Method and apparatus for a Fabry-Perot multiple beam fringe sensor

• US 4,329,058 A
• Filed: 01/22/1979
• Issued: 05/11/1982
• Est. Priority Date: 01/22/1979
• Status: Expired due to Term

• Current Assignee: Rockwell International Corporation
• Original Assignee: Rockwell International Corporation
• Inventors: James, Kenneth A., Strahan, Virgil H., Quick, William H.
• Primary Examiner(s): Church, Craig E.
• Application Number:
  US06/005,265
• Time in Patent Office: 1,205 Days
• Field of Search: 356/357, 356/358, 356/361, 356/352
• US Class Current: 356/480
• CPC Class Codes: G01D 5/266 by interferometric means G01D5/353 takes precedence
• CPC Class Codes: G01D 5/268 using optical fibres G01D5/28 - G01D5/38 take precedence
• CPC Class Codes: G01K 11/12 using changes in colour, translucency or reflectance
• CPC Class Codes: G02B 5/284 of etalon type comprising a resonant cavity other than a thin solid film, e.g. gas, air, solid plates etalons for fibre optic multiplexing G02B6/29358; etalons for spectral measurement G01J3/26
• CPC Class Codes: G02B 6/262 Optical details of coupling light into, or out of, or between fibre ends, e.g. special fibre end shapes or associated optical elements
• CPC Class Codes: G02B 6/29359 Cavity formed by light guide ends, e.g. fibre Fabry Pérot [FFP]

Abstract

A method and the resulting apparatus for implementing a unique multiple beam fringe sensor that is adapted to be interfaced with a low cost, compact fiber optic transmission system in order to provide an accurate digital representation of a physical parameter (e.g. temperature) of a remote sample. The sensor is fabricated so as to include a Fabry-Perot gap formed between the ends of two mated optical fibers. By examining the optical characteristics of light that is transmitted through the Fabry-Perot sensor gap, an indication of gap width can be ascertained. Accordingly, a change in Fabry-Perot sensor gap width is related to a change in the particular physical parameter to be measured.

Claims

1. A method for making an apparatus for optically sensing a physical parameter, said method comprising the steps of:

forming optically flat surfaces on one end of each of a pair of optical fibers,

forming a raised contact means on the flat end surface of a first of said pair of optical fibers,

applying a first spacer means around said raised contact means,

shortening said raised contact means, so that said contact means is recessed with respect to said first spacer means,

mating said first spacer means of said first optical fiber to the flat end surface of the second of said pair of optical fibers, so that a Fabry-Perot gap is formed between said recessed contact means and the flat end surface of said second optical fiber, and

transmitting light through said Fabry-Perot gap and examining the optical characteristics of said light for providing an indication of the physical parameter to be sensed.

2. The method recited in claim 1, including the additional step of shortening said raised contact means at a lower temperature than any of those to which said sensing apparatus is to be exposed.

3. The method recited in claim 1, including the additional step of forming said raised contact means from a material having a temperature coefficient of expansion that is different from that of said first spacer means.

4. The method recited in claim 1 including the additional step of vapor depositing said first spacer means onto the end surface of said first optical fiber and around said raised contact means.

5. The method recited in claim 1, including the additional step of forming said optically flat surfaces by hemispherically terminating the first ends of said pair of optical fibers.

6. The method recited in claim 1, including the additional steps of applying a second spacer means around the outer periphery of the flat end surface of said second optical fiber, so that a central depression is formed within said second spacer means, and

mating the first spacer means of said first optical fiber to the second spacer means of said second optical fiber and aligning said contact means with the depression of said second spacer means to form the Fabry-Perot gap therebetween.

7. The method recited in claim 6, including the additional step of vapor depositing said second spacer means around the periphery of the flat end surface of said second optical fiber.

8. A Fabry-Perot optical sensor for sensing a physical parameter, said sensor comprising:

first and second optical fibers, each of said optical fibers having a first optically flat end thereof,

source means to provide one of said optical fibers with a supply of light,

raised contact means connected to the first end of said first optical fiber, and

spacer means positioned on the first end of said first optical fiber and around said raised contact means, said spacer means being particularly dimensioned so that said contact means is recessed with respect thereto,

said spacer means adapted to be mated to the first end of said second optical fiber to form a Fabry-Perot gap between said raised contact means and the first end of said second optical fiber, the optical characteristics of light being transmitted from said source means through said Fabry-Perot gap via said optical fibers being indicative of the parameter to be sensed.

9. The Fabry-Perot optical sensor recited in claim 8, wherein said raised contact means and said spacer means are formed from respective materials having different temperature coefficients of expansion.

10. The Fabry-Perot optical sensor recited in claim 8, wherein said raised contact means has a cylndrical configuration, the respective ends of said contact means and said second optical fiber that form said Fabry-Perot gap being in parallel alignment with one another.

11. The Fabry-Perot optical sensor recited in claim 8, wherein said source means comprises a source of white light interfaced with the second end of said first optical fiber in order to supply light to said Fabry-Perot gap.

12. The Fabry-Perot optical sensor recited in claim 8, further including photo-electric detection means interfaced with the second end of said second optical fiber and responsive to the optical signals that are transmitted thereto from said Fabry-Perot gap via said second optical fiber, so that an electrical equivalent of said physical parameter can be provided.

13. The Fabry-Perot optical sensor recited in claim 12, further including decoder means, said decoder means adapted to receive the electrical equivalent of the physical parameter from said photo-electric detector in order that a digital representation of said parameter can be provided.

14. An optical transducer for sensing a physical parameter, said transducer comprising:

light source means,

first and second light transmitting means,

Fabry-Perot gap means formed between first ends of said first and second light transmitting means, each of said first ends having a partially reflective surface, said Fabry-Perot gap means receiving incident light signals from said source means via said first light transmitting means and supplying output light signals to said second light transmitting means,

said Fabry-Perot gap means having a dimension that is sensitive to a parameter change, the spectral characteristics of the output light signals being transmitted through said Fabry-Perot gap means providing an indication of the dimension of said gap means and, accordingly, the physical parameter to be sensed, and

means for detecting the spectral characteristics of said output light signals so as to provide the indication of said parameter.

15. An optical transducer for sensing a physical parameter, said transducer comprising:

light source means,

first and second light transmitting means,

Fabry-Perot gap means formed between first ends of said first and second light transmitting means, said Fabry-Perot gap means receiving incident light signals from said source means via said first light transmitting means and supplying output light signals to said second light transmitting means,

said Fabry-Perot gap means having a dimension that is sensitive to a parameter change, the optical characteristics of the light signals being transmitted through said Fabry-Perot gap means providing an indication of the dimension of said gap means and, accordingly, the physical parameter to be sensed, and

spacer means positioned between the first ends of said first and second light transmitting means to form said Fabry-Perot gap means,

said spacer means being fabricated from a material that is responsive to a parameter change for causing corresponding changes in the dimensions of said spacer means and said Fabry-Perot gap means, so as to alter the optical characteristics of the light signals being transmitted through said gap means.

16. The optical transducer recited in claim 15, wherein each of said first and second light transmitting means is an optical fiber,

said optical fibers and said spacer means being fabricated from respective materials having different temperature coefficients of expansion.

17. The optical transducer recited in claim 15, wherein the first ends of said first and second light transmitting means are in substantially parallel alignment with one another.