Methods and apparatus for measuring multiple Fabry-Perot gaps

• US 8,115,937 B2
• Filed: 08/16/2007
• Issued: 02/14/2012
• Est. Priority Date: 08/16/2006
• Status: Active Grant

• Current Assignee: Davidson Instruments Inc.
• Original Assignee: Davidson Instruments Inc.
• Inventors: Needham, David B.
• Primary Examiner(s): Chowdhury, Tarifur
• Assistant Examiner(s): Cook, Jonathon
• Application Number:
  US11/893,434
• Publication Number:
  US 20080043245A1
• Time in Patent Office: 1,643 Days
• Field of Search: 356/477, 356/478, 356/480, 356/506, 356/519
• US Class Current: 356/506
• CPC Class Codes: G01B 2290/25 Fabry-Perot in interferometer, e.g. etalon, cavity
• CPC Class Codes: G01B 9/02025 Interference between three or more discrete surfaces
• CPC Class Codes: G01B 9/02027 Two or more interferometric channels or interferometers
• CPC Class Codes: G01B 9/0209 Low-coherence interferometers
• CPC Class Codes: G01J 5/38 using extension or expansion of solids or fluids

Abstract

Apparatus, methods, and other embodiments associated with measuring multiple Fabry-Perot gaps to determine environmental parameters are described herein. In one embodiment, a system for measuring environmental parameters includes an optical fiber, a first reflective surface, a second reflective surface, a third reflective surface, and a light source. The first reflective surface is positioned proximate to a first end of the optical fiber. The second reflective surface is positioned to form a first Fabry-Perot gap between the first reflective surface and the second reflective surface. The third reflective surface is positioned to form a second Fabry-Perot gap between the second reflective surface and third reflective surface. The light source provides light to the optical fiber, wherein the optical fiber delivers light from the light source to the first Fabry-Perot gap and the second Fabry-Perot gap and the optical fiber receives reflected light from the first Fabry-Perot gap and the second Fabry-Perot gap.

Claims

1. A system for measuring environmental parameters comprising:

an optical fiber;

a first reflective surface positioned proximate to a first end of the optical fiber;

a space between the first end of the optical fiber and the first reflective surface;

a second reflective surface spaced apart from the first reflective surface;

a solid substrate having a thermally sensitive refractive index positioned between the first reflective surface and the second reflective surface to form a first temperature sensitive Fabry-Perot gap between the first reflective surface and the second reflective surface;

a diaphragm;

a third reflective surface connected to a surface of the diaphragm to form a second pressure sensitive Fabry-Perot gap between the second reflective surface and third reflective surface; and

a first light source providing light to the optical fiber, wherein the optical fiber delivers light from the first light source to the first Fabry-Perot gap and the second Fabry-Perot gap and the optical fiber receives reflected light from the first Fabry-Perot gap and the second Fabry-Perot gap.

2. The system of claim 1, wherein the first Fabry-Perot gap and second Fabry-Perot gap are located between the diaphragm and the first end of the optical fiber.

3. The system of claim 2 wherein the third reflective surface is one of the following:

a polished surface of the diaphragm;

a reflective optical coating deposited on the diaphragm;

or a polished glass material bonded to the diaphragm.

4. The system of claim 1 wherein the substrate has plane parallel reflective surfaces that define the first and second reflective surfaces.

5. The system of claim 1 further comprising a detector positioned proximate to a second end of the optical fiber.

6. The system of claim 5 further comprising an optical element positioned between the second end of the optical fiber and the detector, where the optical element is one of the following:

a lens;

a mirror;

a cylindrical lens;

a cylindrical mirror.

7. The system of claim 6 wherein the detector comprises a Fizeau wedge optical cross-correlator attached to a CCD array.

8. The system of claim 1 further comprising a second light source providing light to the optical fiber that is of a different wavelength than the light from the first light source, wherein the optical fiber delivers light from the second light source to the first Fabry-Perot gap and the second Fabry-Perot gap and the optical fiber received light reflected from at least one of the first Fabry-Perot gap and the second Fabry-Perot gap.

9. The system of claim 8 wherein at least one of the first reflective surface, second reflective surface, and third reflective surface is spectrally selective.

10. The system of claim 8 wherein the first light source and second light source are turned on and off in sequence.

11. The system of claim 1 wherein the first reflective surface is secured to the first end of the optical fiber.

12. A system for measuring environmental parameters comprising:

a first Fabry-Perot gap defined by a first reflective surface and a second reflective surface;

a solid substrate having a thermally sensitive refractive index positioned between the first reflective surface and the second reflective surface;

a second Fabry-Perot gap defined between the second reflective surface and a third reflective surface;

a diaphragm connected to the third reflective surface;

an optical fiber having a first end terminating a distance away from the first and second Fabry-Perot gaps;

a broadband light source providing light to a first end of the optical fiber;

a fiber optical coupler positioned at a second end of the optical fiber to spit light to be delivered to the first and second Fabry-Perot gaps and to recombine light reflected from the first and second Fabry-Perot gaps; and

a detector to detect light recombined by the coupler.

13. The system of claim 12 wherein the detector comprises a wedge optical cross-correlator attached to a CCD array.

14. The system of claim 13 further comprising an optical element positioned between the second end of the optical fiber and the detector, where the optical element is one of the following:

a lens;

a mirror;

a cylindrical lens;

a cylindrical mirror.

15. A method for measuring environmental parameters comprising:

providing a first Fabry-Perot gap defined by a first reflective surface and a second reflective surface;

providing a solid substrate having a thermally sensitive refractive index positioned between the first reflective surface and the second reflective surface;

providing a second Fabry-Perot gap defined between the second reflective surface and a third reflective surface;

providing a diaphragm connected to the third reflective surface providing a single optical fiber channel having a first end positioned a distance away from the first and second Fabry-Perot gaps;

providing a light source;

providing light from the light source to the optical fiber channel delivering light from the light source through the optical fiber channel to the first Fabry-Perot gap and the second Fabry-Perot gap;

reflecting light from the first Fabry-Perot gap and the second Fabry-Perot gap to the optical fiber channel;

providing an optical detector; and

delivering light reflected from the first Fabry-Perot gap and the second Fabry-Perot gap through the optical fiber channel to the optical detector.

16. The method of claim 15 further comprising a wedge optical cross-correlator attached to a CCD array.

17. The method of claim 16 further comprising positioning the first Fabry-Perot gap in series with the second Fabry-Perot gap.

18. The method of claim 15 further comprising positioning the first Fabry-Perot gap in parallel with the second Fabry-Perot gap.