Optical measuring device using a spectral modulation sensor having an optically resonant structure

• US 4,678,904 A
• Filed: 07/06/1984
• Issued: 07/07/1987
• Est. Priority Date: 07/06/1984
• Status: Expired due to Term

• Current Assignee: Dynamet Technology, Inc. (Howmet Aerospace, Inc.)
• Original Assignee: Dynamet Technology, Inc. (Howmet Aerospace, Inc.)
• Inventors: Saaski, Elric W., Hartl, James C.
• Primary Examiner(s): Nelms, David C.
• Application Number:
  US06/628,813
• Time in Patent Office: 1,096 Days
• Field of Search: 250/227, 250/231 R, 250/231 P, 250/226, 73/705, 73/717, 73/722, 356/352
• US Class Current: 250/227.27
• CPC Class Codes: G01D 5/268 using optical fibres G01D5/28 - G01D5/38 take precedence
• CPC Class Codes: G01J 3/26 using multiple reflection, e.g. Fabry-Perot interferometer, variable interference filters
• CPC Class Codes: G01K 11/12 using changes in colour, translucency or reflectance
• CPC Class Codes: G01L 9/0079 with Fabry-Perot arrangements
• CPC Class Codes: G01N 2021/0385 Diffusing membrane; Semipermeable membrane
• CPC Class Codes: G01N 2021/772 Tip coated light guide
• CPC Class Codes: G01N 21/45 using interferometric methods; using Schlieren methods
• CPC Class Codes: G01N 21/75 Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated systems in which material is burnt in a flame or plasma G01N21/72, G01N21/73
• CPC Class Codes: G01N 21/7703 using reagent-clad optical fibres or optical waveguides using measurement of total internal reflection or attenuated total reflection G01N21/552; optical fibres or waveguides per se G02B
• CPC Class Codes: G01N 21/7746 the waveguide coupled to a cavity resonator
• CPC Class Codes: G01N 21/80 Indicating pH value
• CPC Class Codes: G01N 21/81 Indicating humidity

Abstract

The invention relates to optical devices for sensing and measuring various physical parameters. More particularly, this invention relates to an optical device having a spectral modulation sensor in which the physical parameter being measured causes spectral changes in the reflectivity and/or transmission of the sensor'"'"'s optically resonant structure, thereby spectrally modulating the output light from the sensor as a function of the physical parameter being measured.

Claims

1. An optical measuring device for measuring a range of values for a sensed physical parameter, comprising:

a source of input measuring light of at least two wavelengths;

an optically resonant structure having an optically sensitive physical characteristic which changes as a function of said sensed physical parameter, said optically resonant structure producing spectrally modulated output measuring light by spectrally modulating said input measuring light as a function of said changes of said optically sensitive physical characteristic by means of corresponding microshifts produced by said changes on at least one operating segment on an output curve, said output curve representing at least one of the reflectivity and transmissivity curves of said optically resonant structure;

said input measuring light, said optically resonant structure and said at least one operating segment being selected such that;

(1) said at least two wavelengths of said input measuring light fall substantially within said at least one operating segment which, over said range of values for said sensed physical parameter, is less than about one resonance cycle in length and is microshifted less than about one resonance cycle, and such that (2) said spectrally modulated output measuring light of said optically resonant structure bears a unique one-to-one relation to said sensed physical parameter over said range of values;

detector means for deriving two electrical signals corresponding to any two different wavelength portions of said spectrally modulated output measuring light and for taking the ratio of said two electrical signals to provide an output measuring electrical signal which is a function of said sensed physical parameter; and

light transmission means for conveying said input measuring light from said source to said optically resonant structure and for conveying said spectrally modulated output measuring light from said optically resonant structure to said detector means.

2. An optical measuring device according to claim 1, wherein said input measuring light and said optically resonant structure are selected such that said at least one operating segment of said output curve is microshifted greater than one-half of a resonance cycle over said range of values.

3. An optical measuring device according to claim 2, wherein said input measuring light and said optically resonant structure are selected such that said unique one-to-one relation is substantially linear over said range of values.

4. An optical measuring device according to claim 2, wherein said light transmission means comprises at least one optical fiber.

