Laser marking system and method of energy control

• US 6,160,568 A
• Filed: 05/26/1998
• Issued: 12/12/2000
• Est. Priority Date: 05/27/1997
• Status: Expired due to Term

• Current Assignee: Lumentum Operations, LLC (Lumentum Holdings Inc.)
• Original Assignee: SDL PLC (RWS Holdings Plc)
• Inventors: Welch, David F., Brodsky, Mark A., Yim, Yong
• Primary Examiner(s): Le, N.
• Assistant Examiner(s): PHAM, HAI CHI
• Application Number:
  US09/085,142
• Time in Patent Office: 931 Days
• Field of Search: 347/237, 347/238, 347/239, 347/247, 347/255, 347/246, 385/126, 385/123, 359/341, 372/6, 372/25, 372/50, 372/24, 372/26, 372/33, 372/75, 372/70
• US Class Current: 347/247
• CPC Class Codes: B23K 26/032 using optical means
• CPC Class Codes: B23K 26/06 Shaping the laser beam, e.g. by masks or multi-focusing
• CPC Class Codes: B23K 26/064 by means of optical elements, e.g. lenses, mirrors or prisms
• CPC Class Codes: B23K 26/0643 comprising mirrors
• CPC Class Codes: B23K 26/0648 comprising lenses
• CPC Class Codes: B23K 26/0665 by beam condensation on the workpiece, e.g. for focusing
• CPC Class Codes: B41M 5/26 Thermography B41M5/20, B41M5/24 take precedence; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used B23K takes precedence; thermographic or photothermographic systems using noble metal compounds G03C1/494
• CPC Class Codes: G06K 1/126 by photographic or thermographic registration recording apparatus for measuring instruments G01D15/00
• CPC Class Codes: H01S 3/067 Fibre lasers
• CPC Class Codes: H01S 3/094007 Cladding pumping, i.e. pump light propagating in a clad surrounding the active core
• CPC Class Codes: H01S 3/1312 by controlling the optical pumping

Abstract

A laser marking system comprises a high power fiber laser consisting of a double clad fiber having a doped core surrounded by an inner pump cladding and providing an optical output for marking; a high power laser diode source for pumping the double clad fiber laser via an input into the inner pump cladding; an optical scanner coupled to receive the marking output from the double clad fiber laser to scan the output over a surface of an article to be marked by sweeping the marking output in one, two or three dimensions to form strokes, the completion of which comprises indicia to be marked the article surface; and a controller to control the operation of the scanner in synchronism with the modulation of the laser diode pump source to initiate the marking output and sweep and modulate the marking optical output in one, two or three dimensions to form strokes comprising the indicia. A main advantage of the fiber laser marking system over CO₂ and YAG laser marking systems is the ability to provide modulation via the semiconductor laser diode at the input to the marking laser rather than having to modulate the optical power beam at the output of the marking laser, such as through an acusto-optic modulator, which provides for a pulse of non-uniform stability across the pulse width with a substantially decrease in the amount of power in the modulated beam output. Also disclosed is circuitry to dampen the ON-time rise of a current signal input for operation of the laser diode pump source to improve the ON-time quality of the marking optical output created by the double clad fiber marking laser.

Claims

1. A laser marking system comprising:

a high power fiber marking laser consisting of a double clad fiber having a doped core surrounded by an inner pump cladding and providing an optical output for marking;

a high power semiconductor laser source for pumping said double clad fiber laser, a light output from said semiconductor laser source optically coupled as an input to said inner pump cladding;

an optical scanner coupled to receive an output beam from said fiber marking laser and scan said output beam over a surface of an article to be marked;

a controller to provide for direct modulation of the semiconductor laser source light output at a modulated rate and pulse width to correspondingly provide a modulated rate and pulse width for said marking laser optical output; and

means to control operation of said scanner in synchronism with modulation of said laser pump source to initiate said marking output and modulate said marking output from said fiber marking laser in multiple dimensions to form strokes comprising discernible indicia on the article surface.

2. The laser marking system of claim 1 further comprising said optical scanner sweeping said fiber marking laser output in multiple dimensions to form strokes comprising discernible indicia formed on the article surface.

