System and method for measuring physical, chemical and biological stimuli using vertical cavity surface emitting lasers with integrated tuner

• US 6,549,687 B1
• Filed: 10/26/2001
• Issued: 04/15/2003
• Est. Priority Date: 10/26/2001
• Status: Active Grant

• Current Assignee: Kyton, LLC
• Original Assignee: Lake Shore Cryotronics, Inc.
• Inventors: Kochergin, Vladimir, Swinehart, Philip
• Primary Examiner(s): Ullah, Akm E.
• Assistant Examiner(s): Lin, Tina M
• Application Number:
  US09/983,999
• Publication Number:
  US 20030081875A1
• Time in Patent Office: 536 Days
• Field of Search: 385/12, 385/18, 385/24, 372/6, 372/20, 372/32, 372/45, 372/96, 372/98, 372/99, 372/107, 356/32, 250/227.11, 250/227.12, 250/227.27, 250/226
• US Class Current: 385/12
• CPC Class Codes: G01N 2021/399 Diode laser
• CPC Class Codes: G01N 21/39 using tunable lasers
• CPC Class Codes: G01N 21/45 using interferometric methods; using Schlieren methods
• CPC Class Codes: G01N 21/553 and using surface plasmons fluorescence excitation G01N21/648; enhanced Raman G01N21/658
• CPC Class Codes: G01N 21/64 Fluorescence; Phosphorescence
• 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: 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 6/29358 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
• CPC Class Codes: H01S 5/18366 Membrane DBR, i.e. a movable DBR on top of the VCSEL

Abstract

An optical sensor diagnostic system utilizing 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 feature with respect to wavelength, the wavelength position of which is affected by an environmental stimulus imposed thereon. The power of the reflected light is converted to an electrical signal by a simple detector and monitored by circuitry that detects changes in reflected power and provides output signals indicative of the environmental stimulus for each sensor.

Claims

1. An optical sensor diagnostic system, comprising:

a tunable 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, said tunable VCSEL including a movable tuning mirror and a capacitive or optical detector for detecting the position of the movable tuning mirror and providing feedback;

at least one optical sensor, disposed in the path of said tunable light, said at least one sensor providing a transmitted light having at least one associated characteristic amplitude feature selected from the group consisting of a minimum, a maximum or a slope located at a particular wavelength within the transmitted wavelength range, said wavelength at each minimum, maximum or sloped transmission amplitude being responsive to an environmental stimulus imposed upon said at least one sensor;

said tunable VCSEL individually illuminating said at least one sensor in a wavelength range spanning said wavelength location of said associated characteristic transmission amplitude feature;

an optical isolator, disposed in the path of said tunable light between said tunable VCSEL and said at least one sensor, for isolating said tunable light source from light reflected from said at least one sensor;

an optical detector, disposed in the path of said transmitted light, for detecting said transmitted light from said at least one sensor and for providing an electrical detection signal indicative of the power of said transmitted light throughout a predetermined wavelength range;

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

at least one wavelength reference independent of said tuning control signal and moveable mirror position detector disposed in the path of the light; 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 at least one sensor due to said environmental stimulus, 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.

2. The optical sensor diagnostic system of claim 1 wherein said at least one sensor comprises plural wavelength division multiplexed optical sensors.

3. The optical sensor diagnostic system of claim 1 wherein said at least one sensor comprises plural time division multiplexed optical sensors.

4. The optical sensor diagnostic system of claim 1 wherein said at least one sensor comprises an environment reference or compensation sensor.

5. The optical sensor diagnostic system of claim 1 wherein said detection and signal processor comprises a tracker, responsive to said electrical detection signal, for adjusting a voltage or other control signal to allow said tunable light to track static and dynamic values of said characteristic transmission amplitude feature for said at least one sensor, thereby providing utilization of the control signal as the output characteristic of the physical stimulus, making unnecessary scanning of the complete wavelength range and greatly increasing the speed of data acquisition.

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

7. 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.

8. The optical sensor diagnostic system of claim 1 wherein said signal processor incorporates a computational element for increasing the accuracy and precision of determining the wavelength position of said characteristic transmission amplitude feature and changes therein for each of said sensor.

