METHOD FOR INCREASING THE CLADDING-TO-CORE RATIO (D/d) OF LOW D/d RATIO CORE ROD IN OPTICAL FIBER PREFORM

PROBLEM TO BE SOLVED: To perform the reduction of production cost and the reduction of manufacturing steps in a glass preform in which a cladding to core diameter ratio (D/d) of a core body piece is low. SOLUTION: An optical fiber preform is fabricated by inserting a number of core body pieces end-to-end inside a glass cylinder, wherein the core body pieces may have a cladding-to-core diameter (D/d) ratio within the range of one to four. The cylinder with the inserted core body pieces is mounted vertically on a furnace and heated so that the cylinder becomes elongated and its outside diameter collapses to form a core rod from which core rod sections with D/d ratios greater than five can be cut. A soot overcladding is deposited on the circumference of a core rod section until the diameter of the deposited soot builds to a determined value. The core rod section with the deposited soot overcladding is consolidated to obtain a finished optical fiber preform. The preform preferably has a D/d ratio of about 15 or more, and an optical fiber may be drawn directly from the preform. COPYRIGHT: (C)2009,JPO&INPIT