DEVICE FOR APPLYING ELECTROMAGNETIC MICROWAVE RADIATION IN A PLASMA INSIDE A HOLLOW GLASS SUBSTRATE TUBE, AND METHOD FOR MANUFACTURING AN OPTICAL PREFORM

摘要

A device for applying electromagnetic microwave radiation in a plasma inside a substrate tube including inner and outer cylindrical walls defining an annular cavity therebetween, the inner wall having a circumferential applicator slit, an elongate microwave guide arranged with a first end in communication with the annular cavity and a second end in communication with a microwave generating means for supplying microwaves to the annular cavity, and means for supplying a cooling gas through the elongate microwave guide to a position near the applicator slit.