3. The laser marking system of claim 1 further comprising means to control the operation of said scanner in synchronism with the modulation of said laser pump source to initiate said marking output and sweep and modulate said marking optical output in multiple dimensions to form strokes comprising the discernible indicia.

4. The laser marking system of claim 1 wherein said double clad fiber has a non-circular geometry for its inner pump cladding.

5. The laser marking system of claim 4 wherein said double clad fiber has an inner pump cladding with a cross-sectional configuration that is shaped like a polygon.

6. The laser marking system of claim 5 wherein said polygon like shape is an octagon.

7. The laser marking system of claim 1 wherein said laser pump source comprises a fiber laser pumped by said semiconductor laser.

8. The laser marking system of claim 7 wherein said semiconductor laser is at least one laser diode array having a plurality of light emitters;

and means to combine light outputs provided from said light emitters for input into said double clad fiber.

9. The laser marking system of claim 1 wherein said fiber marking laser provides for flexibility in aligning said output beam in maintained relation with an optical input to said scanner requiring no further readjustment.

10. The laser marking system of claim 1 wherein said fiber marking laser is turned off in less than about 0.5 milliseconds upon turn-off of said pumping laser source.

11. The marking system of claim 10 wherein said pumping laser source comprises a laser diode source or a laser diode pumped fiber laser source.

12. The marking system of claim 11 wherein said laser diode source comprises at least one laser diode bar.

13. The marking system of claim 1 wherein said pumping laser source comprises a laser diode source or a laser diode pumped fiber laser source.

14. The marking system of claim 13 wherein said laser diode source comprises at least one laser diode bar.

15. The marking system of claim 13 wherein said laser pumping source is operated in a power-on-demand mode so that said laser pumping source is turned-on or modulated at anytime that a marking sequence is to be initiated providing a marking output of a selected length and pulse height.

16. The laser marking system of claim 1 further comprising:

a rigid support housing secured to the output end of said fiber laser, said housing including a lens system for handling said marking beam output;

said optical scanner having an input aperture to receive said marking optical output;

said fiber marking laser providing flexibility for the coupling of said housing to said optical scanner input aperture to permit said marking optical output to be properly aligned for beam scanning via said optical scanner.

17. The marking system of claim 16 wherein said fiber marking laser is a single mode fiber laser.

18. The marking system of claim 16 wherein two-dimensional scanning is provided such that said fiber marking optical output is moved for scanning in first direction and the optical scanner provides for scanning in second direction.

19. The marking system of claim 16 wherein two-dimensional scanning is provided such that said optical scanner comprises movement in two dimensions of the fiber marking optical output end for scanning a surface to be marked.

20. The laser marking system of claim 1 further composing means to dampen ON-time rise of a current signal input for operation of said laser pump source to improve ON-time quality of said marking optical output.

21. A laser marking system comprising:

a high power fiber marking laser consisting of a double clad fiber having a doped core surrounded by an inner pump cladding and providing an optical output for marking;

a high power semiconductor laser source for pumping said double clad fiber laser, a light output from said semiconductor laser source optically coupled as an input to said inner pump cladding;

an optical scanner coupled to receive an output beam from said fiber marking laser and scan said output beam over a surface of an article to be marked;

a controller to provide for direct modulation of the semiconductor laser source light output at a modulated rate and pulse width to correspondingly provide a modulated rate and pulse width for said marking laser optical output; and

means to dampen ON-time rise of a current signal input for operation of said laser pump source to improve ON-time quality of said marking optical output.

22. The laser marking system of claim 21 further comprising means to control operation of said scanner in synchronism with modulation of said laser pump source to initiate said marking output and modulate said marking output in multiple dimensions to form strokes comprising discernible indicia on the article surface.

23. A marking system comprising:

a fiber laser as a light source system for producing an output marking beam having a fast rise time less than 1 millisecond;

a pump laser source for optically pumping said fiber laser; and

pump laser circuitry to cause said pump laser to produce an additional optical output enhancement in the optical pumping of said fiber laser to minimize fiber laser turn-on delay so that an external modulator operative to modulate the output marking beam is not required.

24. The marking system of claim 23 wherein said additional optical output enhancement comprises a larger optical amplitude on fiber laser turn-on or an additional optical dummy pulse prior to fiber laser turn-on.

