FI94048C - Process for producing an optical fiber and using a fiber product containing silica in the manufacture of an optical fiber - Google Patents

Description

94048

The present invention relates to a process for producing an optical fiber preform, in which a fiber is grown on a primary blank of pure or doped silica by winding a layer of silica glass by winding. The invention also relates to the use of a silica-containing viscose fiber in the manufacture of an optical fiber blank.

The fabrication of an optical fiber is basically a two-step process in which the first step comprises the fabrication of an optical fiber preform and the second step the drawing of the preform into a fiber. The main industrial manufacturing processes of the fiber preform are based on gas phase growth: MCVD (Modified Chemical Vapor Deposition), VAD (Vapor-Phase Axial Deposition) and OVD (Outside Vapor Deposition). The finished preform consists of a core blank of doped or pure silica glass and a lower refractive shell formed thereon, which is also doped or pure silica glass. A typical fiber blank is about 1 m in length and 20-60 mm in diameter, and the yield of one blank is in the order of 10-50 km of optical fiber.

The optical fiber has a core portion which is pure or doped amorphous silica and a shell which is also silica glass but which is doped so that its refractive index is lower than that of the core. Both the core and the shell contain alloying materials with which the refractive index values, softening temperatures, etc. of the various parts of the fiber are adjusted to the desired properties important for the use and manufacture of the fiber. The core of the fiber forms the actual optical transmission path in which the signals propagate. The shell acts as a refracting surface to prevent light scattering from the core. Thus, the fiber blank must have the materials required for the core and shell layers in proportion to 3594848 so that the core and shell layers of the fiber are formed in the desired manner simultaneously during the fiber drawing process.

The drawing of the optical fiber takes place by slowly feeding the preform into a tubular oven, where the fiber is drawn from the end of the softened preform at a high speed and wound on a drum after various processing steps.

All manufacturing methods have in common high costs due to the high purity requirements that have been solved in the known solutions for the growth of the blank by means of gaseous raw materials. In addition, most gas formation processes are difficult to control and have a modest production rate.

It is an object of the present invention to provide a method for growing an optical fiber preform which reduces raw material costs and significantly increases production speed. To achieve this, the method according to the invention is characterized in that - a viscose fiber containing silica is wound on the initial blank to form a blank, - the formed blank is heated to burn the organic material of the fibrous product and melt or sinter the silica containing it into a silica-glass layer.

According to the invention, the optical fiber preform is grown in a completely new way by winding a silica-containing fibrous product around the initial preform, after which the obtained preform is sintered or melted into a uniform fibrous preform, whereby the silica-based fibrous product is converted to silica glass. The fibrous product used as a raw material is 30 cheap, and the required winding equipment does not require a large investment, because the silica rod or tube serving as a preform can simply be attached to a rotating spindle, and the silica-containing wire is wound vertically on the rod 35 with vertical control.

3,94048

The various embodiments of the method according to the invention and the use of the fiber product according to the invention are characterized by what is stated in the claims below.

The invention will now be described in more detail by way of example and with reference to the accompanying drawings, in which Figure 1 shows an optical fiber as a finished product, Figure 2 shows an apparatus for making a blank 10, Figure 3 shows an optical fiber drawing apparatus, Figure 4 shows a refractive index measured from a blank according to the invention. .

According to Figure 1, the optical fiber 1 consists of a core 15, a core shell 3 and a protective sheath 4. The diameter of the fiber is typically about 125 μπι. The base material of the core consists of a highly pure amorphous silica glass doped in the desired manner and having a high refractive index. The shell 3 consists of pure, e.g.

20 fluorine-doped silica glass having a lower refractive index than the core. The signals passing through the core of the optical fiber are then completely reflected from the interface between the core and the shell, whereby the light travels along the core with the least possible losses. The protective sheath 4 consists of 25 e.g. conventional plastic insulation.

Figure 2 shows the production of an optical fiber blank according to the invention. In it, the initial blank 5 of high-purity silica is rotatably attached to the mandrel 7 of the lathe 6, for example. to form the initial blank. The required number of rounds is formed, typically several dozen. When the required layer thickness is reached, the preform is heated to 4 94048 either in a sintering furnace or by flame melting to burn the organic material of the fibrous product and form the silica therein as a solid silica glass layer on the initial preform.

Figure 3 shows a fiber drawing apparatus in which fiber 14 is drawn from a blank 13 made in accordance with the invention through a processing apparatus. The apparatus consists mainly of a heating furnace 15 of a blank 13, a diameter adjusting device 16, a sheath forming nozzle 17, a heat-treatment furnace 18, guides 19 and a winding drum 20.

Figure 4 shows the refractive index profile measured from a fired blank made according to the invention.

