Coating of optical waveguides

Abstract

The invention relates to a method for producing an optical waveguide (1), the surface of which is at least partly coated with a coating material. The coating material contained in a target (4) is removed using laser radiation (6) of a processing laser or converted into another aggregate state. The coating material is then deposited on the surface of the waveguide (1) and forms a coating thereon, said coating modifying the light guidance. It is the object of the present invention to provide an improved method for producing optical waveguides, in which guidance of undesired electromagnetic radiation and/or guidance of radiation in undesired areas of the waveguide is avoided. To this effect, the present invention proposes that the laser radiation (7) reflected from the target (4) or transmitted through the target heats-up the waveguide (1), said laser radiation (6) being polarized and impinging the target (4) at a specified angle () between 10 and 80 relative to the surface normal.

Claims

1. Method for producing an optical waveguide (1), a surface of which is at least partly coated with a coating material, said coating material contained in a target (4) being evaporated by means of laser radiation (6) from a process laser whereupon the coating material deposits on the surface of the optical waveguide (1) and forms a coating thereon modifying the light guidance, wherein the optical waveguide (1) is moved either continuously or intermittently in its longitudinal axis relative to the target (4) so that the coating is formed on a cladding section with a pre-definable longitudinal extension, wherein the laser radiation impinges on the target and is partly reflected from the target (4), wherein the reflected laser radiation (7) impinges on the surface of the optical waveguide and heats-up the optical waveguide (1), said laser radiation (6) being polarized and impinging on the target (4) at a specified angle () between 10 and 80 relative to the surface normal, wherein the process laser initially emits continuously at a lower performance rate in order to heat-up the optical waveguide (1), after which the process laser emits in a pulsed mode at a higher performance rate in order to remove the coating material or to convert it into a different aggregate state.

2. Method according to claim 1, wherein the coating material is transparent to a light propagating in the optical waveguide (1) at an application wavelength.

3. Method according to claim 1, wherein the coating material at least partly absorbs the laser radiation from the process laser.

4. Method according to claim 1, wherein the process laser is a CO.sub.2-laser.

5. Method according to claim 1, wherein the coating material is doped or undoped silica glass.

6. Method according to claim 1, wherein the optical waveguide (1) is rotated about its longitudinal axis during formation of the coating.

7. Method according to claim 1, wherein the target (4) circularly encloses the optical waveguide (1) wholly or partly.

8. Method according to claim 7, wherein the target (4) is irradiated from the process laser in a ring-shaped zone (8) wholly or partly enclosing the optical waveguide (1).

9. Method according to claim 1, wherein the optical waveguide (1) is an optical fiber.

10. Method according to claim 1, wherein after formation of the coating a glass capillary is collapsed on the optical waveguide (1) and thus forms a protective sheathing.

11. Method according to claim 1, wherein the formation of the coating is executed under normal atmosphere.

12. Method according to claim 1, wherein the coating is formed over several centimeters along the longitudinal extension of the optical waveguide (1).

13. Method according to claim 1, wherein the diameter of the optical waveguide (1) including coating accounts for 125 m up to 10 mm.

14. Method according to claim 1, wherein the coating material is deposited on the surface (3) of the optical waveguide (1) consecutively in several layers.

Description

(1) Practical examples of the present invention are elucidated in the following based on drawings, wherein:

(2) FIG. 1 shows a schematic representation of the inventive method with a coating material target arranged next to an optical fiber;

(3) FIG. 2 shows a practical example of the invention in which the target circularly encloses the optical fiber.

(4) As outlined hereinabove, the inventive method serves for producing an optical waveguide, for example an optical fiber 1, which is comprised of a fiber core 2 and a fiber cladding 3. By way of implementing the inventive method, the outer surface of the fiber cladding 3 is partly coated with a coating material. The coating material is contained in a target 4 which in the practical example illustrated in FIG. 1 is arranged laterally at a small distance next to fiber 1. With the practical example according to FIG. 2, the target 4 circularly encloses the optical fiber 1. According to FIG. 2, the circular target 4 comprises a central opening 5 which the fiber 1 is guided through. A laser beam 6, for example from a CO.sub.2 laser, impinges the target 4.

(5) The laser radiation 6 is polarized and impinges the target 4 at a specified angle . By means of the angle , one can adjust the magnitude of the portion of the reflected laser radiation 7 which impinges the fiber cladding 3.

(6) Initially, the laser beam 6 is continuously irradiated (cw-mode), whereby a certain temperature of the fiber cladding 3 is adjusted and set. Immediately after this heat-up process, the laser beam 6 is irradiated in pulsed mode, for example with a pulse duration in a range from approx. 100 s to 100 ms in order to remove the coating material from the target 4 (for example by evaporation). The coating material then precipitates on the heated-up fiber 1 and adheres there in stable manner.

(7) The coating material deposited from the target 4 on the fiber 1 may be pure or doped silica glass or even a different transparent material that offers adequately good absorption in the range of the wavelength of the laser radiation 6.

(8) To ensure uniform deposition of the coating material on the surface of the fiber cladding 3 over the entire fiber circumference and over a certain longitudinal extension of the fiber, the fiber 1 in the practical example according to FIG. 1 is rotated about its longitudinal axis. At the same time, the fiber 1 is pushed forward continuously or intermittently along its longitudinal axis in the direction of the arrow.

(9) With the practical example illustrated in FIG. 2, the laser beam 6 illuminates a ring zone 8 on the annular target 4. For this purpose, the laser beam 6 can either be deflected continuously or an annular or ring-segment shaped laser beam 6 is formed by suitable optics. The coating material deposits from all sides over the entire circumference of fiber 1 on its cladding 3.

(10) With a predefined application wavelength, the material of the coating substance deposited on fiber 1 is as highly transparent as the fiber material itself. Therefore, in the inventively applied coating, there is no significant absorption of the radiation propagating in the waveguide. The coating only serves for light scattering in order to eliminate that portion of the radiation propagating in the fiber cladding 3 which is undesired for the relevant application.