FR2839714A1 - Production of a preformer for a coated fibre optic by positioning a coated tube around the shaft of a preformed core and applying a rod-in-tube procedure with improved correspondence between them - Google Patents

Abstract

The production of a preformer for a coated fibre optic consists of: (a) positioning (72) a coated tube around a shaft of a preformed core; (b) heating (76) the coated tube over its length, such that the coated tube deforms on the preformed core to form the preformer for the fibre optic; (c) regulating (82) the radial dimension of a heated part of the shaft of the preformed core and/or the coated tube, in order to improve their correspondence before deforming the coated tube on the shaft of the preformed core.

Description

wind used to heat components in the process.

  The present invention relates to methods and apparatus for the production of preformed fiber optic parts. More

  in particular, the invention relates to so-called "Rod-In-

  Tube "(RIT) (Rod-In-Tube = Rod In Tube) and devices with improved correspondence between core rods

preformed and coated tubes.

  Optical fibers wind fine strands of glass or plastic capable of transmitting optical signals containing relatively large amounts of information over long distances with relatively low attenuation. Optical fibers are typically produced by heating and stretching a portion of a preformed optical part comprising a refractive core surrounded by a protective coating made of glass or other suitable material. Conventionally, there are several methods of manufacturing preformed parts, including a modified chemical vapor deposition (DCVM) process. See, for example, patent N US 4,217,027, issued to MacChesney et al., August 12, 1980 and co-ownership with the present application. Other conventional methods include axial vapor depSt (DAV), exterior vapor deposition (DEV) and chemical vapor deposition at

plasma (DCVP).

  In the DCVM process, precursor gases such as SiCl4 and GeCl4 pass through a tube of rotating silica glass substrate. A blowtorch heats the tube from the outside as the precursor gases pass through it, causing the depSt of glass particles smaller than one micron on the inside surface of the tube. The displacement of the torch along the longitudinal axis of the tube in a plurality of passages forms a layer of glass, to create a preformed tube. When an appropriate number of layers have been deposited, the preformed tube is heated to deform it into a solid rod, typically called a preformed rod, core rod or preformed core rod. The preformed core rod is then introduced into a coated glass tube which is deformed on the preformed core rod using heat and a pressure gradient present around the coated tube. Such a process is typically called Rod-In-Tube (RIT) process, it is

  described in patent N US 4,820,322.

  The preformed part or the coated preformed part which results therefrom presents an area of a first diameter (d) surrounded by a coating area of a second diameter or outside diameter (D). The relationship between the diameter of the coating area (D) and the diameter of the core area (d), known as D / d, is useful for determining different performance parameters of the optical fiber produced from the preformed part. . For example, to obtain an optical fiber having desired transmission characteristics, the D / d ratio must be within the limits of a

  acceptable range of values, but relatively narrow.

  Since the range of acceptable values for this ratio is. typically, relatively narrow, variations in the particular physical dimensions of the core area and the coating area, in particular the diameter and cross-sectional area (SS), largely affect the overall performance of the optical fiber stretched from the preformed part. However, conventional methods of producing preformed core rods (eg, DCVM and DAV) do not always yield preformed core rods of constant diameter and cross-sectional area over the entire length of the preformed core rod. Likewise, conventional processes for producing RIT coated tubes do not always produce tubes of diameters or surfaces of

  constant section from one end to the other.

  Therefore, techniques such as passive matching of tubes are used to reduce the effects of variations in the physical dimensions of preformed core rods and conventionally produced coated tubes on the D / d ratio of the preformed part and, finally, on the transmission and other performance characteristics of the fiber drawn from the preformed part. Passive matching relates to the fitting or matching of preformed core rods with coated tubes similarly sized or with similar dimensional variations. For example, a preformed core rod i with a mean diameter or a medium cross-sectional area (based on a number of measurements over the length of the preformed core rod) is within the limits of a given percentage range less than its normal or preferred value will be used with a coated tube whose corresponding diameter or the corresponding cross-sectional area is also within the limits of a given percentage range less than its normal or preferred value. In this way, in general, preformed core rods which, on average, are smaller than normal will be introduced into coated tubes which, on average, are also smaller than normal by a similar percentage. Such passive matching improves the uniformity of the preformed part and therefore tends to improve the quality and performance of the

  fiber optic stretched from behind.