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

said at least one sensor comprises plural sensors;

said controller comprises a scanner that scans said control signal for the purpose of causing said tunable VCSEL to scan its wavelengths across said characteristic transmission amplitude features of said plural sensors; and

said signal processor determines, in response to said voltage or other control signal, 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 plural sensors is being illuminated, thereby determining the value of the environmental stimulus at the position of said illuminated sensor.

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

said at least one sensor comprises plural sensors;

said controller comprises a scanner that scans said control signal so as to cause said tunable VCSEL to scan across the characteristic transmission amplitude features of said plural sensors and for providing a synchronization signal indicative of when said voltage control signal begins and ends said scanning; and

said signal processor determines, in response to said synchronization signal, which of said plural sensors is being illuminated, thereby determining changes in said wavelength at said characteristic transmission amplitude feature.

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

12. The optical sensor diagnostic system of claim 1 wherein said at least one sensor includes at least one Bragg grating that incorporates phase shift in its structure, said phase shift producing a sharper maximum within said transmitted wavelength band minimum.

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

14. The optical sensor diagnostic system of claim 1 wherein said at least one sensor comprises at least one Surface Plasmon Resonance structure.

15. The optical sensor diagnostic system of claim 1 wherein said at least one sensor comprises at least one thin film or bulk material characteristic absorber material.

16. The system of claim 15 wherein characteristic absorber material comprises one or more vibronic, excitonic or fluorescent materials.

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

18. The optical sensor diagnostic system of claim 1 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.

19. The optical sensor diagnostic system of claim 1 wherein the wavelength reference comprises at least one gas-containing chamber containing acetylene gas.

20. An optical sensor diagnostic system, comprising:

a VCSEL incorporating 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, wherein is provided

at least one optical sensor, disposed in the path of said tunable light, each providing a reflected light having at least one associated characteristic amplitude feature from but, not limited to, the group, a minimum, a maximum or a slope located at a particular wavelength within the reflected wavelength range, said wavelength at each minimum, maximum or sloped reflection amplitude being responsive to an environmental stimulus imposed upon a corresponding sensor;

said tunable VCSEL for individually illuminating each of said sensor in a wavelength range spanning said wavelength location of said associated characteristic reflection amplitude feature;

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;

optical circulator, 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 and directing the light to said detector;

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

capacitive or optical detector that detects the position of the movable tuning mirror and providing feedback; and

at least one wavelength reference independent of said tuning control signal and moveable mirror position detector disposed in the path of the light, and

signal processor responsive to said electrical detection signal, for detecting a wavelength defined on 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 each of said sensor.

21. The optical sensor diagnostic system of claim 20 wherein said optical sensors are wavelength division multiplexed.

22. The optical sensor diagnostic system of claim 20 wherein said optical sensors are time division multiplexed.

23. The optical sensor diagnostic system of claim 20 wherein at least one of said sensors serves as an environment reference or compensation sensor.

24. The optical sensor diagnostic system of claim 20 wherein said detection and signal processor comprises tracker, responsive to said electrical detection signal, for adjusting said voltage or other control signal to allow said tunable light to track static and dynamic values of said characteristic reflection amplitude feature for each of said sensor, thereby providing utilization of the control signal as the output characteristic of the physical stimulus, making unnecessary scanning of the complete wavelength range and greatly increasing the speed of data acquisition.

25. The optical sensor diagnostic system of claim 20 wherein said voltage controller comprises a modulator for modulating said voltage control signal at a predetermined modulation frequency.

26. The optical sensor diagnostic system of claim 20 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.

27. The optical sensor diagnostic system of claim 20 wherein said signal processor performs computations that increase the accuracy and precision of determining the wavelength position of said characteristic reflection amplitude feature and changes therein for each of said sensor.

28. The optical sensor diagnostic system of claim 20 wherein:

said voltage or other controller comprises a scanner that scans said voltage control signal so as to cause said tunable VCSEL to scan its wavelength across said characteristic reflection amplitude feature of any or all of said sensor; and

said signal processor determines, in response to said voltage or other control signal, 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.

