Fiber gain medium marking system pumped or seeded by a modulated laser diode source and method of energy control

• US 6,275,250 B1
• Filed: 01/21/1999
• Issued: 08/14/2001
• Est. Priority Date: 05/26/1998
• Status: Expired due to Fees

• Current Assignee: Lumentum Operations, LLC (Lumentum Holdings Inc.)
• Original Assignee: SDL Inc (RWS Holdings Plc)
• Inventors: Alvarez, Ramon E., Welch, David F., Sanders, Steven, MacCormack, Stuart
• Primary Examiner(s): Le, N.
• Assistant Examiner(s): PHAM, HAI CHI
• Application Number:
  US09/235,125
• Time in Patent Office: 936 Days
• Field of Search: 347/237, 347/238, 347/239, 347/247, 347/255, 347/246, 385/123, 385/126, 385/124, 359/341, 372/6, 372/25, 372/24, 372/50, 372/26, 372/33, 372/38, 372/70, 372/75, 327/108, 327/109
• 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 26/0648 comprising lenses
• CPC Class Codes: B23K 26/0665 by beam condensation on the workpiece, e.g. for focusing
• CPC Class Codes: G06K 1/126 by photographic or thermographic registration recording apparatus for measuring instruments G01D15/00

Abstract

Double clad fiber gain medium systems particularly adapted for marking indicia on surfaces of articles are disclosed. These systems provide a modulated output from a pump or seed semiconductor laser source to a double clad fiber gain medium which provides an amplified marking output scanned over the article surface with an optical scanner forming a plurality of strokes, the completion of which results in the indicia.

Claims

1. A fiber gain medium system comprising:

a marking laser comprising double clad fiber having a doped core surrounded by an inner pump cladding of a prescribed cross-sectional geometry and providing a marking output;

a plurality of semiconductor laser sources for pumping said double clad fiber and comprising a plurality of discrete, separately mounted laser diodes and modulated to provide a modulated output from said marking laser the output of said discrete laser diodes combined together;

said combined output coupled to said double clad fiber inner pump cladding so that brightness conservation is achieved;

an optical scanner coupled to receive the marking output from said marking laser as modulated by said discrete laser diodes and scan the marking output over a surface of an article to be marked; and

a controller to control the operation of said optical scanner in synchronism with modulation of said discrete laser diodes to initiate said modulated marking output in multiple directions via said optical scanner to form strokes comprising discernable indicia on the article surface.

2. The fiber gain medium system of claim 1 wherein said laser diodes are broad area diode lasers.

3. The fiber gain medium system of claim 2 wherein said broad area lasers have an aperture of about 100 μ

m or more.

4. The fiber gain medium system of claim 1 wherein the cross-sectional geometry comprising said multimode core is inscribed to be within the cross-sectional geometry of said inner pump cladding.

5. The fiber gain medium system of claim 1 further comprising a plurality of multimode fibers each with a multimode core respectively coupled at their input ends to receive an output from said laser diodes, said multimode fibers fused at their output ends to form a fiber combiner, said fused output ends together forming a single multimode output for coupling to said double clad fiber.

6. The fiber gain medium system of claim 1 wherein said inner pump cladding cross-sectional geometry is circular.

7. The fiber gain medium system of claim 1 wherein said inner pump cladding cross-sectional geometry is polygon.

8. The fiber gain medium system of claim 7 wherein said inner pump cladding cross-sectional geometry is octagon-shaped.

9. The fiber gain medium system of claim 1 wherein said discrete laser diodes are modulated in unison.

10. The fiber gain medium system of claim 1 wherein said discrete laser diodes are independently modulated relative to one another to achieve different marking contrasts to said indicia.

11. The fiber gain medium system of claim 1 wherein said double clad fiber comprises a fiber laser or fiber amplifier.

12. The fiber gain medium system of claim 1 further comprising an isolator provided between said double clad fiber and said optical scanner for preventing light reflected from the surface of the article from being fed back into said double clad fiber.

13. The fiber gain medium system of claim 1 further comprising:

means to divide said modulated marking output into a plurality of outputs for simultaneous marking of surfaces of a plurality of articles.

14. The fiber gain medium system of claim 1 wherein said double clad fiber comprises a fiber amplifier;

said discrete laser diodes coupled to the core of said double clad fiber for providing a seed input for amplification by said fiber amplifier, and means for pumping said amplifier.

15. The fiber gain medium system of claim 1 wherein said double clad fiber comprises multiple fiber amplifiers.

16. The fiber gain medium system of claim 1 further comprising an isolator provided at the optical output of said double clad fiber for preventing light reflected from the surface of the article from being fed back into said double clad fiber.

17. The fiber gain medium marking system of claim 1 wherein said double clad fiber comprises a fiber laser;

said discrete laser diodes coupled to a double clad fiber inner cladding for providing a pump input to said fiber laser.

18. The fiber gain medium marking system of claim 17 further comprising an isolator provided at the optical output of said double clad fiber for preventing light reflected from the surface of the article from being fed back into said double clad fiber.

19. The fiber gain medium system of claim 1 wherein at least one of said laser diodes is operated continuous wave (cw) to maintain said doped double clad fiber approximate to its operational threshold while the remainder of said laser diodes are modulated to provide a modulated output to said doped double clad fiber.

20. The fiber gain medium system of claim 1 wherein the outputs of said discrete laser diodes are combined together into a multimode fiber.

