Optical fiber feedthrough assembly and method of making same

#The present invention relates to feedthroughs for optical waveguides, and more particularly, to hermetically sealed feedthroughs suitable for use in high pressure, high temperature, and/or other harsh environments.

#In many industries and applications, there is a need to have small diameter wires or optical waveguides penetrate a wall, bulkhead, or other feedthrough member wherein a relatively high fluid or gas differential pressure exists across the feedthrough member. In addition, one or both sides of the feedthrough member may be subjected to relatively high temperatures and other harsh environmental conditions, such as corrosive or volatile gas, fluids and other materials. In the case of electrical wires, these devices, called feedthroughs or penetrators, typically are constructed by using electrically conductive metal ‘pins’ having a low thermal coefficient of expansion. The pins are concentrically located within a hole in a housing, and the resulting annular space is filled with a suitable sealing glass. Critical to the success of such seals is the selection and approximate matching of the thermal expansion rates of the various materials, i.e., the metal housing, sealing glass, and electrical pin. As the temperature range over which the feedthrough is exposed increases, the matching of thermal expansion rates becomes increasingly important in order to avoid failure of the feedthrough by excessive thermal stress at the interface layers between the various materials. This technology is relatively mature for electrical feedthroughs, and commercial devices are readily available that meet service temperatures in excess of 200° C.

#More recently, with the introduction of optical sensors, particularly sensors for use in oil and gas exploration and production, a need has emerged for a bulkhead feedthrough that can seal an optical fiber at high pressures of 20,000 psi and above, and high temperatures of 150° C. to 250° C., with desired service lives of 5 to 10 years. The sensing assembly of FIG. 3 is of the type disclosed in co-pending U.S. patent application Ser. No. 09/440,555 filed Nov. 15, 1999, entitled “Pressure Sensor Packaging For Harsh Environments”, which is assigned to the Assignee of the present invention and is hereby expressly incorporated by reference as part of the present disclosure.

#FIG. 1 is a cross-sectional view of an optical waveguide feedthrough assembly embodying the present invention.

#FIG. 2 is a cross-sectional view of the tubular member of the feedthrough assembly of FIG. 1 for receiving therethrough at least one optical waveguide.

#FIG. 3 is a somewhat schematic, cross-sectional view of an optical sensing assembly employing the optical waveguide feedthrough assembly of FIG. 1.

#In FIG. 1, an optical waveguide feedthrough assembly embodying the present invention is indicated generally by the reference numeral 10. As shown in FIGS. 1 and 2, the feedthrough assembly 10 comprises a feedthrough body or tubular member 12 defining an axially elongated, annular surface 14 extending from approximately one end of the tubular member to the other, and an optical feedthrough cavity 16 formed within the annular surface. The annular surface 14 and feedthrough cavity 16 define an elongated axis 18. As shown in FIG. 1, at least one optical waveguide 20 is received through the feedthrough cavity 16, and is spaced radially inwardly relative to the annular surface 14 to thereby define an axially elongated annular cavity 22 between the optical waveguide 20 and annular surface 14 and extending from one end of the tubular member 12 to the other.

#A flowable adhesive or sealant 24, such as a polymeric sealant as will be more fully described herein below, is received within the annular cavity 22, surrounds the optical waveguide 20, and substantially fills the annular cavity 22 from approximately one end of the tubular member 14 to the other. As described further below, the sealant 24 exhibits liquid and solid phases, and is introduced in its liquid phase into one end of the annular cavity 22 and fills the annular cavity by capillary action. Then, the sealant 24 transitions from its liquid to its solid phase, and exhibits adhesive properties at the interfaces of the sealant and both the annular surface 14 and waveguide 20, to adhesively secure and hermetically seal the waveguide within the tubular member.

#The feedthrough assembly 10 farther comprises a first support 26 defining a first mounting surface 28 formed therethrough for receiving one end of the tubular member 12, and a second mounting surface 30 formed along the outer periphery of the first support. A second support 32 defines an elongated aperture 34 for receiving therethrough the tubular member 12, and a mounting recess 36 formed at one end of the support for receiving and fixedly securing thereto the first support 26. The second support 32 defines an external mounting surface 38 for mounting the optical feedthrough assembly 10 within a feedthrough member 40 in a conventional manner, such as a metal-to-metal seal, o-ring seal, or weldment.