COMPACT, COHERENT, HIGH BRIGHTNESS LIGHT SOURCES FOR THE MID AND FAR IR

• US 20120205352A1
• Filed: 02/14/2011
• Published: 08/16/2012
• Est. Priority Date: 02/14/2011
• Status: Active Grant

• Current Assignee: IMRA America Incorporated (Aisin Corp.)
• Original Assignee: IMRA America Incorporated (Aisin Corp.)
• Inventors: FERMANN, Martin
• Granted Patent: US 8,787,410 B2
• Time in Patent Office: Days
• US Class Current: 219/121.67
• CPC Class Codes: B23K 26/352 for surface treatment
• CPC Class Codes: B23K 26/361 for deburring or mechanical trimming B23K26/351 takes precedence
• CPC Class Codes: B23K 26/362 Laser etching
• 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 3/06741 Photonic crystal fibre, i.e. the fibre having a photonic bandgap
• 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 3/06791 Fibre ring lasers fibre laser gyrometers G01C19/72
• CPC Class Codes: H01S 3/10015 by monitoring or controlling, e.g. attenuating, the input signal
• CPC Class Codes: H01S 3/10092 Coherent seed, e.g. injection locking
• CPC Class Codes: H01S 3/1112 Passive 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 3/1608 erbium
• CPC Class Codes: H01S 3/1616 thulium

Abstract

Compact high brightness light sources for the mid and far IR spectral region, and exemplary applications are disclosed based on passively mode locked Tm fiber comb lasers. In at least one embodiment the coherence of the comb sources is increased in a system utilizing an amplified single-frequency laser to pump the Tm fiber comb laser. The optical bandwidth generated by the passively mode locked Tm fiber comb laser is further decreased by using simultaneous 2^nd and 3^rd order dispersion compensation using either appropriate chirped fiber Bragg gratings for dispersion compensation, or fibers with appropriately selected values of 2^nd and 3^rd order dispersion. Fibers with large anomalous values of third order dispersion, or fibers with large numerical apertures, for example fibers having air-holes formed in the fiber cladding may be utilized.

Claims

1. A fiber-laser based system, comprising;

a passively mode locked fiber oscillator operating at or near a wavelength of 2000 nm, said oscillator comprising a plurality of fiber sections, each section having at least one length of fiber, wherein;

a first fiber section has a positive dispersion value, D2₁,

a second fiber section has a negative dispersion value, D2₂,

said first fiber section has a negative third order dispersion value, D3₁,

said second fiber section has a positive third order dispersion value, D3₂,

and said dispersion values approximately satisfy the relation;

0.2<

(D2₁/D3₁)/(D2₂/D3₂)<

5,

wherein said dispersion values provide overall cavity dispersion in a range of about ±

20,000 fs² per meter intra-cavity fiber length; and

a pump source to pump said passively mode locked fiber oscillator.

2. The fiber-laser based system according to claim 1, wherein said dispersion values approximately satisfy the relation:

0.5<

(D2₁/D3₁)/(D2₂/D3₂)<

2.

3. The fiber-laser based system according to claim 1, wherein said dispersion values approximately satisfy the relation:

0.7<

(D2₁/D3₁)/(D2₂/D3₂)<

1.3.

4. The fiber-laser based system according to claim 1, wherein said passively mode locked fiber oscillator operates in the wavelength range from about 1700 nm to about 2500 nm.

5. The fiber-laser based system according to claim 1, wherein said passively mode locked fiber oscillator comprises a Tm, a Tm:

Ho, or a Ho doped fiber.

6. The fiber-laser based system according to claim 1, further comprising a continuum fiber for super continuum generation.

7. The fiber-laser based system according to claim 6, further comprising a fiber amplifier inserted between said oscillator and said continuum fiber.

8. The fiber-laser based system according to claim 7, wherein said fiber amplifier is capable of higher order soliton compression, nonlinear compression, Raman soliton generation or chirped pulse amplification.

9. The fiber-laser based system according to claim 7, wherein said fiber amplifier is core pumped or cladding pumped.

10. The fiber-laser based system according to claim 9, wherein said fiber amplifier is core pumped with an Er fiber amplifier.

11. The fiber-laser based system according to claim 7, further comprising a highly nonlinear silica fiber spliced directly to the output of said oscillator.

12. The fiber-laser based system according to claim 7, further comprising a highly nonlinear silica fiber spliced directly to the output of said fiber amplifier.

13. The fiber-laser based system according to claim 1, wherein said oscillator is core pumped, and said pump source comprises:

a single-frequency laser; and

an Er fiber amplifier amplifying an output of said single-frequency laser.

14. The fiber-laser based system according to claim 1, further comprising a modulator to vary an output power of said pump source in such a way as to control a carrier envelope offset frequency within said oscillator.

