FIBER COATING ASSEMBLY HAVING A COOLED GUIDE DIE AND METHOD OF USING THE SAME

Abstract: A coating assembly for applying a coating to an optical waveguide fiber includes a guide die having a guide die land region (48), a sleeve for containing pressurized coating material (34), a sizing die (38), and a cooling mechanism (40) operatively associated with the guide die to cool the guide die so that a temperature of the pressurized coating material in an area adjacent the guide die land region is lowered. Maintaining the coating at a relatively cool temperature reduces the likelihood of coating flood.

Description: FIBER COATING ASSEMBLY HAVING A COOLED GUIDE DIE AND METHOD OF USING THE SAME BACKGROUND OF THE INVENTION This invention relates to a novel coating assembly for coating optical waveguide fibers and a method of using the same to suppress coating floods. More specifically, the invention relates to a coating assembly for coating optical fibers that includes a cooling mechanism to suppress flooding of the optical waveguide coating in a guide die. Optical waveguide fibers must exhibit high strength in order to withstand the stresses encountered in incorporating them into a protecting sheathing or cable, installing the cable, and fiber use. While fibers are typically strong as drawn from the preform, this strength is rapidly degraded by surface defects which are introduced into the fiber through handling. To preserve the strength of a newly drawn fiber, it is conventional to apply one or two protective coating layers to the fiber immediately after it is drawn to protect the fiber from surface abrasion. The coating layers generally are composed of an organic or inorganic coating material. In the two layer embodiment, a first, or primary, coating is applied directly to the fiber, and a second, or secondary, coating is applied over the primary coating. The coating steps are typically performed as an integral part of the fiber manufacturing process to ensure that the coating material is applied before the pristine surface of the fiber is damaged. An assembly for coating glass optical waveguide fibers is disclosed in U.S. Patent No. 4,531,959, the relevant portions of which are hereby incorporated by reference, and is shown in Figure 1. The coating assembly 10 generally includes a guide die 12, a flow distribution sleeve 14 positioned below the guide die 12, and a sizing die 16 following the sleeve 14. The coating assembly 10 is shown mounted in a support structure 17. To produce an optical waveguide fiber, drawn fiber material enters the coating assembly 10 through the guide die 12, in the direction of arrow A. Coating material is delivered to the coating assembly 10 through apertures 22 in the sleeve 14. The coating material is delivered under pressure and at a constant temperature via conduits in the direction of arrows B. An upper meniscus of coating material generally forms in the guide die land region 18 at the interface between the fiber and the coating material, as will be explained below in more detail. As the fiber passes through the coating assembly 10, the coating material is accelerated. When the coating material and the fiber enter the sizing die 16, a portion of the coating material is pulled out of the sizing die 16 with the fiber, coating it. Coating material that is not pulled out with the fiber is recirculated within the coating assembly 10. Each element of the coating assembly has a role in producing the coated fiber. The sizing die sets the amount of coating that is applied to the fiber. By tapering the exit of the sizing die, it also performs the function of centering the fiber so that the coating is concentric. See, for example, U.S. Patent No. 4,246,299. A method of controlling the coated diameter is disclosed in U.S. Patent No. 5,366,527, the specification of which is hereby incorporated by reference. The method, referred to as TCSD for Temperature Controlled Sizing Die, involves varying the local temperature of the sizing die to vary the coating viscosity within the sizing die. A lower coating temperature corresponds to a higher coating viscosity. Consequently, a cooler die applies less coating to an optical fiber, and a hotter die applies more coating. Situated above the sizing die, the flow distribution sleeve maintains the coating material under pressure between the sizing die and the guide die. As previously stated, the coating is delivered under pressure at a constant temperature. The fluid pressure of the coating should be sufficiently high that a meniscus forms in the vicinity of the guide die orifice, at a low position along the guide die land region, and not at the lower end of the sleeve. The guide die functions as a cap to the pressurized coating assembly and prevents the coating from flowing out of the top of the coating assembly. When the guide die fails to perform this function due to under- or over-pressurization within the coating assembly, a so-called "coating flood" occurs, and the draw process must be interrupted. Interrupting the draw process is expensive because it decreases machine utilization and reduces the length of useable fiber produced at the draw. At high draw speeds, the incidence of coating flood increases. The conventional practice to minimize the risk of coating flood is to make the guide die smaller for higher draw speeds. For example, fiber draw processes on the order of 20 m/sec or more typically use coating guide dies having a 20 mils (508 μm) internal orifice diameter or smaller, and these orifice diameters typically must be made even smaller if increased draw speeds are employed. Obviously, the more narrow the orifice, the greater the chance of abrasion by the fiber