Tunable laser fluid sensor

• US 20050040337A1
• Filed: 09/28/2004
• Published: 02/24/2005
• Est. Priority Date: 09/12/2001
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Cole, Barrett E., Cox, James A.
• Granted Patent: US 7,145,165 B2
• Time in Patent Office: Days
• US Class Current: 250/343
• CPC Class Codes: G01N 2021/391 Intracavity sample
• CPC Class Codes: G01N 2021/399 Diode laser
• CPC Class Codes: G01N 21/05 Flow-through cuvettes G01N21/09 takes precedence; handling fluid samples G01N1/10
• CPC Class Codes: G01N 21/35 using infrared light G01N21/39 takes precedence
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01N 21/3577 for analysing liquids, e.g. polluted water
• CPC Class Codes: G01N 21/39 using tunable lasers
• 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: G02F 1/0147 based on thermo-optic effects G02F1/132 takes precedence
• CPC Class Codes: G02F 1/015 based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction G02F1/03 takes precedence
• CPC Class Codes: G02F 1/21 by interference
• CPC Class Codes: G02F 1/213 Fabry-Perot type
• CPC Class Codes: G02F 2203/055 wavelength filtering

Abstract

A sensitive fluid sensor for detecting fluids and particularly trace fluids. The sensor may be adjustable for detecting fluids of various absorption lines. To effect such adjustment, a tunable laser may be used. The laser may be an edge emitting diode, a VCSEL or other tunable source. The detection apparatus of the sensor may incorporate a sample cell through which a laser light may go through. The sample cell may comprise a tunable ring-down cavity. The ring-down cavity may be a ring laser cavity like that of a ring laser gyroscope. There may be a photo detector proximate to the ring down cavity connected to a processor.

Claims

1. A fluid sensor comprising:

a tunable light source;

a cavity positioned to receive light from the tunable light source; and

a detector positioned to receive light from the cavity.

2. The sensor of claim 1, wherein the cavity is a ring laser cavity.

3. The sensor of claim 1, wherein the cavity and the light source are tunable to the same wavelength.

4. The sensor of claim 1, wherein the cavity contains a fluid to be detected.

5. The sensor of claim 4, wherein the light source is tunable to the absorption line of the fluid.

6. The sensor of claim 5, wherein the cavity is tunable to an absorption line of the fluid.

7. The sensor of claim 1, wherein the tunable light source is a VCSEL.

8. The sensor of claim 7, wherein the VCSEL comprises:

a substrate;

a first mirror situated on the substrate;

an active area situated on the first mirror; and

a second mirror situated at a variable distance from the first mirror.

9. The sensor of claim 8, wherein the variable distance may be adjusted to tune the VCSEL to a particular wavelength.

10. The sensor of claim 5, wherein the wavelength of the tunable light source may be adjusted to identify a fluid in the cavity.

11. The sensor of claim 1, further comprising a processor connected to the cavity, the tunable light source and the detector.

12. The sensor of claim 1, wherein the tunable light source is a laser diode.

13. The sensor of claim 1, wherein the tunable light source is an edge emitting diode.

14. The sensor of claim 13, wherein the edge emitting diode comprises:

a substrate;

a layer, having a laser cavity with reflective surfaces situated at the edges of the laser cavity, situated on the substrate; and

a moveable mirror proximate to one edge for tuning the laser cavity.

15. The sensor of claim 14, wherein the moveable mirror may be adjusted to tune the laser cavity to a particular wavelength.

16. A fluid sensor comprising:

a tunable light source;

a ring down cavity positioned to receive light from the tunable light source; and

a detector positioned to receive light from the ring down cavity.

17. The sensor of claim 16, wherein the light source is tuned to an absorption line of a fluid in the containing structure.

18. The sensor of claim 17, wherein the ring down cavity comprises:

a containing structure;

a first mirror positioned in the containing structure to receive light from the tunable light source; and

at least another mirror positioned in the containing structure to receive light reflected by the first mirror and reflect it back to the first mirror and vice versa for a plurality of times; and

wherein;

the at least another mirror is moveable to adjust the wavelength of the containing structure; and

the detector is proximate to the at least another mirror to detect light reflected in the containing structure.

19. The sensor of claim 18, wherein:

the ring down cavity is a ring laser cavity; and

the containing structure is tuned to an absorption line of the fluid in the containing structure.

20. The sensor of claim 19, further comprising a processor connected to the tunable light source, the containing structure and the detector.

21. The sensor of claim 20, wherein the processor comprises:

a data acquisition and analysis unit connected to the detector; and

control electronics connected to the tunable light source, the containing structure and the data acquisition and analysis unit.

22. The sensor of claim 16, wherein the tunable light source is a VCSEL.

23. The sensor of claim 22 wherein, the VCSEL comprises:

a substrate;

a first mirror situated on the substrate;

an active area situated on the first mirror; and

a second mirror situated at a variable distance from the first mirror.

24. The sensor of claim 23, wherein the variable distance may be adjusted to tune the VCSEL to a particular wavelength.

25. The sensor of claim 24, wherein the wavelength may be adjusted to determine the kind of fluid in the ring down cavity.

26. The sensor of claim 23, wherein the VCSEL further comprises:

a current spreading layer on the active region; and

an adjustable gap between the second mirror and the current spreading layer.

27. The sensor of claim 26, wherein the VCSEL further comprises:

a first spacer situated between the first mirror and the active region; and

a second spacer situated between the active region and the current spreading layer.

28. The sensor of claim 27, wherein the VCSEL further comprises a current confinement region situated at least partially in the current spreading layer.

29. The sensor of claim 28, wherein the VCSEL has an infrared bandwidth.

30. The sensor of claim 16, wherein the tunable light source is a laser diode.

31. The sensor of claim 19, wherein the tunable light source is an edge emitting diode.

32. The sensor of claim 31, wherein the edge emitting diode comprises:

a substrate;

a layer, having a laser cavity with reflective surfaces situated at the edges of the cavity, situated on the substrate; and

a moveable mirror proximate to one edge for tuning the laser cavity.

33. The sensor of claim 32, wherein the moveable mirror may be adjusted to tune the laser cavity to a particular wavelength.

34. The sensor of claim 33, wherein the wavelength may be adjusted to determine the kind of fluid in the containing structure.

35. A fluid sensor comprising:

means for containing a sample of a fluid;

means for providing light through the sample;

means for detecting light from the sample;

means for detecting and converting light from the sample into electrical signals; and

means for converting the electrical signals into information about the fluid; and

wherein the means for providing light has an adjustable wavelength.

36. The sensor of claim 35, wherein the means for containing a sample comprises a cavity.

37. The sensor of claim 36, wherein the cavity is a ring-down cavity.

38. The sensor of claim 37, wherein the ring-down cavity is a ring laser cavity.