5. An optical measuring device according to claim 2, wherein said optically resonant structure defines a cavity having a pair of opposed reflective surfaces, wherein at least one of said reflective surfaces is displaced as a function of said sensed physical parameter, and wherein said optically sensitive physical characteristic comprises the spatial relationship between said pair of opposed reflective surfaces.

6. An optical measuring device according to claim 5, wherein said at least one displaced surface is bowed as a function of said sensed physical parameter.

7. An optical measuring device according to claim 6, wherein said optically resonant structure which defines said cavity comprises a substrate sealed together with a cover, at least one of which defines said cavity, wherein said cavity is at least substantially evacuated, wherein said at least one reflective surface which is bowed comprises at least a portion of an inner surface of said cover, and wherein said sensed physical parameter comprises the absolute external pressure on at least a portion of an outer surface of said cover.

8. An optical measuring device according to claim 6, wherein said optically resonant structure which defines said cavity comprises a substrate sealed together with a cover, at least one of which defines said cavity, and further comprises conduit means for providing fluid communication between a first source of pressure and said cavity, wherein said at least one displaced surface which is bowed comprises at least a portion of an inner surface of said cover, and wherein said sensed physical parameter comprises the relative pressure difference between said first source of pressure and a second source of pressure acting on an outer surface of said cover.

9. An optical measuring device according to claim 1, wherein said input measuring light comprises at least one relatively narrow band of frequencies, and wherein said band of frequencies has a peak intensity, has a wavelength of peak intensity and a bandwidth at one-half of said peak intensity on the order of about 10% of said wavelength of peak intensity.

10. An optical measuring device according to claim 1, wherein said input measuring light comprises at least one relatively narrow band of frequencies, and wherein said band of frequencies has a peak intensity, has a wavelength of peak intensity and has a bandwidth at one-half of said peak intensity in the range of from greater than 0% to less than about 10% of said wavelength of peak intensity.

11. An optical measuring device according to claim 1, wherein said source of input measuring light comprises a light emitting diode.

12. An optical measuring device according to claim 1, wherein said light transmission means includes at least one optical fiber which both conveys said input measuring light to said optically resonant structure and conveys said spectrally modulated output measuring light from said optically resonant structure to said detector means.

13. An optical measuring device according to claim 1, wherein said input measuring light comprises at least two bands of wavelengths.

14. An optical measuring device according to claim 1, wherein said light source means has a light emission band of frequencies, and wherein, at said input measuring light wavelengths, said band of frequencies has a bandwidth which is substantially less than a resonance cycle containing said operating segment.

15. An optical measuring device according to claim 1, wherein said at least two wavelengths of said input measuring light are selected such that a wavelength separation between said at least two wavelengths is substantially less than a resonance cycle containing said operating segment.

16. An optical measuring device according to claim 15, wherein said wavelength separation is on the order of 10% of an average of said at least two wavelengths.

17. An optical measuring device according to claim 15, wherein said wavelength separation is in the range of from more than zero to less than about 10% of an average of said at least two wavelengths.

18. An optical measuring device according to claim 1, wherein said optically resonant structure means comprises a body defining a cavity having a pair of opposed reflective surfaces;

wherein said body comprises a substrate and a cover, at least one of which defines said cavity; and

wherein said substrate and said light transmission means are at least substantially index matched.

19. An optical measuring device according to claim 18, wherein to help index match said substrate to said light transmission means, said substrate is selected to be made from borosilicate glass.

20. An optical measuring device according to claim 1, wherein said optically resonant structure means comprises a body defining a cavity having a pair of opposed reflective surfaces;

wherein said body comprises a substrate and a cover, at least one of which defines said cavity;

wherein said substrate has a thickness; and

wherein to improve the sensitivity of said optically resonant structure, said thickness of said substrate is selected to be about equal to a diameter of said light transmission means.

21. An optical measuring device according to claim 1, wherein said optically resonant structure means comprises a body defining a cavity having a pair of opposed reflective surfaces;

wherein said body comprises a substrate and a cover, at least one of which defines said cavity;

wherein said substrate and cover are sealed together and contain a vacuum within said cavity; and

wherein to help establish and maintain said vacuum a layer of getter material is deposited in an axially centered ring on at least one of said pair of opposed reflective surfaces.

