PURPOSE: To deposit a glass layer efficiently on the inside circumferential surface of a glass pipe to be supplied therein with gaseous raw materials by a plasma CVD method by putting a heat resistant cylindrical body spacially on the outside circumference of said glass pipe and heating the glass pipe from the inside and outside circumferences.
CONSTITUTION: A heat resistant cylindrical body 2 is put on the outside circumference of a glass pipe 1 via a spacing 3 and a plasma generator 6 is provided freely movably on the outside circumference of the body 2. Gaseous raw materials are supplied into the pipe 1 to generate plasmas P1, P2 in the pipe 1 and the spacing 3. The gaseous raw materials are thermally decomposed by the heat of generation of the plasmas P1, P2 and the fine powder of the glass which is the product of reaction deposits on the inside circumference of the pipe 1 and assumes a fused state, thereby forming a glass layer 7. After the glass layer of a prescribed thickness is formed, the pipe 1 is removed from the body 2 and the hollow part is erased by a collapsing treatment through oxyhydrogen flames, etc., whereby a bar-like optical glass material is obtained.
SEDAKA RIYOUJI
TAKAHASHI HIROSHI
YOSHIDA SUSUMU
FURUKAWA ELECTRIC CO LTD