FR2604169A1 - Process and apparatus for the manufacture of a fluoride glass fibre which has a coating layer - Google Patents

Abstract

Apparatus for the manufacture of a fluoride glass fibre which has a three-layered structure consisting of a fluoride glass core, a fluoride glass sheathing layer and a coating layer, which are made in a single operation, employs an airtight receptacle 16 containing an inert gas or a fluorine-containing gas.

Description

 The present invention relates to a method and apparatus for manufacturing, by a drawing method using crucibles, a fluoride glass fiber having reduced attenuation, long, mechanically resistant and having a coating layer.

 The fluoride glass fiber, whose minimum weakening af is theoretically estimated at 0.001 db / km, is now attracting attention because it is particularly interesting for the realization of the transmission line of an undersea cable. long-distance international optics or an optical transmission system without an amplifier. For use as a long-distance transmission line of this type, fluoride glass fiber must be manufactured in a length of at least 10 kilometers without breaking. The crucible process was previously envisioned as a process for the manufacture of such a long fluoride glass fiber, but it has not been used in practice, due to difficulties in forming a core structure of the fiber-cladding due to glass instability.

However, it has recently been reported that fluoride glass fiber can be made even by the crucible method using 53Zr-20Ba-20Na-4La-3A1 for the fiber core and 39.7Zr-13.3Hf- 18Ba-22Na-4La-3A1 for the cladding layer (Elect. Letters, Nov. 1985,
Flight. 21, No. 24). The application of fluoride glass fiber to the current transmission line requires coating the film with a layer which protects its surface and increases its resistance.

 However, no satisfactory manufacturing process and apparatus has so far been proposed to meet the demand for coating a long glass fiber with fluoride without lowering its transmission characteristics and its mechanical strength.

 One of the aims of the present invention is to create a method and an apparatus for manufacturing a coated fluoride glass fiber, which allows the formation of a coating layer around a long fluoride glass fiber without degradation. its transmission characteristics and its mechanical resistance.

 The present invention is characterized in that, in a single operation, a fluoride glass fiber is formed having a three-layer structure consisting of the core, the cladding layer and the coating layer while maintaining the glass melting section and the stretching section protected from direct contact with air. This allows the coating layer to form without allowing the fiber glass and the cladding glass to react with oxygen and moisture. air and therefore prevents degradation of transmission characteristics.

 The manufacturing process of the present invention comprises a first stage in which the glass of the fiber core and the cladding glass, both made of fluoride glass, are melted in an inert atmosphere or in a series gas. of fluorine a second stage, in which the temperature of the molten glass masses is adjusted to a drawing temperature in a second atmosphere of inert gas and the temperature of a coating material is adjusted so that it is not not broken down at drawing temperature, but has a viscosity equal to or less than the viscosity of the molten glass; and a third stage in which a three-layer structure consisting of the fiber core, the cladding layer and the coating layer is formed in one go.

 The manufacturing apparatus of the present invention includes a glass melting section having first heating means for melting the fiber core glass and the cladding glass, both made of fluoride glass and first means introducing a gas to produce an atmosphere of an inert gas or a fluoride gas; a drawing section comprising a double crucible having two nozzles arranged concentrically to receive the molten glass masses coming from the glass melting section, a container of coating material arranged outside the double crucible and having a nozzle formed concentrically to this, at least a second heating means for heating the glass of the fiber core and the cladding glass in the double crucible and the coating material in the container to the desired temperature, a second means of introduction of gas to achieve an atmosphere of an inert gas, and a winding section in which a three-layer structure consisting of the fiber core, the cladding layer and the coating layer, is pulled out of the drawing section, is formed in one go and the glass fiber thus coated is wound on a winding means.

 Various other characteristics of the invention will also emerge from the detailed description which follows.

 An embodiment of the object of the invention is shown, by way of nonlimiting example, in the accompanying drawings.

 Fig. 1 is a diagram of an apparatus for manufacturing a fluoride glass fiber using a conventional double crucible method.

 Fig. 2 is a diagram of an apparatus for manufacturing a fluoride glass fiber in accordance with the present invention.

 Fig. 3 is a diagram illustrating on an enlarged scale a nozzle structure in the manufacturing apparatus of the present invention.

 Fig. 4 is a diagram illustrating another example of a stretching section B in the manufacturing apparatus of the present invention.

 To explain the differences between the prior art and the present invention, an example of the prior art will first be described.

