Semiconductor laser highpower amplifier system

• US 6,335,941 B1
• Filed: 05/15/2000
• Issued: 01/01/2002
• Est. Priority Date: 02/19/1997
• Status: Expired due to Term

• Current Assignee: Lumentum Operations, LLC (Lumentum Holdings Inc.)
• Original Assignee: SDL Inc (RWS Holdings Plc)
• Inventors: Zanoni, Raymond, Grubb, Stephen G., Welch, David F.
• Primary Examiner(s): Arroyo, Teresa M.
• Assistant Examiner(s): Jackson, Cornelius H.
• Application Number:
  US09/571,711
• Time in Patent Office: 596 Days
• Field of Search: 372/6, 359/179, 359/341
• US Class Current: 372/6
• 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 semiconductor laser source for providing at its output a signal having a peak wavelength, λ

_S;

means to modulate said semiconductor laser source to provide a plurality of pulses and vary any one of pulse amplitude, pulse rate and pulse contour;

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

a fiber delay line coupled between said semiconductor laser source and said first stage fiber gain medium to prevent said semiconductor laser source from being affected by feedback noise from said first stage fiber gain medium; and

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

2. The high power laser optical amplifier system according to claim 1 wherein at least one of said fiber stages is a double clad gain medium having a core for amplifying said signal and an inner pump cladding.

3. The high power laser optical amplifier system according to claim 2 wherein said double clad gain medium is a fiber amplifier.

4. The high power laser optical amplifier system according to claim 2 wherein said double clad gain medium is a fiber laser.

5. The high power laser optical amplifier system according to claim 2 wherein said double clad gain medium is a fiber amplifier or a double pass amplifier.

6. The high power laser optical amplifier system according to claim 1 wherein said first stage gain medium is a single mode fiber amplifier and said second stage gain medium is a double pass amplifier.

7. The high power laser optical amplifier system according to claim 1 wherein said first stage gain medium is a fiber laser and said second stage gain medium is a fiber amplifier.

8. The high power laser optical amplifier system according to claim 1 wherein at least one of said stages comprises a double pass fiber amplifier having a first end for receiving said signal for amplification and a second end coupled to a reflector having a peak reflection at λ

_S, said reflector coupled to a pump source having a peak wavelength, λ

_P, suitable for pumping said double pass fiber amplifier and wavelength transparent to said reflector.

9. The high power laser optical amplifier system according to claim 8 wherein said λ

_S peak reflector comprises a fiber grating.

10. The high power laser optical amplifier system according to claim 1 wherein both of said stages comprise a double pass fiber amplifier having a first end for receiving said signal for amplification and a second end coupled to a reflector having a peak reflection at λ

_S, said reflector coupled to a pump source having a peak wavelength, λ

_P, suitable for pumping said double pass fiber amplifier and wavelength transparent to said reflector.

11. The high power laser optical amplifier system according to claim 10 wherein said λ

_S peak reflector comprises a fiber grating.

12. The high power laser optical amplifier system according to claim 1 wherein said first stage gain medium is a rare earth doped, single mode fiber and said second stage gain medium is a rare earth doped, double clad amplifier.

13. The high power laser optical amplifier system of claim 1 wherein said modulating means varies the contour of said pulses.

14. The high power laser optical amplifier system of claim 1 wherein said modulating means varies the width of said pulses.

15. The high power laser optical amplifier system of claim 1 wherein said modulating means varies the repetition rate of said pulses.

16. The high power laser optical amplifier system according to claim 1 further comprising means for rejecting ASE buildup in said first stage gain medium from backward propagating to said semiconductor laser source.

17. The high power laser optical amplifier system according to claim 1 further comprising means for rejecting propagating ASE buildup in said second stage gain medium from backward propagating toward said first stage gain medium.

18. The high power laser optical amplifier system of claim 1 wherein output from the system is employed for texturing substrate surfaces for a magnetic recording medium.

19. The high power laser optical amplifier system of claim 1 wherein output from the system is employed for heat treatment, surface engraving, surface ablation, cutting, grooving, bump forming, coating, soldering, sealing, surface diffusion and surface conversion to a compound.

20. A high power laser optical amplifier system comprising:

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

_S;

at least one fiber amplifier comprising a fiber with a core doped with an active gain element coupled to receive the signal and provide an amplified output;

a pump source for pumping the fiber amplifier; and

a fiber delay line coupled between said semiconductor laser source and said fiber amplifier to suppress backward scattered light from interfering with operation of said semiconductor laser source.

21. The high power laser optical amplifier system of claim 20 further comprising means coupled between said semiconductor laser source and said fiber amplifier to suppress backward propagating ASE from said fiber amplifier toward said semiconductor laser source.

22. The high power laser optical amplifier system of claim 20 wherein output from the system is employed for heat treatment, surface engraving, surface ablation, surface texturing, cutting, grooving, bump forming, coating, soldering, sealing, surface diffusion and surface conversion to a compound.