SENSORS FOR MEASURING PRESSURE AND TEMPERATURE

Abstract

A Fabry-P?rot sensor assembly includes an optical element defining a Fabry-P?rot optical cavity therein. A ferrule is affixed to the optical element. The ferrule is configured to physically connect to an optic fiber, aligning the optic fiber optically with the cavity. The optical element includes a MgAl.sub.2O.sub.4 spinel or aluminum oxynitride Al.sub.23N.sub.27O.sub.5. A method of making an Fabry-P?rot optical cavity includes using a ceramic processing etching process to remove material from a first optical member to form the cavity therein, leaving a rim of the optical member surrounding the cavity peripherally. The method includes affixing a second optical member to the rim to enclose the cavity.

Claims

1. A Fabry-P?rot sensor assembly comprising: an optical element defining a Fabry-P?rot optical cavity therein; and a sensor ferrule affixed to the optical element, wherein the sensor ferrule is configured to physically connect to an optical fiber, optically aligning and spacing the optical fiber with the optical cavity, wherein the optical element includes MgAl.sub.2O.sub.4 spinel or aluminum oxynitride Al.sub.23N.sub.27O.sub.5.

2. The assembly as recited in claim 1, further comprising the optical fiber affixed within the sensor ferrule optically aligned with the optical cavity along the axis.

3. The assembly as recited in claim 2, further comprising an interrogator optically connected to the optical fiber, wherein the interrogator is configured to illuminate the cavity through the optical fiber, to receive reflected spectrum from the cavity, and to measure temperature and/or pressure of the cavity based on the reflected spectrum.

4. The assembly as recited in claim 1, wherein the sensor ferrule defines a bore for receiving the optical fiber, wherein the bore extends along a longitudinal axis that extends to the optical element, wherein the optical cavity is a second optical member defined between a first optical member and a third optical member spaced apart from the first optical member along the longitudinal axis.

5. The assembly as recited in claim 4, wherein an optical path passes from the bore, through the first optical member, through the optical cavity, reflects off of the third optical member and passes back through the optical cavity and through the first optical member into the bore and back into the fiber.

6. The assembly as recited in claim 4, wherein the third optical member is an endplate with an at least partially mirrored surface for increasing signal reflections in the optical cavity and back into the optical fiber.

7. The assembly as recited in claim 6, wherein the first optical member is a main sensor body, wherein the ferrule is affixed to the main sensor body.

8. The assembly as recited in claim 4, wherein at least one of the first and third optical members is MgAl.sub.2O.sub.4 spinel.

9. The assembly as recited in claim 4, wherein at least one of the first and third optical members is aluminum oxynitride Al.sub.23N.sub.27O.sub.5.

10. The assembly as recited in claim 8, wherein the optical cavity is defined in the first optical member, wherein the first optical member includes a cavity rim surrounding the cavity peripherally, and wherein the end plate is affixed to the cavity rim.

11. The assembly as recited in claim 8, wherein the cavity is defined in the second optical member, wherein the second optical member includes a cavity rim surrounding the cavity peripherally, and wherein the first optical member is affixed to the cavity rim.

12. The assembly as recited in claim 8, further comprising anti-reflective coating on at least one surface of the optical element.

13. The assembly as recited in claim 6, further comprising a cavity ring affixed between the first and third optical members, wherein the cavity is bounded by the cavity ring and the first and third optical members.

14. A method of making a Fabry-P?rot optical cavity comprising: using a ceramic etching process to remove material from a first optical member to form the optical cavity therein, leaving a cavity rim of the optical member surrounding the cavity peripherally; and affixing a third optical member to the cavity rim to enclose the cavity.

15. The method as recited in claim 14, wherein the first optical member includes MgAl.sub.2O.sub.4 spinel.

16. The method as recited in claim 14, wherein the first optical member includes of aluminum oxynitride Al.sub.23N.sub.27O.sub.5.

17. The method as recited in claim 14, wherein the second optical member is of MgAl.sub.2O.sub.4 spinel.

18. The method as recited in claim 14, wherein the second optical member is of aluminum oxynitride Al.sub.23N.sub.27O.sub.5.

19. The method as recited in claim 14, wherein the third optical member is a diaphragm configured to deflect more than the first optical member under external pressure changes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] So that those skilled in the art to which the subject disclosure appertains will readily understand how to make and use the devices and methods of the subject disclosure without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to certain figures, wherein:

[0015] FIG. 1 is a schematic perspective view of an embodiment of a sensor assembly constructed in accordance with the present disclosure, showing the optical fiber, the interrogator, and the Fabry-P?rot optical element with sensor ferrule;

[0016] FIG. 2 is a schematic cross-sectional elevation view of the optical element and ferrule of FIG. 1;

[0017] FIG. 3 is a schematic axial end view of the optical element and sensor ferrule of FIG. 2;

[0018] FIG. 4 is a schematic cross-sectional elevation view of an embodiment of the optical element and sensor ferrule of FIG. 2, showing the optical cavity formed in the first optical member, where the second optical member is the optical cavity itself and the third optical member is a diaphragm; and

[0019] FIG. 5 is a schematic cross-sectional elevation view of an embodiment of the optical element and sensor ferrule of FIG. 2, showing the optical cavity formed by the third optical member, which is the diaphragm.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an embodiment of a sensor assembly in accordance with the disclosure is shown in FIG. 1 and is designated generally by reference character 100. Other embodiments of systems in accordance with the disclosure, or aspects thereof, are provided in FIGS. 2-5, as will be described. The systems and methods described herein can be used to facilitate manufacture of Fabry-P?rot sensors for optically based temperature and pressure measurements.

