PHOTONIC CRYSTAL FIBER ASSEMBLY

• US 20180372961A1
• Filed: 12/22/2016
• Published: 12/27/2018
• Est. Priority Date: 12/23/2015
• Status: Active Grant

• Current Assignee: NKT Photonics A/S (NKT A/S)
• Original Assignee: NKT Photonics A/S (NKT A/S)
• Inventors: Alkeskjold, Thomas Tanggaard, LYNGSOE, Jens Kristian, JAKOBSEN, Christian, Maack, Martin Dybendal, Michieletto, Mattia, Papior, Sidsel Rubner
• Granted Patent: US 10,551,574 B2
• Time in Patent Office: Days
• CPC Class Codes: G02B 6/02314 Plurality of longitudinal structures extending along optical fibre axis, e.g. holes
• CPC Class Codes: G02B 6/02328 Hollow or gas filled core
• CPC Class Codes: G02B 6/3813 for transmission of high energy beam coupling high energy sources and light guides G02B6/4296
• CPC Class Codes: G02B 6/3833 Details of mounting fibres in ferrules; Assembly methods; Manufacture
• CPC Class Codes: G02B 6/3874 using tubes, sleeves to align ferrules
• CPC Class Codes: G02B 6/4296 coupling with sources of high radiant energy, e.g. high power lasers, high temperature light sources

Abstract

The invention comprises a photonic crystal fiber (PCF) assembly comprising a PCF and at least one ferrule structure. The PCF has a center axis and comprises a core region and a cladding region and a first fiber end section with a first fiber end. The ferrule structure has a center axis and is mounted to the first fiber end section. The ferrule structure comprises an inner ferrule arrangement and an outer ferrule arrangement surrounding the first fiber end section. The inner ferrule arrangement comprises an inner ferrule front section proximally to the first fiber end and an inner ferrule rear section distally to the first fiber end, and each of the inner ferrule sections have an inner diameter and in at least a length thereof fully surrounds the PCF. The inner ferrule rear section is anchored in an anchor length section to the first fiber end section and the inner ferrule front section supports the first fiber end section proximally to the first fiber end.

Claims

1. A photonic crystal fiber (PCF) assembly comprising a PCF and at least one ferrule structure, said PCF has a center axis and comprises a core region and a cladding region and a first fiber end section with a first fiber end, said ferrule structure has a center axis and is mounted to said first fiber end section, said ferrule structure comprises an inner ferrule arrangement and an outer ferrule arrangement surrounding the first fiber end section, said inner ferrule arrangement comprises an inner ferrule front section proximally to said first fiber end and an inner ferrule rear section distally to said first fiber end, each of said inner ferrule sections have an inner diameter and in at least a length thereof fully surrounds the PCF, said inner ferrule rear section is anchored in an anchor length section to said first fiber end section and said inner ferrule front section supports said first fiber end section proximally to said first fiber end, said PCF center axis at the first fiber end section and said ferrule structure center axis are preferably substantially parallel, more preferably said PCF center axis at the first fiber end section and said ferrule structure center axis are coincident.

2. The PCF assembly of claim 1, wherein said assembly further comprises an alignment sleeve arranged between the inner ferrule front section and the first fiber end section, such that the inner ferrule front section supports said first fiber end section proximally to said first fiber end via said alignment sleeve, said alignment sleeve preferably being arranged to surround and support said first fiber end section at said first fiber end.

3. The PCF assembly of claim 2, wherein said inner ferrule front section surrounds and holds said alignment sleeve in a preselected axial position, said inner diameter of said inner ferrule front section is slightly larger than a maximal outer diameter of said alignment sleeve, such as from about 0.1 μ

m larger to about 2 mm larger, such as from about 1 μ

m larger to about 1 mm larger, such as from about 0.1 mm larger to about 0.01 mm larger in diameter.

4. The PCF assembly of any one of the preceding claims 2-3, wherein said inner ferrule front section supports said first fiber end section via said alignment sleeve and by mechanically holding said alignment sleeve in axial position, preferably an end of the alignment sleeve and an end of said inner ferrule front section are aligned in a plane perpendicular to the ferrule structure center axis, more preferably said first fiber end, said end of the alignment sleeve and said end of the inner ferrule front section are aligned in a plane perpendicular to the PCF center axis.