25. A fiber laser based marking system comprising:

an optical fiber having a rare earth doped core and pumped by a laser diode source and functioning as a fiber laser;

means for modulating said laser diode source to modulate its light output and coupling its modulated light into said optical fiber;

the modulated light being absorbed along its fiber length in the fiber core and providing a laser marking output;

an optical scanner coupled to receive said laser marking output for scanning the output in two dimensions; and

a computer to control in combination said scanner and modulation of said laser diode source so that the marking output of said fiber laser is scanned in timed relation with the modulation of said laser diode source to form a plurality of sequenced marking strokes that are patterned in two dimensions on a surface of an article to be marked to form discernible indicia thereon.

26. The fiber laser based marking system of claim 25 wherein said fiber laser is a single mode laser.

27. The fiber laser based marking system of claim 26 wherein said fiber laser comprises a double clad fiber.

28. The fiber laser based marking system of claim 25 further comprising:

means to generate marking strokes in predetermined spatial relation to one another to form intelligent indicia on the article surface; and

means to control an excitation level and timing of operation of said laser diode source such that said strokes occur in said predetermined spatial relation at a determined level of marking output power to produce a desired marking contrast and marking depth in the article surface being marked.

29. A laser marking system comprising:

a high power fiber marking laser comprising a fiber having a doped single mode core and providing an optical output for marking;

an optical scanner coupled to receive the optical output from the fiber marking laser to scan the optical output over a surface of an article to be marked;

a laser diode source providing a modulated optical output coupled for pumping said fiber laser;

a drive circuit for providing an electrical signal for controlling changes to a current level of the signal applied to said laser diode source and, correspondingly, changes in an optical output intensity level in the optical output provided from said fiber marking laser;

means to control the operation of the scanner in synchronism with the modulation of the laser diode source to initiate the optical output and modulate the optical output in multiple dimensions to form strokes comprising discernible indicia;

means for detecting the optical output intensity level from said fiber marking laser; and

feedback means for comparing the detected optical output intensity level with a desired level and adjusting the current level to maintain the optical output intensity level at said desired level.

30. A laser marking system comprising:

a high power fiber marking laser comprising a fiber having a doped single mode core and providing an optical output for marking;

a laser diode source providing an optical output coupled for pumping said fiber laser;

a drive circuit for providing an electrical signal for controlling changes to a current level of the signal applied to said laser diode source and, correspondingly, changes in an optical output intensity level in the optical output provided from said fiber marking laser;

means for detecting the optical output intensity level from said fiber marking laser; and

feedback means for comparing the detected optical output intensity level with a desired level and adjusting the current level to maintain the optical output intensity level at said desired level and

an overdrive circuit in said feedback means to provide an initial dampening in applying said electrical signal to said laser diode source.

31. The laser marking system of claim 30 wherein said initial dampening causes the rise time of said electrical signal be reduced in magnitude as said electrical signal nears its peak value.

32. A laser marking system comprising:

a fiber marking laser comprising a double clad fiber having a doped core surrounded by an inner pump cladding and providing an optical output for marking;

a laser source for pumping the double clad fiber laser, an output from the laser source optically coupled as an input to the inner pump cladding;

an optical scanner coupled to receive the output beam from the fiber marking laser to scan the output beam over a surface of an article to be marked;

means to modulate the laser source to provide a modulated marking optical output from the fiber laser; and

means to control the scanner in synchronism with the modulation of the laser pump source to initiate the marking optical output and modulate the marking optical output in multiple dimensions to form strokes comprising discernible indicia.

33. The laser marking system of claim 32 wherein the inner pump cladding of the double clad fiber has a non-circular geometry.

34. The laser marking system of claim 33 wherein the non-circular geometry is a polygon shape.

35. The laser marking system of claim 32 wherein the control means comprises means to dampen ON-time rise of a current signal input for operation of the laser pump source to improve ON-time quality of the marking optical output.

36. The laser marking system of claim 32 wherein the laser pump source comprises a semiconductor laser source or a fiber laser pumped by a semiconductor laser source.

37. The laser marking system of claim 36 wherein the semiconductor laser source comprises at least one laser diode array having a plurality of light emitters with respective light outputs, and means to combine the light outputs for input into the double clad fiber.

