LASER MARKING SYSTEM AND METHOD

Abstract

The present application relates to a laser marking system (100) comprising a laser (110) configured to produce a laser beam, a marking head (130) configured to project the laser beam onto a target, and a negative curvature hollow core fiber (120) configured to transmit the laser beam from the laser (110) to the marking head (130).

Claims

1. A laser marking system comprising: a laser configured to produce a laser beam; a marking head configured to project the laser beam onto a target; and, a negative curvature hollow core fiber configured to transmit the laser beam from the laser to the marking head.

2. (canceled)

3. The laser marking system of claim 1, wherein the laser beam comprises infrared electromagnetic radiation.

4. The laser marking system of claim 1, claim 1, wherein the negative curvature hollow core fiber comprises chalcogenide glass.

5. The laser marking system of claim 1, comprising an umbilical between the laser and the marking head, wherein the negative curvature hollow core fiber is located within the umbilical.

6. (canceled)

7. The laser marking system of claim 1, wherein an end of the negative curvature hollow core fiber is tapered.

8.-11. (canceled)

12. The laser marking system of claim 1, comprising a coupling lens for optically coupling the negative curvature hollow core fiber to another optical component, wherein a ratio of a focal length to a diameter of an entrance pupil of the coupling lens is selected in at least partial dependence on the following equation: $F\#=0.16\pi \frac{D_{\mathrm{core}}}{\lambda }$ where F # is the ratio of a focal length to a diameter of an entrance pupil of the coupling lens, D.sub.core is a core diameter of the negative curvature hollow core fiber, and λ is a wavelength of the laser beam.

13. The laser marking system of claim 12, wherein the ratio of the focal length to the diameter of the entrance pupil of the coupling lens is selected to be within about . . . −5% and about +2% of a value of F # calculated in accordance with claim 12.

14. The laser marking system of claim 1, wherein a beam parameter product of the laser beam is in the inclusive range of about 1.0 mm mrad and about 40.0 mm mrad at the target.

15. The laser marking system of claim 1, wherein a beam parameter product of the laser beam is in the inclusive range of about 0.2 mm mrad and about 10.0 mm mrad at an output of the laser.

16. (canceled)

17. (canceled)

18. The laser marking system of claim 1, comprising an optical alignment system located between the laser and the negative curvature hollow core fiber configured to change a position and/or angle of the laser beam relative to a core of the negative curvature hollow core fiber.

19. The laser marking system of claim 18, wherein the optical alignment system comprises: a first adjustable optical element configured to receive the laser beam from the laser; a second adjustable optical element configured to receive the laser beam from the first adjustable optical element and direct the laser beam towards an input of the core of the negative curvature hollow core fiber; a first detector configured to detect a position of the laser beam relative to the second adjustable optical element; and, a second detector configured to detect a position of the laser beam relative to the input of the core of the negative curvature hollow core fiber.

20-32. (canceled)

33. The laser marking system of claim 1, comprising a first protective aperture located between the laser and the negative curvature hollow core fiber at an input of the core of the negative curvature hollow core fiber, wherein the first protective aperture has a diameter that is substantially equal to a core diameter of the negative curvature hollow core fiber.

34. (canceled)

35. (canceled)

36. The laser marking system of claim 1, wherein the laser beam comprises ultraviolet electromagnetic radiation.

37. The laser marking system of claim 36, wherein the negative curvature hollow core fiber comprises silica.

38. The laser marking system of claim 37, wherein the negative curvature hollow core fiber comprises hydrogen infused silica.

39.-44. (canceled)

45. The laser marking system of claim 1, comprising a second protective aperture located between the marking head and the negative curvature hollow core fiber at an output of the core of the negative curvature hollow core fiber, wherein the second protective aperture has a diameter that is substantially equal to a core diameter of the negative curvature hollow core fiber.

46. A method of marking a target with a laser beam comprising using the laser marking system of claim 1.

47. A method of manufacturing the laser marking system of claim 1 comprising: (a) selecting a desired laser beam spot size at the target and a desired distance between the marking head and the target; (b) selecting designing optical components of the marking head in at least partial dependence on step (a) and determining a beam parameter product of the laser beam at the target; (c) selecting first coupling optics between the negative curvature hollow core fiber and the marking head in at least partial dependence on step (b); (d) selecting a desired beam parameter product of the laser beam between the negative curvature hollow core fiber and the marking head and designing the negative curvature hollow core fiber in at least partial dependence on the beam parameter product of the laser beam between the negative curvature hollow core fiber and the marking head; (e) selecting second coupling optics between the laser and the negative curvature hollow core fiber in at least partial dependence on step (d); and, (f) selecting the laser in at least partial dependence on the beam parameter product of the laser beam between the negative curvature hollow core fiber and the marking head.

48. The method of claim 47, further comprising using forward and/or backward iteration to adjust the laser marking system.

49. A method of manufacturing a laser marking system having a laser configured to generate a laser beam and a marking head configured to project the laser beam onto a target to be marked, the method comprising: connecting the laser to the marking head using a negative curvature hollow core fiber configured to transmit the laser beam from the laser to the marking head.

50. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0097] The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labelled in every drawing. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0098] FIG. 1 schematically depicts a laser marking system according to an embodiment of the invention;

[0099] FIG. 2 schematically depicts a cross-sectional view of a negative curvature hollow core fiber according to an embodiment of the invention;

[0100] FIG. 3 shows a perspective view of portion of a laser marking system according to an embodiment of the invention;

[0101] FIG. 4 schematically depicts a perspective view of some of the internal components of the optical alignment system of FIG. 3;

[0102] FIG. 5 schematically depicts a magnified perspective view of some of the components of the optical alignment system of FIG. 4;

[0103] FIG. 6 schematically depicts a ray trace of a laser beam interacting with the components of FIG. 5;

[0104] FIG. 7 schematically depicts a perspective view of a beam sampler of an optical alignment system according to an embodiment of the invention;

[0105] FIG. 8 schematically depicts a view from the front of a detector of an optical alignment system according to an embodiment of the invention;

[0106] FIG. 9 schematically depicts a ray trace of an aligned laser beam interacting with the components of an optical alignment system according to an embodiment of the invention;

[0107] FIG. 10 schematically depicts a ray trace of a misaligned laser beam interacting with the components of the optical alignment system of FIG. 9;

[0108] FIG. 11 schematically depicts a ray trace of a laser beam interacting with the components of an alternative optical alignment system without alignment compensation according to an embodiment of the invention;

[0109] FIG. 12 schematically depicts the ray trace of FIG. 11 with alignment compensation applied by the optical alignment system;

[0110] FIG. 13 shows a method of designing a laser marking system according to an embodiment of the invention; and

[0111] FIG. 14 shows a method of manufacturing a laser marking system according to an embodiment of the invention.

