FIBER OPTIC SOLDERABLE BULKHEAD FITTING

Abstract: Fiber optic solderable bulkhead fitting has a plated-on built-up metal body (18) of a material which minimizes local stresses thereby minimizing micro-bending losses in the optical fiber (10). The body (18) is sealed by solder (24) within an opening (22) in a bulkhead (20) to provide a sealed passthrough for the optical fiber (10). In another embodiment, two optical fibers (26, 28) have plated-on built-up bodies (30, 32) thereon which serve to align the optical fibers in a connector (42). The connector (42) is then sealed in a bulkhead (38) as was done in the first embodiment.

Description: FIBER OPTIC SOLDERABLE BULKHEAD FITTING BACKGROUND OF THE INVENTION This invention is directed to a fiber optic bulkhead fitting wherein the optical fiber can be soldered to a bulkhead. Optical fibers are suitable for the transmission of digital information and are being increasingly used for that purpose. Optical fibers are superior to the employment of electrical conductors for a number of data transmission needs. However, there has been a problem in passing an optical fiber from one environment, through a bulkhead, to another environment because of the problems of reliably sealing the optical fiber to the bulkhead. Such sealing is necessary to provide sure separation between the spaces separated by the bulkhead. Accor- dingly, there is need for a bulkhead fitting which is compatible with both the optical fiber and the bulkhead to provide complete and reliable sealing. Previous attempts at running an optical fiber through a bulkhead and sealing it with respect thereto have been unsatisfactory because of the microbending losses. When epoxy is used to seal an optical fiber with respect to a structure like a bulkhead, the forces on the optical fiber cause local changes in the index of refrac¬ tion which is the microbending loss. With epoxy, the loss is about 1 decibel. This is a significant loss in such a system and cannot be tolerated in any but short, simple systems. SUMMARY OF THE INVENTION In order to aid in the understanding of this invention, it can be stated in essentially summary form that it is directed to a fiber optic solderable bulkhead fitting wherein the iber- optic has cladding substantially over its entire length and metal is plated on a portion of the cladding to ~ fόrm a metal built-up body structure and the metal built-up structure is sealable with respect to a bulkhead. It is, thus, a purpose and advantage of this invention to provide a fiber optic solderable bulkhead fitting wherein a fiber optic is sealable with respect to the bulkhead to prevent an interchange of materials, such as gasses of liquids, from opposite sides of the bulkhead. It is a further purpose and advantage of this invention to provide a fiber optic solderable bulkhead fitting wherein the optical fiber has a conductive coating thereon and a copper or other selected metal body struc- ture is built up upon the coating so that the metal built-up body structure can, in turn, be sealed directly or indirectly with respect to a bulkhead. Other purposes and advantages of this invention will become apparent from a study of the following portion of the specification, the claims and the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side-elevational view of the first preferred embodiment of the fiber optic solderable bulkhead fitting of this invention, with the bulkhead being broken away and taken in section, and a part of the cladding removed from the optical fiber to show a section of the cladding. -*- FIG. 2 is an exploded side view, partly in perspective, and with the bulkhead taken in section of the- second preferred embodiment of the fiber optic solder¬ able bulkhead fitting in accordance with this invention. 5 ■ DETAILED DESCRIPTION OF THE INVENTION Optical fiber 10 is the general indication of a typical coated optical fiber. Fiber core 12 is substantially transparent to the optical radiation of 10 interest. It preferably carries an optical cladding 14 and an aluminum coating 16. Such fibers can be made sufficiently flexible and optically transmissive to achieve the results required of optical fibers. Copper body 18 is a built-up structure on I*-' coating 16 of fiber 10 when coating 16 is of an inorganic material such as aluminum. Alternatively, copper body 18 is a built-up structure on optical cladding 14 of fiber 10 when coating 16 is of an organic material coating 16 being removed therefrom prior to 20 the beginning of the build-up process. When optical cladding 14 is the exterior or material of the fiber, i.e., organic coating 16 removed, the length on which the body 18 is to be deposited can be made conductive by vapor deposition of silver or gold as a first step. 25 Copper is particularly selected because it can be evenly and easily deposited to eliminate localized forces which cause microbending and consequent trans¬ mission losses. Other metals would be selected for the built-up structural