MXPA00007825A - Optical fiber preform manufacturing apparatus and method for shrinkage and closing of deposited tube - Google Patents

Abstract

Disclosed are an optical fiber preform manufacturing apparatus and method in which processes for shrinking and closing a deposited tube are conducted using a device suitable for those processes, which device is other than the device used in a deposition process for forming the deposited tube on the inner surface of a preform tube, thereby reducing the processing time while reducing the amount of OH penetrated from the preform tube into a vitreous component of the deposited tube, thereby achieving a reduction in OH loss. In accordance with the optical fiber preform manufacturingapparatus and method, operations are conducted which involve setting the heating temperature of a circular heater to a temperature lower than the softening point of a deposited tube, exhausting contaminants existing in the interior of the deposited tube while moving the circular heater at a desired temperature, setting the heating temperature of the circular heater to a temperature not lower than the softening point of the deposited tube, and shrinking and closing the deposited tube while moving the circular heater to a desired temperature.

Description

APPARATUS FOR THE PREPARATION OF PREFORMED OPTIC FIBER AND METHOD FOR CONTRACTION AND CLOSURE OF A PIPE DEPOSITED BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for and a method of manufacturing a preformed optical fiber, and more particularly to an apparatus and method for making a preformed optical fiber to more effectively contract and close a deposited tube. 2. Description of Related Art It is well known to manufacture a preformed optical fiber using a modified chemical vapor deposition (MCVD) method. In a deposition process where a deposited layer is formed in the form of a tube on the inner surface of a preformed tube according to the MCVD method, the deposited tube contracts by itself as the thickness of the deposited layer increases gradually. For this purpose, a burner configured to have a large heating area while using a low flame pressure is normally used in the deposition process. The large heating area of REF: 122075 IitaUt i? I-burner makes it possible to allow an easy transfer of heat to the inner portion of a preformed tube, whereby an improved efficient deposition is achieved. On the other hand, the low flame pressure of the burner produces an undesirable reduced shrinkage of the deposited tube that occurs during the deposition process. However, it is necessary to use a high flame pressure in a process of contraction and closure of the tube directed to the deposited tube, as well as a different process of deposition. Where a convenient burner is used for the deposition process, when it is, for the shrinking and closing process, despite the aforementioned fact, it is necessary to move the burner at a low speed while maintaining a high heat temperature to allow the deposited tube soften to the low flame pressure used. As a result, the processing time of the tube shrinking and closing process occupies a large portion of the total processing time of the preformed optical fiber processing. For this reason, the conventional process of contraction and closure of the tube serves as a major obstacle to a reduction in processing time. The high temperature of heat and the low speed of movement of the burner in the shrink tube and tube closure results in a degradation in the optical characteristics of the finally produced optical fibers, as indicated below. That is, a moisture signal (generally, several ppm) contained in the preformed tube penetrates the layer deposited on the inner surface thereof. The penetrated moisture is coupled to P205 or Si02 of the deposited layer, whereby P-O-H or Si-O-H bonds are formed. OH that reaches the region of the center of the deposited layer is coupled to Si02 or Ge02 of the deposited layer, whereby the Si-OH or Ge-OH bonds are formed while releasing the Si-0 or Ge-0 bonds. . These OH or POH bonds resulting from the coupling of moisture to the compounds of the layer deposited in the respective regions of the deposited layer, serve to generate an optical loss in the optical fiber, finally produced, due to an established absorption band. in a specific wavelength range. The OH penetrated in the center layer forms the mono-oxygen, which results in a degradation in the structural uniformity of the vitreous components in the center layer. This causes non-uniformity in the density of the center layer. As a result, an increase in loss of recreation occurs.

Second, where the preformed tube is heated in a state of rotation at its lower end by the burner, a "circumferential temperature gradient occurs.The temperature gradient causes non-uniformity in the viscosity of the preformed tube., the balance of the tension of the surface in the deposited tube is lost, whereby the deposited tube is deformed in the shape. This causes an increase in the non-circularity of the deposited tube. As the contraction process progresses, the non-circularity of the deposited tube increases, whereby an increase in the polarization mode dispersion occurs. Conventionally, the deposition process, the shrinkage process and the closing process have led to using the same burner, which is only convenient for the deposition process, despite the fact that the processes involve different mechanisms, respectively. For this reason, an increase in the thickness of the deposited layer occurs. This causes various problems such as a deformed geometric structure of the deposited tube, a degradation in the optical characteristics of finally produced optical fibers, and an increased processing time.