15. The fiber-laser based system according to claim 1, wherein said oscillator comprises a saturable absorber.

16. The fiber-laser based system according to claim 1, wherein said oscillator is configured as a ring oscillator.

17. The fiber-laser based system according to claim 1, further comprising an extra-cavity acousto-optic frequency shifter for carrier envelope phase control.

18. The fiber-laser based system according to claim 6, further comprising an f-2f interferometer for carrier phase measurements.

19. The fiber-laser based system according to claim 18, wherein said f-2f interferometer is configured for carrier phase control of said oscillator.

43. The fiber-laser based system according to claim 1, further comprising an intra-cavity electronically addressable optical component inserted into the intra-cavity beam path for carrier phase control.

44. The fiber-laser based system according to claim 43, wherein said intra-cavity electronically addressable optical component comprises an acousto-optic modulator configured for intra-cavity loss and carrier phase control.

45. The fiber-laser based system according to claim 7, further comprising an undoped fiber inserted between said amplifier and said continuum fiber, where said undoped fiber does not produce substantial gain.

46. The fiber-laser based system according to claim 45, wherein said undoped fiber is capable of higher order soliton compression, nonlinear compression or Raman soliton generation.

47. The fiber-laser based system according to claim 45, further comprising a highly nonlinear silica fiber spliced directly to the output of said undoped fiber.

20. An optical sub-surface micromachining apparatus comprising:

A fiber-laser based system generating pulses having pulse widths less than about 100 ps, in a wavelength range from about 1700 to 2500 nm.

21. The optical sub-surface micromachining apparatus according to claim 20, wherein said micro-machining apparatus is configured for machining of silicon.

22. A fiber-laser based system, comprising;

a passively mode locked fiber oscillator comprising a gain fiber having a negative dispersion value D2₁;

at least one fiber section with a positive dispersion value D2₂ wherein the absolute value of D2₁ is at least 1.5 times larger than the absolute value of D2₂;

a chirped fiber grating to compensate for the residual dispersion value of the oscillator, such that the overall cavity dispersion is in a range of about ±

20,000 fs² per meter cavity fiber length; and

a pump source to pump said passively mode locked fiber oscillator.

23-36. -36. (canceled)

37. A fiber-laser based, chirped pulse amplification system, comprising:

a passively mode locked fiber oscillator operating at or near a wavelength of 2000 nm;

a pulse stretcher receiving pulses from said passively mode locked fiber oscillator and producing stretched pulses;

a fiber amplifier amplifying said stretched pulses and producing stretched and amplified pulses;

a linear pulse compressor to compress said stretched and amplified pulses; and

a large mode area fiber configured to nonlinearly compress the pulses output from the linear pulse compressor so as to further compress the pulses.

38-42. -42. (canceled)

48-52. -52. (canceled)

53. A fiber-laser based system comprising:

negative dispersion gain fiber and positive dispersion undoped fiber, wherein the core size of the gain fiber is larger than the core size of the undoped fiber, and wherein said system produces pulses with an approximately parabolic pulse spectrum.

54. A fiber-laser based amplification system, comprising:

a passively mode locked fiber oscillator operating at or near a wavelength of 2000 nm;

a pulse stretcher receiving pulses from said passively mode locked fiber oscillator and producing stretched pulses, said pulse stretcher providing anomalous third order dispersion;

a fiber amplifier amplifying said stretched pulses and producing recompressed and amplified pulses at an output thereof.

55. A fiber-laser based amplification system, according to claim 54, wherein said amplifier is nonlinear and provides a value of self-phase modulation of at least 2.

56. A fiber-laser based amplification system, according to claim 55, wherein the spectrum at the output of said amplifier is broadened due to said self-phase modulation.

57. A fiber-laser based amplification system, according to claim 55, wherein the pulses at the output of said amplifier are nonlinearly compressed due to said self-phase modulation.

58. A fiber-laser based amplification system, according to claim 54, further comprising a highly nonlinear fiber directly spliced to the output of said amplifier.

59. A fiber-laser based amplification system, according to claim 54, further comprising an undoped fiber directly spliced to the output of said amplifier.

60. A fiber-laser based amplification system, according to claim 58, further comprising an undoped fiber directly spliced to the output of said amplifier.

61. A fiber-laser based amplification system, according to claim 59, wherein said undoped fiber is nonlinear and provides a value of self-phase modulation of at least 2.

62. A fiber-laser based amplification system, comprising:

a passively mode locked fiber oscillator operating at a wavelength at or near 2000 nm;

a pulse stretcher receiving pulses from said passively mode locked fiber oscillator and producing stretched pulses;

a fiber amplifier amplifying said stretched pulses and producing recompressed and amplified pulses at an output thereof; and

a highly nonlinear fiber spliced directly to the output of said amplifier;

said highly nonlinear fiber producing an optical continuum.

63. A fiber-laser based amplification system according to claim 62, further comprising an undoped fiber inserted upstream of said highly nonlinear fiber.