GB1515304A - Optical waveguides - Google Patents

Abstract

1515304 Optical waveguides NATIONAL RESEARCH DEVELOPMENT CORP 23 May 1975 [31 May 1974 7 Aug 1974 30 Dec 1974] 24177/74 34813 and 55999 Heading C1M An optical waveguide comprises a core glass formed of P 2 O 5 and SiO 2 and a cladding glass, of lower refractive index, which contains less, or no, P 2 O 5 . The core may comprise SiO 2 , P 2 O 5 (e.g. in amount 4-40% by weight), and, optionally, GeO 2 , TiO 2 , or an oxide of B, Al, Sb, As or Bi. The cladding may be of silica glass or borosilicate glass. Preferably the wave guide is prepared by bubbling O 2 (3) through POCl 3 (1) and SiCl 4 (2) to form a vapour mixture, which mixture is passed through silica tube 10 and reacts therein to form a SiO 2 /P 2 O 5 mixture which is deposited as a glass on the tube interior. The tube 10 is heated to 1250-1550‹C by heater 11, through which the tube 10 passes, to cause the reaction and deposition. Several coatings may be applied by passing the tube 10 repeatedly through heater 11, preferably while varying the composition of the vapour mixture in order to gradually increase the core refractive index and produce a graded-index waveguide. The coated tube 10 may then be collapsed to a rod, preferably while rotating the tube 10, the rod then being drawn down to a fibre waveguide. The tube is preferably collapsed by moving a hot zone along the tube, the collapsed portion of the tube then being cooled by air jets to stabilize. Excess pressure may be maintained in the bore of the tube 10 while it is collapsed, in order to maintain its circularity. In a preferred embodiment, a layer of borosilicate glass 32 is applied to the inside of a silica tube 33 (e.g. using an oxygen/BCl 3 /SiCl 4 mixture) before applying the layers constituting core glass 31, so that the borosilicate layer 32 forms the cladding.