29. The optical sensor diagnostic system of claim 20 wherein:

said voltage or other controller comprises a scanner that scans said voltage control signal so as to cause said tunable VCSEL to scan across the wavelengths of the characteristic reflection features of all of said sensor; and

for providing a synchronization signal indicative of when said voltage control signal begins said scanning; and

said signal processor determines, in response to said synchronization signal, which of said sensor is being illuminated, thereby determining changes in said wavelength at said characteristic reflection amplitude feature.

30. The optical sensor diagnostic system of claim 20 wherein said at least one sensor comprises at least one fiber or planar Bragg grating.

31. The optical sensor diagnostic system of claim 30 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.

32. The optical sensor diagnostic system of claim 20 wherein said at least one sensor comprises at least one Fabry-Perot etalon.

33. The optical sensor diagnostic system of claim 20 wherein said at least one sensor comprises at least one Surface Plasmon Resonance structure.

34. The optical sensor diagnostic system of claim 20 wherein at least one sensor is disposed in a branch waveguide or optical fiber coupled to the main trunk waveguide by a coupler.

35. The optical sensor diagnostic system of claim 34 wherein said at least one sensor comprises at least one thin film or bulk material characteristic absorber material.

36. The characteristic absorber material of claim 35 comprising at least one semiconductor.

37. The characteristic absorber material of claim 36 chosen from the full possible range of alloys and compounds of zinc, cadmium, mercury, silicon, germanium, tin, lead, aluminum, gallium, indium, bismuth, nitrogen, oxygen, phosphorus, arsenic, antimony, sulfur, selenium and tellurium.

38. The characteristic absorber material of claim 35 comprises one or more vibronic, excitonic or fluorescent materials.

39. The characteristic absorber material of claim 35 wherein said sensor comprised of said characteristic absorber material incorporates a mirror at the distal end, providing signal reflection by double-pass transmission.

40. The optical sensor diagnostic system of claim 20 wherein at least one sensor produces a characteristic absorption feature in the form of a slope, wherein:

the said wavelength indicative of the characteristic absorption slope is determined by taking the first derivative of the light amplitude with respect to the wavelength, and by analytically extracting the wavelength position of resulting said first wavelength derivative extremum, or, alternatively,

the said wavelength indicative of the characteristic absorption slope is determined by taking the second derivative of the light amplitude with respect to the wavelength and by analytically extracting the wavelength positions of said second wavelength derivative zeros.

41. The optical sensor diagnostic system of claim 20 wherein said environmental stimulus is any combination of mechanical stress, temperature, pressure, electrical current, electrical field, magnetic field or chemical or biological material on said sensors.

42. The optical sensor diagnostic system of claim 20 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.

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

44. The optical sensor diagnostic system of claim 20 wherein a said sensor comprising an optical fiber having a core waveguide and a cladding or cladding/buffer layer surrounding the core waveguide, in addition incorporating an input/output end and a terminal reflection end, wherein the terminal reflection end is defined by an end face of the core waveguide in contact with a mirrored layer such that the light is caused to reverse its direction of propagation and exits the input/output end, said sensing area is defined by a surface of the optical fiber core waveguide free from the surrounding cladding or cladding/buffer layer.

45. The optical sensor diagnostic system of claim 44 wherein the said sensing area further contains at least one additional functional layer adhered to the surface plasmon resonance-supporting metal layer.

46. The optical sensor diagnostic system of claim 45 wherein the at least one additional layer comprises a chemically reactive layer.

47. The optical sensor diagnostic system of claim 45 wherein the at least one additional layer comprises a biologically reactive layer.

48. The optical sensor diagnostic system of claim 44 wherein the said plasmon resonance supporting metal is one or more layers of elements or alloys chosen from the group silver, gold, copper or aluminum.

49. The optical fiber sensor according to claim 44 further incorporating a polarizer positioned anywhere between said tunable VCSEL and said sensor, said polarizer selecting light with polarization P.

50. The optical fiber sensor according to claim 45 further comprising a first polarizer positioned between the said tunable VCSEL and said circulator, said polarizer selecting light with polarization state between S and P polarizations.

51. The optical fiber sensor according to claim 50 further comprising a second polarizer positioned between the said sensor and said detector, said second polarizer being oriented with respect to the said first polarizer such that a phase-polarization enhancement is obtained of the ratio of the power amplitudes at wavelengths outside the said minimum of reflection feature to the power amplitude at the exact minimum of reflection.