Yb: and Nd: mode-locked oscillators and fiber systems incorporated in solid-state short pulse laser systems

• US 9,590,386 B2
• Filed: 09/10/2014
• Issued: 03/07/2017
• Est. Priority Date: 12/07/2004
• Status: Active Grant

• Current Assignee: IMRA America Incorporated (Aisin Corp.)
• Original Assignee: IMRA America Incorporated (Aisin Corp.)
• Inventors: Harter, Donald J., Cho, Gyu C., Liu, Zhenlin, Fermann, Martin E., Gu, Xinhua, Nati, Salvatore F., Shah, Lawrence, Hartl, Ingmar, Bendett, Mark
• Primary Examiner(s): Rodriguez, Armando
• Application Number:
  US14/482,093
• Publication Number:
  US 20140376084A1
• Time in Patent Office: 909 Days
• US Class Current: 1/1
• 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 3/0085 Modulating the output, i.e. the laser beam is modulated outside the laser cavity
• CPC Class Codes: H01S 3/0092 Nonlinear frequency conversion, e.g. second harmonic generation [SHG] or sum- or difference-frequency generation outside the laser cavity nonlinear frequency conversion per se G02F1/35
• CPC Class Codes: H01S 3/06712 Polarising fibre; Polariser
• CPC Class Codes: H01S 3/06725 Fibre characterized by a specific dispersion, e.g. for pulse shaping in soliton lasers or for dispersion compensating [DCF]
• CPC Class Codes: H01S 3/0675 Resonators including a grating structure, e.g. distributed Bragg reflectors [DBR] or distributed feedback [DFB] fibre lasers
• CPC Class Codes: H01S 3/06754 Fibre amplifiers H01S3/06708 takes precedence
• CPC Class Codes: H01S 3/06758 Tandem amplifiers
• CPC Class Codes: H01S 3/094003 the pumped medium being a fibre
• CPC Class Codes: H01S 3/094019 Side pumped fibre, whereby pump light is coupled laterally into the fibre via an optical component like a prism, or a grating, or via V-groove coupling
• CPC Class Codes: H01S 3/094042 of a fibre laser
• CPC Class Codes: H01S 3/094076 Pulsed or modulated pumping H01S3/1024 takes precedence
• CPC Class Codes: H01S 3/09415 the pumping beam being parallel to the lasing mode of the pumped medium, e.g. end-pumping
• CPC Class Codes: H01S 3/1086 using scattering effects, e.g. Raman or Brillouin effect
• CPC Class Codes: H01S 3/109 Frequency multiplication, e.g. harmonic generation
• CPC Class Codes: H01S 3/1106 Mode locking
• CPC Class Codes: H01S 3/1118 Semiconductor saturable absorbers, e.g. semiconductor saturable absorber mirrors [SESAMs]; Solid-state saturable absorbers, e.g. carbon nanotube [CNT] based
• CPC Class Codes: H01S 3/113 using intracavity saturable absorbers
• CPC Class Codes: H01S 3/1305 : Feedback control systems
• CPC Class Codes: H01S 3/1611 : neodymium
• CPC Class Codes: H01S 3/1618 : ytterbium
• CPC Class Codes: H01S 3/1643 : YAG
• CPC Class Codes: H01S 3/235 : Regenerative amplifiers

Abstract

The invention describes classes of robust fiber laser systems usable as pulse sources for Nd: or Yb: based regenerative amplifiers intended for industrial settings. The invention modifies adapts and incorporates several recent advances in FCPA systems to use as the input source for this new class of regenerative amplifier.

Claims

1. A pulse source, comprising:

a seed source emitting seed pulses;

at least one fiber amplifier receiving said seed pulses;

a monitor for one or more parameters of said pulse source, said monitor being operatively coupled to at least said seed source and responsive to one or more parameters of said seed source;

one or more pump laser diodes for pumping said seed source and said at least one fiber amplifier; and

a bulk optical amplifier receiving amplified pulses from said at least one amplifier and producing output pulses,

wherein said bulk optical amplifier comprises a regenerative amplifier, a rod, slab, or thin disk, and said monitor is operatively coupled to at least one of said seed source, said bulk optical amplifier, or said one or more pump diodes.

2. The pulse source according to claim 1, said pulse source comprising a pulse conditioner disposed between said seed source and said bulk optical amplifier, said pulse conditioner configured for at least one of:

spectral narrowing, broadening or shaping, wavelength converting, temporal pulse compression or stretching, pulse attenuation, or lowering of the repetition rate of a pulse train generated by said seed source.

3. The pulse source according to claim 1, wherein said monitor comprises a controller operatively coupled to said seed source, said monitor being configured to adjust at least one of mode locked frequency, optical power, or mode lock calibration.

4. The pulse source according to claim 1, wherein said monitor comprises a controller having at least one module for extracting a tap signal for feedback control.

5. The pulse source according to claim 1, wherein said monitor comprises a device for monitoring one or more of pulse width, wavelength, repetition rate, polarization and temporal delay characteristics of pulses produced by said seed source.

6. The pulse source according to claim 1, wherein said monitor comprises a controller configured to control one or more of a power and spectrum generated with said pulse source.

7. The pulse source according to claim 1, wherein said seed source comprises a mode locked fiber oscillator, and said monitor comprises a controller having a mode-lock start-up and search algorithm.

