Polygonal optical fiber preform production, by applying vacuum and heat to precollapsed tubular glass sheath enclosing polygonal glass core rod

摘要

Production of a preform for optical fibers, comprising a core in a sheath, involves introducing a polygonal glass core rod (1) into a treatment plant; precollapsing a tubular glass sheath (3) to give a cross-section to enclose the rod while leaving a gap (5) on all sides; pushing the sheath onto the rod; and applying vacuum (6). A furnace (9) causes controlled fusion of the rod and sheath, plus further collapsing so that sheath glass flows in radial and azimuthal directions. Production of a preform for polygonal optical fibers, comprising a polygonal core enclosed in a transparent glass sheath of different refractive index, involves forming a monolithic polygonal glass core rod (1); introducing the rod into a treatment plant; precollapsing a tubular glass sheath (3) to give a cross-sectional shape which encloses the rod while leaving a predetermined gap (5) on all sides of the rod; pushing the sheath onto the rod; and applying vacuum (6) in the space between the rod and sheath. The plant also includes a furnace (9) to cause (i) controlled sheathing by mutual fusion of the rod and sheath and (ii) further collapsing of the sheath such that the sheath glass flows in both radial and azimuthal directions.