Compact coherent high brightness light source for the mid-IR and far IR

• US 8,861,555 B2
• Filed: 11/20/2012
• Issued: 10/14/2014
• Est. Priority Date: 11/25/2011
• Status: Active Grant

• Current Assignee: IMRA America Incorporated (Aisin Corp.)
• Original Assignee: IMRA America Incorporated (Aisin Corp.)
• Inventors: Fermann, Martin E., Hartl, Ingmar, Bethge, Jens
• Primary Examiner(s): Park, Kinam
• Application Number:
  US13/682,309
• Publication Number:
  US 20140219296A1
• Time in Patent Office: 693 Days
• Field of Search: 372/4, 372/6, 372/18, 372/22, 372/23
• US Class Current: 372/4
• CPC Class Codes: G02B 6/02038 with core or cladding having graded refractive index
• CPC Class Codes: G02F 1/3528 for producing a supercontinuum
• CPC Class Codes: G02F 1/3534 Three-wave interaction, e.g. sum-difference frequency generation G02F1/3532 takes precedence
• CPC Class Codes: G02F 1/365 in an optical waveguide structure G02F1/377, G02F1/395 take precedence
• 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 3/067 Fibre lasers
• 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 3/094046 of a Raman fibre laser
• CPC Class Codes: H01S 3/109 Frequency multiplication, e.g. harmonic generation
• CPC Class Codes: H01S 3/1106 Mode locking
• CPC Class Codes: H01S 3/30 using scattering effects, e.g. stimulated Brillouin or Raman effects
• CPC Class Codes: H01S 3/302 in an optical fibre

Abstract

Compact laser systems are disclosed which include ultrafast laser sources in combination with nonlinear crystals or waveguides. In some implementations fiber based mid-IR sources producing very short pulses and/or mid-IR sources based on a mode locked fiber lasers are utilized. A difference frequency generator receives outputs from the ultrafast sources, and generates an output including a difference frequency. The output power from the difference frequency generator can further be enhanced via the implementation of large core dispersion shifted fibers. Exemplary applications of the compact, high brightness mid-IR light sources include medical applications, spectroscopy, ranging, sensing and metrology.

Claims

1. An optical source producing an output at a wavelength>

5000 nm, comprising;

a mode locked fiber laser producing a primary output within the wavelength range from 1700-2300 nm;

a highly nonlinear waveguide receiving said primary output and shifting a least part of said primary output, thereby producing a secondary output shifted relative to said primary output; and

a nonlinear crystal configured for frequency generation at a difference frequency between said primary and secondary outputs, and producing an output at a wavelength>

5000 nm, said output having an average power>

100 μ

W.

2. The optical source according to claim 1, wherein said output at a wavelength>

5000 nm is generated via difference frequency generation.

3. The optical source according to claim 1, wherein said output at wavelengths>

5000 nm is generated via at least one optical parametric amplifier stage.

4. The optical source according to claim 1, wherein said primary source comprises a Tm or Ho fiber source.

5. The optical source according to claim 1, wherein said non-linear crystal for difference frequency generation comprises optically patterned GaAs.

6. The optical source according to claim 1, wherein said non-linear crystal for difference frequency generation is periodically poled and/or arranged as a fan-out crystal.

7. The optical source according to claim 1, wherein said output is wavelength tunable via adjustment of said nonlinear crystal with respect to an input beam.

8. The optical source according to claim 6, wherein said output is wavelength tunable by translating said fan-out crystal with respect to an input beam.

9. The optical source according to claim 6, wherein said output is wavelength tunable via adjustment of said periodically poled crystal with respect to an input beam.

10. The optical source according to claim 1, wherein said primary output is generated with a laser system comprising a Tm mode locked fiber.

11. The optical source according to claim 1, wherein said highly non-linear waveguide comprises a highly non-linear fiber.

12. The optical source according to claim 11, wherein said highly non-linear fiber comprises a single mode or multimode fluoride fiber.

13. The optical source according to claim 1, wherein said source is capable of being tuned over a range of wavelengths in the mid-IR and/or far IR wavelength regime.

14. The optical source according to claim 1, wherein said source is arranged such that wavelengths are tunable by controlling input power to said non-linear waveguide.

15. The optical source according to claim 14, wherein wavelengths are tunable over a range of up to about 15 μ

m.

16. The optical source according to claim 1, wherein said primary output comprises a pulse width less than about 150 fs.

17. The optical source according to claim 1, wherein said primary output comprises a pulse width less than about 50 fs.

18. The optical source according to claim 1, wherein said primary and secondary outputs comprise respective non-soliton and Raman soliton portions.

36. The optical source according to claim 1, further comprising:

a frequency shifter inserted in a path of either the primary or secondary output.

37. The optical source according to claim 36, wherein said frequency shifter comprises an acousto-optic frequency shifter.