SUMMARY OF THE INVENTION The present invention has been made to overcome the problems described above. Accordingly, it is an object of the present invention to provide an apparatus and method of making preformed optical fiber wherein the processes for contracting and closing a deposited tube lead to using an appropriate device for the processes, where the device is none other than the device used in a deposition process to form the tube deposited on the internal surface of a preformed tube, whereby the processing time is reduced while reducing the amount of OH penetrated from the preformed tube into a vitreous component of the deposited tube. whereby a reduction in OH loss is achieved. According to one aspect, the present invention provides a preformed optical fiber processing apparatus for the contraction and closure of a deposited tube comprising: a lathe to support a tube deposited in such a way that it extends vertically, the deposited tube has a coated layer and a center layer while sealing one end thereof; a circular heater placed around the deposited tube while it is spaced circumferentially independent of the deposited tube by a desired distance, the circular heater serves to supply heat to the deposited tube supported by the lathe and moves up and down at a desired speed; a vacuum pump is connected to the other end of the deposited tube and adapted to pump the air that exists inside the deposited tube using a vacuum; and a process control unit for setting the heating temperature of the circular heater to a desired temperature, and directing the control operation for the contraction and closing processes of the deposited tube while the circular heater moves up and down. According to another aspect, the present invention provides a method of manufacturing preformed optical fiber comprising the steps of: depositing a coated layer and a core layer on an inner surface of a preformed tube, whereby a deposited tube is formed; the contraction end of the deposited tube, whereby one end of the deposited tube is sealed; place the deposited tube in such a way that it extends vertically through the circular heater; move the circular heater to the sealed end of the deposited tube, and then adjust a heating temperature of the circular heater so that it is not less than that of a softening of the deposited tube; and heating the deposited tube while moving the circular heater at a desired speed, whereby the deposited tube contracts and closes.

BRIEF DESCRIPTION OF THE DRAWINGS The above objects and advantages of the present invention will become clearer by describing the preferred embodiments in detail thereof with reference to the accompanying drawings in which: Figure 1 is a view illustrating an appropriate deposition apparatus for a MCVD process; Figure 2 is a view illustrating an apparatus for manufacturing preformed optical fiber capable of directing the shrinkage and closure processes according to the present invention; Figure 3 is a flow diagram illustrating a method for making the preformed optical fiber according to the present invention; and Figures 4a and 4b are views illustrating respectively examples where a burner or a furnace is used as heat means.

