Abstract:
A sealed fiber-optic bundle feedthrough by which a multitude of fiber-optic elements may be passed through an opening or port in a wall or structure separating two environments at different pressures or temperatures while maintaining the desired pressure or temperature in each environment. The feedthrough comprises a rigid sleeve of suitable material, a bundle of individual optical fibers, and a resin-based sealing material that bonds the individual optical fibers to each other and to the rigid sleeve.

Description:
RELATED APPLICATION 
     The present application claims the benefit of U.S. Provisional Patent Application No. 60/183,381 filed on Feb. 18, 2000 under 35 U.S.C. 119(e). 
    
    
     UNITED STATES GOVERNMENT GRANT 
     The United States Government has rights in this invention by virtue of United States Department of Energy Grant No. DE-FG02-97ER14579. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to fiber-optic bundles, and more particularly to the passage of fiber-optic bundles through walls or other physical structures while maintaining the environmental conditions within the wall or structure. 
     BACKGROUND OF THE INVENTION 
     The collection and measurement of light emitted from various sources can be achieved through the use of fiber-optic technology. For example, various kinds of light, such as visible light, infrared, ultraviolet, and flourescent light are transmissible through optical fiber. Extensive work to improve this technology continues because of the increasing importance of light transmission in communications and in various scientific endeavors. 
     Light sources are often enclosed in controlled environments using chambers capable of creating a variety of pressure and temperature conditions. The fiber optics must therefore pass through a wall of the chamber while allowing the chamber to maintain the desired environmental conditions. A hermetic seal at this feedthrough allows the chamber to maintain this condition. 
     In the past, fiber-optic bulkhead feedthroughs have been developed employing metallic film optical fiber protection and a compression method of assembly to hermetically seal the plurality of fibers within the feedthrough housing. Another feedthrough module includes a housing and one or a plurality of fibers each fed through a separate hole in the housing with a sealing material used to hermetically seal the fibers in the holes. 
     Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method and apparatus for hermetically sealing fiber-optic bundles passing through a wall or other structure. The invention allows environmental conditions (e.g., pressure, temperature, moisture, etc.) to be maintained within a chamber or enclosure into which a fiber-optic bundle extends. One embodiment of the invention comprises a rigid sleeve, a flange for attaching the sleeve to a wall, a bundle of optical fibers, and a resin-derived solid polymer sealant intimately bonded to each of the optical fibers in the bundle and to an inner surface of the sleeve. Preferably, the resin-derived solid polymer sealant is derived from an epoxy resin. 
     The hermetically sealed fiber-optic bundle feedthrough can be used to transmit an optical signal, many optical signals, an optical image, or many optical images from one environment to another environment where the two environments are separated by a sealing material that can sustain high fluid or gas pressure differentials and/or high temperature differentials. The optical fibers that extend into either environment are flexible and can be arranged to collect and deliver light in a multitude of configurations. The hermetically sealed fiber-optic bundle feedthrough can be used wherever a large amount of optical information needs to be transmitted from one environment to another. 
     One embodiment of the present invention provides a sealed feedthrough for a barrier. The feedthrough includes a sleeve assembly, a fiber-optic bundle, and a sealing material. The sleeve assembly is disposed adjacent the opening in the barrier and is sealed to the barrier. The sleeve assembly includes a sleeve having two ends and an interior surface defining an opening between the two ends. The fiber-optic bundle extends into the opening of the sleeve and includes a plurality of optical fibers. The sealing material is disposed within the opening of the sleeve, between the optical fibers, and between the bundle and the interior surface of the sleeve, thereby creating a seal between the two ends of the sleeve. 
     In one embodiment of the feedthrough, the sleeve assembly includes a flange to seal the sleeve to the barrier. 
     In another embodiment of the feedthrough, the flange includes a base portion, a tube portion, and a means for sealing the tube portion to the sleeve. 
     In yet another embodiment of the feedthrough, a compression O-ring seal is disposed between the flange and the barrier. In this or other embodiments, a compression O-ring seal may also be disposed between the flange and the sleeve. 
     In certain embodiments of the feedthrough, the fiber-optic bundle includes between 100 and 100,000 optical fibers, but it is envisioned that more than 100,000 optical fibers could be included in the fiber-optic bundle. In one particular embodiment, the fiber-optic bundle includes approximately 70,000 optical fibers. 
     In yet another embodiment of the feedthrough, the optical fibers are separated from each other by the sealing material providing additional optical isolation. 
     In certain embodiments of the feedthrough, a sealing flange is attached to the outside of the sleeve. The flange includes a first compression O-ring for sealing to the sleeve and a second compression O-ring for sealing to the barrier. In other embodiments, the sleeve includes an integrally formed flange. 
     In certain embodiments of the feedthrough, the sealing material is an epoxy resin. 
     The present invention further relates to methods of manufacturing hermetically sealed bundle feedthroughs. One such method includes the steps of providing a rigid sleeve, placing a fiber-optic bundle having a plurality of optical fibers through the sleeve, coating the fibers immediately adjacent to one end of the sleeve with a sealing material, pulling the fibers coated with sealing material into the sleeve, and curing the sealing material. 
     Another method provides the additional step of combing the fiber-optic bundle to separate the optical fibers. 
     Yet another method provides the additional step of wrapping an end of the optical bundle with tape. 
     Yet still another method provides the additional step of attaching a flange to an exterior surface of the sleeve. In this method, the attaching step may include the steps of placing an O-ring on the sleeve and compressing the O-ring with the sealing flange, thereby sealing the sleeve to the sealing flange. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a fiber-optic bundle feedthrough of the present invention having a rigid sleeve and optical fibers therein. 
     FIG. 2 is an end view of the sealed bundle showing the separation of the individual fibers of the bundle as separated and sealed with the solid polymer sealant. 