coming in contact with the orifice walls. Consequently, it is difficult to increase the draw speed above 20 m/sec without also increasing the susceptibility of the fiber to further abrasions caused by the more narrow orifice of the coating guide die. This conventional approach works fairly well in practice and is consistent with the theoretical understanding of fluid mechanics in a guide die, i.e., that smaller guide dies have higher over-pressurization limits. A significant drawback to using smaller guide dies, however, is that the fiber is more susceptible to pre-coating abrasions. The clearance between the fiber and the guide die decreases as the guide die orifice is decreased. Fiber vibration and draw misalignment are inevitable under production conditions. When the fiber is perturbed from the guide die centerline, as occurs during fiber vibration or draw misalignment, the fiber is more likely to rub against the wall of the smaller-diameter guide die. This rubbing is called pre-coating abrasion, as it occurs before the coating is applied. Pre-coating abrasions are detrimental because they can dramatically weaken the fiber and/or create coating defects. A weakened fiber is more likely to break at the draw, in off-line proof testing, or in the field. Thus, while the use of smaller guide dies may somewhat remedy coating flood at high speeds, the smaller guide dies also increase the likelihood of undesirable pre-coating abrasions. The difficulties suggested in the preceding are not intended to be exhaustive but rather are among many which tend to reduce the effectiveness of conventional fiber coating assemblies and methods of fiber coating. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that such apparatuses and methods appearing in the past will admit to worthwhile improvement. SUMMARY OF THE INVENTION There are several advantages achieved by the present invention. For example, the invention provides a fiber coating assembly that will minimize coating flood at high draw speeds. Another advantage of the invention is that the fiber coating assembly operates at a high speed and in a stable fashion. Yet another advantage of the invention is that the fiber coating assembly employs a relatively large diameter guide die to minimize the incidents of pre-coating abrasions. A preferred embodiment of the invention which is intended to accomplish at least some of the foregoing advantages includes a coating assembly having a guide die with a die land region, a sleeve for containing pressurized coating material, and a sizing die. The coating assembly further includes a cooling mechanism operatively associated with the guide die to cool the guide die so that a temperature of the pressurized coating material in an area adjacent the guide die land region is lowered. The cooling mechanism operates as a heat sink. The mechanism locally cools the pressurized coating material and reduces viscous heating generated at high draw speeds. Uncontrolled viscous heating would otherwise lead to a lowering of coating viscosity, increasing the likelihood of coating flood. Accordingly, the present coating assembly maintains the pressurized coating material near the guide die land region at a relatively cool temperature, which reduces the likelihood of coating flood in the guide die. The cooling mechanism may be mounted to an outer wall of the guide die. The cooling mechanism may completely encircle at least a section of the outer wall, or, alternatively, the cooling mechanism may intermittently encircle the outer wall to spot cool the guide die. Although it is most important that the lower third of the guide die's outer wall be cooled, the cooling mechanism may extend along the entire length of the outer wall. The cooling mechanism may comprise a cooling jacket mounted around the guide die and a fluid communication line to transfer cooling fluid (gas or liquid) to the cooling jacket. In another embodiment, the cooling mechanism may comprise a thermoelectric chip in thermal communication with the guide die. The thermoelectric chip operates as a heat pump to draw heat from the guide die, thus cooling the coating fluid in a region adjacent the guide die. A method for preventing coating flood in an optical waveguide coating assembly in accordance with the invention comprises the steps of passing an optical waveguide fiber through a guide die and a coating sleeve containing pressurized coating material, and maintaining the guide die at a temperature less than 90 C. The guide die may also be maintained at a temperature lower than an inlet temperature of the coating material; that is, at a temperature lower than the temperature of the coating material as it enters the coating sleeve of the coating assembly. In other words, the guide die is maintained at a temperature lower than it would be in the absence of any active cooling. The guide die may be maintained at a relatively cool temperature by mounting a cooling mechanism to the guide die. For example, a cooling jacket may be mounted to an outer wall of the guide die. Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate a presently preferred embodiment of the invention, and, together with the general description given above and the detailed description of the preferred embodiment given below, serve to explain the principles of the invention. Figure 1 is a cross-sectional view of a conventional coating assembly for coating optical waveguide fibers; Figure 2 is a cross-sectional view of a coating assembly for coating optical waveguide fibers in accordance with the invention; Figures 3A-3C are cross-sectional views of a guide die and sleeve of a conventional coating assembly that show possible meniscus configurations in the guide die land region of the guide die; Figure 4 is a cross-sectional side view of a second embodiment of a coating assembly for coating optical waveguide fibers in accordance with the invention; Figure 5 is a cross-sectional side view of a third embodiment of a coating assembly for coating optical waveguide fibers in accordance with the invention; and Figure 6 is a cross-sectional side view of a fourth embodiment of a coating assembly for coating optical waveguide fibers in accordance with the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, wherein like numerals indicate like parts, and initially to Figure 2, there will be seen a coating assembly, generally indicated 30, for coating optical waveguide fibers in accordance with the invention. The coating assembly 30 is particularly suited to coating optical waveguide fibers at draw speeds faster than 5 m/sec, when coating flood conditions may arise, such as, for example, 20 m/sec or greater, more preferably 25 m/sec or more, and most preferably 30 m/sec or more. The coating assembly includes a guide die 32, a flow distribution sleeve 34 having apertures 36 for passage therethrough of a coating material 37, and a sizing die 38. Various coating materials such as UV curable, heat curable, and thermoplastic polymeric materials are suitable for use in the present coating assembly. The coating material is delivered through apertures 36 under pressure at a constant temperature, namely, the inlet temperature. Maintaining the coating material under pressure insures that the level of coating material inside the die assembly is maintained at substantially the same level throughout the fiber manufacturing process. The coating assembly 30 also includes a cooling mechanism 40 operatively associated with the guide die 32 to cool the guide die 32, particularly a guide die land region 48, so that the temperature of the pressurized coating material 37 in an area adjacent to the guide die 32 is lowered. In Figure 2, the cooling mechanism 40 is mounted to and encircles an outer wall 42 of the guide die 32. The cooling mechanism 40 serves as a localized heat sink to cool the guide die 32. Locally cooling the guide die 32 suppresses coating flood at high draw speeds, as will be described below in more detail. When an uncoated fiber 44 (or a fiber with only a primary coat) enters the coating assembly 30 through the guide die 32, an upper meniscus 46 of coating material 37 is formed at the interface between the fiber 44 and the coating material 37. This upper meniscus 46 can assume generally three configurations in the guide die land region 48, as shown in Figures 3 A to 3C. The meniscus 46a can be pinned at the corner of the guide die land region, as shown in Figure 3A. The meniscus 46b can float within the guide die land region, as shown in Figure 3B. Finally, the meniscus 46c can rise near the top of the guide die land region or even higher, as shown in Figure 3C. This last configuration represents a coating flood condition, where the upper meniscus becomes visible to an observer looking down into the guide die. Optical waveguide fibers can be more economically produced by increasing the fiber draw speed. However, at fast draw speeds, such as, for example, 20 m/sec or greater, more preferably 25 m/sec or more, and most preferably 30 m/sec or more, the draw process becomes more challenging and the likelihood of coating flood increases. Coating assemblies have a window of stable operation. The upper limit of that window represents the maximum pressure that can be supported by the coating assembly at a given speed without coating flood. The limit is sometimes referred to as an "over-pressurization limit. " If this limit is exceeded, the upper meniscus swells, i.e., the coating material rises in the guide die land, and coating material may leak out the top of the coating assembly through the guide die. This condition is shown in Figure 3C. Experimental data shows that the over-pressurization limit decreases at higher coating speeds, such as draw speeds in excess of 5 m/sec, for example, 20 m/sec or greater, more preferably 25 m/sec or more, and most preferably 30 m/sec or more. For these high draw speeds, there is a lack of correlation between models used to predict the over-pressurization limit and experimental data. The models apparently do not account for phenomena that occur at higher draw speeds. A hypothesis for explaining this divergence is that, as the draw speed is increased, the viscosity of the coating in the guide die land region decreases below a nominal value corresponding to the inlet temperature of the coating, that is, approximately 50 C. Two mechanisms are likely to cause this localized decrease in the coating viscosity: shear thinning and viscous heating. Shear thinning is a phenomenon commonly seen with non-Newtonian fluids, such as polymers. As the fluid is subjected to larger shear rates, the molecules in the fluid align themselves such that the fluid's viscosity drops below its value at zero shear. Viscous heating is a phenomenon seen with both Newtonian fluids and non- Newtonian fluids. As fluid is subjected to larger shear rates, friction between the fluid molecules generates heat. This generation of heat locally increases the temperature of the fluid. In the case of optical waveguide fibers, shear stresses develop due to the speed of the fiber through the coating material. These shear stresses generate heat and raise the temperature of the coating material. An increase in the coating material's temperature decreases its viscosity. A significant amount of viscous heating occurs in the guide die land; this viscous heating can cause local coating temperatures