FI68606B - TILLVERKNINGSMETOD FOER EN ICKE-CYLINDERSYMMETRISK OCH POLARISATIONSBEVARANDE OPTISK FIBER - Google Patents

Description

68606

METHOD OF MANUFACTURING A NON-CYLINDER SYMMETRIC AND POLARIZATION-RESISTANT OPTICAL FIBER - TTLLVERKNINGSMETOD FÖR EN ICKE-CYLINDERSYMMETRISK OCH POLARISATIONSBEVARANDE OPTISK FIBER

The present invention relates to a method of manufacturing a non-cylindrically symmetrical and polarizing optical fiber.

Only a few methods of making a polarization-preserving fibrous material are known. Manufacturing methods have been complicated and impractical and are generally not patented. A patented method of manufacturing a polarization-preserving fiber is described in Japanese Patent Publication I 5702 7208 to E12, which, however, uses a VAD manufacturing method. The problem with this method is e.g. 15 to obtain a homogeneous fiber quality reproducibly.

One of the conventional methods of making fibers is the CVD method, which is disclosed, for example, in U.S. Patent No. 3,373,292. Among the methods for producing ordinary fibrous material, the Modified Chemical Vapor Deposition (MCVI) method has been developed from CVD methods for producing high-quality optical fibers.

The state of the art of the MCVD method is apparent, for example, from U.S. Patent No. 4,217,027.

The MCVD process is characterized in that the glass-forming gas-phase reaction takes place inside a quartz tube mounted on a glass lathe. In addition, the method is characterized in that the quartz tube used as the substrate-tin is heated locally by a burner in the hot zone caused by which the glass-forming reaction takes place. The tube is rotated at a constant speed to minimize tube deformation; at the same time, the burner moves smoothly and a layer 35 of glass forming the inner shell or core area of the optical fiber is formed on the inner wall of the tube.

By several sweeps of the burner and by varying the composition of the glass from one layer to another, the desired dimensions and refractive index distribution are obtained for the fiber shell and 2 68606 cores. Finally, the tube is closed by collapse.

The fiber blank obtained after the growth step is drawn into a fiber.

5 Even if the blank is non-circular, the surface tension forces act during the drawing phase so that the finished fiber usually becomes round. It is essential in the MCVD method that the tube is rotated evenly in a glass lathe, thus avoiding changes in the shape of the tube and obtaining a circular geometry for the fiber.

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In different methods, the asymmetry is usually obtained in complex ways, e.g. by using quartz crystal rods in the fiber making step. The asymmetry can also be achieved by collapsing the tube under vacuum or by grinding the edges of the blank 15. Various other fabrication techniques exist and are generally characterized by asymmetry created by machining the blank in different ways or by adding more quartz rods, etc. inside or outside the tube. These methods are cumbersome and difficult to implement and control of dimensions and geometry is difficult. Often the attenuation of the fibers is also high and the end result thus failed.

The object of the present invention is to eliminate the disadvantages listed in the known solution models. The method for producing a non-cylindrically symmetrical and polarizing optical fiber according to the invention is characterized by the features of the characterizing part of claim 1.

When using the production method according to the invention, many advantages are achieved compared to the known solutions. A non-cylindrical-symmetrical (= non-circular) geometry can be easily obtained for the inner shell and core of the fiber by varying the rotational speed of the tube at different angles of rotation, whereby a larger amount of material grows at different angles of the tube.

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Essential to the method is that when the rotational motion is stopped by the thermophoretic force of the gravity of the ground or other force 3 68606 with the tube in place, the glass particles formed in the reaction drift asymmetrically on the lower surface or other surfaces of the tube. In this case, for example, a thicker layer of glass is formed on the lower surface than on the sides. The method is easy to automate by using a motor with which the desired deceleration at different angles can be realized (e.g. a step motor). In the experiments performed, the method has been found to work well. In addition, the fibers produced have been found to have low attenuation and have had the desired preservative property of the Polari Foundation.

One embodiment of the method according to the invention can be considered to be a fiber made to preserve polarization by first preparing an inner shell (e.g. SiO 2 glass) with a coefficient of thermal expansion different from that of the core and quartz shell (e.g. SiC). ^ s). In this case, the thermal stresses have caused an asymmetrical (e.g. elliptical) refractive index distribution to the fiber core through the elasto-optical phenomenon, which causes the 20 polarization levels to be maintained. Using the method according to the invention, the asymmetrical inner shell of such a fiber can be produced e.g. by rotating the tube half a turn, stopping the tube, further rotating half a turn, etc.), whereby the fiber shell grows thicker at different angles of rotation. The rotation can also be slowed down several times during the same rotation, resulting in varying geometries.

The fibers produced have been found to have the desired structure 50 and properties. In addition, the method has been simpler and less expensive than previous manufacturing methods.

In the following, the invention will be explained in detail with reference to the accompanying drawing.

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Pattern. 1 shows the structure of an optical fiber.

Figure 2 shows the growth of the fiber.

68606 4

Figure 3 shows the fabrication of a non-cylindrical optical fiber structure.

Figure 4 shows the structure of a polarizing fiber.

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Figure 1 illustrates the structure of an optical fiber consisting of a core 1, an inner shell 2 and a shell 3.

Figure 2 illustrates the growth of the fiber, which takes place in such a way that the substrate is quartz tube 1, around which layers 2 are grown by the MCVD method. In the growth step, the hole 3 in the tube where the reaction takes place. After cultivation, the tubes are sealed by koi chipping.

15 Figure 3 shows the fabrication of a non-cylindrically symmetrical optical fiber structure with an angle of rotation «. At the values of the rotation angle a = 0 and a = 180 °, grown layers 1 are formed inside the quartz tube 2.

Figure 4 illustrates the structure of a preserving fiber in which a part 1, an elliptical inner shell 2 (e.g., I 2 O 2 doped) and a core 3 are formed of a quartz tube.

The various embodiments of the invention may vary considerably within the scope of the following claims.

Claims (4)

A method of manufacturing a non-cylindrically symmetrical and polarizing optical fiber, in which layers (1) layers of different thicknesses (1) of glass on the inner surface of a substrate tube (2) are deposited at different angles, the tube is collapsed into a closed blank and an optical fiber is drawn therefrom the substrate tube (2) is rotated in pulses, intermittently (non-uniformly) to produce an elliptical or other non-circular geometric shape on the optical fiber blank, the rotational speed varying at different angles (a) or the tube being stationary for part of the time in the reaction caused an asymmetric distribution of the particles on the inner surface of the substrate tube. 15 Method according to Claim 1, characterized in that the desired geometry and the composition of the glass are obtained by adjusting the layer thickness (1) of the inner shell of the optical fiber by adjusting the desired refractive index distribution. 20 A method according to claim 1 or 2, characterized in that all or only a part of the fiber layers can have different thicknesses at different angles, wherein at different angles the layers of different thicknesses can be present in either the cores or the inner shell or both. Method according to Claim 1, 2 or 3, characterized in that the inner shell or core of the fiber can also be circular, the other being elliptical in shape or otherwise non-circular.