DETAILED DESCRIPTION

[0112] Aspects and embodiments disclosed herein are not limited to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. Aspects and embodiments disclosed herein are capable of being practiced or of being carried out in various ways.

[0113] Aspects and embodiments disclosed herein include a marking head for projecting a radiation beam of a laser scanning or marking system and a laser scanning or marking system including such a system. Laser marking systems may be utilized in production lines for marking various types of articles. Laser marking systems may be utilized to imprint bar codes, unique identifying marks, expiration dates, or other information on items passing through a production line. In some implementations, carbon dioxide (CO.sub.2) gas lasers may be used in laser marking systems. Carbon dioxide lasers may produce beams of infrared radiation in four principal wavelength bands centering on 9.3, 9.6, 10.2, and 10.6 micrometers (μm). In other implementations, a laser configured to produce near infrared radiation may be used in laser marking systems. In alternative implementations, a laser configured to produce ultraviolet radiation may be used in laser marking systems. Lasers utilized in laser marking systems are typically operated at laser power levels in the tens of watts.

[0114] Laser scanning or marking systems are not limited to using CO.sub.2 lasers. In some implementations, fiber lasers or diode lasers may be used in laser marking systems. In some aspects and embodiments, optical scanners or markers may utilize lasers that operate in the ultraviolet, visible, or near infrared wavelengths or any other type of laser or optical illumination source. The use of visible radiation beams in laser scanner systems may be advantageous in that a user can see the laser beam where it illuminates an object being scanned so the user can adjust the position of the laser scanner or object being scanned so that the laser illuminates a desired portion of the object.

[0115] Embodiments of laser scanners disclosed herein may include a marking head comprising at least two mirror turning devices such as piezoelectric or magnet drives, direct current drives, stepper motors, servomotors, or galvanometers having mirrors attached. The mirrors used in embodiments of the laser marking system disclosed herein may be silver coated or gold-coated mirrors or any other suitably coated material. Windows and lenses used in embodiments of the laser scanner/marker disclosed herein may be, for example, germanium, zinc selenide, quartz, BK7 borosilicate glass, SUPRSIL provided by Heraeus, a German company, ultraviolet grade fused silica or any other suitable material.

[0116] FIG. 1 schematically depicts a laser marking system 100 according to an embodiment of the invention. The laser marking system 100 comprises a laser 110 configured to produce a laser beam (not shown). The laser beam may comprise infrared radiation having a wavelength of between about 8 μm and about 11 μm, e.g. about 10.6 μm. The laser beam may comprise near infrared electromagnetic radiation having a wavelength of between about 0.78 μm and about 3 μm, e.g. about 1.06 μm. The laser beam may comprise ultraviolet electromagnetic radiation having a wavelength of between about 100 nm and about 400 nm, e.g. about 265 nm or about 355 nm.

[0117] The laser marking system 100 further comprises a marking head 130 configured to project the laser beam onto a target (not shown) to be marked by the laser marking system 100. The marking head 130 may comprise an electromagnetic radiation steering mechanism (not shown) configured to steer the laser beam exiting the marking head 130. The marking head 130 may further comprise a variable optical path length assembly (not shown) configured to adjust a focal plane of the laser marking system 100. The marking head 130 may further comprise focusing optics (not shown) and/or a collimator (not shown).

[0118] The marking head 130 may be substantially cylindrical. The marking head 130 may have a first dimension in a first direction of less than around 400 mm and a second dimension in a second direction perpendicular to the first direction of less than around 60 mm. The marking head 130 may have a third dimension in a third direction perpendicular to the first direction and the second direction of less than around 60 mm.

[0119] The marking head 130 may comprise a cooling system (not shown) for providing cooling to a component (e.g. actuators of the electromagnetic radiation steering mechanism and/or the variable optical path length assembly). The marking head 130 may further comprise a detector (not shown) configured to detect a presence of the target to be marked. The detector may comprise a camera. The laser marking system 100 may further comprise an encoder (not shown) for converting marking instructions to control signals for the marking head 130.

[0120] The laser marking system 100 may further comprise a user interface (not shown), e.g. a graphical user interface. The user interface may form part of a controller of the laser marking system (not shown). The user interface may comprise a screen for providing visual signals to a user and/or a speaker for providing audio signals to a user. The laser marking system 100 may comprise a transceiver for remote control of the laser marking system 100. The laser marking system 100 may comprise a connection (e.g. an Internet connection of an Ethernet connection) for integration with other devices (e.g. on a production line of which the laser marking system forms a part) via the Internet of Things.

[0121] The laser marking system 100 further comprises a negative curvature hollow core fiber 120 configured to transmit the laser beam from the laser 110 to the marking head 130. The negative curvature hollow core fiber 120 is described and shown in more detail with respect to FIG. 2.

[0122] The laser marking system 100 of FIG. 1 comprises a flexible umbilical 140 between the laser 110 and the marking head 130. The negative curvature hollow core fiber 120 is located within the umbilical 140. The umbilical 140 may have a length of about 3 meters or more. The umbilical 140 may have a length of about 10 meters or less.

[0123] A laser marking process using the laser marking system may include providing radiation to the negative curvature hollow core fiber 120 by coupling the laser 110 to the umbilical 140. The negative curvature hollow core fiber 120 may direct the laser beam to a collimator of the marking head 130. The collimator may condition the laser beam in a desired manner before directing the laser beam to other components of the marking head 130 such as the variable optical path length assembly (which may alter a focal plane of the laser marking system 100 in a desired manner) and/or the electromagnetic radiation steering mechanism (which may steer the laser beam exiting the marking head 130 in a desired manner).

