METHOD FOR PRODUCING A TUBULAR SEMIFINISHED PRODUCT FROM QUARTZ GLASS, METHOD FOR PRODUCING AN OPTICAL COMPONENT USING THE SEMIFINISHED PRODUCT, AND SEMIFINISHED PRODUCT CONSISTING OF QUARTZ GLASS DOPED WITH FLUORINE

Abstract

The aim of the invention is to improve a generally known method for producing quartz glass doped with fluorine, wherein SiO.sub.2 particles are formed in the presence of fluorine by means of a plasma deposition process, deposited in layers on an outer envelope of a cylindrical quartz glass substrate body rotating about its longitudinal axis, and vitrified to form a layer of quartz glass with a fluorine content of at least 1.5 wt. %, in such a way that a quartz glass semifinished product with a high fluorine content, characterised by a high basic transmission in the UV wavelength range, is obtained. To this end, the substrate body has at least one reservoir layer of quartz glass at least in the region of the outer envelope thereof, having a minimum hydroxyl group content of 200 wt. ppm and/or a minimum hydrogen content of 110.sup.17 molecules/cm.sup.3, and the substrate body is either fully or partially removed following the deposition of the quartz glass layer doped with fluorine.

Claims

1. A method of producing a tubular semifinished product of quartz glass, said method comprising: forming SiO.sub.2 particles in the presence of fluorine by a plasma deposition process; depositing said particles in layers on an outer surface of a cylindrical substrate body of quartz glass rotating about a longitudinal axis; vitrifying the particles so as to form a layer of quartz glass with a fluorine content of at least 1.5% by wt., wherein at least in a region of an outer surface thereof, the substrate body comprises a reservoir layer of quartz glass having at least one of a hydroxyl group content of 200 wt. ppm or more or a hydrogen content of 110.sup.17 molecules/cm.sup.3 or more, and wherein, after the deposition of the particles that form the fluorine-containing quartz glass layer, the substrate body is either partly or fully removed.

2. The method according to claim 1, wherein the reservoir layer has a hydroxyl group content of at least 300 wt. ppm.

3. The method according to claim 1, wherein the reservoir layer has a hydrogen content of at least 510.sup.17 molecules/cm.sup.3.

4. The method according to claim 1, wherein the reservoir layer has both a hydroxyl group content of 200 wt. ppm or more and a hydrogen content of 110.sup.17 molecules/cm.sup.3 or more.

5. The method according to claim 1, wherein the reservoir layer has a thickness of at least 0.5 mm.

6. The method according to claim 1, wherein the layer of fluorine-containing quartz glass produced by said deposition has a thickness of less than 10 mm.

7. The method according to claim 1, wherein the substrate body has an outer diameter of at least 70 mm.

8. The method according to claim 1, wherein the substrate body is formed as a tube.

9. The method according to claim 1, wherein a fluorine content of at least 4.5% by wt. is set in the fluorine-containing quartz glass layer.

10. A method for producing an optical component, said method comprising: producing a tubular semifinished product having an inner bore and consisting of fluorine-doped quartz glass, according to claim 1, inserting a core rod into the inner bore; and elongating the semifinished product and the inserted core rod so as to form the optical component.

11. (canceled)

12. (canceled)

13. (canceled)

14. (canceled)

15. (canceled)

16. (canceled)

17. The method according to claim 1, wherein the reservoir layer has a hydroxyl group content of at least 500 wt. ppm.

18. The method according to claim 1, wherein the reservoir layer has a hydrogen content of at least 110.sup.18 molecules/cm.sup.3.

19. The method according to claim 1, wherein the reservoir layer has a thickness of at least 1 mm.

20. The method according to claim 1, wherein the layer of fluorine-containing quartz glass produced by said deposition has a thickness of less than 5 mm.

Description

EMBODIMENT

[0054] The invention will be explained in detail hereinafter with reference to embodiments and a patent drawing. The drawing is a schematic illustration showing in detail in:

[0055] FIG. 1 a device for performing the POD method for depositing fluorine-doped quartz glass; and

[0056] FIG. 2 a diagram with transmission curves of different quartz glass qualities in the wavelength range of 190 nm to 800 nm

[0057] FIG. 1 schematically shows a device for performing the POD method for depositing fluorine-doped quartz glass on a carrier tube 3.

EXAMPLE 1

[0058] The carrier tube 3 consists of quartz glass doped with hydrogen. The mean hydrogen content is 110.sup.18 molecules/cm.sup.3. It has an inner diameter of 44 mm and an outer diameter of 54 mm and thus a wall thickness of 5 mm. The carrier tube 3 simultaneously serves as a reservoir layer 10 within the meaning of the invention.

[0059] A layer 4 of fluorine-doped quartz glass is produced on the carrier tube 3 (the reservoir layer 10) by means of a POD method. To this end SiCl.sub.4, oxygen and SF.sub.6 are supplied to a plasma burner 1 and converted into SiO.sub.2 particles in a hydrogen-free burner flame 2 assigned to the plasma burner 1. The plasma flame 2 is produced within a reaction sleeve 8 of quartz glass that is surrounded by a high-frequency coil 7.

[0060] As the plasma burner 1 is reversingly moved along the carrier tube 3 from one end to the other, the SiO.sub.2 particles are deposited in layers, starting on the cylindrical outer surface 5 of the carrier tube 3 rotating about its longitudinal axis 6. It is thereby possible to incorporate a high fluorine concentration of 5 wt. % with a homogeneous axial and radial distribution in the quartz glass network of the layer 4.