22. An optical measuring device according to claim 21, wherein said getter material is iron.

23. A spectral modulation sensor for sensing a range of values for a sensed physical parameter and generating in response spectrally modulated output light, comprising:

an optically resonant structure defining a cavity having a pair of opposed reflective surfaces, wherein at least one of said reflective surfaces is adapted to bow as a function of said sensed physical parameter;

said optically resonant structure having an optically sensitive physical characteristic which is adapted to change as a function of said sensed physical parameter and which comprises the spatial relationship between said pair of opposed reflective surfaces;

wherein said optically resonant structure is adapted to receive input measuring light and to spectrally modulate said input measuring light as a function of said changes of said optically sensitive physical characteristic by means of corresponding microshifts produced by said changes on at least one operating segment on at least one of said optically resonant structure'"'"'s reflectivity and transmissivity curves to generate spectrally modulated output measuring light which is spectrally modulated as a function of said sensed physical parameter.

24. A spectral modulation sensor according to claim 23, wherein said sensed physical parameter is pressure on at least one side of said at least one of said reflective surfaces which is adapted to bow as a function of said sensed physical parameter.

25. A spectral modulation sensor according to claim 23, wherein said optically resonant structure means comprises a body defining a cavity having a pair of opposed reflective surfaces;

wherein said body comprises a substrate and a cover, at least one of which defines said cavity; and

wherein said substrate and said light transmission means are at least substantially index matched.

26. A spectral modulation sensor according to claim 25, wherein to help index match said substrate to said light transmission means, said substrate is selected to be made from borosilicate glass.

27. A spectral modulation sensor according to claim 23, wherein said optically resonant structure means comprises a body defining a cavity having a pair of opposed reflective surfaces;

wherein said body comprises a substrate and a cover, at least one of which defines said cavity;

wherein said substrate has a thickness; and

wherein to improve the sensitivity of said optically resonant structure, said thickness of said substrate is selected to be about equal to a diameter of said light transmission means.

28. A spectral modulation sensor according to claim 23, wherein said optically resonant structure means comprises a body defining a cavity having a pair of opposed reflective surfaces;

wherein said body comprises a substrate and a cover, at least one of which defines said cavity;

wherein said substrate and cover are sealed together and contain a vacuum within said cavity; and

wherein to help establish and maintain said vacuum a layer of getter material is deposited in an axially centered ring on at least one of said pair of opposed reflective surfaces.

29. A spectral modulation sensor according to claim 28, wherein said getter material is iron.

30. An optical measuring device for measuring a range of values for a sensed physical parameter, comprising:

a source of input measuring light of at least one waveband covering at least one wavelength;

an optically resonant structure defining a cavity having a pair of opposed reflective surfaces, at least one of said reflective surfaces bowing as a function of said sensed physical parameter, said optically resonant structure having an optically sensitive physical characteristic which changes as a function of said sensed physical parameter and which comprises the spatial relationship between said pair of opposed reflective surfaces, said optically resonant structure producing modulated output measuring light by modulating said input measuring light as a function of said changes of said optically sensitive physical characteristic by means of corresponding microshifts produced by said changes on at least one operating segment on an output curve, said output curve representing at least one of the reflectivity and transmissivity curves of said optically resonant structure;

said input measuring light, said optically resonant structure and said at least one operating segment being selected such that;

(1) said at least one waveband of said input measuring light falls substantially within said at least one operating segment which, over said range of values for said sensed physical parameter, is less than about one resonance cycle in length and is microshifted less than about one resonance cycle, and such that (2) said modulated output measuring light of said optically resonant structure bears a unique one-to-one relation to said sensed physical parameter over said range of values;

said modulated output measuring light falling within a respective said at least one waveband of said input measuring light;

detector means for deriving an ouput measuring electrical signal from said modulated output measuring light as a function of said sensed physical parameter; and

light transmission means for conveying said input measuring light from said source to said optically resonant structure and for conveying said modulated output measuring light from said optically resonant structure to said detector means.

31. An optical measuring device according to claim 30, wherein there are at least two wavelengths of said input measuring light, and wherein said detector means are for deriving two electrical signals corresponding to any two different wavelength portions of said spectrally modulated output measuring light and are for taking the ratio of said two electrical signals to provide said output measuring electrical signal which is a function of said sensed physical parameter.