  However, although the passive matching of the tube allows a certain improvement in the quality and the yield of the optical fiber, it would be desirable to have other methods and devices which further improve the dimensional uniformity of the preformed core and the zones of coating relative to each other, thereby further improving the quality and

  yield of the stretched optical fiber from preformed parts.

  The embodiments of the invention include a method of

  production of preformed optical fiber parts and manufacture of optical fiber from preformed parts. The method comprises the steps of positioning a coated tube around a preformed core rod, heating the coated tube along its length in the presence of a pressure gradient, so that it deforms on the preformed core, to form the preformed piece of coated optical fiber, and to adjust the radial dimension of the heated part of the preformed core rod and / or of the coated tube, to bring into active correspondence the radial dimensions of the preformed core rod along its length with corresponding parts of the coated tube. The adjustment step changes the radial dimension of a part of the preformed core rod and / or the coated tube, for example, by applying a compressive force, to increase the radial dimensions by decreasing the axial dimensions and, alternatively , also by applying a drawing force, to decrease the radial dimensions by increasing the axial dimensions (of the preformed core rod and / or of the coated tube). Compression and / or decompression forces are applied, for example, as the area of interest of the preformed core rod and the coated tube is heated to deform the coated tube on the preformed core rod. Active matching by the adjustment step reduces variations in the physical dimensions of the preformed core rod and / or the coated tube, which improves the transmission performance and other characteristics of the fiber drawn from the preformed part created, for example, by maintaining a relatively constant D / d ratio of the preformed part. In the drawings: FIG. 1 is a sectional view of an apparatus for producing a preformed piece of optical fiber according to embodiments of the invention, illustrating a preformed core rod positioned inside a coated tube before deforming the coated tube around the preformed core rod, to produce the preformed part; - Figure 2 is a sectional view of a preformed piece of optical fiber illustrating the dimensions of the core area and the coating area; - Figure 3 is a simplified block diagram of a process for producing a preformed piece of optical fiber according to embodiments of the invention; and - Figure 4 is a sectional view of a device coated during drawing (RPE) for the production of a preformed piece of fiber

  optics according to embodiments of the invention, illustrating a

  coating tube positioned around a preformed core rod and deforming around the preformed core rod, before the optical fiber is drawn from the resulting preformed part.

  In the following description, similar elements are

  designated by the same reference number, in order to improve the s

  understanding of the invention by description of the drawings. So,

  although specific features, configurations and arrangements are described below, it should be understood that this is done for illustration purposes only. A person skilled in the art will recognize that other steps, configurations and arrangements are useful, without however deviating from the spirit and the objective of the invention. Referring now to FIG. 1, an apparatus is illustrated. 10 for the production of a preformed part coated using a RodIn-Tube (RIT) process, according to embodiments of the invention. A preformed core rod 14 (also known as a preformed rod or core rod) is positioned inside a coated tube 16. The preformed core rod 14 is made by any suitable method, including conventional methods such as chemical deposit at modified value (DCVM) or axial vapor deposition (DAV). A first end 22 of the coated tube 16 is joined to a first end 24 of the preformed core rod 14, for example, by deforming a portion of the coated tube 16 on the preformed core rod 14 using heat and heat. 'appropriate pressure. A second end 26 is configured to be mounted in a support 32 or other device

  holding device or suitable clamping device.

  An adjustable spacer 34 or other suitable spacing means is positioned in the second end 26 of the coated tube 16, to provide position support for the preformed core rod 14. The distal end 36 of the adjustable spacer 34 includes , for example, a quartz disc 38, or other suitable structure, intended to form an interface with a second end 28 of the preformed core rod 14. Alternatively, the distal end of the adjustable spacer 34 comes into direct contact with the second end 28 of the preformed core rod 14. As it

  will be described in more detail below, according to embodiments

  of the invention, the spacer 34 is configured to apply a compressive force and / or a stretching force to the preformed core rod 14, for example, as the

  coated tube 16 is deformed on the preformed core rod 14.