It is observed that the relative refractive index is relatively uniform (near zero) in the region of the core material (weather-15 de ± 10 mm), and decreases sharply in this case in the area of the boron-doped shell (radius> 10 mm).

The silica used in the process according to the invention. the zid-containing fiber is preferably a silica-viscose material made by pressing a homogeneous solution of silica-dimonomer and viscose through a spinneret into a polymerization and regeneration solution. Thus, a fiber or filament of a silica viscose material is prepared by polymerizing monomeric silica in a cellulose matrix. This results in a fibrous product, i.e. a silica-25 viscose material fiber, which can be washed and dried in the same way as in a conventional viscose process. A process for the preparation of this type of fiber is described in more detail in, for example, FR patent 1364238 and GB patent 1155292.

30 A yarn having very similar properties to viscose yarn can be easily spun from the viscose silica fiber made. Thus, a yarn with a completely homogeneous structure is provided, from which a yarn can be wound on the initial blank or used as a suitable textile product or ribbon, such as 94048 fabric, knit, braid, fabric, felt or nonwoven.

The following are some of the results of empirical experiments performed within the scope of the invention on the treatment and preform formation of a silica-containing fibrous product.

Example 1 In this case, a quartz bar was used as the initial blank, which was attached to a lathe acting as a winding device. The silica-based fiber product was wound on a quartz rod using an automatic, pneumatically operated divider as shown in Figure 2. A 2x25 tex yarn with a silica content of 30-35% was used as the fiber product. After spooling, the fiber product was melted as such with a hydrogen-burner (about 2000 ° C) on the surface of a quartz rod.

It was found that only a thin layer of unalloyed fiber product is made to melt.

Example 2 A silica-based fiber product was purified as follows:

The fiber product was wound on a perforated, conical starting spool. The polish on which the fibrous product was placed was immersed in hot water and rinsed with deionized water. A 0.5M oxalic acid solution was pumped through the spool and the fibrous product, followed by a solution containing 1M ammonium chloride solution supplemented with 2% hydrogen peroxide was pumped through the spool and the fibrous product. The pH of the solution was adjusted to 9 with ammonia. Deionized water was then pumped through the spool and the fiber product, after which the spool and the fiber product were dried at 70 ° C. After this treatment, the fibrous product was wound on a quartz rod into a blank as shown in Fig. 2. The fibrous product was blended by immersing the preform in 0.5M boric acid solution until the fibrous product based on silica was wetted. The fiber product t 6 94048 was then dried, remixed and dried again.

The blank was then fired into a solid blank as in Example 1.

Due to the doping, the softening point of the silica glass was significantly reduced, and the fiber product melted into a homogeneous layer on top of the initial blank.

Example 3

The fiber product was pretreated as in Example 10, but instead of boric acid, the fiber product was blended using diammonium hydrogen phosphate (DAP) as a 0.5 M solution.

The results were similar to Example 1, although the melting of the fiber product was slower.

15 Example 4

The fiber product was pretreated and blended as in Example 2, but the fiber product was sintered in an oven. At 1450 ° C in the form of a fabric wound on a blank. The fiber product formed a shell on the initial blank in the desired manner, although the homogeneity of the layer was not of the same order as in the results obtained in Example 2. It has been estimated that inhomogeneities can be achieved by better attachment of the fiber product to the initial blank throughout the process. Repetition of Example 4 with phosphorus doping of the fiber product 25 (cf. Example 3) gave similar results.

It will be apparent to those skilled in the art that the various embodiments of the invention are not limited to the examples set forth above, but may vary within the scope of the following claims.

Claims (5)

94048 A method for producing an optical fiber blank, in which a fiber is grown on a primary blank (5) of pure or doped silica 5 by winding a layer of silica glass, characterized in that - a silica-containing viscose fiber (8) is wound on the initial blank (5) to form a blank (13) , 10. the formed preform is heated to burn the organic material of the fibrous product and melt or sinter the silica contained therein into a silica-glass layer on top of the initial preform. Process according to Claim 1, characterized in that a dopant lowering the softening point of the silica, such as boric acid (B 2 O 3), is added to the fibrous product (8) containing silica. Method according to Claim 1 or 2, characterized in that the fibrous product (8) 20 containing silica is purified with deionized water, oxalic acid solution and ammonium chloride solution before being wound on the initial blank (5). Method according to one of Claims 1 to 3, characterized in that the fibrous product (8) containing silica is woven or formed into a textile or a textile strip. Use of a silica-containing viscose fiber (8) in the manufacture of an optical fiber preform (13), wherein a fibrous layer is grown on top of a silica preform (5) which, when fired or sintered, forms a silica glass jacket layer on said preform. 8 94048