METHOD AND APPARATUS FOR RECOATING A FIBER OPTIC SPLICE

Abstract: A fiber optic splice recoat includes a flexible outer sleeve positioned over the splice area filled with a UV curable recoat material. The flexible outer sleeve is positioned over one of a pair of optical fibers to be spliced together. The glass fibers of the cables are spliced and the sleeve is positioned over the spliced area. The sleeve is filed with a UV curable recoat material and is subjected to UV energy to cure the recoat material. A fixture is provided for supporting the cables during the splice and recoat operations. The fixture is further provided with a handle to keep the positioning blocks spaced at a predetermined distance.

Description: METHOD AND APPARATUS FOR RECOATING A FIBER OPTIC SPLICE Technical Field This invention relates to an optical fiber splice recoat for use in a harsh environment. Background Art Fiber optics has been replacing electronics in many applications. The field of oil well monitoring, for instance, has presented many challenges for using fiber optic cables. The optical fibers typically require a coating to protect the glass fiber from moisture and other environmental contamination as well as protect the fiber from damage during handling or processing. In addition the deployment of optical fibers into an oil well requires extremely long continuous lengths of sealed fiber. It is not always practical to supply fiber optic cables in the required lengths, which necessitates that lengths of cable be spliced together. It is also necessary to splice lengths of fiber optic transmission cables in the field, without the luxury of a sterile laboratory and sophisticated equipment. The use of fiber optic based components in the oil well industry has proved to be very problematic because of the harsh environments to which the fibers are potentially exposed. For instance it is common for the pressures within a well bore hole to exceed 20 kpsi and temperatures to exceed 150 degrees C. In addition, the fluids within a well bore hole include oil, water, natural gas, hydrogen, and mud and can be quite corrosive and have extremely deleterious effects on the mechanical reliability and optical quality of a fiber optic transmission cable. Optical fibers typically consist of a core glass material that is surrounded by a cladding and finally an external buffer or coating material. The buffer material is typically a plastic or polymer material that is applied to the fiber to provide the moisture barrier and mechanical protection described herein above. In certain applications, the optical fibers are disposed within a metal capillary tube to provide further protection to the optical fiber from harsh environments and handling. The coating material also serves to protect the optical fiber from contact with the metal capillary during handling and bending. When optical fibers are spliced together, the buffer material is removed to accomplish the delicate splice of the glass fiber leaving a section of cable exposed without buffer material. In many cases, such as the high temperature harsh environment of oil wells, it is necessary to recoat the fiber with a compatible buffer material. In many cases the metal capillary tube is also spliced in a manner intended to protect the recoated splice area. An example of such a splice protector is disclosed in copending U.S. Patent Application Serial Number 09/384,079 (Attorney Docket No. CC-0075A) filed August 26, 1999, entitled "Transmission Splice Protector and Method", commonly assigned to the Applicant and is disclosed herein in its entirety. Many prior art methods of recoating optical fibers include the insertion of the bare optical fiber into a mold within which a recoat material or sleeve is cast to encapsulate the fiber and effectuate a recoat thereby. Materials that have been used to recoat the fibers include glass, polymers, epoxies, acrylics, and polyimides among others. It has generally proved very difficult to align the fibers within the molds to ensure a consistent coating thickness. Most known methods use heat to cure the recoat material, although UV curing materials are known. Heat curing materials typically require that the mold be placed in an oven, or be integrally heated, for long periods of time to complete the cure of the materials. UV curing materials are typically either more brittle or have lower adhesion strengths to the glass than the heat curable materials when exposed to harsh environments. It is also known to provide a sleeve over the splice area and to inject an epoxy or other adhesive at the ends of the sleeve to adhere the coated portion of the fibers to the sleeve whereby the sleeve alone acts as a splice protector and the epoxy directs loads around the glass splice into the sleeve. It is typical to use these sleeves for laboratory or testing work, as breadboard type splices, but they do not function well in harsh environments where the optical fiber and splice may need to be manipulated or bent around a radius. For instance, in one of these known methods a rigid sleeve is used to support the splice, which precludes the splice section from bending, and typically over stressing the fiber adjacent to the splice if the fiber is manipulated around a radius. Problems also result in another known method wherein a flexible sleeve is used and the unsupported section, i.e. between the epoxy coated ends, buckles against the fiber when a bend is attempted typically damaging the fiber. What is needed is a fiber recoat and method which