greater than the inlet temperature of the coating. The increase in temperature significantly decreases coating viscosity in the guide die land region. Therefore, the inventors of the subject application have determined that viscous heating is the primary mechanism that causes the over-pressurization limit to decrease at high fiber draw speeds. Accordingly, the cooling mechanism 40 manages and lowers the temperature in the guide die land region 48 by removing heat via conduction through the guide die wall 42. Referring back to Figure 2, extraction of heat from the guide die wall 42 is accomplished via the cooling mechanism 40, which is in the form of a cooling jacket. Locally cooling the guide die land region reduces the coating temperature rise generated by viscous heating. A lower coating temperature corresponds to a higher coating viscosity. A higher coating viscosity increases the over-pressurization limit of the coating assembly, which makes the coating assembly less susceptible to flooding. The cooling jacket 40 shown in Figure 2 is placed around, and completely encircles, the outer wall 42 of the guide die 32. Because the guide die diffuses heat, temperature control of the outer wall 42 will change the temperature of the inner wall, including the land region 48, of the guide die. Thus, the cooling jacket 40 is capable of lowering the temperature of the outer wall 42, thereby lowering the temperature of the inner wall. The cooling jacket 40 includes fluid conduits 50 attached thereto, through which cooling fluid (gas or liquid), such as chilled helium or chilled water, passes to maintain the temperature of the cooling jacket 40 at an optimal cooling temperature. Fluid passes through an entry conduit into the cooling jacket 40 and then passes out an exit conduit in the direction indicated by arrows C. The optimal temperature of the cooling fluid may be varied to vary the temperature of the cooling jacket 40. Once determined, the optimal temperature of the cooling jacket 40 is preferably maintained constant. The optimal temperature is determined by experimentation or mathematical modeling. The coating assembly 30 may further include a temperature control member 49 mounted adjacent the sizing die 38, preferably to a base of the sizing die 38. The temperature control member 49 controls the coating diameter of the fiber as it is drawn through the sizing die, as disclosed in U.S. Patent No. 5,366,527. It will be understood by those of skill in the art that the cooling jacket 40 may be designed in alternative manners to achieve the same cooling effect. For example, the cooling jacket may be designed to extend along only part of the length of the guide die outer wall 42. In one embodiment, the cooling jacket 40 extends only along the lower section of the guide die outer wall 42. The cooling jacket preferably extends, for example, at least as long as the length in Figure 2, corresponding to the lower third of the outer wall. This length approximates the length of the land region 48, defined here as the region where the internal diameter of the guide die remains substantially constant. In such an embodiment, cooling is localized to the most significant region of the guide die in that, under normal conditions, the coating material resides in this lower guide die land region. However, because heat diffusion occurs throughout the guide die, heat will be drawn from all regions, including the upper section, of the guide die. In another embodiment, the cooling mechanism may intermittently encircle the outer wall of the guide die. In other words, the cooling mechanism does not "jacket" the outer wall of the guide die, but rather thermally communicates with it only in certain spots to spot cool the guide die. Because heat diffuses throughout the guide die, cooling the outer wall of the guide die only in certain spots will prove satisfactory in many circumstances. In a second embodiment of the present invention, as shown in Figure 4, the cooling jacket 40 may be controlled by an external control system 52 that determines an optimal temperature based on data gathered from a sensor 54 mounted to the guide die. The sensor 54 monitors information indicative of viscous heating in the area of the guide die land region 48. For example, the sensor 54 may monitor the temperature of the guide die of the inner wall at the guide die land region, or it may monitor the height of the upper meniscus in the guide die land region. The control system 52 communicates with a temperature control system 56 that controls the temperature of the cooling fluid (gas or liquid) in response to data from the control system 52. The cooling fluid temperature is varied, depending on sensed conditions in the guide die land region, to maintain optimal operating conditions. This embodiment may be used where experimentation has resulted in a data set of sensed variables, such as guide die inner wall temperature and upper meniscus height, and corresponding optimal temperatures. A third embodiment of the present invention is shown in Figure 5. A guide die 60 is positioned above a flow distribution sleeve 62, which, as in the previous embodiments, serves as the entrance for the coating material 64 into the coating assembly. A sizing die 66 is positioned below the flow distribution sleeve 62. In this embodiment, the guide die 60 has a generally planar upper surface. A thermoelectric chip 68 is located on an upper surface of the guide die 60 and thermally communicates with the guide die 60. The thermoelectric chip 68 employs the Peltier effect to operate as a heat pump to cool the guide die 60. For details on the Peltier effect, see, for example: Caillat et al. , "Thermoelectric