[0124] FIG. 2 schematically depicts a cross-sectional view of a negative curvature hollow core fiber 120 according to an embodiment of the invention. The negative curvature hollow core fiber 120 comprises a hollow core 215 having a core diameter 230. The negative curvature hollow core fiber 120 further comprises a cladding 210 having an inner surface with an inner diameter 212 and an outer surface having an outer diameter 214. The inner diameter 212 and the outer diameter 214 may at least partially depend on the core diameter 230 and/or a number and size of capillaries 220. The negative curvature hollow core fiber 120 further comprises capillaries 220 located on the inner surface of the cladding 210. The capillaries 220 may form part of the cladding 210. The capillaries 220 may be configured to provide anti-resonance effects by reflecting and confining the laser beam within the hollow core 215. The capillaries 220 may be generally arch-shaped. The capillaries 220 may have other shapes. For example, the capillaries 220 may have generally circular, oval or conical shapes. The capillaries 220 may form one or more ring structures around the core 215 of the negative curvature hollow core fiber 120. Each ring of capillaries 220 may comprise a different numbers of capillaries 220, different sized capillaries 220 and/or different shaped capillaries 220. The capillaries 220 may be formed from fibers. The capillaries 220 each have a wall having an inner diameter 222 and an outer diameter 224. A ratio of the inner diameter 222 of each capillary 220 to the outer diameter 224 of each capillary 120 may be about 0.8 or more. A ratio of the inner diameter 222 of each capillary 220 to the outer diameter 224 of each capillary 120 may be about 0.9 or less. It will be appreciated that this range of ratios of inner and outer capillary diameters is merely an example in respect of a negative curvature hollow core fiber configured to transmit infrared radiation produced by a CO.sub.2 laser. The range of ratios will vary depending on the planned application of the negative curvature hollow core fiber (e.g. wavelength of light to be transmitted, cross-sectional size and length of the negative curvature hollow core fiber, etc.).

[0125] Thicknesses of the capillary walls may be selected in accordance with the following equation:

[00004]$t=\frac{\left(m-0.5\right)\lambda }{2\sqrt{n_1^2-1}};m=1,2,3,.Math.$

where t is the capillary wall thickness, λ is the wavelength of radiation that the negative curvature hollow core fiber is configured to transmit, n.sub.1 is the refractive index of the capillary material, and m is a positive integer. Capillary walls having thickness that satisfy the equation may provide anti-resonant effects that reduce the optical coupling of the laser beam between the core 215 and the cladding 210, thereby reducing radiative losses within the negative curvature hollow core fiber 120. Multiple capillary wall thicknesses are possible for each wavelength of light as determined by the value of the positive integer m. The thicknesses of the capillary walls may be within the inclusive range of about −5% to about +5% of the calculated value of t.

[0126] The thicknesses of the capillary walls may be selected at least partially based on a refractive index of the capillaries and/or a wavelength of radiation that is to be transmitted by the negative curvature hollow core fiber and/or a geometry of the anti-resonant structure (e.g. number of capillaries, diameters of the capillaries, spacing of capillaries, shapes of capillaries). The thicknesses of the capillary walls may be about 0.3 μm or more for transmitting infrared radiation (e.g. produced by a CO.sub.2 laser). The thicknesses of the capillary walls may be about 15 μm or less for transmitting infrared radiation (e.g. produced by a CO.sub.2 laser). The thicknesses of the capillary walls may be about 0.3 μm or more for transmitting near infrared radiation. The thicknesses of the capillary walls may be about 3 μm or less for transmitting near infrared radiation. The thicknesses of the capillary walls may be about 100 nm or more for transmitting ultraviolet radiation. The thicknesses of the capillary walls may be about 600 nm or less for transmitting ultraviolet radiation.

[0127] The negative curvature hollow core fiber 120 may be an anti-resonant negative curvature hollow core fiber. That is, the cladding 210 of the negative curvature hollow core fiber 120 may comprise features (e.g. the capillaries 220) configured to reduce or inhibit optical coupling between a core of the negative curvature hollow core fiber 120 and the cladding 210, resulting in reduced radiative losses at desired wavelengths (e.g. infrared, near infrared and/or ultraviolet wavelengths).

[0128] The core diameter 230 of the negative curvature hollow core fiber 120 may at least partially depend on a wavelength of radiation that is to be transmitted by the negative curvature hollow core fiber 120. For example, the negative curvature hollow core fiber 120 may have a core diameter 230 of between about 150 μm and about 300 μm for infrared laser marking applications (e.g. wavelengths having a range of between about 8 μm and about 11 μm). As another example, the negative curvature hollow core fiber 120 may have a core diameter 230 of between about 20 μm and about 100 μm for near infrared laser marking applications (e.g. wavelengths having a range of between about 0.78 μm and about 3 μm). As a further example, the negative curvature hollow core fiber 120 may have a core diameter 230 of between about 10 μm and about 20 μm for ultraviolet laser marking applications (e.g. wavelengths having a range of between about 100 nm and about 400 nm).

[0129] The core diameter 230 may be selected at least partially based on a refractive index of the capillaries 220 and/or a wavelength of radiation that is to be transmitted by the negative curvature hollow core fiber 120 and/or a geometry of the anti-resonant structure (e.g. number of capillaries, diameter of capillaries, spacing of capillaries, shapes of capillaries). For example, in the case of a ring of generally round or generally circular capillaries, the core diameter 230 of the negative curvature hollow core fiber 120 may be selected in at least partial dependence on the following equation:

[00005]$D_{\mathrm{core}}=\frac{\left(d_{\mathrm{tube}}+2t+ℊ\right)}{\sin \left(\frac{\pi }{N}\right)}-\left(d_{\mathrm{tube}}+2t\right)$

where D.sub.core is the core diameter of the negative curvature hollow core fiber, d.sub.tube is the diameter of the capillaries, t is the capillary wall thicknesses, g is the gap distance between adjacent capillaries, and N is the number of capillaries. This equation may be used to estimate the core diameter 230 of other capillary structures and geometries such as, for example, the generally arched capillaries of FIG. 2 and/or generally oval, generally conical, etc. shapes. For example, the term representing the diameters of the generally round or generally circular capillaries may be replaced by a term representing a greatest diameter of a shape of the capillaries 220. In general, a smaller core diameter 230 may provide improved laser beam quality but may also experience greater radiative losses, and desirable balances between these factors may be found for different applications. The core diameter of the negative curvature hollow core fiber may be within the inclusive range of about −10% and about +10% of the calculated value of D.sub.core.