provides a continuous moisture barrier and physical protection for handling and manipulation for use in a harsh, high temperature, environment. Summary of the Invention Objects of the present invention include provision of an optical fiber splice recoat for survival within a harsh environment. It is an object of the present invention to provide a fiber optic splice recoat for recoating a glass fiber in a splice area of a optical fiber. The recoat comprises a flexible outer sleeve positioned generally concentrically about the glass fiber in the splice area and includes a compatible recoat material disposed within and substantially filling the flexible outer sleeve. The sleeve and the recoat material provide a moisture barrier seal about the splice area. In one embodiment of the present invention the outer sleeve of the fiber optic splice recoat comprises a tube transparent to UV light and the recoat material is a UV curable material. In another embodiment the outer sleeve comprises a partial tube transparent to UV light. It is another object of the present invention to provide a fixture for performing a fiber optic splice recoat on a optical fiber. The fixture includes a pair of mounting blocks, each mounting block having a v-groove disposed therein and sized to receive the optical fiber, and a clamp positioned on each the mounting block for releasably securing the fiber optic cable in the v-groove. The fixture comprises a handle attached to the blocks positioning the blocks a predetermined distance apart and axially aligned about the v-grooves and a positioning block axially aligned with the v- grooves to support the splice outer sleeve during a recoat operation. The fixture further includes a guide pin disposed in a work base and cooperates with a guide hole disposed in one of the mounting blocks for positioning the mounting blocks on the work base. It is yet another object of the present invention to provide a method of recoating a splice area of a pair of optical fibers wherein the optical fibers have a glass fiber surrounded by a buffer material. In accordance with the invention the method comprises stripping a predetermined length of buffer material from each cable, splicing the glass fiber of each cable together, positioning a flexible outer sleeve over the splice, filling the outer sleeve with a compatible recoat material and curing the recoat material within the outer sleeve. The foregoing and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of exemplary embodiments thereof. Brief Description of the Drawings Fig. 1 is a perspective end view of an optical fiber; Fig. 2 is a perspective end view of the optical fiber of Fig. 1 with a portion of the buffer material stripped off; Fig. 3 is a perspective view of a fiber optic splice recoat, in accordance with the present invention; Fig. 4 is a section view of the fiber optic splice recoat of Fig. 3 taken substantially along cut line 4-4; Fig. 5 is a perspective view of a pair of optical fibers showing the splice outer sleeve, in accordance with the present invention; Fig. 6 is a perspective view of the optical fibers of Fig. 5 spliced together; Fig. 7 is a perspective view of the spliced optical fibers of Fig. 6 showing the outer sleeve positioned over the splice area, in accordance with the present invention; Fig. 8 is a perspective view of a fiber optic splice recoat, showing the injection of the recoat material and application of UV energy, in accordance with the present invention; Fig. 9 is a perspective view of an alternative embodiment of an outer sleeve in accordance with the present invention; Fig. 10 is a perspective view of the spliced optical fibers of Fig. 9 showing the outer sleeve positioned over the splice area, in accordance with the present invention; Fig 11 is a cross sectional view of view of a fiber optic splice recoat of Fig. 10; Fig. 12 is a top view of a fiber optic splice recoat fixture, in accordance with the present invention; Fig. 13 is a front view of the fiber optic splice recoat fixture of Fig. 12; and Fig. 14 is a section view of the fiber optic splice recoat fixture of Fig. 12 taken substantially along lines 14-14. Best Mode for Carrying Out the Invention Referring to Fig. 1, a conventional optical fiber 10 is shown which includes a buffer layer 12 and a glass fiber 14. Buffer layer 12 may include multiple concentric layers of material. In certain applications optical fiber 10 may be disposed within one or more protective capillary tubes including one or more buffer layers (not shown). In order to splice two lengths of optical fiber 10 it is necessary to remove a length of buffer material 12 as is best shown with reference to FIG. 2 leaving a length of glass fiber 14 exposed. The glass fiber 14 is spliced to a similar glass fiber by any known method to effectuate an optical splice therebetween. In an embodiment of the present invention the cladded glass fiber 14 is approximately 125 μm and buffer material 14 may be comprised of multiple layers. It is known to remove the buffer material 14 by many methods including the broad categories of mechanical, thermal and chemical stripping. With reference to FIGS. 3 and 4, the fiber optic splice recoat 13 of the present invention includes an outer sleeve 16 approximately concentrically positioned over the splice area 15 between optical fibers 10, 11 and overlapping buffer material 12 on both cables. Splice area 15 is comprised of the stripped portion of the glass fiber 14 and the overlapping portion of the buffer material 12. Outer sleeve 16 is