[0021] The Fabry-P?rot sensor, i.e. etalon, assembly 100 includes an optical element 102 defining a Fabry-P?rot optical cavity 104 therein. A sensor ferrule 106 is affixed to the optical element 102. The sensor ferrule 106 is physically connected to an optical fiber 108 which may have its own fiber ferrule, thereby aligning the optical fiber 108 optically with the cavity 104 thereby ensuring optical alignment with the optical element 102. The optical element 102 includes MgAl.sub.2O.sub.4 spinel, and the sensor ferrule 106 optionally includes MgAl.sub.2O.sub.4 spinel. The optical fiber 108 is affixed within a bore 110 the ferrule 106 optically aligned with the cavity 104. Additionally, bore 110 may also accommodate a fiber ferrule on the sensor end of 108 in order to facilitate optical alignment and spacing of the core of the optical fiber with the optical element 102 (FIG. 4 shows a cavity in the sensor ferrule that can accommodate a fiber with ferrule. FIG. 5 shows a configuration for a fiber without the fiber ferrule). An interrogator 112 is optically connected to the optical fiber 108, i.e. to an end of the optical fiber 108 opposite then end of the optical fiber 108 that is connected to the sensor ferrule 106. The interrogator 112 is thus configured to illuminate the optical cavity 104 through the optical fiber 108, to receive reflected spectrum from the cavity 104, and to measure temperature and/or pressure exhibited on the optical element 102 based on the reflected spectrum.

[0022] With reference now to FIG. 2, the sensor ferrule 106 defines a bore 110 for receiving the optical fiber 108. The bore 110 extends along a longitudinal axis A that extends through the cavity 104. The cavity 104 is defined axially between a first optical member 114 and a third optical member 116 that are spaced apart from one another along the longitudinal axis A. An optical path is comprised from the bore 110 and fiber 108 along the axis A, through the first optical member 114, and through the second optical member, cavity 104, subsequently reflecting off of the third optical member 116 and eventually passing back through the cavity 104 and back through the first optical member 114 into the bore 110 and fiber 108. Note that it is possible to directly couple the fiber core with the first optical member 114. FIG. 3 shows the cavity 104, bore 110, and the combination of the sensor ferrule 106 and optical element 102 as viewed into the longitudinal axis of FIG. 2. An anti-reflective coating can be included on at least one surface of the optical element 102 including the exposed surface of the first optical member 114 to the end of bore 110, which is most desirable, the inside cavity 104 which constitutes the second optical member, or the exterior axial face of the endplate. In certain application, it may be desirable to make use of a reflective coating 118 on the third optical member 116 in order to improve signal to noise response. Likewise, it is contemplated that a mirrored ring 117 on the surface of the first optical member 114 can be included, faying with the second optical member, cavity 104, provided that the mirrored surface of the ring does not interfere with light propagation along axis A of the end of bore 110 that interfaces with the first optical member 114.

[0023] With continued reference to FIG. 2, the third optical member 116 is an endplate, i.e. a diaphragm that can deflect under pressure changes, with an at least partially mirrored surface 118 inside the cavity 104 for increasing signal reflections through the cavity 104. The first optical member 114 constitutes a main sensor body, which is thicker/stiffer than the diaphragm of the optical member 116 such that it does not deflect under pressure changes as much as the diaphragm. The sensor ferrule 106 is affixed to the main sensor body 114. A cavity ring 120 is affixed between the first and third optical members 114, 116 hereby generating the pressure sensitive depth of the second optical member, optical cavity 104. The optical cavity 104 is bounded by the cavity ring 120 and by the first and third optical members 114, 116. At least one of cavity ring 120, the first optical member 114, and the third optical member 116 is transparent ceramic, e.g. spinel (magnesium aluminate, nominally MgAl.sub.2O.sub.4) or aluminum oxynitride (nominally Al.sub.23N.sub.27O.sub.5). For instance, the cavity ring 120 can be of MgAl.sub.2O.sub.4 spinel. The sensor ferrule 106 includes external mating and locking features, i.e., radially inward extending features 122, or radially outward extending features 124 as shown in FIG. 5, configured for mechanical attachment of the sensor ferrule 106 to a housing or assembly.