5. The PCF assembly of the preceding claims 2-4, wherein said alignment sleeve surrounds said PCF proximally to the first fiber end, preferably said first fiber end and an end of the alignment sleeve are aligned in a plane perpendicular to the PCF center axis, said alignment sleeve has a length in the axial direction which is preferably at least about 1 mm, such as from about 2 mm to about 5 cm, such as from about 5 mm to about 2 cm.

6. The PCF assembly of any one of the preceding claims 2-5, wherein said alignment sleeve supports said first fiber end section, by having an inner diameter at least along a support section thereof which is adapted to the outer diameter of the first fiber end section, preferably the inner diameter of the support section of the alignment sleeve is up to about 0.5 mm larger than the inner diameter, such as up to about 0.1 mm, such as up to about 0.01 mm.

7. The PCF assembly of any one of the preceding claims 2-6, wherein said alignment sleeve supports said first fiber end section by being collapsed onto the first fiber end section in its whole length or in said support section, said alignment sleeve is preferably a capillary tube which has been applied to surround the PCF and collapsed by heat in at least said support section thereof such as a mid-section thereof to thereby being arranged to support the PCF first fiber end section, said alignment sleeve preferably being fused to said optical fiber preferably without any intermediate material.

8. The PCF assembly of any one of the preceding claims 2-7, wherein said alignment sleeve is of glass, preferably silica glass, such as fused silica glass, fused quartz and/or doped silica, and/or borosilicate glass, such as a borosilicate glass comprising approximately 96% silica and 4% boron trioxide.

9. The PCF assembly of any one of the preceding claims 2-8, wherein said alignment sleeve has a refractive index of up to 1.45 for light at 1 μ

m, such as for light in the range 1-2 μ

m.

10. The PCF assembly of any one of the preceding claims 2-9, wherein said alignment sleeve is of down doped silica, such as silica doped with fluorine and/or boron.

11. The PCF assembly of any one of the preceding claims 2-10, wherein said alignment sleeve has a refractive index which is less than an effective refractive index of the cladding region.

12. The PCF assembly of any one of the preceding claims 2-11, wherein said alignment sleeve is hold within said inner ferrule front section without any intermediate material between the alignment sleeve and the inner ferrule front section, preferably said alignment sleeve is mechanically hold and/or fused to said inner ferrule front section.

13. The PCF assembly of any one of the preceding claims, wherein said inner ferrule front section and said inner ferrule rear section are not directly fixed to each other, preferably said inner ferrule front section and said inner ferrule rear section are arranged to have an intermediate gab in axial direction, preferably said gap provides a distance in axial direction between the inner ferrule front section and the inner ferrule rear section, said distance is preferably in the range from about 1 mm to about 10 cm, such as from about 5 mm to about 2 cm.

14. The PCF assembly of any one of the preceding claims, wherein said inner ferrule front section supports said first fiber end section proximally to the first fiber end directly, preferably by mechanically holding said first fiber end section proximally to the first fiber end in axial position, preferably an end of said inner ferrule front section and said first fiber end are aligned in a plane perpendicular to the PCF center axis.

15. The PCF assembly of any one of the preceding claims, wherein said ferrule structure comprises a hermetic solder element arranged to surround said first fiber end section to form an annular hermetic seal between the first fiber end section and said inner ferrule rear section, said hermetic solder element is arranged closer to the front annular section than the anchor length section of the inner ferrule rear section, preferably said anchoring length section of the inner ferrule rear section is not fully annular, said anchoring length section of the inner ferrule rear section is preferably extending from about 20 degrees to about 350 degrees, such as about 180 degrees around the PCF.

16. The PCF assembly of any one of the preceding claims, wherein said PCF is free of polymer coating in the first fiber end section from the anchoring section of the inner ferrule rear section to the first fiber end.

17. The PCF assembly of any one of the preceding claims, wherein said inner ferrule front section is of an at least partly transparent material at a wavelength between about 200 nm and about 4 μ

m, said inner ferrule front section is e.g. of fused or crystallized quartz, such as of substantially undoped silica having a refractive index of 1.45 for light at 1 μ

m.

18. The PCF assembly of any one of the preceding claims, wherein said inner ferrule rear section is of fused or crystallized quartz or of a metal or alloy.

19. The PCF assembly of any one of the preceding claims, wherein said outer ferrule arrangement is of metal, ceramic or glass such as silica.

20. The PCF assembly of any one of the preceding claims, wherein said outer ferrule arrangement is fixed to each of said inner ferrule front section and said inner ferrule rear section of said inner ferrule arrangement to hold them in a fixed position relative to each other, such that the first fiber end section of the PCF is preferably supported to be substantially straight within said ferrule structure, said outer ferrule arrangement is preferably fixed to said inner ferrule arrangement by glue, by solder and/or by being fused or laser welded.