[0130] Aspects of the laser marking system 100 may be designed and/or operated in at least partial dependence on the core diameter 230 of the negative curvature hollow core fiber 120 such that acceptable coupling occurs between the negative curvature hollow core fiber 120 and the laser 110 and/or marking head 130. In general, selecting a cross-sectional radius of the laser beam for improved coupling into the negative curvature hollow core fiber 120 may at least partially depend on the wavelengths of radiation within the laser beam and/or the core diameter 230.

[0131] In an example embodiment involving transmitting infrared radiation produced by a CO.sub.2 laser, the negative curvature hollow core fiber 120 may have a core diameter 230 of about 300 μm or less. In this example, the laser beam may be controlled by optics in the laser 110 to have a cross-sectional radius of about 91 μm or more when entering the negative curvature hollow core fiber 120 from the laser 130. The laser beam may have a cross-sectional radius of about 100 μm or less when entering the negative curvature hollow core fiber 120 from the laser.

[0132] The laser marking system may comprise one or more coupling lenses for optically coupling the negative curvature hollow core fiber to one or more other optical elements. An optimum ratio of a focal length to a diameter of an entrance pupil (i.e. an optimum F #) of the coupling lens for coupling into the negative curvature hollow core fiber may be selected in at least partial dependence on the following equation:

[00006]$F{\#}_{\mathrm{Opt}}=0.16\pi \frac{D_{\mathrm{core}}}{\lambda }$

where D.sub.core is the core diameter of the negative curvature hollow core fiber, and A is the wavelength of radiation that the negative curvature hollow core fiber is configured to transmit. In practice, if the F # of the coupling lens is less than F #.sub.Opt then more optical power may be coupled into higher order modes within the negative curvature hollow core fiber and thereby be attenuated. In practice, if the F # of the coupling lens is less than F #.sub.Opt then the optical power may be clipped at an entrance to the negative curvature hollow core fiber, which may in turn result in heating and possible thermal damage caused to the entrance of the negative curvature hollow core fiber. As such, the F # of the coupling lens may preferably be within the inclusive range of −5% and 2% of F #.sub.Opt.

[0133] The F # of the coupling lens may be selected in at least partial dependence on properties of the laser beam (e.g. a wavelength of the laser beam) that is to be transmitted and/or a geometry of the negative curvature hollow core fiber itself. A ratio of a focal length of a coupling lens located between the laser 110 and the negative curvature hollow core fiber 120 to a diameter of an entrance pupil of the negative curvature hollow core fiber 120 may at least partially depend on the core diameter 230.

[0134] For example, when transmitting an infrared laser beam produced by a CO.sub.2 laser, the ratio of a focal length of the coupling lens located between the laser 110 and the negative curvature hollow core fiber 120 to a diameter of an entrance pupil of the negative curvature hollow core fiber 120 may be about 15.4 or more. The ratio of a focal length of the coupling lens located between the laser 110 and the negative curvature hollow core fiber 120 to a diameter of an entrance pupil of the negative curvature hollow core fiber 120 may be about 17.0 or less.

[0135] A cross-sectional radius of the laser beam when entering the negative curvature hollow core fiber may be selected in at least partial dependence on properties of the laser beam (e.g. a wavelength and/or power of the laser beam) that is to be transmitted and/or a geometry of the negative curvature hollow core fiber itself. For example, for transmitting infrared light generated by a CO2 laser, and referring again to FIG. 1, a beam parameter product of the laser beam may be about 4.0 or less at the target. As yet further examples, a beam parameter product of the laser beam may be about 3.5 or less at the target. The beam parameter product of the laser beam may be about 3.5 or less at an output of the laser 110. The beam parameter product of the laser beam may be about 3.0 or less at the output of the laser 110. The laser beam at an output of the laser 110 may have a cross-sectional radius of about 0.7 mm or more. The laser beam at the output of the laser 110 may have a cross-sectional radius of about 1.3 mm or less. The laser beam at the output of the laser 110 may have a divergence of about 2.3 mrad or more. The laser beam at the output of the laser 110 may have a divergence of about 4.3 mrad or less. It will be appreciated that values merely provide an example, and that the ranges of cross-sectional radii, beam parameter products and half-angle divergences will vary depending on the planned application of the negative curvature hollow core fiber (e.g. wavelength of light to be transmitted, cross-sectional size and length of the negative curvature hollow core fiber, etc.).

[0136] The negative curvature hollow core fiber 120 may comprise silica, e.g. fused silica. Silica advantageously transmits ultraviolet radiation with relatively low radiative losses. The negative curvature hollow core fiber 120 may comprise chalcogenide glass. Chalcogenide glass may be used to transmit infrared radiation and/or near infrared radiation. The chalcogenide glass may comprise one or more of the following materials: As30Se50Te20 (not suitable for near infrared transmission); As2S3; As2Se3; Ge15As25Se40Te20 (not suitable for near infrared transmission); and, As40S30Se30. The chalcogenide glass may comprise other combinations and/or dopants such as rare earth elements such as, for example, La, Tb, Tl, Ge, Sb, As, Ga. Chalcogenide glass advantageously transmits infrared radiation with relatively low radiative losses. A thickness and spacing between the capillaries may be selected to reduce radiative losses at desired wavelengths of radiation. The desired wavelengths of radiation may comprise infrared radiation produced by a CO.sub.2 laser, near infrared radiation produced by a solid-state laser, e.g. comprising a Nd:YAG (neodymium doped yttrium aluminum garnet—a YAG laser) crystal or a Nd:VO.sub.4 (neodymium doped yttrium orthovanadate—a vanadate laser) crystal, and/or ultraviolet radiation produced by a solid-state laser comprising a non-linear optical element, e.g. a non-linear crystal such as KTP (potassium titanyl phosphate), KTA (potassium titanyl arsenate) or BBO (beta barium borate).