19. A source producing infrared pulses, comprising:

a laser system producing short optical pulses;

a nonlinear optical waveguide receiving said short optical pulses, said nonlinear waveguide spectrally broadening a short optical pulse in such a way as to produce, as an output from said nonlinear waveguide, at least two distal spectral regions within said broadened spectrum, and at least two corresponding short pulses in the time domain; and

a difference frequency generator comprising a nonlinear crystal receiving said waveguide output and generating an output signal having an optical frequency that is a difference between a first optical frequency and a second optical frequency, said first optical frequency contained in a first of said two distal regions and said second optical frequency contained in a second of said two distal spectral regions;

wherein the two pulses corresponding to the two distal spectral regions propagate essentially collinearly from the waveguide output to the nonlinear crystal input.

20. The source of infrared pulses according to claim 19, said source further comprising a group delay adjustment stage inserted between nonlinear waveguide output and nonlinear crystal input, said group delay adjustment stage configured to allow adjustment of the group delay between the two distal spectral regions.

21. The source of infrared pulses according to claim 20, wherein said group delay adjustment stage comprises at least one optical prism.

22. The source of infrared pulses according to claim 20, wherein said group delay adjustment stage comprises a section of bulk material.

23. The source of infrared pulses according to claim 19, said source further comprising a chirp adjustment stage upstream from said nonlinear waveguide, and configured for adjustment of the chirp of the pulses being received by said nonlinear waveguide.

24. The source of infrared pulses according to claim 23, wherein said chirp adjustment stage comprises at least one of an optical prism and grating.

25. The source of infrared pulses according to claim 19, wherein said nonlinear waveguide comprises a nonlinear optical fiber or a nonlinear waveguide.

26. The source of infrared pulses according to claim 19 wherein said laser system comprises one of a fiber, a waveguide, a diode laser, a solid-state laser system or a combination thereof.

27. The source of infrared pulses according to claim 19, wherein said laser system comprises a Er, Er/Yb, Tm, Tm/Yb or Ho fiber laser.

28. The source of infrared pulses according to claim 19, wherein said nonlinear waveguide is arranged with slightly anomalous dispersion at the center wavelength of the pulses produced by said laser system.

29. The source of infrared pulses according to claim 19, wherein said nonlinear waveguide comprises germanosilicate or lead silicate glass.

30. The source of infrared pulses according to claim 19, wherein said nonlinear waveguide comprises a soft optical glass.

31. The source of infrared pulses according to claim 19, wherein said nonlinear waveguide comprises a germanosilicate optical fiber with a core diameter>

10 μ

m.

32. The source of infrared pulses according to claim 19, wherein said nonlinear waveguide comprises a gas filled hollow-core optical fiber.

33. A dispersion shifted germanosilicate optical fiber, comprising:

a cladding;

a core within said cladding and having a diameter larger than 10 μ

m and a germanium concentration>

10 mole %; and

a zero dispersion wavelength longer than 1400 nm.

34. A dispersion shifted germanosilicate optical fiber according to claim 33, said optical fiber comprising:

a refractive index difference between core and cladding which is substantially smaller than the refractive index difference between the glass comprising the core and silica glass.

35. A dispersion shifted germanosilicate optical fiber according to claim 33, wherein said fiber is configured for optical frequency shifting of short optical pulses.

38. A source producing infrared pulses in the 2000 nm spectral region, comprising:

a laser system producing short optical pulses;

a nonlinear optical waveguide receiving said short optical pulses, said nonlinear waveguide spectrally broadening a short optical pulse in such a way as to produce, as an output from said nonlinear waveguide, at least two distal spectral regions within said broadened spectrum, and at least two corresponding short pulses in the time domain;

a difference frequency generator comprising a nonlinear crystal receiving said waveguide output and generating an output signal having an optical frequency that is a difference between a first optical frequency and a second optical frequency, said first optical frequency contained in a first of said two distal regions and said second optical frequency contained in a second of said two distal spectral regions; and

a group delay adjustment stage allowing adjustment of the group delay between the two distal spectral regions to ensure temporal overlap of the two pulses corresponding to said spectral regions, at least during propagation of the two pulses in the non-linear crystal of said difference frequency generator.

39. A source producing infrared pulses in the 2000 nm spectral region according to claim 38, further comprising a fiber amplifier amplifying the output from said difference frequency generator.

40. A source producing infrared pulses in the 2000 nm spectral region according to claim 39, said fiber amplifier comprising a Tm, a Tm/Ho or a Ho amplifier.

41. A source according to claim 38, said group delay adjustment stage allowing for essentially collinear propagation of the two distal spectral regions from the waveguide output to the nonlinear crystal input.

42. A source according to claim 38, wherein said group delay adjustment stage comprises:

separate beam paths;

optical components arranged for separation and/or recombination of the two distal spectral regions; and

zero, one, or more delay stages for adjustment of the group delay.

43. A source according to claim 38, said laser system producing short optical pulses comprising at least a mode locked laser.

44. A source according to claim 43, said laser system further comprising a mode locked fiber laser.

45. A source according to claim 44, said laser system further comprising at least one pulse compression stage.

46. The optical source according to claim 38, further comprising:

a frequency shifter configured for frequency shifting the spectrum of either of said two distal spectral regions.

47. The optical source according to claim 46, wherein said frequency shifter comprises an acousto-optic frequency shifter.