, and wherein the computer comprises a memory comprising information about material parameters.

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