DETAILED DESCRIPTION OF THE PREFERRED MODALITY The present invention describes a preformed optical fiber processing method and apparatus that involve a process for depositing a gas reaction product of raw material on the inner surface of a preformed tube, whereby a deposited tube, and a process for the contraction and closing of the deposited tube, whereby a preformed optical fiber is obtained. The deposition process is carried out according to a well-known method of deposition, for example, an MCVD method. On the other hand, the process of contraction and closure is simply and rapidly carried out in accordance with the present invention. Figure 1 is a view illustrating an appropriate deposition apparatus for an MCVD process. This deposition apparatus is used to deposit a reaction product of gas of raw material on the inner surface of a preformed tube. Referring to Figure 1, a lathe 11 is illustrated, which serves to support a preformed tube 12. A heat means 14 for partially heating the preformed tube 12 when viewed in the longitudinal and circumferential directions of the preformed tube 12. In the Figure 1, the region where the preformed tube is heated, is denoted by the reference number 13. The preformed tube 2 rotates in one direction, for example, the direction indicated by the arrow 15a in Figure 1. The heating means 14 is moves in the directions indicated by arrows 15b in Figure 1 according to the operation of a movement member (not shown). Accordingly, the heating region 13 is defined not only by moving along the entire length of the preformed tube 12, but also by rotating around the circumference of the preformed tube 12. The raw material gas is introduced from a supply unit 19 of raw material gas in the preformed tube 12 by means of an inlet tube 17. The gas supply unit 19 of raw material contains a reactant of a liquid phase therein and supplies this reactant to the preformed tube 12 using the gas transported The discharge materials are discharged from the preformed tube 12 through an outlet 18. The flow velocity of the raw material gas is controlled by a mixing valve (not shown) and a shut-off valve (not shown). According to the MCVD method, the gas of highly pure raw material such as SiCl 4, GeCl 4, or POCI is blown in a preformed glass tube together with oxygen. When heat is applied to the preformed glass tube using a heat medium, a thermal oxidation is generated, so that an oxide is deposited in the form of soot on the inner surface of the preformed tube. At this time, a coated layer and a core layer are deposited on the inner surface of the preformed tube under the condition that the refractive indices of the layers are adjusted by precisely controlling the concentration of the gas of raw material. Therefore, a deposited tube is formed on the inner surface of the preformed tube. After completing the deposition process, the preformed tube is heated again by the heat medium, so that the deposited tube contracts. Thus, a preformed optical fiber is obtained. Figure 2 is a view illustrating an apparatus for manufacturing preformed optical fiber capable of directing the shrinkage and closure processes according to the present invention. This apparatus is adapted to contract and close the deposited tube produced by the apparatus of Figure 1. As shown in Figure 2, the preformed optical fiber processing apparatus according to the present invention includes a lathe 21 for supporting a tube. deposited, to be treated, by its upper and lower support members 22 and 23 in such a way that the deposited tube extends vertically. The preformed optical fiber processing apparatus includes a circular heater 24 for heating the deposited tube, a vacuum pump 25 for pumping air or other contaminants that exist in the deposited tube using a vacuum, a pressure meter 26 for measuring the pressure of pumping of the vacuum pump 25, a chlorine gas injector 27 for supplying the chlorine gas in the deposited tube, and valves, i.e., a vacuum discharge valve 26 and a gas supply valve 28. For the 24 circular heater, a burner or an oven can be used. The circular heater 24 is configured to provide a sufficient amount of heat while controlling the flame pressure, to be suitable for the shrinkage and closing processes, as compared to the heating means of Figure 1 appropriate for the deposition process. In the apparatus for manufacturing preformed optical fiber having the aforementioned configuration, a deposited tube 20b, which can be processed by the apparatus of Figure 1, is supported by the lathe 21. The deposited tube 20b has a sealed end to which a rod 20a is connected. The support member ? m - *. ^^ m ^ - - ^ Jt J «flHi-K -» «- MWr * l» l.l-to ». - 'IBW .. < The upper i 22 supports the rod 20a connected to the sealed end of the deposited tube 20b considering that the lower support member 23 supports the other end of the deposited tube 20b, where the end is open. The lathe 21 also has a length adjusting member 20c adapted to adjust the length of tube support of the lathe 21. The circular heater 24, which serves to supply heat to the deposited tube 20b is placed around the deposited tube 20b while spaced radially independent of the deposited tube 20b through a desired distance. The circular heater 24 is vertically movable along the deposited tube 20b at a desired speed. The chlorine gas injector 27 supplies the chlorine gas to the deposited tube 20b through the lower support member 23 of the lathe 21 to remove the moisture that exists in the deposited tube 20b. The apparatus for making the preformed optical fiber also includes a control unit not shown. The control unit carries out the control operations for the contraction and closing processes of the deposited tube 20b. That is, the control unit sets the heating temperature of the circular heater 24 to a desired temperature, and rotates the deposited tube 20b supported between the upper and lower support members 22 and 23 at a desired speed while vertically moving the deposited tube. 20b. First, the heating temperature of the circular heater 24 is adjusted to be lower than the softening point of the deposited tube 20b. In this state, the circular heater 24 moves at a desired speed. During the movement of the circular heater 24, the contaminants that exist in the deposition tube 22b are then discharged in accordance with an operation of the vacuum pump 27. After this, the heating temperature of the circular heater 24 is again adjusted to which is not less than the softening point of the deposited tube 20b. In this state, the processes of contraction