Method of making an optical fiber by melting particulate glass in a glass cladding tube

A method for making a continuous-clad filament including a core and a cladding adjacent said core region, comprising the steps of:

• a) providing a core cullet feedstock having a particle diameter between about 100-5,000 μm and a known melting point;
• b) providing a rigid cladding structure having a softening point higher than the melting point of said core feedstock, wherein said cladding has a composition that is chemically compatible with said core;
• c) introducing said cullet into said cladding structure;
• d) heating an end of said core containing cladding structure in a furnace to near the softening point of said cladding;
• and
• e) drawing said core containing cladding into a continuous clad filament;
• wherein the core cullet is a glass having a composition consisting essentially, in mole %, of:
• SiO2 0-90 GeO2 0-90 Na2O 0-25 Li2O 0-10 K2O 0-25 Rb2O 0-25 Cs2O 0-25 Al2O3 5-40 Ga2O3 5-40 RE2(1)O3 0-40 RE2(2)O3 0-1 Er2O3 0.001-5 Yb2O3 0-5 PbO 0-15 RO 0-20 ZnO 0-10 ZrO2 0-2 TiO2 0-2 Nb2O5 0-10 Ta2O5 0-10 P2O5 0-5 B2O3 0-15 As2O3 0-10 Sb2O3 0-20 Na2Cl2 0-10 Bi2O3 0-5, and
• up to 15 weight % fluorine in the form of at least one of a fluorinated component of the glass composition and a batch constituent selected from a group consisting of at least one of AlF3, REF3, NH5F2, NaF, Na2SiF6, Na3AlF6,
• where
• RE(1) is at least one of Y, La, Gd, and Lu;
• RE(2) is at least one of Ce, Pr, Nd, Sm, Eu, Th, Dy, Ho, and Tm;
• R is at least one of Ba, Ca, Mg, and Sr;
• (SiO2+GeO2) is in the range (40-90);
• and
• (Al2O3+Ga2O3)>(RO+“alk”2O+RE2O3) where “alk” is at least one of Li, Na, K, Cs, and Rb.