Fiberoptic coupler sensor and a measurement method

• US 6,677,576 B1
• Filed: 05/11/2001
• Issued: 01/13/2004
• Est. Priority Date: 09/18/1998
• Status: Expired due to Fees

• Current Assignee: European Community, EUROPEAN COMMUNITY REPRESENTED BY
• Original Assignee: European Community
• Inventors: Hussey, Conleth D., OʼSullivan, Paul F., OʼBrien, Elaine M., Whelan, Maurice P., Kenny, Robert P., Lucia, Alfredo C.
• Primary Examiner(s): Porta, David
• Assistant Examiner(s): Lee, Patrick J.
• Application Number:
  US09/787,523
• Time in Patent Office: 977 Days
• Field of Search: 250/227.14, 250/227.11, 250/216, 250/227.16, 250/340, 250/385, 356/28-29, 356/32, 356/35, 356/73.1, 385/12-13, 385/43, 385/50, 385/123, 385/136, 385/7-8, 385/16, 385/95-96, 734/88, 736/53, 737/05, 738/610.8, 738/611.8, 732/041.1, 340/555-557
• US Class Current: 250/227.14
• CPC Class Codes: A61B 5/02154 by optical transmission
• CPC Class Codes: A61B 5/031 Intracranial pressure
• CPC Class Codes: A61B 5/6856 with a distal loop
• CPC Class Codes: G01D 5/35345 using Amplitude variations to detect the measured quantity
• CPC Class Codes: G02B 2006/12138 Sensor
• CPC Class Codes: G02B 6/2835 formed or shaped by thermal treatment, e.g. couplers

Abstract

Sensors and sensing apparatus are described, based on fused tapered fiber optic couplers with the taper waist portion formed into a loop or cleaved to provide a reflecting end. Light is typically input to the taper waist portion along a single input fiber, and bending of the loop or cleaved taper waist portion causes changes in the coupling ratio between the output fibers. The taper waist portion may be formed into a loop with a small bend radius without loss, and sensors embodying the claimed invention are particularly suitable for in-vivo measurement of pressure, the taper waist portions advantageously being arranged in contact with a membrane which deflects according to surrounding pressure. Further embodiments are described which are suitable for measurement of fluid flow velocity and/or acceleration.

Claims

1. Sensing apparatus including:

a sensor comprising

a fused tapered fibre optic coupler formed of two optical fibres fused together to provide a fused portion which is drawn down to form a taper waist portion, the coupler having an input end comprising an input unfused portion of one of said two optical fibres and an output end comprising an output unfused portion of one of said two optical fibres;

a light source arranged to input light to the taper waist portion along the input unfused portion; and

a light detector arranged to generate a signal indicative of a parameter of the light transmitted to the output unfused portion from the taper waist portion,

characterised in that the taper waist portion is formed as a loop and at least part of the loop is arranged to bend in response to a measurand.

2. Sensing apparatus in accordance with claim 1, wherein the sensor further comprises bending means arranged to bend at least part of said loop according to the measurand.

3. Sensing apparatus in accordance with claim 2, wherein said loop is formed substantially in a plane, and the bending means is arranged to bend the loop in said plane.

4. Sensing apparatus in accordance with claim 2, wherein said loop is formed substantially in a plane, and the bending means is arranged to bend the loop out of said plane.

5. Sensing apparatus in accordance with claim 1, wherein said loop is substantially U-shaped, incorporating a 180°

bend.

6. Sensing apparatus in accordance with claim 1, wherein the input end further comprises a second input unfused portion, the second input unfused portion being an unfused portion of the other one of said two optical fibres, the input unfused portions being arranged substantially in a plane, and the loop is formed in a plane perpendicular to the plane of the input unfused portions.

7. Sensing apparatus in accordance with claim 1, wherein said input and output unfused portions are arranged substantially in a first plane, and the loop is formed substantially in said first plane.

8. Sensing apparatus in accordance with claim 1, wherein the output end further comprises a second output unfused portion, the second output unfused portion being an unfused portion of the other one of said two optical fibres, and the apparatus further includes a second light detector, the light detectors being arranged to generate respective signals indicative of a parameter of the light transmitted to each output unfused portion.

18. Sensing apparatus in accordance with claim 8, further comprising means for generating a signal indicative of the ratio of said respective signals.

19. Sensing apparatus in accordance with claim 8, further comprising means for generating a signal indicative of the ratio of the sum to the difference of said respective signals.

20. Sensing apparatus in accordance with claim 1, wherein said two optical fibres are single-mode fibres, each comprising a core surrounded by cladding material of lower refractive index, the core being dimensioned to allow only a single, fundamental mode of light to propagate down the fibre, said fundamental mode being guided by the boundary between the core and cladding material.

