Fiber-coupled, high-speed, angled-dual-axis optical coherence scanning microscopes

• US 6,710,316 B2
• Filed: 07/01/2002
• Issued: 03/23/2004
• Est. Priority Date: 07/28/2000
• Status: Expired due to Fees

• Current Assignee: Optical Biopsy Technologies LLC
• Original Assignee: Optical Biopsy Technologies LLC
• Inventors: Kino, Gordon S., Mandella, Michael J., Garrett, Mark H.
• Primary Examiner(s): Bruce, David V.
• Assistant Examiner(s): KAO, CHIH CHENG G
• Application Number:
  US10/189,297
• Publication Number:
  US 20030001071A1
• Time in Patent Office: 631 Days
• Field of Search: 250/201.3, 250/234, 250/235, 250/216, 359/203, 359/205, 359/206, 359/210, 359/212, 359/214, 359/215, 359/223, 359/368, 359/372, 359/373, 359/385, 359/389
• US Class Current: 250/201.3
• CPC Class Codes: G01B 2290/45 Multiple detectors for detecting interferometer signals
• CPC Class Codes: G01B 2290/65 Spatial scanning object beam
• CPC Class Codes: G01B 2290/70 Using polarization in the interferometer
• CPC Class Codes: G01B 9/02003 using beat frequencies
• CPC Class Codes: G01B 9/02022 contacting one object by grazing incidence
• CPC Class Codes: G01B 9/02058 by particular optical compensation or alignment elements, e.g. dispersion compensation
• CPC Class Codes: G01B 9/0209 Low-coherence interferometers
• CPC Class Codes: G02B 21/002 Scanning microscopes scanning near field optical microscopes G01Q60/18

Abstract

This invention provides an angled-dual-axis optical coherence scanning microscope comprising a fiber-coupled, high-speed angled-dual-axis confocal scanning head and a vertical scanning unit. The angled-dual-axis confocal scanning head is configured such that an illumination beam and an observation beam intersect optimally at an angle θ within an object and the scanning is achieved by pivoting the illumination and observation beams jointly using a high-speed scanning element. The vertical scanning unit causes the angled-dual-axis confocal scanning head to move towards or away from the object, thereby yielding a vertical cross-section scan of the object, while keeping the optical path lengths of the illumination and observation beams unchanged. By incorporating MEMS scanning mirrors and fiber-optic components, the angled-dual-axis optical coherence scanning microscope of the present invention can be miniaturized to provide a particularly powerful tool for in vivo medical imaging applications.

Claims

1. An apparatus for performing angled-dual-axis optical coherence scanning microscopy within a sample, comprising:

a) a light-generating means for generating an illumination beam and a reference beam;

b) an angled-dual-axis confocal scanning microscope, comprising;

i) a first single-mode optical waveguide having first and second ends, from said first end said illumination beam emerges;

ii) a second single-mode optical waveguide having first and second ends;

iii) an angled-dual-axis focusing means for focusing said illumination beam to an illumination focal volume along an illumination axis within said sample and for receiving an observation beam emanated from an observation focal volume along an observation axis within said sample such that said observation beam is focused onto said first end of said second single-mode optical waveguide; and

iv) a bi-axial scanning mirror;

wherein said illumination axis and said observation axis intersect at an angle within said sample, such that said illumination focal volume and said observation focal volume intersect at a confocal overlapping volume, and wherein said bi-axial scanning mirror is capable of directing said illumination and observation beams in such a way that said illumination axis and said observation axis remain intersecting at said angle and that said confocal overlapping volume moves within said sample; and

c) a beam-combining means for combining said reference beam and said observation beam, such that coherent interference between said reference beam and said observation beam is produced.

2. The apparatus of claim 1 wherein said light-generating means comprises:

a) a light source for emitting an output beam; and

b) a beam-splitting means in optical communication with said light source and said angled-dual-axis confocal scanning microscope, such that a portion of said output beam is passed into said second end of said first single-mode optical waveguide and a remainder of said output beam is routed into a first end of a reference single-mode optical waveguide, wherein said portion of said output beam constitutes said illumination beam and said remainder of said output beam serves as said reference beam.