  A source of defect 42 or other suitable device or arrangement establishes a pressure gradient in the area between the coated tube 16 and the preformed core rod 14. Heating of the coated tube 16 while maintaining the pressure gradient between the coated tube 16 and the preformed core rod 14 causes the coated tube 16 to deform around the preformed core rod 14, for example,

  in accordance with the conventional Rod-In-Tube (RIT) process.

  In the illustrated arrangement, the spacer 34 is included or contained in the medium of established vice. The spacer 34 is coupled to a control device 44, such as a motor device or other suitable means for controlling the displacement of the spacer 34. For example, the spacer 34 is coupled to the control device 44 by means of 'a bellows 46 which allows the generally axial displacement of the spacer 34 (generally illustrated by an arrow 52), to apply a compressive force and / or a force

  drawing on the preformed core rod 14.

  Alternatively, the compressive force and / or the wind drawing force applied to the coated tube 16, for example, by the support 32 or other device for holding or fitting the appropriate force application. The support 32 or other force application arrangement is configured so as to move in the directions generally illustrated by an arrow 54, to apply a compression force and / or a drawing force on the coated tube 16 which is mounted in the support 32. The control device 44 or other suitable control arrangement is coupled to the support 32 or other force application arrangement, for

  order the movement of the latter.

  According to embodiments of the invention, the application

  a compressive force and / or a drawing force on the preformed core rod 14 and / or on the coated tube 16 modifies the radial dimension (for example, the diameter and / or the cross-sectional area) of the preformed core rod 14 and / or the coated tube 16, for example, as the coated tube 16 is deformed on the preformed core rod 14. More specifically, a compressive force generally increases the radial dimension of the preformed core rod 14 and / or the coated tube 16 by reducing its axial length. On the other hand, a pulling (or drawing) force generally decreases the radial dimension of the preformed core rod 14

  and / or of the coated tube 16 by increasing its axial length.

  In this way, the embodiments of the invention

  actively affect and control the radial dimension of the preformed core rod 14 and / or the coated tube 16 and their reciprocal positions relative to each other, thereby creating a more active alignment of the dimensions of the core rod preformed 14 and / or revatu tube 16 at different axial locations along the latter. Typically, the physical dimensions of the preformed core rod 14 and of the coated tube 16 are determined before the preformed core rod 14 is introduced into the coated tube 16. Such information is transmitted to the control device 44. in this way, the control device 44 controls the radial dimension of the preformed core rod 14 and / or of the coated tube 16, based on their dimensions. This active mapping acts to reduce variations in the physical dimensions of the preformed core rod 14 and / or the coated tube 16. These reductions improve the transmission performance and other characteristics of the fiber drawn from the workpiece. preformed created, for example, by maintaining a D / d ratio

constant of the preformed part.

  Referring now to Figure 2, there is shown a sectional view of a preformed piece of optical fiber 60 illustrating the dimensions of the core area and the coating area. The preformed piece of optical fiber comprises a deposited core zone 62 of a first diameter (d), surrounded by a first coating zone or deposited coating zone 64. The deposited core zone 62 and the first coating zone 64 wind designed layer by layer, for example, inside a substrate tube 66 and, en-quite, the tube is deformed, to form a massive rod. The massive rod is surrounded by a coating area 67 having a

outside diameter (D).

  As described above, the relationship between the diameter of the coating area (D) and the diameter of the core area (d), known as D / d, is useful for determining different performance parameters of an optical fiber. produced from this preformed part, including the overall quality and performance of the optical fiber produced from the preformed part. For example, Dtd affects the cut wavelength of the optical fiber produced from this preformed part. The cut wavelength is the wavelength above which the optical fiber behaves like a multi-mode fiber (staircase tindice) and below which it behaves like a single mode fiber. Likewise, D / d affects the diameter of mode fields / DCM), which is a measure of the width of the light intensity in a

  single mode fiber (also known as nodal field diameter).