[0137] An end (not shown) of the negative curvature hollow core fiber 120 may be tapered to improve a coupling efficiency of the negative curvature hollow core fiber 120 with the laser 110 and/or the marking head 130, thereby improving an efficiency of the laser marking system 100.

[0138] FIG. 3 shows a perspective view of portion 300 of a laser marking system according to an embodiment of the invention. The portion 300 of the laser marking system comprises a laser 110, an optical alignment system 310, a negative curvature hollow core fiber 120, and an optical coupling 320 for connecting the negative curvature hollow core fiber 120 to a marking head (not shown). The optical alignment system 310 is optically coupled to an output of a laser 110. The optical alignment system 310 is located between the laser 110 and the negative curvature hollow core fiber 120. The optical alignment system 310 is configured to change a position and/or angle of the laser beam relative to an input of the core of the negative curvature hollow core fiber 120. An end of the negative curvature hollow core fiber 120 fiber may be tapered into a lens of the optical coupling 320 for coupling into the marking head.

[0139] FIG. 4 schematically depicts a perspective view of some of the internal components of the optical alignment system 310 of FIG. 3. An end cap 400 of the laser is optically coupled to an input of the optical alignment system 310. The optical alignment system 310 comprises a first adjustable optical element 410 configured to receive the laser beam from the laser. The optical alignment system 310 further comprises a second adjustable optical element 420 configured to receive the laser beam from the first adjustable optical element 410 and direct the laser beam towards an input of the core of the negative curvature hollow core fiber (not shown). The optical alignment system 310 further comprises a first detector 430 configured to detect a position of the laser beam relative to the second adjustable optical element 420. The optical alignment system 310 further comprises a second detector 440 configured to detect a position of the laser beam relative to the input of the core of the negative curvature hollow core fiber. The first and second detectors 430, 440 may be configured to detect angular and/or translational positions of the laser beam relative to the second adjustable optical element 420 and the input of the core of the negative curvature hollow core fiber.

[0140] In the example of FIG. 4, the first adjustable optical element 410 comprises a first rotatable reflector 415 and the second adjustable optical element 420 comprises a second rotatable reflector 425. The two rotatable reflectors 415, 425 may each be affixed to a mount 417, 427 having adjustment means 419, 429 such as screws or motors (e.g. linear motors) configured to change a rotational position of the rotatable reflectors 415, 425. Both rotatable reflectors 415, 425 may be rotatable about a plurality of rotation axes. For example, the rotatable reflectors 415, 425 may be rotatable about first and second substantially orthogonal rotation axes such that a position of the laser beam reflected by the rotatable reflectors is adjustable in two dimensions. That is, a “tip” of a rotatable reflector about a first rotational axis may provide an “x” adjustment of the position of the laser beam and a “tilt” of the rotatable reflector about a substantially orthogonal rotational axis may provide a “y” adjustment of the position of the laser beam. The adjustment means 419 of the first rotatable reflector 415 may be configured to position the laser beam on a desired location on the surface of the second rotatable reflector 420. The adjustment means 429 of the second rotatable reflector 420 may be configured to position the laser beam such that the laser beam is substantially co-axial with a desired optical axis of the laser marking system. In this manner, any misalignment error from any source of misalignment may be compensated for by rotating the first and/or second rotatable reflectors 415, 425 of the optical alignment system 310.

[0141] In the example of FIG. 4, the optical alignment system 310 comprises a first beam sampler 450 located between the first rotatable reflector 415 and the second rotatable reflector 425. The first beam sampler 450 is configured to direct a portion of the laser beam to the first detector 430. The first beam sampler 450 is preferably placed as close to the input side or the output side of the second rotatable reflector 425 as possible. The first beam sampler 450 may comprise a beam splitter, such as an optical flat having one side coated to reflect a small percentage (e.g. <1%) of the laser beam to the first detector 430. The other side of the optical flat may comprise an anti-reflection coating that allows the remaining percentage of the laser beam to transmit through the first beam sampler 450 towards the second rotatable reflector 425. The refraction of the laser beam caused by transmitting through the beam splitter may be compensated for by positioning the second rotatable reflector 420 accordingly and/or by placing a second optical flat of substantially the same thickness at a complimentary angle in the laser beam path after the first beam sampler 450.

[0142] The optical alignment system further comprises a second beam sampler 460 located between the second rotatable reflector 420 and the input of the core of the negative curvature hollow core fiber. The second beam sampler 460 is configured to direct a portion of the laser beam to the second detector 440. The second beam sampler 460 may comprise a beam splitter, such as an optical flat having one side coated to reflect a small percentage (e.g. <1%) of the laser beam to the second detector 440. The other side of the optical flat may comprise an anti-reflection coating that allows the remaining percentage of the laser beam to transmit through the second beam sampler 460 towards the input of the core of the negative curvature hollow core fiber. The refraction of the laser beam caused by transmitting through the beam splitter may be compensated for by positioning the input of the core of the negative curvature hollow core fiber accordingly and/or by placing a second optical flat of substantially the same thickness at a complimentary angle in the laser beam path after the second beam sampler 460.

[0143] FIG. 5 schematically depicts a magnified perspective view of some of the components of the optical alignment system of FIG. 4. FIG. 5 shows the second detector 440 and the second beam sampler 460 of FIG. 4 with housing tubes removed. A coupling lens 500 (that was not visible in FIG. 4 but is now visible in FIG. 5) may be provided to capture the laser beam reflected from the second rotatable reflector (not shown) and focus the laser beam towards the second beam sampler 460. The second beam sampler 460 comprises first and second optical flats 510, 520. The optical flats 510, 520 may comprise GaAs. The first optical flat 510 may be coated to direct a portion of the laser beam to the second detector 440. A remaining portion of the laser beam may transmit through the first optical flat 510 and be incident upon the second optical flat 520. The second optical flat 520 is configured to compensate for refraction effects caused by the laser beam transmitting through the first optical flat 510. That is, the laser beam transmits through the second optical flat 520 towards the input 530 of the negative curvature hollow core fiber and the second optical flat 520 refracts the laser beam to account for the refraction caused by the first optical flat 510. The second detector 440 is configured to detect an angular and/or translational position of the laser beam with respect to the input 530 of the negative curvature hollow core fiber and/or an optical axis of the laser marking system. The second detector 440 may comprise a quadrant detector configured to provide positional information of the laser beam, e.g. in the form of Cartesian coordinates.

