SYSTEM AND METHOD FOR MEASURING PHYSICAL STIMULI USING VERTICAL CAVITY SURFACE EMITTING LASERS WITH INTEGRATED TUNING MEANS

• US 20040202400A1
• Filed: 12/22/2003
• Published: 10/14/2004
• Est. Priority Date: 04/14/2003
• Status: Active Grant

• Current Assignee: Kyton, LLC
• Original Assignee: Lake Shore Cryotronics, Inc.
• Inventors: Kochergin, Vladimir, Swinehart, Philip
• Granted Patent: US 6,836,578 B2
• Time in Patent Office: Days
• US Class Current: 385/12
• CPC Class Codes: G01D 5/35316 using a Bragg gratings
• CPC Class Codes: G01K 11/3206 at discrete locations in the fibre, e.g. using Bragg scattering
• CPC Class Codes: G01N 21/39 using tunable lasers
• CPC Class Codes: G01N 21/45 using interferometric methods; using Schlieren methods
• CPC Class Codes: G02B 26/001 based on interference in an adjustable optical cavity interference filters G02B5/28; devices or arrangements using multiple reflections in spectrometry or monochromators G01J3/26
• CPC Class Codes: G02B 6/29317 Light guides of the optical fibre type
• CPC Class Codes: G02B 6/29319 With a cascade of diffractive elements or of diffraction operations forming interferometer by splitting and recombining G02B6/29347 - G02B6/29358
• CPC Class Codes: G02B 6/29358 Multiple beam interferometer external to a light guide, e.g. Fabry-Pérot, etalon, VIPA plate, OTDL plate, continuous interferometer, parallel plate resonator G02B6/29347, G02B6/29349, G02B6/2935, G02B6/29361 take precedence; resonator evanescently coupled to light guide G02B6/29335
• CPC Class Codes: G02B 6/42 Coupling light guides with opto-electronic elements
• CPC Class Codes: G02B 6/4202 for coupling an active element with fibres without intermediate optical elements, e.g. fibres with plane ends, fibres with shaped ends, bundles
• CPC Class Codes: G02B 6/4206 Optical features G02B6/4207, G02B6/421 take precedence

Abstract

An optical sensor diagnostic system utilizes a tunable Vertical Cavity Surface Emitting Laser (VCSEL) that incorporates an integrated MEMS tuning mechanism provides variable wavelength light into an optical fiber with improved wavelength scanning speed and greater simplicity of construction. Sensors, such as Bragg gratings, are disposed along the fiber in the light path. Each sensor reflects or transmits light exhibiting a characteristic amplitude and/or phase feature with respect to wavelength, the wavelength position of which is affected by an environmental stimulus imposed thereon. The light reflected or transmitted through each sensor is mixed with light passed through an optical reference path and then converted to an electrical signal by a simple detector and monitored by circuitry that applies signal processing to the detected power spectral distribution, by this means providing output signals indicative of the environmental stimulus on each sensor.

Claims

1. An optical sensor diagnostic system, comprising:

a tunable VCSEL incorporating an integrated MEMS wavelength tuner that provides wavelength-tunable light in response to a tuning control signal,;

an optical waveguide optically coupled to said VCSEL, said tunable light being launched into said optical waveguide;

at least one optical sensor disposed in the path of said tunable light, said tunable VCSEL individually illuminating said sensor, said sensor providing a transmitted light having altered amplitude and/or phase at least over some wavelengths within the transmitted wavelength range, said spectral distribution of said altered amplitude and/or phase being responsive to an environmental stimulus;

an optical reference path to be optically compared with the sensing path;

an optical detector, disposed in the path of said transmitted light, for detecting said transmitted light from said sensor and the optical reference path and for providing an electrical detection signal indicative of the power of said transmitted light throughout the appropriate wavelength range;

a controller coupled to said tunable VCSEL, said controller providing a variable tuning control signal to said tunable VCSEL indicative of the desired wavelength of said tunable light;

a capacitive or optical reference that determines the wavelength of the light emitted by said tunable VCSEL as a function of time and providing feedback; and

a signal processor responsive to said electrical detection signal, for detecting a wavelength defined on the characteristic transmission amplitude feature in order to quantitatively detect the effect on said sensor due to said environmental stimulus, for detecting changes in said wavelength at the characteristic transmission amplitude feature caused by changes in said environmental stimulus, and for providing a signal indicative of said stimulus or change therein for said sensor.