properties of (BixSbι-x) 2 Te2 Single Crystal Solid Solutions Grown by the T.H.M. Method," J. Phys. Chem. Solids, vol. 53, no. 8, pp. 121-29, 1992. As a heat pump, the thermoelectric chip 68 requires a thermal reservoir to remove heat from the top of the chip 68. The reservoir (not shown) may consist of a heat sink that is in thermal communication with the chip 68. The temperature of the heat sink is maintained at a constant level with, for example, a recirculating water or liquid bath. To cool the guide die 60, the heat sink removes heat from the top surface of the thermoelectric chip 60. This in turn removes heat from upper surface of the guide die 60, and thus from guide die land region, which cools the temperature of the coating material in the guide die land region. Cooling the coating material reduces viscous heating and increases the coating viscosity, increases the over-pressurization limit, and consequently decreases the likelihood of coating flood. The voltage level and the polarity applied to the thermoelectric chip 68 can be adjusted to control the temperature of the guide die 60. Figure 6 shows a fourth embodiment of the present invention. Like the embodiment of Figure 5, a guide die 70 is positioned above a flow distribution sleeve 72, which serves as the entrance for the coating material 74 into the coating assembly. A sizing die 76 is positioned below the flow distribution sleeve 72. In this fourth embodiment, the guide die 70 has an angled upper surface. A thermoelectric chip 78 is located on the angled, upper surface of the guide die 70 and thermally communicates with the guide die 70. This thermoelectric chip 78 operates in the same way as the thermoelectric chip 68 of Figure 5. The coating assembly of Figure 6 also includes a thermocouple device 80 located on an inner surface of the guide die 70 in the guide die land region 82. The thermocouple device 80 measures the temperature of the land region 82. This temperature reading then may be used to control operation of the thermoelectric chip 78 to appropriately cool the guide die 70. The thermocouple device 80 is located in a thermocouple access hole 84 bored through the guide die 70. Two leads 86a and 86b of the thermocouple device 80 extend through the access hole 84 to an exterior of the guide die 70 so that temperature readings may be taken. These temperature readings may be fed to a controller (not shown) that is electrically connected to the thermoelectric chip 78. The controller may then adjust the voltage or current applied to the thermoelectric chip 78 to control its temperature. The thermocouple access hole 84 is preferably filled with an epoxy material. The present coating assembly may be used to apply a coating layer to a bare fiber or to an intermediate coated layer that has previously been applied to the fiber to obtain a composite coating. A method for preventing coating flood in an optical waveguide coating assembly in accordance with the invention comprises the steps of passing an optical waveguide fiber through a guide die and a coating sleeve containing pressurized coating material, and preferably maintaining the guide die at a temperature less than 90 C, more preferably at a temperature less than 75 C, and most preferably less than 60 C. The guide die may also be maintained at a temperature less than an inlet temperature of the coating material, such as less than 50 C. Without attempting to set forth all of the desirable features of the present invention, the present invention provides a coating assembly that is capable of operating at a high draw speed and that addresses the problem of coating flood without resort to a small orifice guide die. Prior to the present invention, guide dies having small orifices have been employed at high draw speeds. Fiber manufacturers have resorted to small orifice guide dies because of the fluid dynamic phenomenon occurring at high draw speeds. As the draw speed increases, viscous heating occurs. The viscous heating lowers the coating viscosity in the guide die land region. Low coating viscosity leads to a lower over-pressurization limit and may result in coating flood. Smaller orifice guide dies remedy coating flood by increasing the over-pressurization limit. In the past, guide dies having a minimum orifice diameter of approximately 20 mils (508 μm) or smaller have been used for draw speeds of approximately 20 m/sec or faster. The orifice diameter must generally be decreased as the speed increases. For example, in processes having draw speeds of 25 m/sec or more, prior to the present invention, guide dies having internal diameters of as small as 13 mils (330.2 μm) had to be employed to successfully coat the fiber. An undesirable side effect of a smaller orifice guide die is an increased risk of pre-coating abrasions. By utilizing the cooled guide die assembly of the present invention, however, speeds in excess of 25 m/sec, and even 30 m/sec, can be achieved in guide dies having minimum orifice diameters greater than 15 mils (381 μm), and more preferably 20 mils (508 μm) or more. The cooling mechanism of the present coating assembly locally cools the coating material and lowers viscous heating that occurs at high draw speeds. Lowering the temperature of the coating material in the guide die land region lowers coating viscosity, which increases the over-pressurization limit and decreases the incidence of coating flood. Thus, the present invention permits use of a relatively large diameter guide die at a fast draw speed, absent the high risk of pre- coating abrasions. Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, and representative devices, shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims.

