Method of bundling rods so as to form an optical fiber preform

A method for providing a glass preform for use as a source for drawing an optical fiber having a reduced capacity for propagation of amplified spontaneous emission, the method comprising the steps of:

• collecting a plurality of first glass rods into a substantially contiguous bundle, wherein each of said first glass rods comprises a chemical composition and has a substantially uniform shape;
• and
• removing and replacing one or more groups of contiguous first glass rods with an equivalent number of groups comprising second glass rods, said second glass rods comprising a chemical composition and having a substantially uniform shape, said second glass rods comprising a physical or chemical property having a different value than a value of said same physical or chemical property of said first glass rods, and wherein said second glass rods comprise a means for eliminating or substantially reducing propagation of amplified spontaneous emission;
• heating said contiguous bundle to a glass fusion temperature and causing said contiguous bundle to fuse to form a solid glass preform such that said chemical composition of each of said first glass rods is maintained in a location proximate or about coincident with a position of each said glass rods within said contiguous bundle.

A method for providing a glass preform for use as a source for drawing an optical fiber, the method comprising the step of:

• providing first and second quantities of glass rods, wherein each of said glass rods has a substantially uniform shape, said first quantity comprising one or more rare-earth dopant elements, said second quantity comprising first and second refractive indices, wherein said first refractive index is greater than a target refractive index, and said second refractive index is less than said target refractive index;
• collecting said first quantity of glass rods into a substantially contiguous bundle of rods and forming thereby a first bundle, said first bundle for forming a preform core region having a substantially uniform radial and longitudinal chemical composition;
• uniformly surrounding said first bundle with said second quantity of glass rods forming thereby a contiguous and substantially concentric cylindrical annulus about said first bundle, wherein said first and second refractive indices are distributed throughout said cylindrical annulus so as to provide an average refractive index within said cylindrical annulus substantially equal to said target refractive index, said second quantity of glass rods forming a cylindrical preform cladding region surrounding said preform core region to provide a glass preform bundle;
• inserting said glass preform bundle into a glass tube wherein said glass tube has an inside diameter chosen to contain said glass preform bundle, and wherein said glass tube is evacuated and sealed at first and second ends such that said preform bundle is enclosed under an internal pressure below 1 atmosphere, and wherein further said preform bundle is restrained at each end within said sealed glass tube by a porous packing plug;
• and
• heating said glass tube and said glass preform bundle to a glass fusion temperature thereby causing said glass tube and said glass preform bundle to fuse in place to form a solid glass preform such that said preform core region radial and longitudinal chemical composition and said cladding region average refractive index are maintained.