Abstract: A method activates the inner surface of a substrate tube via plasma etching with a fluorine-containing etching gas. An exemplary method includes the steps of (i) supplying a supply flow of gas to the interior of a substrate tube, wherein the supply flow includes a main gas flow and a fluorine-containing etching gas flow, (ii) inducing a plasma via electromagnetic radiation to create a plasma zone within the substrate tube's interior, and (iii) longitudinally reciprocating the plasma zone over the length of the substrate tube between a reversal point near the supply side and a reversal point near the discharge side of the substrate tube. The flow of the fluorine-containing etching gas is typically provided when the plasma zone is near the supply side reversal point.

Abstract: A method for manufacturing an optical preform including the steps of providing a substrate tube having deposited layers of glass on an inside surface thereof, increasing an outer diameter of the substrate tube by means of applying a traversing heat source to heat the substrate tube to above a softening temperature thereof and by providing an internal pressure in the substrate tube higher than an ambient pressure, and collapsing the substrate tube of increased outer diameter by means of applying the traversing heat source to heat the substrate tube to above the softening temperature thereof such that an optical preform is manufactured.

Abstract: A method activates the inner surface of a substrate tube via plasma etching with a fluorine-containing etching gas. An exemplary method includes the steps of (i) supplying a supply flow of gas to the interior of a substrate tube, wherein the supply flow includes a main gas flow and a fluorine-containing etching gas flow, (ii) inducing a plasma via electromagnetic radiation to create a plasma zone within the substrate tube's interior, and (iii) longitudinally reciprocating the plasma zone over the length of the substrate tube between a reversal point near the supply side and a reversal point near the discharge side of the substrate tube. The flow of the fluorine-containing etching gas is typically provided when the plasma zone is near the supply side reversal point.

Abstract: A method for manufacturing an optical preform including the steps of providing a substrate tube having deposited layers of glass on an inside surface thereof, increasing an outer diameter of the substrate tube by means of applying a traversing heat source to heat the substrate tube to above a softening temperature thereof and by providing an internal pressure in the substrate tube higher than an ambient pressure, and collapsing the substrate tube of increased outer diameter by means of applying the traversing heat source to heat the substrate tube to above the softening temperature thereof such that an optical preform is manufactured.