21. A fiber gain medium marking system comprising:

a double clad fiber having a doped core surrounded by an inner pump cladding and providing an optical output for marking at wavelengths in excess of 1,000 μ

m due to the inherent gain bandwidth of said fiber;

a semiconductor laser source for pumping or seeding said double clad fiber;

an optical scanner coupled to receive the optical output from said double clad fiber for scanning said output in at least one dimension over a surface of an article to be marked with said output;

said article comprising a silicon surface with optimum absorption range at wavelengths below about 1,000 μ

m; and

a frequency conversion device provided in optical alignment between the marking output of said double clad fiber and said optical scanner for frequency doubling of said double clad fiber marking output to provide a wavelength below about 1,000 μ

m within the optimum absorptive range of the silicon surface.

22. The fiber gain medium system of claim 21 wherein said frequency conversion device is a quasi-phase matching device.

23. The fiber gain medium system of claim 22 wherein said quasi-phase matching device is a periodically polled lithium niobate (PPLN) device.

24. The fiber gain medium system of claim 21 wherein said frequency conversion device is a bulk phase matching device.

25. The fiber gain medium system of claim 24 wherein said bulk phase matching device comprises angle tuning or temperature tuning.

26. The fiber gain medium system of claim 21 wherein the optimum absorptive range of the silicon surface is within the green spectrum of light.

27. A fiber gain medium system comprising:

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

a semiconductor laser source for pumping or seeding said marking laser;

a drive circuit for providing a modulated output for controlling a current level provided to said semiconductor laser source and, correspondingly, the optical output intensity level provided to said marking laser;

an optical scanner coupled to receive the marking output from said marking laser as modulated by said semiconductor laser source and scan said marking output over a surface of an article to be marked;

a controller to control the operation of said optical scanner in synchronism with modulation of said semiconductor laser source to provide a modulated marking output from said scanner scanned in multiple directions to form strokes comprising discernable indicia on the article surface; and

a circuit control to provide an initially higher peak value in the initiation of the modulated marking output prior to a subsequent steady-state condition to produce a faster initial ON-time response between an application of the modulation of the semiconductor laser source and the modulated output of said marking laser.

28. The fiber gain medium system of claim 27 further comprising means for detecting the optical output power level of said optical output from said double clad fiber;

and

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

29. The fiber gain medium system of claim 27 wherein said double clad fiber is a fiber laser.

30. The fiber gain medium system of claim 27 wherein said double clad fiber is a fiber amplifier.

31. A method of energy control in a fiber gain medium comprising the steps of:

providing a drive circuit for producing a modulated output to control the light output provided from a laser diode source pumping or seeding a fiber marking gain medium;

modulating the diode laser source to provide a corresponding modulated marking output;

scanning the modulated marking output over a surface of an article to be marked in multiple directions to form strokes comprising discernable indicia on the article surface;

controlling the operation of the optical scanner in synchronism with modulation of the laser diode source to provide a modulated marking output from the scanner with scanning thereof in multiple directions to form strokes comprising discernable indicia on the article surface;

controlling the modulated marking output to have an ON-time period with an initial peak value at the beginning of the ON-time period higher than a subsequent steady-state condition of the period; and

reducing the rise time to the initial peak value at the beginning of an ON-time period of the modulated marking output prior to clamping the same to its subsequent steady-state condition reducing the response time between initiation of the modulated marking output and the onset of the laser diode modulated output.

32. The method of energy control of claim 31 comprising the further step of optically isolating the fiber gain medium from any light reflected back from the surface of the article.

33. The method of energy control of claim 31 wherein said fiber gain medium is a fiber laser.

34. The method of energy control of claim 33 comprising the further step of optically isolating the fiber laser from any light reflected back into the fiber laser.

35. The method of energy control of claim 31 wherein said fiber gain medium is a fiber amplifier.

36. The method of energy control of claim 31 wherein said fiber gain medium is a plurality of fiber amplifiers.

37. A fiber gain medium system comprising:

a gain medium comprising a fiber having a doped core and providing an optical marking output;

a plurality of semiconductor laser sources for pumping said gain and comprising a plurality of discrete, separately mounted laser diodes and modulated to provide a modulated output from said gain medium;

an optical scanner coupled to receive the marking output from said marking laser as modulated by said discrete laser diodes and scan the marking output over a surface of an article to be marked; and

a controller to control the operation of said optical scanner synchronously with combined modulation of said discrete laser diodes to initiate said modulated marking output in multiple directions via said optical scanner to form strokes comprising discernable indicia on the article surface;

said discrete laser diodes independently modulated relative to one another to achieve different marking contrasts for said discernable indicia.

38. The fiber gain medium system of claim 37 wherein the outputs of said discrete laser diodes are combined together into a multimode core of a multimode fiber.

39. The fiber gain medium system of claim 37 further comprising a plurality of multimode fibers each with a multimode core respectively coupled at their input ends to receive an output from said laser diodes, said multimode fibers fused at their output ends to form a fiber combiner, said fused output ends together forming a single multimode output for coupling to said double clad fiber.

40. The fiber gain medium system of claim 37 wherein said modulated marking output is divided into a plurality of outputs for simultaneous marking of surfaces of a plurality of articles.

41. The fiber gain medium system of claim 37 wherein said gain medium is a fiber laser or a fiber amplifier.