A thermosetting or hardened resin
UV has been used as a coating material for optical fibers of the prior art. Fig. 1 shows a conventional method of forming the coating layer in the drawing method using crucibles. The reference 1 indicates the glass for the core of the fiber (hereinafter referred to as glass for the fiber), 2 the glass for cladding (hereinafter referred to as cladding glass), 3 a crucible for glass 1, 4 a crucible for glass 2, 5 an electric oven for heating crucibles for melting glass, 6 a control instrument for controlling the diameter of the fiber, 7 a container for coating the fiber with resin, 8 a coating material (a coating resin), 9 an oven for solidifying the resin applied to the fiber, 10 a drive roller for drawing the fiber, 11 a fiber winding drum, and 40 the current fiber stretching.

 The manufacture of the coated glass fiber by the apparatus shown, begins by heating the glass 1 for the core of the fiber and the cladding glass 2 to a drawing temperature by means of the electric oven 5, followed by the drawing of the fiber while adjusting the speed of rotation of the drive roller .10 so that the diameter of the fiber measured by the control device 6 is kept constant. After adjusting the drive speed of the drive roller 10 for drawing a fiber having the desired constant diameter, the coating container 9 is placed in a predetermined position, in which the coating resin 8 is brought. The resin 8 is applied so as to form a thin layer on the fiber 40 when the latter passes through a small diameter orifice made at the bottom of the container 7, and the resin thus applied is solidified by the furnace 9, forming the coating layer .

 The application of this process to the coating of. fluoride glass fiber poses a problem because fluoride glass is much more reactive than oxide glass (quartz glass, multi-component glass, etc.) used until now. That is, the mass of molten glass (a meniscus) pulled out of the crucible when exposed directly to air, reacts with oxygen and humidity in the air, which leads to precipitation of the crystalline phase in the surface of the fiber, thus increasing the loss of transmission of the fiber, and reducing its resistance. To avoid this, it is necessary, in the manufacture of fluoride glass fiber, that the mass of glass melted at high temperature is placed in a completely inert atmosphere.

However, as the fiber 40 is drawn continuously from the crucibles 3 and 4 towards the winding drum 11, it is extremely difficult to maintain, in the atmosphere, only the meniscus of the mass of molten glass; therefore, the conventional method described above is not suitable for use in the coating of fluoride glass fiber.

 Thus, there was no satisfactory manufacturing process and apparatus that would meet the pressing demand for coating long fluoride glass fibers without lowering their transmission characteristics or mechanical strength.

 The present invention will be described below in detail with reference to FIGS. 2 to 4.

 Fig. 2 is a diagram showing the apparatus of the present invention, which apparatus generally comprises a glass melting section A, a stretching section B and a winding section C. As the winding section C is identical in construction to that used in the example of the prior art shown in FIG. 1, only the glass melting section A and the drawing section B which constitute the essential point of the present invention will be described below in detail.

 The glass melting section A comprises crucibles 12 for melting fluoride glass, a glass melt 13 for the fiber core, a sheath glass melt 14, a frame 15 for carrying the crucibles 12, a container 16 for holding the molten glass masses 13 and 14 in an inert gas atmosphere, a cover 17 for the container 16, a gasket 18 for sealing the air between the container 16 and its cover 17, a gas inlet orifice 19 which is a first means for introducing the gas to produce an atmosphere of inert gas or fluoride gas surrounding the molten glass masses 13 and 14, a gas outlet orifice 20 associated with the first means for introducing the gas, inlet orifices 21 for an inert gas for extruding the masses of molten glass 13 and 14, and an electric oven 22 which is a first heating means for melting the fluoride glass.

The drawing section B comprises a gas inlet port 23 which is a second means for introducing gas to fill the container 16 with an atmosphere of inert gas, a gas outlet port 24 associated with the second means d introduction of the gas, pipes 25 for introducing the masses of molten glass 13 and 14 coming from the glass melting section A into the drawing section B, a gasket 26 for sealing the air between the glass melting section
A and the drawing section B, a crucible 27 for the glass for the core of the fiber, which is equipped with a nozzle, a crucible 28 for the cladding glass, which is also equipped with a nozzle arranged at the outside of the crucible nozzle 27, concentrically thereto, a mass of molten glass 29 for the core of the fiber, a mass of sheathed molten glass 30, a container of coating material 31 with a nozzle disposed outside that of the crucible 28, concentrically therewith, a thermoplastic coating material 32 which is not broken down at the drawing temperature of the molten glass masses 29 and 30 and having a viscosity equal to or less than the viscosity of the molten glass masses 29 and 30, a heater 33 which is a second heating means for keeping the molten glass masses 29 and 30 present in the crucibles 27 and 28 at the drawing temperature, a heater 34 which is another second heating means to adjust the viscosity of the gain material ge 32 at an appropriate value, a pipe 35 for introducing a gas into the container of coating material 31 to extrude therefrom the cladding material 32 with gas pressure, a gas pressure regulator 36 for regulating the pressure of the gas in the gas introduction pipe 35, and a high pressure gas inlet 37. As described below, an appropriate choice of the coating material 32 will allow the heater 33 to be omitted for crucibles 27 and 28 in which case the heater 34 for the coating material 32 will suffice as a second heating means.

