OPTICAL FIBRE

Abstract: An optical fibre with a core of glass and a cladding of plastics. In accordance with the invention, the glass is a sodium borosilicate glass containing refractive index-raising oxides, while the plastics is an optically low-attenuation plastics with a low refrective index, whereby a high numerical aperture is obtained in the optical fibre.

Description: OPTICAL FIBRE TECHNICAL FIELD ,*. The present invention relates to an optical fibre with a core of glass and a cladding of plastics. BACKGROUND ART In known such fibres the glass is often quartz glass with a low refractive index, while the cladding consists of high attenuation silicon rubber or other high- 5 attenuation, plastics. Due to the low refractive index of quartz glass, the numerical aperture of such fibres will be low while the high-attenuation plastics increases the attenuation in the fibre. Accordingly, these fibres are not suitable for transmitting large light powers over distances of medium length, e.g. some hundres of meters. 10 A method of transmitting high light power with the aid of such fibres would be to increase their diameter. However, this results in the fibres being more expensive while they will be less flexible at the same time. DISCLOSURE OF INVENTION The object of the present invention is to provide an optical fibre with a high numerical aperture, the fibre thus being suitable for transmitting high light 15 powers over distances of medium length. This is provided by the fibre in accordance with the invention being given the characterizing features disclosed in the claims. BEST MODE FOR CARRYING OUT THE INVENTION The optical fibre in accordance with the invention includes a core of glass and a cladding of plastics. According to the invention, the glass is sodium borosilicate 20 glass with refractive index-raising oxides, while the plastics is an optically low- OMFI attenuation plastics with a low refractive index. The refractive index-raising oxides which are intended to give the glass a refractive index of at least 1,52 comprise combinations of PbO, BaO, CaO, MgO, Zr0 2 and ZnO, while the optically low-attenuation plastics, which should have a refractive index of 1,42 at most, comprises such as optically pure silicon rubber of the type supplied by the firm SHIN ETSU and which has a refractive index of 1,41 at 25°C. A first glass core is produced having the following composition expressed in percent by weight: Na z O 17,2 15,0 B 2°3 MgO 1,2 ZnO 3,1 A1 2 0 3 3,1 Zr0 2 6,6 As 0, 0,1 The refractive index of this glass core was 1,52. With a sheath of plastics according to the above, the fibre was given a numerical aperture of 0,57. A second class core was produced with the following composition, also expressed in percent by weight: SiO z 51,4 Na 2 0 18,3 14,9 B 2°3 BaO 9,2 Zr0 2 6,1 As 9 0, 0,1 The refractive index of this glass core attained 1,55. With a cladding of plastics in accordance with the above this other fibre was given a numerical aperture of 0.64. , The thickness of the silicon rubber cladding is preferably selected to be between 10 and 50 micrometers. To protect the cladding, this is coated with a protective coating of epoxyacrylate, for example. l

Claims: CLAIMS 1 Optical fibre with a core of glass and a cladding of plastics, characterized in that for obtaining a high numerical aperture the glass is a sodium borosilicate glass with oxides for increasing its refractive index, while the plastics is an optically low-attenuation plastics with a low refractive index. 2 Fibre as claimed in claim 1, characterized in that the oxides comprise combinations of PbO, BaO, CaO, MgO, Zro„ and ZnO, while the plastics comprises optically pure silicon rubber. 3 Fibre as claimed in claim 1 or 2, characterized in that the refractive index of the glass core attains at least 1,52, while the refractive index of the plastics cladding is at most 1,42. 4 Fibre as claimed in any of claims 1-3, characterized in that the thickness of the plastics sheath attains to between 10 and 50 micrometers. 5 Fibre as claimed in claim 2, characterized in that the cladding is given a protective coating. 6 Fibre as claimed in claim 5, characterized in that the protective coating consists of epoxyacrylate.

Inventors: VACHA LUBOS, VACHA, LUBOS
Applicants: ERICSSON TELEFON AB L M, TELEFONAKTIEBOLAGET L M ERICSSON
Application year: 1984
Main classification: G02B5
IPC codes: C03C13, C03C25, G02B1, G02B6