WO2003066541A1

WO2003066541A1 - Coated articles

Info

Publication number: WO2003066541A1
Application number: PCT/IB2003/000338
Authority: WO
Inventors: Herman Philip Godfried
Original assignee: Element Six NV
Current assignee: Element Six NV
Priority date: 2002-02-05
Filing date: 2003-02-03
Publication date: 2003-08-14
Anticipated expiration: 2004-08-05
Also published as: AU2003205946A1

Abstract

An optical fibre or infrared waveguide which has an area or areas which are sensitive to high intensity radiation, in use. Such area or areas are provided with a coating reflective to high intensity radiation.

Description

COATED ARTICLES

BACKGROUND OF THE INVENTION

This invention relates to coated articles and more particularly, coated high power optical fibres and infrared waveguides.

Optical radiation at visible and near-infrared wavelengths may be transported through solid core glass optical fibres. Although the glass is highly transparent for the radiation, the buffer coating and sometimes the cladding which is provided around the fibre may be easily damaged by any stray radiation incident upon the fibre.

Infrared radiation with wavelength longer than approximately 3μm cannot be transmitted through ordinary glass fibres, due to absorption by the glass. Fibres consisting of materials such as KRS-5 have been employed. These materials are, however, toxic. Radiation with the highest power or intensity (e.g. as emitted by a CO₂ laser) currently are transmitted through hollow (quartz-) glass fibres coated on the inside surface with a Ag/Agl reflective coating. These fibres are called waveguides. The coating is, however, temperature sensitive and degrades at elevated temperatures. In particular the waveguide is sensitive to IR radiation striking the glass wall, which then, on being absorbed by the glass, heats up the waveguide and thereby degrades or destroys the coating. This type of damage occurs at temperatures where the quartz-glass itself is not affected at all. SUMMARY OF THE INVENTION

According to the present invention, a coating reflective to high intensity radiation such as visible or IR radiation is provided on an area or areas of an optical fibre or infrared waveguide sensitive to such radiation in use.

According to a further aspect of the invention, an optical fibre comprises a solid core of glass fibre having an outer coating susceptible to damage by high intensity radiation, the area or areas of the outer coating exposed to such radiation, in use, being provided with a coating reflective to such radiation.

The optical fibre will generally be a quartz-glass fibre.

The outer coating will generally comprise a buffer coating or a glass cladding, or a combination thereof.

The area or areas provided with the reflective coating will generally be at or around the end of the fibre through which the radiation passes.

According to another aspect of the invention, an infrared waveguide comprises a hollow tube made of a material which heats on absorption of visible or IR radiation, or similar high intensity radiation, the tube having a coating reflective to the radiation on the inner surface and a coating reflective to the radiation on the area or areas of the outer surface which are exposed to such radiation, in use.

Generally, the coating on the outer surface will be provided on the surface, e.g. the end surface of the tube, which is exposed to incoming radiation, in use.

The hollow tube will generally be a quartz-glass tube. The reflective coating on the inner surface of the hollow tube will be bonded to the tube and will typically be a coating comprising layers of Ag and Agl.

The coating on the outer surface of the waveguide will also be bonded to the glass tube and is preferably resistant to high temperature, and highly reflective to the radiation.

Examples of suitable coatings reflective to high intensity radiation for the practice of the invention are those which have a higher reflectivity at the wavelength of the radiation. For example, coatings of gold, silver, silver iodide, aluminium and copper are suitable. It is preferable that the coating is bonded to the surface or coating to which it is applied. This may be achieved through a layer of a suitable bonding or adhesion promoter. A layer functioning as a diffusion barrier may be provided between the bonding or adhesion layer and the layer which is reflective to the high intensity radiation.