21. The PCF assembly of any one of the preceding claims, wherein said first fiber end section is mounted in said ferrule structure substantially without application of stress generating pressure being applied to the fiber.

22. The PCF assembly of any one of the preceding claims, wherein said first fiber end section is mounted in said ferrule structure without any direct bonds to the fiber beyond one or more bonds to the inner ferrule rear section including the anchoring.

23. The PCF assembly of any one of the preceding claims, wherein said ferrule structure comprises an end cap arranged in front of said first fiber end, said end cap being mounted with a distance or without a distance to the inner ferrule front section, said end cap preferably being fixed directly to the inner ferrule front section or to an outer ferrule front section of the outer ferrule arrangement.

24. The PCF assembly of claim 23, wherein said end cap is fixed to said outer ferrule front section of the outer ferrule arrangement, said outer ferrule arrangement preferably comprises said outer ferrule front section and outer ferrule rear section, wherein said outer ferrule rear section is fixed to both the inner ferrule rear section and the inner ferrule front section and said outer ferrule front section is fixed to said inner ferrule front section.

25. The PCF assembly of claim 23 or claim 24, wherein said end cap is an anti-reflection coated silica end cap, said end cap preferably is or comprises a lens.

26. The PCF assembly of any one of the preceding claims, wherein said PCF is a hollow core fiber or a solid core fiber, preferably said first fiber end (facet) has a metallic or anti-reflex coating.

27. The PCF assembly of any one of the preceding claims, wherein said PCF has a core diameter of less than 100 μ

m, preferably of about 50 μ

m or less, such as from about 5 μ

m to about 40 μ

m.

28. The PCF assembly of any one of claims 23 and 25-27, wherein the PCF is a hollow core fiber and said end cap is fixed to said outer ferrule front section of the outer ferrule arrangement to provide an end cap space between said end cap and said inner ferrule front section, optionally said hollow core has a collapsed end part and a metallic or anti-reflex coating on the fiber facet.

29. The PCF assembly of claim 28, wherein the inner ferrule arrangement comprises a passage into said end cap space for injecting and/or withdrawing fluids, said passage is preferably provided by at least one additional through hole in each of said inner ferrule front section and said inner ferrule rear section, said additional through holes are preferably substantially parallel to the axis of the ferrule structure, more preferably the additional through hole comprises a valve arrangement at an exit from the inner ferrule rear section.

30. The PCF assembly of any one of the preceding claims, wherein said inner ferrule front section has a rear end, at least an in radial direction outer part of said rear end is angled relative to the center axis of the ferrule structure to out-couple light propagating in the inner ferrule arrangement, such as an in radial direction semi annular or annular outer part of said rear end is angled relative to the center axis of the ferrule structure to out-couple light propagating in the inner ferrule arrangement.

31. The PCF assembly of any one of the preceding claims, wherein said inner ferrule front section has a rear end, at least an in radial direction inner part of said rear end is angled relative to the center axis to form a funnel shape.

32. The PCF assembly of any one of the preceding claims, wherein said inner ferrule front section has a rear end, said rear end is coated with a reflective coating to back-reflect light, such as light propagating in the ferrule.

33. The PCF assembly of any one of the preceding claims, wherein said inner ferrule front section has a front end, said front end is coated with a reflective coating to protect the ferrule structure against incident and/or back-reflected light.

34. The PCF assembly of any one of the preceding claims, wherein said inner ferrule rear section has a front end, said front end is angled relative to the center axis of the ferrule structure and/or said front end is coated with a reflective coating to protect against incident and/or back-reflected light.

35. The PCF assembly of any one of the preceding claims, wherein said first fiber end section has at least one mode stripper length section, said mode stripper length section comprises a mode stripping high index material and or/a scatting layer applied in contact with the optical fiber at said mode stripper length section and/or said fiber in said mode stripper length section has a roughness Ra value of at least about 0.1 μ

m.

36. The PCF assembly of claim 35, wherein said mode stripper length section of said PCF is positioned between said inner ferrule front section and said inner ferrule rear section.

37. The PCF assembly of claim 35, wherein at least one of said inner ferrule front section and said inner ferrule rear section has a carving exposing said PCF said mode stripper length section of said PCF, said carving preferably partly surrounds the fiber preferably such that it extends at least about 20 degrees.