38. The laser marking system of claim 36 wherein the semiconductor laser source is operated in a power-on-demand mode in that the semiconductor laser source is turned-on or modulated at anytime that a marking sequence is to be initiated providing a marking output that may be of any selected length and pulse height.

39. The laser marking system of claim 36 further comprising means to control an excitation level of the semiconductor laser source such that marking strokes occur in a predetermined spatial relation at a determined level of marking output power to produce a desired marking contrast at a marking depth in the article surface.

40. The laser marking system of claim 32 wherein the fiber marking laser provides for flexibility in aligning its output beam in maintained relation with an optical input to the scanner requiring no further readjustment.

41. The laser marking system of claim 32 further comprising:

a drive circuit for providing an electrical signal for controlling the laser source and changes in a current level provided to the laser source and, correspondingly, change in an optical output intensity provided from the fiber marking laser;

means for detecting the optical output intensity level from the fiber marking laser; and

feedback means to compare the detected optical output intensity level with a desired level and adjusting the current level to maintain the optical output intensity level at the desired level.

42. The laser marking system of claim 41 further comprising an overdrive circuit in said feedback means to provide initial dampening in applying of the electrical signal to the laser source.

43. The laser marking system of claim 42 wherein the initial dampening causes a rise time of the electrical signal to be reduced in magnitude as the electrical signal nears its peak value.

44. The laser marking system of claim 41 comprising a controller for providing marking signals to the driver circuit representative of indicia strokes of indicia to be formed on the article via a plurality of optical marking signals provided from the fiber marking laser to the optical scanner.

45. The laser marking system of claim 44 wherein a dummy pulse is provided via said controller prior to the initiation of a first marking signal for an initial indicia stroke of an indicia to be formed on the article surface when the marking system has been idle for a period of time so that a full marking stroke for the initial indicia stroke is generated.

46. The laser marking system of claim 44 wherein a preconditioning pulse is provided via said controller prior to the initiation of a first marking signal for an initial indicia stroke of an indicia to be formed on the article surface when the marking system has been idle for a period of time so that some residual energy is present in the fiber marking laser upon initiation of a first marking signal to the fiber marking laser.

47. A method of controlling energization in a laser marking system for marking indicia on a surface of an article, comprising the steps of:

providing a laser pump source optically coupled to pump a fiber marking laser having a single mode, rare earth doped core and providing an optical marking output for marking the article surface;

modulating the laser pump source in accordance with the indicia to be marked on the article surface with a pump signal representative of a predetermined marking intensity level of the optical marking output;

monitoring the marking output to detect the intensity level of the optical marking output;

comparing the detected marking output intensity level with the predetermined marking intensity level; and

changing a value of the pump signal to a value representative of the predetermined marking intensity level.

48. The method of claim 47 wherein the fiber marking laser comprises a double clad fiber and the laser pump source is optically coupled to an inner pump cladding of the double clad fiber.

49. The method of claim 48 wherein the inner pump cladding of the double clad fiber has a noncircular geometry.

50. The method of claim 47 wherein the noncircular geometry is a polygon shape.

51. A method of controlling energization in a laser marking system for marking indicia on a surface of an article where each indicia formed comprises one or more strokes, comprising the steps of:

providing a laser pump source optically coupled to a fiber marking laser;

providing a plurality of electrical marking signals, representative of the indicia strokes, to modulate the laser pump source providing a plurality of optical marking signals, representative of the indicia strokes;

launching the optical marking signals into the fiber marking laser to provide a plurality of laser pulses representative of the indicia strokes at its output for marking the article surface; and

providing an initial optical marking signal to the fiber marking laser prior to the initiation of one or more marking signals when the marking system has been idle for a period of time.

52. The method of claim 51 wherein the initial optical marking signal is a dummy pulse to provide for completion of a full indicia stroke for the first stroke of an indicia to be formed.

53. The method of claim 51 wherein the initial optical marking signal is a preconditioning pulse to provide some residual energy in the fiber marking laser upon initiation of a first marking signal to the fiber marking laser.

54. The method of claim 51 wherein the idle period of time is about one second or more.

55. The method of claim 51 comprising the further steps of:

providing a multiple dimensional scanner to receive the laser pulses from the fiber marking laser; and

synchronously scanning the pulses received from the fiber marking laser to provide marking indicia on the article surface.