3. The apparatus of claim 2 wherein said light source comprises an element selected from the group consisting of optical fiber amplifiers, fiber lasers, semiconductor optical amplifiers, semiconductor lasers, and diode-pumped solid state lasers, and broadband OCT light sources.

4. The apparatus of claim 2 wherein said light source comprises an unpolarized light source.

5. The apparatus of claim 2 wherein said light source comprises a polarized light source.

6. The apparatus of claim 2 wherein said light source has a coherence length less than 100 microns.

7. The apparatus of claim 2 wherein said light source is capable of producing light in the wavelength range of 0.8 to 1.6 microns.

8. The apparatus of claim 1 wherein said first and second single-mode optical waveguides are single-mode optical fibers.

9. The apparatus of claim 8 wherein said reference beam is routed into a first end of a reference single-mode optical fiber, and wherein said beam-combining means comprises a fiber-optic coupler, whereby said reference single-mode optical fiber and said second single-mode optical fiber are joined by said fiber-optic coupler.

10. The apparatus of claim 9 wherein said fiber-optic coupler is a polarization maintaining fiber-optic coupler.

11. The apparatus of claim 9 wherein said light-generating means comprises a light source having first and second output-ports, wherein said first output-port is optically coupled to said second end of said first single-mode optical fiber, transmitting said illumination beam to said first single-mode optical fiber, and wherein said second output port is optically coupled to a first end of said reference single-mode optical fiber, providing said reference beam.

12. The apparatus of claim 11 wherein said light source comprises an element selected from the group consisting of optical fiber amplifiers, fiber lasers, semiconductor optical amplifiers, semiconductor lasers, and diode-pumped solid state lasers.

13. The apparatus of claim 11 wherein said fiber-optic coupler is a polarization maintaining fiber-optic coupler.

14. The apparatus of claim 8 wherein said angled-dual-axis focusing means and said first ends of said first and second single-mode optical fibers are mechanically coupled to a substrate.

15. The apparatus of claim 14 wherein said substrate comprises a silicon substrate etched with V-grooves.

16. The apparatus of claim 1 wherein said bi-axial scanning mirror is in optical communication with said angled-dual-axis focusing means and said sample, wherein said bi-axial scanning mirror causes said confocal overlapping volume to move along a transverse cross-section within said sample, thereby producing a transverse cross-sectional scan.

17. The apparatus of claim 16 wherein said bi-axial scanning mirror comprises one or more elements selected from the group consisting of silicon scanning mirrors, fast steering mirrors, flexure-type scanning mirrors, and Micro-Electro-Mechanical-Systems (MEMS) scanning micro-mirrors.

18. The apparatus of claim 16 wherein said bi-axial scanning mirror comprises a single scanning mirror, wherein said scanning mirror is flat and can be pivoted about two orthogonal axes.

19. The apparatus of claim 18 wherein said scanning mirror is a silicon micro-machined mirror.

20. The apparatus of claim 16 wherein said bi-axial scanning mirror comprises a gimbaled assembly comprising a scanning mirror and a frame, wherein said assembly is configured such that said scanning mirror can rotate relative to said frame about a first pivoting axis and said frame along with said scanning mirror can rotate about a second pivoting axis, thereby providing rotation of said mirror in two orthogonal directions.

21. The apparatus of claim 20 wherein said scanning mirror is a silicon micro-machined mirror.

22. The apparatus of claim 1 wherein said bi-axial scanning mirror can be pivoted about two orthogonal axes, and wherein said bi-axial scanning mirror causes said confocal overlapping volume to move along a transverse cross-section within said sample, thereby producing a transverse cross-sectional scan.

23. The apparatus of claim 22 wherein said bi-axial scanning mirror is a silicon micro-machined mirror.

24. The apparatus of claim 22 further comprising a vertical scanning means, wherein said vertical scanning means comprises:

a) a vertical translation means; and

b) a compensation means for ensuring said intersection of said illumination focal volume and said observation focal volume;

wherein said translation means is capable of causing said angled-dual-axis focusing means to move relative to said sample for providing transverse cross-sectional scans at selectable depths within said sample.