An example of a suitable multiple coating is one comprising an inner layer of titanium, an intermediate layer of platinum and an outer layer of gold. In this particular example the titanium layer is an adhesion promoter. Other materials that can be used to promote bonding to the glass are, for example, Cr and V. The top or outer layer is gold and provides the desired high reflectivity. Other suitable top layer materials are, for example, Ag, Agl, Al or Cu. The Pt layer functions as a diffusion barrier between the Ti and Au layers for providing stability at high temperatures. Other materials such as W and Ni can also be used.

For waveguides, the thickness of the outer reflective coating will vary according to the application to which the waveguide or fibre is to be put. The outer coating has a typical configuration of Ti/Pt/Au = 60 nm / 100 nm / 1 μm. The thickness of the Au layer can vary from 0.1 μm to approximately 5 μm. BRIEF DESCRIPTION OF THE DRAWING

Figure 1 is a perspective view of an embodiment of an infrared waveguide of the invention, and Figure 2 is a perspective view of an embodiment of a solid core glass optical fibre of the invention

DESCRIPTION OF EMBODIMENTS

An embodiment of the invention will now be described with reference to Figure 1 of the accompanying drawing. Referring to Figure 1 , a waveguide for infrared radiation comprises a hollow tube 10 having a coating bonded to the inner surface 12 and a coating bonded to the outer surface 18 and to the end surface 14 of the end 16 of the tube. The coatings cover the surface 12 completely and the end part of surface 18 close to end 16 and are bonded to these surfaces. The coatings are reflective, and preferably highly reflective, to infrared radiation. The hollow tube is preferably a quartz-glass tube.

In one example of use, IR radiation (laser light) may pass into the tube 10 through the front end 16. In so doing, some of the radiation may impinge on the coated surfaces 12, 14 and 18. In another example IR radiation, which exited the tube 10 through the front end 16, may be (partially) reflected from some other surface and impinge on the coated end surfaces 12, 14 and 18.

An example of a particularly suitable coating for the inner surface 12 is one comprising a layer of silver to which is bonded a layer of silver iodide. A particularly suitable coating for the outer end surface 14 and the end part of 18 is one comprising a layer of titanium to which is bonded a layer of platinum to which is bonded an outer layer of gold. The thickness of the layers may, for example, be 60/120/1000 nm respectively. The metal layers may be applied by sputter coating. During sputter coating on the surfaces 14 and 18, some of the titanium/platinum/gold may be deposited on the inner surface 12 thus providing extra protection for the glass.

It has been found that for glass tubes having an outer diameter of 1 mm and an inner diameter of 0,53 mm and coated in the manner described above, such waveguides can withstand direct radiation impinging on the tube end 16 at power levels in excess of 10 Watts for periods in excess of 1 minute. No damage was visible to the coating on the surfaces 12, 14 and 18. When exposing identical waveguides, but without an applied coating on the end surfaces 14 and 18, to laser-light with all other conditions, i.e. incident light power, light distribution, temperature and waveguide monitoring, being the same, the quartz-glass waveguide melted in less than 10 seconds starting near its front end surface 14, indicating that temperatures in excess of 1000°C had been generated in the glass tube.

The waveguide of the invention has particular application to transmitting laser light to a diamond blade such as that described in International publication WO 01/00100A1. The laser light is introduced into the rear end of such a diamond blade which is partly reflective. Thus, part of the light emitted from the waveguide to the diamond blade is reflected back to the waveguide thereby reducing excessive heating in the waveguide. With the outer end surface coating described above, it was found that the heating effect could be suppressed completely. In a particular series of tests at temperatures at 100°C, where reflected light from a diamond surface of up to 1.8 Watt impinged on the Ti/Pt/Au coated end surface of the waveguide, no damage was observed during the duration of the test which was 10 minutes and also over the total accumulated exposure time in excess of 15 minutes for each waveguide tested. Another embodiment of the invention will now be described with reference to Figure 2 of the accompanying drawing. Referring to Figure 2, an optical fibre for transmission of visible and near-infrared radiation comprises a solid glass core 20 having a glass cladding layer 22 around it made of a glass material with an index of refraction that is lower than the index of refraction of the glass material of the core. The optical fibre is further provided with a protective buffer coating 24 typically made out of some plastic material such as polyimide. Radiation enters into and exits from the optical fibre through the end face 26 of the core 20. A coating reflective to visible or IR radiation is applied to the end faces 28 and 30 of the cladding layer 22 and buffer coating 24, respectively, and a part of the outer surface 32 of the buffer coating 24 in the region of the end face 30. These reflective coatings are bonded to the surfaces to which they are applied and are reflective, and preferably highly reflective, to the visible or near-infrared radiation incident upon them.