  To stretch an optical fiber having the desired transmission characteristics, the ratio D / d of the preformed part must be within the limits of an acceptable range of values, but relatively narrow. For example, it is often desired that D / d be in the range of about 4 to about 6. However, depending on the particular application of the fiber, other values and ranges

  are often acceptable or desired.

  Referring now to Figure 3, with continuous reference to Figures 1 and 2, there is illustrated a method 70 of making a preformed piece of optical fiber according to the embodiments of the invention. A step 72 of the method 70 consists in positioning or otherwise forming the coated tube 16 around the preformed core rod 14. For example, as illustrated in FIGS. 1 and 2, when it is positioned, the coated tube 16 is usually

  coaxial with the preformed core rod 14.

  Another step 74 of method 70 consists in establishing a pressure gradient in the coated tube, that is to say between the preformed core rod 14 and the coated tube 16. As described above, one end of the rod of preformed core 14 and a corresponding end of the coated tube are typically closed, for example, by deforming a portion of the coated tube 16 on a portion of the preformed core rod 14. For example, as illustrated in FIG. 1, a part of the first end 22 of the coated tube 16 is deformed on a part of the first end 24 of the preformed core rod 14. The pressure gradient is established between the preformed core rod 14 and the coated tube, for example, using the source of defect 42 or some other suitable means. Typically, the pressure outside the coated tube 16 is greater than the pressure between the outside of the preformed core rod 14 and the inside of the coated tube 16. For example, the pressure gradient is within the range of about 0.10 a

  about 0.50 times the atmospheric pressure.

  Another step 76 of method 70 is to heat the preformed core rod 14 and the coated tube 16, for example, in the range of about 1600 to 1700 C. For example, the heating step 76 applies heat to successive axial parts of the tube

  coated 16, that is to say over the axial length of the coated tube 16.

  The heating step 76 causes the heated portion of the coated tube 16 to deform on the corresponding portion of the preformed core rod 14, thereby partially forming a preformed piece of coated optical fiber. In this way, the entire coated tube 16 is deformed on the preformed core rod 14, thus forming a preformed piece of revalued optical fiber, for example, the core rod

  optical fiber preform 14 illustrated in FIG. 2.

  Another step 78 of method 70 is to stretch the optical fiber from the heated portion of the preformed piece of optical fiber. The stretching step 78 is performed, for example, when the preformed piece of optical fiber of the invention has been manufactured. Alternatively, in a coating process during stretching (RPE), the stretching step 78 is carried out as the preformed piece of coated optical fiber is formed, that is to say that the coated tube 16 is deformed on the core rod

  preformed 14 in the drawing tower oven. These embodiments

  alternatives will be described in more detail below, for example, in

reference to figure 4.

  According to embodiments of the invention, another step

  82 of method 70 consists in modifying or adjusting the radial dimension of the preformed core rod 14 and / or of the coated tube 16, for example, by applying a compressive force and / or a drawing force on axial parts of the preformed core rod 14 and / or the coated tube 16 at different times during the deformation of the coated tube 16 on the preformed core rod 14. For example, compressive and / or stretching forces are typically applied , as the axial part of the preformed core rod 14 and / or the revatu tube 16, the radial dimension of which has to be adjusted, has been heated. In this way, the applied forces adjust the radial dimension of the axial part of the preformed core rod 14 and / or of the coated tube 16, for example, just before the deformation of this axial part of the coated tube 16 on the corresponding axial part. of the preformed core rod 14. The radial dimension includes, for example, the diameter and / or the

section area.