 Fig. 3 is a diagram showing the stretching portion of the fiber carrying a coating layer of the stretching section B in the present invention. The crucible 27 for the glass for the core of the fiber and the crucible 28 for the cladding glass constitute a double crucible around which is placed the crucible for the coating material, and nozzles fixed to the lower end parts of the crucibles for glass for the fiber core, the cladding glass and the coating material are arranged concentrically in this order from the inside to the outside. To prevent the molten glass mass 29 for the fiber core , the mass of sheathed molten glass 30 and the coating material 32 to flow out of the respective nozzles before the drawing operation, there is provided a lower pad 38 carrying protrusions in several stages which conform to the parts of end of the nozzles, and a rod 39 for moving the lower pad 38 up and down.

 As described above, the fluoride glass making apparatus of the present invention has a construction in which the glass melting section A and the drawing section B are arranged in sealed containers separate air and in the stretching section B, the molten glass mass 29 for the fiber & e, the cladding glass mass 30 and the coating material 32 can be stretched simultaneously without exposure to the air.

 A description will be given in the following of the manufacture of the fibers using the apparatus of the invention of FIG. 2, using 53ZrF4-20BaF2-20NaF-4LaF3-3ALF3 as glass 13 for the fiber core, 39.7ZrF4-13.3HfF4-18BaF2-22NaF-4LaF3-3ALF3 as cladding glass 14, and fluorine rubber as coating material 32.

(1) First stage
(1) An inert gas such as argon, nitrogen or helium or a fluorinated gaseous derivative is introduced from the gas inlet orifice 19 to produce an atmosphere of inert gas or fluorinated gas in the chamber of the container 16 which is defined by the frame 15 and the cover 17 of the container 16. At the same time, an atmosphere of inert gas is produced in the drawing section B of the container 16.

 (2) Raw glass material for the fiber core and the cladding layer, introduced into the glass melting crucible 12, is melted by heating 8 8000C approximately with the electric oven 22 for one hour.

 (3) Next, the glass melts 13 and 14 are cooled to or around 500C.

 (4) Argon is introduced through the inert gas inlet 21 so that the glass melt 13 for the fiber friendliness and the cladding glass melt 14 are sent under the pressure of argon from the melting section of glass A to crucibles 27 and 28 of the drawing section B by pipes 25.

(2) Second stage
(5) The glass melt 29 for the friendliness of the fiber and the sheath melt 30 thus injected into the crucibles 27 and 28 are heated by the heater 33, to a drawing temperature of 3250C.

 (6) The fluororubber 32 introduced into the container of coating material 31 is melted by heating to around 2800C by means of the heater 34 which is the second heating means.

(3) Third stage
(7) Argon is injected through the high pressure gas inlet (37) and its pressure is adjusted by the regulator 36 to 1 bar.

 (8) The bottom pad 38 is moved with the rod 39 and the mass of the molten glass 29 for the fiber friendliness, the mass of molten glass of the cladding 30 and the molten mass of the coating material 32 are drawn to starting from the respective nozzles at a speed of 15 m / min, forming the fiber 40 of three-layer structure which is wound on the winding drum 11.

 Through the stages described above, a fluoride glass fiber with a three-layer structure, consisting of a body of 15 ttm in diameter, a cladding layer of 150 Fm in diameter and a coating layer of 5 m thick can be produced to a length of around 700 m without any break. The fiber 40 thus produced was not broken by operations such as winding on the drum 11. None of the factors which would decrease the strength of the fiber such as precipitation of the crystalline phase and "wounds" in the surface fiber, was only observed under the microscope.