[0144] FIG. 6 schematically depicts a ray trace of a laser beam interacting with the components of FIG. 5. Radiation incident on the coupling lens 500 is captured and focused towards the second beam sampler 460. The first optical flat 510 may be coated to direct a portion of the laser beam to the second detector 440. The remaining portion of the laser beam transmits through the first optical flat 510 and is incident upon the second optical flat 520. As can be seen, a small translational offset is introduced to the portion of radiation that transmits through the first optical flat 510 due to refraction effects. The second optical flat 520 may have a thickness that is substantially equal to the first optical flat 510. The second optical flat 520 may be angled relative to the first optical fat 510 such that the translational shift of the laser beam after passing through the first optical flat 510 is substantially reversed by refractive effect of the second optical flat 520.

[0145] FIG. 7 schematically depicts a perspective view of an alternative beam sampler 700 of an optical alignment system according to an embodiment of the invention. Instead of using optical flats such as those used in the beam sampler of FIGS. 4-6, the beam sampler 700 of FIG. 7 comprises a reflective element 710 having an alignment aperture 720 that is aligned with an optical axis 730 of the laser marking system. The alignment aperture 720 has a diameter that is substantially equal to a diameter of the laser beam (not shown). If the laser beam is aligned with the optical axis 730, then the laser beam passes through the alignment aperture 720 towards the second rotatable reflector or the negative curvature hollow core fiber. If the laser beam is not aligned with the optical axis 730, then at least some of the laser beam is reflected by the reflective element 710 towards the first or second detector (not shown). In this configuration, the signal from the first and/or second detector may be used to control the rotational position of the first and/or second rotatable reflectors to reduce the amount of the laser beam that is incident upon the first and/or second detector, thereby aligning the laser beam with the optical axis 730. Also shown in FIG. 7 is a coupling lens 500 configured to focus the laser beam onto the beam sampler 700.

[0146] FIG. 8 schematically depicts a view from the front of a detector 800 of an optical alignment system according to an embodiment of the invention. The detector 800 may be used as the first detector and/or the second detector. The detector 800 may be located between the first rotatable reflector (not shown) and the second rotatable reflector (not shown). The detector 800 comprises an alignment aperture 810 that is aligned with an optical axis (not shown) of the laser marking system. The alignment aperture has a diameter 820 that is substantially equal to a diameter of the laser beam incident on the detector 800. In the example of FIG. 8, the detector 800 is a quadrant detector. Any unwanted deviation of the laser beam from the desired optical axis of the laser making system is detected by the quadrant detector. The detector may provide a feedback signal to a controller of the first and/or second rotatable reflector. The controller may rotate the first and/or second rotatable reflector in accordance with the detector signal and thereby reflect the laser beam such that the laser beam is aligned with the optical axis of the laser marking system.

[0147] FIG. 9 schematically depicts a ray trace of an aligned laser beam 900 interacting with the components of an optical alignment system according to an embodiment of the invention. The laser beam 900 is reflected by the first rotatable reflector 415 towards the second rotatable reflector 425. In the example of FIG. 9, the first detector 430 is a quadrant detector located behind the second rotatable reflector 425. The first detector 430 is configured to detect a position and/or angle of a portion of the laser beam 900 that transmits through the second rotatable reflector 425. The second rotatable reflector 425 may have a reflectivity of between about 97% and about 99.7%. The second rotatable reflector 425 has a non-zero thickness through which a portion of the laser beam 900 transmits. The transmitted portion of the laser beam may undergo refraction when passing through the second rotatable reflector 425 and change direction, much like the translational offset of the laser beam caused by the first optical flat shown in FIG. 6. A center point of the first detector 430 may be positioned offset a center point of the second rotatable reflector 425 to account for the change in direction of the transmitted portion of the laser beam caused by refraction through the second rotatable reflector 425.

[0148] The optical alignment system further comprises a controller 910 configured to receive signals from the first and second detectors 430, 440 and use the signals to control rotational positions of the first and second rotatable reflectors 415, 425.

[0149] The portion of the laser beam 900 that does not transmit through the second rotatable reflector 425 is reflected by the second rotatable reflector 425 towards a coupling lens 500. The coupling lens 500 focuses the laser beam 900 towards a beam sampler 700. In the example of FIG. 9, the beam sampler 700 comprises a reflective element 710 having an alignment aperture 720 that is aligned with an optical axis of the laser marking system. The alignment aperture 720 has a diameter that is substantially equal to a diameter of the laser beam 900. As is the case for the beam sampler of FIG. 7, if the laser beam 900 is aligned with the optical axis of the laser marking system then the laser beam 900 passes through the alignment aperture 720 towards the input of the core of the negative curvature hollow core fiber. If the laser beam 900 is not aligned with the optical axis of the laser marking system then at least some of the laser beam is reflected by the reflective element 710 towards the second detector 440. In this configuration, the signal from the second detector 440 may be used to control the rotational position of the second rotatable reflector 425 to reduce the amount of the laser beam 900 that is incident upon the second detector 440, thereby aligning the laser beam with the optical axis of the laser marking system. In the example of FIG. 9, the laser beam 900 is aligned with the optical axis of the laser marking system and no radiation is incident on the second detector 440.

[0150] The portion of the laser beam 900 that transmits through the beam sampler 700 is incident on a first protective cap 915 comprising a first protective aperture 920. The first protective cap 915 is located proximate an input of the core of the negative curvature hollow core fiber (not shown). The laser marking system may comprise a second protective cap (not shown) comprising a second protective aperture (not shown). The second protective cap may be located proximate an output of the core of the negative curvature hollow core fiber. The first and second protective apertures 920 have a diameter that is substantially equal to a core diameter of the negative curvature hollow core fiber. The first and second protective apertures 920 are configured to protect the cladding of the negative curvature hollow core fiber from damage caused by the focused laser beam 900 and/or backscattered laser radiation that may otherwise re-enter the laser marking system. That is, radiation that is not aligned with the core of the negative curvature hollow core fiber is prevented from damaging the cladding and/or capillaries of the fiber by being blocked by the first protective cap 915. The first and/or second protective apertures 920 may each comprise a protective pin-hole having the same diameter as the core of the negative curvature hollow core fiber and may be placed at the input and output ends of the negative curvature hollow core fiber. The pin-holes may be part of the negative curvature hollow core fiber mount or a separate device. The first and/or second protective caps 915 may be replaceable and may be considered to be sacrificial devices to protect the more expensive negative curvature hollow core fiber.

