o sub 3 30 as sub 2 o sub 3 1 example 6 sio sub 2 42 bao 10 na sub 2 o sub 3 22 b sub 2 o sub 3 25 as sub 2 o sub 3 1 ______________________________________ an estimated index profile for the above compositions is shown in fig2 the grading profile index for this profile is calculated to be 3 13 which would correspond to a bandwidth five times that of a stepped fiber instead of forming the core glass from batch material 12 within tube 10 previously melted ultra pure glass which is in powder or granular form hereinafter referred to as 34 cullet 34 may be used as a raw material to obtain a highly purified cullet suitable for use in manufacturing a low loss fiber the glassy liquid 24 within tube 10 may be quenched in ultra pure deionized water for example this will cause the glass to solidify in the form of a granular or powder like cullet the cullet may then be stored under ultra clean conditions until it is to be used at which time the cullet is melted and fined within a tube 10 as described the advantage in using a cullet is that the two melting steps may provide better outgassing thus yielding less bubbles and better homogeneity other techniques may also be used to provide a suitable cullet for example in a 34 skull 34 melting technique a 34 skull 34 of pure glass is first coated on a container the.