2. The optical sensor diagnostic system of claim 1 wherein at least one wavelength reference independent of said tuning control signal and moveable mirror position detecting is disposed in the path of the light.

3. The optical sensor diagnostic system of claim 2 wherein at least one wavelength reference, not affected by any environmental stimulus, comprising at least one of the group of a Bragg grating, a phase shift Bragg grating, a Fabry-Perot etalon or a gas-containing chamber, is disposed in the optical path.

4. The optical sensor diagnostic system of claim 3 wherein the gas-containing chamber contains acetylene gas.

5. The optical sensor diagnostic system of claim 1 wherein optical isolation is disposed in the path of said tunable light between said tunable VCSEL and said sensor for isolating said tunable light source from light reflected from said sensor .

6. The optical sensor diagnostic system of claim 1 wherein said interferometer reference path is disposed in the path of said tunable light between said tunable VCSEL and said sensor.

7. The optical sensor diagnostic system of claim 6 wherein said interferometer reference path comprises a section of an optical fiber having the optical length chosen to provide maximum resolution of the optical sensor diagnostic system.

8. The optical sensor diagnostic system of claim 7 wherein said section of an optical fiber is defined by one or two reflectors disposed along the reference path.

9. The optical sensor diagnostic system of claim 8 wherein one of said reflectors is the part of one of the sensor .

10. The optical sensor diagnostic system of claim 1 wherein said optical detector comprises a photodiode.

11. The optical sensor diagnostic system of claim 1 wherein said interferometer reference path is disposed in the path of said tunable light between said sensor and said optical detector.

12. The optical sensor diagnostic system of claim 11 wherein said interferometer reference path comprises a section of an optical fiber having the optical length chosen to provide maximum resolution of the optical sensor diagnostic system.

13. The optical sensor diagnostic system of claim 12 wherein said section of an optical fiber is defined by one or two reflectors disposed along the reference path.

14. The optical sensor diagnostic system of claim 13 wherein one of said reflectors is the part of one of the sensor .

15. The optical sensor diagnostic system of claim 1 wherein said interferometer reference path is physically separate from the optical path that connects the VCSEL, sensor array and optical detectors and constitutes a section of an optical fiber having the optical length chosen to provide maximum resolution of the optical sensor diagnostic system is provided within the reference path.

16. The optical sensor diagnostic system of claim 15 wherein an optical splitter is disposed in the path of said tunable light between said tunable VCSEL and said at least one sensor, for splitting the light into two physically separate optical paths, one directing light toward the sensor or sensor array and another directing the light to the interferometer reference path.

17. The optical sensor diagnostic system of claim 15 wherein an optical combiner is disposed in the path of said tunable light between said tunable VCSEL and optical detector, for combining the light transmitted through the said at least one sensor and through the said interferometer reference optical path.

18. The optical sensor diagnostic system of claim 15 wherein said section of an optical fiber is defined by one or two reflector disposed along the reference path.

19. The optical sensor diagnostic system of claim 15 wherein a variable time delay device is disposed along the said interferometer reference path.

20. The optical sensor diagnostic system of claim 15 wherein a frequency shifter is disposed along the said interferometer reference path.

21. The optical sensor diagnostic system of claim 1 wherein said at least one sensor comprises at least one fiber or planar Bragg grating.

22. The optical sensor diagnostic system of claim 21 wherein at least one Bragg grating of at least one sensor comprises at least one incorporated phase shift in its structure, said phase shift producing a sharper maximum within said transmitted wavelength band minimum.

23. The optical sensor diagnostic system of claim 1 wherein said at least one sensor comprises at least one Fabry-Perot etalon.

24. The optical sensor diagnostic system of claim 23 wherein said at least one Fabry-Perot etalon comprises a section of the fiber between two Bragg gratings having the same periods or periods close enough together for the required sensing accuracy.

25. The optical sensor diagnostic system of claim 1 wherein said environmental stimulus is any combination of mechanical stress, temperature, pressure, electrical current, electrical field, magnetic field, chemical or biological effect on said sensor.

26. The optical sensor diagnostic system of claim 1 wherein at least one of said sensors serves as an environment reference or compensation sensor.

27. The optical sensor diagnostic system of claim 1 wherein at least some of said optical sensors are wavelength division multiplexed.

