Semiconductor laser high power amplifier system

• US 6,347,007 B1
• Filed: 06/02/2000
• Issued: 02/12/2002
• Est. Priority Date: 02/19/1997
• Status: Expired due to Term

• Current Assignee: Lumentum Operations, LLC (Lumentum Holdings Inc.)
• Original Assignee: SDL PLC (RWS Holdings Plc)
• Inventors: Zanoni, Raymond, Grubb, Stephen G., Welch, David F.
• Primary Examiner(s): Moskowitz, Nelson
• Application Number:
  US09/586,405
• Time in Patent Office: 620 Days
• Field of Search: 359/124, 359/334, 359/337, 359/347, 359/337.2, 359/337.21, 372/18, 372/19
• US Class Current: 359/337.21
• 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: H01S 2301/02 ASE (amplified spontaneous emission), noise; Reduction thereof
• CPC Class Codes: H01S 3/005 Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping shaping laser beam for working metal or other materials B23K26/06; optical elements, systems or apparatus in general G02B
• CPC Class Codes: H01S 3/0057 Temporal shaping, e.g. pulse compression, frequency chirping soliton generation and propagation G02F1/3513, H01S3/063 and H01S3/108
• CPC Class Codes: H01S 3/0064 Anti-reflection devices, e.g. optical isolaters absorbing layers for marking or protecting purposes in laser working B23K26/50; magneto-optical non-reciprocal devices G02F1/093, G02F1/0955
• CPC Class Codes: H01S 3/06729 Peculiar transverse fibre profile
• CPC Class Codes: H01S 3/06754 Fibre amplifiers H01S3/06708 takes precedence
• CPC Class Codes: H01S 3/06787 Bidirectional amplifier
• CPC Class Codes: H01S 3/094003 the pumped medium being a fibre
• CPC Class Codes: H01S 3/094015 with pump light recycling, i.e. with reinjection of the unused pump light back into the fiber, e.g. by reflectors or circulators
• CPC Class Codes: H01S 3/094026 for synchronously pumping, e.g. for mode locking
• CPC Class Codes: H01S 3/094042 of a fibre laser
• CPC Class Codes: H01S 3/094061 Shared pump, i.e. pump light of a single pump source is used to pump plural gain media in parallel
• CPC Class Codes: H01S 3/10023 by functional association of additional optical elements, e.g. filters, gratings, reflectors
• CPC Class Codes: H01S 3/2316 Cascaded amplifiers
• CPC Class Codes: H01S 3/2333 Double-pass amplifiers
• CPC Class Codes: H01S 5/06216 Pulse modulation or generation

Abstract

A high power laser optical amplifier system for material processing comprises multiple stage fiber amplifiers with rejection of propagating ASE buildup in and between the amplifier stages as well as elimination of SBS noise providing output powers in the range of about 10 μJ to about 100 μJ or more. The system is driven with a time varying drive signal from a modulated semiconductor laser signal source to produce an optical output allowing modification of the material while controlling its thermal sensitivity by varying pulse shapes or pulse widths supplied at a desire repetition rate via modulation of a semiconductor laser signal source to the system to precisely control the applied power application of the beam relative to the thermal sensitivity of the material to be processed. The high power fiber amplifier system has particular utility in high power applications requiring process treatment of surfaces, such as polymeric, organic, ceramic and metal surfaces, e.g., material processing, surface texturing, heat treatment, surface engraving, fine micro-machining, surface ablation, cutting, grooving, bump forming, coating, soldering, sealing, surface diffusion and surface conversion to a compound. A particular example is given for texturing of disk surfaces of magnetic disk media prior to the deposition or coating of a thin magnetic film on the textured surfaces to prevent slider stiction.

