EFFECT OF SOME REFRACTIVE-INDEX MODIFIERS ON BOTH NUMERICAL APERTURE AND MECHANICAL STRENGTH OF FLUOROZIRCONATE FIBERS

The effect of incorporating large amounts of some fluoride additives s uch as LiF, PbF2, HfF4 on both the numerical aperture and the mechanic al strength of ZrF4 based glass fibres has been investigated. Fibres w ith core-cladding refractive index difference as high as 65 X 10(-3) h ave been achieved with appropriate glass compositions. The tensile str ength of multimode fibres tends to decrease from about 600 to 400 MPa with increasing PbF2 or HfF4 glass content, and high numerical apertur e-small core diameter single mode fibres with strength within 500-550 MPa are achievable.