The method for fabricating an
optical fiber comprises the steps of inserting a primary
optical fiber preform (11) having a first primary axis (x1) and an outer surface (111) into an overcladding tube (12) having a second primary axis (x2) and an inner surface (120), so that said outer surface and inner surface define an
interior space (15) ; holding the primary preform (11) in a centrally inserted position within the overcladding tube (12) with said first and second primary axes (x1, x2) in substantial alignment with each other; supplying overcladding grain (13) into the
interior space (15) that is limited at the lower end of the overcladding tube (12) by means of a closure (125); generating a condition of reduced pressure within the
interior space (15) that is limited at the upper end of the overcladding tube (12) by means of an adjoiner (3), which holds the primary
optical fiber preform (11) and the overcladding tube (12) in position; and heating the unprocessed secondary preform (1), that consists of the primary preform (11), the overcladding tube (12) and the overcladding grain (13), at its lower end to a softened state and simultaneously or subsequently drawing an optical
fiber therefrom.