Properties of tellurite-based high numerical aperture fibers with diamagnetic core and cladding glasses

•6 glass systems i.e. TeO2–ZnO–K2O–GeO2–SiO2 etc. were studied as core/cladding pair.•Well matched core/cladding pair for high numerical aperture fiber was selected.•The structural and properties of core/cladding glasses were investigated.•The Verdet constant of high numerical aperture was close to that of bulk glass.•The high NA fiber has a good core and cladding interface and a NA as high as 0.9.

The fabrication and characterization of a tellurite based high numerical aperture magneto-optical glass fiber are presented. Different glass groups were investigated in terms of their structural, thermal, mechanical, optical and magnetic performance as a core/cladding pair and their refractive index contributions to the numerical aperture. A well matched core/cladding pair was selected: 75%TeO2–20%ZnO–5%Na2O (mol.%) for core glass, 42%TeO2–18%ZnO–15%K2O–20%Ge2O–5SiO2 (mol.%) for cladding glass. The fibers have a good cross section and a numerical aperture as high as 0.9. The Verdet constant of this high numerical aperture fiber was close to that of bulk glass.