38. The PCF assembly of any one of the preceding claims, wherein the ferrule structure comprises a mode stripper coating arranged in direct contact with an outer surface of the inner ferrule front section, the mode stripper coating is preferably contained between the inner ferrule front section and the outer ferrule arrangement.

39. The PCF assembly of any one of the preceding claims, wherein the ferrule structure comprises an outer alignment jacket surrounding the outer ferrule arrangement, said outer alignment jacket preferably comprises means for alignment, preferably for alignment in the axial direction (z-direction), for alignment in the radial directions (x,y-directions) and/or for rotational alignment.

40. The PCF assembly of claim 39, wherein said means for alignment comprises one or more flanges, such as flanges for mounting with positioning control.

41. The PCF assembly of claim 39 or claim 40, wherein said means for alignment comprises a marker for rotational fiber orientation e.g. for PM orientation.

42. The PCF assembly of any one of the preceding claims, wherein the ferrule structure is configured for cooling by a cooling fluid said outer ferrule arrangement and/or said outer alignment jacket comprising passages with at least one inlet and at least one exit for said cooling fluid.

43. The PCF assembly of any one of the preceding claims, wherein said assembly further comprises one or more sensors, such as one or more optical sensors and/or electrical sensors and/or chemical sensors for monitoring temperature, for monitoring connector performance and/or for monitoring fiber damage.

44. The PCF assembly of any one of the preceding claims, wherein said assembly comprises a second ferrule structure connected to a second end section of the PCF, said second ferrule structure preferably is as the ferrule structure according to any one of the preceding claims.

45. A laser system comprising a PCF assembly according to any one of the preceding claims.

46. The laser system of claim 45, wherein said laser system comprises a laser light source, said PCF assembly being optically connected to said laser light source for receiving light from said laser light source and being adapted for delivering said light to a light employing station of an apparatus, preferably said first fiber end with said ferrule structure being adapted for being connected to said user apparatus.

47. The laser system of claim 45 or claim 46, wherein said laser light source is configured for generating laser light pulses, preferably said laser light source is a femtosecond laser source.

48. The laser system of claim 47, wherein said laser light source has a pump duration of from about 30 fs to about 30 ps, such as from about 100 fs to about 10 ps.

49. The laser system of claim 47 or claim 48, wherein said laser light source has a peak power determined at the exit of the laser light source which is at least about 5 kW, such as at least about 10 kW, such as at least about 30 kW, such as at least about 50 kW.

50. The laser system of any one of claims 47-49, wherein said laser light source is a mode locked laser, such as an actively mode locked laser or a passively mode locked laser, said mode locked laser preferably comprises one or more amplifiers.

51. The laser system of any one of claims 45-50, wherein said PCF is a hollow core PCF, preferably said hollow core PCF is configured for guiding light comprising at least one wavelength in the range from about 200 nm to about 4.5 μ

m, preferably at least one wavelength in the range from 1000 nm to about 1100 nm.

52. The laser system of claim 51, wherein said PCF is configured for guiding a continuum of light wavelengths, preferably spanning over at least about 0.1 μ

m, such as at least about 0.3 μ

m, such as at least about 0.5 μ

m.

53. The laser system of claim 51 or claim 52, wherein said hollow core PCF comprises an outer cladding region and a number N of hollow tubes surrounded by said outer cladding region, wherein each of said hollow tubes is fused to said outer cladding to form a ring defining an inner cladding region and said hollow core region surrounded by said inner cladding region, preferably N is from 6 to 12, more preferably N is 7.

55. The laser system of any one of claims 45-50, wherein said PCF is a solid core PCF, preferably said solid core PCF is a microstructured solid core PCF comprising a plurality of non-solid and/or solid cladding inclusions, said solid core PCF is preferably configured for guiding light comprising at least one wavelength in the range from about 200 nm to about 4.5 μ

m, preferably at least one wavelength in the range from 1000 nm to about 1100 nm.

56. The laser system of any one of claims 45-55, wherein PCF has a core region diameter of from about 3 μ

m to about 100 μ

m, such as from about 10 μ

m to about 50 μ

m, such as from about 10 μ

m to about 30 μ

m.