body when found to be suitable for 30 this even, localized-force-free deposition. The copper body 18 is built up by electroplating. A suitable electroplating bath is prepared as follows: Two " , hundred twenty-five grams of copper sulphate are dissolved per liter of water. Fifty-five grams of sulfuric acid are also added per liter to provide the copper plating electrolyte. Added to the plating elec¬ trolyte solution is one-half milliliter of UBAC solution No. 1 per liter of electrolyte. This material is available from Udylite-O ic, 21441 Hoover Road, Warren, Michigan 48089. This mixture acts to improve the fineness of the copper grain in the electrolytic buildup. In the alternative, blackstrap molasses is also useful for the purpose of improving the fineness * of the copper again. It is critical to the plating that the plating current be a maximum of 180 milliamperes per square inch. A higher current accelerates the ions in the plating solution and this, in turn, produces random orientation which results in graininess. Currents lower than the maximum current improve the fineness of the copper grain. The preferred current is 90 milliamperes per square inch. The plating voltage is from 0 to 3 volts, and the electrolyte temperature is maintained at 70 to 80 degrees F. The concentration of UBAC solution No. i in the electrolyte is maintained during the plating operation. The plating operation must be carefully performed to minimize stresses in the copper plate body which would cause microbending. Microbending, localized changes in the optical fiber's index of refraction, is caused by forces applied to fiber 10. Copper body 18 is thereby deposited without substantial effect upon fiber 10. The result is that the copper body 18 produces a transmission loss of less than 0.1 decibels in the fiber. Plating continues until the copper body 18 is built up to the desired size. Bulkhead 20, illustrated in FIG. 1, is an example of a bulkhead through which the optical fiber 10 is to pass and be sealed with respect thereto. Opening 22 is formed in bulkhead 20 and fiber 10 carrying copper body 18 is placed through the opening with the copper body 18 within opening 22. Thereupon, the optical fiber is sealed in place by the application of solder 24 to completely hermetically seal the fiber within the opening. In order to prevent damage to the optical fiber with its cladding, a lower temperature solder such as a lead-tin or lead-indium solder is preferably employed. In this way, optical fiber 10 passes through bulkhead 20 and is completely sealed. by solder 24 with respect thereto. FIG. 2 illustrates a second preferred embodiment of the bulkhead fitting of this invention. Optical -fibers 26 and 28 respectively carry built-up structures 30 and 32 on the facing ends thereof. The built-up structures respectively carry mating surfaces 34 and 36 thereon so that the fibers can be physically positioned as described below. Optical fibers 26 and 28 are the same as optical fiber 10 in FIG. 1 while built-up structures 30 and 32 are built up in the same way as the copper body built-up structure 18 also of FIG. 1. Bulkhead 38 has an opening 40 therethrough into which is secured connector 42 by means of sealing material 44. Sealing material 44 is compatible with both the body 46 of connector.42 and the bulkhead 38. Sealing material 44 is preferably a solder to provide a secure seal. Connector 42 has faces 48 and 50 which receive the mating surfaces 34 and 38 to positively align the ends of the optical fibers 26 and 28 respectively. Body 46 is closed in the center by means of window 52 which optically connects the fibers 26 and 28. Window 52 is of suitable optical properties for the wave length to be transmitted and can be a lens such as a Selfoc self-focusing leans, a Fresnel lens, and the lenses may be made of such materials as glass, quartz, sapphire, or germanium, depending upon the optical requirements. In a preferred embodiment, the connector . body 46 is built up on window 52 as a copper body built-up structure as previously described. Mating surfaces 34 and 36 as well as their joining faces 48 and 50 are machined to provide the optimum optical coupling. While the fibers 10, 26 and 28 are described as being metal-coated fibers, and such is the most preferred embodiment, it is also clear that the built-up body can also be plated onto bare fibers or organically coated fibers by first applying an electrically conductive layer, such as an evaporated-on silver or gold film. However, when using organically coated fibers it is preferrable to remove the organic coating prior to applying the electrically conductive layer. This invention has been described in its presently contemplated best mode, and it is clear that it is susceptible to numerous modifications, modes and embodiments within the ability of those skilled in the art and without the exercise of the inventive faculty. Accordingly, the scope of this invention is defined by the scope of the following claims.