comprised of a flexible tube that allows transmission of UV light and once positioned over the splice area 15 is substantially filled with recoat material 18. Outer sleeve 16 is approximately .078 larger in diameter than transmission cables 10, 1 1 in a specific example and is approximately 1.5 inches long and overlaps the buffer material 12 by approximately .5 inches. In a particular embodiment outer sleeve 16 is comprised of a Teflon® material having a wall thickness of approximately .011 inches but may comprise any compatible flexible tubing capable of withstanding the harsh environment of the particular application. Recoat material 18 is a flowable UV curable material and in a particular embodiment comprises an acrylate or silicone, such as Optigard® manufactured by Dow Corning, but may comprise any flowable UV material capable of withstanding the harsh environment of the particular application. In accordance with the present invention, outer sleeve 16 serves as an in-situ mold for recoat material 18 and further serves to support the recoat material after cure. As described here before UV curable recoat materials in general do not adhere well to the cladded glass 14 and without the mechanical support of outer sleeve 16 would not provide the mechanical robustness of the present invention. As such, splice recoat 13 provides a robust moisture barrier about glass fiber 14 and further allows for the bending and handling of the spliced transmission cables 10, 11. Referring to FIG. 5, in operation two fiber optical cables 10, 11 to be spliced together are prepared by exposing bare glass fiber 14 by at least stripping buffer material 12. Outer sleeve 16 is positioned concentrically about cable 1 1 as shown, however the sleeve could be positioned about either cable 10, 1 1. Once positioned about the cable 1 1 the glass fibers 14 are spliced in any known manner in splice area 15 as best shown in FIG. 6. Outer sleeve 16 is positioned over splice area 15 as best shown in FIG. 7 overlapping the buffer material 12 of both transmission cables 10, 11. Recoat material 18 is inserted within outer sleeve 16 as best shown with reference to FIG. 8 in the direction indicated by arrow 20 to substantially fill the gap between the outer sleeve and glass fiber 14. A syringe may be used to insert the recoat material 18 into outer sleeve 16, but any known method that substantially fills the sleeve could be used. In the example given above approximately 1.13 cc of recoat material 18 is required to fill the gap. The splice area 15 is then exposed to a UV light source 22 which projects UV light beam 24 through the outer sleeve 16 to cure recoat material 18. In a particular embodiment Xenon Corporation, model RC-250 B, ultra violet gun is used to cure recoat material 18. The fully cured recoat material 18 of the fiber splice recoat is shown in FIGS. 3 and 4 and provides mechanical protection and a moisture barrier for the fiber splice area 15. Referring now to FIGS. 9, 10 and 11, there is shown an alternative embodiment of the present invention wherein the outer sleeve is comprised of a partial tube 70. Outer sleeve 70 as shown may comprise any portion of a full tube capable of accepting and providing a molding and support vessel for recoat material 18. As described herein above outer sleeve 70 is positioned concentrically around optical fiber 14 in splice area 15 and then is substantially filled with recoat material 18 to seal the fiber therein as best seen in FIG. 11. The advantage of outer sleeve 70 over other embodiments is that permits the installation of the outer sleeve over the fiber 14 after a splice has been performed. It has been found to be advantageous to use a fixture 30 as shown in FIGS. 12 and 13 to position and support the transmission cables and outer sleeve 16 (FIGS. 4, 7, 10 and 11) during the recoating process. Once the buffer material 12 is removed, each of the optical fibers described herein above are positioned in the v-grooves 32, 33 of mounting blocks 34, 35 and the metal clamps 38, 39 are rotated into the closed position (not shown) as is known in the prior art. Also as is known, compliant friction pads 40, 41 cooperate with recesses 42, 43 in blocks 34, 35 to secure the transmission cables within the fixture 30 magnets 44, 45 maintain a biasing force on metal clamps 38, 39 to releasably hold the transmission cables in the v-grooves 32, 33. As best shown in FIG. 14, clamp 38, and similarly clamp 39, rotates about a hinge 46 between the open position and to a closed position. In accordance with the present invention fixture 30 is provided with an integral handle 47 to link mounting blocks 34, 35 together to transport the optical fiber after splicing to work base 60 to provide a strain free positioning of the spliced cable for subsequent recoating. Base 49 is provided with a positioning hole 50 that cooperates with pin 51 attached to work base 60 to provide for positioning of the fixture the work base. Work base 60 further includes alignment dowels 52, 53 that cooperate with the edges of base 48 to further align fixture 30 on work base 60. The positioning features described are shown by way of example as alignment dowels 52, 53 and pin 51, allow for positioning in the work base 60 which may include a fiber splice machine such as an Ericsson FSU-975 Fusion Splicer or other work base. The present invention further includes positioning block 61 mounted to work base 60 having a trapezoidal groove 62 positioned therein and sized to accept and align outer tube 16 concentrically