Clad glass composition and mother glass rod for gradient-index rod lens formed using the same, gradient-index rod lens and method of manufacturing the same, rod lens array, and image processor

摘要

The present invention provides a clad glass composition that is excellent in devitrification resistance and that prevents the whole mother glass rod from devitrifying by preventing a core glass composition from devitrifying in forming a mother glass rod using a concentric crucible drawing method. The clad glass composition forms a clad of a mother glass rod for a gradient-index rod lens having a core/clad structure. The clad glass composition includes the following components, indicated by mol %: 45 to 65% SiO₂; 0.5 to 10% TiO₂; 0 to 15% B₂O₃; 0 to 7% Al₂O₃; 0.1 to 10% Bi₂O₃; 0 to 5% Li₂O; 5 to 30% Na₂O; 0 to 10% K₂O; 0 to 15% MgO; 0 to 10% CaO; 0 to 10% SrO; 0.5 to 10% BaO; 0 to 10% Cs₂O; 0 to 10% ZnO; 0 to 7% Y₂O₃; 0 to 7% Nb₂O₅; 0 to 7% In₂O₃; 0 to 7% La₂O₃; 0 to 10% Ta₂O₅; 0 to 7% ZrO₂; and 0 to 1% Sb₂O₃, where the total of Li₂O+Na₂O+K₂O is in the range of 5 to 35 mol %, the total of MgO+CaO+SrO+BaO is in the range of 2 to 20 mol %, the total of Li₂O+Na₂O+K₂O+MgO+CaO+SrO+BaO is in the range of 7 to 50 mol %, and the total of Cs₂O+ZnO+Y₂O₃+Nb₂O₅+In₂O₃+La₂O₃+ZrO₂+Ta₂O₅ is in the range of 0 to 15 mol %. In the clad glass composition, at least two molar ratios selected from the group consisting of MgO/(MgO+CaO+SrO+BaO); CaO/(MgO+CaO+SrO+BaO); SrO/(MgO+CaO+SrO+BaO); and BaO/(MgO+CaO+SrO+BaO) are at least 0.1. The clad glass composition is substantially free from lead and has a refractive index in the range of 1.56 to 1.68.