Claims: CLAIMS What is Claimed is: 1. A fiber optic solderable bulkhead fitting comprising: an optical fiber; a metallic built-up structure deposited on a portion of said optical fiber to form a metallic body; and means for sealing said metallic body to a bulkhead so that optical signals can pass through said bulkhead within said optical fiber, where * in said bulkhead is sealed against passage of material. 2. The fiber optic solderable bulkhead fitting of Claim 1 wherein said optical fiber has said metallic body built up intermediate the ends of said fiber so that said fiber can pass through an opening in a bulkhead and said metallic body can be sealed within the opening for closing the opening the bulkhead. 3. The fiber optic solderable bulkhead fitting of Claim 2 wherein there is a bulkhead having an opening therethrough and said optical fiber passes through said opening and said metallic body on said optical fiber is soldered to said bulkhead at said opening. 4. The fiber optic solderable bulkhead fitting of Claim 1 wherein said optical fiber comprises first and second connected optical fibers, each having a facing end and having a metallic built-up body thereon at said facing ends, a connector for sealing in the opening of a bulkhead, said connector having faces for receiving said built-up bodies to provide optical connection between said optical fibers. 1 5. The fiber optic solderable bulkhead fitting of Claim 4 wherein said connector contains a lens for optically connecting said optical fibers. 1 6. The fiber optic solderable bulkhead fitting of Claim 5 wherein said lens is selected from the group consisting of a Selfoc and Fresnel lens. 1 7. The fiber optic solderable bulkhead fitting of Claim 6 wherein said lens is made of material selected from the group consisting of glass, quartz, sapphire and germanium. 1 8. The fiber optic solderable. bulkhead fitting of Claim 5 wherein said lens is made of material selected from the group consisting of glass, quartz, sapphire and germanium. 1 9. The fiber optic solderable bulkhead fitting of Claim 4 wherein said connector has a body which is solderable within an opening in a bulkhead and contains a lens therein, said body having faces adjacent said lens 5 on opposite ends of said body for positioning on opposite sides of the bulkhead, said faces being configured to receive mating surfaces on said built-up metallic bodies on said optical fibers so that said connector is for closing an opening in a bulkhead and receives said built- 10 up metallic bodies for optically aligning said optical fibers. 1 10. The fiber optic solderable bulkhead fitting of Claim 9 wherein said connector is a metallic body built up on said lens. 11. The fiber optic solderable bulkhead fitting of Claim 10 wherein said lens is selected from the group consisting of a Selfoc and Fresnel lens. 12. The fiber optic solderable bulkhead fitting of Claim 11 wherein said lens is made of material selected from the group consisting of glass, quartz, sapphire and germanium. 13. The fiber optic solderable bulkhead fitting of Claim 9 wherein said lens is made of material selected from the group consisting of glass, quartz, sapphire and germanium. 14. A fiber optic solderable bulkhead fitting comprising: a bulkhead having an opening therethrough; an optical fiber passing through said opening, said optical fiber having a cladding thereon; a metallic built-up body on said cladding, said metallic built-up body being made of a material which minimizes local stresses on said optical fiber; and solder engaged both with said bulkhead and said built-up body to seal said optical fiber with respect to said bulkhead and close the opening within said bulkhead. 15. The fiber optic solderable bulkhead fitting of Claim 14 wherein said built-up body is made of electro¬ plated copper. 16. A fiber optic solderable bulkhead fitting . comprising: a bulkhead having an opening therethrough a connector positioned within said opening and sealed with respect thereto, said connector having first and second faces thereon, with said first and second faces being positioned on opposite sides of said bulkhead; and first and second optical fibers each having an end, first and second metallic built-up bodies respec¬ tively on said fibers adjacent the ends thereof, said bodies each having a mating surface thereon so that when said metallic built-up bodies are engaged with said faces on said connector, said optical fibers are in optical communication. 17. The fiber optic solderable bulkhead fitting of Claim 16 wherein said built-up bodies are metallic copper bodies plated onto said optical fibers adjacent the ends thereof. 18. The fiber optic solderable bulkhead fitting of Claim 17 wherein said connector contains a lens to optically interconnect said first and second fibers. 19. The method of passing an optical signal through a bulkhead while sealing the bulkhead against material transfer comprising the steps of: building up a metallic body on an optical fiber by plating; and sealing said built-up body with respect to the bulkhead. 20. The method of Claim 19 wherein the building up step on the fiber is performed intermediate the ends of the fiber and further including the intermediate step of: passing the fiber through an opening in a bulkhead and thereafter sealing the body with respect to the bulkhead.

Inventors: PIKULSKI JOSEPH L, RAMER O GLENN, PIKULSKI, JOSEPH, L., RAMER, O., GLENN
Applicants: HUGHES AIRCRAFT CO, HUGHES AIRCRAFT COMPANY
Application year: 1985
Main classification: G02B6
IPC codes: G02B6