Claims: WE CLAIM 1. A coating assembly for applying a coating to an optical waveguide fiber, comprising: a guide die; a sleeve for containing pressurized coating material; a sizing die; and a cooling mechanism operatively associated with said guide die to cool said guide die. 2. An assembly as claimed in claim 1, wherein said guide die includes an outer wall and said cooling mechanism is mounted to said outer wall. 3. An assembly as claimed in claim 2, wherein said cooling mechanism completely encircles at least a section of said outer wall of said guide die. 4. An assembly as claimed in claim 3, wherein said cooling mechanism extends along an entire length of said outer wall of said guide die. 5. An assembly as claimed in claim 2, wherein said cooling mechanism intermittently encircles said outer wall to spot cool said guide die. 6. An assembly as claimed in claim 1, wherein said cooling mechanism comprises a cooling jacket mounted around said guide die and a fluid communication line to transfer cooling fluid to said cooling jacket. 7. An assembly as claimed in claim 1, wherein said cooling mechanism comprises a thermoelectric chip in thermal communication with said guide die. 8. An assembly as claimed in claim 7, wherein said assembly further comprises a sensor mounted to said guide die for measuring at least one of a temperature of said guide die and a height of coating material in said guide die, and a controller for electrically communicating with said sensor and said thermoelectric chip. 9. An assembly as claimed in claim 8, wherein said sensor is a thermocouple device. 10. A method for preventing coating flood in an optical waveguide coating assembly, comprising the steps of: passing an optical waveguide fiber through a guide die and a coating sleeve containing pressurized coating material; and maintaining said guide die at a temperature less than 90 C. 11. A method as claimed in claim 10, wherein said guide die is maintained at a temperature less than 75 C. 12. A method as claimed in claim 10, wherein said guide die is maintained at a temperature less than 60 C. 13. A method as claimed in claim 10, wherein said guide die is maintained at a temperature less than an inlet temperature of the pressurized coating material. 14. A method as claimed in claim 13, wherein the inlet temperature is approximately 50 C. 15. A method as claimed in claim 10, wherein said maintaining step comprises utilizing a cooling mechanism to cool said guide die. 16. A method as claimed in claim 15, wherein said cooling mechanism in said utilizing step comprises a cooling jacket mounted to an outer wall of said guide die. 17. A method of coating an optical waveguide fiber comprising the steps of: passing an optical waveguide fiber through a guide die containing pressurized coating material at a speed of 25 m/sec or greater; and during said passing step, maintaining said guide die at a temperature sufficient to enable complete coating of the fiber, said guide die having a minimum internal diameter of 15 mils or greater. 18. A method as claimed in claim 17, wherein said passing step comprises passing the fiber through the guide die at a speed of 30 m/sec or greater. 19. A method as claimed in claim 17, wherein said guide die has a minimum internal diameter of 20 mils or greater. 20. A method for preventing coating flood in an optical waveguide coating assembly, comprising the steps of: passing an optical waveguide fiber through a guide die and a coating sleeve containing pressurized coating material; and maintaining said guide die at a temperature less than a temperature of said guide die in the absence of any active cooling.

Inventors: ABBOTT JOHN S III, CHLUDZINSKI PAUL A, NEILSON DOUGLAS G, ABBOTT, JOHN, S., III, CHLUDZINSKI, PAUL, A., NEILSON, DOUGLAS, G.
Applicants: CORNING INC, CORNING INCORPORATED
Application year: 1999
Main classification: G02B6
IPC codes: C03C25, G02B6