25. The apparatus of claim 24 wherein said compensation means comprises a fluid filling a space between said angled-dual-axis focusing means and said sample, wherein said fluid is substantially transparent to said illumination beam and said observation beam, and wherein said fluid has an index of refraction that is substantially the same as an index of refraction of said sample, such that the optical path lengths of said illumination beam and said observation beam remain substantially unchanged in the course of varying selectable scan depths.

26. The apparatus of claim 25 further comprising a window assembly interposed between said angled-dual-axis focusing means and said fluid for passage of said illumination beam and said observation beam.

27. The apparatus of claim 26 wherein said window assembly comprises a transparent flat window means.

28. The apparatus of claim 26 wherein said window assembly comprises first and second transparent window means having flat faces in an angled arrangement, such that said illumination axis is perpendicular to a first flat face of said first window means and said observation axis is perpendicular to a first flat face of said second window means.

29. The apparatus of claim 28 wherein said first and second transparent window means comprise optical elements that are transparent and have an index of refraction closely matching that of water.

30. The apparatus of claim 25 further comprising a transparent window means interposed between said fluid and said sample for passage of said illumination beam and said observation beam.

31. The apparatus of claim 25 wherein said fluid is contained in a sealed hydraulic system, wherein said hydraulic system includes a reservoir for replenishing and receiving excess fluid in the course of said vertical scan.

32. The apparatus of claim 1 wherein said angled-dual-axis focusing means comprises one or more elements selected from the group consisting of refractive lenses, diffractive lenses, GRIN lenses, focusing gratings, micro-lenses, holographic optical elements, binary lenses, curved mirrors, flat mirrors, and prisms.

33. The apparatus of claim 32 wherein said one or more elements comprise a single refractive lens, where said refractive lens provides said illumination axis and said observation axis.

34. The apparatus of claim 32 wherein said one or more elements comprise an illumination focusing element and an observation focusing element, wherein said illumination focusing element provides said illumination axis, and wherein said observation focusing element provides said observation axis.

35. The apparatus of claim 34 wherein said illumination focusing element and said observation focusing element are of the same type, comprising a focusing element selected from the group consisting of refractive lenses, diffractive lenses, GRIN lenses, micro-lenses, binary lenses, and curved mirrors.

36. The apparatus of claim 35 wherein said focusing element has a numerical aperture (NA) in the range of 0.1 to 0.4.

37. The apparatus of claim 34 further comprising a first collimating lens, wherein said first collimating lens receives said illumination beam from said first end of said first single-mode optical waveguide and passes a substantially collimated illumination beam to said illumination focusing element.

38. The apparatus of claim 37 further comprising a second collimating lens, wherein said second collimating lens receives said observation beam from said observation focusing element and focuses said observation beam to said first end of said second single-mode optical waveguide.

39. The apparatus of claim 34 further comprising one or more mirrors for beam-aligning and beam-deflecting, wherein said one or more mirrors receive said illumination beam from said illumination focusing element and direct said illumination beam to said illumination focal volume within said sample, and wherein said one or more mirrors collect said observation beam emanated from said observation focal volume and pass said observation beam to said observation focusing element.

40. The apparatus of claim 1 wherein said first and second single-mode optical waveguides comprises one or more elements selected from the group consisting of single-mode fibers, polarization maintaining fibers, birefringent fibers, polarization maintaining waveguides, and buried waveguides.

41. The apparatus of claim 1 wherein said observation beam comprises scattered light emanated from said confocal overlapping volume within said sample.

42. The apparatus of claim 1 wherein said observation beam comprises reflected light emanated from said confocal overlapping volume within said sample.

43. The apparatus of claim 1 wherein said illumination focal volume and said observation focal volume are diffraction-limited, determined by main lobes of said illumination beam'"'"'s point-spread function and said observation beam'"'"'s point-spread function.

44. The apparatus of claim 43 wherein said confocal overlapping volume is diffraction-limited.

45. The apparatus of claim 1 further comprising a frequency shifting means for shifting the frequency of said observation beam.