  For example, in the arrangement illustrated in FIG. 1, the control device 44 or other suitable control means pushes the spacer 34 (with or without the quartz disc 38), to axially apply a compressive force to the rod of preformed core 14. In this way, the preformed core rod 14 tends to compress axially, in particular at places along the length of the preformed core rod 14 which have been heated and which are relatively malleable. Such compression results in an increase in diameter, cross-sectional area or other radial dimension of the preformed core rod 14, in particular at heated and malleable locations along the length of the preformed core rod 14. Thus, depending from the moment of application of the compressive force and as a function of the part or the axial parts of the preformed core rod 14 which are heated, the radial dimensions of the preformed core rod 14 are freely adjusted, for example, relative to a corresponding place of the tube

seen again 16.

  Likewise, the arrangement for making preformed pieces of optical fiber can also be configured to apply a drawing force which pulls or extends the axial length of the preformed core rod 14 at different times or at

  different places along the length of the preformed core rod 14.

  In this way, the preformed core rod 14 tends to decompress axially, in particular at the heated places along the length of

the preformed core rod 14.

  It should be noted that, in arrangements such as that illustrated in FIG. 1, in the absence of the spacer or other support means, the tendency of the preformed core rod 14 is to move towards the second end of the coated tube 16. Thus, the arrangements such as that illustrated in FIG. 1, typically control compression and decompression by controlling only the degree of the compressive force applied to the rod

  of preformed kernel 14. However, the embodiments of

  The invention also includes arrangements in which compression and decompression are controlled by controlling the compressive force that the stretching force applied to the preformed core rod 14 and / or to the coated tube 16. As described more high, the application of the compression and / or stretching force is controlled by the control device 44 or other

appropriate means.

  Likewise, alternatively, the control device 44 controls the application of compression and / or stretching forces on the coated tube 16, for example, by means of the support 32 or other suitable means. That is, the support 32 or other suitable means couples to the coated tube 16 applies a compressive force

  and / or drawing on the coated tube 16, as described above.

  According to the embodiments of the invention, the device for

  control 44 is coupled to the support 32 or other appropriate means and controls the displacement of the latter, which in turn controls the application of compression and / or stretching forces on the coated tube 16. The application of forces compression and / or drawing on the rev8tu tube 16 is done alone or in addition to the application of a compression and / or drawing force on the core rod

preformed 14.

  As described above, the adjustment step 82 allows active matching of the preformed core rod 14 and its coated tube 16 surrounding it (which is subsequently deformed on this back). More specifically, the adjustment step 82 actively matches the radial dimensions of the preformed core rod 14 and the corresponding parts of the coated tube 16 surrounding it, thereby improving dimensional uniformity therebetween

during the RIT process.

  Embodiments of the invention have been described below.

  above as part of arrangements in which the deformation of the coated tube 16 on the preformed core rod 14 is carried out, typically, while the coated tube 16 and the

  preformed core rod 14 wind mounted in a vertical bane.

  However, the embodiments of the present invention are

  useful with alternative layouts, including layouts

  of Coating During Drawing (RPE).

  In RPE arrangements, the deformation of the coated tube 16 on the preformed core rod 14 takes place in a drawing tower oven, which is also used for drawing the optical fiber

  from the resulting pre-formed piece of optical fiber.

  This deformation is carried out by introducing the preformed core rod 14 into a coated tube 16 and then displacing the preformed core rod and the coated tube coaxially in the drawing tower oven, which causes the deformation of the coated tube on the preformed core rod, before drawing the fiber. The

  embodiments of the invention are useful with such

  amenities. As described above, the stretching step 78 of the process 70 is typically carried out when the preformed piece of optical fiber has been manufactured. However, in a coating process during stretching (tRPE), the stretching step 78 is carried out as the preformed piece of optical fiber is formed, that is to say as and as the coated tube 16 is deformed on the preformed core rod 14 in the drawing tower oven. The part of the coated tube 16 deformed on a corresponding part of the preformed core rod 14 becomes the part of

  the preformed part which is ready to be stretched in optical fiber.

  Referring now to Figure 4, there is illustrated a coating apparatus during drawing (RPE) 90 intended to make a preformed piece of optical fiber and an optical fiber from

  of this behind according to alternative embodiments of

  the invention. The apparatus includes an oven 92, or other suitable heat source, appropriately positioned to heat the preformed core rod 14 and the coated tube 16. Thus, with reference to the process illustrated in Figure 3, with continuous reference

  in Figure 4, according to the alternative embodiments of

  the invention wherein RPE arrangements and process steps are used, the heating step 76 and the drawing step 78

  wind made using the same heat source 92.

