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  Applicator for high-speed gel buffering of flextube optical fiber bundlesRelated Patent Categories: Coating Processes, Optical Element Produced, Polarizer, Windshield, Optical Fiber, Projection Screen, Or Retroreflector, Optical Fiber, Rod, Filament, Or WaveguideThe Patent Description & Claims data below is from USPTO Patent Application 20060159845. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention generally relates to the field of fiber optic cables, in particular the present invention is directed to a method and apparatus for applying water barrier gels to optical fibers or fiber bundles at high speeds. [0003] 2. Discussion of Related Art [0004] Optical fibers are very small diameter glass strands which are capable of transmitting an optical signal over great distances, at high speeds, and with extremely low signal loss as compared to standard wire or cable networks. Optical fiber has found increasingly widespread application and currently constitutes the backbone of the worldwide telecommunication network. Because of this development, there has been a growing need for better quality optical fibers with a decrease in production time and costs, while ensuring adequate material strength for continued operation in increasingly harsh conditions. An important aspect for making better optical fibers is the reduction of structural faults or impurities in the protective coatings applied to the optical fiber during manufacture. [0005] In general, optical fibers are manufactured from relatively large diameter glass preforms. Fiber optic preforms are generally made with three concentric glass layers. The inner layer, or core, is made of a very high quality, high purity SiO.sub.2 glass, which for example, may be about 5 mm in diameter. This high purity core is the portion of the optical fiber in which the optical data is transmitted. Concentrically positioned around the high purity core is a second layer of glass, or cladding, with a lower index of refraction then the inner core, and generally is less pure. The difference in refraction indices between the core and cladding allows the optical signals in the core to be continuously reflected back into the core as they travel along the fiber. The combination of the core and cladding layers is often referred to as the "primary preform." The optical fiber is then formed by heating and softening a portion of the preform, and rapidly drawing the softened portion with specialized equipment. The length of the drawn optical fiber is typically several thousands of times the length of the primary preform. Optical fibers intended for manufacture of telecommunications cables are typically coated with one or more polymer layers. The polymers provide mechanical protection of the fiber surface, and are colored for identification purposes. The coated optical fibers, singly or in groups, are typically covered with one or more of a number of jackets that provide structural support and environmental protections. The aggregate of the optical fiber, jackets, and additional integrated mechanical supports, is typically referred to as an optical fiber cable. [0006] Exposure to water or humid air causes chemical changes in the surface of the optical fiber, resulting in a degradation of its ability to carry information. The most common method used to prevent or mitigate this degradation, is to reduce or eliminate water contact on the fiber surface by substantially filling the protective housings with a water barrier compound such as a hydrophobic fluid. For a number of reasons, including cable behavior during installation and long-term stability of the cables during use, the hydrophobic fluid is typically a gel. Gels tend to flow when mechanically stressed, but tend to remain static when under a low mechanical load. [0007] Known methods for applying gel to fibers include drawing the fibers through a reservoir filled with gel so that the fibers are coated. However, the use of such a method often results in an inconsistent coating on the fibers due to air entrapped air. Accordingly, gel applicators have been developed, such as the device disclosed in Griser et al. U.S. Pat. No. 5,395,557, which attempts to reduce air entrapment by using a reservoir filled with pressurized gel. This device includes a housing having a cavity through which a plurality of separated optical fibers are fed. Gel is provided to the cavity from a gel reservoir via a pump. The optical fibers are then drawn through the gel so that the fibers are coated with the gel. The gel is provided under pressure in an attempt to reduce air gaps that may form upon the fibers. However, this technique has numerous draw backs. For example, a relatively large driving pressure is placed upon the gel in the reservoir to reduce air entrainment. Rapid application of barrier gel with this method requires relatively long and narrow application regions to prevent uncontrolled ejection of fluid from application regions, due to the large pressures. [0008] Consequently, an apparatus for applying gel to a plurality of optical fibers, which substantially overcomes the above-recited drawbacks is highly desirable and needed in the optical fiber industry. SUMMARY OF THE INVENTION [0009] The present invention is directed to eliminating the above problems associated with the application of water barrier fluids, such as a gel, to optical fibers and optical fiber bundles. Thus, the invention improves the quality of the optical fiber cable and manufacturing process used to apply the gel. [0010] The present invention addresses the above problems by providing a gel application apparatus that applies the gel with a flow having a high velocity in a direction normal to the surface of the optical fibers, as the fibers pass between an entrance die and an exit die. This creates a linear velocity great enough to overcome the kinetic energy of an air boundary layer traveling along with the fibers through the die entrance. Thus, the method and apparatus is capable of accurately and efficiently coating optical fibers while eliminating unwanted air pockets. [0011] More specifically, the present invention relates to an apparatus for applying a coating of a water barrier fluid, such as a gel to an optical fiber including a die having an entrance side and exit side. An orifice is formed in the die which extends through the entrance side and exit side in a width-wise direction, and which is dimensioned to allow for an optical fiber to be drawn therethough. A cavity is formed in the die, and is in fluid communication with the orifice. A fluid insertion opening is formed in the die for injecting fluid into the cavity. When a fluid is injected into the cavity it travels through the cavity and out of a circumferential exit gap, such that it coats a portion of the optical fiber. The circumferential gap is formed at a meeting point between an inner portion of the cavity and the respective orifices of the entrance and the exit die. [0012] The present invention still further provides for an apparatus for applying a coating to several optical fibers or a bundle of optical fibers, including an entrance die having an orifice which is dimensioned to allow for a bundle of optical fibers to be drawn therethrough. Also, an exit die having an orifice is provided. The entrance die and the exit die, respectively, have inner sides, which define a cavity. The cavity is in fluid communication with the orifice of the entrance die and the orifice of the exit die, such that a circumferential gap is formed at a meeting point between the cavity and the respective orifices of the entrance die and the exit die. Thus, the circumferential gap is radially surrounded by an extension of the cavity, to define a critical flow region. A plurality of baffles are formed in the exit die, which are operative to inject fluid into the cavity. Also provided is a main body, which supports the entrance die and the exit die. The main body includes a passageway which is in fluid communication with the plurality of baffles. A retaining ring is also included, which secures the entrance die and the exit die to the main body. [0013] Additionally, when fluid is passed through the circumferential gap toward the plurality of fibers it travels at a velocity which is sufficient to overcome kinetic energy of an air boundary layer traveling along with the optical fibers drawn through the entrance die, prior to the fibers being drawn through the exit die. [0014] Still further the invention provides for a method of applying a water barrier fluid, such as a gel to one or more optical fibers, including the steps of drawing an optical fiber through an orifice formed in a die; and injecting a fluid into a cavity formed in the die, wherein the cavity is in fluid communication with the orifice, and wherein the fluid is pressurized out of the orifice and onto the optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS [0015] The advantages, nature and various additional features of the invention will appear more fully upon consideration of illustrative embodiments of the invention which are schematically set forth in the drawings, in which: [0016] FIG. 1 is front view of an exemplary arrangement of fibers having a gel provided thereon, according to the present invention; [0017] FIG. 2 is an exploded perspective view of an applicator according to the present invention; [0018] FIG. 3 is a sectional view of an applicator according to the present invention being supported by a base; and [0019] FIG. 4 is an enlarged sectional view of a critical flow region of the applicator. DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS [0020] The present invention will be explained in further detail by making reference to the accompanying drawings, which do not limit the scope of the invention in any way. Continue reading... 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