28. The optical sensor diagnostic system of claim 1 wherein said voltage or other controller comprises a modulator for modulating said voltage control signal at a predetermined modulation frequency.

29. The optical sensor diagnostic system of claim 1 wherein:

said voltage or other controller comprises means for scanning said control signal for the purpose of causing said tunable VCSEL to scan its wavelengths across said characteristic transmission amplitude and/or phase features of any or all of said sensor; and

said signal processor comprises means responsive to said voltage or other control signal for determining the wavelength of said tunable light from the magnitude of said voltage or other control signal and/or mirror position feedback signal and for determining which of said sensor is being illuminated, thereby determining the value of the environmental stimulus at the position of said individual sensor.

30. The optical sensor diagnostic system of claim 1 wherein:

said voltage or other controller comprises means for scanning said control signal so as to cause said tunable VCSEL to scan across the characteristic transmission amplitude and/or phase features of all of said sensor and for providing a synchronization signal indicative of when said voltage control signal begins and ends said scanning; and

said signal processor comprises means responsive to said synchronization signal for determining which of said sensor is being illuminated, thereby determining the value of the environmental stimulus at the position of said individual sensor.

31. The optical sensor diagnostic system of claim 1 wherein said signal processor comprises a demodulator operating at said modulation frequency, for demodulating said electrical detection signal and for providing a demodulated signal indicative thereof.

32. The optical sensor diagnostic system of claim 1 wherein said signal processor includes:

digitizing the read values from the optical detector;

forming data arrays comprising the digitized reading values, and

producing a discrete Fourier Transform based on the digitized read values and wavelengths at which said read values have been taken;

determining the spatial domain waveform from the said discrete Fourier Transform, and

determining the value of the environmental stimulus at the position of each individual sensor.

33. The optical sensor diagnostic system of claim 32 wherein filtering of the discrete Fourier Transform is performed such that the Fourier coefficients at low frequencies and at high frequencies are set substantially to zero.

34. The optical sensor diagnostic system of claim 32 wherein the signal processor incorporates computational means for increasing the accuracy and precision of determining the value of the environmental stimulus at the position of each individual sensor.

35. The optical sensor diagnostic system of claim 1 wherein said signal processor include:

digitizing the read values from the optical detector;

forming data arrays comprising the digitized reading values, and

producing a discrete Fourier Transform based on the digitized read values and wavelengths at which said read values have been taken;

performing filtering of the discrete Fourier Transform spectra;

producing a discrete Inverse Fourier Transform based on the filtered discrete Fourier Transform spectra, and

determining the value of the environmental stimulus at the position of each individual sensor.

36. The optical sensor diagnostic system of claim 35 wherein filtering of the discrete Fourier Transform is performed such that the Fourier coefficients at low frequencies and at high frequencies are set substantially zero.

37. The optical sensor diagnostic system of claim 35 wherein the signal processor incorporates computational means for increasing the accuracy and precision of determining the value of the environmental stimulus at the position of each individual sensor.

38. The optical sensor diagnostic system of claim 35 wherein the value of the environmental stimulus at the position of each individual sensor is determined from the difference in the current wavelength position of said characteristic transmission amplitude and/or phase features and the digitally stored value of said wavelength position of said characteristic transmission amplitude.

39. An optical sensor diagnostic system, comprising:

a VCSEL incorporating an integrated MEMS wavelength tuner for providing wavelength-tunable light in response to a tuning control signal, said tunable light being launched into an optical waveguide,

at least one optical sensor, disposed in the path of said tunable light, said tunable VCSEL illuminating said sensor, said sensor providing a reflected light having altered amplitude and/or phase at least over some wavelengths within the reflected wavelength range, said spectral distribution of said altered amplitude and/or phase being responsive to an environmental stimulus imposed thereupon;

an optical reference path;

an optical divider, disposed in the path of said tunable light between said tunable VCSEL and said sensor, for directing said tunable light from said VCSEL to said sensor and in addition to said optical reference path and for redirecting the light reflected from said sensor and from said optical reference path to said detector;

an optical detector, disposed in the path of said reflected light, for detecting said reflected light from each of said sensor and for providing an electrical detection signal indicative of the power of said reflected light throughout the appropriate wavelength range;

a voltage or other controller for providing a variable tuning control signal to said tunable VCSEL indicative of the desired wavelength of said tunable light;

a capacitive, piezoresistive or optical arrangement for identification of the wavelength of the light emitted by said tunable VCSEL and providing feedback; and

a signal processor responsive to said electrical detection signal, for detecting a wavelength defined by the characteristic reflection amplitude feature in order to quantitatively detect the effect on said sensor due to said environmental stimulus, changes in said wavelength at the characteristic reflection amplitude feature caused by changes in said environmental stimulus, and for providing a signal indicative of said stimulus or change therein for said sensor .