  In operation, the specific physical dimensions of the preformed core rod 14 and of the coated tube 16 are determined and transmitted to the control device 44. The preformed embedded rod 14 is introduced into the coated tube 16 and the two wind displaced, together, axially in the oven 92. The control device 44 uses the information of the physical dimensions to coordinate the displacement of the spacer 34 and / or of the support 32, to increase and / or decrease the radial dimensions of the preformed core rod 14 and / or of the coated tube 16. Since the control device 44 also controls the axial displacement of the preformed core rod 14 and of the coated tube 16 (for example, in the oven 92), the control device 44 coordinates the variation of axial dimensions of the preformed core rod 14 and / or of the coated tube 16 with their axial displacement, to regulate the dimensions of the preformed core rod 14 and / or of the coated tube 16 over their lengths . In this way, the control device 44 controls the overall radial dimensions of the preformed core rod 14 and the revatu tube 16, to actively match the radial dimensions of the preformed core rod 14 and the parts

  of the rev8tu tube 16 surrounding it.

Claims (11)

RESELL I CAT IONS   1. Method (70) for producing a preformed piece of coated optical fiber, comprising the steps consisting in: positioning (72) a coated tube around a preformed core rod; and heating (76) the revolving tube along its length, so that the rev8tu tube deforms on the preformed core, to form the preformed piece of coated optical fiber, characterized in that the method comprises an adjustment step (82) of the dimension of a heated part of at least one of the preformed core rod and the coated tube, to improve their matching before deforming the coated tube on the rod preformed nucleus.   2. Method according to claim l, characterized in that the adjustment step comprises a variation in the dimension of a heated part of the preformed core rod relative to a   corresponding axial position of the rev8tu tube.   3. Method according to claim l, characterized in that the adjustment step comprises an increase in the dimension of the preformed core rod by reducing the axial length of at least a first part of the preformed core rod and / or by decreasing the size of the preformed core rod by increasing the length   axial of at least a second part of the pre-formed drowned rod.   4. Method according to claim l, characterized in that the adjustment step comprises a variation of the dimension of a heated part of the coated tube relative to an axial position   corresponding to the preformed core rod.   5. Method according to claim l, characterized in that the adjustment step comprises an increase in the size of the coated tube by reducing the axial length of at least a first part of the coated tube and / or by reducing the size of the tube rev8tu by increasing the axial length by at least a second part of the rev8tu tube.   6. Method according to claim 1, characterized in that it comprises a step consisting in establishing (74) a pressure gradient between the inside of the coated tube and the outside of the coated tube, in which the pressure outside of the rev8tu tube is greater than the pressure inside the rev8tu tube. 7. Method according to claim 1, characterized in that it comprises a step consisting in stretching (78) an optical fiber to   from the preformed piece of coated optical fiber.   8. Method according to claim 7, characterized in that the stretching step and the wind heating step carried out using from the same heat source.   9. Method according to claim 1, characterized in that the positioning step comprises positioning the coated tube around the pre-formed core rod so that the tube   rev8tu and the preformed core rod are substantially coaxial.   10. The method of claim 1, characterized in that the adjustment step comprises an increase in the dimension of at least a first heated portion of the preformed core rod relative to a corresponding axial position of the coated tube by applying a compression force on the preformed core rod and / or by reducing the dimension of at least a second heated portion of the preformed core rod relative to a corresponding axial position of the coated tube by applying a force   drawing on the preformed core rod.   11. Method according to claim 1, characterized in that the adjustment step comprises an increase in the dimension of at least a first heated part of the coated tube with respect to a corresponding axial position of the preformed core rod by applying a compression force on the coated tube and / or by reducing the dimension of at least a second heated portion of the coated tube relative to a corresponding axial position of the preformed core rod by applying a drawing force on the