21. Sensing apparatus in accordance with claim 20, wherein said core has a diameter smaller than 15 μ

m.

22. Sensing apparatus in accordance with claim 20, wherein said taper waist portion is dimensioned such that the fundamental mode cannot substantially be guided by a boundary between cladding material and core material in the taper waist portion, but can propagate along the taper waist portion guided by an external boundary of said cladding material.

23. Sensing apparatus in accordance with claim 20, wherein said taper waist portion has a substantially uniform cross section along its length, said cross section having a diameter of less than 30 μ

m.

24. Sensing apparatus in accordance with claim 20, wherein said loop comprises a bend having a radius of curvature smaller than 0.5 mm.

25. Sensing apparatus in accordance with claims 24 wherein said 180°

bend has a radius of curvature smaller than 0.5 mm.

26. Sensing apparatus in accordance with claim 1, wherein the taper waist portion has a substantially elliptical cross section having a major axis of symmetry.

27. Sensing apparatus in accordance with claim 1, wherein the taper waist portion has a cross section substantially resembling two overlapping circles, the cross section having a major axis of symmetry through the nominal centres of said circles.

28. Sensing apparatus in accordance with claim 1, wherein the taper waist portion has a substantially uniform cross section having at least a major axis of symmetry.

29. Sensing apparatus in accordance with claim 26, wherein said loop has been formed by bending the taper waist portion in a plane perpendicular to said major axis.

30. Sensing apparatus in accordance with claim 26 wherein said major axis is substantially parallel to said plane.

31. Sensing apparatus in accordance with claim 1, further comprising a tubular probe body, said sensor being arranged inside said body, and wherein said bending means comprises a resilient membrane,

one side of at least part of the membrane being arranged to communicate with a region outside the probe body and a second side of said at least part of the membrane being arranged to communicate with a region inside the probe body,

said at least part of said membrane being arranged to undergo a deflection according to a pressure difference between said regions and to communicate said deflection to the taper waist portion.

32. Sensing apparatus in accordance with claim 31 wherein an end of the probe body is obliquely terminated with respect to a longitudinal axis of the probe body, the membrane is arranged to seal said obliquely terminated end, and the sensor is arranged to hold a part of the taper waist portion in contact with the membrane.

33. Sensing apparatus in accordance with claim 31 wherein at least part of the probe body is flexible.

34. Sensing apparatus in accordance with claim 31 wherein the probe body comprises a rigid portion, at least part of at least one unfused portion of the sensor is fixed with respect to the rigid portion and the membrane seals an orifice in the rigid portion.

9. Sensing apparatus including:

a sensor comprising

a taper waist portion of optical fibre formed by fusing together and drawing down respective portions of at least two optical fibres, the taper waist portion having a first end and a second end, and

a taper transition portion of optical fibre optically connecting the first end of the taper waist portion to at least one unfused portion of optical fibre, each unfused portion being an unfused portion of a respective one of said at least two optical fibres; and

a light source arranged to input light to the first end of the taper waist portion along one of said at least one unfused portions,

characterised in that the sensor further comprises

means for reflecting at least some of the input light propagating along the taper waist portion from the first to the second end back along the taper waist portion to the first end,

the sensing apparatus further comprises

a light detector arranged to generate a signal indicative of a parameter of the reflected input light transmitted to one of said at least one unfused portions from the first end of the taper waist portion,

and at least part of the taper waist portion is arranged to bend in response to a measurand.

10. Sensing apparatus in accordance with claim 9, wherein the sensor further comprises bending means arranged to bend at least part of the taper waist portion according to the measurand.

11. Sensing apparatus in accordance with claim 9, wherein the taper transition portion optically connects the first end of the taper waist portion to two said unfused portions, and the apparatus further includes a second light detector, the light detectors being arranged to generate respective signals indicative of a parameter of the reflected input light transmitted to each unfused portion.

12. Sensing apparatus in accordance with claim 9, wherein the optical fibre portions of the sensor are provided by at least part of a fused tapered coupler.

13. Sensing apparatus in accordance with claim 9, wherein the taper waist portion terminates at said second end at a substantially planar surface arranged to reflect said propagating light.

14. Sensing apparatus in accordance with claim 13, wherein said surface has been formed by cutting.

15. Sensing apparatus in accordance with claim 13 wherein said surface is mirrored.

16. Sensing apparatus in accordance with claim 10, wherein said taper waist portion is arranged to lie substantially in a plane and the bending means is arranged to bend the taper waist portion in said plane.