40. The optical sensor diagnostic system of claim 39 wherein at least one wavelength reference independent of said tuning control signal and moveable mirror position detector is disposed in the path of the light.

41. The optical sensor diagnostic system of claim 40 wherein at least one wavelength reference, not affected by any environmental stimulus, comprising at least one of the group of a Bragg grating, a phase shift Bragg grating, a Fabry-Perot etalon or a gas-containing chamber, is disposed in the optical path.

42. The optical sensor diagnostic system of claim 41 wherein the gas-containing chamber contains acetylene gas.

43. The optical sensor diagnostic system of claim 39 wherein said optical divider comprises an optical coupler.

44. The optical sensor diagnostic system of claim 43 wherein optical isolator is disposed in the path of said tunable light between said tunable VCSEL and said divider, for isolating said tunable light source from light reflected from the sensor .

45. The optical sensor diagnostic system of claim 39 wherein said optical divider comprises an optical circulator.

46. The optical sensor diagnostic system of claim 39 wherein said optical reference path is disposed in the path of said tunable light between said tunable VCSEL and said sensor .

47. The optical sensor diagnostic system of claim 46 wherein said optical reference path comprises a section of an optical fiber having its optical length chosen to provide maximum resolution of the optical sensor diagnostic system.

48. The optical sensor diagnostic system of claim 47 wherein said section of an optical fiber is defined by one or two reflector disposed along the reference path.

49. The optical sensor diagnostic system of claim 48 wherein one of said reflector is a part of one of the sensor .

50. The optical sensor diagnostic system of claim 39 wherein said optical detector comprises a photodiode.

51. The optical sensor diagnostic system of claim 39 wherein said optical reference path is physically separate from the optical path connecting the VCSEL, sensor array and optical detector and a section of optical fiber having its optical length chosen to provide maximum resolution of the optical sensor diagnostic system is provided within the reference path.

52. The optical sensor diagnostic system of claim 51 wherein an optical splitter is disposed in the path of said tunable light between said tunable VCSEL and said at least one sensor , for the purpose of splitting the light into two physically separate optical paths, one directing light toward the sensor or sensor array and another to the optical reference path.

53. The optical sensor diagnostic system of claim 51 wherein an optical combiner is disposed in the path of said tunable light between said optical sensor and optical detector, for combining the light reflected from the said at least one sensor and from the said optical reference path.

54. The optical sensor diagnostic system of claim 51 wherein said section of an optical fiber is defined by one or two reflector disposed along the reference path.

55. The optical sensor diagnostic system of claim 51 wherein a variable time delay means is disposed along the said reference path.

56. The optical sensor diagnostic system of claim 51 wherein a frequency shifter is disposed along the said reference path.

57. The optical sensor diagnostic system of claim 51 wherein said at least one sensor comprises at least one fiber or planar Bragg grating.

58. The optical sensor diagnostic system of claim 57 wherein at least one Bragg grating of at least one sensor comprises at least one incorporated phase shift in its structure, said phase shift producing a sharper minimum within said reflected wavelength band maximum.

59. The optical sensor diagnostic system of claim 39 wherein said at least one sensor comprises at least one Fabry-Perot etalon.

60. The optical sensor diagnostic system of claim 59 wherein said at least one Fabry-Perot etalon comprises section of the fiber between two Bragg gratings having the same or close enough periods.

61. The optical sensor diagnostic system of claim 39 wherein said environmental stimulus is any combination of mechanical stress, temperature, pressure, electrical current, electrical field or magnetic field on said sensor .

62. The optical sensor diagnostic system of claim 39 wherein at least one of said sensors serves as an environment reference or compensation sensor.

63. The optical sensor diagnostic system of claim 39 wherein at least some of said optical sensors are wavelength division multiplexed.

64. The optical sensor diagnostic system of claim 39 wherein said voltage or other controller comprises modulator for modulating said voltage control signal at a predetermined modulation frequency.