46. The apparatus of claim 45 wherein said frequency shifting means is optically coupled to said first optical waveguide.

47. The apparatus of claim 45 wherein said frequency shifting means is optically coupled to said second optical waveguide.

48. The apparatus of claim 45 wherein said frequency shifting means comprises an element selected from the group consisting of piezoelectric fiber stretchers, electro-optic phase modulators, and acousto-optic frequency shifters.

49. The apparatus of claim 1 further comprising a frequency shifting means optically coupled to said reference beam, for shifting the frequency of said reference beam.

50. The apparatus of claim 49 wherein said frequency shifting means comprises an element selected from the group consisting of piezoelectric fiber stretchers, electro-optic phase modulators, and acousto-optic frequency shifters.

51. The apparatus of claim 1 further comprising an optical amplifier optically coupled to said second optical waveguide for amplifying said observation beam.

52. The apparatus of claim 1 further comprising an adjustable optical delay device optically coupled to said first optical waveguide.

53. The apparatus of claim 1 further comprising an adjustable optical delay device optically coupled to said second optical waveguide.

54. The apparatus of claim 1 further comprising an adjustable optical delay device for adjusting an optical path length of said reference beam.

55. The apparatus of claim 1 wherein said illumination beam is a polarized beam, and wherein said first and second optical waveguides are polarization maintaining (PM) waveguides capable of supporting two orthogonal polarizations.

56. A method for performing angled-dual-axis optical coherence scanning microscopy within a sample, comprising:

a) producing an illumination beam and a reference beam from a light-generating means, wherein said light-generating means has a predetermined coherence length;

b) routing said reference beam along a reference path;

c) transmitting said illumination beam along an illumination path including a first single-mode optical waveguide;

d) focusing said illumination beam emerging from said first single-mode optical waveguide to an illumination focal volume along an illumination axis within said sample;

e) receiving an observation beam emanated from an observation focal volume along an observation axis within said sample, wherein said illumination axis and said observation axis intersect at an angle within said sample, such that said illumination focal volume and said observation focal volume intersect at a confocal overlapping volume;

f) focusing said observation beam into a second single-mode optical waveguide;

g) combining said reference beam and said observation beam such that coherent interference is produced; and

h) directing said illumination beam and said observation beam via a bi-axial scanning mirror in such a way that said illumination axis and said observation axis remain intersecting at said angle and said confocal overlapping volume scans within said sample, while repeating said step g).

57. The method of claim 56 further comprising the step of compensating for the changes in optical path lengths of said illumination and observation beams in the course of scanning, so as to maintain said coherent interference.

58. The method of claim 56 further comprising the step of modulating the phase of said observation beam, such that said coherent interference between said reference beam and said observation beam is modulated at a beat frequency.

59. The method of claim 56 further comprising the step of modulating the phase of said reference beam, such that said coherent interference between said reference beam and said observation beam is modulated at a beat frequency.

60. The method of claim 56 further comprising the step of shifting the frequency of said observation beam, such that said coherent interference between said reference beam and said observation beam is modulated at a beat frequency.

61. The method of claim 56 further comprising the step of shifting the frequency of said reference beam, such that said coherent interference between said reference beam and said observation beam is modulated at a beat frequency.

62. The method of claim 56 further comprising the step of adjusting an optical path length traversed by said observation beam, so as to maintain said coherent interference between said reference beam and said observation beam when combined.

63. The method of claim 56 further comprising the step of adjusting an optical path length traversed by said reference beam, so as to maintain said coherent interference between said reference beam and said observation beam when combined.

64. The method of claim 56 further comprising the step of optically amplifying said observation beam.

65. The method of claim 56 further comprising:

a) polarizing said reference beam and said illumination beam such that said reference beam and said illumination beam are polarized beams;

b) rotating a polarization of said reference beam relative to said observation beam such that one polarization mode of said observation beam and said reference beam have substantially the same polarization; and

c) combining said reference beam and said one polarization mode of said observation beam such that coherence interference is produced.