[0151] FIG. 10 schematically depicts a ray trace of a misaligned laser beam 950 interacting with the components of the optical alignment system of FIG. 9. As can be seen, a portion of the laser beam 950 is reflected by the beam sampler 700 towards the second detector 440. The second detector 440 is configured to detect the portion of the laser beam 950 and send a signal to the controller 910. The controller 910 is configured to use the signal to change the rotational position of the second rotatable reflector 425 to re-align the laser beam 950 with the optical axis of the laser marking system.

[0152] FIG. 11 schematically depicts a ray trace of a laser beam 950 interacting with the components of an alternative optical alignment system without alignment compensation according to an embodiment of the invention. The optical alignment system of FIG. 11 is the same as the optical alignment system of FIGS. 9 and 10 except that the beam sampler 460 comprises first and second optical flats 510, 520 rather than a reflective element having an alignment aperture.

[0153] FIG. 12 schematically depicts the ray trace of FIG. 11 with alignment compensation applied by the optical alignment system. The first and second rotatable reflectors 415, 425 have been rotated by the controller 910 in at least partial dependence on the signals received from the first detector 430 and the second detector 440. The first and second rotatable reflectors 415, 425 have been rotated such that the laser beam 900 is aligned with the optical axis of the laser marking system. The compensation applied by the optical alignment system is best seen when comparing the position of the laser beam 900 on the coupling lens 500 in FIGS. 11 and 12. As can be seen, the laser beam 900 is offset from the center of the coupling lens 500 in FIG. 11, and is centered on the coupling lens 500 in FIG. 12.

[0154] FIG. 13 shows a method of designing a laser marking system according to an embodiment of the invention. A first step S1 of the method includes selecting a desired laser beam spot size at the target and a desired distance between the marking head and the target. The desired laser beam spot size at the target and the desired distance between the marking head and the target may be application specific (e.g. the pattern to be marked, the material and/or shape of the target, etc.). The desired laser beam spot size may be about 100 μm or more. The desired laser beam spot size may be about 500 μm or less. The desired distance between the marking head and the target may be about 50 mm or more. The desired laser beam spot size may be about 250 μm. The desired distance between the marking head and the target may be about 250 mm or less. The desired distance between the marking head and the target may be about 125 mm.

[0155] A second step S2 of the method includes designing optical components of the marking head in at least partial dependence on the first step S1 and determining a beam parameter product of the laser beam at the target. The beam parameter product of the laser beam at the target may be defined as the product of the radius of the laser beam and the divergence of the laser beam at the target. The radius of the laser beam and the divergence of the laser beam at the target may be determined using the following equations:

[00007]${\omega }_o=\frac{2*\lambda }{\pi }*\left(\frac{f}{D}\right)$$\theta ={\sin }^{-1}\frac{D}{2*f}$

where ω.sub.o is the radius of the laser beam, f is the focal length, D is the diameter of the laser beam at a focusing lens, and θ is the half-angle divergence of the beam in mrad. The focal length of the focusing lens may be approximately the same as the distance between the marking head and the target.

[0156] A third step S3 of the method includes designing first coupling optics between the negative curvature hollow core fiber and the marking head in at least partial dependence on the second step S2. The first coupling optics may be configured to convert a divergent laser beam exiting the negative curvature hollow core fiber into a collimated laser beam entering the marking head. The first coupling optics may comprise one or more lenses of a material having a relatively high transmissivity (e.g. coated lenses for a transmissivity of about 99% or more) at the desired wavelength (e.g. infrared, near infrared or ultraviolet wavelengths). Alternatively, the first coupling optics may comprise one or more mirrors having a relatively high reflectivity (e.g. a reflectivity of about 99% or more). The lenses used in the first coupling optics may comprise one or more materials such as zinc selenide, zinc sulphide, germanium, gallium arsenide or other materials that are sufficiently transparent at infrared wavelengths (e.g. wavelengths of radiation generated by a CO.sub.2 laser). For near infrared transmission, the lenses used in the first coupling optic may comprise one or materials such as fused silica, a crown glass (e.g. borosilicate or BK7) and/or a synthetic fused silica such as SUPRSIL provided by Heraeus, a German company. For ultraviolet transmission, the lenses used in the first coupling optic may comprise, for example, ultraviolet grade fused silica. A geometry of the lenses (e.g. a diameter and curvature of the lens surfaces) used in the first coupling optics may at least partially depend on the diameter and/or divergence of the laser beam at the target and/or the optical components of the marking head with which the laser beam interacts before reaching the target.

[0157] A fourth step S4 of the method includes selecting a desired beam parameter product of the laser beam between the negative curvature hollow core fiber and the marking head and designing the negative curvature hollow core fiber in at least partial dependence on the beam parameter product of the laser beam between the negative curvature hollow core fiber and the marking head. Designing the laser marking system such that the beam parameter product at the target is greater than the beam parameter product between the negative curvature hollow core fiber and the marking head may reduce radiative loses and/or improve a performance and efficiency of the laser marking system.

[0158] The relevant design parameters for designing the negative curvature hollow core fiber may comprise the following: [0159] the materials of the negative curvature hollow core fiber; [0160] the wavelength at which the negative curvature hollow core fiber losses are to be reduced; [0161] the number of rings of capillary fibers making up the cladding; [0162] the number of capillary fibers making up each ring; [0163] the ratio of the inner and outer diameters of the capillary fibers; [0164] the shape of the capillary fibers; [0165] the distance between the capillary fibers in each ring; [0166] the core diameter of the negative curvature hollow core fiber; [0167] the inner and outer diameters of the cladding; [0168] the length of the taper at the end(s) of the negative curvature hollow core fiber; and/or, [0169] the ratio of the diameter of the negative curvature hollow core fiber at the beginning and end of the taper(s).