32. An optical measuring device according to claim 30, wherein said input measuring light and said optically resonant structure are selected such that said at least one operating segment of said output curve is microshifted greater than one-half of a resonance cycle over said range of values.

33. An optical measuring device according to claim 32, wherein said input measuring light and said optically resonant structure are selected such that said unique one-to-one relation is substantially linear over said range of values.

34. An optical measuring device according to claim 32, whrein said light transmission means comprises at least one optical fiber.

35. An optical measuring device according to claim 30, wherein said optically resonant structure which defines said cavity comprises a substrate sealed together with a cover, at least one of which defines said cavity, wherein said cavity is at least substantially evacuated, wherein said at least one reflective surface which is bowed comprises at least a portion of an inner surface of said cover, and wherein said sensed physical parameter comprises the absolute external pressure on at least a portion of an outer surface of said cover.

36. An optical measuring device according to claim 30, wherein said optically resonant structure which defines said cavity comprises a substrate sealed together with a cover, at least one of which defines said cavity, and further comprises conduit means for providing fluid communication between a first source of pressure and said cavity, wherein said at least one displaced surface which is bowed comprises at least a portion of an inner surface of said cover, and wherein said sensed physical parameter comprises the relative pressure difference between said first source of pressure and a second source of pressure acting on an outer surface of said cover.

37. An optical measuring device according to claim 30, wherein said input measuring light comprises at least one relatively narrow band of frequencies, and wherein said band of frequencies has a peak intensity, has a wavelength of peak intensity and a bandwidth at one-half of said peak intensity on the order of about 10% of said wavelength of peak intensity.

38. An optical measuring device according to claim 30, wherein said input measuring light comprises at least one relatively narrow band of frequencies, and wherein said band of frequencies has a peak intensity, has a wavelength of peak intensity and has a bandwidth at one-half of said peak intensity in the range of from greater than 0% to less than about 10% of said wavelength of peak intensity.

39. An optical measuring device according to claim 30, wherein said source of input measuring light comprises a light emitting diode.

40. An optical measuring device according to claim 30, wherein said light transmission means includes at least one optical fiber which both conveys said input measuring light to said optically resonant structure and conveys said spectrally modulated output light from said optically resonant structure to said detector means.

41. An optical measuring device according to claim 30, wherein said input measuring light comprises at least two bands of wavelengths.

42. An optical measuring device according to claim 30, wherein said light source means has a light emission band of frequencies, and wherein, at said input measuring light wavelengths, said band of frequencies has a bandwidth which is substantially less than a resonance cycle containing said operating segment.

43. An optical measuring device according to claim 30, wherein said at least two wavelengths of said input measuring light are selected such that a wavelength separation between said at least two wavelengths is substantially less than a resonance cycle containing said operating segment.

44. An optical measuring device according to claim 43, wherein said wavelength separation is on the order of 10% of an average of said at least two wavelengths.

45. An optical measuring device according to claim 43, wherein said wavelength separation is in the range of from more than zero to less than about 10% of an average of said at least two wavelengths.

46. An optical measuring device according to claim 30, wherein said optically resonant structure means comprises a body defining a cavity having a pair of opposed reflective surfaces;

wherein said body comprises a substrate and a cover, at least one of which defines said cavity; and

wherein said substrate and said light transmission means are at least substantially index matched.

47. An optical measuring device according to claim 46, wherein to help index match said substrate to said light transmission means, said substrate is selected to be made from borosilicate glass.

48. An optical measuring device according to claim 30, wherein said optically resonant structure means comprises a body defining a cavity having a pair of opposed reflective surfaces;

wherein said body comprises a substate and a cover, at least one of which defines said cavity;

wherein said substrate has a thickness; and

wherein to improve the sensitivity of said optically resonant structure, said thickness of said substrate is selected to be about equal to a diameter of said light transmission means.

49. An optical measuring device according to claim 30, wherein said optically resonant structure means comprises a body defining a cavity having a pair of opposed reflective surfaces;

wherein said body comprises a substrate and a cover, at least one of which defines said cavity;

wherein said substrate and cover are sealed together and contain a vacuum within said cavity; and

wherein to help establish and maintain said vacuum a layer of getter material is deposited in an axially centered ring on at least one of said pair of opposed reflective surfaces.

50. An optical measuring device according to claim 49, wherein said getter material is iron.