and closure of the deposited tube 20b are carried out. Where an oven is used for the circular heater 24, the inert gas such as argon or nitrogen is provided to the furnace to prevent oxidation thereof in a heat generating region. According to the apparatus of the present invention, the deposited tube is placed vertically during the process of contraction and closing of the tube. Heat is supplied to the deposited cube placed vertically by means of the circular heater placed around the deposited tube while using a ákiti ^ lki ^ high flame pressure. During heating, the deposited tube is evacuated using a vacuum. By virtue of the characteristics, it is possible to considerably reduce the time of the process while preventing the deposited tube from having a non-circularity, as compared with conventional methods. Figure 3 is a flow diagram illustrating an apparatus for making the preformed optical fiber according to the present invention. According to this method, first a coated layer and a central layer are deposited on the inner surface of a preformed tube placed horizontally, using the apparatus shown in Figure 1, whereby a deposited tube is formed (Step 31). Subsequently, the deposited tube is locally heated at one end thereof corresponding to a region where the chemical raw gas is discharged during the deposition process, whereby the end is sealed (Step 32). A rod is attached horizontally to the sealed end of the deposited tube (Step 33). The deposited tube attached to the rod is separated from the lathe, and then fed to the lathe to contract / close the tube shown in Figure 3. On the lathe to contract / close the tube, the tube deposited it is then placed vertically in such a way that it extends vertically through the circular heater while the rod is directed upwards (Step 34). Later, the circular heater moves to the junction between the deposited tube and the rod. The heating temperature of the circular heater is then adjusted to be lower than the softening point of the deposited tube. In this state, the circular heater moves up and down at a low speed to heat the deposited tube. At the same time, the vacuum discharge valve opens to remove contaminants, including moisture, from the inside of the deposited tube (Step 36). The movements of the circular heater are carried out in such a manner that when the deposited tube, which moves downward from the junction to the lower end thereof, reaches the lower end, the direction of movement is changed to allow the deposited tube to move upwardly to the Union. After the evacuation of the deposited tube, the heating temperature of the circular heater is adjusted again so that it is not lower than the softening point of the deposited tube (Step 37). When the circular heater reaches a predetermined temperature during the operation thereof, it is maintained at that temperature for 2 or 3 minutes to obtain a temperature stability. Then, the vacuum pump is operated to keep the inside of the tube deposited in a negative pressure state. In this state, the deposited tube is heated under the condition in which it moves downwardly at a desired speed, whereby shrinkage and closure thereof is caused (Step 38). The shrinkage and closure processes of step 38 are conducted under the condition that the deposited tube rotates at a desired speed of, typically, 10 rpm or less. The contraction of the deposited tube can be achieved by directing the contraction process in a time or several times. After the contraction of the deposited tube, the deposited tube is closed to form a solid preform. Where a furnace is used for the circular heater, inert gas such as argon or nitrogen is supplied to the interior of the furnace to prevent oxidation thereof in a heat generating region. Figures 4a and 4b are views illustrating respectively the examples where a burner or a furnace is used as the circular heater. In the case of Figure 4a, a circular burner 41 applies heat to a l ^^ | A deposited tube having a central / coated layer 43 deposited on the inner surface of a preformed tube 42, around the deposited tube, while moving downwards, whereby the deposited tube contracts and closes. During this heating process, a vacuum is generated inside the deposited tube to allow the deposited tube to contract and close more easily. In the case of Figure 4b, a circular furnace 45 applies heat to a deposited tube having a coated / central deposited layer 47 deposited on the inner surface of a preformed tube 46, around the deposited tube, while moving downwards, so which is contracted and the deposited tube is closed. As is clear from the foregoing description, the present invention provides an apparatus and method for the preparation of preformed optical fiber wherein the processes for contracting and closing a deposited tube are directed using a convenient device for these processes, where the device is no other that the device used in a deposition process to form the tube deposited on the inner surface of a preformed tube, whereby the processing time is reduced to a degree corresponding to half of the conventional method or less. This is because the processing time of the shrinkage and closing process of the tube occupies a larger portion (2/3 or more) of the time "of the total processing of the preformed optical fiber processing process." In accordance with the present invention, The shrinking and closing process is carried out under the condition that a negative pressure is applied to the inside of the deposited tube, therefore it is possible to further reduce the processing time considerably while reducing the period of time, so that the deposited tube is exposed to a high temperature This produces a reduction in the amount of OH penetrated from the tube preformed in a vitreous component of the deposited tube, by which a reduction in the OH loss is achieved, since a circular burner or furnace circular is used as the heating medium for the processes of contraction and closure, there will be a small gradient of surface temperature or not ie in association with the heat applied to the deposited tube. Accordingly, it is possible to reduce a non-circularity of the deposited tube. This produces a reduction in polarization mode dispersion. While the present invention has been shown in a particular manner and has been described with reference to a particular embodiment thereof, it will be understood by those skilled in the art that various changes may be made in form and detail herein without departing from the scope of the invention. invention as defined by the appended claims.