[0170] A fifth step S5 of the method includes designing second coupling optics between the laser and the negative curvature hollow core fiber in at least partial dependence on the fourth step S4. The relevant design parameters for designing the second coupling optics may be the same the relevant design parameters for the output coupling optics as described for the third step S3. An additional constraint may be that the minimal coupling loss occurs when the laser beam spot size between the laser and the negative curvature hollow core fiber conforms to the following equation:

[00008]$\frac{2*{\omega }_o}{d}\cong 0.64$

where ω.sub.o is the radius of the laser beam between the laser and the negative curvature hollow core fiber and d is the diameter of the core of the negative curvature hollow core fiber.

[0171] A sixth step S6 of the method includes designing the laser in at least partial dependence on the beam parameter product of the laser beam between the negative curvature hollow core fiber and the marking head. The relevant design parameters for coupling the laser to the negative curvature hollow core fiber may comprise the diameter of the laser beam output by the laser and/or the divergence of the laser beam output by the laser. The beam parameter product of the laser (i.e. the product of the laser beam radius and the laser beam divergence) may be less than that of all the following components of the laser marking system. For example, the beam parameter product of the laser may be about 3.5 or less to reduce radiative losses through the laser marking system.

[0172] The method may further comprise a seventh step (not shown) including using forward and/or backward iteration to adjust the laser marking system. Forward and/or backward iteration may involve considering factors such as the tolerances of the components of the laser marking system, the availability of materials, costs, and performance variances, and determining suitable compromises between these factors. If the design of the laser marking system begins with the marking head and progresses through the negative curvature hollow core fiber back to the laser, then if constraints on the laser design prevent meeting the desired design goal, it may be necessary to reverse the design process with the new constrained laser design. This process may be iterated to achieve an improved performance with the modified design parameters.

[0173] The optical components of the laser marking system (e.g. first and second coupling optics and/or the optical components of the marking head), like any fabricated part, are manufactured within design tolerances. In general, the tighter the tolerance, the costlier the component. A typical optical component may be made to standard manufacturing tolerances on design parameters such as centration, diameter, surface quality, flatness, parallelism, etc. In most laser marking applications, the standard tolerances are sufficient and no further compensation is required. The same is true for the mechanical components holding the optical components in the system. Parts can be machined to very tight tolerance at a cost. However, in the case of trying to couple a laser beam having a 200 μm spot size into a 300 μm diameter core of a negative curvature hollow core fiber, the stack-up of tolerance errors may become a problem. These are errors that may negatively affect coupling efficiency and may not be directly related to the laser marking process except with regards to a reduction in radiative power delivered to the target. The impact of such errors may be reduced by “hard” and “soft” alignment techniques.

[0174] Hard alignment techniques comprise processes and tools used during the manufacturing process to ensure satisfaction of system specifications. For example, a laser in a typical marking system is mounted on a base plate that has position adjusting screws. The laser and the base plate are put on a specially designed tooling to permit adjustment of the screws to position the laser beam from the output of the laser to a particular point on a reference target. In this way, when the laser is put in a laser marking system and attached to a marking head, the laser beam is automatically aligned to the optics in the marking head and no further adjustment is required. Likewise, a lens may be positioned in its mount using set-screws and tooling to compensate for centration errors. These are all means of compensation that are done during the manufacturing process and are fixed in place when completed.

[0175] Soft alignment comprises techniques that may be implemented “off-line” by service personnel, customers, or controlled dynamically. This may include using the optical alignment system (e.g. the first and second rotatable reflectors) to adjust a position and/or angle of the laser beam. The first rotatable reflector may keep the laser beam positioned on a desired point (the point where the design optical axis intersects a surface of the second rotatable reflector) on the second rotatable reflector. The second rotatable reflector may adjust a position and/or angle of the laser beam to keep the laser beam aligned with the optical axis of the laser marking system. In this way, the two rotatable reflectors compensate for tolerance errors of all optical components of the laser marking system upstream of the first and second rotatable reflectors.

[0176] For example, thermal movement due to expansion and contraction of materials and vibration due to internal cooling devices and external sources such as other equipment may cause unwanted movement of the optical components that have not been compensated for by the hard and soft alignment techniques. Hard alignment techniques may be used to compensate, such as mounting optical components using vibration isolation materials, expansion coefficients of materials used may be matched with one another, etc. Soft alignment techniques may be used to compensate, such as controlling the optical alignment system (e.g. the first and second rotatable reflectors) using motor driven adjustment screws on the rotatable reflectors and feedback from the first and/or second detectors.

[0177] FIG. 14 shows a method of manufacturing a laser marking system according to an embodiment of the invention. A first step S10 of the method includes providing a laser configured to generate a laser beam. A second step S11 of the method includes providing a marking head configured to project the laser beam onto a target to be marked. A third step S12 of the method includes connecting the laser to the marking head using a negative curvature hollow core fiber configured to transmit the laser beam from the laser to the marking head.

[0178] Having thus described several aspects of at least one implementation, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the disclosure. The acts of methods disclosed herein may be performed in alternate orders than illustrated, and one or more acts may be omitted, substituted, or added. One or more features of any one example disclosed herein may be combined with or substituted for one or more features of any other example disclosed. Accordingly, the foregoing description and drawings are by way of example only.

[0179] The phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. As used herein, the term “plurality” refers to two or more items or components. As used herein, dimensions which are described as being “substantially” similar may be considered to be within about 25% of one another. The terms “comprising,” “including,” “carrying,” “having,” “containing,” and “involving,” whether in the written description or the claims and the like, are open-ended terms, i.e., to mean “including but not limited to.” Thus, the use of such terms is meant to encompass the items listed thereafter, and equivalents thereof, as well as additional items. Only the transitional phrases “consisting of” and “consisting essentially of,” are closed or semi-closed transitional phrases, respectively, with respect to the claims. Use of ordinal terms such as “first,” “second,” “third,” and the like in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

[0180] The laser marking system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, and/or other types of optical components, or any combination thereof, for directing, shaping, and/or controlling electromagnetic radiation.

[0181] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.