     FIG. 3 is enlarged view of insert A of FIG. 2 showing the optical fibers, sealant, and rigid sleeve in greater detail. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a hermetically sealed optical bundle feedthrough, identified generally by reference numeral  20 , attached to environmental chamber wall or barrier  10  at opening  12 . Feedthrough  20  includes sleeve  22 , fiber bundle  24 , flange  30 , compression cap  46 , and O-ring seals  32  and  34 . Fiber bundle  24  includes a plurality of optical fibers  26  which are bonded to each other and inner surface  36  of sleeve  22  with sealant  28 . 
     Sleeve  22  has an outer surface  38  and an inner surface  36  which defines hole  40 . Sleeve  22  is rigid and may be formed in a variety of configurations, and from a variety of materials. Hole  40  for the passage of the fiber bundle may take on a variety of shapes, such as round, oval, rectangular, etc. Sleeve  22  may be formed of a metallic or other hard material, including plastic such as a vinyl chloride polymer. 
     In the embodiment of FIG. 1, the diameter of sleeve  22  is less than or equal to the diameter of opening  12  in chamber wall  10 . The area of hole  40  in sleeve  22  is dependent on the number of fibers  26  in bundle  24 . The minimum possible outside diameter of sleeve  22  is dependent on the size and shape of hole  40 . 
     Flange  30  includes base  42 , tube  44 , and compression cap  46  and is mounted adjacent opening or port  12  in wall  10 . Flange  30  is similarly made of metal or other hard material. Base  42  of flange  30  is mounted to wall  10  using any common method, such as but not limited to welding or the use of a plurality of fasteners. O-ring compression seal  34  may be used with some or all of these methods. Tube  44  includes threads  48  which mate with compression cap  46  to seal outer surface  38  of sleeve  22  to tube  44  using O-ring compression seal  32 . Other common methods of sealing sleeve  22  to tube  44  can be utilized, such as but not limited to sleeve  22  having external threads which mate with internal threads on either tube  44  or opening  12 , or welding sleeve  22  to tube  44  or wall  10  adjacent opening  12 . Also envisioned is manufacturing sleeve  22  to include the flange, thus eliminating parts and the potential for leakage between sleeve  22  and flange  30 . 
     Fibers  26  can be made of glass, quartz, plastic, or any other suitable material in a solid or hollow form and in a variety of thicknesses. The number of fibers  26  in bundle  24  passing through hole  40  of sleeve  22  can vary widely depending on the intended use. For example, between about 100 to 100,000 individual fibers may be used. Also, discrete smaller bundles within the total bundle may be present, or discrete bundles may pass through separate holes in sleeve  22 . 
     Fibers  26  of bundle  24  are bonded together with solid polymer sealant  28  and the bound fiber bundle itself is bonded to inner surface  36  of sleeve  22 . Individual optical fibers  26  within bundle  24  are surrounded by solid polymer sealant  28  such that each of fibers  26  is separated from its neighboring fibers  26  by sealant  28 . 
     Solid resin derived polymer sealant  28  is preferably derived from an epoxy resin. Characteristically, the resin cures at a rate slow enough to allow the resin in a liquid form to penetrate fiber bundle  24  and surround fibers  26  therein prior to solidifying. However, other sealing materials with similar properties could be utilized to seal fibers  26  to each other and to inner surface  36  of sleeve  22 . 
     Referring now to FIG. 2, a cross-section of sleeve  22  shows fiber-optic bundle  24  within hole  40  in sleeve  22 . A layer of sealant  28  separates individual fibers  26  from each other and from inner surface  36  of sleeve  22 . Sealant  28  creates a hermetic seal between each of individual fibers  26  and between fibers  26  and inner surface  36  of sleeve  22 . 
     Referring now to FIG. 3, an enlarged view of a section of feedthrough sleeve  22  shows in greater detail a plurality of 50 micron fibers  26  within sleeve  22 . Each of fibers  26  is separated from the other fibers  26  by a layer of sealant  28  creating a seal between the fibers and providing additional optical isolation between the fibers. 
     One embodiment of the fiber-optic bundle feedthrough of the present invention is prepared by forming a bundle of optical fibers, soaking the bundled fibers in the liquid resin, inserting the soaked fibers into the rigid outer sleeve, and allowing the resin to cure. 
     The fibers are combed together to make sure that there are no knots or kinks in the bundle. One end of the bundle is wrapped with tape, so that the fibers can be easily pushed through the sleeve. Once the fiber tip covered with tape is exposed, the fibers are pulled through the tube the appropriate distance. Immediately beyond the other side of the tube, the fibers are immersed into a sealant (such as epoxy) for a few minutes. It is important to cover each of the fibers with sealant so that they can adhere to each other and the inside surface of the sleeve. Then the coated part of the fiber bundle is pulled back into the sleeve. 
     Once the sealant has completely hardened, the feedthrough is attached to a wall of an environmental chamber. A flange is attached to the chamber wall and the sleeve is directed through the flange and is sealed with a compression O-ring along its outer surface. Once the feedthrough is sealed to the wall, the environment inside the chamber may be adjusted by pumping air out using a vacuum system, heating or cooling, or other means to obtain the desired environmental conditions. 
     One embodiment of the fiber-optic bundle feedthrough of this invention allows transmission of collected light from an environment within a vacuum chamber, which can approach 10 −10  Torr, to an environment at standard atmospheric conditions of pressure and humidity, while maintaining vacuum conditions in the source chamber. 
     Although the present invention has been described with reference to particular means, materials, embodiments, and methods from the foregoing description, one skilled in the art can easily ascertain the essential characteristics of the present invention and various changes and modifications may be made to adapt the various uses and characteristics without departing from the spirit and scope of the present invention as described herein.