about spliced fiber 14 in the splice area 15 (FIG. 6). In operation the cables are positioned within the fixture 30 and the clamps 38, 39 are moved to a closed positioned wherein the magnets 44, 45 secure the cables in v-grooves 32, 33 between the compliant friction pads 40, 41. Once positioned therein, an operator (not shown) may place the fixture in a splicer to perform a fusion, or other similar, splice of the glass fiber 14. The operator may then transport the spliced cables using the handle 47 of fixture 30 without stressing the newly formed splice. The method of performing the splice recoat 13 outlined herein above may then be performed while the cables are secured in the fixture 30 by positioning the fixture on work base 60 using alignment dowels 52, 53 and guide pin 51. Outer tube 16 is then slid over splice area 15 as described herein above and positioned within trapezoid groove 62, although a v-groove or other positioning feature may be used. With regard to the embodiments show in FIGS. 12-14 outer sleeve 70 is placed within trapezoid groove 62 directly without the need to install the sleeve prior to splicing. A UV light source 22 (FIG. 8) may then be positioned above positioning block 61 to cure the recoat material 18 within outer sleeve 16. Once cured the clamps are rotated into the open position shown in the figures and the splice recoat 13 is removed from the fixture 30. It should be understood that, unless otherwise stated herein, any of the features, characteristics, alternatives or modifications described regarding a particular embodiment herein might also be applied, used, or incorporated with any other embodiment described herein. Also, the drawings shown herein are not drawn to scale. Although the invention has been described and illustrated with respect to exemplary embodiments thereof, the foregoing and various other additions and omissions may be made therein and thereto without departing from the spirit and scope of the present invention.

Claims: Claims What is claimed is: 1. A fiber optic splice recoat, for recoating a glass fiber in a splice area of a optical fiber, said recoat comprising: a flexible outer sleeve positioned generally concentrically about said glass fiber in said splice area; a compatible recoat material disposed within and substantially filling said flexible outer sleeve; and said recoat material providing a moisture barrier seal about said splice area. 2. The fiber optic splice recoat of claim 1 wherein said outer sleeve comprises a tube transparent to UV light. 3. The fiber optic splice recoat of claim 1 wherein said recoat material is a UV curable material. 4. The fiber optic splice recoat of claim 1 wherein said outer sleeve is comprised of a Teflon® material. 5. The fiber optic splice recoat of claim 1 wherein said outer sleeve comprises a partial tube transparent to UV light. 6. A fixture for performing a fiber optic splice recoat on a optical fiber, wherein said fixture includes a pair of mounting blocks, each mounting block having a v-groove disposed therein and sized to receive said optical fiber, a clamp positioned on each said mounting block for releasably securing said fiber optic cable in said v-groove, said fixture comprising: a handle attached to said blocks positioning said blocks a predetermined distance apart and axially aligned about said v-grooves; and a positioning block axially aligned with said v-grooves. 7. The fixture of claim 6 wherein said positioning block is removably attached to a work base. 8. The fixture of claim 7 further comprising: a guide pin disposed in said work base; and a guide hole disposed in one of said mounting blocks for positioning said mounting blocks on said work base. 9. The fixture of claim 8 further comprising a pair of alignment dowels disposed in said work base and cooperating with one of said mounting blocks axially aligning said v-grooves with an alignment groove in said positioning block. 10. The fixture of claim 12 wherein said alignment groove comprises a trapezoidal shape. 11. The fixture of claim 12 further comprising a recess area disposed in said mounting blocks and cooperating with said compliant friction pads to secure said optical fiber within said v-grooves. 12. The fixture of claim 7 wherein said work base comprises a fiber splice machine. 13. A method of recoating a splice area of a pair of optical fibers, said optical fibers having a glass fiber surrounded by a buffer material, said method comprising: stripping a predetermined length of buffer material from each cable; splicing said glass fiber of each cable together; positioning a flexible outer sleeve over said splice; filling said outer sleeve with a compatible recoat material; and curing said recoat material within said outer sleeve. 14. The method of claim 13 wherein said flexible outer sleeve comprises a tube, said method further comprising sliding said flexible outer sleeve onto one of said cables prior to said splicing. 15. The method of claim 13 wherein said curing is performed using ultraviolet energy 16. The method of claim 13 further comprising positioning said cables within a fixture prior to said splicing. 17. The method of claim 16 further comprising removing said spliced cable from said fixture.

Inventors: CHIPMAN CHRISTOPHER, DEMAILLE VON SCHMIDT ROBERT H, DUNPHY JAMES R, NORTON DOUGLAS A, CHIPMAN, CHRISTOPHER, DEMAILLE VON SCHMIDT, ROBERT, H., DUNPHY, JAMES, R., NORTON, DOUGLAS, A.
Applicants: CIDRA CORP, CIDRA CORPORATION
Application year: 2000
Main classification: G02B6
IPC codes: G02B6