65. The optical sensor diagnostic system of claim 39 wherein:

said voltage or other controller comprises means for scanning said control signal for the purpose of causing said tunable VCSEL to scan its wavelengths across said characteristic reflection amplitude and/or phase features of any or all of said sensor; and

said signal processor comprises means responsive to said voltage or other control signal for determining the wavelength of said tunable light from the magnitude of said voltage or other control signal and/or mirror position feedback signal and for determining which of said sensor is being illuminated, thereby determining the value of the environmental stimulus at the position of said individual sensor.

66. The optical sensor diagnostic system of claim 39 wherein:

said voltage or other controller comprises means for scanning said control signal so as to cause said tunable VCSEL to scan across the characteristic reflection amplitude and/or phase features of all of said sensor and for providing a synchronization signal indicative of when said voltage control signal begins and ends said scanning; and

said signal processor comprises means responsive to said synchronization signal for determining which of said sensor is being illuminated, thereby determining the value of the environmental stimulus at the position of said individual sensor.

67. The optical sensor diagnostic system of claim 39 wherein said signal processor comprises demodulator operating at said modulation frequency, for demodulating said electrical detection signal and for providing a demodulated signal indicative thereof.

68. The optical sensor diagnostic system of claim 39 wherein said signal processor include:

digitizing the read values from the optical detector;

forming data arrays comprising the digitized read values;

producing a discrete Fourier Transform based on the digitized read values and wavelengths at which said read values have been taken;

determining the spatial domain waveform from the said discrete Fourier Transform, and

determining the value of the environmental stimulus at the position of each individual sensor.

69. The optical sensor diagnostic system of claim 68 wherein filtering of the discrete Fourier Transform is performed such as the Fourier coefficients at low frequencies and at high frequencies are set adequately near zero.

70. The optical sensor diagnostic system of claim 68 wherein the signal processor incorporates computational means for increasing the accuracy and precision of determining the value of the environmental stimulus at the position of each individual sensor.

71. The optical sensor diagnostic system of claim 39 wherein said signal processor include:

digitizing the read values from the optical detector;

forming arrays comprising the digitized read values;

producing a discrete Fourier Transform based on the digitized read values and wavelengths at which said read values have been taken;

perform filtering of the discrete Fourier Transform spectra;

producing a discrete Inverse Fourier Transform based on the filtered discrete Fourier Transform spectra, and

determining the value of the environmental stimulus at the position of each individual sensor.

72. The optical sensor diagnostic system of claim 71 wherein filtering of the discrete Fourier Transform is performed such that the Fourier coefficients at low frequencies and at high frequencies are set substantially to zero.

73. The optical sensor diagnostic system of claim 71 wherein the signal processor incorporates computational means for increasing the accuracy and precision of determining the value of the environmental stimulus at the position of each individual sensor.

74. The optical sensor diagnostic system of claim 71 wherein the value of the environmental stimulus at the position of each individual sensor is determined from the difference in the current wavelength position of said characteristic reflection amplitude features and a digitally stored value of said wavelength position of said characteristic reflection amplitude features.

75. The optical sensor diagnostic system of claim 39 wherein at least one sensor is disposed in a branch waveguide or optical fiber coupled to the main waveguide.

76. An optical sensor diagnostic method comprising:

tuning an on-chip tunable VCSEL to provide wavelength-tunable light, including providing a variable tuning control signal to said tunable VCSEL indicative of a desired wavelength of said tunable light and providing feedback responsive at least in part to the wavelength of the light emitted by said tunable VCSEL;

directing some of said tunable light from said VCSEL to at least one optical sensor to illuminate said sensor with said tunable light, said sensor providing a reflected light having altered amplitude and/or phase at least over some wavelengths within a reflected wavelength range, said spectral distribution of said altered amplitude and/or phase being responsive to an environmental stimulus imposed upon said sensor;

directing some of said tunable light along an optical reference path;

redirecting at least some of the light reflected from said sensor and from said optical reference path to an optical detector;

detecting, with said optical detector, said reflected light from said sensor and providing an electrical detection signal indicative of the power of said reflected light throughout the reflected wavelength range; and

detecting a wavelength defined by a characteristic reflection amplitude feature to quantitatively detect the effect on said sensor due to said environmental stimulus, changes in said wavelength at the characteristic reflection amplitude feature caused by changes in said environmental stimulus, and providing a signal indicative of said stimulus or change therein for said sensor.