Confocal optical scanning system employing a fiber laser

• US 5,887,009 A
• Filed: 05/22/1997
• Issued: 03/23/1999
• Est. Priority Date: 05/22/1997
• Status: Expired due to Fees

• Current Assignee: Optical Biopsy Technologies LLC
• Original Assignee: Optical Biopsy Technologies LLC
• Inventors: Mandella, Michael, Garrett, Mark H.
• Primary Examiner(s): Bovernick, Rodney
• Assistant Examiner(s): Wise, Robert E.
• Application Number:
  US08/861,590
• Time in Patent Office: 670 Days
• Field of Search: 372/6, 250/227.14, 250/227.17, 250/227.18, 250/227.23, 356/5.09, 356/5.1, 356/5.14, 356/4.07, 356/400, 356/448
• US Class Current: 372/6
• CPC Class Codes: B82Y 15/00 Nanotechnology for interacting, sensing or actuating, e.g. quantum dots as markers in protein assays or molecular motors
• CPC Class Codes: G02B 21/0056 based on optical coherence, e.g. phase-contrast arrangements, interference arrangements
• CPC Class Codes: G02B 21/0068 arrangements using polarisation

Abstract

A confocal optical scanning system using a flexible optical emissive fiber or fiber laser and having a lasing cavity defined within the fiber. The system in-couples a signal beam produced when a probe beam generated by the fiber laser is reflected from a scanned object back into the lasing cavity. The perturbation created in the cavity by the in-coupling of the signal beam is detected by a transducer. Specifically, the perturbation may be the signal beam itself, an oscillation mode of the cavity induced by the in-coupled signal beam or a combination of the signal beam and the probe beam. In a preferred embodiment of the invention the system also has a polarizing assembly for altering a signal polarization of the signal beam and rotate it to either a resonant polarization supported by the cavity or a non-resonant polarization not supported by the cavity.

Claims

1. A confocal optical scanning system for scanning an object, said system comprising:

a) a flexible optical fiber laser having a lasing cavity and being driven by a pump source to generate a probe beam;

b) a reflecting means in said fiber laser for defining a first end of said lasing cavity;

c) an output coupling means in said fiber laser for defining a second end of said lasing cavity and for out-coupling said probe beam;

d) beam shaping means for focusing said probe beam on a scan point on or within said object and focusing a signal beam reflected from said scan point such that said signal beam is in-coupled into said second end of said lasing cavity;

e) a transducer for detecting an optical perturbation in said lasing cavity; and

f) a scanning means for moving said scan point relative to said object.

2. The system of claim 1 wherein said optical perturbation in said lasing cavity is said signal beam.

3. The system of claim 2 further comprising a polarization altering means for altering a signal polarization of said signal beam to a resonant polarization supported by said lasing cavity.

4. The system of claim 3 further comprising a Brewster grating in said fiber laser for out-coupling said signal beam to said transducer.

5. The system of claim 3 wherein said polarization altering means comprises at least one element selected from the group consisting of Faraday rotators, polarizing filters, retardation plates and polarizing plates.

6. The system of claim 2 further comprising a polarization altering means for altering a signal polarization of said signal beam to a non-resonant polarization not supported by said lasing cavity.

7. The system of claim 6 further comprising a Brewster grating in said fiber laser for out-coupling said signal beam to said transducer.

8. The system of claim 6 wherein said polarizing means comprises at least one element selected from the group consisting of Faraday rotators, polarizing filters, retardation plates and polarizing plates.

9. The system of claim 1 wherein said optical perturbation in said lasing cavity comprises an oscillation mode of said lasing cavity induced by said signal beam.

10. The system of claim 9 further comprising an out-coupling element for out-coupling said oscillation mode to said transducer.

11. The system of claim 1 wherein said optical perturbation in said lasing cavity comprises a combination of said signal beam and said probe beam.

12. The system of claim 11 further comprising a polarization altering means for altering a signal polarization of said signal beam to a resonant polarization supported by said lasing cavity, said probe beam comprising said resonant polarization.

13. The system of claim 12 wherein said polarization altering means comprises at least one element selected from the group consisting of Faraday rotators, polarizing filters, retardation plates and polarizing plates.

14. The system of claim 1 further comprising a deflecting means for deflecting said optical perturbation to said transducer.

15. The system of claim 1 wherein said pump source is selected from the group consisting of semiconductor lasers and fiber lasers.

16. The system of claim 1 wherein said reflecting means is a Distributed Bragg Reflector (DBR).

17. The system of claim 1 wherein said output coupling means is a Distributed Bragg Reflector (DBR).

18. The system of claim 1 wherein said fiber laser comprises a fiber selected from the group consisting of birefringent fibers, polarization maintaining fibers, single-mode fibers, double-clad fibers and multi-mode fibers.

19. The system of claim 18 wherein said fiber comprises a rare-earth doped active central core.

20. The system of claim 18 wherein said fiber is a double-clad fiber having an active central core surrounded by an inner cladding and said inner cladding is surrounded by an outer cladding and a pump beam generated by said pump source is coupled into said inner cladding.

21. The system of claim 20 further comprising an end-pumping coupling means for in-coupling said pump beam into said inner cladding from an end of said fiber.

22. The system of claim 20 further comprising a side-pumping coupling means for in-coupling said pump beam into said inner cladding through the side wall of said inner cladding.

23. The system of claim 1 wherein said scanning means comprises at least one element selected from the group consisting of mirrors, reflectors, acousto-optic deflectors, electro-optic deflectors, mechanical scanning mechanisms and Micro-Electro-Mechanical-Systems (MEMS) scanning micro-mirrors.