[0061] The rotational speed of the carrier tube 3 and the translational speed of the plasma burner 1 are adjusted such that the individual quartz glass layers have a mean thickness of about 12 m. A layer 4 of fluorine-doped quartz glass with a thickness of 10 mm is thereby produced.

[0062] After completion of the deposition process a heated etching-gas stream that contains SF.sub.6 is introduced into the bore 9 of the carrier tube 3. The etching-gas stream is configured such that the carrier tube 3 (the reservoir layer 10) is completely removed and only the glass layer 4 is maintained in tubular form with an inner diameter of 54 mm and a wall thickness of about 10 mm. As an alternative, the carrier tube 3 is removed by machining.

[0063] A sample of the fluorine-doped quartz glass tube is subjected to a hydrogen treatment at a temperature of 450 C. for a period of 10 h at a pressure of 5 atm.

[0064] Both the quartz glass tube loaded with hydrogen and the quartz glass tube not loaded with hydrogen were subsequently drawn in an elongation process at a draw ratio of 11 (length ratios before and after the elongation process) without any tools into a thin-walled quartz glass tube with an outer diameter of 31 mm and a wall thickness of 2 mm and inflated in this process. To this end an inner pressure raised by 5 mbar in comparison with the outer pressure applied on the outside is maintained in the inner bore.

[0065] The quartz glass tube obtained thereby is used as an overcladding tube for producing a preform for optical fibers. A core rod is here inserted into the inner bore and the assembly consisting of quartz glass tube and core rod is elongated into a preform.

COMPARATIVE EXAMPLE 1 (STANDARD METHOD)

[0066] The carrier tube 3 consists of undoped quartz glass with a mean hydrogen content of less than 110.sup.16 molecules/cm.sup.3 and a low hydroxyl group content of less than 1 wt. ppm. It has an inner diameter of 30 mm and an outer diameter of 40 mm and thus a wall thickness of 5 mm.

[0067] A layer 4 of fluorine-doped quartz glass with a thickness of 15 mm is produced on the carrier tube 3 with the help of the POD method of Example 1, and the carrier tube 3 is subsequently removed by introducing a heated SF.sub.6-containing etching-gas stream through the bore 9.

[0068] A sample of the fluorine-doped quartz glass tube obtained thereby is loaded with hydrogen, as has been described with reference to Example 1, and the quartz glass tube loaded with hydrogen and also the quartz glass tube not loaded with hydrogen were subsequently elongated and used as an overcladding tube for producing a preform for optical fibers.

[0069] FIG. 2 shows transmission curves of the quartz glass tubes produced according to Example 1 (curves 23 and 24) and Comparative Example 1 (curves 21 and 22), (each time prior to the elongation process) in the wavelength range between 190 nm and 800 nm. The basic transmission T in % (based on a layer thickness of 2 mm) is plotted on the Y-axis, and the wavelength X in nm on the X-axis.

[0070] Curve 21 shows the basic transmission of a quartz glass tube produced according to the comparative example (standard OVD method). Particularly in the UV wavelength range between 190 nm and 400 nm, the fluorine-doped quartz glass exhibits a significantly reduced basic transmission which is less than 85% at wavelengths below 250 nm. Owing to the later loading of the quartz glass with hydrogen it was possible to improve the transmission to a certain extent within the whole wavelength range, particularly in the UV range (curve 22), but without being thereby able to raise the basic transmission T at wavelengths below 250 nm to more than 85%.

[0071] By contrast, the highly fluorine-doped quartz glass (curve 23) produced in conformity with Example 1 exhibits a much higher basic transmission T which is above 90% especially in the UV wavelength range at a wavelength of 250 nm. The transmission curve 24 of the hydrogen-treated sample (Example 1) differs therefrom only slightly. A significant improvement of the basic transmission is thus no longer achievable in the quartz glass of Example 1 by way of hydrogen loading.

Example 2

[0072] A carrier rod which consists of undoped quartz glass having a hydroxyl group content of 700 wt. ppm is used as the substrate body. It has an outer diameter of 60 mm. The carrier rod simultaneously serves as a reservoir layer within the meaning of the invention.

[0073] A layer of fluorine-doped quartz glass with a thickness of 10 mm is produced on the carrier rod by means of a POD method, as has been described with reference to Example 1.

[0074] After completion of the deposition process the carrier rod is drilled out, with an inner bore being formed having a diameter of 56 mm. This yields a quartz glass tube consisting of an outer layer of a fluorine-doped quartz glass and an inner layer with a thickness of 2 mm of undoped quartz glass, which corresponds to a semifinished product according to the invention. The remaining wall of the original carrier rod with a wall thickness of 2 m is completely removed by passing an SF.sub.6-containing etching-gas stream therethrough.

[0075] The quartz glass tube was subsequently drawn in an elongation process at a draw ratio of 12 without any tools into a thin-walled quartz glass tube having an outer diameter of 31 mm and a wall thickness of 2 mm and was inflated in this process. To this end an inner pressure raised by 5 mbar in comparison with the outer pressure applied on the outside was maintained in the inner bore.

[0076] The fluorine-doped quartz glass tube obtained thereby is distinguished by a basic transmission in the UV wavelength range that corresponds substantially to that of curve 23 in FIG. 2. It is used as an overcladding tube for producing a preform for optical fibers in that a core rod is inserted into the inner bore, and the assembly consisting of quartz glass tube and core rod is elongated into a preform.