17. Sensing apparatus in accordance with claim 9, wherein said unfused portion or portions and said taper waist portion are substantially co-planar.

35. A sensor comprising a fused tapered fibre optic coupler formed of two optical fibres fused together to provide a fused portion which is drawn down to form a taper waist portion, the coupler having an input end comprising an input unfused portion of one of said two optical fibres and an output end comprising an output unfused portion of one of said two optical fibres,

characterised in that the taper waist portion is formed as a loop.

36. A sensor in accordance with claim 35, further comprising bending means arranged to bend at least part of the loop according to a measurand.

37. A sensor in accordance with claim 36, further comprising a sensor body having a substantially rigid portion, wherein at least one of the input and output unfused portions is attached to the rigid portion, and the bending means is arranged to deflect the loop with respect to the rigid portion.

41. Sensing apparatus in accordance with claim 37, wherein said rigid portion is tubular and comprises an obliquely terminated end, the bending means comprises a resilient membrane sealing the obliquely terminated end and arranged to deflect according to a pressure difference across it, and at least one of the unfused portions is attached by attachment means to an inside surface of the tubular rigid portion, the attachment means being arranged to hold part of the taper waist portion in contact with the membrane.

38. A sensor comprising

a taper waist portion of optical fibre formed by fusing together and drawing down respective portions of at least two optical fibres, the taper waist portion having a first end and a second end, and

a taper transition portion of optical fibre optically connecting the first end of the taper waist portion to at least one unfused portion of optical fibre, each unfused portion being an unfused portion of a respective one of said at least two optical fibres,

characterised in that the sensor further comprises means for reflecting light propagating along the taper waist portion from the first to the second end back along the taper waist portion to the first end.

39. A sensor in accordance with claim 38, further comprising bending means arranged to bend at least part of the taper waist portion according to a measurand.

40. A sensor in accordance with claim 39, further comprising a body having a substantially rigid portion, wherein at least one of said at least one unfused portions is attached to the rigid portion, and the bending means is arranged to deflect the taper waist portion with respect to the rigid portion.

42. A measurement method comprising the steps of:

forming a loop from a taper waist portion of a fused tapered fibre optic coupler;

inputting light to the taper waist portion along a nominal input fibre of the coupler;

generating a signal indicative of a parameter of the light transmitted to a nominal output fibre of the coupler from the taper waist portion;

distorting the loop according a measurand; and

using the signal to provide an indication of the measurand.

43. A measurement method in accordance with claim 42, wherein said signal is indicative of the intensity of the light transmitted to the nominal output fibre, the method further comprising the steps of:

generating a second signal indicative of the intensity of the light transmitted to a second nominal output fibre of the coupler from the taper waist portion;

generating a further signal from said signal and said second signal, the further signal being indicative of a splitting ratio of light powers transmitted to each of said nominal output fibres; and

using the further signal as an indication of the measurand.

44. A measurement method in accordance with claim 42 wherein said step of forming a loop comprises the step of forming a substantially planar loop.

45. A measurement method in accordance with claim 44, wherein said step of distorting at least part of the loop comprises bending at least part of the loop out of its nominal plane.

46. A measurement method in accordance with claim 42, wherein said step of forming a loop comprises the step of forming a u-shaped loop having a 180°

bend.

47. A measurement method comprising the steps of:

inputting light to a taper waist portion of a fused tapered fibre optic coupler along a nominal input fibre of the coupler;

reflecting at least a portion of the light propagating along the taper waist portion from the input fibre back towards the input fibre;

generating a signal indicative of a parameter of the reflected light transmitted to a nominal input fibre of the coupler from the taper waist portion;

distorting at least part of the taper waist portion according to a measurand; and

using the signal to provide an indication of the measurand.

48. A measurement method in accordance with claim 47, further comprising the step of cleaving the taper waist portion to provide a reflecting surface, and said step of reflecting comprises reflecting said portion of the light from said surface.

49. A measurement method in accordance with claim 47 wherein said signal is indicative of the intensity of the light transmitted to the nominal input fibre from the taper waist portion, the method further comprising the steps of:

generating a second signal indicative of the intensity of the reflected light transmitted to a second nominal input fibre of the coupler from the taper waist portion;

generating a further signal from said signal and said signal, the further signal being indicative of a splitting ratio of light powers transmitted to each of said nominal input fibres; and

using the further signal as an indication of the measurand.

50. A measurement method in accordance with claim 49, wherein the nominal input fibres and the taper waist portion lie substantially in a common plane, and said distorting step comprises bending the taper waist portion in said common plane.