24. The system of claim 1 wherein said beam shaping means comprises at least one element selected from the group consisting of focusing lenses, GRIN lenses, focusing gratings, micro-lenses, diffractive lenses, refractive lenses, Holographic Optical Elements (HOE), Solid Immersion Lenses (SIL) and binary lenses.

25. The system of claim 1 further comprising an intensity modulating means for controlling the intensity of said probe beam at said scan point.

26. The system of claim 25 wherein said intensity modulating means comprises an optical switch between said output coupling means and said object.

27. The system of claim 26 wherein said optical switch is a Micro-Optical-Electro-Mechanical-System (MOEMS) device.

28. The system of claim 25 wherein said intensity modulating means comprises at least one element selected from the group consisting of electro-optic modulators, acousto-optic modulators and liquid crystal modulators located between said output coupling means and said object.

29. The system of claim 1 wherein said fiber laser is an upconversion fiber laser.

30. The system of claim 29 wherein said upconversion fiber laser comprises a fiber having a rare-earth doped fluorozirconate central core.

31. The system of claim 29 wherein said output coupling means is a an uncoated cleaved end of said upconversion fiber laser.

32. The system of claim 29 wherein said pump source comprises at least two semiconductor lasers generating pump beams at different pump wavelengths.

33. The system of claim 32 wherein said probe beam is modulated in intensity by modulating the intensity of one of said at least two semiconductor lasers.

34. The system of claim 1 wherein said probe beam has a power level sufficient to alter a property of said object at said scan point.

35. The system of claim 1 wherein said object is an optical data storage disk.

36. The system of claim 35 wherein said probe beam has a power level sufficient to write data into said optical data storage disk.

37. The system of claim 1 wherein said transducer comprises a photodiode.

38. The system of claim 37 wherein said photodiode is located adjacent to one end of said fiber laser.

39. The system of claim 1 further comprising a pulsing means for pulsing said probe beam.

40. The system of claim 39 wherein said pulsing means comprises at least one element selected from the group consisting of Q-switches, waveguide acousto-optic shutters, electro-optic shutters and integrated Kerr shutters.

41. The system of claim 39 wherein said pulsing means comprises said pump source.

42. A confocal optical scanning system for scanning an object, said system comprising:

a) a flexible optical emissive fiber being driven by a pump source and a seed source to generate a probe beam;

b) a first end of said emissive fiber for in-coupling a seed beam from said seed source;

c) a second end of said emissive fiber for out-coupling said probe beam;

d) pump coupling means for coupling a pump beam from said pump source into said emissive fiber;

e) beam shaping means for focusing said probe beam on a scan point on or within said object and focusing a signal beam reflected from said point such that said signal beam is in-coupled into said second end of said emissive fiber;

f) a transducer for detecting said signal beam in said emissive fiber; and

g) a scanning means for moving said scan point relative to said object.

43. The system of claim 42 wherein said pump source and said seed source are selected from the group consisting of semiconductor lasers and fiber lasers.

44. The system of claim 42 wherein said transducer is a photodiode.

45. The system of claim 44 wherein said photodiode is located adjacent to said first end of said emissive fiber.

46. The system of claim 42 wherein said emissive fiber is of the type selected from the group consisting of birefringent fibers, polarization maintaining fibers, single-mode fibers, double-clad fibers and multi-mode fibers.

47. The system of claim 42 wherein said emissive fiber comprises a rare-earth doped active central core.

48. The system of claim 42 wherein said emissive fiber is a double-clad fiber having an active central core surrounded by an inner cladding and said inner cladding is surrounded by an outer cladding and said pump beam is coupled into said inner cladding.

49. The system of claim 48 wherein said pump coupling means is located at said first end of said emissive fiber such that said pump beam is in-coupled into said inner cladding at said first end.

50. The system of claim 48 wherein said pump coupling means is a side-pumping coupling means for in-coupling said pump beam into said inner cladding through the side wall of said inner cladding.

51. The system of claim 42 wherein said scanning means comprises at least one element selected from the group consisting of mirrors, reflectors, acousto-optic deflectors, electro-optic deflectors, mechanical scanning mechanisms and Micro-Electro-Mechanical-Systems (MEMS) scanning micro-mirrors.

52. The system of claim 42 wherein beam shaping means comprises at least one element selected from the group consisting of focusing lenses, GRIN lenses, focusing gratings, micro-lenses, diffractive lenses, refractive lenses, Holographic Optical Elements (HOE), Solid Immersion Lenses (SIL) and binary lenses.

53. The system of claim 42 wherein said emissive fiber is of the upconversion type such that said probe beam has a shorter wavelength than the wavelength of said pump beam.

54. The system of claim 53 wherein said emissive fiber has a rare-earth doped fluorozirconate central core.

55. The system of claim 53 wherein said pump source comprises at least two semiconductor lasers operating at different wavelengths.

56. The system of claim 55 wherein said probe beam is modulated in intensity by modulating the intensity of one of said at least two semiconductor lasers.

57. The system of claim 42 wherein said object is an optical data storage disk.

58. The system of claim 57 wherein said probe beam has a power level sufficient to write data into said optical data storage disk.

59. The system of claim 42 wherein said probe beam is modulated in intensity by modulating the intensity of said pump source.

60. The system of claim 42 wherein said probe beam is modulated in intensity by modulating the intensity of said seed source.

61. The system of claim 42 wherein said seed source is a fiber laser integral to said emissive fiber.

62. The system of claim 61 wherein said fiber laser is integrated to said emissive fiber through at least one Distributed Bragg Reflector (DBR).