 In the above, fluorinated rubber is used as a coating material 32, but there are many other resins whose quality would not change from the physico-chemical point of view at the drawing temperature (320-3300C) of the glass with fluoride and whose viscosities are equal to or less than the viscosity of the fluoride glass at the drawing temperature, such as fluorinated resins, polycarbonate resins and a chalcogenide glass. The use of these resins will not pose any problem in the practice of the invention. Among the fluorinated resins, a polymer of ethylene and of tetrafluoroethylene (ETFT) has a melting viscosity of 104 to 105 poises at 300 to 3309C, which is practically equal to the viscosity of the fluoride glass. description of an apparatus and a manufacturing process in the case of the use of such a resin as a coating material 32.

 Fig. 4 is a diagram showing another example of the stretching section B according to the present invention. This example differs from the stretching section of fig. 2 by omitting the heater 33 which is the second heating means for bringing the glass melt 29 for the fiber core 29 and the sheath melt 30 to the drawing temperature.

 As the omission of the heater 33 allows the inner wall of the material coating container 31 to also be used as a crucible 28 for the cladding glass, the crucibles 27 and 28 and the container 31 of the stretching section B can be combined in a triple crucible structure allowing the simplification of the apparatus.

 The manufacturing process is also simplified, because substages 5 and 6 of the second stage can be carried out at once by the heater 34.

 Although, in the manufacturing process described above, the material of fluoride glass has been specified for clarity, the present invention is also applicable to the manufacture of other fluoride glass fibers.

 As described above, in accordance with the present invention, since the fiber manufacturing stages are all carried out in controlled atmospheres, it is not possible for impurities to be mixed with the fiber as the phase crystalline precipitates in the surface of the fiber by reaction of oxygen with humidity, and that lesions in the fiber occur during the manufacturing process; that is, there are few factors which adversely affect the strength of the fiber. In addition, fiber manufacturing is easy to mechanize and automate. Therefore, the method and apparatus for manufacturing the coated fluoride glass fiber of the present invention have excellent production efficiency and industrial productivity.

 Consequently, the present invention allows the manufacture of a long fiber glass coated with fluoride, very resistant, of low cost, having a low transmission loss for use in optical communication, in particular. It is therefore very useful.

Claims (3)

Claims  1 - Apparatus for manufacturing a fluoride glass fiber, characterized in that the glass melting section provided for melting the fluoride glass for the friend of the fluoride glass fiber and the fluoride glass of the sheathing layer of fluoride glass fiber is disposed in an airtight container separate from the fiber stretching section to stretch fluoride glass fiber coated with a coating layer so that the fluoride glass layer of three-layer structure consisting of the core for the fiber, the cladding layer and the coating layer is formed in one go.  2 - Apparatus for manufacturing a coated fluoride glass fiber comprising: a glass melting section comprising a first heating means by which the glass for the fiber core and the glass for a sheathing layer of the fibers both made of a fluoride glass are heated to a temperature above their melting points, and a first means for introducing gas to produce an atmosphere of an inert gas or a fluoride gas to enclose therein the melts for the fiber core and the cladding layer; a drawing section in which the glass melts supplied from the glass melting section are drawn into a fiber, the drawing section comprising a double crucible provided with two nozzles arranged concentrically to accommodate glass melts in an inert gas atmosphere, a container of coating material disposed inside the double crucible and having a nozzle disposed concentrically with these two nozzles, at least one second heating means for heating the molten glass masses in the double crucibles and a coating material in the container at the desired temperature and a second gas introduction means for introducing the inert gas; and a winding section in which a three-layer structure consisting of the fiber friendliness, the cladding layer and the coating layer is formed in one step and the coated fluoride glass fiber thus obtained is wound on a winding drum.  3 - Process for manufacturing a coated fluoride glass fiber comprising: a first stage in which the glass for the core of the fiber and the glass for the sheathing layer of the fiber, both consisting of a glass fluorides are melted in a glass melting section maintained in an atmosphere of an inert gas or fluoride gas, and the molten glass masses are sent respectively to a double crucible having nozzles arranged concentrically, and placed in a stretch section maintained in an inert gas atmosphere; a second stage in which the temperature of the molten glass is adjusted to a value suitable for their drawing and the temperature of a coating material, which is introduced into the container for supplying a coating material disposed outside of the double crucible, concentric therewith, and provided with a nozzle and which is not decomposed at the drawing temperature, and adjusted so that the viscosity of the coating material can be equal to or less than the viscosity of the glass melts  and a third stage in which the coating material is extruded so as to adhere to the surface of the external mass of the molten masses of glass flowing from the nozzles of the double crucible which will ultimately form the cladding layer, so that a structure three-layer consisting of the fiber friendliness, the cladding layer and the coating layer is formed in one go.