8. The pulse source according to claim 1, wherein said parameter comprises a gain of said at least one fiber amplifier.

9. The pulse source according to claim 1, wherein said monitor comprises a beam manipulator comprising:

one or more of an optical gating device, a power meter, a non-linear crystal, and a spectrometer.

10. The pulse source according to claim 1, wherein said seed source comprises a mode locked fiber oscillator, said oscillator comprising:

concatenated sections of optical fiber comprising at least one section of polarization maintaining fiber.

11. The pulse source according to claim 1, further comprising a feedback controller coupled to one or more of said seed source and said at least one fiber amplifier.

12. The pulse source according to claim 1, further comprising a variable attenuator disposed between said seed source and said at least one fiber amplifier, said variable attenuator having an adjustable transmission such that optical energy coupled from said seed source to said at least one fiber amplifier can be reduced.

13. The pulse source according to claim 1, further comprising:

a pulse compressor disposed downstream from said bulk optical amplifier and a pulse stretcher disposed upstream of at least one fiber amplifier.

14. The pulse source according to claim 13, wherein said compressor recompresses pulses emitted from said bulk optical amplifier to near the bandwidth limit.

15. The pulse source according to claim 1, wherein at least one fiber amplifier produces a pulse having pulse energy greater than 20 nJ.

16. The pulse source according to claim 1, wherein said seed source comprises a mode locked fiber oscillator.

17. The pulse source according to claim 1, wherein seed source comprises a laser diode with multiple drive signals.

18. The pulse source according to claim 1, wherein said at least one fiber amplifier comprises a non-linear amplifier that generates self-phase modulation, said self- phase modulation spectrally compressing pulses propagating in said non-linear amplifier to a spectral width smaller than an injected spectral width of said seed pulses, whereby a spectral width of pulses emerging from said at least one fiber amplifier is spectrally narrowed as compared to said injected spectral width, and said spectrally narrowed pulses are matched to a gain bandwidth of said bulk optical amplifier, and wherein said pulse source further comprising a frequency converter disposed downstream from said at least one fiber amplifier, said frequency converter receiving spectrally narrowed pulses from said at least one fiber amplifier.

19. The pulse source according to claim 1, wherein a gain medium of said bulk optical amplifier comprises Yb:

YAG, Nd;

YAG, Nd;

YLF, Nd;

YVO.sub.4, Nd;

glass, Yb, glass, Nd;

KGW, or a narrow bandwidth Nd-based crystal.

20. The pulse source according to claim 1, said pulse source comprising an electro-optic or acousto-optic modulator disposed between said seed source and said bulk optical amplifier, said modulator configured as a pulse picker to reduce a repetition rate to within a range of 1 KHz to 1 MHz.

21. The pulse source according to claim 1, further comprising a frequency converter disposed at an output of said bulk amplifier.

22. The pulse source according to claim 1, further comprising a pulse stretcher comprising a first length of optical fiber, said pulse stretcher configured to receive and temporally stretch said seed pulses.

23. The pulse source according to claim 22, further comprising a pulse compressor disposed downstream from said at least one fiber amplifier, said pulse compressor configured to compress said temporally stretched and amplified pulses and to produce compressed output pulses.

24. The pulse source according to claim 23, wherein said pulse source comprises a bulk amplifier disposed upstream from said compressor, and said compressor recompresses the pulses emitted from said bulk optical amplifier to near the bandwidth limit, said compressor comprising one or more of a bulk optic component, single grating compressor, a dispersive prism, a grism, a dispersive delay line, a fiber or bulk Bragg grating, and a chirped periodically poled crystal.

25. The pulse source according to claim 1, wherein said seed source comprises a mode locked fiber oscillator, and said one or more parameters comprise at least a frequency of said mode locked fiber oscillator.

26. The pulse source according to claim 1, wherein said seed source comprises a mode locked fiber oscillator, and said at least one of said one or more parameters is representative of mode lock startup of said mode locked fiber oscillator.

27. The pulse source according to claim 1, wherein at least one of said one or more parameters is both measurable and controllable by said monitor having a sensor and controller.

28. The pulse source according to claim 1, wherein said seed source comprises a mode locked fiber oscillator, and said mode-locked fiber oscillator generates broadband pulses having a bandwidth comparable to the bandwidth of the mode-locked fiber oscillator gain medium;

and wherein said seed source comprises one or both of a first pulse compressor or dispersion compensator, said seed source generating seed pulses having pulse widths in the range from about 20 fs to about 200 fs.

29. The pulse source according to claim 1, wherein said monitor comprises a sensor and a controller.

30. The pulse source according to claim 29, wherein said monitor is configured to adjust a seed source parameter.

31. The pulse source according to claim 29, wherein said monitor is configured to adjust a parameter of said at least one fiber amplifier.

32. The pulse source according to claim 1, wherein pulse source further comprises:

a fiber with positive group-velocity dispersion (GVD) and self-phase modulation (SPM) optically coupled to said seed source and producing pulses compressible to pulse widths of about 10 ps or less, said fiber disposed between said seed source and said bulk optical amplifier; and

a pulse compressor disposed downstream from said bulk optical amplifier arranged to produce compressed output pulses having pulse widths of about 10 ps or less,

wherein said fiber with GVD and SPM comprises a multimode amplifier fiber, and said at least one fiber amplifier comprises said fiber with GVD and SPM.

33. The pulse source according to claim 1, wherein said at least one fiber amplifier is operably arranged as a fiber amplifier chain.