Claims

1. A high power laser optical amplifier system comprising:

a laser source that is modulated between active and inactive states so as to provide at its output a pulsed signal having a peak wavelength, λ

_s;

a first stage fiber gain medium coupled to receive said signal for amplification;

a second stage gain medium couple to said first stage fiber gain medium to receive the amplified signal from said first stage fiber gain medium for further amplification;

means at the output of said laser source for operating said laser source in multiple longitudinal modes to suppress the generation of SBS in said stage gain medium; and

an optical signal path between the laser source and the first stage fiber gain medium having a predetermined length such that SBS energy that might be returned to the laser source from the first stage fiber gain medium arrives at the laser source during its inactive states.

2. The high power laser optical amplifier system of claim 1 wherein said means comprises a broadband fiber grating coupled between said laser source and said first stage fiber gain medium.

3. The high power laser optical amplifier system of claim 1 wherein the system comprises a fiber delay line coupled between said laser source and said first stage fiber gain medium.

4. The high power laser optical amplifier system of claim 1 wherein said laser source is a semiconductor laser or fiber laser.

5. The high power laser optical amplifier system of claim 1 further comprising an optical circulator coupler to receive the amplified signal output from first stage fiber gain medium.

6. The high power laser optical amplifier system of claim 5 wherein said second stage fiber gain medium is coupled to a port of said circulator, such that a signal output from the first stage fiber gain medium passes through the circulator before reaching the second stage fiber gain medium.

7. The high power laser optical amplifier system of claim 1 wherein said first and second stage fiber gain mediums are pumped by the same pump source.

8. The high power laser optical amplifier system of claim 7 wherein in said pump source is a semiconductor laser source or fiber laser source.

9. The high power laser optical amplifier system of claim 1 wherein said first;

and second stage fiber gain medium are pumped by separate pump sources.

10. The high power laser optical amplifier system of claim 9 wherein in said pump source is a semiconductor laser source or fiber laser source.

11. The high power laser optical amplifier system of claim 1 wherein the amplified signal from the system has a pulsed character that is appropriate for texturing substrate surfaces during the preparation of a magnetic recording medium.

12. The high power laser optical amplifier system of claim 11 wherein the amplified signal is a pulsed signal via modulation of said laser source, and the amplified signal is coupled to beam splitting means for distribution of portions of said output beam to plural of said substrate surfaces for concurrent texturing of the surfaces.

13. The high power laser optical amplifier system of claim 12 wherein said plural surfaces comprise two surfaces.

14. The high power laser optical amplifier system of claim 12 wherein said plural surfaces comprise several surfaces.

15. The high power laser optical amplifier system of claim 12 wherein said beam splitting means comprises a star coupler.

16. The high power laser optical amplifier system of claim 1 wherein said first stage fiber gain medium is a single mode fiber doped with its core doped with a rare earth dopant and said second stage fiber gain medium is a double clad fiber with its core doped with a rare earth dopant.

17. The high power laser optical amplifier system of claim 1 further comprising a narrow band WDM coupler coupled between said laser source and said first stage fiber gain medium to suppress backward propagating ASE toward said laser source.

18. The high power laser optical amplifier system of claim 17 wherein said narrow band WDM has second ports for loss coupling of said backward propagating ASE.

19. The high power laser optical amplifier system of claim 17 wherein said narrow band WDM coupler has an input port to receive said source signal, two output ports each terminating in a fiber pigtail, a fiber grating in each of said fiber pigtails, said fiber gratings highly reflective of said given wavelength but loss transmissive of propagating ASE, and a third output port coupled to first stage fiber gain medium.

20. The high power laser optical amplifier system of claim 1 wherein said laser source is a MOPA.

21. The high power laser optical amplifier system of claim 1 wherein optical coupling of said first and second stage gain medium is accomplished with an optical circulator.

22. The high power laser optical amplifier system of claim 1 further comprising means in said system to suppress system noise.

23. The high power laser optical amplifier system of claim 22 wherein said noise suppression means comprises a delay fiber line coupled between said laser source and said first stage fiber gain medium.

24. The high power laser optical amplifier system of claim 22 wherein said noise suppression means comprises a fiber coupler coupled between said laser source and said first stage fiber gain medium having second ports for loss coupling of backward propagating ASE.