[0024] With reference now to FIG. 4, the cavity ring 120 can be omitted since the first optical member 114 defines the unburdened optical cavity 104. The first and third optical members 114, 116 can be directly affixed to one another, wherein at least one of the first and third optical members 114, 116 is a single piece of transparent ceramic, e.g. spinel (magnesium aluminate, nominally MgAl.sub.2O.sub.4) or aluminum oxynitride (nominally Al.sub.23N.sub.27O.sub.5). In FIG. 4, the second optical member, optical cavity 104, is defined in the first optical member 114, which includes a cavity rim 126 formed of the same transparent ceramic as the rest of the first optical member 114, surrounding the optical cavity 104 peripherally as does the ring 120 in FIG. 2. The end plate, i.e. optical member 116 or diaphragm, is affixed to the cavity rim 126 after the optical cavity 104 is formed in the first optical member 114 as described below. With reference now to FIG. 5, the optical cavity 104 can be defined by the second optical member 116 instead. The third optical member 116 in FIG. 5 hereby includes a cavity rim 128, i.e. of the same transparent ceramic as the rest of the second optical member 116. The cavity rim 128 in FIG. 5 surrounds the cavity peripherally just as the cavity rim 126 in FIG. 4 or the cavity ring in FIG. 2. In FIG. 5, the cavity rim 128 is affixed to the first optical member 114 after the cavity 118 is formed in the third optical member 116.

[0025] A method of making a Fabry-P?rot optical cavity as described above with respect to FIGS. 4-5 includes using a ceramic processing etching process to remove material from an optical member 114, 116 to form the optical member, optical cavity 104 therein, leaving a cavity rim 126, 128 of the optical member 114, 116 thereby surrounding the optical cavity 104 peripherally. The method includes affixing the remaining optical member 114, 116 (from which the cavity 104 was not formed) to the cavity rim 126, 128 to enclose the optical cavity 104. It is also contemplated that the optical cavity could be partially removed from both optical members 114, 116 without departing from the scope of this disclosure. Whether the first or third optical member 114, 116, or both, have material removed to form the optical cavity 104, the remaining structure of the third optical member 116 needs to have a diaphragm thin enough to deflect for the measurements of interest, as described above.

[0026] This is an approach to measuring pressure and temperature using a Fabry-P?rot cavity and optical fiber without the need to have all or any single crystal aluminum oxide (or sapphire, nominally Al.sub.2O.sub.3) elements. The optical element 102 enclosing the optical cavity 104 can be made of spinel ceramic or single crystal (nominally MgAl.sub.2O.sub.4) or aluminum oxynitride ceramic or single crystal (nominally Al.sub.23N.sub.27O.sub.5). MgAl.sub.2O.sub.4 Spinel and aluminum oxynitride have similar transmittance of light over the wavelengths of light of interest (roughly 500 nm to 4 microns) as sapphire to support different fiber optic interrogation methodologies. As and additional improvement, MgAl.sub.2O.sub.4 spinel ceramic and aluminum oxynitride ceramic exhibit no birefringence due to their crystal structure (cubic) whereas sapphire has trigonal crystal structure which exhibits birefringence when incident light is off the c-plane. Thus, MgAl.sub.2O.sub.4 spinel and aluminum oxynitride do not suffer the burden of sapphire manufacturing that is associated with the c-plane alignment and tolerancing which would otherwise compromise light propagation through the device and henceforth reduce signal. Additionally, MgAl.sub.2O.sub.4 spinel and aluminum oxynitride can be manufactured using ceramic processing techniques versus the variations of the Czochralski process used for sapphire manufacturing.

[0027] Systems and method as disclosed herein provide potential benefits including the following: lower cost of materials, more cost effective manufacturing, ease of machining, and simpler housing attachments. This approach enables possible attachment of the optical element 102 to the ferrule 106 using bonding approaches similar to glass. The optical structures can be manufactured to high dimensional tolerances using bisque fire methods with secondary machining or machining in the green ceramic state (unfired) followed by sintering. Standard sintering processes may also be used that are lower in temperature (<1650? C.) than the sapphire processing temperature (nominally 2070? C.). It is also contemplated that Hot Isostatic Press (HIP) methods can be utilized in different ways. One option would be to HIP the entire structure together, or HIP certain pieces of the assembly separately and sinter the pieces together to form a bond. In addition, combinations of ceramic and single crystal of either MgAl.sub.2O.sub.4 spinel or aluminum oxynitride can be used. This opens up a multitude of manufacturing options which are not available to components made out of sapphire.

[0028] In addition to the previously stated potential advantages over sapphire based sensors, the optical sensors disclosed herein are inherently advantageous over micro-electromechanical system (MEMS) sensors for the chosen measurand. Unlike MEMS sensors, the aforementioned optical sensors do not have preferential directionality (i.e., the measurements can be made regardless of sensor orientation).

[0029] The methods and systems of the present disclosure, as described above and as shown in the drawings, provide for facilitating the manufacture of Fabry-P?rot sensors for optically based temperature and pressure measurements. While the apparatus and methods of the subject disclosure have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the scope of the subject disclosure.