57. A set of correlated ferrule elements suitable for a PCF assembly according to any one of claims 1-44, said set of ferrule elements comprises

an inner ferrule front section and an inner ferrule rear section for forming an inner ferrule arrangement;

and

an outer ferrule arrangement,

wherein each of said inner ferrule front section, inner ferrule rear section and outer ferrule arrangement has a length and a center axis and comprises a main hollow through hole parallel with or coincident to said respective center axes, said set of correlated ferrule elements preferably further comprises an alignment sleeve having a length and a center axis and comprises a main hollow through hole parallel with or coincident to said center axis.

58. The set of correlated ferrule elements of claim 45, wherein the elements are correlated such that the alignment sleeve can be positioned in the main hollow through hole of the inner ferrule front section and the inner ferrule front section and the inner ferrule rear section can be mounted in the main hollow through hole of the outer ferrule arrangement for forming said inner ferrule arrangement.

59. The set of correlated ferrule elements of claim 57 or claim 58, wherein said alignment sleeve is a capillary tube and wherein said main hollow through hole of the alignment sleeve is has an inner diameter which is about 2 mm or less, such as about 1 mm or less such as about 0.5 mm or less, said alignment sleeve is preferably collapsible in at least a part of its length.

60. The set of correlated ferrule elements of any one of claims 57-59, wherein said alignment sleeve has a length in axial direction which is preferably at least about 1 mm, such as from about 2 mm to about 5 cm.

61. The set of correlated ferrule elements of any one of claims 57-60, wherein said set further comprises an end cap which is configured for being arranged in front of said inner ferrule front section by being mounted to said inner ferrule front section or by being mounted to an outer ferrule front section of the outer ferrule arrangement, said end cap is preferably an anti-reflection coated silica end cap.

62. The set of correlated ferrule elements of any one of claims 57-61, wherein each of said inner ferrule front section and said inner ferrule rear section comprises one or more additional through holes for providing a fluid passage, said additional through holes are preferably substantially parallel to the axis of the respective inner ferrule sections, more preferably the additional through hole at an exit from the inner ferrule rear section comprises a valve arrangement.

63. The set of correlated ferrule elements of any one of claims 57-62, wherein said inner ferrule front section has a rear end, at least an in radial direction outer part of said rear end is angled relative to the center axis of the inner ferrule front section and/or said rear end is coated with a reflective coating.

64. The set of correlated ferrule elements of any one of claims 57-63, wherein said inner ferrule front section has a front end, said front end is coated with a reflective coating.

65. The set of correlated ferrule elements of any one of claims 57-64, wherein said inner ferrule rear section has a front end, said front end is angled relative to the center axis of the inner ferrule rear section and/or said front end is coated with a reflective coating.

66. The set of correlated ferrule elements of any one of claims 57-65, wherein at least one of said inner ferrule front section and said inner ferrule rear section has a carving into its main hollow through hole, said carving preferably has an extension in an annular direction which extends at least about 20 degrees.

67. The set of correlated ferrule elements of any one of claims 57-66, wherein the set further comprises an outer alignment jacket correlated to the outer ferrule arrangement such that it can be arranged to surround the outer ferrule arrangement, said outer alignment jacket preferably comprises means for alignment.

68. An apparatus comprising a laser system according to any one of claim 45-56, wherein said PCF assembly is configured for delivering light to a light receiving station of said apparatus.

69. The apparatus of claim 68, wherein the apparatus is an illumination apparatus configured for illuminating a target, said illumination apparatus is preferably selected from a microscope, a spectroscope or an endoscope.

70. The apparatus of claim 69 wherein the illumination source is adapted for fluorescence Imaging;

Fluorescence Lifetime Imaging (FLIM);

Total Internal Reflection Fluorescence (TIRF) Microscopy;

fluorescence resonance energy transfer (FRET);

pulse interleave excitation foster resonance energy transfer (PIE-FRET);

broadband Spectroscopy;

nanophotonics;

flow cytometry;

industrial inspection, such as metrology;

ringdown spectroscopy, such as gas sensing;

analytical spectroscopy, such as hyperspectral spectroscopy, crop analysis e.g. of fruits and time of flight spectroscopy (TCSPC);

single Molecule Imaging and/or combinations thereof.

71. The apparatus of claim 68, wherein the apparatus is a microprocessing apparat, preferably for material processing, such as drilling, marking, cutting and/or scribing.

72. The apparatus of claim 68, wherein the apparatus is a surgery apparat, such as an apparatus for eye surgery (opthamology).

54. The laser system of claim 453, wherein said hollow tubes are not touching each other, preferably said hollow tubes are arranged with a substantially equal distance to adjacent hollow tubes.