| abstract |
Doped silica solution is sprayed from nozzle 14 onto the inside of axially rotating silica tube 1 (itself optionally doped) which is heated by tubular furnace 23, part 23b of which causes solvent evaporation at 200-800 DEG C and part 23a of which causes subsequent densification of the film at 500-2000 DEG C. Nozzle 14 and furnace 23 are conjointly reciprocated axially of tube 1 by movement (f2) of carriage 17. The refractive index of successively deposited layers is varied stepwise or gradually by adjusting the amount of dopants (P2O5, B2O3, compounds of Ge, Ti, Al, As, Nb, Sb) in the solution. <IMAGE> |