It is noted that in relation to this date, the least known method for the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects or products to which it refers. % tetaae < ^^ faith '

Claims (13)

1. - Having described the invention as above, claimed as property contained in the following claims: 1. An apparatus for the manufacture of optical fiber preformed for the contraction and closure of a deposited tube, characterized in that it comprises: a lathe to support a tube deposited in such a way as to extend vertically, the deposited tube has a coated layer and a central layer while sealing at one end thereof; a circular heater placed around the deposited tube while circumferentially spaced apart from the deposited tube by a desired distance, the circular heater serving to supply heat to the deposited tube supported by the lathe moves up and down at a desired speed; a vacuum pump is connected to the other end of the deposited tube and adapted to pump the air that exists inside the deposited tube using a vacuum; and a process control unit to set a heating temperature of the circular heater ^ gg at a desired temperature, and directing an operation-control for the processes of contraction and closing of the deposited tube while the circular heater moves up and down.
2. 2. The apparatus for the production of preformed optical fiber according to claim 1, characterized in that the winch comprises: a top support member for supporting the sealed end of the deposited tube; and a lower support member for supporting the other end of the deposited tube, the lower support member cooperates with the upper support member to rotate the deposited tube at a desired speed during the processes of contraction and closure of the tube.
3. 3. The apparatus for the preparation of preformed optical fiber according to claim 1, characterized in that it additionally comprises: a chlorine gas injector to supply the chlorine gas to the interior of the deposited tube to eliminate the humidity generated inside the deposited tube to the heat of the circular heater.
4. 4. The apparatus for manufacturing preformed optical fiber according to claim 1, characterized in that the circular heater comprises a furnace.
5. 5. The apparatus for manufacturing preformed optical fiber according to claim 1, characterized in that the circular heater comprises a burner.
6. 6. The apparatus for the preparation of preformed optical fiber according to claim 4, characterized in that it additionally comprises an inert gas injector for supplying the inert gas to the furnace to prevent an oxidation of the furnace in a heat generating region.
7. 7. The apparatus for the preparation of preformed optical fiber according to claim 1, characterized in that the process control unit directs the sequential control operations to set the heating temperature of the circular heater to a temperature lower than the softening point of the deposited tube, discharging contaminants that exist inside the deposited tube while moving the circular heater to a desired temperature, setting the heating temperature of the circular heater to a temperature no lower than the softening point of the deposited tube, and contracting and closing the deposited tube while moving the circular heater to a desired temperature.
8. 8. The apparatus for the preparation of preformed optical fiber in accordance with the claim 1, characterized in that the process control unit directs a control operation to rotate the deposited tube supported by the lathe at a desired speed during the shrinking and closing processes.
9. 9. A method for the preparation of preformed optical fiber, characterized in that it comprises the steps of: depositing a coated layer and a central layer on an internal surface of a preformed tube, whereby a deposited tube is formed; contracting one end of the deposited tube, whereby one end of the deposited tube is sealed; l $ * & v? Vms * »? er & • .- > and ^ = ^ ss ^ ^^^ place the tube deposited in such a way that it extends vertically through a circular heater; moving the circular heater to the sealed end of the deposited tube, and then adjusting a heating temperature of the circular heater so that it is not less than the softening point of the deposited tube; and heating the deposited tube while moving the circular heater at a desired speed, whereby the deposited tube contracts and closes.
10. 10. The method of manufacturing preformed optical fiber according to claim 9, characterized in that it additionally comprises the steps of: moving the circular heater to the sealed end of the deposited tube, and then adjusting the heating temperature of the circular heater which is lower than that of a softening point of the deposited tube; and heating the deposited tube while moving the circular heater at a desired speed, whereby the contaminants existing inside the deposited tube are discharged.
11. 11. The method of manufacturing preformed optical fiber according to claim 9, characterized in that the step of contraction and closure is carried out under the condition in which the deposited tube rotates at a desired speed, and the inside of the deposited tube is maintained at a negative pressure.
12. 12. The method of manufacturing preformed optical fiber according to claim 9, characterized in that the circular heater is a furnace, and the inert gas is supplied to the furnace to prevent oxidation of the furnace in a heat generating region.
13. 13. The method of manufacturing preformed optical fiber according to claim 9, characterized in that the step of contraction and closure is carried out under the condition in which the chlorine gas is supplied to the interior of the deposited tube, whereby it is eliminated the humidity generated inside the deposited tube due to the heat of the circular heater. i ^^^ MÍÍMÍÍÍÍMMMMÍÍ IÍMHHÍMILii SUMMARY OF THE INVENTION An apparatus and method for the elaboration of preformed optical fiber are described wherein the processes for contracting and closing a deposited tube are carried out using an appropriate device for the processes, where the device is not other than that used in a deposition process for forming the tube deposited on the inner surface of a preformed tube, whereby the processing time is reduced while reducing the amount of OH penetrated from the preformed tube of a vitreous component of the deposited tube, whereby a reduction is achieved in the loss of OH. According to the apparatus and method for the elaboration of preformed optical fiber, operations are carried out that involve fixing the heating temperature of a circular heater at a temperature lower than the softening point of a deposited tube, discharging the contaminants that exist in the inside of the tube deposited while moving the circular heater to a desired temperature, set the heating temperature of the circular heater to a temperature no lower than the softening point of the deposited tube, and contract and close the deposited tube while moving the heated circular to a desired temperature.