High purity glass objects, esp. optical waveguide fibres - made by CVD of two glass layers of mandrel using flame hydrolysis burner, then removing mandrel and collapsing layers by heating

摘要

This is an addn. to 2827303, and describes the mfr. of glass objects by flame hydrolysis, using a mandrel onto which two layers of glass particles are deposited. The outer, layer has a lower refractive index than the inner layer. The mandrel is removed, and the layers are heated (I) to consolidate the glass and to close the hole left by the mandrel. At temp. (I), the underlayer has viscosity(V1), and the top layer has viscosity (V2), where V1/V2 is smaller than 1/2, but large enough to prevent the inner layer sepg. from the outer layer coating. The blank is then made into the desired object by the method described in 2827303. Economic mfr. of fibres provides waveguides with high numerical aperture, e.g. 0.24.