25. The high power laser optical amplifier system of claim 22 wherein said noise suppression means comprises an optical circulator for coupling said first stage fiber gain medium to said second stage fiber gain medium.

26. The high power laser optical amplifier system of claim 22 wherein said noise suppression means comprises fiber coupler coupled between said laser source and said first fiber amplifier, said fiber coupler having an input port to receive said source signal, two output ports each terminating in a fiber pigtail, a fiber grating in each of said fiber pigtails, said fiber gratings highly reflective of said given wavelength but loss transmissive of propagating ASE, and a third output port coupled to said first stage fiber gain medium.

27. The high power laser optical amplifier system of claim 1 wherein a pulse energy of said pulsed signal output from said second stage fiber gain medium is in excess of 1 μ

J.

28. The high power laser optical amplifier system of claim 1 wherein a pulse width of said pulsed signal output from said second stage fiber gain medium is in the range of about 10 nsec to about 200 nsec.

29. The high power laser optical amplifier system of claim 1 wherein a pulse repetition rate of said pulsed signal output from said second stage fiber gain medium is in the range of about 1 kHz to about 100 kHz.

30. The high power laser optical amplifier system of claim 1 wherein long-term pulse to pulse energy stability of the system is less than 1% rms.

31. The high power laser optical amplifier system of claim 1 wherein said first stage fiber gain medium comprises a first two pass fiber amplifier with a core doped with an active gain element and having a first end coupled to said optical circulator and having a second end coupled to a first pump source for pumping said core, a highly reflective fiber grating incorporated between said first fiber amplifier and said first pump source for reflecting said signal wavelength but transmissive of pump source emission;

and

said second stage fiber gain medium comprises a second two pass fiber amplifier with a core doped with. an active gain element and having a first end coupled to said optical circulator and having a second end coupled to a second pump source for pumping said core, a highly reflective fiber grating incorporated between said second fiber amplifier and said second pump source for reflecting said signal wavelength but transmissive of pump source emission.

32. The high power laser optical amplifier system of claim 31 wherein said first fiber amplifier is a single mode fiber and said second fiber amplifier is a multimode fiber.

33. The high power laser optical amplifier system of claim 31 wherein said second fiber amplifier is a double clad fiber.

34. The high power laser optical amplifier system of claim 31 wherein the system is employed for texturing substrate surfaces for a magnetic recording medium.

35. The high power laser optical amplifier system of claim 31 wherein a signal output of the system is a pulsed signal through modulation of said laser source, said signal is coupled to beam splitting means for distribution of portions of said output beam to plural of said substrate surfaces for concurrent texturing of said surfaces.

36. The high power laser optical amplifier system of claim 35 wherein said plural surfaces comprise two surfaces.

37. The high power laser optical amplifier system of claim 35 wherein said plural surfaces comprise several surfaces.

38. The high power laser optical amplifier system of claim 35 wherein said beam splitting means comprises a star coupler.

39. The high power laser optical amplifier system of claim 35 wherein said beam splitting means comprises a plurality of beam splitting mirrors.

40. A high power laser optical amplifier system comprising:

a laser source for providing at its output a signal having a peak wavelength, λ

_s;

a first stage fiber gain medium coupled to receive said signal for amplification;

a second stage gain medium couple to said first stage fiber gain medium to receive the amplified signal from said first stage fiber gain medium for further amplification; and

a fiber coupler between the laser source and the first fiber amplifier, the fiber coupler having an input port to receive said source signal, first and second output ports terminating, respectively, in first and second fiber gratings, and a third output port coupled to said first stage fiber gain medium, said fiber gratings being highly reflective at λ

_s but highly transmissive at a wavelength of SBS noise propagating from the first stage gain medium toward the coupler, the gratings also providing feedback to the laser source and having a relatively wide reflectivity bandwidth such that the laser source operates in multiple longitudinal modes.

41. A high power laser optical amplifier system according to claim 40 wherein the fiber coupler is a 3 dB coupler.