Claims

1. An optical fibre or infrared waveguide having an area or areas sensitive to high intensity radiation, the area or areas being provided with a coating reflective to high intensity radiation.

2. A fibre or waveguide according to claim 1 wherein the high intensity radiation is visible or IR radiation.

3. A fibre or waveguide according to claim 1 or claim 2 wherein the area or areas sensitive to high intensity radiation are at or around an end of the fibre or waveguide.

4. An optical fibre comprising a solid core of glass fibre having an outer coating susceptible to damage by high intensity radiation, the area or areas of the outer coating exposed to such radiation, in use, being provided with a coating reflective to such radiation.

5. An optical fibre according to claim 4 which is a quartz-glass fibre.

6. An optical fibre according to claim 4 or claim 5 wherein the outer coating comprises a buffer coating, a glass cladding or a combination thereof.

7. An optical fibre according to any one of claims 4 to 6 wherein the area or areas provided with the reflective coating are at or around the end of the fibre through which the radiation passes.

8. An infrared waveguide comprises a hollow tube made of a material which heats on absorption of high intensity radiation, the tube having a coating reflective to the radiation on the inner surface and a coating reflective to the radiation on the area or areas of the outer surface which are exposed to such radiation, in use.

9. An infrared waveguide according to claim 8 wherein the area or areas of the outer surface provided with the coating reflective to high intensity radiation are located at the end surface of the tube which is exposed to incoming radiation, in use.

10. An infrared waveguide according to claim 8 or claim 9 wherein the hollow tube is a quartz-glass tube.

11. An infrared waveguide according to any one of claims 8 to 10 wherein the reflective coating on the inner surface of the hollow tube is bonded to the tube.

12. An infrared waveguide according to any one of claims 8 to 11 wherein the reflective coating on the inner surface of the hollow tube comprises layers of Ag and Agl.

13. An optical fibre or infrared waveguide according to any one of the preceding claims wherein the coating reflective to high intensity radiation has a high reflectivity at the wavelength of the radiation.

14. An optical fibre or infrared waveguide according to any one of the preceding claims wherein the coating is a material selected from gold, silver, silver iodide, aluminium and copper.

15. An optical fibre or infrared waveguide according to any one of the preceding claims wherein a bonding layer is provided between the coating reflective to high intensity radiation and the surface or coating to which it is applied.

16. An optical fibre or infrared waveguide according to claim 15 wherein the bonding layer is a metal selected from titanium, chromium and vanadium.

17. An optical fibre or infrared waveguide according to claim 15 or claim 16 wherein a layer which functions as a diffusion barrier is provided between the coating reflective to high intensity radiation and the bonding layer.

18. An optical fibre or infrared waveguide according to claim 17 wherein the layer functioning as a diffusion barrier is a metal selected from platinum, tungsten or nickel.

19. An optical fibre or infrared waveguide according to claim 17 or claim 18 wherein the coating comprises an inner layer of a metal selected from titanium, chromium and vanadium, an intermediate layer of a metal selected from platinum, tungsten and nickel and an outer layer of a material selected from gold, silver, silver iodide, aluminium and copper.

20. An optical fibre substantially as herein described with reference to Figure 2.

21. An infrared waveguide substantially as herein described with reference to Figure 1.